Patent Application
20240421783
The field of representative embodiments of this disclosure relates to methods, apparatus and/or implementations concerning or relating to driver circuits, and in particular to switching driver circuits as may be used to drive a transducer.
Many electronic devices include transducer driver circuitry for driving a transducer with a suitable driving signal, for instance for driving an audio output transducer of the host device or a connected accessory, with an audio driving signal.
In some applications the driver circuitry may include a switching amplifier stage, e.g. a class-D amplifier output stage or the like, for generating the drive signal. Switching amplifier stages can be relatively power efficient and thus can be advantageously used in some applications. A switching amplifier stage generally operates to switch an output node between defined high-side and low-side switching voltages, with a duty cycle that provides a desired average output voltage over the course of the duty cycle for the drive signal.
At least one of the high-side and low-side voltages for the output driver may be generated from a suitable input voltage, e.g. a battery voltage, by a DC-DC converter. In some cases, the DC-DC converter may be a variable voltage converter operable to selectively vary the switching voltage in use.
In the driver circuit of
In the example of
Using a variable voltage charge pump to provide a selectively variable high-side switching voltage allows a high voltage to be used when required to provide a relatively high voltage drive signal. For example, with a differential output stage 102, an output drive voltage of a magnitude up to near 3×VBatt may be generated by operating the charge pump 103 in the three times mode and driving one output node of the class-D output stage with a duty cycle (in terms of proportion of time spent connected to the high-side switch voltage compared to the low-side switching voltage) at or near 100% and the other output node with a duty cycle at or near 0%. However, for lower signal levels, e.g. with a magnitude below 2×VBatt or below VBatt, the charge pump 103 may be operated in the two times mode or one times mode respectively. Varying the output voltage of the charge pump 103 in this way can improve power efficiency.
Whilst a driver circuit such as illustrated in
Embodiments of the present disclosure relate to improved switching driver circuits and to methods of operation.
According to an aspect of the disclosure there is provided a driver apparatus for driving a transducer based on an input signal comprising:
In some examples, the first set of switching voltages may comprise first and second supply voltages received by the driver apparatus. In some examples, the driver apparatus comprises a DC-DC converter configured to generate at least a third supply voltage from at least one of the first and second supply voltages. The DC-DC converter may comprise a charge-pump or inductive boost converter. In some examples, the first supply voltage may be less positive or more negative than the second supply voltage and the DC-DC converter may be configured to generate the third supply voltage as V3=V2+(V2−V1), where V1 is the first supply voltage and V2 is the second supply voltage.
In some examples, at least one of the first, second and third input voltages may be the same as a voltage of the first set of switching voltages. In some examples, the first set of switching voltages may comprise first and second supply voltages received by the driver apparatus and the first input voltage may the same as the second supply voltage and each of the second and third input voltages may be the same the first supply voltage.
The driver apparatus may further comprise a second driver output node. The switch network may be further configured to selectively connect the second driver output node to the output voltage node of the flying capacitor driver or to any of the first set of at least three different switching voltages. The controller may be further configured to control the switch network and flying capacitor driver to generate a first drive signal at the second driver output node based on the input signal so as to drive a transducer connected between the first and second driver output nodes with a differential drive signal. The switch network may comprise: switches for selectively connecting the first and second output nodes respectively to a first voltage rail and switches for selectively connecting the first and second driver output nodes respectively to a second voltage rail; and switches for selectively connecting either of at least two of the first set of switching voltages to the first voltage rail, wherein the output voltage node of the flying capacitor driver may, in use, coupled to one of the first and second output nodes via the second voltage rail. In some implementations, the switch network may further comprise switches for selectively connecting the first and second driver output nodes respectively to one of the first set of switching voltages which is different to the voltages than can selectively connected to the first voltage rail.
The controller may be operable: in a first mode in which each of the first and second driver output nodes is switched between first and second supply voltages of the first set of switching voltages; in a second mode in which one of the first and second driver output nodes is switched between said first and second supply voltages and the other one of the first and second driver output nodes is connected to the output voltage node of the flying capacitor driver which operates to switch the voltage output node between the first supply voltage and the boosted voltage; and in a third mode in which one of the first and second driver output nodes is switched between the second supply voltage and a third supply voltage of the first set of switching voltages. The driver apparatus may comprise a DC-DC converter configured to generate said third supply voltage from said first and second supply voltages.
In some examples, the driver apparatus may further comprise a second flying capacitor driver. The controller may be operable to control the first and second flying capacitor drivers together to modulate the first output node between the boosted voltage generated by the first flying capacitor driver and an additional boosted voltage generated by the second flying capacitor driver.
In some examples, the first set of switching voltages, and the boosted voltage generated by the flying capacitor driver, may together form a set of equally spaced voltage levels. In some examples, the first set of switching voltage levels may comprise a received ground voltage, a received positive supply voltage and a boosted voltage equal to twice the received positive supply voltage.
The driver apparatus may be an audio driver apparatus for driving an audio output transducer based on an audio input signal. Embodiments also relate to an integrated circuit comprising the driver apparatus and to an electronic device comprising the driver apparatus.
In another aspect, there is provided a driver apparatus for driving a transducer based on an input signal comprising:
In another aspect, there is provided a driver apparatus for driving a transducer based on an input signal comprising: a first driver output node for outputting a first drive signal; a switch network operable in a direct mode to selectively connect the first driver output node to any of a first set of at least three different continuous voltages; wherein the switch network is further operable in an indirect mode to connect the output node to a flying capacitor so as to drive the output node to a voltage boosted by the flying capacitor.
In another aspect, there is provided a transducer driver configured to receive an input signal and first and second supply voltages and to generate an output signal for driving a, the transducer driver comprising: a combined charge pump and driver operable, in use, with at least one primary capacitor to selectively provide at least a first generated voltage based on the first and second supply voltages; a flying-capacitor driver operable, in use, with at least one secondary capacitor to provide at least a second generated voltage based on the first and second supply voltages; and an output bridge configured to selectively receive the first and second supply voltages, the first generated voltage and the second generated voltage to generate the output signal based on the input signal.
The combined charge pump and driver may be operable, in use, with first and second primary capacitors. The flying-capacitor driver is operable, in use, with first and second secondary capacitors.
It should be noted that, unless expressly indicated to the contrary herein or otherwise clearly incompatible, then any feature described herein may be implemented in combination with any one or more other described features.
For a better understanding of examples of the present disclosure, and to show more clearly how the examples may be carried into effect, reference will now be made, by way of example only, to the following drawings in which:
The description below sets forth example embodiments according to this disclosure. Further example embodiments and implementations will be apparent to those having ordinary skill in the art. Further, those having ordinary skill in the art will recognize that various equivalent techniques may be applied in lieu of, or in conjunction with, the embodiments discussed below, and all such equivalents should be deemed as being encompassed by the present disclosure.
Embodiments of the disclosure relate to driver circuitry for driving a transducer and, in particular, to switching driver circuitry in which an output node can be switched between different switching voltages with a controlled duty cycle. Embodiments of the disclosure also relate to methods of operation of driver circuitry.
In embodiments of the disclosure, a driver apparatus may comprise a switch network configured to selectively switch an output node between any of first set of a plurality of switching voltages, where the first set of voltages are different to one another and, in use, the relevant switching voltage is maintained at a corresponding switching voltage node substantially continuously throughout the whole of the switching cycle of the driver. In use, the output node may be switched between different switching voltages of the first set with a controlled duty cycle so as to generate an output drive signal.
At least one of the first set of switching voltages may comprise a system voltage, i.e. a defined DC voltage that is provided to the driver apparatus, such as an input supply or reference voltage. For example, the first set of switching voltages may comprise a positive input supply voltage, such as a battery voltage, received by the driver apparatus and/or a defined ground reference. At least one of first set of switching voltages may also include at least one supply voltage generated by a DC-DC converter of the driver apparatus, e.g. from a charge pump or inductive boost converter or the like, which may be powered by the input power supply voltages. In some embodiments, the first set of switching voltages may comprise at least three switching voltages.
The voltages of the first set of switching voltages may, in use, be maintained at respective switching voltage nodes and the output node may be switched between selected ones of the first set of switching voltage nodes to provide the desired voltage modulation at the output node.
In addition, the output node can be selectively connected to an output voltage node of a flying capacitor driver. The flying capacitor driver is configured for use with a first terminal of the flying capacitor connected to the output voltage node and is operable to switch a second terminal of the flying capacitor between two different voltages, which may comprise one or more of the system voltages, to modulate the voltage at the output voltage node. The flying capacitor driver may be configured such that at least one the voltages generated at the output voltage node, in use, is an additional voltage which is different to any of the switching voltages of the first set. It will be understood that this additional voltage is generated in a discontinuous manner, i.e. the additional voltage may be generated for only part of the switching cycle of the driver apparatus. Conveniently the other voltage to which the output voltage node of the flying capacitor driver is modulated is the same as one of the voltages of the first set of voltages. When the output node is connected to the output voltage node of the flying capacitor driver, the flying capacitor driver may be switched with a controlled duty cycle based on the input signal so as to modulate the voltage driver output node.
A third, different, supply voltage V3 is generated by a DC-DC converter 203, which may comprise a charge pump or an inductive converter or the like. In this example the DC-DC converter may generate the voltage V3 using the received system voltages V1 and V2. The output node 202a can be selectively connected to the supply voltage V3 output by the charge pump by switching path S3a.
Each of the voltages V1, V2 and V3 is, in use, maintained in a substantially continuous manner, that is, the relevant voltage is maintained at a substantially constant level during a switching cycle and the voltage at the relevant switching node thus does not substantially vary over the course of a full switching cycle of the driver apparatus 200. Where the DC-DC converter is a switched mode converter, such as a charge pump, the DC-DC converter is operable to maintain the supply voltage throughout a full switching cycle of the DC-DC converter. The voltage at the relevant switching node is thus substantially independent of the input signal for the driver apparatus. It will, of course, be understood that the output voltage of a DC-DC converter such as a charge pump or inductive boost converter or the like may exhibit some voltage ripple due to the operation of the DC-DC converter, but the extent of such ripple is relative small and a switched DC-DC converter such as a charge pump generally comprises an energy storage element such as a reservoir capacitor to maintain the output voltage throughout the whole of switching cycle of the DC-DC converter.
It should be noted that the voltage V3, generated by the DC-DC converter is generated in a substantially continuous manner when the DC-DC converter is active. This does not, however, mean that the DC-DC converter need be continuously active. If, for instance, the supply voltage generated by the DC-DC converter is only used for switching for relatively high magnitude output signals, in some cases the DC-DC converter may be controlled to be inactive if the signal magnitude is relatively low. However, when active, the DC-DC converter operates to maintain its output supply voltage V3 in a continuous manner.
The voltages V1, V2 and V3 provide a first set of switching voltages and, in use, the output node 202a may be switched between a selected pair of these switching voltages with a controlled duty cycle so as to provide the desired output signal. The output node 202a is switched between these voltages by controlling the relevant switching paths S1a, S2a and S3a to connect the output node to the relevant supply voltages with a controlled duty-cycle. Such operation can be seen as direct-coupled switching, or a direct charge transfer mode of operation, as the output node 202a is switched to be directly coupled to the relevant DC voltage supplies. As noted above, the DC supply voltages may, for example, be derived from a battery, an inductive switched mode power supply, or a switched capacitor power supply and maintain the voltage in substantially continuous fashion, i.e. are generally able to supply current for an extended period of time, for example greater than the period of the output drive signal at the lowest needed frequency. The terms “direct-coupled” and “DC-coupled” shall be used herein to refer to such switching of the output node between such supply voltages.
In addition, the output node 202a may be selectively coupled, via switching path S0a, to an output voltage node 204 of a flying capacitor driver 206. The output voltage node 204 is coupled to a first terminal of a capacitor 205. The second terminal of capacitor 205 is configured to be selectively switched between two different voltages Vac1 and Vac2 by switches Sac1 and Sac2. The first terminal of the capacitor 205 may also be selectively connected to a voltage Vac3, by switch Sac3. In use, the capacitor 205 may be cyclically charged and then connected to provide voltage boosting (positive or negative) of one of the voltages Vac1 and Vac2 to generate a boosted voltage at the switching voltage node and thus the capacitor 205 is used as a flying capacitor. The voltages Vac1, Vac2 and Vac3 may, in some implementations, be selected such that the boosted voltage generated at the output voltage node 204 is different to any of the voltages V1, V2 and V3. The voltage Vac1 is different to the voltage Vac2 and, if the switches Sac1 and Sac3 are operated in phase with one another, then Vac1 and Vac3 are also different from one another so that the capacitor 205 is charged by the voltage difference between Vac1 and Vac3 when both these switches are closed. Vac2 and Vac3 may be the same as one another or different. It will be understood that Vac1 may be more or less positive that Vac2 and/or Vac3. Conveniently at least one, and possibly all, of the voltages Vac1, Vac2 and Vac3 is provided by the supply voltage V1, V2 and V3, but any other system voltage could be used to provide one or more of these voltages.
For example, consider that the supply voltage V2 is used for Vac1 and that the supply voltage V1 is used for both Vac2 and Vac3, with the supply voltage V2 being more positive than V1. In use, in one state with the second terminal of the capacitor 205 connected to Vac1=V2 and the first terminal of the capacitor 205 connected to Vac3=V1, the capacitor is charged to a voltage +(V2−V1) with the positive plate at the second terminal. In this state the output voltage node 204 is at the voltage Vac3=V1. In a second state, the second terminal of the capacitor 205 is instead connected to Vac2=V1 and the first terminal of the capacitor 205 is disconnected from Vac3. In this state the capacitor 205 provides negative boosting of the supply voltage Vac2, which thus generates a negatively boosted voltage V0 at the output voltage node, where V0=−(V2−V1). In this example, the output voltage node 204 can thus be switched between the voltages V1 and V0, with the duty cycle being controlled by the switching of switches Sac1, Sac2 and Sac3. The capacitor 205, together with the switches Sac1, Sac2 and Sac3 can thus be seen as a flying capacitor based auxiliary driver or charge pump 206 for driving the output node.
The capacitor 205 can thus be selectively switched to provide selective boosting to provide a voltage V0, which may be different to the voltages V1, V2 and V3. Such operation can be seen as an indirect-coupled switching, or an indirect charge transfer mode of operation, as, in operation when the voltage V0 is generated, the output node is indirectly coupled to the supply Vac2 via the capacitor. The voltage V0 is not maintained continuously throughout the whole switching cycle of the driver apparatus. As used herein, the terms “indirect-coupled” or “indirect switching” will be used to refer to such operation and the term “AC-coupled” will also be used to such operation.
The driver apparatus 200 is thus operable in a direct-coupled mode of operation and can switch the output between selected ones of the supply voltages V1, V2, V3 and also operable in an indirect-coupled mode of operation, to generate at least one additional voltage V0. The driver apparatus 200 is thus a mixed direct-coupled and indirect-coupled switching driver. Energy can be transferred to the load 201 via a mix of “DC-coupled” and “AC-coupled” paths according to the required output signal.
The DC supply voltages V1, V2 and V3 and the at least one additional boosted voltage V0 are chosen to provide a desired output voltage range for the single ended drive signal at the output node 202a. The difference between the highest voltage level (i.e. most positive/least negative) and the lowest voltage level (i.e. least positive or most negative) from the voltages V1, V2, V3 and V0 is selected to provide a desired output range for the output drive signal. The other voltages are selected to provide intermediate voltages levels. In use, the driver apparatus 200 may be controlled so as to only switch the output node between adjacent voltage levels.
For instance, if V3>V2>V1>V0 (in terms being more positive), then the output node may be switched between the voltages V2 and V3 with a controlled duty cycle to provide an (average) output voltage at the output node 202a in the range between V2 and V3. To provide a lower (average) output voltage, the output node may be switched V1 and V2 to provide an (average) output voltage in the range between V1 and V2 or switched between V0 and V1 to provide an average voltage in this range.
The output voltage 301 at the output node can thus vary within substantially all of a full voltage range defined between V3 and V0. However, across the whole of this output voltage range, the output node is switched between two switching voltages that differ by less than the full voltage range, i.e. the magnitude of the voltage modulation applied to the output node over each switching cycle is less than the full voltage output range.
By contrast, for the switching driver discussed with reference to
In some cases, the voltages levels V1, V2, V3 and V0 may be arranged so that voltage difference between successive voltages levels may be substantially the same as one another. Where V1 and V2 are received system voltages, the voltage V3 may be generated to differ from V1 by an amount equal in magnitude to (V2−V1) and likewise V0 may be generated so as to differ from one of V1, V2 and V3 by the same magnitude. For example, if V1 is ground and V2 is an input voltage VP, then one of V3 and V0 may be generated as 2VP and the other generated as −VP, although other combinations would be possible.
As noted,
Referring back to
Thus, considering the example of the different voltage levels of
In the example of
Driving the load with the boosted voltage V0 generated by the flying capacitor can be relatively power efficient, as charge transferred from the supply to the capacitor is then transferred to the load without significant wastage. However, the duty cycle of switching of the capacitor 205 is dependent on the required output signal voltage and thus is input signal dependent. This results in a duty-cycle dependent impedance variation. A significant signal dependent impedance variation can generally be undesirable.
By using a mix of direct-coupled and indirect-coupled switching, embodiments of the present disclosure provide an advantageous balance between power efficiency and impedance variation. This may also allow use of a reduced number of capacitors compared to the driver illustrated in
The embodiment of
The charge pump 203 comprises a capacitor C1 arranged as a flying capacitor with switches S1, S2, S3 and S4. Switches S1 and S2 selectively connect a first terminal of the capacitor C1 to the system voltages VP and ground respectively, whilst switch S3 selectively connects the second terminal to system voltage VP and switch S4 selectively couples the second terminal of capacitor C1 to the charge pump output for the voltage 2VP.
In use, switches S2 and S3 are switched together and in antiphase with switches S1 and S4. The charge pump 203 thus cycles between a first state, with switches S2 and S3 closed (and switches S1 and S4 open), to charge the flying capacitor C1 to the voltage VP with the second terminal being positive, and a second state with switches S1 and S4 closed (and switches S1 and S4 open), such that the system voltage VP is connected to the first terminal of capacitor C1 and the second terminal of capacitor C1 is boosted to 2VP. This state charges the reservoir capacitor C2, connected between the system voltage VP and the charge pump output, and thus provides an output voltage of 2VP, which is maintained by the capacitor C2.
The switches S1 to S4 of the charge pump 203 are switched at a charge pump frequency which is independent of the output signal being output by the driver apparatus, and which is thus independent of the duty cycles at the output nodes 202a and 202b.
The driver apparatus 400 also comprises a differential output bridge 401 for the output nodes 202a and 202b. In the example of
The driver apparatus also comprises a flying capacitor auxiliary driver 206 as discussed with reference to
Switch S11 thus provides the switching path Sla discussed with reference to
The embodiment of
In use, the various switches S5 to S18 of the driver apparatus are controlled by a controller 403 based on an input signal Sin, for example an input audio signal, to generate a corresponding differential output signal. The controller 403 may be configured to operate the driver apparatus selectively in different modes of operation to provide a differential output voltage in the range of +4VP to −4VP based on the input signal Sin. The controller 403 thus receives the input signal Sin and generates a series of switch control signals Scon for controlling the switches. The controller 403 may also control the switches S1-S4 of the charge pump 203 but the control of these switches may be independent of the input signal Sin.
For a relatively low-magnitude output signal, i.e. for a differential output magnitude below a first threshold, where the first threshold is a magnitude of VP or lower, the driver apparatus 400 can be operated in a first mode in which each of the output nodes 202a and 202b is switched between voltages ground and VP.
In this first mode of operation, switch S6 is closed to connect the input supply voltage VP to the high-side rail and switch S5 is open to disconnect the output of the charge pump 203 from this rail. Switches S9 and S10 are also open to disconnect the output nodes from the low-side rail.
The switches S7 and S11 are switched in antiphase with a controlled duty-cycle to switch the output node between the voltage VP (at the high-side rail) and ground. Likewise, the switches S8 and S12 are also switched with a controlled duty cycle for the output node 202b.
Each of the output node 202a and 202b is thus switched between the voltages ground and VP with respective controlled duty cycles to provide the desired output voltage based on the input signal.
In this first mode of operation, the switches S1 to S4 of the charge pump may be switched at the charge pump frequency as discussed above to maintain the voltage on capacitor C2. In addition, switches S13 and S15 of the first flying capacitor auxiliary driver 206 may be kept closed so that the capacitor 205 is charged to the voltage VP. Switches S16, S17 and S18 may be kept open, or in some cases switches S16 and S18 could be closed so as to provide some pre-charging of capacitor C4 (which is used in a fourth mode as discussed below).
For a higher intermediate magnitude output signal, i.e. for a differential output magnitude between the first threshold and a second higher threshold, where the second threshold is a magnitude of 2VP or lower, the driver apparatus 400 can be operated in a second mode in which one of the output nodes 202a and 202b (depending on the required polarity) is switched between voltages ground and VP and the other output node is switched between voltages-VP and ground.
If the polarity of the differential output is defined as being positive when the voltage at the output node 202a is more positive that the voltage at the output node 202b, then for a positive output signal in the second mode of operation the output node 202a would be switched between VP and ground, whilst the output node 202b is switched between-VP and ground.
In this case, switch S6 is again closed to connect the input voltage VP to the high-side rail, with switch S5 open, and switches S7 and S11 are again switched with a controlled duty-cycle, whilst switch S9 is open.
In this case switch S10 is closed to connect the output node 202b to the low-side rail, with switches S8 and S12 open. Switch S16 is closed to connect the low-side rail to the first flying capacitor auxiliary driver 206. Switches S13 and S15 are switched together in antiphase with switch S14 with a controlled duty cycle based on the input signal Sin. As described with reference to
The output node 202a is thus switched between the voltages ground and VP, whilst the output node 202b is switched between the voltage-VP and ground, with respective controlled duty cycles to provide the desired output voltage based on the input signal.
For a still higher intermediate magnitude output signal, i.e. for a differential output magnitude between the second threshold and a third higher threshold, where the third threshold is a magnitude of 3VP or lower, the driver apparatus 400 can be operated in a third mode in which one of the output nodes 202a and 202b (depending on the required polarity) is switched between voltages VP and 2VP and the other output node is switched between voltage-VP and ground.
For a positive differential output, the output node 202a may be switched between the voltages VP and 2VP. In this case, switch S7 is closed throughout the switching cycle to connect the output node to the high-side rail (with switches S9 and S11 open) and the switches S5 and S6 are switched with a controlled duty cycle to switch the voltage at the high-side rail between VP and 2VP. The output node 202b is connected to the low-side rail by switch S10 and the flying capacitor auxiliary driver 206 operates in the same manner as in the second mode.
The output node 202a is thus switched between the voltages VP and 2VP, whilst the output node 202b is switched between the voltage-VP and ground, with respective controlled duty cycles to provide the desired output voltage based on the input signal.
For a still higher magnitude output signal, i.e. for a differential output magnitude above the third threshold, the driver apparatus 400 can be operated in a fourth mode in which one of the output nodes 202a and 202b (depending on the required polarity) is switched between voltages VP and 2VP and the other output node is switched between voltage −2VP and −VP.
For a positive differential output, the output node 202a may be switched between the voltages VP and 2VP. In this case, switch S7 is closed throughout the switching cycle to connect the output node to the high-side rail (with switches S9 and S11 open) and the switches S5 and S6 are switched with a controlled duty cycle to switch the voltage at the high-side rail between VP and 2VP in a similar fashion as in the third mode.
The output node 202b is connected to the low-side rail with switch S10 closed (and switches S8 and S12 open). In this case, the first flying capacitor auxiliary driver 206 cooperates with the second flying capacitor auxiliary driver 402 to switch the voltage at the low-side rail between −VP and −2VP. These auxiliary drivers are controlled between two states with a controlled duty cycle based on the input signal Sin.
In the first state, switches S14 and S16 are closed (with switches S13 and S15 open). The capacitor 205, charged to VP, is thus connected between ground and the low-side rail, with the positive plate connected to ground. This drives the low-voltage rail, and hence the output node 202b to a voltage-VP. In this first state switch S18 is also closed, with switch S17 open, so that capacitor C4 is charged to a voltage of 2VP.
In the second state, switch S16 is open to isolate the first flying capacitor auxiliary driver 206 from the low-side rail, and switch S17 is closed (with switch S18 open) to connect capacitor C4 between ground and the low-side rail, with its positive plate connected to ground. This drives the low-side rail to −2VP. In this first state, switches S13 and S15 may also be closed, with switch S14 open, to recharge the capacitor 205.
Thus, in the fourth mode, the first flying capacitor auxiliary driver acts as a helper charge pump for the second flying capacitor auxiliary driver.
The output node 202a is thus switched between the voltages VP and 2VP, whilst the output node 202b is switched between the voltages −2VP and −VP, with respective controlled duty cycles to provide the desired output voltage based on the input signal.
It will be seen from
In some implementations it would, however, be possible in at least one alternative mode to modulate the voltage on one side of the load only, whilst holding the voltage on the other side of the load substantially constant throughout the switching cycle. For instance, in an alternative to the fourth mode illustrated in
The controller 403 therefore receives the input signal Sin and generates appropriate control signals Scon for the switches of the driver apparatus 400 to provide a corresponding output signal. Depending on the signal magnitude, the controller operates in the appropriate mode and controls the duty cycles on both sides of the load. As the input signal varies, the controller controllably adjusts the duty cycles accordingly within a given mode of operation, until a threshold for changing mode is reached, at which point the controller 403 transitions to the new mode of operation, with appropriate changes in duty cycle to account for the change in switching voltages and maintain the correct differential voltage.
The driver apparatus 400 may be implemented using FET devices for the switches. Each switch may be implemented by one or more suitable FET devices. The FET devices will be configured, as will be understood by one skilled in the art, to avoid unwanted conduction via a body diode of the FET device in the off state. At least some switches may comprise at least two FETs in series in a back-to-back arrangement, such that, whatever the polarity of the voltage across the switch in the off state, one of the body diodes is reverse biased and prevents current flow. For instance, switch S11 is arranged to selectively connect the output node 202a to the voltage V1, which may be ground in the example of
It will be understood that the FET devices should have a voltage rating, in terms of the voltage that can be safely tolerated across the device when in the off state, e.g. the drain-source standoff voltage, that is sufficient for the maximum expected voltage across that device in an off state. As used herein, the term voltage stress shall be taken to mean a drain-source voltage across the FET device when in the off state.
For the example of
The FET device(s) that are used to implement these switches may thus have a voltage rating or safe operating threshold that is suitable for a voltage stress of (at least) a magnitude equal to 4VP. As noted above, and as will be understood by one skilled in the art, voltage transients induced by the changing currents through the different switching paths and/or back-power effects due to a phase lag between the voltage and current, may result in the maximum voltage stress being higher than just that due to the nominal switching voltages, which may also be taken into account.
In implementations where the nominal values of the system voltages, e.g. supply voltage VP and ground, are substantially fixed and non-varying, the maximum voltage stress across each of the switches can be determined, for the worst case expected operating conditions, and devices with an appropriate voltage tolerance selected for use.
In some implementations, however, the value of at least one of the system voltages may be variable in use, i.e. the value of an input supply voltage VP may vary in use. For example, in a battery powered device, the voltage VP may be derived from a battery voltage VBatt and may vary depending on the state of charge of the battery. For instance, in some examples a battery voltage may vary from around 4.5V at or near full charge to say around 3.5V or lower at low charge. Further, such a device that is operable with a battery voltage may additionally be operable to receive power from an external power supply, e.g. via a mains adapter or via some USB or similar power supply. In such a device, some power management circuit may manage the voltage supply depending on whether a source of external power is available or not and, when the source of external power is available, the supply voltage VP may be supplied at a higher voltage, say of the order of 5.5V or higher. This means that the voltage difference between the various switching voltages, which depends on the received supply voltage, may also vary.
The switches of the switching driver apparatus 400 could be implemented by devices with a suitable voltage rating for the maximum voltage stress expected across the device in any switch state of any of the modes of operation, when operating with the maximum expected value of VP. For switches S7, S8, S9 and S10, which may experience a voltage stress of 4VP (or greater depending on any voltage transients/back-power effects) across the switch when operating in the fourth mode, these switches may thus be implemented by devices that have a suitable voltage rating of at least four times the highest expected value of the input supply voltage VP.
This may, however, require devices with a relatively high voltage rating, and devices with a high voltage rating may be larger and/or more expensive and/or can have a greater power consumption than devices with a lower voltage rating.
In some implementations, to avoid the need to use devices with such high voltage ratings, the controller 403 may be configured so as to control the mode of operation of the switching driver apparatus 400 and/or the switching pattern or modulation within a given mode of operation, based on the value of the relevant system voltage, e.g. based on the value of the supply voltage VP, and may be configured to avoid switch states that result in an overly high stress across the devices when the voltage VP is high. Thus, one or more switches that may be expected to experience the highest voltage stress due to the nominal values of the switching voltages in a given switch state, may be implemented with a voltage tolerance which is only suitable for operation in that switch state for a lower range of the possible values of the input supply voltage VP. Operation in that switch state may only be allowed when the value of the supply voltage is within this lower range and operation in that switch state may be prevented if the input supply voltage VP exceeds that lower range. In other words, at least some devices could be implemented with a safe operating threshold that could be exceeded by operating in some switch states for some expected levels of supply voltage VP, but the switching driver apparatus 400 is controlled to avoid such switch states and to maintain the voltage stress across the devices within the safe operating area, i.e. below the safe operating threshold.
For instance, consider that the supply voltage VP may, in use, have different values within a range of say 3.5V to 5.5V. As noted above, the maximum expected voltage stress due to the nominal value of the switching voltages may have a magnitude of 4VP in a state of the fourth mode of operation for switches S7, S8, S9 and S10. The devices used for these switches may be implemented with a voltage tolerance that allows for safe operation in this state when the supply voltage VP has a value at the lower end of the range of possible supply voltages, and may, purely for example, be implemented with a voltage rating of, say, 18V. In this example, if the supply voltage VP is lower than 4.5V, then the voltage stress of 4VP due to the nominal values of the switching voltage would not exceed the voltage tolerance. Ignoring, for now, any voltage transients/back power effects, if the value of the supply voltage were lower than 4.5V, the controller 403 may control the switching driver to operate in any of the described switch states in any of the four modes of operation, including, if and when required, the switch state that leads to a voltage stress of 4VP across switches S8 and S9 or S7 and S10. However, if the supply voltage is greater than 4.5V, the controller 403 may prevent operation in the switch state in the fourth mode that leads to a voltage stress of 4VP across the relevant switches.
In practice, however, the effect of any expected additional induced voltages or back-power effects also should be taken into account in determining whether to allow operation in this switch state. In some implementations, this may be achieved by determining an expected maximum addition to the voltage stress that could be expected in the worst-case operating conditions, which could be determined, for example, through simulation, modelling and/or test. Such a determined maximum addition could be used as a safety margin, i.e. such that operation in a switch state that leads to a nominal voltage stress of 4VP is only allowed when the value of 4VP is lower than the voltage rating of the switch by more than the determined safety margin. In some implementations, however, the controller 403 may be configured to receive an indication of at least one operating parameter of the switching driver apparatus which is indicative of said additional induced voltages or back-power effects that may add to the voltage stress, and may be configured to determine the expected voltage stress across the device for the present operating conditions and to permit or deny operation in the relevant switch state accordingly.
It will also be understood that the nominal voltage stress of 4VP arises when one output node is driven to the highest switching voltage +2VP which is generated by the charge pump 203 and the other output node is driven to the lowest switching voltage-2VP generated by the flying capacitor driver 402. Whilst these voltages are nominally equal to +2VP and −VP respectively, in practice, losses etc. may mean that these generated voltages are not exactly equal to +2VP and −2VP. In some implementation one or more of these generated voltages may be monitored and used to determine the expected voltage stress across the relevant switches, in addition to, or instead of, the supply voltage VP.
In some implementations, if it is determined that, because of the value of the supply voltage VP, operation in the fourth mode could potentially lead to a voltage stress across one or more of the switches of the switching driver which is above the relevant safe operating threshold, the controller 403 may be configured to prevent operation in the fourth mode of operation at all. Thus, for high magnitude output signals, the switching driver apparatus 400 may be operated in the third mode, with a first driver output node modulated between +2VP and +VP and the second driver output node modulated between ground and −VP, but it would not be operated in the fourth mode where the second driver output node is modulated between −VP and −2VP. Operation in the fourth mode may thus be gated by a digital control.
However, it will be noted that the voltage stress of 4VP only occurs when one output node is driven to the highest switching voltage, i.e. +2VP, at the same time that the other output node is driven to the lowest switching voltage, i.e. −2VP, and this state only occurs for some duty cycles of operation in the fourth mode. In the illustrated example switching waveforms of
In theory the range of acceptable switching patterns could include any switching pattern where the period during which one output node is switched to the voltage +2VP is no greater in duration than the corresponding period during which the other output node is switched to the voltage-VP and a limit of duty-cycle might be a duty-cycle where one node was switched from +VP to +2Vp at the same time that the other output node was switched from −2VP to −VP and vice versa. In practice, however, there may be some skew in the rise and fall of the voltages at the relevant output nodes which it may be beneficial to take into account, i.e. the time of the rise/fall of voltage at one node may have some skew compared to the fall/rise in voltage at the other node, and thus the limiting of the acceptable switching patterns, i.e the limiting of the acceptable range of duty cycle may take such skew into account.
Note, if operation in a switch state that leads to a nominal voltage stress of 4VP were prevented, it would not be possible, to operate in the alternative fourth mode of operation discussed above, where one output node is held at a substantially constant voltage of +2VP and the other output node is modulated between −VP and −2VP, as this would necessarily lead to an instance of the unwanted switch state.
In some implementations, the voltage tolerance of the relevant switches may be sufficient that a nominal voltage stress of 3VP across the switches may be safely tolerated across the whole expected range of the supply voltage, which thus could allow the switching driver to be operated in this restricted fourth mode of operation up to the maximum expected value of the supply voltage VP, e.g. for a supply voltage value VP of 5.5V in the example discussed above. This would also mean that there would be no limit on operation in the third mode, where the maximum voltage stress due to the nominal switching voltages will be 3VP, across the whole range of supply voltage. However, in at least some implementations it is possible that for the highest expected supply voltages VP, e.g. a supply voltage at 5.5V in the example above, then in at least some operating conditions, voltage transients and/or back-power effects could add the voltage stress of 3VP due to the nominal switching voltages and exceed the voltage rating of the devices of the relevant switches. If this were the case, then controller 403 may be configured to prevent any operation in the fourth mode and to control operation in the third mode of operation to prevent the switch state where one output node is at +2VP at the same time that the other output node is at −VP, i.e. to control the switching pattern in the third mode to ensure that the period when one output node is switched to +2VP only occurs when the other output node is switched to ground, so as to limit the maximum voltage stress due to the nominal switching values to 2VP. In this case there may be some limitation in switching pattern/duty cycle in a similar manner as discussed above.
It will be understood that preventing operation in the fourth mode of operation, or limiting the modulation pattern/duty-cycle that is permitted in a given mode of operation, can limit the maximum output voltage that the switching driver apparatus can achieve. For instance, if operation in the switch state of the fourth mode which leads to a differential voltage of magnitude 4VP is prevented, the switching driver will be limited to a maximum output voltage of magnitude up to 3VP. However, it will be understood that such limiting may only applied when the supply voltage VP has a relatively high value, and in such a case a maximum output voltage of magnitude 3VP may be sufficient to achieve a desired range of output voltage.
For instance, consider the example discussed above where the input supply voltage is assumed to be able to take different value in the range of 3.5 to 5.5V. For an input supply voltage VP at the lower end of this range, the switching driver apparatus 400 may operate in the fourth mode to generate an output voltage with a magnitude up to a nominal value of 4VP. At the lowest supply voltage value of 3.5V, this could generate an output voltage with a magnitude up to a nominal value of 14V. At the high end of the range of supply voltage, the switching driver may be configured to prevent operation in the switch state that generates a differential voltage of 4VP and the maximum nominal output voltage of the switching driver may be limited to 3VP, but this would still provide an output voltage magnitude of up to 15.5V for the highest supply voltage value of 5.5V.
In general, as illustrated in
The first and second primary capacitors may be configured as flying and reservoir capacitors respectively. The combined charge pump and driver may comprise the charge pump 203 discussed with reference to
A flying capacitor auxiliary driver is also operable to provide at least a second generated voltage. The flying capacitor auxiliary driver 703 may be configured to provide a voltage V0 by indirect-coupled or AC coupled switching, e.g. through use of a flying capacitor. The combined charge pump and driver 703 may thus comprise driver capability so as to drive the output bridge between different switching voltages with a controlled duty cycle by switching of a flying capacitor. The flying capacitor driver 703 is operable, in use, with at least one capacitor, which may be referred to as a secondary capacitor. In the example of
The controller 704 is configured to control the switching of operation of the output stage 701, combined charge pump and driver 702 to implement different modes of operation, where the output nodes of the output stage 701 are modulated between different combinations of switching voltages in the different modes, and to also control the duty cycle of modulation of the output nodes between the relevant switching voltage in the relevant modes.
In some implementations, at least one of the supply voltages, e.g. the supply voltage V2, and hence the generated voltages V3 and V0, may be variable in use. In some such implementations, the controller 704 may be configured to limit the modes of operation and/or the modulation/duty-cycle within a mode of operation, to prevent an undue voltage stress across a component of the driver apparatus, e.g. across a switch of the output stage in the off state. The controller 704 may thus receive an indication of the variable supply voltage and/or an indication of at least one of the generated voltages and determine whether to allow operation in a given switch state. The controller 704 may also receive an indication of one or more operating parameters of the driver apparatus that may also contribute to voltage stress across the relevant components, for instance parameters indicative of voltage transients due to switching, e.g. slew rates and/or back-power effects and or any skew in the rise and fall timings of the voltages at the output nodes.
The controller 704 also comprises a limiter which is configured to determine a voltage limit for operation of the switching driver. The limiter is configured to receive an indication of one or more of the supply voltage V2, e.g. the supply voltage VP, the charge pump voltage V702 of combined charge pump and driver 702 and the output voltage V703 of the flying capacitor auxiliary driver 703. The limiter may also receive one or more indicators of system parameters that can impact voltage stress across switches of the switching driver, for instance an indication of rise/fall edge skew between the output voltages and/or any back-power effects. The limiter may thus determine a limit for the maximum voltage difference that can be tolerated due to the nominal switching voltages, taking the operating parameters of the switching driver into account. This limit can be digitally controlled, programmable and can be dynamically adjusted.
In this example the limiter receives the output of the loop filter 705 which is input to the quantizer 706. This effectively represents the voltage demand of the switching driver (based on the input signal) and the limiter thus determines whether the voltage demand would exceed the determined limit. If so, the limiter acts to provide limiting or clipping at the output of the quantizer so as to limit the switching pattern and avoid exceeding the maximum limit. The limiting is applied proactively at the PWM quantizer to ensure switching patterns for the current switching cycle do not exceed the safe operating area for the relevant devices.
The embodiment of
The switching apparatus 800 comprises an output stage 801 for driving the output nodes 202a and 202b. The output stage 801 in this embodiment comprises switches SW5a and SW5b for selectively connecting the output node 202a to respective high-side and low side-rails for the output node 202a. Likewise switches SW4b and SW5b selectively connect the output node to high-side and low-side rails for output node 202b. The output stage 801 in this example may thus be seen as an H-bridge.
A driver 802a is operable to provide voltages for the high-side and low-side rails for output node 202a. The driver 802a comprises a capacitor CP1a coupled between the high-side and low-side voltage rails. A switch SW6a selectively couples the high-side voltage rail to a voltage select node which can be selectively connected to either of the system voltages V1 or V2, i.e. ground and VP in this example, by switches SW7a and SW8a. Likewise, SW3a selectively couples the low-side voltage rail to a voltage select node which can be selectively connected to either of the system voltages V1 or V2 by switches SW1a and SW2a.
In use, the driver 802a can supply the system voltages V2 and V1 as voltages to the high-side and low-side rails for DC-coupled switching. In addition, the driver 802a can selectively connect the capacitor CP1a in series with one of these supply voltages to provide positive or negative boosting of the relevant supply voltage to provide an indirect (or AC coupled) switching voltage, as will be described in more detail below.
A driver 802b is coupled to the high-side and low-side rails for the output node 202b. The driver 802b has generally the same structure as the driver 802a and thus has components corresponding those of the driver 802a (identified by the same reference but with the suffix b in
The driver apparatus 800 also comprises a charge pump 803. The charge pump 803 is configured to be operable to provide a supply voltage to, in this example, the low-side rail for either of the output nodes 202a or 202b. The charge pump driver 803 comprises a capacitor CP2 and switches S9 and S10 for selectively connecting a first terminal of capacitor CP2 to either of the system voltages V2 or V1, and switch SW11 for selectively connecting a first terminal of capacitor CP2 to V1, i.e. ground in this example. Switches SW12 and SW13 selectively connect the charge pump driver to the low-sides rails for output nodes 202a and 202b respectively. In use, when the charge pump 803 is active to supply a voltage to one of the low side rails, the respective capacitor CP1a or CP2b connected to that voltage rail may be used as a reservoir capacitor, as will be discussed in more detail below.
In use, the various switches of the driver apparatus are controlled by a controller 804 based on an input signal Sin, for example an input audio signal, to generate a corresponding differential output signal. The controller 804 may be configured to operate the driver apparatus selectively in different modes of operation to provide a differential output voltage in the range of +3VP to −3VP based on the input signal Sin. The controller 804 thus receives the input signal Sin and generates a series of switch control signals Scon for controlling the switches.
For a relatively low-magnitude output signal, i.e. for a differential output magnitude below a first threshold, where the first threshold is a magnitude of VP or lower, the driver apparatus 800 can be operated in a first mode in which each of the output nodes 202a and 202b is switched between voltages which are ground and VP.
In the first mode, for driver apparatus 800, switches SW1a, SW3a, SW8a and S6a are also closed (with switches SW2a and SW7a open) to connect the high-side and low-side voltage rails of driver 802a to the voltage VP and ground respectively, and the corresponding switches of driver 802b are switched in the same way. The switches SW4a and SW5a are switched in antiphase with a controlled duty-cycle to switch the output node 202a between the voltage VP at the high-side rail and ground at the low-side rail. Likewise the switches SW4b and SW5b are also switched with a controlled duty cycle for the output node 202b.
Each of the output nodes 202a and 202b is thus switched between the voltages ground and VP with respective controlled duty cycles to provide the desired output voltage based on the input signal.
In additional, as the capacitors CP1a and CP1b are connected between the respective high-side and low-side rails of the relevant driver, each of these capacitors is charged to the voltage VP.
In this first mode of operation, switches SW12 and SW13 are open to disconnect the charge pump 803 from the low-side rails. Switches SW9 and SW11 may be closed, with switch SW10 open, to charge the capacitor CP2 to a voltage VP.
For a higher intermediate magnitude output signal, i.e. for a differential output magnitude between the first threshold and a second higher threshold, where the second threshold is a magnitude of 2VP or lower, the driver apparatus 800 can be operated in a second mode in which one of the output nodes 202a and 202b (depending on the required polarity) is switched between voltages ground and VP and the other output node is switched between −VP and ground.
If the polarity of the differential output is defined as being positive when the voltage at the output node 202a is more positive that the voltage at the output node 202b, then for a positive output signal in the second mode of operation the output node 202a would be switched between ground and VP, whilst the output node 202b is switched between −VP and ground.
In this case, driver 802a may be operated in the same way as in the first mode. For driver 802b, switch SW4b may be closed, with switch SW5b open, to connect the output node 202b to the low-side rail. In this mode, the driver 802a may cycle between two states with a controlled duty-cycle to vary the voltages at the low-side voltage rail. In one state, switches SW1b, SW3b, SW6b and SW8b may be closed (with switches SW2b and SW7b open) so that the low-side rail is driven to ground and the capacitor CP1b is charged to a voltage of VP. In the other state, switches SW6b and SW7b are closed (with switches SW1b, SW2b, SW3b and SW8b open) so that the capacitor CP1b is connected between V1, ground in this example, and the low-side rail with its positive plate connected to V1. This provides negative boosting of the voltage V1 and, in this example, drives the low-side rail to the voltage-VP.
The driver 802b in this mode thus provides an indirect-coupled switching voltage, with the advantages of power efficiency discussed above.
The output node 202a is thus switched between the voltages ground and VP, whilst the output node 202b is switched between the voltage-VP and ground, with respective controlled duty cycles to provide the desired output voltage based on the input signal.
Again, in this second mode of operation for the driver apparatus, switches SW12 and SW13 are open to disconnect the charge pump 803 from the low-side rails and switches SW9 and SW11 may be closed, with switch SW10 open, to charge the capacitor CP2 to a voltage VP.
For a still higher intermediate magnitude output signal, i.e. for a differential output magnitude between the second threshold and a third higher threshold, where the third threshold is a magnitude of 3VP or lower, the driver apparatus 800 can be operated in a third mode in which one of the output nodes 202a and 202b (depending on the required polarity) is switched between voltages VP and 2VP and the other output node is switched between voltage-VP and ground.
For a positive differential output, the output node 202a may be switched between the voltages VP and 2VP. In this case, switch SW5a may be closed throughout the switching cycle to connect the output node 202a to the high-side rail (with switch SW4a open). The driver 802a then cycles between two states with a controlled duty cycle so as to modulate the voltage at the high-side rail between VP and 2VP.
In one state, switches SW1a, SW3a, SW6a and SW8a are closed (with switches SW2a and SW7a open) to connect the high-side rail to the voltage VP and to charge the capacitor CP1a to the voltage VP. In the other state, switches SW2a and SW3a are closed (with switches SW1a, SW6a, SW7a and SW8a open) to connect the capacitor CP1a between the voltage V2, i.e. VP in this example, and the high-side rail, so as to provide a boosted voltage at the high-side rail, equal to +2VP in this example.
In this mode of operation, the driver 802a thus operates to provide an indirect-coupled positive boosted voltage of 2VP.
The driver 802b may operate in the same way as the second mode.
The output node 202a is thus switched between the voltages VP and 2VP, whilst the output node 202b is switched between the voltage-VP and ground, with respective controlled duty cycles to provide the desired output voltage based on the input signal.
Again, in this third mode of operation for the driver apparatus 800, switches SW12 and SW13 are open to disconnect the charge pump 803 from the low-side rails and switches SW9 and SW11 may be closed, with switch SW10 open, to charge the capacitor CP2 to a voltage VP.
In this third mode of operation for the driver apparatus 800, the drivers 802a and 802b on both sides of the load are operating in an indirect-coupled mode to generate an indirect-coupled boosted voltage.
As discussed above, whilst such indirect-coupled switching can be power efficient, it can result in an undesirable duty-cycle dependent impedance variation. This impedance variation is dependent on duty-cycle, and the extent of the variation depends on the proportion of time the relevant AC-coupled boosted voltage is connected to the output node.
To reduce this variation, the driver apparatus 800 is also operable in a fourth mode when the differential output magnitude between the second threshold and third thresholds. In the fourth mode, one of the output nodes 202a and 202b (depending on the required polarity) is switched between voltages VP and 2VP but the other output node is held constant throughout the switching cycle at the voltage-VP. The voltage-VP is generated by the charge pump 803 at the low-side rail for the relevant output node.
The controller may operate in the fourth mode when the differential output magnitude is between the second threshold and third thresholds, and where, for the relevant output node that would otherwise be switching between −VP and ground, the proportion of the switching cycle that would be spent at the indirect-coupled boosted voltage-VP would be above a threshold. For example, the threshold could be 50%. Thus, if the relevant output node would spend 50% or more of the switching cycle connected to −VP if operating in the third mode (which corresponds, in this case, to a duty cycle for that output node of less than 0.5), the controller 804 can control the driver apparatus to operate in the fourth mode instead.
For a positive differential output, the output node 202a may be switched between the voltages VP and 2VP and the output node 202b may be held static at the voltage-VP.
The driver 802a may thus be operated in the same way as in the third mode.
To generate the static voltage-VP, switch SW4b is closed, with switch SW5b open, to connect the output node 202b to the low-side rail. Switches SW6b and SW7b of the driver 802b are closed (with the other switches of the driver 802b open) so as to connect capacitor CP1b between the low-side rail and ground so that the capacitor CP1b can acts as a reservoir capacitor for the charge pump 803.
The charge pump 803 then controls switches SW9 and SW11 together and in antiphase with switches SW10 and SW13 to repeatedly charge capacitor CP2 to VP, and then connect the capacitor CP2 between ground and the low-side rail, with its positive plate connected to ground, so as to drive the low-voltage rail to −VP. This charges the capacitor CP1b to maintain the voltage at the low-side rail. The switches SW9, SW10, SW11 and, in this case, SW13, are cycled at a defined charge pump switching frequency which is independent of the duty cycle of the switching node 202a.
In this mode of operation, the charge pump 803 thus operates, together with the capacitor Cp1b of the driver 802b, to provide a continuous supply voltage at the low-side rail, and the output node is directly coupled to this supply voltage.
The output node 202a is thus switched between the voltages VP and 2VP with a controlled duty cycle, whilst the output node 202b is held static, through the switching cycle at the voltage-VP and ground, to provide the desired output voltage based on the input signal.
It will be understood, however, that the charge pump 803 could alternatively be arranged to provide a positive boosted supply voltage to the high side rail, i.e. to provide a supply voltage of +2VP. In this case, the fourth mode may correspond to one output node being held static with the supply voltage 2VP and the other output node being switched with a controlled duty cycle between −VP and ground. In some implementations there could be two charge pumps, coupled to the high-side and low-side rails respectively.
Note that the second mode of operation of the driver apparatus is described as a mode where one of the output nodes switches between −VP and ground, and the other node switches between ground and VP. It would be possible to implement an alternative second mode, that provides the same range of differential output voltage, by switching one output node between ground and VP, whilst the other output node is switched between +VP and +2VP.
It will also be understood that the voltages VP and ground are given as an example only.
It will also be understood that in some implementations the supply voltage VP could be variable in use, e.g. derived from a battery voltage and/or in some instanced from an external power supply. The switches of the switching driver apparatus 800 may, for example, be implemented by suitable FET devices and the FET devices may have a suitable voltage rating for the maximum voltage stress expected in normal operation for the maximum expected supply voltage. In some cases, however, at least some switches could be implemented by devices with a voltage rating which that could exceeded in some switch states for some expected values of supply voltage VP, and the controller 804 may, in a similar manner as discussed with reference to
In general, as illustrated in
Embodiments of the disclosure thus relate to driver apparatus that operates with a multi-level switching voltages and which operates with a mixed direct-coupled and indirect-coupled energy transfer.
In some embodiments, there is provided a system and method for providing a multi-level output voltage, comprising: a plurality of voltage nodes to receive supply voltages, the supply voltages at separate voltage levels; at least one flying capacitor arranged to provide stored charge, the charge derived from the local voltage sources; and a switch network arranged to selectively couple one of the supply voltages or the flying capacitor to a voltage output node. The system may be configured to operate in at least two modes: a direct charge transfer mode, known as a DC-coupled mode, where at least one of the supply voltages is coupled to the voltage output node to provide an output voltage; and an indirect charge transfer mode, known as an AC-coupled mode, where the at least one flying capacitor is coupled to the voltage output node to provide an output voltage.
The supply voltages may comprise a system supply voltage or reference voltage (e.g. Vdd, −Vdd, Gnd), and at least one voltage source generated from a system supply voltage or reference voltage using a charge pump (e.g. 2Vdd). Preferably, the system comprises at least three voltage nodes to receive supply voltages.
The direct mode is understood as a configuration where a power supply is coupled to the output node to provide an output voltage. The direct mode may be a DC-coupled mode, where the output node is coupled to a semi-stable power supply. When in the direct charge transfer mode, the output impedance of the semi-stable power supply is signal independent. The indirect mode is understood as a configuration where stored charge on a capacitor is coupled to the output node to provide an output voltage. The capacitor is further coupled to a voltage source or power supply via switches, where adjustment of the switch connection can result in movement of the output voltage. The indirect mode may be an AC-coupled mode, where a capacitor is provided with switches to connect to the voltage sources and the output node, and where the transition of switched drives the output voltage. When in the indirect charge transfer mode, the output impedance of the indirect charge transfer network is signal dependent.
The combination of the two operational modes enables a higher peak power deliverable to be supported without too much duty-cycle dependent impedance constraints
Some embodiments relate to a system and method for providing a multi-level output voltage, comprising first, second and third voltage supplies at different voltage levels; a fourth voltage supply, wherein the fourth voltage supply is provided by a flying capacitor transitioning between two of the first, second and third voltage supplies; and switch network configured to selectively couple the first, second, third and fourth voltage supplies to an output node, to provide a multi-level output voltage. The third voltage supply may be derived from the first and second voltage supplies using a charge pump. The system may be operable in a direct mode (or DC-coupled mode) and in an indirect mode (or AC-coupled mode), as described above.
In some embodiments there is also provided a multi-level converter or driver apparatus (such as an amplifier) having a supply voltage (VP) comprising: an output bridge arranged to receive an input signal (e.g. an audio input signal) and to output an output voltage for driving a load; at least one charge pump arranged to output a multiple of a supply voltage (e.g. 2VP); a first negative flying capacitor-based driver; and a switch network. The switch network is controlled to selectively couple the output bridge with the supply voltage, ground, the charge pump, and the first negative flying capacitor-based driver, where the switching of the switch network is controlled based on the input signal.
Preferably, the switch network is configured to switch the negative flying capacitor-based driver such that one end of the flying capacitor is coupled to the output voltage node, where the voltage at the other end of the flying capacitor can be switched to adjust the output voltage level. The converter may be operable in a direct mode and an indirect mode, as described above.
In some examples, the converter may further comprise a second negative flying capacitor-based driver, the second flying capacitor-based driver adapted to store twice the charge of the first negative flying capacitor-based driver; and wherein the switch network is controlled to selectively couple the output bridge with the second negative flying capacitor-based driver.
Some embodiments relate to a multi-level converter or driver apparatus (such as an amplifier, e.g. a loudspeaker amplifier) comprising: a first combined charge pump driver, e.g. a speaker driver, to receive an input signal and provide an output signal to a first load terminal; a second combined charge pump driver, e.g. a speaker driver, to receive an input signal and provide an output signal to a second load terminal; at least one auxiliary charge pump; and a switch network, wherein the at least one auxiliary charge pump is configured to be selectively coupled with the first and/or second combined charge pump drivers, to provide additional charge levels to the first and/or second combined charge pump drivers.
The connection of the auxiliary charge pump to the drivers may be based on an input signal received by the multi-level converter, e.g. an audio input signal. It will be understood that the converter may comprise a low-side auxiliary charge pump, a high-side auxiliary charge pump, or both.
Some embodiments relate to a multi-level converter (such as an amplifier) arranged to receive a supply voltage and provide an output voltage at an output terminal, the converter comprising: at least one driver, e.g. a speaker driver, having an integrated direct charge pump; at least one auxiliary supply, preferably provided as an auxiliary helper charge pump; and a switch network coupling the driver and negative supply. The converter may be operable in at least two modes: a direct mode, where the driver with integrated charge pump generates an output voltage based on the supply voltage, and a hybrid mode, where the auxiliary supply is coupled with the driver to provide an increased output voltage level.
Preferably, the integrated direct charge pump comprises a switch to drive an output voltage based on the supply voltage, the integrated direct charge pump further comprising a capacitor operable to drive an output voltage based on a multiple of the supply voltage.
As used herein, the term DC-coupled may be understood as switching between two voltage levels, preferably using resistive switches. This can be extended to three or more voltages, with more switches. By way of example, DC voltages may be derived from a battery, an inductive switched mode power supply, or a switched cap power supply. Such power sources are assumed to be able to supply current for an extended period of time, for example greater than the period of the class D output signals at the lowest needed frequency.
As used herein, the term AC-coupled may be understood as an output driven to a voltage level by switching terminal T1 of a capacitor between two voltages while terminal T2 of the capacitor is coupled to the output. This can result in the load terminal driven outside of the range of the DC coupled power supplies. The capacitor and the load have a time constant, inherently limiting the duration of the pulse. If the load has an impedance of R, the capacitor a value of C, then RC would normally be chosen to be 1-100× the class D switching frequency.
For a system having a nominal 5V supply, 0V and 5V terminals, AC coupling alone could be used to achieve {0,5,10} V output or {−5,0,5} V. Alternative DC coupling alone with voltages, {0,5,10} V from three different rails could be used. However, an advantage of the above-described system comes with combining the AC- and DC-coupling systems for at least four levels of output. Two of the states are available directly from the power supply, i.e. DC coupled. Another DC state is made possible by a switched capacitor DC-DC converter. A fourth state is AC coupled. Using S to notate supply, and D and A for DC/AC coupled respectively, an example configuration of output voltages can be as follows:
The last two output voltage configurations are possible by using the DC supply for the source of the T1 capacitor terminal drive. If multiple supplies are available, the AC drive boost does not have to be the same supply as the main supply. For example, if 0V 2V 5V are the available rails, output choices of {0,5,7} would be possible.
The driver apparatus of embodiments of the disclosure may be suitable for driving an output transducer. The output transducer may be, in some implementations, be an audio output transducer such as a loudspeaker or the like. The output transducer may be a haptic output transducer. In some implementation the output transducer may be driven in series with an inductor, i.e. there may be an inductor in an output path between an output node of the switching driver and the load. In some implementations the transducer may be a piezoelectric or ceramic transducer.
Embodiments may be implemented as an integrated circuit. Embodiments may be implemented in a host device, especially a portable and/or battery powered host device such as a mobile computing device for example a laptop, notebook or tablet computer, or a mobile communication device such as a mobile telephone, for example a smartphone. The device could be a wearable device such as a smartwatch. The host device could be a games console, a remote-control device, a home automation controller or a domestic appliance, a toy, a machine such as a robot, an audio player, a video player. It will be understood that embodiments may be implemented as part of a system provided in a home appliance or in a vehicle or interactive display. There is further provided a host device incorporating the above-described embodiments.
The skilled person will recognise that some aspects of the above-described apparatus and methods, for instance aspects of controlling the switching control signals to implement the different modes, may be embodied as processor control code, for example on a non-volatile carrier medium such as a disk, CD- or DVD-ROM, programmed memory such as read only memory (Firmware), or on a data carrier such as an optical or electrical signal carrier. For some applications, embodiments may be implemented on a DSP (Digital Signal Processor), ASIC (Application Specific Integrated Circuit) or FPGA (Field Programmable Gate Array). Thus, the code may comprise conventional program code or microcode or, for example code for setting up or controlling an ASIC or FPGA. The code may also comprise code for dynamically configuring re-configurable apparatus such as re-programmable logic gate arrays. Similarly, the code may comprise code for a hardware description language such as Verilog™ or VHDL (Very high-speed integrated circuit Hardware Description Language). As the skilled person will appreciate, the code may be distributed between a plurality of coupled components in communication with one another. Where appropriate, the embodiments may also be implemented using code running on a field-(re) programmable analogue array or similar device in order to configure analogue hardware.
It should be noted that the above-mentioned embodiments illustrate rather than limit the invention, and that those skilled in the art will be able to design many alternative embodiments without departing from the scope of the appended claims. The word “comprising” does not exclude the presence of elements or steps other than those listed in a claim, “a” or “an” does not exclude a plurality, and a single feature or other unit may fulfil the functions of several units recited in the claims. Any reference numerals or labels in the claims shall not be construed so as to limit their scope.
As used herein, when two or more elements are referred to as “coupled” to one another, such term indicates that such two or more elements are in electronic communication or mechanical communication, as applicable, whether connected indirectly or directly, with or without intervening elements.
This disclosure encompasses all changes, substitutions, variations, alterations, and modifications to the example embodiments herein that a person having ordinary skill in the art would comprehend. Similarly, where appropriate, the appended claims encompass all changes, substitutions, variations, alterations, and modifications to the example embodiments herein that a person having ordinary skill in the art would comprehend. Moreover, reference in the appended claims to an apparatus or system or a component of an apparatus or system being adapted to, arranged to, capable of, configured to, enabled to, operable to, or operative to perform a particular function encompasses that apparatus, system, or component, whether or not it or that particular function is activated, turned on, or unlocked, as long as that apparatus, system, or component is so adapted, arranged, capable, configured, enabled, operable, or operative. Accordingly, modifications, additions, or omissions may be made to the systems, apparatuses, and methods described herein without departing from the scope of the disclosure. For example, the components of the systems and apparatuses may be integrated or separated. Moreover, the operations of the systems and apparatuses disclosed herein may be performed by more, fewer, or other components and the methods described may include more, fewer, or other steps. Additionally, steps may be performed in any suitable order. As used in this document, “each” refers to each member of a set or each member of a subset of a set.
Although exemplary embodiments are illustrated in the figures and described below, the principles of the present disclosure may be implemented using any number of techniques, whether currently known or not. The present disclosure should in no way be limited to the exemplary implementations and techniques illustrated in the drawings and described above.
Unless otherwise specifically noted, articles depicted in the drawings are not necessarily drawn to scale.
All examples and conditional language recited herein are intended for pedagogical objects to aid the reader in understanding the disclosure and the concepts contributed by the inventor to furthering the art, and are construed as being without limitation to such specifically recited examples and conditions. Although embodiments of the present disclosure have been described in detail, it should be understood that various changes, substitutions, and alterations could be made hereto without departing from the spirit and scope of the disclosure.
Although specific advantages have been enumerated above, various embodiments may include some, none, or all of the enumerated advantages. Additionally, other technical advantages may become readily apparent to one of ordinary skill in the art after review of the foregoing figures and description.
To aid the Patent Office and any readers of any patent issued on this application in interpreting the claims appended hereto, applicants wish to note that they do not intend any of the appended claims or claim elements to invoke 35 U.S.C. § 112 (f) unless the words “means for” or “step for” are explicitly used in the particular claim.
| Number | Date | Country | |
|---|---|---|---|
| 63278606 | Nov 2021 | US | |
| 63220469 | Jul 2021 | US | |
| 63190582 | May 2021 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 17678527 | Feb 2022 | US |
| Child | 18820727 | US |
