Patent Application
20240072746
Aspects disclosed herein generally provide for, but not limited to, a fully differential amplifier. In one aspect, the fully differential amplifier may be implemented in an audio system or a method for providing an audio system. This aspect and others will be discussed in more detail herein.
One example of a differential amplifier includes a summing and feedback network for developing an output signal of which the magnitude is proportional to the differential mode component of an input signal received at first and second input terminals of an apparatus. The summing network is connected to the first and second input terminals and to the feedback network. A first differential amplifier has an inverting input connected to a first intermediate node of the summing network, and a second differential amplifier has an inverting input connected to the second intermediate node of the summing network. A bridging resistor is connected between the inverting inputs of the first and second differential amplifiers.
In at least one embodiment, a fully differential amplifier is provided. The fully differential amplifier includes a first amplifying circuit, a second amplifying circuit, a summing circuit, a compensation circuit, and a common-mode gain setting network. The first amplifying circuit is configured to receive a first input voltage signal and to provide first output voltage signal. The second amplifying circuit is configured to receive a second input voltage signal and to provide second output voltage signal. The summing circuit is configured to provide a common mode component of the first input voltage signal and the second input voltage signal. The compensation circuit is configured to amplify the common mode component of the first input voltage signal and the second input voltage signal and to output an injection signal. The common gain setting network includes a plurality of resistors to receive the injection signal, common gain setting network is configured to interface with the first amplifying circuit, the second amplifying circuit, and the compensation circuit to prevent the common mode component from being present in the first output voltage signal and the second output voltage signal based on at least splitting the injection signal with the plurality of resistors to provide a first injection signal to an inverting input of the first amplifying circuit and to provide a second injection signal to an inverting input of the second amplifying circuit.
In at least another embodiment, a fully differential amplifier is provided. The fully differential amplifier includes a first amplifying circuit, a second amplifying circuit, a third amplifying circuit, a fourth amplifying circuit, a common gain setting network, and a summing network. The first amplifying circuit is configured to receive a first input voltage signal and to provide first output voltage signal. The second amplifying circuit is configured to receive a second input voltage signal and to provide a second output voltage signal. The third amplifying circuit is configured to receive the first input voltage signal and to provide a third output voltage signal. The fourth amplifying circuit is configured to receive the second input voltage signal and to provide a fourth output voltage signal. The common gain setting network includes a plurality of resistors to receive an injection signal and is configured to interface with the first amplifying circuit and the second amplifying circuit. The summing network includes a plurality of resistors is configured to provide a first common mode component and a second common mode component and to provide a first compensation signal to an inverting input of the first amplifying circuit and a second compensation signal to an inverting input of the second amplifying circuit in response to receiving the third output voltage signal and the fourth output voltage signal to prevent the common mode component from being present in the first output voltage signal and the second output voltage signal.
In at least another embodiment, a fully differential amplifier is provided. The fully differential amplifier includes a first amplifying circuit, a second amplifying circuit, a summing circuit, a compensation circuit, and a common-mode gain setting network. The first amplifying circuit receives a first input voltage signal and provides a first output voltage signal. The second amplifying circuit to receive a second input voltage signal and to provide a second output voltage signal. The summing circuit to provide a common mode component of the first input voltage signal and the second input voltage signal. The compensation circuit to amplify the common mode component of the first input voltage signal and the second input voltage signal and output an injection signal. The common gain setting network including a plurality of resistors to receive the injection signal and to interface with the first amplifying circuit, the second amplifying circuit, and the compensation circuit to prevent the common mode component from being present in the first output voltage signal and the second output voltage signal based at least on splitting the injection signal with the plurality of resistors to provide a first injection signal to the first amplifying circuit and to provide a second injection signal to the second amplifying circuit.
The embodiments of the present disclosure are pointed out with particularity in the appended claims. However, other features of the various embodiments will become more apparent and will be best understood by referring to the following detailed description in conjunction with the accompany drawings in which:
As required, detailed embodiments of the present invention are disclosed herein; however, it is to be understood that the disclosed embodiments are merely exemplary of the invention that may be embodied in various and alternative forms. The figures are not necessarily to scale; some features may be exaggerated or minimized to show details of particular components. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a representative basis for teaching one skilled in the art to variously employ the present invention.
The disclosed fully differential amplifiers may provide for equal output voltages with an opposite polarity from the amplifier in addition to equal distortion and improved stability with unknown loads. In addition, the disclosed fully differential amplifier may be implemented with a common mode feedforward loop. The disclosed fully differential amplifier may be used in any number of dual differential amplifier applications, for example, driving analog to digital converters (ADCs), as a bridge amplifier, etc.
In general, a differential-mode signal appears differentially on a pair of amplifier inputs (e.g., inputs to first and second amplifying circuits 102 and 104). A common mode signal appears equally (with respect to a local common terminal) on both amplifier inputs (e.g., inputs to first and second amplifying circuits 102 and 104). Usually, the common-mode signal is an undesired or unwanted signal that should be rejected by the differential amplifier 100. A common mode input voltage is generally expressed as an average of the two input voltages with respect to a local ground or common and may be shown as:
(VIn1+VIn2)/2
The common gain setting feedback network 105 provides feedback to the first amplifying circuit 102 and the second amplifying circuit 104. In general, a gain of the first and second amplifying circuits 102 and 104 may be very high and uncontrollable. The common gain-setting feedback network 105 sets a differential gain that is defined by (resistor 108 (RF2)+resistor 110 (RF2))/resistor 106 (RF1)). Alternatively, a differential gain may be defined by (VOut1−VOut2)/(VIn1−VIn2).
One property of the amplifier 100 is that a common mode gain for the first and the second amplifying circuits 102, 104 (e.g., the inputs provided to the non-inverting inputs of the first and second amplifying circuits 102 and 104) is equal to unity irrespective of the differential gain that is set by the resistors 106, 108, and 110. In general, a common mode rejection ratio is equal to the differential gain of the amplifier 100. The node voltages may be defined as follows:
(VOut1−VIn1)/RF2=(VIn1−VIn2)/RF1=(VIn2−VOut2)/RF2,
then the differential gain is given by:
(VOut1−VOut2)/(VIn1−VIn2)=2*RF2/R1+1
and the common mode gain is given by:
(VOut1+VOut2)/(VIn1+VIn2)=1
The output voltage VOut1 may depend not only on a differential voltage VIn1−VIn2, but also on the common mode input voltage, (VIn1+VIn2)/2. In general, it is not desirable for the amplifier 100 to pass a common mode signal (e.g., or the common mode input voltage (e.g., (VIn1+VIn2)/2) through the first and the second amplifying circuits 102 and 104)). While the amplifier 100 may have some advantages, the amplifier may not reject the common mode input voltage. It may be desirable to reject or prevent the common mode input voltage from being present on the output signals (e.g., VOut1 and VOut2).
In general, the output signals (e.g., VOut1 and VOut2) of the amplifier 300 are applied through the resistors 358 and 360 to the inverting input of the compensation amplifier 330. Such resistors 358 and 360 may have similar resistance values. The resistor 312 may be implemented as a gain-setting resistor to provide feedback from the output of the compensation amplifier 330 to the inverting input thereof. The compensation amplifier 330 compares the input voltage received on the inverting input with zero. The amplified difference from the output of the compensation amplifier 330 is applied through the resistors 352 and 354 to non-inverting inputs of the amplifying circuits 302 and 304 in the opposite phase to the common mode input signal. Since such an opposing voltage creates a negative common mode feedback signal, this condition may eliminate input common mode voltage on an output of the first and second amplifying circuits 302, 304. The amplifier 300 provides a common mode feedback loop to suppress at least a portion of the common mode component (e.g., at least a portion of (VIn1+VIn2)/2)) in the output signals (e.g., VOut1 or VOut2).
In general, the output signals (e.g., VOut1 and VOut2) are applied through equal-valued resistors 458 and 460 to the non-inverting input of the compensation amplifier 440. The resistors 458 and 460 may have a similar resistance value as one another. The resistors 412 and 414 may set a common mode gain. The output signal of the compensation amplifier 440 is injected in the common gain-setting feedback network 405. The compensation amplifier 440 compares a sum of the output voltages (e.g., VOut1 and VOut2) to zero. An output of the compensation amplifier 440 may then be transferred through the resistors 406 and 407 to the inverting inputs of the first and the second amplifying circuits 402 and 404. This aspect may create a negative common mode signal feedback path thereby eliminating the common mode input signal of the first and the second amplifying circuits 402 and 404. The resistors 406 and 407 may have a similar resistance value as one another.
The degree of common mode rejection on the output of the compensation amplifier 440 depends on, for example, the gain of the compensation amplifier 440, matching of the component values (or resistors), and matching of the gain of the main amplifying paths. The degree of matching of the main amplifying paths depends upon the loads parameters that can be unpredictable. Unmatched load values can add uncontrollable differential component to the input of the compensation amplifier 440. It may be desirable to provide a fully differential gain amplifier circuit that is not sensitive to load matching and does not include a large number of amplifying circuits in the signal path.
The input signals (e.g., VIn1 and VIn2) are applied to the non-inverting inputs of the first and the second amplifying circuits 502, 504, respectively in addition to the resistors 510, 512, respectively of the summing network 509. The compensation amplifier 540 amplifies an output provided by the summing network 509 (e.g., the resistors 514 and 516) to generate an amplified output. The compensation amplifier 540 provides (or injects) the amplified output into the common gain setting network 505. The voltage on the noninverting input of the compensation amplifier 540 may be written as VIn1 minus a voltage drop on the resistor 510, or VIn1−(VIn1−VIn2)*RIn1/(RIn1+RIn2), where (VIn1−VIn2)/(RIn1+RIn2) is a current that flows through the resistors 510 and 512 that are in series with one another.
In general, VIn1−(VIn1−VIn2)*RIn1/(RIn1+RIn2) may be simplified as (VIn1*RIn2+Vin2*RIn1)/(RIn1+RIn2) and assuming RIn1=RIn2 then (VIn1+VIn2)/2. The first and the second amplifying circuits 502 and 504 each have a large open loop gain, so the input signal between their inputs is negligible (e.g., near zero). For the first amplifying circuit 502 amplifier the following equation can be written:
(VOut1−VIn1)/RF2=(VIn1−VIn2)/RF1+(VIn1−VIn1−VIn2)/RF3,
thus the sum of the currents through the resistors 522 is equal to the sum of the current through the resistors 517 and 518.
The following may be derived from the equations noted above in connection with the first amplifying circuit 502:
(VOut1−VIn1)/RF2=(VIn1−VIn2)/RF1+(VIn1−VIn1−VIn2)/RF3; or
VOut1=RF2(VIn1(1/RF1+1/RF2)−VIn2(1/RF1+1/RF3)).
Assuming that if RF2=RF3, then VOut1=(RF2/RF1+1) (VIn1−VIn2); if VIn1=VIn2 then VOut1=0
The same set of equations may be written for the second amplifying circuit 504:
(VOut2−VIn2)/RF2=(VIn2−VIn1)/RF1+(VIn2−VIn1−VIn2)/RF3; or
VOut2=RF2(VIn2(1/RF1+1/RF2)−VIn1(1/RF1+1/RF3)).
If RF2=RF3,then VOut2=(RF2/RF1+1)(VIn2−VIn2); if VIn1=VIn2 then VOut2=0VOut2=(RF2/RF1+1)(VIn2−VIn1),
differential gain is given by:
(VOut1−VOut2)/(VIn1−VIn2)=2*RF2/RF1+1 and
the common mode gain is given by:
(VOut1+VOut2)/(VIn1+VIn2)=0
These equations (or balance equations) illustrate that (VIn1+VIn2)/2 (or the common mode component) is not present in the output signal (e.g., (VOut1 or VOut2)) which is the desired result.
Thus, exhibited above, VOut1 (or the output voltage) may generally depend on the differential voltage which is defined by VIn1−VIn2. The function of the differential amplifier 500 is to amplify the difference (e.g., VIn1−VIn2) and suppress the common mode component (e.g., VIn1+VIn2)/2).
In operation and based at least on the above passages disclosed above, the first amplifying circuit 502 receives a first input voltage signal (e.g., VIn1) and provides a first output voltage signal (e.g., VOut1). The second amplifying circuit 504 receives a second voltage signal (e.g., VIn2) and provides second output voltage signal (e.g., VOut2). The summing network 509 provides the common mode component (e.g., (VIn1+VIn2)/2) of the first input voltage signal and the second input voltage signal. The compensation amplifier 540 is configured to amplify the common mode component of the first input voltage signal and the second input voltage signal and output an injection signal. The common gain setting network 505 includes a plurality of resistors (e.g., 517, 518, 520, 522, 524) to receive the injection signal and being configured to interface with the first amplifying circuit 502, the second amplifying circuit 504 and the compensation amplifier 540 to prevent the common mode component from being present in the first output voltage signal and the second output voltage signal (e.g., VOut2) based on at least splitting the injection signal with the plurality of resistors (e.g., 517, 518, 520, 522, 524) to provide a first injection signal to an inverting input of the first amplifying circuit 502 and to provide a second injection signal to an inverting input of the second amplifying circuit 504.
The resistor 518 receives the first injection signal and the resistor 520 receives the second injection signal. A first resistance value of the resistors 518, 520 are similar to one another. An output from the resistor 518 is transmitted to the inverting input of the first amplifying circuit 502. The resistor 520 is transmitted to the inverting input of the second amplifying circuit 504.
The resistor 522 receives an output from the resistor 518 and the resistor 524 receives an output from the second resistor 520. A second resistance value of the resistors 522 and 524 are similar to one another. The first resistance value of the resistors 518 and 520 is similar to the second resistance value of the resistors. The resistor 517 generally sets the differential gain (e.g., (Vout1−Vout2/Vin1−Vin2) for the amplifier 500. The differential gain is independent from the common mode component.
In one example, there may be three building blocks in series in the common mode feedforward path. This may involve a summing network, an amplifier circuit with associated components and an injection circuit. The difference between common mode path as illustrated for the amplifier 500 in connection with
The amplifier 700 of
In operation and based at least on the above passages disclosed above, the third amplifying circuit 740 receives the first input voltage signal (e.g., VIn1) and provides a first output voltage signal (e.g., VOut1). The fourth amplifying circuit 742 receives the second voltage signal (e.g., VIn2) and provides the second output voltage signal (e.g., Vout2). The first amplifying circuit 702 receives the first input voltage signal (e.g., VIn1) and provides a third output voltage signal. The second amplifying circuit 704 configured to receive configured to receive the second input voltage signal (e.g., VIn2) and provide a fourth output voltage signal. The common gain setting network 705 include the resistors 722, 724, 728 to receive an injection signal. The common gain setting network 705 interfaces with the first amplifying circuit 740, the second amplifying circuit 704. The summing network 709 includes the resistors 718, 720, 726, 730 and is configured to provide a first common mode component and a second common mode component and to provide a first compensation signal to an inverting input of the third amplifying circuit 740 and a second compensation signal to an inverting input of the fourth amplifying circuit 742 in response to receiving the third output voltage signal and the fourth output voltage signal to prevent a first common mode component from being present in the first output voltage signal and a second common mode component from being present in the second output voltage signal.
The resistor 718 receives the third output voltage signal and the resistor 720 receives the fourth output voltage signal. A first resistance value of the resistors 718 and 720 are similar to one another. The resistor 718 transmits an output and the resistor 720 transmits an output to the inverting input of the third amplifying circuit 740.
The resistor 726 receives the third output voltage signal and the resistor 730 receives the fourth output voltage signal. A second resistance value of the resistors 726, 730 are similar to one another.
The resistor 720 transmits an output and the resistor 730 transmits an output to the inverting input of the fourth amplifying circuit 742. The first resistance value of the resistors 718 and 720 is similar to the second resistance value of the resistors 726, 730. The resistor 722 sets a differential gain (Vout1−Vout2)/(Vin1−Vin2) for the amplifier 700 and the differential gain is independent from the common mode component.
The first compensation circuit 807a detects or senses common mode signals (or inputs VIn1 and VIn2) as provided to non-inverting inputs of the first and second amplifying circuits 802 and 804, respectively. The first compensation circuit 807a injects a signal into the gain-setting network 805. A resultant signal from the first compensation circuit 807a is provided to the gain setting network 805 in such manner that a final result of the common mode component (e.g (VIn1+VIn2)/2) in the output signals (e.g., VOut1, VOut2) is zero. Similar to that noted above, the common mode component (or common mode input signal) may be defined as (VIn1+VIn2)/2 and is provided as an input to the first compensation circuit 807a. While the first compensation circuit 807a may effectively remove a substantial portion of the common mode input signal, the second compensation circuit 807b may suppress any residual common mode components that may be-presented on the amplifier output terminals after operation of the first compensation circuit 807a.
The amplifier 800 generally utilizes an additional common mode suppression path (e.g., the first compensation circuit 807a) along with a common mode feedback path (e.g., the second compensation circuit 807b). This may provide better suppression of the common mode component (e.g., (VIn1+VIn2)/2 in the output signal (e.g., VOut1, VOut2) and/or provide relaxed requirements for signal path component (e.g., resistor) tolerances.
While exemplary embodiments are described above, it is not intended that these embodiments describe all possible forms of the invention. Rather, the words used in the specification are words of description rather than limitation, and it is understood that various changes may be made without departing from the spirit and scope of the invention. Additionally, the features of various implementing embodiments may be combined to form further embodiments of the invention.
