Transconductance unit and fourth-order Gm-C filter

Abstract

The invention discloses a transconductance unit and a fourth-order Gm-C filter. The transconductance unit comprises a differential input pair transistor, a current source module and a negative feedback module. Grid electrodes of the differential input geminate transistors are used for inputting differential signals, drain electrodes of the differential input geminate transistors are connected with a first power supply end and a control end of the negative feedback module, an input end of the negative feedback module is connected with the first power supply end, an output end of the negative feedback module is connected with a control end of the current source module, and an input end of the current source module is connected with a second power supply end; the output end of the current source module is connected with the source electrode of the differential input geminate transistor; the negative feedback module is used for forming a feedback signal according to the drain potential of the differential input geminate transistors and outputting the feedback signal to the control end of the current source module, and the current source module is used for adjusting the source potential of the differential input geminate transistors according to the feedback signal. The linearity of the differential input pair transistors can be improved, so that the linearity of the transconductance unit can be improved, and meanwhile, the noise performance of the transconductance unit can be improved.

Description

Technical Field

[0001] The embodiments of the present invention relate to the technical field of analog circuits, and in particular, to a transconductance unit and a fourth-order Gm-C filter. Background Art

[0002] The transconductance (Gm) unit and the Gm-C filter are common analog circuit structures, which are widely used in electronic circuit fields such as wearable devices, analog front-end circuits, and continuous-time modulators. The Gm unit is generally used to convert the input analog voltage signal into a current signal. The output end of the Gm unit is connected to a capacitor, which can integrate the current signal generated by the Gm unit on the capacitor, thereby achieving the filtering effect. When the Gm unit forms a Gm-C filter, the Gm-C filter belongs to an open-loop structure filter, which has great advantages in the fields of high bandwidth or low power consumption. However, the disadvantage of the open-loop structure filter is that the linearity is poor, which greatly limits the application of the Gm-C filter in the fields of high linearity and high precision. Summary of the Invention

[0003] The present invention provides a transconductance unit and a fourth-order Gm-C filter to improve the linearity of the transconductance unit, thereby improving the linearity of the fourth-order Gm-C filter.

[0004] In a first aspect, an embodiment of the present invention provides a transconductance unit, including a differential input pair transistor, a current source module, and a negative feedback module;

[0005] The gate of the differential input pair transistor is used to input a differential signal. The drain of the differential input pair transistor is connected to the first power supply terminal and the control terminal of the negative feedback module. The input terminal of the negative feedback module is connected to the first power supply terminal. The output terminal of the negative feedback module is connected to the control terminal of the current source module. The input terminal of the current source module is connected to the second power supply terminal. The output terminal of the current source module is connected to the source of the differential input pair transistor. The negative feedback module is used to form a feedback signal according to the drain potential of the differential input pair transistor and output it to the control terminal of the current source module. The current source module is used to adjust the source potential of the differential input pair transistor according to the feedback signal.

[0006] Optionally, the negative feedback module includes a negative feedback transistor. The gate of the negative feedback transistor is connected to the drain of the differential input pair transistor. The source of the negative feedback transistor is connected to the control terminal of the current source module. The drain of the negative feedback transistor is connected to the first power supply terminal.

[0007] Optionally, the transconductance unit further includes a first voltage-dividing transistor. The gate and source of the first voltage-dividing transistor are connected to the first power supply terminal. The drain of the first voltage-dividing transistor is connected to the drain of the negative feedback transistor.

[0008] Optionally, the gate thickness of the first voltage-dividing transistor is greater than the gate thickness of the negative feedback transistor.

[0009] Optionally, the transconductance unit further includes a first current transistor; the gate of the first current transistor is used to input a first control signal, the drain of the first current transistor is connected to the source of the negative feedback transistor, and the source of the first current transistor is connected to the second power supply terminal.

[0010] Optionally, the transconductance unit further includes at least one load transistor; the source of the first load transistor is connected to the first power supply terminal, the drain of the first load transistor is connected to the source of the next load transistor, the drain of the last load transistor is connected to the drain of the differential input pair transistor, and the gate of the load transistor is used to input a second control signal.

[0011] Optionally, the transconductance unit further includes an amplification module, the control terminal of the amplification module is connected to the output terminal of the negative feedback module, the first input terminal of the amplification module is connected to the first power supply terminal, the second input terminal of the amplification module is connected to the second power supply terminal, the output terminal of the amplification module serves as the output terminal of the transconductance unit, and the amplification module is used to amplify the feedback signal.

[0012] Optionally, the amplification module includes a first transistor, a second transistor, a third transistor, and a fourth transistor;

[0013] The source of the first transistor is connected to the first power supply terminal, the drain of the first transistor is connected to the source of the second transistor, the gate of the first transistor is used to input a third control signal, the drain of the second transistor is connected to the drain of the third transistor and serves as the output terminal of the amplification module, the gate of the second transistor is used to input a fourth control signal, the source of the third transistor is connected to the drain of the fourth transistor, the gate of the third transistor is used to input a fifth control signal; the source of the fourth transistor is connected to the second power supply terminal, and the gate of the fourth transistor is connected to the output terminal of the negative feedback module.

[0014] Optionally, the gate thickness of the second transistor is greater than the gate thickness of the first transistor, and the gate thickness of the third transistor is greater than the gate thickness of the fourth transistor.

[0015] In a second aspect, an embodiment of the present invention further provides a fourth-order Gm-C filter, which is characterized by including a first transconductance unit, a second transconductance unit, a third transconductance unit, a fourth transconductance unit, a first capacitor, a second capacitor, a third capacitor, and a fourth capacitor;

[0016] The first transconductance unit, the second transconductance unit, the third transconductance unit, and the fourth transconductance unit are the transconductance units described in the first aspect;

[0017] The positive input terminal of the first transconductance unit serves as the input terminal of the fourth-order Gm-C filter. The output terminal of the first transconductance unit is connected to the positive input terminal of the second transconductance unit, the first pole of the first capacitor, and the output terminal of the fourth transconductance unit. The output terminal of the second transconductance unit is connected to the positive input terminal of the third transconductance unit, the first pole of the second capacitor, and the output terminal of the fourth transconductance unit. The output terminal of the third transconductance unit is connected to the positive input terminal of the fourth transconductance unit, the output terminal of the fourth transconductance unit, the first pole of the third capacitor, and the negative input terminal of the second transconductance unit. The output terminal of the fourth transconductance unit is connected to the first pole of the fourth capacitor and serves as the output terminal of the fourth-order Gm-C filter. The second poles of the first capacitor, the second capacitor, the third capacitor, and the fourth capacitor are grounded.

[0018] In the technical solution of the embodiment of the present invention, by setting a negative feedback module to feedback the change trend of the drain potential of the differential input pair transistor to the control terminal of the current source module, the current source module controls the source potential of the differential input pair transistor according to the voltage feedback by the negative feedback module, so that the change trend of the source potential of the differential input pair transistor is opposite to the change trend of the drain potential, thereby enabling the change trend of the gate potential of the differential input pair transistor to be the same as the change trend of the source potential, improving the linearity of the differential input pair transistor, thereby improving the linearity of the transconductance unit, and at the same time improving the noise performance of the transconductance unit. Description of the Drawings

[0019] Figure 1 It is a schematic structural diagram of a transconductance unit provided by an embodiment of the present invention;

[0020] Figure 2 It is a schematic structural diagram of another transconductance unit provided by an embodiment of the present invention;

[0021] Figure 3 It is a schematic structural diagram of another transconductance unit provided by an embodiment of the present invention;

[0022] Figure 4 It is a schematic structural diagram of a common-mode feedback module provided by an embodiment of the present invention;

[0023] Figure 5 It is a schematic structural diagram of a fourth-order Gm-C filter provided by an embodiment of the present invention. Detailed Embodiments

[0024] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It can be understood that the specific embodiments described herein are only for explaining the present invention, rather than limiting the present invention. Additionally, it should be noted that for the sake of description, only the parts related to the present invention rather than all the structures are shown in the drawings.

[0025] Figure 1 It is a schematic structural diagram of a transconductance unit provided by an embodiment of the present invention. As Figure 1 shown, the transconductance unit includes a differential input pair of transistors M1, a current source module 110, and a negative feedback module 120; the gates of the differential input pair of transistors M1 are used to input differential signals, the drains of the differential input pair of transistors M1 are connected to the first power supply terminal VDD and the control terminal of the negative feedback module 120, the input terminal of the negative feedback module 120 is connected to the first power supply terminal VDD, the output terminal of the negative feedback module 120 is connected to the control terminal of the current source module 110, the input terminal of the current source module 110 is connected to the second power supply terminal VSS, and the output terminal of the current source module 110 is connected to the source of the differential input pair of transistors M1; the negative feedback module 120 is used to form a feedback signal according to the drain potential of the differential input pair of transistors M1 and output it to the control terminal of the current source module 110, and the current source module 110 is used to adjust the source potential of the differential input pair of transistors M1 according to the feedback signal.

[0026] Specifically, the differential signal includes a first differential signal INP and a second differential signal INN. As Figure 1 shown, the differential input pair of transistors M1 includes an N-type first differential input pair of transistors M1a and a second differential input pair of transistors M1b. The gate of the first differential input pair of transistors M1a serves as the first input terminal of the transconductance unit and is used to input the first differential signal INP, and the gate of the second differential input pair of transistors M1b serves as the second input terminal of the transconductance unit and is used to input the second differential signal INN. The drains of the first differential input pair of transistors M1a and the second differential input pair of transistors M1b can be connected to the first power supply terminal VDD through an impedance, and at the same time, the sources of the first differential input pair of transistors M1a and the second differential input pair of transistors M1b are connected to the second power supply terminal VSS through the current source module 110, so that the current source module 110 can provide current for the differential input pair of transistors M1. At this time, the differential input pair of transistors M1 is in a common-source connection mode. When the differential input signal increases, the drain potential of the differential input pair of transistors M1 decreases. Exemplarily, as Figure 1As shown, when the voltage of the first differential signal INP rises, the gate potential of the first differential input pair transistor M1a increases, causing the drain potential of the first differential input pair transistor M1a to decrease. At this time, the negative feedback module 120 includes a first negative feedback unit 121 and a second negative feedback unit 122. The current source module 110 may include a pair of symmetrically connected transistors, namely a first N-type transistor M2a and a second N-type transistor M2b. The control terminal of the first negative feedback unit 121 is connected to the drain of the first differential input pair transistor M1a. The input terminal of the first negative feedback unit 121 is connected to the first power supply terminal VDD through an impedance. The output terminal of the first negative feedback unit 121 is connected to the gate of the first N-type transistor M2a. The control terminal of the second negative feedback unit 122 is connected to the drain of the second differential input pair transistor M1b. The input terminal of the second negative feedback unit 122 is connected to the first power supply terminal VDD through an impedance. The output terminal of the second negative feedback unit 122 is connected to the gate of the second N-type transistor M2b. The sources of the first N-type transistor M2a and the second N-type transistor M2b are both connected to the second power supply terminal VSS. The drain of the first N-type transistor M2a is connected to the source of the first differential input pair transistor M1a. The drain of the second N-type transistor M2b is connected to the source of the second differential input pair transistor M1b. At this time, the first N-type transistor M2a and the second N-type transistor M2b are also in a common-source connection mode. When the gate potentials of the first N-type transistor M2a and the second N-type transistor M2b decrease, the drain potentials of the first N-type transistor M2a and the second N-type transistor M2b increase. When the drain potential of the differential input pair transistor M1 decreases, the negative feedback module 120 can feedback the change trend of the drain potential of the differential input pair transistor M1 to the control terminal of the current source module 110, causing the potential of the control terminal of the current source module 110 to decrease. The change trend of the output terminal potential of the current source module 110 is anti-correlated with the change trend of the control terminal potential of the current source module 110. At this time, the output terminal potential of the current source module 110 rises, that is, the source potential of the differential input pair transistor M1 rises, so that the change trend of the gate potential of the differential input pair transistor M1 is the same as the change trend of the source potential, improving the linearity of the differential input pair transistor M1, and thus improving the linearity of the transconductance unit.

[0027] Exemplarily, such as Figure 1As shown, when the voltage of the first differential signal INP rises, the gate potential of the first differential input pair transistor M1a increases, causing the drain potential of the first differential input pair transistor M1a to decrease. At this time, the first negative feedback unit 121 feeds back the change trend of the drain potential of the first differential input pair transistor M1a to the gate of the first N-type transistor M2a, that is, the gate potential of the first N-type transistor M2a decreases, causing the drain potential of the first N-type transistor M2a to increase, that is, the source potential of the first differential input pair transistor M1a increases. At this time, the change trends of the gate potential and the source potential of the first differential input pair transistor M1a are the same, improving the linearity of the differential input pair transistor M1, and thus the linearity of the transconductance unit can be improved.

[0028] Continue to refer to Figure 1 , the transconductance unit further includes a first resistor R1, and the first resistor R1 is connected between the source of the first differential input pair transistor M1a and the source of the second differential input pair transistor M1b. When the linearity of the differential input pair transistor M1 is improved, the resistance value requirement for the first resistor R1 can be reduced, improving the noise performance of the transconductance unit.

[0029] Continue to refer to Figure 1 , the differential input pair transistor M1, the first N-type transistor M2a, and the second N-type transistor M2b are all thin gate transistors to ensure the dynamic performance of the differential input pair transistor M1 and the current source module 110.

[0030] The technical solution of this embodiment feeds back the change trend of the drain potential of the differential input pair transistor to the control end of the current source module through the setting of the negative feedback module, and the current source module controls the source potential of the differential input pair transistor according to the voltage fed back by the negative feedback module, so that the change trend of the source potential of the differential input pair transistor is opposite to the change trend of the drain potential, so that the change trend of the gate potential of the differential input pair transistor can be the same as the change trend of the source potential, improving the linearity of the differential input pair transistor, and thus the linearity of the transconductance unit can be improved, and at the same time the noise performance of the transconductance unit can be improved.

[0031] Figure 2 It is a schematic structural diagram of another transconductance unit provided by an embodiment of the present invention. As Figure 2 shown, the negative feedback module 120 includes a negative feedback transistor M3. The gate of the negative feedback transistor M3 is connected to the drain of the differential input pair transistor M1, the source of the negative feedback transistor M3 is connected to the control end of the current source module 110, and the drain of the negative feedback transistor M3 is connected to the first power supply terminal VDD.

[0032] Specifically, as Figure 2As shown, the negative feedback transistor M3 may include a first negative feedback transistor M3a and a second negative feedback transistor M3b. The gate of the first negative feedback transistor M3a is connected to the drain of the first differential input pair transistor M1a. The source of the first negative feedback transistor M3a is connected to the gate of the first N-type transistor M2a. The drain of the first negative feedback transistor M3a is connected to the first power supply terminal VDD through an impedance. The gate of the second negative feedback transistor M3b is connected to the drain of the second differential input pair transistor M1b. The source of the second negative feedback transistor M3b is connected to the gate of the second N-type transistor M2b. The drain of the second negative feedback transistor M3b is connected to the first power supply terminal VDD through an impedance. At this time, the first negative feedback transistor M3a and the second negative feedback transistor M3b are connected in common drain. The changing trends of the gate potential and the source potential of the first negative feedback transistor M3a and the second negative feedback transistor M3b are the same. Thus, when the differential signal increases and the drain potential of the differential input pair transistor M1 decreases, the source potential of the negative feedback transistor M3 decreases, causing the potential of the control terminal of the current source module 110 to decrease, and further causing the potential of the output terminal of the current source module 110 to increase, that is, the source potential of the differential input pair transistor M1 increases, making the changing trend of the gate potential of the differential input pair transistor M1 the same as that of the source potential, thereby improving the linearity of the differential input pair transistor M1. Exemplarily, when the potential of the differential signal increases, the drain potential of the first differential input pair transistor M1a decreases, that is, the gate potential of the first negative feedback transistor M3a decreases, causing the source potential of the first negative feedback transistor M3a to decrease, that is, the gate potential of the first N-type transistor M2a decreases, and further causing the drain potential of the first N-type transistor M2a to increase, that is, the source potential of the first differential input pair transistor M1a increases, making the changing trend of the gate potential of the differential input pair transistor M1 the same as that of the source potential, thereby improving the linearity of the differential input pair transistor M1. Exemplarily, the negative feedback transistor M3 is a thin gate transistor to ensure the dynamic performance of the negative feedback transistor M3.

[0033] Continuing to refer to Figure 2 , the transconductance unit further includes a first voltage dividing transistor M4. The gate and the source of the first voltage dividing transistor M4 are connected to the first power supply terminal VDD. The drain of the first voltage dividing transistor M4 is connected to the drain of the negative feedback transistor M3.

[0034] Specifically, the first voltage-dividing transistor M4 is connected between the negative feedback transistor M3 and the first power supply terminal VDD. By dividing the voltage between the first power supply terminal VDD and the second power supply terminal VSS through the first voltage-dividing transistor M4, when the voltage provided by the first power supply terminal VDD is relatively large, damage to the negative feedback transistor M3 can be avoided, the reliability of the transconductance unit is improved, and at the same time, the voltage swing that the transconductance unit can withstand is increased, further improving the linearity of the transconductance unit. Exemplarily, the first voltage-dividing transistor M4 includes a first voltage-dividing transistor M4a and a second voltage-dividing transistor M4b. The gate and source of the first voltage-dividing transistor M4a are connected to the first power supply terminal VDD, and the drain of the first voltage-dividing transistor M4a is connected to the drain of the first negative feedback transistor M3a. The gate and source of the second voltage-dividing transistor M4b are connected to the first power supply terminal VDD, and the drain of the second voltage-dividing transistor M4b is connected to the drain of the second negative feedback transistor M3b. At this time, the first voltage-dividing transistor M4a is used to protect the first negative feedback transistor M3a, and the second voltage-dividing transistor M4b is used to protect the second negative feedback transistor M3b.

[0035] Continue to refer to Figure 2 , the gate thickness of the first voltage-dividing transistor M4 is greater than the gate thickness of the negative feedback transistor M3.

[0036] Specifically, the first voltage-dividing transistor M4 can be a thick-gate transistor, so that the first voltage-dividing transistor M4 has better high-voltage resistance performance, thereby better protecting the negative feedback transistor M3 and preventing the negative feedback transistor M3 from being broken down. At the same time, the voltage swing that the transconductance unit can withstand can be increased. Exemplarily, the first voltage provided by the first power supply terminal VDD can be 1.8V.

[0037] Continue to refer to Figure 2 , the transconductance unit further includes a first current transistor M5; the gate of the first current transistor M5 is used to input a first control signal Vb1, the drain of the first current transistor M5 is connected to the source of the negative feedback transistor M3, and the source of the first current transistor M5 is connected to the second power supply terminal VSS.

[0038] Specifically, the first current transistor M5 is connected between the negative feedback transistor M3 and the second power supply terminal VSS, and can provide a bias current for the negative feedback transistor M3 so that the negative feedback transistor M3 can operate normally. Exemplarily, such as Figure 2As shown, the first current transistor M5 includes a first sub-current transistor M5a and a second sub-current transistor M5b. The sources of the first sub-current transistor M5a and the second sub-current transistor M5b are connected to the second power supply terminal VSS. The drain of the first sub-current transistor M5a is connected to the source of the first negative feedback transistor M3a, and the drain of the second sub-current transistor M5b is connected to the source of the second negative feedback transistor M3b. The gates of the first sub-current transistor M5a and the second sub-current transistor M5b are used to input the first control signal Vb1. When the first control signal Vb1 is at a high level, the first sub-current transistor M5a and the second sub-current transistor M5b respectively provide bias currents for the first negative feedback transistor M3a and the second negative feedback transistor M3b, enabling the first negative feedback transistor M3a and the second negative feedback transistor M3b to operate normally.

[0039] Continuing to refer to Figure 2 , the transconductance unit further includes at least one load transistor; the source of the first load transistor is connected to the first power supply terminal VDD, the drain of the first load transistor is connected to the source of the next load transistor, and the drain of the last load transistor is connected to the drain of the differential input pair transistor M1. The gate of the load transistor is used to input the second control signal Vb2.

[0040] Specifically, Figure 2 exemplarily shows that the transconductance unit includes two load transistors, namely the first load transistor M6 and the second load transistor M7. At this time, the second control signal Vb2 includes a first sub-control signal Vb21 and a second sub-control signal Vb22. The first load transistor M6 includes a first sub-load transistor M6a and a second sub-load transistor M6b, and the second load transistor M7 includes a third sub-load transistor M7a and a fourth sub-load transistor M7b. The sources of the first sub-load transistor M6a and the second sub-load transistor M6b are connected to the first power supply terminal VDD. The gates of the first sub-load transistor M6a and the second sub-load transistor M6b are used to input the first sub-control signal Vb21. The drain of the first sub-load transistor M6a is connected to the source of the third sub-load transistor M7a, and the drain of the second sub-load transistor M6b is connected to the source of the fourth sub-load transistor M7b. The drain of the third sub-load transistor M7a is connected to the drain of the first differential input pair transistor M1a, and the drain of the fourth sub-load transistor M7b is connected to the drain of the second differential input pair transistor M1b. The gates of the third sub-load transistor M7a and the fourth sub-load transistor M7b are used to input the second sub-control signal Vb22. After the differential input pair transistor M1 converts the input differential voltage signal into a current signal, a voltage can be formed through the load transistor as the drain potential of the differential input pair transistor M1 to drive the negative feedback transistor M3.

[0041] Figure 3 This is a schematic structural diagram of another transconductance unit provided by an embodiment of the present invention. As Figure 3 shown, the transconductance unit further includes an amplification module 130. The control end of the amplification module 130 is connected to the output end of the negative feedback module 120. The first input end of the amplification module 130 is connected to the first power supply terminal VDD, the second input end of the amplification module 130 is connected to the second power supply terminal VSS, and the output end of the amplification module 130 serves as the output end of the transconductance unit. The amplification module 130 is used to amplify the feedback signal.

[0042] Specifically, the control end of the amplification module 130 is connected to the output end of the negative feedback module 120, so that the amplification module 130 can serve as the output stage of the transconductance unit. After the negative feedback module 120 feeds back the drain potential of the differential input pair transistor M1 to the control end of the amplification module 130, the amplification module 130 can amplify the drain potential of the differential input pair transistor M1, thereby further improving the voltage gain of the transconductance unit, and further suppressing the non-ideal factors of the subsequent stage and improving the linearity of the transconductance unit. Exemplarily, the non-ideal factors of the subsequent stage include noise and nonlinearity generated by the subsequent stage. Exemplarily, the negative feedback module 120 includes a first negative feedback unit 121 and a second negative feedback unit 122, and the amplification module 130 includes a first amplification unit 131 and a second amplification unit 132. The control end of the first amplification unit 131 is connected to the output end of the first negative feedback unit 121, the control end of the second amplification unit 132 is connected to the output end of the second negative feedback unit 122, the first input ends of the first amplification unit 131 and the second amplification unit 132 are connected to the first power supply terminal VDD, and the second input ends of the first amplification unit 131 and the second amplification unit 132 are connected to the second power supply terminal VSS, so that the first amplification unit 131 amplifies the feedback signal provided by the first negative feedback unit 121, and the second amplification unit 132 amplifies the feedback signal provided by the second negative feedback unit 122, enabling the amplification module 130 to amplify the differential signal output by the differential input pair transistor M1 simultaneously.

[0043] Continue to refer to Figure 3, the amplification module 130 includes a first transistor M8, a second transistor M9, a third transistor M10, and a fourth transistor M11; the source of the first transistor M8 is connected to the first power supply terminal VDD, the drain of the first transistor M8 is connected to the source of the second transistor M9, the gate of the first transistor M8 is used to input a third control signal Vb3, the drain of the second transistor M9 is connected to the drain of the third transistor M10 and serves as the output terminal of the amplification module 130, the gate of the second transistor M9 is used to input a fourth control signal Vb4, the source of the third transistor M10 is connected to the drain of the fourth transistor M11, and the gate of the third transistor M10 is used to input a fifth control signal Vb5; the source of the fourth transistor M11 is connected to the second power supply terminal VSS, and the gate of the fourth transistor M11 is connected to the output terminal of the negative feedback module 120.

[0044] Specifically, Figure 3 exemplarily shows that the first transistor M8, the second transistor M9, the third transistor M10, and the fourth transistor M11 each include two transistors, represented by a and b respectively. The gate of the fourth transistor M11 is connected to the output terminal of the negative feedback module 120, that is, the gate of one fourth transistor M11a is connected to the gate of the first N-type transistor M2a, and the gate of the other fourth transistor M11b is connected to the gate of the second N-type transistor M2b. At this time, the fourth transistor M11 and the N-type transistor M2 form a current mirror, and the fourth transistor M11 can mirror the output current of the negative feedback module 120 to the drain of the fourth transistor M11. The third transistor M10 converts the output current into a voltage signal. At the same time, the first transistor M8 and the second transistor M9 form a cascode amplification structure to perform two-stage amplification on the voltage signal, thereby increasing the gain of the transconductance unit, further suppressing the non-ideal factors of the subsequent stage, and improving the linearity of the transconductance unit. At this time, the drain of one second transistor M9a serves as the output terminal OUTP of the first amplification unit 131, and the drain of the other second transistor M9b serves as the output terminal OUTN of the second amplification unit 132.

[0045] Continuing to refer to Figure 3 , the gate thickness of the second transistor M9 is greater than the gate thickness of the first transistor M8, and the gate thickness of the third transistor M10 is greater than the gate thickness of the fourth transistor M11.

[0046] Specifically, as Figure 3 shown, the first transistor M8 and the fourth transistor M11 can be thin-gate transistors to ensure the performance of the amplification module 130. The second transistor M9 and the third transistor M10 can be thick-gate transistors, which can prevent the first transistor M8 and the fourth transistor M11 from being broken down when the voltage provided by the first power supply terminal VDD is relatively large, and can improve the reliability of the transconductance unit.

[0047] In some embodiments, the transconductance unit further includes a common-mode feedback module. Figure 4 FIG. is a schematic structural diagram of a common-mode feedback module provided by an embodiment of the present invention. As Figure 4 shown, the common-mode feedback module includes a fifth transistor M12, a sixth transistor M13, a seventh transistor M14, an eighth transistor M15, and a ninth transistor M16. The gate of the fifth transistor M12 is connected to the output terminal OUTP of the first amplification unit 131, and the gate of the sixth transistor M13 is connected to the output terminal OUTN of the second amplification unit 132. The drain of the fifth transistor M12 is connected to the gate and drain of the eighth transistor M15. The source of the eighth transistor M15 and the source of the ninth transistor M16 are connected to the third power supply terminal AVDD. The gate of the ninth transistor M16 is connected to the gate of the eighth transistor M15, and the drain of the sixth transistor M13 is connected to the drain of the ninth transistor M16 and serves as the output terminal OUT of the common-mode feedback module, which is connected to the gate of the load transistor for adjusting the second control signal Vb2. The source of the fifth transistor M12 and the source of the sixth transistor M13 are connected to the drain of the seventh transistor M14. The gate of the seventh transistor M14 is connected to the control signal terminal VB, and the source of the seventh transistor M14 is connected to the fourth power supply terminal AVSS. The seventh transistor M14 can provide a bias current for the source of the fifth transistor M12 and the source of the sixth transistor M13. The eighth transistor M15 and the ninth transistor M16 form a current mirror, so that the currents of the fifth transistor M12 and the sixth transistor M13 are equal. During the operation of the common-mode feedback module, the fifth transistor M12 and the sixth transistor M13 can extract the common-mode voltage from the signals output by the amplification module 130, compare and amplify it, and then output it to the gate of the load transistor to control the bias voltage provided by the load transistor for the differential input pair transistor M1, thereby stabilizing the common-mode voltage output by the transconductance unit. Exemplarily, referring to Figure 3 and Figure 4 , the output terminal OUT of the common-mode feedback module can be connected to the gate of the first load transistor M6 to control the bias voltage provided by the first load transistor M6 for the differential input pair transistor M1.

[0048] The embodiment of the present invention also provides a fourth-order Gm-C filter. Figure 5 FIG. is a schematic structural diagram of a fourth-order Gm-C filter provided by an embodiment of the present invention. As Figure 5As shown in the figure, the fourth-order Gm-C filter includes a first transconductance unit 101, a second transconductance unit 102, a third transconductance unit 103, a fourth transconductance unit 104, a first capacitor C1, a second capacitor C2, a third capacitor C3, and a fourth capacitor C4; the first transconductance unit 101, the second transconductance unit 102, the third transconductance unit 103, and the fourth transconductance unit 104 are transconductance units provided by any embodiment of the present invention; the positive input terminal 1+ of the first transconductance unit 101 serves as the input terminal INPUT of the fourth-order Gm-C filter, and the output terminal of the first transconductance unit 101 is connected to the positive input terminal 2+ of the second transconductance unit 102, the first pole of the first capacitor C1, and the output terminal of the fourth transconductance unit 104. The output terminal of the second transconductance unit 102 is connected to the positive input terminal 3+ of the third transconductance unit 103, the first pole of the second capacitor C2, and the output terminal of the fourth transconductance unit 104. The output terminal of the third transconductance unit 103 is connected to the positive input terminal 4+ of the fourth transconductance unit 104, the output terminal of the fourth transconductance unit 104, the first pole of the third capacitor C3, and the negative input terminal 2- of the second transconductance unit 102. The output terminal of the fourth transconductance unit 104 is connected to the first pole of the fourth capacitor C4 and serves as the output terminal OUTPUT of the fourth-order Gm-C filter; the second poles of the first capacitor C1, the second capacitor C2, the third capacitor C3, and the fourth capacitor C4 are grounded to GND.

[0049] Specifically, the first transconductance unit 101, the second transconductance unit 102, the third transconductance unit 103, and the fourth transconductance unit 104 are transconductance units provided by any embodiment of the present invention, and thus have the same beneficial effects as the transconductance units provided by any embodiment of the present invention, which will not be elaborated here.

[0050] In addition, the signal input at the input terminal INPUT of the fourth-order Gm-C filter can be a differential signal. The output terminals of the first transconductance unit 101, the second transconductance unit 102, and the third transconductance unit 103 are all directly connected to the output terminal OUTPUT of the fourth-order Gm-C filter, so that the first transconductance unit 101, the second transconductance unit 102, and the third transconductance unit 103 form a feedforward structure, which can reduce the signal components in the main branches of the first transconductance unit 101 to the fourth transconductance unit 104, and further improve the linearity of the fourth-order Gm-C filter. Moreover, the feedforward structure of the first transconductance unit 101, the second transconductance unit 102, and the third transconductance unit 103 can form multiple zeros in the fourth-order Gm-C filter. The output terminal of the third transconductance unit 103 is connected to the negative input terminal 2- of the second transconductance unit 102, so that the differential signal output by the third transconductance unit 103 is fed back to the second transconductance unit 102, which can form a pole in the fourth-order Gm-C filter. Thus, the transfer function of the fourth-order Gm-C filter can be adjusted by adjusting the zeros and poles of the fourth-order Gm-C filter, and the filtering effect of the fourth-order Gm-C filter can be improved.

[0051] Note that the above are only the preferred embodiments of the present invention and the technical principles applied. Those skilled in the art will understand that the present invention is not limited to the specific embodiments described herein. Various obvious changes, re-adjustments, and substitutions can be made by those skilled in the art without departing from the protection scope of the present invention. Therefore, although the present invention has been described in detail through the above embodiments, the present invention is not limited to the above embodiments only. Without departing from the concept of the present invention, more other equivalent embodiments can be included, and the scope of the present invention is determined by the scope of the appended claims.

Claims

1. A transconductance unit, characterized in that: It includes a differential input pair tube, a current source module and a negative feedback module; The gate of the differential input pair of tubes is used to input a differential signal, the drain of the differential input pair of tubes is connected to the first power supply terminal and the control terminal of the negative feedback module, the input terminal of the negative feedback module is connected to the first power supply terminal, the output terminal of the negative feedback module is connected to the control terminal of the current source module, the input terminal of the current source module is connected to the second power supply terminal, and the output terminal of the current source module is connected to the source of the differential input pair of tubes; the negative feedback module is used to form a feedback signal according to the drain potential of the differential input pair of tubes, and output it to the control terminal of the current source module, and the current source module is used to adjust the source potential of the differential input pair of tubes according to the feedback signal.

2. The transconductance unit according to claim 1, characterized in that: The negative feedback module includes a negative feedback transistor, the gate of the negative feedback transistor is connected to the drain of the differential input terminal, the source of the negative feedback transistor is connected to the control terminal of the current source module, and the drain of the negative feedback transistor is connected to the first power supply terminal.

3. The transconductance unit according to claim 2, characterized in that: It also includes a first voltage-dividing transistor, wherein the gate and source of the first voltage-dividing transistor are connected to the first power supply terminal, and the drain of the first voltage-dividing transistor is connected to the drain of the negative feedback transistor.

4. The transconductance unit according to claim 3, characterized in that: The gate thickness of the first voltage-dividing transistor is greater than the gate thickness of the negative feedback transistor.

5. The transconductance unit according to claim 2, characterized in that: It also includes a first current transistor; the gate of the first current transistor is used to input a first control signal, the drain of the first current transistor is connected to the source of the negative feedback transistor, and the source of the first current transistor is connected to the second power supply terminal.

6. The transconductance unit according to claim 1, characterized in that: It also includes at least one load transistor; the source of the first load transistor is connected to the first power supply terminal, the drain of the first load transistor is connected to the source of the next load transistor, the drain of the last load transistor is connected to the drain of the differential input pair tube, and the gate of the load transistor is used to input a second control signal.

7. The transconductance unit according to any one of claims 1 to 6, characterized in that: It also includes an amplification module, wherein the control end of the amplification module is connected to the output end of the negative feedback module, the first input end of the amplification module is connected to the first power supply end, the second input end of the amplification module is connected to the second power supply end, the output end of the amplification module serves as the output end of the transconductance unit, and the amplification module is used to amplify the feedback signal.

8. The transconductance unit according to claim 7, characterized in that: The amplification module includes a first transistor, a second transistor, a third transistor and a fourth transistor; The source of the first transistor is connected to the first power supply terminal, the drain of the first transistor is connected to the source of the second transistor, the gate of the first transistor is used to input a third control signal, the drain of the second transistor is connected to the drain of the third transistor and serves as the output terminal of the amplification module, the gate of the second transistor is used to input a fourth control signal, the source of the third transistor is connected to the drain of the fourth transistor, and the gate of the third transistor is used to input a fifth control signal; the source of the fourth transistor is connected to the second power supply terminal, and the gate of the fourth transistor is connected to the output terminal of the negative feedback module.

9. The transconductance unit according to claim 8, characterized in that: The gate thickness of the second transistor is greater than the gate thickness of the first transistor, and the gate thickness of the third transistor is greater than the gate thickness of the fourth transistor.

10. A fourth-order Gm-C filter, characterized in that: It includes a first transconductance unit, a second transconductance unit, a third transconductance unit, a fourth transconductance unit, a first capacitor, a second capacitor, a third capacitor and a fourth capacitor; The first transconductance unit, the second transconductance unit, the third transconductance unit and the fourth transconductance unit are the transconductance units according to any one of claims 1 to 9; The positive input end of the first transconductance unit serves as the input end of the fourth-order Gm-C filter, the output end of the first transconductance unit is connected to the positive input end of the second transconductance unit, the first pole of the first capacitor and the output end of the fourth transconductance unit, the output end of the second transconductance unit is connected to the positive input end of the third transconductance unit, the first pole of the second capacitor and the output end of the fourth transconductance unit, the output end of the third transconductance unit is connected to the positive input end of the fourth transconductance unit, the output end of the fourth transconductance unit, the first pole of the third capacitor and the negative input end of the second transconductance unit, the output end of the fourth transconductance unit is connected to the first pole of the fourth capacitor and serves as the output end of the fourth-order Gm-C filter; the second pole of the first capacitor, the second pole of the second capacitor, the second pole of the third capacitor and the second pole of the fourth capacitor are grounded.

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