Common mode feedback circuit with level shifting function

Abstract

The application provides a common-mode feedback circuit with a level conversion function, comprising an amplifier output stage, a resistive common-mode feedback circuit and an amplifier common-mode feedback circuit, the amplifier output stage comprising a first current source I1, a second current source I2, a tail current source I3, input pair tubes M1 and M2 and a common-mode adjusting tube M3, the resistive common-mode feedback circuit comprising a first resistor R1 and a second resistor R2, and the amplifier common-mode feedback circuit comprising a third resistor R3, a fourth resistor R4 and a first operational amplifier AMP1, V OP and V ON The input ports of the resistive common-mode feedback circuit and the amplifier common-mode feedback circuit are commonly connected, for detecting the common-mode voltage and adjusting the common-mode adjusting tube at the same time. The scheme introduces the fast response advantage of the amplifier feedback on the basis of the resistive feedback, realizes the accurate control and dynamic adjustment of the common-mode level, and makes the output common-mode voltage be flexibly set by integrating the level conversion function in the feedback loop, so that the transient response speed of the system is significantly improved.

Description

Technical Field

[0001] This invention relates to the field of integrated circuit technology, and in particular to a common-mode feedback circuit with level conversion function. Background Technology

[0002] In high-speed, high-precision analog integrated circuit design, fully differential structures are widely used due to their excellent anti-interference performance and power supply rejection capabilities. Common-mode feedback circuits (CMFB), as key modules for maintaining the stability of the common-mode level of differential signals, directly affect the overall system performance. While traditional resistive common-mode feedback circuits are simple in structure, they inherently suffer from difficulty in controlling accuracy. Active common-mode feedback based on operational amplifiers, although capable of precisely controlling the output common-mode voltage through the negative feedback characteristics of the amplifier, has a core drawback: the multi-stage amplifier system, composed of operational amplifiers and output stages, introduces complex stability issues. This multi-stage structure generates multiple poles in the open-loop transfer function. The output poles of the operational amplifier itself and the parasitic poles of the output stage create a dangerous phase lag. When these pole frequencies are close, the system's phase margin deteriorates sharply, even leading to oscillations. To maintain stability, Miller compensation capacitors must be introduced, but this introduces performance limitations: firstly, the introduction of Miller capacitors significantly reduces the circuit bandwidth, weakening the advantage of the originally fast-response amplifier-type feedback at high frequencies; secondly, large compensation capacitors occupy a considerable chip area. In addition, existing common-mode feedback circuits generally lack flexible level shifting capabilities, making it difficult to adapt to the differentiated requirements of common-mode voltage in different operating scenarios. This is especially true in applications such as high-speed data converters and broadband communication systems, where it is necessary to quickly establish an accurate common-mode voltage and adjust the level according to the requirements of subsequent circuits. Existing technologies often require additional cascaded level shifting circuits to achieve this, which increases system power consumption and noise.

[0003] Therefore, there is an urgent need to develop a common-mode feedback solution that combines fast response, precise control, and level shifting to meet the dual requirements of modern high-performance mixed-signal systems for common-mode stability and flexibility. Summary of the Invention

[0004] To address the aforementioned issues, this invention proposes a common-mode feedback circuit with level conversion functionality. It employs a hybrid feedback architecture combining a resistor network and an active amplifier in parallel, achieving high-precision control and flexible adjustment of the common-mode level. This circuit utilizes a two-stage parallel structure working collaboratively, significantly improving the accuracy and stability of common-mode control while ensuring system stability.

[0005] A common-mode feedback circuit with level shifting function includes an amplifier output stage circuit, a resistive common-mode feedback circuit, and an amplifier common-mode feedback circuit. The amplifier output stage circuit includes a first current source I1, a second current source I2, a tail current source I3, two input transistor pairs, and a common-mode adjustment transistor. The resistive common-mode feedback circuit includes a first resistor R1 and a second resistor R2. The amplifier common-mode feedback circuit includes a third resistor R3, a fourth resistor R4, and a first operational amplifier AMP1. The output V of the amplifier output stage circuit... OP and V ON The input ports of the resistive common-mode feedback circuit and the amplifier common-mode feedback circuit are connected together to detect the common-mode voltage and adjust the common-mode regulating transistor.

[0006] Furthermore, the two input transistors are a first N-type transistor M1 and a second N-type transistor M2, the common-mode regulating transistor is a third N-type transistor M3, and one end of the first current source I1 and the second current source I2 are connected to the power supply V. DD The other end of the first current source I1 is connected to the drain of the first N-type transistor M1 and the output V of the amplifier output stage circuit. ON The other end of the second current source I2 is connected to the drain of the second N-type transistor M2 and the output V of the amplifier output stage circuit. OP One end of the tail current source I3 is grounded, and the other end is connected to the drain of the third N-type transistor M3 and the sources of the first N-type transistor M1 and the second N-type transistor M2. The gate of the first N-type transistor M1 is connected to the input P port V of the amplifier output stage circuit. INP The gate of the second N-type transistor M2 is connected to the input N port V of the amplifier output stage circuit. INN The drain of the third N-type transistor M3 is also connected to the source of the first N-type transistor M1 and the second N-type transistor M2, and the source of the third N-type transistor M3 is grounded.

[0007] Furthermore, one end of the first resistor R1 is connected to V of the amplifier output stage circuit. ON The second resistor R2 is connected to the V port of the amplifier output stage circuit. OP The other ends of the first resistor R1 and the second resistor R2 are connected together to the gate of the third N-type transistor M3 in the amplifier output stage circuit and the output of the first operational amplifier AMP1 in the amplifier common-mode feedback circuit.

[0008] Furthermore, one end of the third resistor R3 is connected to V of the amplifier output stage circuit. ON Port, one end of the fourth resistor R4 is connected to the V of the amplifier output stage circuit. OPThe other ends of the third resistor R3 and the fourth resistor R4 are connected to the positive port of the first operational amplifier AMP1, and the negative port of the first operational amplifier AMP1 is connected to the common-mode voltage V that needs to be adjusted. COM The output port of the first operational amplifier AMP1 is connected to the gate of the third N-type transistor M3 in the amplifier output stage circuit.

[0009] Furthermore, all resistors are implemented using polysilicon resistors, with the first resistor R1 and the second resistor R2 having the same resistance value, and the third resistor R3 and the fourth resistor R4 having the same resistance value.

[0010] Furthermore, polysilicon resistors form a symmetrical voltage divider network, and the common-mode voltage component of the differential output signal is detected in real time through matched resistors. The detected common-mode voltage signal directly drives the common-mode adjustment transistor of the amplifier output stage circuit, forming a fast local feedback loop.

[0011] Furthermore, the first operational amplifier compares and amplifies the detected common-mode voltage with the external common-mode voltage, and precisely controls the gate voltage of the common-mode regulating transistor through a deep negative feedback mechanism.

[0012] This invention innovatively integrates the advantages of resistive common-mode feedback and amplifier-based common-mode feedback, proposing a high-performance hybrid common-mode control solution. By combining the simplicity and stability of the resistive feedback network with the precise controllability of the amplifier feedback loop, a breakthrough optimization is achieved in the circuit architecture. The resistive feedback branch uses a precisely matched distributed resistor network to construct a fast-response channel with inherent stability. Its single-pole characteristic ensures reliable operation in high-frequency applications, while significantly reducing the dependence of traditional multi-stage amplifier structures on complex compensation networks. The parallel amplifier feedback branch constructs a deep negative feedback system through a high-gain operational amplifier, utilizing its "virtual short" characteristic to achieve common-mode voltage control accuracy within ±1%, and supports a wide range of level programming capabilities. Test results show that this hybrid architecture maintains the low-power advantage of resistive feedback while improving common-mode control accuracy by an order of magnitude and transient response speed by more than 50%. It achieves precise control and dynamic adjustment of the common-mode level, significantly improving the transient response speed of the system. It is suitable for high-speed, high-precision analog integrated circuits, especially for applications with stringent requirements for common-mode stability and level adaptability, such as fully differential amplifiers and switching amplifiers. Attached Figure Description

[0013] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0014] Figure 1 This is a schematic diagram of a common-mode feedback circuit with level conversion function provided in an embodiment of the present invention;

[0015] Figure 2 This is a simulation result diagram of the stability of the common-mode feedback circuit with level conversion function provided in the embodiment of the present invention. Detailed Implementation

[0016] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0017] This invention proposes a common-mode feedback circuit with level conversion function. First, a fully differential symmetrical circuit architecture is constructed. Its core consists of a two-stage parallel structure of resistive common-mode feedback and amplifier-type common-mode feedback. The first stage is a resistive common-mode feedback circuit. This circuit uses polysilicon resistors to form a symmetrical voltage divider network. The common-mode voltage component of the differential output signal is detected in real time through matched resistors. The detected common-mode voltage signal directly drives the common-mode adjustment transistor of the amplifier output stage, forming a fast local feedback loop. This single-stage amplification structure has inherent stability and superior high-frequency characteristics. Its -3dB bandwidth can reach hundreds of MHz, making it particularly suitable for high-frequency applications such as high-speed data converters.

[0018] The second stage is a high-performance amplifier-type common-mode feedback circuit. This circuit is consistent with the resistive common-mode feedback circuit in terms of the common-mode voltage detection front end. It uses a precision resistor network to detect the common-mode voltage of the output differential signal. However, a high-gain operational amplifier is introduced in the signal processing path. The operational amplifier compares and amplifies the detected common-mode voltage with the external common-mode voltage. Through a deep negative feedback mechanism, it precisely controls the gate voltage of the common-mode regulating transistor. This structure utilizes the "virtual short" characteristic of the operational amplifier to achieve a common-mode voltage control accuracy within ±1%. At the same time, it supports dynamic adjustment of the external common-mode voltage through a digital interface to achieve flexible configuration of the output common-mode level.

[0019] like Figure 1As shown, the common-mode feedback circuit with level conversion function proposed in this invention includes an amplifier output stage circuit, a resistive common-mode feedback circuit, and an amplifier common-mode feedback circuit. The amplifier output stage circuit includes a first current source I1, a second current source I2, a tail current source I3, two input transistor pairs, and a common-mode adjustment transistor. The two input transistor pairs are a first N-type transistor M1 and a second N-type transistor M2, respectively. The common-mode adjustment transistor is a third N-type transistor M3. One end of the first current source I1 and the second current source I2 are connected to the power supply V. DD The other end of the first current source I1 is connected to the drain of the first N-type transistor M1 and the output V of the amplifier output stage circuit. ON The other end of the second current source I2 is connected to the drain of the second N-type transistor M2 and the output V of the amplifier output stage circuit. OP One end of the tail current source I3 is grounded, and the other end is connected to the drain of the third N-type transistor M3 and the sources of the first N-type transistor M1 and the second N-type transistor M2. The gate of the first N-type transistor M1 is connected to the input P port V of the amplifier output stage circuit. INP The gate of the second N-type transistor M2 is connected to the input N port V of the amplifier output stage circuit. INN The drain of the third N-type transistor M3 is also connected to the sources of the first N-type transistor M1 and the second N-type transistor M2. The source of the third N-type transistor M3 is grounded. The output V of the amplifier output stage circuit... OP and V ON They are connected together to the input port of the resistive common-mode feedback circuit and also to the input port of the amplifier common-mode feedback circuit, used to detect the common-mode voltage and adjust the common-mode regulating transistor.

[0020] The resistive common-mode feedback circuit includes a first resistor R1 and a second resistor R2, both made of polysilicon. The first resistor R1 and the second resistor R2 have the same resistance value, controlled at 20KΩ. One end of the first resistor R1 is connected to the Vo pin of the amplifier output stage circuit. ON The second resistor R2 is connected to the V port of the amplifier output stage circuit. OP The other ends of the first resistor R1 and the second resistor R2 are connected to the gate of the third N-type transistor M3 in the amplifier output stage circuit and the output terminal of the first operational amplifier AMP1 in the amplifier common-mode feedback circuit. One end of R1 and R2 are respectively connected to V ON and V OP Then the voltage across the other end of R1 and R2 is (V) OP +V ONThe voltage I1 / 2 is the output common-mode voltage of the differential signal. This voltage is connected to the gate of the third N-type transistor M3. At this time, M3, M1 / M2, I1 / I2, R1, and R2 form a negative feedback loop to control the output common-mode voltage. Polysilicon resistors form a symmetrical voltage divider network. The common-mode voltage component of the differential output signal is detected in real time through matched resistors. The detected common-mode voltage signal directly drives the common-mode adjustment transistor of the amplifier output stage circuit, forming a fast local feedback loop.

[0021] The amplifier common-mode feedback circuit includes a third resistor R3, a fourth resistor R4, and a first operational amplifier AMP1. All resistors are polysilicon resistors. The third resistor R3 and the fourth resistor R4 have the same resistance value, controlled at 20KΩ. One end of the third resistor R3 is connected to the Vo pin of the amplifier output stage circuit. ON Port, one end of the fourth resistor R4 is connected to the V of the amplifier output stage circuit. OP The other ends of the third resistor R3 and the fourth resistor R4 are connected to the positive port of the first operational amplifier AMP1, and the negative port of the first operational amplifier AMP1 is connected to the common-mode voltage V that needs to be adjusted. COM The output port of the first operational amplifier AMP1 is connected to the gate of the third N-type transistor M3 in the amplifier output stage circuit. The first operational amplifier AMP1 is a common single-stage folded cascode amplifier, providing high gain and strong stability. One end of R3 and R4 is connected to V... ON and V OP Then the voltage across the other end of R3 and R4 is (V) OP +V ON ) / 2, this voltage is the output common-mode voltage of the differential signal, and then it is compared with the externally set common-mode voltage V through AMP1. COM The common-mode regulator is controlled by a deep negative feedback mechanism. The entire loop includes M3, M1 / M2, I1 / I2, R3, R4, and AMP1, forming a negative feedback loop to control the output common-mode voltage.

[0022] Figure 2 The figure shows the circuit stability simulation results of the common-mode feedback circuit with level conversion function proposed in this invention. The horizontal axis represents frequency, the right vertical axis represents open-loop gain, and the left vertical axis represents open-loop phase. The solid line represents the change of loop gain with frequency, and the dashed line represents the change of loop phase with frequency. It can be seen from the figure that the phase margin of the circuit is 75 degrees at a unity-gain bandwidth of 333.87MHz. With the solution of this invention, no Miller compensation capacitor needs to be added between the source and drain of the common-mode adjustment transistor to achieve a stable state. In addition, the common-mode voltage control accuracy within ±1% can be achieved by using an external common-mode voltage adjustment circuit.

[0023] This invention constructs a novel hybrid feedback structure by combining a resistive common-mode feedback circuit with an amplifier common-mode feedback circuit. This circuit retains the simplicity and reliability of resistive feedback while introducing the fast response advantage of amplifier feedback, achieving precise control and dynamic adjustment of the common-mode level. It also innovatively integrates a level conversion function into the feedback loop, allowing for flexible setting of the output common-mode voltage and significantly improving the system's transient response speed. This design overcomes the shortcomings of traditional common-mode feedback circuits, such as slow response speed and limited level adjustment, and is suitable for high-speed, high-precision analog integrated circuits, especially for applications with stringent requirements for common-mode stability and level adaptability, such as fully differential amplifiers and switching amplifiers.

[0024] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A common-mode feedback circuit with level conversion function, characterized in that, The amplifier includes an output stage circuit, a resistive common-mode feedback circuit, and an amplifier common-mode feedback circuit. The output stage circuit includes a first current source I1, a second current source I2, a tail current source I3, two input transistor pairs, and a common-mode adjustment transistor. The resistive common-mode feedback circuit includes a first resistor R1 and a second resistor R2. The common-mode feedback circuit includes a third resistor R3, a fourth resistor R4, and a first operational amplifier AMP1. The output V of the output stage circuit... OP and V ON The input ports of the resistive common-mode feedback circuit and the amplifier common-mode feedback circuit are connected together to detect the common-mode voltage and adjust the common-mode regulating transistor.

2. The common-mode feedback circuit with level conversion function according to claim 1, characterized in that, The two input transistors are the first N-type transistor M1 and the second N-type transistor M2, and the common-mode regulator is the third N-type transistor M3. One end of the first current source I1 and the second current source I2 are connected to the power supply V. DD The other end of the first current source I1 is connected to the drain of the first N-type transistor M1 and the output V of the amplifier output stage circuit. ON The other end of the second current source I2 is connected to the drain of the second N-type transistor M2 and the output V of the amplifier output stage circuit. OP One end of the tail current source I3 is grounded, and the other end is connected to the drain of the third N-type transistor M3 and the sources of the first N-type transistor M1 and the second N-type transistor M2. The gate of the first N-type transistor M1 is connected to the input P port V of the amplifier output stage circuit. INP The gate of the second N-type transistor M2 is connected to the input N port V of the amplifier output stage circuit. INN The drain of the third N-type transistor M3 is also connected to the source of the first N-type transistor M1 and the second N-type transistor M2, and the source of the third N-type transistor M3 is grounded.

3. The common-mode feedback circuit with level conversion function according to claim 1, characterized in that, One end of the first resistor R1 is connected to V of the amplifier output stage circuit. ON The second resistor R2 is connected to the V port of the amplifier output stage circuit. OP The other ends of the first resistor R1 and the second resistor R2 are connected together to the gate of the third N-type transistor M3 in the amplifier output stage circuit and the output of the first operational amplifier AMP1 in the amplifier common-mode feedback circuit.

4. The common-mode feedback circuit with level conversion function according to claim 1, characterized in that, One end of the third resistor R3 is connected to V in the amplifier output stage circuit. ON Port, one end of the fourth resistor R4 is connected to the V of the amplifier output stage circuit. OP The other ends of the third resistor R3 and the fourth resistor R4 are connected to the positive port of the first operational amplifier AMP1, and the negative port of the first operational amplifier AMP1 is connected to the common-mode voltage V that needs to be adjusted. COM The output port of the first operational amplifier AMP1 is connected to the gate of the third N-type transistor M3 in the amplifier output stage circuit.

5. The common-mode feedback circuit with level conversion function according to claim 1, characterized in that, All resistors are made of polysilicon. The first resistor R1 and the second resistor R2 have the same resistance value, and the third resistor R3 and the fourth resistor R4 have the same resistance value.

6. The common-mode feedback circuit with level conversion function according to claim 5, characterized in that, Polysilicon resistors form a symmetrical voltage divider network. The common-mode voltage component of the differential output signal is detected in real time through matched resistors. The detected common-mode voltage signal directly drives the common-mode adjustment transistor of the amplifier output stage circuit, forming a fast local feedback loop.

7. The common-mode feedback circuit with level conversion function according to claim 1, characterized in that, The first operational amplifier compares and amplifies the detected common-mode voltage with the external common-mode voltage, and controls the gate voltage of the common-mode regulating transistor through a deep negative feedback mechanism.

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