Compensation circuit with fully differential structure and operational amplifier chip
By introducing a compensation circuit with a fully differential structure and a Miller compensation circuit into the differential op amp circuit, a negative feedback path is built, which solves the problem of oscillation of the differential op amp circuit and improves the stability and applicability of the loop.
Patent Information
- Application Number
- CN202411378223.1
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-09-30
- Publication Date
- 2025-05-02
AI Technical Summary
Differential op amp circuits are prone to oscillation, resulting in unstable loops.
The compensation circuit with a fully differential structure, including a differential op amp circuit and a Miller compensation circuit, builds a negative feedback path through an inverting amplifier, amplifies the equivalent capacitor, adjusts the zero pole position, and ensures the stability of the loop.
Effectively reduce loop compensation capacitors, improve loop stability, and have a wide range of application.
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Figure CN119921691A_ABST
Abstract
Description
Technical Field
[0001] The present application relates to the technical field of integrated circuit design, and in particular to a compensation circuit and an operational amplifier chip with a fully differential structure. Background Art
[0002] In analog integrated circuit design, there are many non-ideal factors that affect circuit performance, signal transmission and processing, such as noise, temperature, process deviation, device mismatch, etc. Fully differential op amps (fully differential operational amplifiers) can process two input signals, enhance the quality of the signal through differential amplification, significantly improve the stability and accuracy of the signal, and effectively eliminate common-mode noise. With the continuous upgrading of electronic products, the precision requirements for electronic products are getting higher and higher; the use of fully differential op amps is becoming more and more widespread, and its loop application is becoming more and more complex. The loop stability of differential op amps is also particularly important.
[0003] Traditional differential op amps are prone to oscillation, which is caused by the positive feedback formed by the parasitic capacitance and inductance inside the amplifier. In most integrated circuits, a feedback system is often constructed to attenuate disturbances and improve the poor anti-interference performance of the circuit's open-loop system. In related technologies, negative feedback circuits can usually be used to obtain accurate amplifier gain, but since the negative feedback circuit needs to feed back the system output to the system input, the deviation of device parameters from the design value during the production process may cause negative feedback to become positive feedback, causing the system to oscillate. Summary of the invention
[0004] The embodiments of the present application provide a compensation circuit and an operational amplifier chip with a fully differential structure, which can at least solve the problem that the differential operational amplifier circuit is prone to oscillation.
[0005] In a first aspect, an embodiment of the present application provides a compensation circuit of a fully differential structure, comprising: a differential operational amplifier circuit and a Miller compensation circuit; wherein: The differential operational amplifier circuit includes a cascaded fully differential operational amplifier and a differential operational amplifier; the fully differential operational amplifier is used to convert the initial differential signal of the received signal source into a double-ended differential signal, and transmit the double-ended differential signal to the differential operational amplifier; the differential operational amplifier is used to convert the double-ended differential signal into a single-ended AC signal and then output it; The Miller compensation circuit comprises a first Miller compensation unit, a second Miller compensation unit and an inverting amplifier; the first Miller compensation unit is connected across the non-inverting input terminal and the output terminal of the differential operational amplifier; one end of the second Miller compensation unit is connected to the inverting input terminal of the differential operational amplifier, and the other end is connected to the output terminal of the differential operational amplifier through the inverting amplifier; the first Miller compensation unit and the second Miller compensation unit are used to amplify the equivalent capacitance of the differential operational amplifier; the inverting amplifier is used to invert the single-ended AC signal to realize negative feedback from the output terminal of the differential operational amplifier to the non-inverting input terminal.
[0006] Furthermore, the Miller compensation circuit also includes a first resistor, a second resistor, a third resistor, a fourth resistor and a bias voltage source; the first resistor and the second resistor are connected in series between the output terminal of the differential operational amplifier and the output terminal of the inverting amplifier, and the common connection terminal of the first resistor and the second resistor is connected to the inverting input terminal of the inverting amplifier; one end of the third resistor is connected to the non-inverting input terminal of the inverting amplifier, and the other end is connected to the bias voltage source; one end of the fourth resistor is connected to the common connection terminal between the non-inverting input terminal of the inverting amplifier and the first resistor, and the other end is grounded.
[0007] Furthermore, the operating parameters of the Miller compensation circuit satisfy the following calculation formula:
[0008] in, It represents the voltage value at the inverting input terminal of the inverting amplifier. Represents the output voltage value of the differential op amp, represents the voltage value at the output of the inverting amplifier, represents the resistance value of the first resistor, Represents the resistance value of the second resistor.
[0009] Furthermore, the first Miller compensation unit includes a first compensation capacitor and a fifth resistor connected in series to the first compensation capacitor; and the second Miller compensation unit is a second compensation capacitor.
[0010] Furthermore, the main pole of the transfer function of the compensation circuit is expressed as:
[0011] in, represents the main pole, Represents the output impedance of the fully differential op amp, represents the gain of the differential op amp, Indicates the capacitance of the first compensation capacitor or the second compensation capacitor.
[0012] Furthermore, the fully differential operational amplifier includes an input stage, an output stage, and a gain stage connected between the input stage and the output stage; the input stage is used to receive an initial differential signal; the gain stage is used to amplify the initial differential signal to obtain a double-ended differential signal; and the output stage is used to transmit the double-ended differential signal to the differential operational amplifier.
[0013] Furthermore, the input stage and the output stage are arranged symmetrically.
[0014] Furthermore, the fully differential operational amplifier also includes a common-mode suppression network connected in parallel to the input stage, and the common-mode suppression network is used to eliminate the common-mode signal of the signal source.
[0015] Furthermore, the input stage and the output stage are respectively provided with a chopping switch, and the chopping switch is used to realize the phase exchange between the initial differential signal and the two-ended differential signal, so that the initial differential signals of different phases form a two-ended differential signal after conversion by the fully differential operational amplifier, and the two-ended differential signal includes a positive phase output component corresponding to the in-phase input terminal of the differential operational amplifier and an inverting phase output component corresponding to the inverting input terminal of the differential operational amplifier.
[0016] A second aspect of an embodiment of the present application provides an operational amplifier chip, comprising a compensation circuit of a fully differential structure as described in the first aspect above.
[0017] As can be seen from the above, the compensation circuit and op amp chip of the fully differential structure provided by the present application have the following beneficial effects compared with the prior art: a double-ended to single-ended differential op amp is directly used to construct a Miller compensation loop, that is, the Miller compensation loop is directly bridged between the input and output of the double-ended to single-ended differential op amp through an inverting amplifier to construct a negative feedback path from the output of the differential op amp to its in-phase input, which has a large amplification factor, can reduce the loop compensation capacitance, has strong loop stability, and has a wide range of applications. BRIEF DESCRIPTION OF THE DRAWINGS
[0018] Figure 1 This is the schematic diagram of the circuit principle of Miller compensation; Figure 2 A schematic diagram of the overall structure of a fully differential compensation circuit provided in an embodiment of the present application; Figure 3 A schematic diagram of a specific compensation circuit provided in the embodiment of the present application; Figure 4 The overall structural diagram of a differential operational amplifier circuit applied to chopping technology provided in an embodiment of the present application. DETAILED DESCRIPTION
[0019] In order to make the purpose, features, and advantages of the invention of this application more obvious and easy to understand, the technical solutions in the embodiments of this application will be clearly and completely described below in conjunction with the drawings in the embodiments of this application. Obviously, the described embodiments are only part of the embodiments of this application, not all of them. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative work are within the scope of protection of this application.
[0020] In the description of the embodiments of the present application, it should be understood that the terms "length", "width", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", etc., indicating the orientation or position relationship, are based on the orientation or position relationship shown in the accompanying drawings, and are only for the convenience of describing the embodiments of the present application and simplifying the description, and do not indicate or imply that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention.
[0021] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of the features. In the description of the embodiments of the present application, the meaning of "multiple" is two or more, unless otherwise clearly and specifically defined.
[0022] In the embodiments of the present application, unless otherwise clearly specified and limited, the terms "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral one; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the embodiments of the present application can be understood according to the specific circumstances.
[0023] In the related art, in order to solve the problem that the differential operational amplifier circuit is prone to oscillation, loop compensation can usually be introduced when the differential operational amplifier is used in a closed loop to adjust the zero and pole positions to ensure loop stability. For example, Miller compensation can be used (the compensation principle diagram is shown in Figure 1 Miller compensation can be achieved from Figure 1 The conversion of the circuit (a) to the circuit (b) yields:
[0024]
[0025] in, It represents the gain from point X to point Y, which can be expressed as ; represents the equivalent resistance at point X; Represents the equivalent resistance at point Y; Indicates the resistance value connected in series between point X and point Y.
[0026] It can be seen that at the high-impedance node of the differential op amp circuit, a capacitor is connected across the negative feedback gain stage. The capacitor is amplified by the Miller effect and forms a low-frequency pole with the high-impedance node. By reasonably setting the zero-pole parameters, loop stability can be achieved.
[0027] Furthermore, the equivalent capacitance at the input of the fully differential op amp can be amplified by connecting a compensation capacitor across the gain stage of the fully differential op amp. However, this implementation method is only applicable to the fully differential structure of a multi-stage op amp and cannot be used to solve the fully differential structure of a single-stage op amp. In addition, the gain of the compensation capacitor is small, that is, the Maitreya effect is small, and a larger compensation capacitor is required to construct a lower-frequency pole.
[0028] Based on the above technical problems existing in the related art, an embodiment of the present application provides a compensation circuit and an operational amplifier chip with a fully differential structure.
[0029] Example: like Figure 2-4 As shown, in this embodiment, the compensation circuit of the fully differential structure includes a differential operational amplifier circuit and a Miller compensation circuit; wherein the differential operational amplifier circuit includes a cascaded fully differential operational amplifier AMP1 and a differential operational amplifier AMP2; the fully differential operational amplifier AMP1 is used to convert the initial differential signal of the received signal source into a double-ended differential signal, and transmit the double-ended differential signal to the differential operational amplifier AMP2; the differential operational amplifier AMP2 is used to convert the double-ended differential signal into a single-ended AC signal and then output it; the Miller compensation circuit includes a first Miller compensation unit, a second Miller compensation unit and an inverting amplifier AMP3; the first Miller compensation unit is connected across Between the non-inverting input terminal Vinp2 and the output terminal Vout of the differential operational amplifier AMP2; one end of the second Miller compensation unit is connected to the inverting input terminal Vinn2 of the differential operational amplifier AMP2, and the other end is connected to the output terminal Vout of the differential operational amplifier AMP2 through the inverting amplifier AMP3; the first Miller compensation unit and the second Miller compensation unit are used to amplify the equivalent capacitance of the differential operational amplifier AMP2; the inverting amplifier AMP3 is used to reverse the single-ended AC signal outputted from the output terminal Vout to realize negative feedback from the output terminal Vout of the differential operational amplifier AMP2 to the non-inverting input terminal Vinp2.
[0030] Specifically, the differential op amp circuit in this embodiment can be a structure of a fully differential op amp cascaded differential op amp, the fully differential op amp AMP1 can suppress input mismatch, and the differential op amp AMP2 can realize the output of double-ended to single-ended. Through the setting of the first Miller compensation unit and the second Miller compensation unit, a Miller compensation structure is added to the second end of the differential op amp AMP2 to construct a low-frequency pole, adjust the zero pole position, and ensure the stability of the loop. In addition, the related art directly connects the Miller compensation structure to the in-phase input terminal Vinp2 of the differential op amp AMP2, which may form positive feedback and produce oscillation, while this embodiment provides the use of an inverting amplifier AMP3, inverts the single-ended AC signal output by the differential op amp AMP2, and constructs a negative feedback path from the output terminal Vout of the differential op amp AMP2 to the in-phase input terminal, which can realize loop compensation of the output terminal of various types of fully differential op amps AMP1 (for example: single-stage op amps, multi-stage op amps).
[0031] Furthermore, if Figure 3 As shown, in some implementations of this embodiment, the Miller compensation circuit also includes a first resistor R1, a second resistor R2, a third resistor R3, a fourth resistor R4 and a bias voltage source VBIAS; the first resistor R1 and the second resistor R2 are connected in series between the output terminal Vout of the differential amplifier AMP2 and the output terminal of the inverting amplifier AMP3, and the common connection terminal A of the first resistor R1 and the second resistor R2 is connected to the inverting input terminal of the inverting amplifier AMP3; one end of the third resistor R3 is connected to the non-inverting input terminal of the inverting amplifier AMP3, and the other end is connected to the fixed bias voltage source VBIAS; one end of the fourth resistor R4 is connected to the common connection terminal B between the non-inverting input terminal of the inverting amplifier AMP3 and the first resistor R1, and the other end is grounded. By setting each resistor to adjust the feedback coefficient accurately, positive feedback can be effectively suppressed and the stability of the inverting amplifier AMP3 can be improved. It can be understood that in actual application, the size of each resistor can be selected according to the type and required bandwidth of the inverting amplifier AMP3, and no limitation is made here.
[0032] In this embodiment, the operating parameters of the Miller compensation circuit satisfy the following calculation formula:
[0033] in, represents the voltage value of the inverting input terminal of the inverting amplifier AMP3, Represents the output voltage value of the differential operational amplifier AMP2, represents the voltage value of the output terminal F of the inverting amplifier AMP3, represents the resistance value of the first resistor, Represents the resistance value of the second resistor.
[0034] Furthermore, in some implementations of this embodiment, due to the virtual short effect of the operational amplifier, , when the signal is small, is the AC ground, therefore, the operating parameters of the Miller compensation circuit satisfy the following calculation formula:
[0035]
[0036] Thus, the resistance values of the first resistor R1 and the second resistor R2 can be equal, that is, , the 1:1 inversion of the single-ended AC signal output by the differential op amp AMP2 can be achieved, and the voltage at the F terminal is , thus a negative feedback path from the output terminal Vout of the differential operational amplifier AMP2 to the non-inverting input terminal Vinp2 can be obtained through the inverting amplifier AMP3.
[0037] In some implementations of this embodiment, the first Miller compensation unit includes a first compensation capacitor Cc1 and a fifth resistor Rc connected in series to the first compensation capacitor Cc1; the second Miller compensation unit is a second compensation capacitor Cc2. That is, since the fully differential operational amplifier AMP1 is symmetrical, the first Miller compensation unit and the second Miller compensation unit can be respectively set at the two output ends of the fully differential operational amplifier AMP1, and then the pole position of the transfer function can be adjusted by reasonable parameter setting to improve the stability of the loop.
[0038] Further, in some implementations of this embodiment, the main pole of the transfer function of the compensation circuit is expressed as:
[0039] in, represents the main pole, It represents the output impedance of the fully differential op amp AMP1. represents the gain of differential op amp AMP2, Represents the capacitance value of the first compensation capacitor Cc1 or the second compensation capacitor Cc2.
[0040] like Figure 2-4 As shown, in some implementations of this embodiment, the fully differential operational amplifier AMP1 includes an input stage, an output stage, and a gain stage connected between the input stage and the output stage; the input stage is used to receive an initial differential signal; the gain stage is used to amplify the initial differential signal to obtain a double-ended differential signal; the output stage is used to transmit the double-ended differential signal to the differential operational amplifier AMP2.
[0041] Specifically, the input stage includes a non-inverting input terminal Vinp and an inverting input terminal Vinn, which are used to receive and amplify the initial differential signal of the signal source. The gain stage can be a single-stage operational amplifier circuit or a multi-stage operational amplifier circuit, and further amplification of the initial differential signal is achieved through gain design. The output stage includes a positive-phase output terminal and an inverting output terminal, the positive-phase output terminal is used to connect to the non-inverting input terminal Vinp2 of the differential operational amplifier AMP2, and the inverting output terminal is used to connect to the inverting input terminal Vinn2 of the differential operational amplifier AMP2.
[0042] Furthermore, in some implementations of this embodiment, the input stage and the output stage are symmetrically arranged, and the active suppression of input signal mismatch can be achieved through the symmetrical layout of the input stage and the output stage and the balanced circuit configuration, that is, the signal mismatch caused by the mismatch of the input components can be effectively offset, ensuring that the signal processing of the differential operational amplifier AMP2 in the next stage is more accurate. In some implementations, the fully differential operational amplifier AMP1 also includes a common mode suppression network connected in parallel to the input stage, and the common mode suppression network can be used to eliminate the common mode signal of the signal source.
[0043] In some implementations of this embodiment, the differential operational amplifier circuit of this embodiment can be applied to chopping technology. Figure 4 As shown, chopping switches can be respectively provided at the input stage and the output stage. The chopping switches can be used to realize the phase exchange between the initial differential signal and the two-ended differential signal, so that the initial differential signals of different phases can form two-ended differential signals after being converted by the fully differential operational amplifier AMP1. The two-ended differential signal includes a positive phase output component corresponding to the in-phase input terminal Vinp2 of the differential operational amplifier AMP2 and an inverting phase output component corresponding to the inverting input terminal Vinn2 of the differential operational amplifier AMP2.
[0044] Specifically, the chopper switch can sample and hold the signal by quickly cutting off the input signal, thereby reducing the impact of low-frequency noise; through secondary phase conversion, the noise is effectively suppressed when the signal is restored. Exemplarily, during the operation of the differential op amp circuit, when the initial output signal connected is in phase 1, Vinp is connected to Vinp1, and after the gain stage, Vop1 is connected to Vinp2; when the initial output signal connected is in phase 2, Vinp is connected to Vinn1, and after the gain stage, Von1 is connected to Vinp2; therefore, no matter in which phase, the overall external performance of the cascade system of the fully differential op amp AMP1 and the differential op amp AMP2 is to use Vinp as the in-phase input terminal and Vin as the inverting input terminal, without affecting the connection relationship of the peripheral circuit.
[0045] The embodiment of the present application also provides a high-precision, low-offset operational amplifier chip. The operational amplifier chip includes the compensation circuit in the above embodiment and can be applied to a high-precision data acquisition system.
[0046] The above is a description of the compensation circuit and operational amplifier chip of the fully differential structure provided in this application. The above is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.
Claims
1. A compensation circuit of a fully differential structure, characterized in that: include: A differential operational amplifier circuit, comprising a cascaded fully differential operational amplifier and a differential operational amplifier; the fully differential operational amplifier is used to convert an initial differential signal received from a signal source into a double-ended differential signal, and transmit the double-ended differential signal to the differential operational amplifier; the differential operational amplifier is used to convert the double-ended differential signal into a single-ended AC signal and then output it; A Miller compensation circuit, comprising a first Miller compensation unit, a second Miller compensation unit and an inverting amplifier; The first Miller compensation unit is connected across the non-inverting input terminal and the output terminal of the differential operational amplifier; one end of the second Miller compensation unit is connected to the inverting input terminal of the differential operational amplifier, and the other end is connected to the output terminal of the differential operational amplifier through the inverting amplifier; the first Miller compensation unit and the second Miller compensation unit are used to amplify the equivalent capacitance of the differential operational amplifier; the inverting amplifier is used to invert the single-ended AC signal to achieve negative feedback from the output terminal of the differential operational amplifier to the non-inverting input terminal.
2. The fully differential compensation circuit according to claim 1, characterized in that: The Miller compensation circuit also includes a first resistor, a second resistor, a third resistor, a fourth resistor and a bias voltage source; the first resistor and the second resistor are connected in series between the output end of the differential operational amplifier and the output end of the inverting amplifier, and the common connection end of the first resistor and the second resistor is connected to the inverting input end of the inverting amplifier; One end of the third resistor is connected to the non-inverting input terminal of the inverting amplifier, and the other end is connected to the bias voltage source; one end of the fourth resistor is connected to the common connection terminal between the non-inverting input terminal of the inverting amplifier and the first resistor, and the other end is grounded.
3. The compensation circuit of the fully differential structure according to claim 2, characterized in that: The operating parameters of the Miller compensation circuit satisfy the following calculation formula: in, represents the voltage value of the inverting input terminal of the inverting amplifier, represents the output voltage value of the differential operational amplifier, represents the voltage value at the output of the inverting amplifier, represents the resistance value of the first resistor, represents the resistance value of the second resistor.
4. The fully differential compensation circuit according to claim 2, characterized in that: The first Miller compensation unit includes a first compensation capacitor and a fifth resistor connected in series to the first compensation capacitor; the second Miller compensation unit is a second compensation capacitor.
5. The fully differential compensation circuit according to claim 4, characterized in that: The main pole of the transfer function of the compensation circuit is expressed as: in, represents the main pole, represents the output impedance of the fully differential operational amplifier, represents the gain of the differential op amp, Indicates the capacitance of the first compensation capacitor or the second compensation capacitor.
6. The fully differential compensation circuit according to claim 1, characterized in that: The fully differential operational amplifier comprises an input stage, an output stage and a gain stage connected between the input stage and the output stage; the input stage is used to receive the initial differential signal; the gain stage is used to amplify the initial differential signal to obtain the double-ended differential signal; The output stage is used to transmit the double-ended differential signal to the differential operational amplifier.
7. The compensation circuit of the fully differential structure according to claim 6, characterized in that: The input stage and the output stage are symmetrically arranged.
8. The fully differential compensation circuit according to claim 6, characterized in that: The fully differential operational amplifier further includes a common mode suppression network connected in parallel to the input stage, and the common mode suppression network is used to eliminate the common mode signal of the signal source.
9. The compensation circuit of the fully differential structure according to claim 6, characterized in that: The input stage and the output stage are also respectively provided with a chopper switch, and the chopper switch is used to realize the phase exchange between the initial differential signal and the two-ended differential signal, so that the initial differential signals with different phases can form the two-ended differential signal after conversion by the fully differential operational amplifier, and the two-ended differential signal includes a positive phase output component corresponding to the in-phase input terminal of the differential operational amplifier and an inverting phase output component corresponding to the inverting input terminal of the differential operational amplifier.
10. An operational amplifier chip, characterized in that: A compensation circuit comprising a fully differential structure as claimed in any one of claims 1 to 9.