An alternating current coupling amplification circuit and a method for amplitude attenuation thereof

Abstract

The application provides an AC coupling amplification circuit and an amplitude attenuation method thereof, which comprises a differential input port, a plurality of gain ratio capacitors, a main loop operational amplifier, a common mode feedback operational amplifier, a DC servo loop operational amplifier, a differential output port and an amplitude attenuation module; the differential input port is connected with the plurality of gain ratio capacitors and then connected with the main loop operational amplifier and the DC servo loop operational amplifier respectively; the main loop operational amplifier is further connected with the common mode feedback operational amplifier and the amplitude attenuation module respectively; the differential output port is connected with the main loop operational amplifier, the common mode feedback operational amplifier and the amplitude attenuation module respectively; the first input end and the second input end of the DC servo loop operational amplifier are connected with the amplitude attenuation module respectively; and the reference signal input end of the DC servo loop operational amplifier is connected with the reference signal input end of the common mode feedback operational amplifier. The application solves the problem of intermodulation under the condition of large signal output.

Description

Technical Field

[0001] This invention belongs to the field of electronic technology, and in particular relates to an AC-coupled amplifier circuit and its amplitude attenuation method. Background Technology

[0002] In low-power, weak signal measurement scenarios, a low-noise, high DC input impedance AC-coupled amplifier within the chip is essential. An AC-coupled amplifier is an electronic circuit that converts a small-amplitude input voltage signal into a large-amplitude, fixed output voltage signal. AC-coupled amplifier circuits can be single-ended or dual-ended (also called differential amplifiers). However, in high-speed electronic circuits, dual-ended differential limiting amplifiers are more common. Besides distortion during signal amplification, when multiple signals of different frequencies are amplified simultaneously, the large output swing can generate new signals. Due to the wide frequency range of signals, i.e., under large signal output conditions, the inherent poor linearity of the AC-coupled amplifier circuit will produce new frequency components, leading to signal intermodulation. These new frequency components are not desired and interfere with the identification of the required signal. Therefore, existing AC-coupled amplifier circuits suffer from intermodulation problems under large signal output conditions. Summary of the Invention

[0003] This invention provides an AC-coupled amplifier circuit designed to solve the intermodulation problem in the prior art under large signal output conditions.

[0004] This invention provides an AC-coupled amplifier circuit, comprising:

[0005] Differential input port, multiple gain ratio capacitors, main loop operational amplifier, common mode feedback operational amplifier, DC servo loop operational amplifier, differential output port, and amplitude attenuation module;

[0006] The differential input port is connected in series with multiple gain ratio capacitors and then connected to the main loop operational amplifier and the DC servo loop operational amplifier through multiple gain ratio capacitors respectively.

[0007] The main loop operational amplifier is also connected to the common-mode feedback operational amplifier and the amplitude attenuation module, respectively.

[0008] The differential output port is connected to the main loop operational amplifier, the common-mode feedback operational amplifier, and the amplitude attenuation module, respectively.

[0009] The first input terminal and the second input terminal of the DC servo loop operational amplifier are respectively connected to the amplitude attenuation module;

[0010] The reference signal input terminal of the DC servo loop operational amplifier is connected to the reference signal input terminal of the common-mode feedback operational amplifier.

[0011] Furthermore, the amplitude attenuation module includes a first resistor, a second resistor, a third resistor, and a fourth resistor;

[0012] The first resistor, the second resistor, the third resistor, and the fourth resistor are connected in series between the common-mode feedback operational amplifier and the DC servo loop operational amplifier.

[0013] The end of the first resistor furthest from the second resistor is connected to the common-mode feedback operational amplifier, the differential output port, and the main loop operational amplifier, respectively.

[0014] The first input terminal of the DC servo loop operational amplifier is connected to the connection line between the first resistor and the second resistor;

[0015] The second input terminal of the DC servo loop operational amplifier is connected to the connection line between the third resistor and the fourth resistor;

[0016] The end of the fourth resistor furthest from the third resistor is connected to the common-mode feedback operational amplifier, the differential output port, and the main loop operational amplifier, respectively.

[0017] or

[0018] The first resistor, the second resistor, the third resistor, and the fourth resistor are connected in series inside the common-mode feedback operational amplifier.

[0019] The end of the first resistor furthest from the second resistor is connected to both the differential output port and the main loop operational amplifier.

[0020] The first input terminal of the DC servo loop operational amplifier is located on the connection line between the first resistor and the second resistor;

[0021] The second input terminal of the DC servo loop operational amplifier is located on the connection line between the third resistor and the fourth resistor;

[0022] The end of the fourth resistor furthest from the third resistor is connected to both the differential output port and the main loop operational amplifier.

[0023] The common-mode signal terminal of the common-mode feedback operational amplifier is connected to the connection line between the second resistor and the third resistor.

[0024] Furthermore, the first resistor and the fourth resistor have the same resistance value, and the second resistor and the third resistor have the same resistance value.

[0025] Furthermore, the differential input port includes a first differential input port and a second differential input port;

[0026] The plurality of gain proportional capacitors include a first gain proportional capacitor, a second gain proportional capacitor, a third gain proportional capacitor, and a fourth gain proportional capacitor.

[0027] The first differential input port is connected to one end of the first gain proportional capacitor, and the other end of the first gain proportional capacitor is connected to one end of the fourth gain proportional capacitor, the main loop operational amplifier, and the DC servo loop operational amplifier, respectively. The other end of the fourth gain proportional capacitor is connected to the main loop operational amplifier.

[0028] The second differential input port is connected to one end of the second gain proportional capacitor, and the other end of the second gain proportional capacitor is connected to one end of the third gain proportional capacitor, the main loop operational amplifier, and the DC servo loop operational amplifier, respectively. The other end of the third gain proportional capacitor is connected to the main loop operational amplifier.

[0029] Furthermore, the first gain proportional capacitor has the same capacitance value as the second gain proportional capacitor, and the third gain proportional capacitor has the same capacitance value as the fourth gain proportional capacitor.

[0030] Furthermore, the differential output port includes a first differential output port and a second differential output port;

[0031] The first differential output port is connected to the main loop operational amplifier, the end of the first resistor furthest from the second resistor, and the common-mode feedback operational amplifier, respectively.

[0032] The second differential output port is connected to the main loop operational amplifier, the end of the fourth resistor furthest from the third resistor, and the common-mode feedback operational amplifier, respectively.

[0033] Furthermore, the first differential output port of the differential output port is connected to the main loop operational amplifier and the end of the first resistor furthest from the second resistor, respectively;

[0034] The second differential output port of the differential output port is connected to the main loop operational amplifier and the end of the fourth resistor that is furthest from the third resistor.

[0035] Furthermore, the amplitude attenuation module is a MOS transistor or an operational amplifier.

[0036] This invention also provides an amplitude attenuation method for an AC-coupled amplifier circuit, which is applied to the amplifier circuit provided in the above embodiments. The method includes the following steps:

[0037] The amplitude attenuation module controls the swing of the input signal of the DC servo loop operational amplifier based on a preset attenuation factor, so that the DC servo loop operational amplifier can work normally.

[0038] Furthermore, the specific steps for controlling the swing of the input signal of the DC servo loop operational amplifier include: voltage division control via resistors in the amplitude attenuation module; or control via common-mode feedback resistors of the resistor taps in the amplitude attenuation module within the common-mode feedback operational amplifier.

[0039] The beneficial effects achieved by this invention are as follows: By adding an amplitude attenuation module to the input terminal of the DC servo loop operational amplifier, the swing of the input signal of the DC servo loop operational amplifier is reduced. Thus, the DC servo loop operational amplifier can still work normally when it outputs a large swing signal at the differential output port, thereby solving the intermodulation problem of AC coupled amplifier circuit under large signal output conditions. Attached Figure Description

[0040] Figure 1 This is a circuit diagram of an AC-coupled amplifier circuit provided in an embodiment of the present invention;

[0041] Figure 2 This is a circuit diagram of another AC-coupled amplifier circuit provided in an embodiment of the present invention;

[0042] Figure 3 This is a circuit diagram of another AC-coupled amplifier circuit provided in an embodiment of the present invention;

[0043] Figure 4 This is a spectrum diagram of the output of an AC-coupled amplifier circuit provided in an embodiment of the present invention;

[0044] Figure 5 This is a flowchart of an amplitude attenuation method for an AC-coupled amplifier circuit provided in an embodiment of the present invention.

[0045] The components are as follows: 1. AC-coupled amplifier circuit; 2. First differential input port; 3. Second differential input port; 4. First input terminal of main loop operational amplifier; 5. Second input terminal of main loop operational amplifier; 6. Main loop operational amplifier; 7. First output terminal of main loop operational amplifier; 8. Control signal input terminal; 9. Second output terminal of main loop operational amplifier; 10. Control signal output terminal; 11. Common-mode feedback operational amplifier; 12. First input terminal of common-mode feedback operational amplifier; 13. Reference signal input terminal; 14. Second input terminal of common-mode feedback operational amplifier; 15. Amplitude attenuation module; 16. First input terminal of DC servo loop operational amplifier; 17. Reference signal input terminal; 18. Second input terminal of DC servo loop operational amplifier; 19. First output terminal of DC servo loop operational amplifier; 20. DC servo loop operational amplifier; 21. Second output terminal of DC servo loop operational amplifier; 22. Common-mode signal terminal. Detailed Implementation

[0046] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0047] Example 1

[0048] like Figure 1 As shown, Figure 1 This is a circuit diagram of an AC-coupled amplifier circuit provided in an embodiment of the present invention.

[0049] The AC-coupled amplifier circuit 1 includes a differential input port, multiple gain ratio capacitors, a main loop operational amplifier 6, a common-mode feedback operational amplifier 11, a DC servo loop operational amplifier 20, a differential output port, and an amplitude attenuation module 15.

[0050] The main loop operational amplifier 6 is equipped with a first input terminal 4, a second input terminal 5, a first output terminal 7, a second output terminal 9, and a control signal input terminal 8.

[0051] The common-mode feedback operational amplifier 11 is provided with a control signal output terminal 10, a first input terminal 12, a second input terminal 14, and a reference signal input terminal 13. The common-mode feedback operational amplifier 11 is mainly used to ensure that the common-mode output signal of the differential output port remains unchanged and equal.

[0052] The DC servo loop operational amplifier 20 is equipped with a first input terminal 16, a second input terminal 18, a first output terminal 19, a second output terminal 21, and a reference signal input terminal 17. The output of the DC servo loop operational amplifier 20 is needed to clamp the DC point of the input point of the main loop operational amplifier 6 to ensure that the main loop operational amplifier 6 operates normally.

[0053] In this embodiment of the invention, the differential input port is connected in series with multiple gain ratio capacitors and then connected to the main loop operational amplifier 6 and the DC servo loop operational amplifier 20 through multiple gain ratio capacitors respectively.

[0054] Specifically, the differential input port includes a first differential input port 2 (INP) and a second differential input port 3 (INN).

[0055] The plurality of gain proportional capacitors include a first gain proportional capacitor C1, a second gain proportional capacitor C2, a third gain proportional capacitor C3, and a fourth gain proportional capacitor C4.

[0056] The first differential input port 2 (INP) is connected to one end of the first gain proportional capacitor C1. The other end of the first gain proportional capacitor C1 is connected to one end of the fourth gain proportional capacitor C4, the main loop operational amplifier 6 (the first input terminal 4 of the main loop operational amplifier 6), and the DC servo loop operational amplifier 20 (the first output terminal 19 of the DC servo loop operational amplifier 20). The other end of the fourth gain proportional capacitor C4 is connected to the main loop operational amplifier 6 (the first output terminal 7 of the main loop operational amplifier 6).

[0057] The second differential input port 3 (INN) is connected to one end of the second gain proportional capacitor C2. The other end of the second gain proportional capacitor C2 is connected to one end of the third gain proportional capacitor C3, the main loop operational amplifier 6 (the second input terminal 5 of the main loop operational amplifier 6), and the DC servo loop operational amplifier 20 (the second output terminal 21 of the DC servo loop operational amplifier 20). The other end of the third gain proportional capacitor C3 is connected to the main loop operational amplifier 6 (the second output terminal 9 of the main loop operational amplifier 6).

[0058] The first gain proportional capacitor C1 has the same capacitance value as the second gain proportional capacitor C2, which can be expressed as C1 = C2. The third gain proportional capacitor C3 has the same capacitance value as the fourth gain proportional capacitor C4, which can be expressed as C3 = C4.

[0059] The main loop operational amplifier 6 is an ultra-high gain stage, which ensures that the overall circuit gain is equal to the capacitor ratio C1 / C4 through the loop.

[0060] In this embodiment of the invention, the main loop operational amplifier 6 is also connected to the common-mode feedback operational amplifier 11 and the amplitude attenuation module 15.

[0061] Specifically, the control signal input terminal 8 of the main loop operational amplifier 6 is connected to the control signal output terminal 10 of the common-mode feedback operational amplifier 11. In this way, the control signal VCMFB generated by the common-mode feedback operational amplifier 11 can be transmitted to the main loop operational amplifier 6 through the control signal output terminal 10 and the control signal input terminal 8 of the main loop operational amplifier 6.

[0062] The first output terminal 7 of the main loop operational amplifier 6 is connected to the first input terminal 12 of the common-mode feedback operational amplifier 11 and the amplitude attenuation module 15, respectively.

[0063] The second output terminal 9 of the main loop operational amplifier 6 is connected to the second input terminal 14 of the common-mode feedback operational amplifier 11 and the amplitude attenuation module 15, respectively.

[0064] In this embodiment of the invention, the differential output port is connected to the main loop operational amplifier 6, the common-mode feedback operational amplifier 11, and the amplitude attenuation module 15, respectively.

[0065] The first input terminal 16 and the second input terminal 18 of the DC servo loop operational amplifier 20 are respectively connected to the amplitude attenuation module 15.

[0066] The reference signal input terminal 17 of the DC servo loop operational amplifier 20 is connected to the reference signal input terminal 13 of the common-mode feedback operational amplifier 11. The reference signal input terminal 13 is an external input reference signal.

[0067] Specifically, the differential output ports include a first differential output port OUTN and a second differential output port OUTP. The first differential output port OUTN is connected to the first output terminal 7 of the main loop operational amplifier 6, the first input terminal 12 of the common-mode feedback operational amplifier 11, and the amplitude attenuation module 15, respectively. Thus, the input signal of the DC servo loop operational amplifier 20 is obtained by attenuating the differential-mode signal from the differential output ports through the amplitude attenuation module 15. The first input terminal 12 and the second input terminal 14 of the common-mode feedback operational amplifier 11 can extract the common-mode signal VOCM from the first differential output port OUTN and the second differential output port OUTP, respectively, compare it with the input reference signal VCM, generate a control signal VCMFB, and feed it back to the main loop operational amplifier 6. Through loop feedback, the DC point of the first differential output port OUTN and the second differential output port OUTP is maintained at the input reference signal VCM.

[0068] In this embodiment of the invention, by adding an amplitude attenuation module 15 to the input terminal of the DC servo loop operational amplifier 20, the swing of the signal at the input terminal of the DC servo loop operational amplifier 20 is reduced. Therefore, the DC servo loop operational amplifier 20 can still operate normally even when outputting a large-swing signal at the differential output port. This solves the intermodulation problem of the AC-coupled amplifier circuit 1 under large signal output conditions.

[0069] Example 2

[0070] like Figure 2 As shown, Figure 2 This is a circuit diagram of another AC-coupled amplifier circuit provided in an embodiment of the present invention. The amplitude attenuation module 15 includes a first resistor R1, a second resistor R2, a third resistor R3, and a fourth resistor R4.

[0071] The first resistor R1, the second resistor R2, the third resistor R3, and the fourth resistor R4 are connected in series between the common-mode feedback operational amplifier 11 and the DC servo loop operational amplifier 20.

[0072] The end of the first resistor R1 furthest from the second resistor R2 is connected to the common-mode feedback operational amplifier 11 (the first input terminal 12 of the common-mode feedback operational amplifier 11), the differential output port (the first differential output port OUTN of the differential output port), and the main loop operational amplifier 6 (the first output terminal 7 of the main loop operational amplifier 6).

[0073] The first input terminal 16 of the DC servo loop operational amplifier 20 is connected to the connection line between the first resistor R1 and the second resistor R2.

[0074] The second input terminal 18 of the DC servo loop operational amplifier 20 is connected to the connection line between the third resistor R3 and the fourth resistor R4.

[0075] The end of the fourth resistor R4 furthest from the third resistor R3 is connected to the common-mode feedback operational amplifier 11 (the second input terminal 14 of the common-mode feedback operational amplifier 11), the differential output port (the second differential output port OUTP), and the main loop operational amplifier 6 (the second output terminal 9 of the main loop operational amplifier 6).

[0076] Specifically, the amplitude attenuation module 15 uses a resistor voltage divider to achieve the amplitude attenuation function. The attenuation circuit is composed of a first resistor R1, a second resistor R2, a third resistor R3, and a fourth resistor R4 connected in series. The first resistor R1 and the fourth resistor R4 have the same resistance value, which can be expressed as R1 = R4. The second resistor R2 and the third resistor R3 have the same resistance value, which can be expressed as R2 = R3. The input signal at the first input terminal 16 of the DC servo loop operational amplifier 20 is obtained by attenuating the differential signal of the first differential output port OUTN through a gain attenuation of R2 / (R1+R2). One input signal at the second input terminal 18 of the DC servo loop operational amplifier 20 is obtained by attenuating the differential signal of the second differential output port OUTP through a gain attenuation of R3 / (R4+R3). This facilitates the comparison between the input signals from the first input terminal 16 and the second input terminal 18 and the input reference signal VCM, generating the first output terminal 19 and the second output terminal 21 of the DC servo loop operational amplifier 20. These outputs are then fed back to the first input terminal 4 and the second input terminal 5 of the main loop operational amplifier 6, ensuring the normal operation of the main loop operational amplifier 6. This also solves the intermodulation problem of this AC-coupled amplifier circuit 1 under large signal output conditions.

[0077] In another embodiment of the present invention, such as Figure 3 As shown, Figure 3 This is a circuit diagram of another AC-coupled amplifier circuit provided in an embodiment of the present invention. The common-mode feedback operational amplifier 11 uses resistors to extract the common-mode signal VOCM from the first differential output port OUTN and the second differential output port OUTP. Therefore, the amplitude attenuation module 15 can share the common-mode signal extraction module of the common-mode feedback operational amplifier 11. The first resistor R1, the second resistor R2, the third resistor R3, and the fourth resistor R4 of the amplitude attenuation module 15 are sequentially connected in series inside the common-mode feedback operational amplifier 11.

[0078] The end of the first resistor R1 furthest from the second resistor R2 is connected to the differential output port (first differential output port OUTN) and the main loop operational amplifier 6 (first output terminal 7 of the main loop operational amplifier 6).

[0079] The first input terminal 16 of the DC servo loop operational amplifier 20 is located on the connection line between the first resistor R1 and the second resistor R2.

[0080] The second input terminal 18 of the DC servo loop operational amplifier 20 is located on the connection line between the third resistor R3 and the fourth resistor R4.

[0081] The end of the fourth resistor R4 furthest from the third resistor R3 is connected to the differential output port (second differential output port OUTP) and the main loop operational amplifier 6 (second output terminal 9 of the main loop operational amplifier 6).

[0082] The common-mode signal terminal 24 of the common-mode feedback operational amplifier 11 is connected to the connection line between the second resistor R2 and the third resistor R3.

[0083] The first differential output port OUTN of the differential output port is connected to the main loop operational amplifier 6 (the first output terminal 7 of the main loop operational amplifier 6) and the end of the first resistor R1 that is furthest from the second resistor R2.

[0084] The second differential output port OUTP of the differential output port is connected to the main loop operational amplifier 6 (the second output terminal 9 of the main loop operational amplifier 6) and the end of the fourth resistor R4 that is away from the third resistor R3.

[0085] Specifically, a tap is taken from the internal resistor of the common-mode feedback operational amplifier 11 and used as the input of the DC servo loop operational amplifier 20, such as... Figure 3 The common-mode signal detection circuit (amplitude attenuation module 15) inside the common-mode feedback operational amplifier 11 is implemented using a first resistor R1, a second resistor R2, a third resistor R3, and a fourth resistor R4. The first resistor R1 and the fourth resistor R4 have the same resistance value, which can be expressed as R1 = R4. The second resistor R2 and the third resistor R3 have the same resistance value, which can be expressed as R2 = R3. The first differential output port OUTN and the second differential output port OUTP extract the common-mode signal VOCM from the common-mode signal terminal 24 formed by the first resistor R1, the second resistor R2, the third resistor R3, and the fourth resistor R4 of the common-mode feedback operational amplifier 11. The common-mode feedback operational amplifier 11 compares the common-mode signal VOCM with the reference signal VCM and generates a control signal VCMFB, which is sent to the main loop operational amplifier 6. The input signal at the first input terminal 16 of the DC servo loop operational amplifier 20 is obtained by tapping the middle of the first resistor R1 and the second resistor R2, and the input signal at the second input terminal 18 of the DC servo loop operational amplifier 20 is obtained by tapping the middle of the third resistor R3 and the fourth resistor R4. Its attenuation factor is R3 / (R4+R3) or R2 / (R1+R2).

[0086] This facilitates the comparison of the input signals from the first input terminal 16 and the second input terminal 18 with the input reference signal VCM by the DC servo loop operational amplifier 20, generating the first output terminal 19 and the second output terminal 21 of the DC servo loop operational amplifier, which are then fed back to the first input terminal 4 and the second input terminal 5 of the main loop operational amplifier 6 to ensure the normal operation of the main loop operational amplifier 6. This also solves the intermodulation problem of this AC-coupled amplifier circuit 1 under large signal output conditions. Compared to... Figure 2 AC-coupled amplifier circuit 1 in the middle, Figure 3 The AC-coupled amplifier circuit 1 in the design reduces power consumption and area.

[0087] In this embodiment of the invention, the amplitude attenuation module 15 is not limited to using a resistor; amplitude attenuation devices using MOSFETs, operational amplifiers, or other similar methods can also achieve the desired effect. The circuit configuration of the amplitude attenuation module 15 is not limited to resistor voltage dividers, MOSFET voltage dividers, operational amplifiers, or other similar implementations.

[0088] For example, such as Figure 4 As shown, Figure 4 When the amplitude attenuation module 15 is attenuated by 60 times, and 0.4V peak-to-peak 1kHz and 5.5kHz differential signals are input to the differential input ports (first differential input port 2 (INP) and second differential input port 3 (INN)), the differential output spectra of the first differential output port OUTN and the second differential output port OUTP are as follows: Figure 4 As can be seen from the spectrum, the energy at 3.5kHz and 7.5kHz is significantly reduced, and the harmonic energy is also significantly reduced, resulting in a substantial improvement in intermodulation distortion.

[0089] In this embodiment of the invention, one approach is to directly use a resistor voltage divider to generate an amplitude attenuation circuit. Another approach is to place the amplitude attenuation module 15 inside the common-mode feedback operational amplifier 11, thereby using a resistor tapped from inside the common-mode feedback operational amplifier 11 to reuse the common-mode feedback resistor, further reducing power consumption and area, and solving the intermodulation problem of this AC-coupled amplifier circuit 1 under large signal output conditions.

[0090] Example 3

[0091] like Figure 5 As shown, Figure 5 This is a flowchart illustrating an amplitude attenuation method for an AC-coupled amplifier circuit according to an embodiment of the present invention. The method is applied to the amplifier circuit provided in the above embodiment and includes the following steps:

[0092] Step 101: Control the swing of the input signal of the DC servo loop operational amplifier based on a preset attenuation factor using the amplitude attenuation module, so that the DC servo loop operational amplifier can work normally.

[0093] In this embodiment of the invention, the amplitude attenuation module reduces the swing of the input signal of the DC servo loop operational amplifier based on a preset attenuation factor, thereby controlling the DC servo loop amplifier to operate normally even when the differential output has a large swing. This solves the intermodulation problem of the AC-coupled amplifier under large signal output conditions.

[0094] Furthermore, step 101 includes: voltage division control via resistors in the amplitude attenuation module; or control via common-mode feedback resistors using resistor taps in the amplitude attenuation module within the common-mode feedback operational amplifier.

[0095] In this embodiment of the invention, when controlled by a resistor divider in the amplitude attenuation module, the circuit diagram of the amplitude attenuation module is as follows: Figure 2 As shown, an input amplitude attenuation module can be implemented using a resistor voltage divider. Resistors R1, R2, R3, and R4 form an attenuation circuit, with R1 = R4 and R2 = R3. One input signal of the DC servo loop operational amplifier is the differential signal of OUTN, which is attenuated by a preset attenuation factor R2 / (R1+R2). The other input signal is the differential signal of OUTP, which is attenuated by a preset attenuation factor R3 / (R4+R3). Therefore, the amplitude attenuation circuit can be directly generated through the voltage divider of resistors R1, R2, R3, and R4 to achieve the amplitude reduction function, reducing the swing of the input signal of the DC servo loop operational amplifier, and thus controlling the DC servo loop amplifier to operate normally even with a large swing at the differential output. This solves the intermodulation problem of AC-coupled amplifiers under large signal output conditions.

[0096] In the embodiments of the present invention, when the common-mode feedback resistor of the resistor tap of the amplitude attenuation module inside the multiplexed common-mode feedback operational amplifier is used for control, the circuit diagram of the amplitude attenuation module is as follows: Figure 3As shown, a tap can be used from the resistors inside the common-mode feedback operational amplifier (because the amplitude attenuation module is located inside the common-mode feedback operational amplifier) ​​as the input to the DC servo loop operational amplifier. The common-mode signal detection circuit inside the common-mode feedback operational amplifier is implemented using resistors, R1 = R4, R2 = R3. The first differential output port OUTN and the second differential output port OUTP extract the common-mode signal VOCM through resistors R1, R2, R3, and R4 of the common-mode feedback operational amplifier. VOCM is compared with VCM and generated by the common-mode feedback operational amplifier to produce VCMFB, which is then sent to the main loop operational amplifier. Thus, one input signal of the DC servo loop operational amplifier is obtained by tapping from the middle of resistors R1 and R2, and the other input signal is obtained by tapping from the middle of resistors R3 and R4. The preset attenuation factor is R3 / (R4+R3) or R2 / (R1+R2). This reduces power consumption and area, while also achieving amplitude reduction, decreasing the swing of the input signal of the DC servo loop operational amplifier. This allows the DC servo loop amplifier to operate normally even with a large swing at the differential output. Thus, it solves the intermodulation problem of AC-coupled amplifiers under large signal output conditions.

[0097] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. An AC-coupled amplifier circuit, characterized in that, include: Differential input port, multiple gain ratio capacitors, main loop operational amplifier, common mode feedback operational amplifier, DC servo loop operational amplifier, differential output port, and amplitude attenuation module; The differential input port is connected in series with multiple gain ratio capacitors and then connected to the main loop operational amplifier and the DC servo loop operational amplifier through multiple gain ratio capacitors respectively. The differential input port includes a first differential input port and a second differential input port; The plurality of gain proportional capacitors include a first gain proportional capacitor, a second gain proportional capacitor, a third gain proportional capacitor, and a fourth gain proportional capacitor. The first differential input port is connected to one end of the first gain proportional capacitor, and the other end of the first gain proportional capacitor is connected to one end of the fourth gain proportional capacitor, the first input terminal of the main loop operational amplifier, and the first output terminal of the DC servo loop operational amplifier, respectively. The other end of the fourth gain proportional capacitor is connected to the first output terminal of the main loop operational amplifier. The second differential input port is connected to one end of the second gain proportional capacitor, and the other end of the second gain proportional capacitor is connected to one end of the third gain proportional capacitor, the second input terminal of the main loop operational amplifier, and the second output terminal of the DC servo loop operational amplifier, respectively. The other end of the third gain proportional capacitor is connected to the second output terminal of the main loop operational amplifier. The first output terminal of the main loop operational amplifier is connected to the first input terminal of the common-mode feedback operational amplifier and the first input terminal of the amplitude attenuation module, respectively; the second output terminal of the main loop operational amplifier is connected to the second input terminal of the common-mode feedback operational amplifier and the second input terminal of the amplitude attenuation module, respectively; the differential output port includes a first differential output port and a second differential output port; The first differential output port is connected to the first output terminal of the main loop operational amplifier, the first input terminal of the amplitude attenuation module, and the first output terminal of the common-mode feedback operational amplifier, respectively. The second differential output port is connected to the second output terminal of the main loop operational amplifier, the second input terminal of the amplitude attenuation module, and the second output terminal of the common-mode feedback operational amplifier, respectively. The first input terminal and the second input terminal of the DC servo loop operational amplifier are respectively connected to the first output terminal and the second output terminal of the amplitude attenuation module; The reference signal input terminal of the DC servo loop operational amplifier is connected to the reference signal input terminal of the common-mode feedback operational amplifier.

2. The AC-coupled amplifier circuit as described in claim 1, characterized in that, The amplitude attenuation module includes a first resistor, a second resistor, a third resistor, and a fourth resistor; The first resistor, the second resistor, the third resistor, and the fourth resistor are connected in series between the common-mode feedback operational amplifier and the DC servo loop operational amplifier. The end of the first resistor furthest from the second resistor is connected to the first input terminal of the common-mode feedback operational amplifier, the first differential output port, and the first output terminal of the main loop operational amplifier, respectively. The first input terminal of the DC servo loop operational amplifier is connected to the connection line between the first resistor and the second resistor; The second input terminal of the DC servo loop operational amplifier is connected to the connection line between the third resistor and the fourth resistor; The end of the fourth resistor furthest from the third resistor is connected to the second input terminal of the common-mode feedback operational amplifier, the second differential output port, and the second output terminal of the main loop operational amplifier, respectively. or The common-mode feedback operational amplifier includes a first resistor, a second resistor, a third resistor, and a fourth resistor; The end of the first resistor furthest from the second resistor is connected to both the first differential output port and the first output terminal of the main loop operational amplifier. The first input terminal of the DC servo loop operational amplifier is located on the connection line between the first resistor and the second resistor; The second input terminal of the DC servo loop operational amplifier is located on the connection line between the third resistor and the fourth resistor; The end of the fourth resistor furthest from the third resistor is connected to the second differential output port and the second output terminal of the main loop operational amplifier, respectively. The common-mode signal terminal of the common-mode feedback operational amplifier is connected to the connection line between the second resistor and the third resistor.

3. The AC-coupled amplifier circuit as described in claim 2, characterized in that, The first resistor has the same resistance value as the fourth resistor, and the second resistor has the same resistance value as the third resistor.

4. The AC-coupled amplifier circuit as described in claim 1, characterized in that, The first gain proportional capacitor has the same capacitance value as the second gain proportional capacitor, and the third gain proportional capacitor has the same capacitance value as the fourth gain proportional capacitor.

5. The AC-coupled amplifier circuit as described in claim 1, characterized in that, The amplitude attenuation module also includes a MOSFET or an operational amplifier.

6. A method for amplitude attenuation in an AC-coupled amplifier circuit, characterized in that, The method, when applied to any one of the amplifier circuits described in 1-5, includes the following steps: The amplitude attenuation module controls the swing of the input signal of the DC servo loop operational amplifier based on a preset attenuation factor, so that the DC servo loop operational amplifier can work normally.

7. The amplitude attenuation method for the AC-coupled amplifier circuit as described in claim 6, characterized in that, The specific steps for controlling the swing of the input signal of the DC servo loop operational amplifier include: voltage division control via resistors in the amplitude attenuation module; or control via common-mode feedback resistors of the resistor taps in the amplitude attenuation module within the common-mode feedback operational amplifier.

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