High-stability common-mode feedback circuit

Abstract

The invention discloses a high-stability common-mode feedback circuit which is used for accurately adjusting the common-mode level of a differential amplifier. The circuit comprises an amplifying circuit module, a common-mode detection module and a substrate adjusting module, by introducing a substrate adjusting technology, the size of an amplifying tube is reduced, and the stability and bandwidth of common-mode feedback are remarkably improved. Wherein the common-mode detection module adopts a source follower structure and detects common-mode voltage of differential output in real time; the substrate adjusting module can greatly reduce the size of the common-mode adjusting transistor in the common-mode feedback amplifier by adjusting the body port voltage of the common-mode adjusting transistor in the common-mode feedback module and reducing the threshold voltage of the transistor and utilizing the back gate characteristic of the transistor, the parasitic capacitance of the common-mode adjusting transistor is reduced, and the performance of the common-mode feedback amplifier is improved. And meanwhile, the common-mode level stability in a wide input range is realized, and the method is suitable for scenes such as high-speed analog-to-digital converters and low-noise amplifiers which have strict requirements on the common-mode stability.

Description

Technical Field

[0001] This invention belongs to the field of integrated circuits, and specifically relates to a highly stable common-mode feedback circuit. Background Technology

[0002] In analog integrated circuit design, common-mode feedback circuits are crucial for maintaining the stable operation of differential amplifiers. Traditional common-mode feedback circuits typically achieve common-mode control by adjusting the gate voltage of the common-mode regulator. While this method is simple and direct, it has significant performance limitations. To obtain sufficient regulation capability, a larger regulator transistor is required, which inevitably introduces large parasitic capacitance, limiting the circuit's bandwidth and potentially causing stability issues. Although back-gate modulation has been applied in transistor characteristic regulation, its advantages have not been fully realized in the common-mode feedback field. This invention addresses these technical problems by innovatively proposing a high-stability common-mode feedback circuit based on back-gate modulation. By utilizing the transistor's body terminal for common-mode level adjustment, this scheme effectively overcomes the limitations of traditional gate control methods. Back-gate modulation not only achieves the same regulation capability with a smaller device size and significantly reduces parasitic capacitance, but also improves the accuracy of common-mode control through sensitive threshold voltage adjustment. This architecture also integrates a dynamic bias mechanism, which can optimize the back-gate voltage in real time based on common-mode error, maintaining system stability while ensuring fast response. Compared with traditional solutions, this invention shows significant advantages in terms of bandwidth enhancement, phase margin improvement, and stability, providing a better common-mode control solution for high-speed and high-precision analog circuit design. Summary of the Invention

[0003] This invention provides a highly stable common-mode feedback circuit based on transistor back-gate control. Its core lies in the innovative use of the transistor's back-gate terminal to achieve precise control of the common-mode level. This circuit architecture significantly improves system stability and operating bandwidth while maintaining high precision by optimizing key performance bottlenecks present in traditional common-mode feedback.

[0004] The technical solution of this invention is as follows:

[0005] A high-stability common-mode feedback circuit includes an amplifier circuit module, a common-mode detection module, and a substrate adjustment module;

[0006] The amplifier circuit module generates a differential output signal based on the input signal;

[0007] The common-mode detection module detects the common-mode level of the differential output signal of the amplifier circuit module in real time and transmits the detection result to the common-mode adjustment transistor.

[0008] The substrate adjustment module generates a body voltage through a negative feedback network and sends the body voltage to the substrate end of the common-mode adjustment transistor.

[0009] The common-mode regulator adjusts the threshold voltage based on the body voltage, thereby enhancing the conduction capability by lowering the threshold voltage.

[0010] Furthermore, the amplifier circuit module includes a first current source, a second current source, a third current source, a first MOSFET, and a second MOSFET; wherein, the input terminal of the first current source is connected to a power supply, and the output terminal is connected to the drain of the first MOSFET; the input terminal of the second current source is connected to a power supply, and the output terminal is connected to the drain of the second MOSFET; the first MOSFET and the second MOSFET are an input pair, the gate of the first MOSFET is the first input port of the amplifier circuit module, connected to the positive terminal of the differential input signal; the gate of the second MOSFET is the second input port of the amplifier circuit module, connected to the negative terminal of the differential input signal; the connection point of the first MOSFET and the first current source is the first output port of the amplifier circuit module, and the connection point of the second MOSFET and the second current source is the second output port of the amplifier circuit module; the sources of the first MOSFET and the second MOSFET are connected together to the input terminal of the third current source, and the output terminal of the third current source is grounded;

[0011] The common-mode detection module includes a third MOSFET, a fourth MOSFET, a fifth MOSFET, and a fourth current source. The drain of the third MOSFET is connected to a power supply, and its gate is connected to the first output terminal of the amplifier circuit module. The drain of the fourth MOSFET is connected to a power supply, and its gate is connected to the second output terminal of the amplifier circuit module. The sources of the third and fourth MOSFETs are connected to the input terminal of the fourth current source and the gate of the fifth MOSFET. The third, fourth, and fourth current sources constitute a source follower. The fifth MOSFET is a common-mode adjustment transistor, and its drain is connected to the sources of the first and second MOSFETs. The source of the fifth MOSFET and the output terminal of the fourth current source are grounded.

[0012] The substrate conditioning module includes a fifth current source, a sixth MOSFET, a seventh MOSFET, an eighth MOSFET, a ninth MOSFET, a tenth MOSFET, and an amplifier; wherein, the input terminal of the fifth current source is connected to a power supply, and the output terminal is connected to the drain of the sixth MOSFET, the gate of the eighth MOSFET, the gate of the ninth MOSFET, and the negative input terminal of the amplifier; the gate of the sixth MOSFET is connected to the input common-mode voltage V. CM,IN This voltage is the common-mode voltage value of the positive and negative terminals of the differential signal. Its source is connected to the drain of the eighth MOSFET, and the source of the eighth MOSFET is grounded. The gate of the seventh MOSFET is connected to the common-mode output voltage V. CM,INIts drain is connected to the source of the tenth MOSFET and the positive input terminal of the amplifier; the source of the seventh MOSFET is connected to the drain of the ninth MOSFET, and the source of the ninth MOSFET is grounded; the drain of the tenth MOSFET is connected to the power supply, and its gate is connected to the external reference voltage V. CM This voltage is supplied externally, V REF It is V CM The voltage value after level shifting, which is V CM With V REF There exists a fixed voltage difference, and then V REF The amplifier and amplification circuit form a feedback structure to control the substrate voltage and adjust the common-mode voltage at the positive and negative terminals of the differential signal; the output terminal of the amplifier is connected to the substrate of the eighth MOS transistor, the substrate of the ninth MOS transistor, and the substrate of the fifth MOS transistor.

[0013] The beneficial effects of this invention are as follows: the technical solution of this invention achieves a comprehensive improvement in the performance of the common-mode feedback circuit through an innovative back-gate adjustment mechanism, demonstrating significant advantages in several key indicators. The negative bias voltage generated by the negative feedback network effectively reduces the threshold voltage of the common-mode regulating transistor, allowing for a significant reduction in transistor size while maintaining the same transconductance performance. This innovative design directly leads to a significant reduction in parasitic capacitance; simulation data shows a reduction of approximately 100%, providing a fundamental guarantee for the circuit's high-frequency response performance. Regarding operating bandwidth, thanks to the reduced device size and optimized compensation structure, the loop bandwidth is more than twice that of traditional solutions. According to loop stability simulation results, a phase margin of over 65 degrees can still be maintained at a frequency of 430MHz, fully meeting the requirements of demanding applications such as high-speed data conversion. Attached Figure Description

[0014] Figure 1 This is a schematic diagram of the common-mode feedback circuit in a specific embodiment of the present invention.

[0015] Figure 2 The following are simulation results of the stability of the common-mode feedback circuit in a specific embodiment of the present invention. Detailed Implementation

[0016] The present invention will now be further described with reference to the accompanying drawings and embodiments.

[0017] The common-mode feedback circuit of this invention mainly consists of three parts: an amplifier circuit module, a common-mode detection module, and a substrate adjustment module. The common-mode detection module uses a source follower machine and a current mirror structure to detect the common-mode level of the differential output signal of the amplifier circuit module in real time and transmits the detection result to the common-mode adjustment transistor. The substrate adjustment module includes a negative feedback circuit specifically for generating the body voltage. The body terminal of the common-mode adjustment transistor receives the body voltage from the substrate adjustment module. By changing the back gate bias voltage, the threshold voltage of the transistor is adjusted, reducing the size of the adjustment transistor and simultaneously achieving precise control of the output common-mode level.

[0018] Compared with traditional gate control methods, the back-gate modulation mechanism of this invention has multiple technical advantages. First, because back-gate modulation is more sensitive to the characteristics of transistors, the required common-mode control transistor size can be significantly reduced, which significantly reduces the parasitic capacitance of the circuit and improves the operating bandwidth. Second, back-gate control avoids the matching error problem caused by traditional large-size control transistors, thus improving the accuracy of common-mode control.

[0019] This invention provides a high-stability common-mode feedback circuit based on back-gate voltage regulation. Its core innovation lies in employing a unique negative voltage generation circuit to achieve precise control of the common-mode regulating transistor's body terminal. This technical solution significantly reduces the device size while maintaining sufficient regulation capability by actively lowering the threshold voltage of the regulating transistor, thereby achieving superior frequency response characteristics and stability. The substrate regulation module includes an innovative negative feedback network consisting of a source follower, an error amplifier, and an auxiliary current source. The source follower buffers the input common-mode reference voltage, and the error amplifier compares the common-mode detection signal with the common-mode reference level, outputting the required negative bias voltage. This negative voltage is directly applied to the body terminal of the common-mode regulating transistor, enhancing its conduction capability by lowering the transistor's threshold voltage. This unique back-gate biasing method allows the size of the common-mode regulating transistor to be reduced by more than 50% compared to traditional solutions while maintaining the same regulation capability requirements, thereby reducing parasitic capacitance by approximately 100% and significantly improving the circuit's operating bandwidth.

[0020] The common-mode feedback circuit of this invention is particularly suitable for high-speed, high-precision analog circuit systems, such as fully differential operational amplifiers and analog-to-digital converter front-ends. In practical applications, this circuit exhibits excellent performance indicators: under typical operating conditions, the size of the common-mode regulator can be reduced by more than 50% compared to traditional solutions, parasitic capacitance is reduced by approximately 100%, loop bandwidth is increased by more than 2 times, while maintaining excellent phase margin and temperature stability. These technical advantages make this invention of significant practical value in applications with stringent common-mode control requirements, such as high-speed data conversion and precision measurement.

[0021] Example:

[0022] This embodiment is implemented using a 0.18μm CMOS process. The core of the common-mode feedback circuit consists of three parts: an amplifier circuit module, a common-mode detection module, and a substrate adjustment module. Figure 1 As shown, the amplifier circuit module mainly includes a tail current source I3, input transistors M1 / M2, and a common-mode adjustment transistor M5. One end of the tail current source I3 is connected to ground, and the other end is connected to the drain of the fifth N-type transistor and the source of the first two N-type transistors. In this embodiment, the current of the tail current source I3 is 3.6mA. The gates of the first two N-type transistors are connected to the P port VINP and the N port VINN of the input amplifier, respectively. One end of the first two current sources is connected to the power supply, and the other ends are connected to the drain of the first two N-type transistors and the output stages VOP and VON of the amplifier circuit module, respectively. The output stage of the amplifier circuit module is connected to the input port of the common-mode feedback circuit, used to detect the common-mode voltage and adjust the common-mode adjustment transistor simultaneously.

[0023] The common-mode detection circuit includes a third N-type transistor, a fourth N-type transistor, a fifth N-type transistor, and a tail current source I4. The gates of the third and fourth N-type transistors are connected to the output ports VON and VOP of the amplifier module, respectively. Their drains are connected to a power supply of 1.8V. Their sources are connected to one end of the tail current source, and the network is named VCM, SENSE. The other end of the tail current source is connected to ground. The third and fourth N-type transistors and the tail current source I4 form a source follower to perform common-mode detection on the output of the amplifier module. CM，SENSE It is connected to the gate of the fifth transistor, which is a common-mode regulator that can adjust the common-mode voltage of the amplifier module.

[0024] The substrate adjustment module is the core innovation of this embodiment. Its specific implementation includes fifth, sixth, seventh, eighth, ninth, and tenth-N type transistors and an amplifier. The negative feedback circuit formed by the fifth, sixth, seventh, eighth, ninth, and tenth-N type transistors and the amplifier is used to generate the body bias voltage required at the common-mode adjustment transistor's body terminal. The gate of the tenth transistor is connected to the input port V... CM Connection, V CM The voltage provided to the external reference source is used to control the common-mode output of the amplifier module. The drain of the tenth transistor and one end of the fifth current source are connected to the power supply, which is 1.8V. The source of the tenth transistor is simultaneously connected to the positive port of the first amplifier and the drain of the seventh N-type transistor. The other end of the fifth current source is simultaneously connected to the negative port of the first amplifier, the drain of the sixth N-type transistor, and the gates of the eighth and ninth N-type transistors. The gates of the sixth and seventh N-type transistors are connected to the input common-mode voltage V. CM,INThis voltage is generated by an external circuit and is also the common-mode voltage at the amplifier's input port. The sources of the 6th and 7th N-type transistors are connected to the drains of the 8th and 9th N-type transistors, respectively. The sources of the 8th and 9th N-type transistors are connected to ground, while their bodies are connected to the output stage V of the first amplifier. SUB .

[0025] like Figure 2 The results are simulation results of the common-mode feedback circuit stability. As can be seen from the figure, the phase margin of the circuit reaches 65 degrees at a unity-gain bandwidth of 430MHz. At a power supply voltage of 1.8V, the back gate bias voltage can reduce the threshold voltage of the regulating transistor by 150mV to 300mV. This allows the transistor size to be reduced by 50% and the parasitic capacitance to be reduced by 100% while maintaining the same transconductance. The loop bandwidth is more than twice that of the traditional solution.

Claims

1. A high-stability common-mode feedback circuit, characterized in that, Includes an amplifier circuit module, a common-mode detection module, and a substrate conditioning module; The amplifier circuit module generates a differential output signal based on the input signal; The common-mode detection module detects the common-mode level of the differential output signal of the amplifier circuit module in real time and transmits the detection result to the common-mode adjustment transistor. The substrate adjustment module generates a body voltage through a negative feedback network and sends the body voltage to the substrate end of the common-mode adjustment transistor. The common-mode regulator adjusts the threshold voltage based on the body voltage, thereby enhancing the conduction capability by lowering the threshold voltage.

2. The high-stability common-mode feedback circuit according to claim 1, characterized in that, The amplifier circuit module includes a first current source, a second current source, a third current source, a first MOSFET, and a second MOSFET. The input terminal of the first current source is connected to a power supply, and its output terminal is connected to the drain of the first MOSFET. The input terminal of the second current source is connected to a power supply, and its output terminal is connected to the drain of the second MOSFET. The first MOSFET and the second MOSFET are an input pair. The gate of the first MOSFET is the first input port of the amplifier circuit module, connected to the positive terminal of the differential input signal. The gate of the second MOSFET is the second input port of the amplifier circuit module, connected to the negative terminal of the differential input signal. The connection point between the first MOSFET and the first current source is the first output port of the amplifier circuit module, and the connection point between the second MOSFET and the second current source is the second output port of the amplifier circuit module. The sources of the first MOSFET and the second MOSFET are connected together to the input terminal of the third current source, and the output terminal of the third current source is grounded. The common-mode detection module includes a third MOSFET, a fourth MOSFET, a fifth MOSFET, and a fourth current source. The drain of the third MOSFET is connected to a power supply, and its gate is connected to the first output terminal of the amplifier circuit module. The drain of the fourth MOSFET is connected to a power supply, and its gate is connected to the second output terminal of the amplifier circuit module. The sources of the third and fourth MOSFETs are connected to the input terminal of the fourth current source and the gate of the fifth MOSFET. The third, fourth, and fourth current sources constitute a source follower. The fifth MOSFET is a common-mode adjustment transistor, and its drain is connected to the sources of the first and second MOSFETs. The source of the fifth MOSFET and the output terminal of the fourth current source are grounded. The substrate conditioning module includes a fifth current source, a sixth MOSFET, a seventh MOSFET, an eighth MOSFET, a ninth MOSFET, a tenth MOSFET, and an amplifier; wherein, the input terminal of the fifth current source is connected to a power supply, and the output terminal is connected to the drain of the sixth MOSFET, the gate of the eighth MOSFET, the gate of the ninth MOSFET, and the negative input terminal of the amplifier; the gate of the sixth MOSFET is connected to the input common-mode voltage V. CM,IN V CM,IN The common-mode voltage value of the positive and negative terminals of the differential signal is connected to the source of the eighth MOSFET, and the source of the eighth MOSFET is grounded; the gate of the seventh MOSFET is connected to the common-mode output voltage V. CM,IN Its drain is connected to the source of the tenth MOSFET and the positive input terminal of the amplifier; the source of the seventh MOSFET is connected to the drain of the ninth MOSFET, and the source of the ninth MOSFET is grounded; the drain of the tenth MOSFET is connected to the power supply, and its gate is connected to the external reference voltage V. CM V CM The output voltage V of the source of the tenth MOSFET is provided externally. REF It is V CM The voltage value after level shifting, i.e., V CM With V REF There exists a fixed voltage difference, and then V REF The amplifier and amplification circuit form a feedback structure to control the substrate voltage and adjust the common-mode voltage at the positive and negative terminals of the differential signal; the output terminal of the amplifier is connected to the substrate of the eighth MOS transistor, the substrate of the ninth MOS transistor, and the substrate of the fifth MOS transistor.

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