Patent Application
20230327621
This application claims the benefit of French Application No 2203131, filed on Apr. 6, 2022, which application is hereby incorporated herein by reference.
The present disclosure relates generally to electronics circuits and electronic devices, and, more particularly, to electronics circuits and devices for copying a current.
Devices for copying a current, such as current mirrors implemented with MOS transistors (“Metal Oxide Semiconductor” transistors), are known. These known devices receive an input current on an input node and provide an output current on an output node, such that the output current is an image of the input current. Said in other words, the output current is determined by the input current. For example, the output current is proportional, for example equal, to the input current.
In these known devices, a modification in the value of the input current results in a corresponding modification in the value of the output current.
Embodiments address all or some of the drawbacks of known devices for copying a current.
For example, in known devices for copying a current, when the output current is used for charging or discharging a capacitive element, when a modification in the value of the input current occurs, a corresponding modification in the value of the output current may be delayed with respect to the modification in the value of the input current. It would be preferable, for example, to reduce the delay between the modification of the input current and the corresponding modification of the output current.
One embodiment addresses all or some of the drawbacks of known devices for copying a current.
One embodiment provides a device comprising:
According to one embodiment, the drain of the first transistor is connected to the output node.
According to one embodiment, the device further comprises a second MOS transistor having a channel of the same type as the channel of the first MOS transistor, the second MOS transistor coupling the drain of the first MOS transistor to the output node and being series-connected with the first MOS transistor.
According to one embodiment, the biasing circuit comprises a third MOS transistor having a channel of the same type as the channel of the first MOS transistor, the third MOS transistor having a drain and a gate connected with each other, and a source connected to the first node, the gate of the third MOS transistor being connected to the second terminal of the second resistor.
According to one embodiment, the third MOS transistor is series-connected with the first resistor.
According to one embodiment, the third MOS transistor has its drain connected to the second terminal of the first resistor.
According to one embodiment, the bias circuit further comprises a current source series-connected with the third MOS transistor.
According to one embodiment, the second terminal of the first resistor is connected to the first node.
According to one embodiment, the bias circuit further comprises a second capacitor connected between the gate of the third MOS transistor and the first node.
One embodiment provides an amplifier, for example a transconductance amplifier, comprising:
One embodiment provides an amplifier comprising:
According to one embodiment, the amplifier further comprises a supplementary amplifier, for example a supplementary transconductance amplifier, having a first input coupled, preferably connected, to the gate of the first MOS transistor of the differential pair, a second input coupled, preferably connected, to the gate of the second transistor of the differential pair, and an output coupled, preferably connected, to the output node of the amplifier.
According to one embodiment, the biasing circuit of the first device is also the biasing circuit of the second device.
According to one embodiment, the amplifier further comprises a first circuit coupled to the output node of the first device, the output node of the amplifier and the node configured to receive the second supply potential, wherein the first circuit is configured to receive the second current of the first device and to provide a current proportional to this second current to the output node of the amplifier.
According to one embodiment, the amplifier is adapted to implement a transimpedance function between its inputs and its output node.
The foregoing features and advantages, as well as others, will be described in detail in the following description of specific embodiments given by way of illustration and not limitation with reference to the accompanying drawings, in which:
and
Like features have been designated by like references in the various figures. In particular, the structural and/or functional features that are common among the various embodiments may have the same references and may dispose identical structural, dimensional and material properties.
For the sake of clarity, only the operations and elements that are useful for an understanding of the embodiments described herein have been illustrated and described in detail. In particular, the known circuits comprising a device for copying a current have not been described in detail, the described embodiments being compatible with these known circuits.
Unless indicated otherwise, when reference is made to two elements connected together, this signifies a direct connection without any intermediate elements other than conductors, and when reference is made to two elements coupled together, this signifies that these two elements can be connected or they can be coupled via one or more other elements.
In the following disclosure, unless indicated otherwise, when reference is made to absolute positional qualifiers, such as the terms “front”, “back”, “top”, “bottom”, “left”, “right”, etc., or to relative positional qualifiers, such as the terms “above”, “below”, “higher”, “lower”, etc., or to qualifiers of orientation, such as “horizontal”, “vertical”, etc., reference is made to the orientation shown in the figures.
Unless specified otherwise, the expressions “around”, “approximately”, “substantially” and “in the order of” signify within 10%, and preferably within 5%.
In the following description, unless specified otherwise, when reference is made to the gate of a MOS transistor, this signify the front gate of the MOS transistor.
The amplifier AMP comprises an input node IN1, an input node IN2 and an output node OUT. The amplifier AMP is configured to provide, on its output node OUT, a current Tout representative of a voltage difference between its nodes IN1 and IN2.
The amplifier AMP comprises a differential pair Diff. The differential pair Diff comprises a MOS transistor D1 and a MOS transistor D2. The transistor D1 has a gate connected to the input node IN1. The transistor D2 has a gate connected to the input node IN2.
The amplifier AMP comprises a current source boo. The current source wo couples a node 102 configured to receive a supply voltage VDD to a conduction terminal of each of the transistors D1 and D2. The current source 100 is configured to bias the differential pair Diff, and, more particularly, to bias the transistors D1 and D2.
The amplifier AMP comprises a device 104 for copying a current and a device 106 for copying a current. Preferably, device 104 is identical to device 106.
Device 104, respectively 106, has an input node 104i, respectively 106i, coupled, preferably connected, to a conduction terminal of transistor D1, respectively D2, the other conduction terminal of transistor D1, respectively D2, being coupled, preferably connected, to the current source 100. Node 104i is configured to receive an input current I1 from the differential pair Diff, node 106i being configured to receive an input current I2 from the differential pair. Device 104, respectively 106, has an output node 1040, respectively 106o, configured to provide an output current I3, respectively I4. Current I3, respectively I4, is determined by current I1, respectively I2. Device 104, respectively 106, couples the differential pair Diff, for example the transistor D1, respectively D2, to a node 108 configured to receive a supply voltage VSS.
More generally, the differential pair Diff comprises a first branch controlled by the input node IM which couples the current source 100 to device 104 and provides the current I1 to device 104, and a second branch controlled by the input node IN2 which couples the current source 100 to the device 106 and provides the current I2 to the device 106.
Device 104, respectively 106, has its input node 104i, respectively 106i, coupled, preferably connected, to a conduction terminal of transistor D1, respectively D2, the other conduction terminal of transistor D1, respectively D2, being coupled, preferably connected, to the current source 100. Node 104i is configured to receive an input current I1 from the differential pair Diff, node 106i being configured to receive an input current I2 from the differential pair Diff.
In the example of
In the example of
The output node 106o of device 106 is coupled, preferably connected, to the output node OUT of the amplifier AMP. In other words, the node 106o is coupled to node OUT such that current I4 is provided to node OUT.
The output node 1040 of device 104 is coupled to the output node OUT of the amplifier AMP. In other words, the node 1040 is coupled to node OUT such that a current I5 determined by the current I3 is provided to node OUT. Current I5 is for example proportional, preferably equal, to current I3.
Thus, the current Iout is determined by a difference between currents I5 and I4. Current Tout is provided to a load (not represented) connected to the output node OUT, for example a load comprising a capacitive element coupling node OUT to node 108.
The amplifier AMP comprises a circuit 114 coupling the node 1040 to the node OUT. The circuit 114 is configured to receive current I3 from the device 104 and to provide current I5 to node OUT, the current I5 being determined by current I3. More particularly, circuit 114 is coupled to nodes 1040, 102 and OUT.
In the example of
In the amplifier AMP, when a voltage step is applied between the inputs IN1 and IN2, a corresponding modification in the voltage on the output node OUT has a slew rate which is limited by the capacitance value of the node OUT and the value of the transconductance gain gm between the voltage across the nodes IN1 and IN2 and the current Tout. Further, the bandwidth of the amplifier AMP is also limited by the capacitance value of the node OUT and the value of the transconductance gain gm.
In devices 104 and 106, current I3, respectively I4, is equal to K*I1, respectively K*I2, K being a proportionality coefficient. The slew rate and the bandwidth of the amplifier AMP may be increased by increasing the value of coefficient K. However, this increases the surface occupied by the devices 104 and 106 and the power consumption of the amplifier AMP.
The present disclosure provides a device for copying a current in which a modification in the input current of the device leads to a corresponding modification in the output current of the device which is faster than in a known current mirror receiving the same modification in its input current and having transistors with sizes similar or identical to the sizes of the transistor of the provided device.
To achieve this goal, the disclosed device for copying a current comprises a first resistor having a terminal connected to the input node of the disclosed device and another terminal coupled to a first node configured for receiving a supply voltage. The output current of the disclosed device is flowing across a MOS transistor, referenced M2 in the following disclosure. Transistor M2 has a source connected to the first node, a drain coupled, for example connected, to the output node of the disclosed device, and a gate coupled to the input node of the disclosed device by a capacitor. The disclosed device further comprises a biasing circuit providing a biasing voltage to a second node coupled to the gate of the MOS transistor M2 by second resistor. The capacitor coupling the input node of the disclosed device to the gate of the MOS transistor M2 is preferably different from an intrinsic or parasitic capacitance.
Thus, when a modification of the current received by the input node of the disclosed device occurs, for example a transient event corresponding to an increase or a decrease of the value of the input current, this current modification is converted by the first resistor into a corresponding voltage modification on the input node of the disclosed device, and is transmitted on the gate of the transistor M2 by the capacitor, thus resulting in a corresponding modification of the current across the MOS transistor M2. The voltage across the second resistor is not null during the modification of the input and output currents, or, said otherwise, during the transient event, and is null in a steady state where the input and output currents of the device are constant.
The amplifier AMP1 is similar to the amplifier AMP, and only the differences between these two amplifiers will be described in detail.
More particularly, the amplifier AMP1 differs from the amplifier AMP by the fact that device 104, respectively 106, of amplifier AMP is replaced by a device 1041, respectively 1061, for copying a current. Preferably, devices 1041 and 1061 are identical.
Similarly to device 104, respectively 106, the device 1041, respectively 1061, has an input node 1041i, configured to receive the input current I1, respectively I2, from the differential pair Diff, and an output node 10410, respectively 10610, configured to provide the current I3, respectively I4.
Thus, in the amplifier AMP1, node 1041i is connected to the branch of the differential pair Diff controlled by the input IN1, node 1061i is connected to the branch of the differential pair Diff controlled by the input IN2. Further, node 10610 is coupled, preferably connected, to node OUT of the amplifier AMP1, such that current I4 is provided to node OUT. Node 10410 is coupled, preferably connected, to circuit 114 for providing current I3 to circuit 114 which, in turn, provides current I5 to node OUT.
Each of the devices 1041 and 1061 comprises two resistors RA and RS, a capacitor C and a MOS transistor M2.
The source of the transistor M2 of device 1041, respectively 1061, is connected to node 108. The drain of the transistor M2 of device 1041, respectively 1061, is coupled to the node 10410, respectively 10610, of the device 1041, respectively 1061.
More particularly, in one embodiment, as illustrated by
In the example of
The capacitor C of the device 1041, respectively 1061, couples the input node 1041i, respectively 1061i, to the gate of the transistor M2 of the device 1041, respectively 1061. Capacitor C may be implemented using one or a plurality of capacitive components.
The resistor RA of the device 1041, respectively 1061, has a first terminal connected the input node 1041i, respectively 1061i, of the device 1041, respectively 1061. The second terminal of the resistor RA of device 1041, respectively 1061, is coupled to node 108. Resistor RA may be implemented using one or a plurality of resistive components.
The resistor RS of the device 1041, respectively 1061, has a first terminal connected to the gate of transistor M2 of the device 1041, respectively 1061, the second terminal of the resistor RS of device 1041, respectively 1061, being configured to receive a bias voltage from a biasing circuit 200 of the device 1041, respectively 1061. Resistor RS may be implemented using one or a plurality of resistive components.
The biasing circuit 200 of each device 1041 and 1061 comprises a MOS transistor M1 having a channel of the same type than the one of the MOS transistor M2. Transistor M1 of device 1041, respectively 1061, has a gate connected to the resistor RS of the device 1041, respectively 1061, and, more specifically, to the terminal of the resistor RS opposite to the terminal of the resistor RS connected to the gate of transistor M2 of the device 1041, respectively 1061. Further, each transistor M1 has its gate and its drain connected with each other. Said in other words, each transistor M1 is diode-mounted.
In one embodiment, as illustrated by
More particularly, in the embodiment illustrated by
More particularly, in
In
At the instant t1, a voltage step is applied between the inputs IN1 and IN2. In the example of
In the amplifier AMP, the increase of current I1 result in an increase of the voltage across transistor M1 of device 104, thus of the voltage on the gate of transistor M2 of this device 104. Conversely, the decrease of current I2 results in a decrease of the voltage across transistor M1 of device 106, thus of the voltage on the gate of transistor M2 of this device 106. It follows that current I3 increases and current I4 decreases, resulting in a step increase of current Iout of amplifier AMP.
The same occurs in the amplifier AMP1, but, because of resistors RA of devices 1041 and 1061, the voltage increase on node 1041i is higher than the voltage increase on node 104i of amplifier AMP, and the voltage decrease on node 1061i is higher than the voltage decrease on node 106i of the amplifier AMP. Further, as the voltage variations on nodes 1041i and 1061i are transmitted by capacitors C to the gate of transistors M2 of the respective devices 1041 and 1061, the increase of the voltage on the gate of transistor M2 is higher in device 1041 (see curve 304) than in device 104 (see curve 306), and the decrease of the voltage on the gate of transistor M2 is higher in device 1061 (see curve 308) than in device 106 (see curve 310). As a result, the increase of the current Iout is higher in the amplifier AMP1 (see curve 300) than in the amplifier AMP (see curve 302).
From the instant t1, the voltage on the gate of the transistor M2 of device 1041, respectively 1061, decreases, respectively increases, until being equal to the voltage on the gate of the transistor M2 of device 104, respectively 106, at a rate at least partly determined by the value of the capacitor C. Said in other words, from the instant t1, the voltage on the gate of the transistor M2 of device 1041, respectively 1061, decreases, respectively increases, until the device 1041, respectively 1061, is in a steady state.
Thus, when a modification of the voltage between inputs IN1 and IN2 results in an increase of the current Tout, a capacitive load connected to node OUT of the amplifier AMP1 is charged faster than if this load was connected to the node OUT of amplifier AMP.
At an instant t2 posterior to instant t1, a new step of voltage is applied between the inputs IN1 and IN2. In the example of
In the amplifier AMP, the increase of current I2 result in an increase of the voltage across transistor M1 of device 106, thus of the voltage on the gate of transistor M2 of this device 106. Conversely, the decrease of current I1 result in a decrease of the voltage across transistor M1 of device 104, thus of the voltage on the gate of transistor M2 of this device 104. It follows that current I4 increases and current I3 decreases, resulting in a decrease of current Iout of amplifier AMP.
The same occurs in the amplifier AMP1, but, because of resistors RA, the voltage increase on node 1061i is higher than on node 106i, and the voltage decrease on node 1041i is higher than on node 104i. As voltage variations on nodes 1041i and 1061i are transmitted by capacitors C to the gates of transistors M2 of the respective devices 1041 and 1061, the voltage increase on the gate of transistor M2 is higher in device 1061 (see curve 308) than in device 106 (see curve 310), and the voltage decrease on the gate of transistor M2 is higher in device 1041 (see curve 304) than in device 104 (see curve 306). As a result, the decrease of the current Iout is higher in the amplifier AMP1 (see curve 300) than in the amplifier AMP (see curve 302).
From the instant t2, the voltage on the gate of the transistor M2 of device 1061, respectively 1041, decreases, respectively increases, until being equal to the voltage on the gate of the transistor M2 of device 106, respectively 104, at a rate at least partly determined by the value of the capacitor C. Said in other words, from the instant t2, the voltage on the gate of the transistor M2 of device 1061, respectively 1041, decreases, respectively increases, until the device 1061, respectively 1041, is in a steady state.
Thus, when a modification of the voltage between inputs IN1 and IN2 results in a decrease of the current Tout, a capacitive load connected to node OUT of the amplifier AMP1 is discharged faster than if this load was connected to the node OUT of amplifier AMP.
Thus, devices 1041 and 1061 allow to increase the slew rate of the amplifier AMP1 with respect to the one of the amplifier AMP. Devices 1041 and 1061 further allow for increasing the gain of the amplifier AMP1 in the middle frequency band with respect to the one of the amplifier AMP, while leaving the gain in the low frequency band, or, said otherwise, the DC gain, of the amplifier AMP1 unchanged compared to the one of the amplifier AMP.
Further, devices 1041 and 1061 allow to increase the transconductance gain gm during a transient event compare with the one of the amplifier AMP.
More specifically, compared to the device 1041 of
The gate of the transistor M2b is configured to receive a bias voltage Vb, such that transistor M2b operates in saturation.
The transistor M2b allows for increasing the output impedance of the device 1041 of
In one embodiment, as illustrated by
The device 1041 of
In order to avoid the voltage drop across the transistor M1b of device 1041 of
According to one embodiment, as illustrated by
Transistors M3 and M4 have channels of the same type than the channel of the transistor M2 and M2b. For example, the size of the transistor M3 is identical to the size of transistor M1b of
The current source 502 is connected between node 102 and transistor M3. For example, the current source 502 has a first terminal connected to node 102 and a second terminal connected to the drain of transistor M3. For example, the current source 502 is configured to deliver a current having half the value of the current delivered by the current source 100 of the amplifier AMP1 (
The transistors M3 and M4 are each diode-mounted, the drain of the transistor M3 being connected to the gate of the transistor M3, and the drain of the transistor M4 being connected to the gate of the transistor M4.
The gate of the transistor M3 is connected to the gate of the transistor M2b.
A capacitor (not shown on
Although one specific embodiment of the circuit 500 has been described in relation with
Furthermore, when the devices 1041 and 1061 of the amplifier AMP1 of
More particularly, the amplifier AMP1 of
More particularly, compared to the devices 1041 and 1061 previously described, in each of the devices 1041 and 1061 of
In the embodiment illustrated by
The biasing circuit 201 of device 1041 is configured to provide a bias voltage to the resistor RS of device 1041, on a terminal of resistor RS opposite to the terminal of the resistor RS connected to the gate of the transistor M2 of device 1041. In the embodiment of
According to one embodiment, the biasing circuit 201 comprises, as the biasing circuit 200, the MOS transistor M1 having a channel of the same type than the one of the MOS transistor M2. Transistor M1 of circuit 201 has its gate and its drain connected with each other, or, said in other words, transistor M1 is diode mounted. The source of transistor M1 is connected to the node 108. The gate of transistor M1 of circuit 201 of device 1041 is connected to the resistor RS of the device 1041, and, more specifically, to the terminal of the resistor RS opposite to the terminal of the resistor RS connected to the gate of transistor M2 of the device 1041. In the embodiment illustrated by
Compared to the biasing circuit 200 of device 1041, the biasing circuit 201 of circuit 1041 is not series-connected with the resistor RA of device 1041. More particularly, the transistor M1 of the biasing circuit of the device 1041, respectively 106i, is not series-connected with the resistor RA of this device. Instead, the resistor RA of each device 1041, 106i is connected to node 108.
The biasing circuit 201 further comprises a current source 600. The current source 600 is series-connected with the transistor M1. The current source 600 couples the drain of the transistor M1 to the node 102. For example, the source 600 has a first terminal connected to the node 102, and a second terminal coupled, for example connected as illustrated by
A capacitor C1 may be connected between the gate of transistor M1 and the node 108. In alternative examples, capacitor C1 is omitted.
In the embodiment of
In each device 1041, 1061 of
Thus, when the devices 1041 and 106i of
The biasing amplifier AMP3, for example a transimpedance amplifier, is part of the amplifier AMP1. The amplifier AMP3 as an input connected to the input IN1, a further input connected to the input IN2, and an output connected to the node OUT. The biasing amplifier AMP3 is configured to determine the steady state value, or DC value, of the current Tout based on the steady state value, or DC component, of the voltage between nodes IN1 and IN2.
Although in the example of
In such a case, in each device 1041, 1061, transistor M2 is coupled to the output node of the device by the transistor M2b, as previously described in relation with
Alternatively, when transistor M2 of devices 1041, respectively 1061, is coupled to the node 10410, respectively 10610, by a corresponding transistor M2b, instead of providing a biasing circuit 500, the biasing circuit 201 of the device further comprises the transistor M3 described in relation with
In all the above described embodiments, the amplifier AMP1 is preferably used as a transimpedance amplifier. However, the amplifier AMP1 may also be used as a comparator. In this last case, when the transistors M2 of the devices 1041 and 1061 are each biased by a corresponding circuit 200 comprising the transistor M1, an hysteresis functionality may be implemented, for example, by adding two supplementary MOS transistors having the same channel type as the one of the transistor M1, a first one of these two supplementary transistors having a source coupled, preferably connected, to node 108, a gate connected to the gate of the transistor M2 of device 1041, and a drain coupled, preferably connected, to node 1061i, a second one of these two supplementary transistors having a source coupled, preferably connected, to node 108, a gate connected to the gate of the transistor M2 of device 1061, and a drain coupled, preferably connected, to node 1041i.
Furthermore, although the devices 1041 and 1061 have been described as being part of the amplifier AMP1, each of the devices 1041 and 1061 may be used for implementing a current mirror in circuits others than a transconductance amplifier, in particular when the gate of transistor M2 of the device is biased by a circuit 200.
Furthermore, although the circuit 114 of the amplifier AMP1 may be a known current mirror, it could also be implemented by a device similar to device 1041 previously described wherein the node 108 is replaced by node 102 and the transistors of the device are PMOS transistors.
Various embodiments and variants have been described. Those skilled in the art will understand that certain features of these embodiments can be combined and other variants will readily occur to those skilled in the art. In particular, in the example described above, the voltage VDD on node 102 is higher than voltage VSS on node 108. In other examples (not shown), the voltage VDD on node 102 is lower than voltage VSS on node 108, and the channel-type of all the described transistors is inverted, the P-type channel transistors becoming N-type channel transistors and the N-type channel transistors becoming P-type channel transistors. More generally, when voltages on nodes 1041i and 10410, respectively 1061i and 10610, of device 1041, respectively 1061, are lower than voltage VSS on node 108, the transistors of the device 1041, respectively 1061, are PMOS transistors instead of NMOS transistors as in the examples previously described.
Finally, the practical implementation of the embodiments and variants described herein is within the capabilities of those skilled in the art based on the functional description provided hereinabove. In particular, the values of the currents delivered by the current sources 502 and 600 are not limited to the examples given above, and those skilled in the art are capable of implementing the biasing circuits 201 and 500 with other current values.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2203131 | Apr 2022 | FR | national |
