A chopping operational amplifier circuit applied to voltage isolation

Abstract

The application relates to a chopping operational amplifier circuit applied to voltage isolation, which mainly comprises transconductance amplifiers amp1, amp2, amp3, amp4, amp5, chopping modulation circuits CHIN, CHOUT, CHfb, CHRRL, capacitors Cin1, Cin2, Cfb1, Cfb2, Cs1, Cs2, Cm1, Cm21a, Cm21b, Cm22a, Cm22b, resistors res1, res2, and a chopping modulation signal f chop The chopping modulation circuit CHIN modulates the analog voltage signal input from the high-voltage end into a voltage signal with a frequency of f chop , and couples the voltage signal to the low-voltage end through the isolation capacitors Cin1 and Cin2; the bias resistors res1 and res2 of the low-voltage end provide the transconductance amplifier amp1 of the low-voltage end with a direct current bias signal again; the CHOUT modulates the offset voltage V OFFSET of the transconductance amplifier amp1 and the 1 / f noise into high frequency, and re-modulates the output current signal of the amp1 into the frequency input from the high-voltage end; finally, the size of the output voltage is input signal Vout=Vin x (Cfb / Cin), and the ripple elimination ring eliminates the ripple generated by the offset voltage of the transconductance amplifiers amp1, amp2 and amp3.

Description

Technical Field

[0001] This invention belongs to the field of analog integrated circuit design technology, and specifically relates to a chopper operational amplifier circuit applied to voltage isolation. Background Technology

[0002] Industrial applications such as motor drives, photovoltaic inverters, and uninterruptible power supplies (UPS), and automotive applications such as on-board chargers (OBCs), traction inverters, and DC / DC converters operate at high voltage and current levels. These systems are exposed to harsh environments, such as electrical noise, vibration, mechanical shock, extreme temperatures, and contaminant intrusion. These systems require robust and reliable isolation technologies to separate high-voltage circuits from low-voltage circuits.

[0003] Popular existing isolation technologies include isolated amplifiers and isolated modulators. Both internally use a Σ-δ modulator with an internal reference voltage and clock generator to convert the analog input signal into a digital bitstream. The transmitter sends the modulator's output to an isolation barrier, separating the high-voltage and low-voltage sides. The main difference lies in the receiver. With an isolated amplifier, the received bitstream and clock are synchronized by an analog filter on the low-voltage side and presented as an analog signal. With an isolated modulator, the receiver output provides a high-frequency digital bitstream containing only 0s and 1s. The average time of this digital stream's output is proportional to the analog input voltage, and the measured signal is reconstructed into an analog signal through a digital filter.

[0004] The patent CN110138346A uses a digital-plus-analog method to eliminate ripple caused by offset voltage. The performance of ripple elimination is limited by the accuracy of the digital part itself, and the digital module occupies a large area. Its feedforward section uses a common two-stage operational amplifier. Based on the Miller capacitor used, it can be preliminarily analyzed that the position of its main pole is determined by the first-stage operational amplifier. This limits the transconductance of the input transistor of the first-stage operational amplifier, and the overall power consumption of the circuit is relatively large.

[0005] Compared to the aforementioned patent, this invention employs a ripple cancellation loop to eliminate ripple caused by offset voltage. The performance of the ripple cancellation loop is mainly determined by transconductance amplifiers amp4 and amp5, and is not limited by digital modules. It also occupies a relatively small area. Furthermore, the feedforward section uses a three-stage operational amplifier with an NMC (nested Miller compensation) circuit. The dominant pole of the feedforward section is determined by transconductance amplifier amp2, which allows for the use of larger sizes for the input transistors of transconductance amplifier amp1. This effectively reduces 1 / f noise and minimizes input transistor mismatch. Moreover, the transconductance amplifier amp3 adopts a class AB output configuration, which enables it to maintain low static power consumption while having good driving capability. Summary of the Invention

[0006] This invention aims to solve the problems of the prior art mentioned above. It proposes a chopper operational amplifier circuit for voltage isolation. The technical solution of this invention is as follows:

[0007] A voltage-isolated chopper operational amplifier circuit includes: transconductance amplifiers amp1, amp2, amp3, amp4, amp5; chopper modulation circuits CHIN, CHOUT, CHFB, CHRRL; capacitors Cin1, Cin2, Cfb1, Cfb2, Cs1, Cs2, Cint1, Cint2, Cm1, Cm21a, Cm21b, Cm22a, Cm22b; resistors res1, res2; and a chopper modulation signal f. chopThe input terminal VIN is connected to the chopper modulation circuit CHIN. The chopper modulation circuit CHIN is connected to capacitors Cin1 and Cin2 respectively. Capacitor Cin1 is connected to the negative terminal of transconductance amplifier amp1, and capacitor Cin2 is connected to the positive terminal of transconductance amplifier amp1. The output terminal of transconductance amplifier amp1 is connected to the chopper modulation circuit CHOUT. The chopper modulation circuit CHOUT is connected to the input terminal of transconductance amplifier amp2. The output terminal of transconductance amplifier amp2 is connected to transconductance amplifier amp3. Capacitors Cm21a and Cm22a are connected from the positive output terminal of transconductance amplifier amp3 to the positive and negative input terminals of amp2 respectively. Capacitors Cm21b and Cm22b are connected from the transconductance amplifier amp3 to the positive and negative input terminals of amp2 respectively. The negative output terminal of mp3 is connected to the positive and negative input terminals on the other side of amp2. Capacitors Cm1 and Cm2 are connected from the positive and negative output terminals of transconductance amplifier amp3 to the negative and positive input terminals of transconductance amplifier amp2, respectively. One output terminal of transconductance amplifier amp3 is connected to chopper modulation circuit CHFB and capacitors Cfb1 and Cfb2. Capacitors Cfb1 and Cfb2 are connected to capacitors Cin1 and Cin2, respectively. The other output terminal is connected to chopper modulation circuit CHRRL, transconductance amplifier amp4 and amp5 in sequence, and then connected to the output terminal of transconductance amplifier amp1. Capacitors Cint1 and Cint2 are connected across the two sides of transconductance amplifier amp4, respectively.

[0008] Furthermore, the chopper modulation circuit Chin is used to modulate the analog input signal at the high-voltage end to a frequency of f. chop The voltage signal;

[0009] The resistors res1 and res2, along with the capacitors Cin1 and Cin2, form a high-pass filter that filters out the DC signal at the high-voltage end and acts as a bias resistor, providing a suitable static operating point for the transconductance amplifier amp1.

[0010] The input of the transconductance amplifier amp1 comes from the analog AC voltage signal coupled from the high voltage end by capacitors Cin1 and Cin2, and converts the input voltage signal into a current signal.

[0011] The chopper modulation circuit CHOUT is used to modulate the AC current signal output from the transconductance amplifier amp1 from frequency f. chop The analog signal frequency is down-converted to the high-voltage side, and the offset voltage V of the transconductance amplifier amp1 is converted. OFFSET and 1 / f noise upconverted to frequency f chop ;

[0012] The capacitors Cm1, Cm21, and Cm22 form an integrating circuit around the transconductance amplifiers amp2 and amp3, which integrates the current signal output from amp1 into a voltage signal presented at the output terminal. The output value Vout = Vin × (Cfb / Cin).

[0013] The capacitors Cfb1 / Cin1 and Cfb2 / Cin2 are the feedback coefficients of the overall circuit, which determine the magnitude of the closed-loop gain of the overall circuit.

[0014] The capacitors Cs1 and Cs2, the chopper modulation circuit CHRRL, and the transconductance amplifiers amp4 and amp5 form a ripple cancellation loop, ultimately generating a compensation current Icom that is V of amp1. OFFSET The resulting offset current I OFFSET Compensation is performed to ultimately eliminate ripple.

[0015] Furthermore, the isolation input capacitors Cin1 and Cin2 isolate the high-voltage end and the low-voltage end, thus protecting the low-voltage end. The chopper modulation circuit CHIN modulates the input AC signal into a high frequency, which is then isolated by capacitors Cin1 and Cin2 from the high common-mode voltage of the high-voltage end from affecting the low-voltage end.

[0016] Furthermore, the overall circuit structure adopts a nested Miller compensation (NMC) three-stage operational amplifier structure, with the last stage using class-AB output. Class-AB output can provide large dynamic current while maintaining low quiescent current, thus enhancing the driving capability.

[0017] Furthermore, the chopper modulation circuit CHIN and chopper modulation circuit CHUOT respectively function as up-conversion and down-conversion circuits. CHIN modulates the AC signal to a frequency similar to the chopper frequency f. chop At the same high frequency, CHOUT modulates the current signal output from transconductance amplifier amp1 to the same frequency as the input signal at the high voltage end, and modulates the V of amp1. OFFSET The 1 / f noise is modulated to a high frequency, which also acts as an envelope detector to recover the waveform of the signal. At the same time, capacitors Cm1, Cm21, and Cm22 form an integrating circuit around transconductance amplifiers amp2 and amp3 to present the output current of amp1 and the voltage signal at the output terminal. However, due to the offset voltage of the transconductance amplifier and the residual voltage generated in the chopper modulation circuit due to the excessively high chopper frequency, it will also be presented at the output terminal.

[0018] Furthermore, the input capacitors Cs1 and Cs2 of the ripple cancellation loop RRL will convert the offset AC current signal I at the output terminal. OFFSET Coupled to the input of the chopper modulation circuit CHRRL, the CHRRL will couple the I... OFFSETThe signal is down-converted to DC, integrated into a voltage signal by an integrating circuit formed around transconductance amplifier amp4 using capacitors Cint1 and Cint2, and finally converted into a compensated current signal I by transconductance amplifier amp5. COM For offset current I OFFSET It performs compensation to eliminate ripple.

[0019] The advantages and beneficial effects of this invention are as follows:

[0020] 1. In order to isolate the high-voltage end and the low-voltage end, this invention eliminates the damage caused by the high common-mode voltage of the high-voltage end to the circuit of the low-voltage end. The traditional structure commonly used at present is to convert the analog signal under test to digital and digital to analog several times. This greatly increases the delay time. At the same time, it is also subject to the accuracy limitation of the internal circuit, which reduces the accuracy of the reconstructed analog signal and increases distortion.

[0021] 2. The main operational amplifier structure in this invention adopts nested Miller compensation, and the third-stage operational amplifier adopts Class-AB output. This maintains a low static current while having a large dynamic current to drive the ripple elimination loop and subsequent circuits. At the same time, capacitors Cm1, Cm21, and Cm22 can suppress ripple to a certain extent.

[0022] 3. The chopper operational amplifier circuit of the present invention applied to voltage isolation includes ripple cancellation for transconductance amplifier amp1. For isolation technology, the main purpose is to reconstruct the analog signal input from the high-voltage side at the low-voltage side while maintaining high linearity and low distortion. Therefore, the input transistors of amp1 are large-size PMOS transistors, which effectively reduces 1 / f noise. However, the error caused by the offset voltage of amp1 is unavoidable. Therefore, a ripple cancellation loop composed of capacitors Cs1, Cs2, Cint1, Cint2 and transconductance amplifiers amp4 and amp5 is used to compensate for the offset current caused by the offset voltage. This effectively suppresses the generation of ripple, improves the linearity of the reconstructed signal and reduces distortion. Attached Figure Description

[0023] Figure 1 This is a voltage isolation chopper operation circuit diagram of a preferred embodiment of the present invention;

[0024] Figure 2 The operational amplifier feedforward section of this invention;

[0025] Figure 3 The ripple elimination loop of the present invention;

[0026] Figure 4 The common-mode input voltage of the high-voltage and low-voltage terminals of this invention;

[0027] Figure 5 PSS simulation diagram of the present invention without ripple elimination loop;

[0028] Figure 6 PSS simulation diagram of the present invention with added ripple elimination loop;

[0029] Figure 7 PAC simulation diagram of the present invention;

[0030] Figure 8 Simulation diagram of pnoise in this invention;

[0031] Figure 9 The Fourier analysis diagram of this invention. Detailed Implementation

[0032] The technical solutions of the embodiments of the present invention will be clearly and thoroughly described below with reference to the accompanying drawings. The described embodiments are merely some embodiments of the present invention.

[0033] The technical solution of the present invention to solve the above-mentioned technical problems is:

[0034] like Figure 1 As shown, a chopper operational amplifier circuit for voltage isolation is illustrated. This circuit mainly includes transconductance amplifiers amp1, amp2, amp3, amp4, and amp5; chopper modulation circuits CHin, CHout, CHfb, and CHRRL; capacitors Cin1, Cin2, Cfb1, Cfb2, Cs1, Cs2, Cm1, Cm21, and Cm22; resistors res1 and res2; and a chopper modulation signal f. chop .

[0035] The function of the chopper modulation circuit CHin is to modulate the analog input signal at the high-voltage end to a frequency of f. chop The voltage signal.

[0036] The function of resistors res1 and res2 is to form a high-pass filter with capacitor Cin, filter out the DC signal at the high-voltage end, and act as a bias resistor to provide a suitable static operating point for transconductance amplifier amp1.

[0037] The transconductance amplifier amp1 receives an analog AC voltage signal coupled from the high-voltage side of Cin, and converts the input voltage signal into a current signal.

[0038] The function of the chopper modulation circuit CHout is to reduce the AC current signal output from amp1 to frequency f. chop The analog signal frequency is down-converted to the high-voltage end, and the V of amp1 is converted. OFFSETand 1 / f noise upconverted to frequency f chop .

[0039] The capacitors Cm1, Cm21, and Cm22 form an integrating circuit around the transconductance amplifiers amp2 and amp3, integrating the current signal output from amp1 into a voltage signal, which is then presented at the output terminal. Its output magnitude, Vout = Vin × (Cfb / Cin).

[0040] The capacitor Cfb / Cin is the feedback coefficient of the overall circuit, which determines the magnitude of the closed-loop gain of the overall circuit.

[0041] The capacitors Cs1 and Cs2, the chopper modulation circuit CHRRL, and the transconductance amplifiers amp4 and amp5 form a ripple cancellation loop, ultimately generating a compensation current Icom that is V of amp1. OFFSET The resulting offset current I OFFSET Compensation is performed to ultimately eliminate ripple.

[0042] Designed based on Butterworth closed-loop response Figure 2 The pole location of the operational amplifier feedforward section is determined by the requirement for low noise in the main transconductance amplifier amp1. Therefore, amp1 is chosen as the second pole, and the first pole is determined by the second-stage transconductance amplifier amp2. Appropriate Miller capacitors Cm1, Cm21, and Cm22 are selected to ensure phase margin and reduce the output ripple in advance. Based on the requirement of 10 times closed-loop gain and 1MHz chopping frequency, the GBW of the circuit should be greater than 1MHz. Therefore, the transconductance of amp1 is designed to be 1.2ms, the transconductance of amp2 to be 60us, and the transconductance of amp3 to be 2.2ms. The size of capacitor Cm1 is 20pF, and the size of Cm21 and Cm22 is 10pF.

[0043] Ripple elimination loop such as Figure 3 As shown, the input terminal of the ripple circuit is at the output terminal of the main operational amplifier. The AC current signal at the output terminal is coupled through capacitors Cs1 and Cs2, and integrated into a voltage signal by an integrator formed by capacitors Cint1 and Cint2 surrounding transconductance amplifier amp4. Then, it is amplified into a compensation current Icom by transconductance amplifier amp5 to compensate for the offset current I caused by the offset voltage. OFFSET This achieves the effect of eliminating ripple caused by voltage misalignment.

[0044] Simulation results

[0045] Figure 4This demonstrates the different voltages at the high-voltage and low-voltage ends. The common-mode voltage set at the high-voltage end is 20V, and the peak-to-peak value of the input AC signal is 40mV. The isolation capacitor Cin isolates the common-mode voltage at the high-voltage end. The common-mode voltage set at the low-voltage end is clamped to 2.5V by resistors res1 and res2. However, due to the delay effect of RC, the low-voltage end signal will not be exactly the same as the high-voltage end signal. It can be clearly seen that capacitor Cin effectively prevents the common-mode voltage at the high-voltage end from damaging the low-voltage end circuit and couples the input AC signal to the low-voltage end. Figure 5 and Figure 6 The PSS simulations show the output waveforms with and without a ripple cancellation loop. During the simulation, a 10mV DC level was applied to the non-inverting input of the transconductance amplifier amp1 to simulate the offset voltage. Figure 5 It can be seen that the output waveform has very obvious ripple, with a ripple magnitude of 156mV. Figure 6 As can be seen from the comparison, the output waveform with the added ripple cancellation loop is... Figure 5 This resulted in a very significant improvement, with the ripple voltage dropping from 156mV to only 112uV. Figure 7 The PAC simulation shows a low-frequency gain of 20.05dB. The 0.5dB gain is due to the parasitic capacitance of the transconductance amplifier input transistor. The phase margin of 60deg will decrease on both the gain and phase curves. This is because the overall transfer function of the circuit changes after adding the ripple cancellation loop, which has the properties of a notch filter. Figure 8 The pnoise simulation shows that the equivalent input noise is 3.05nV / sqrt(Hz) at a frequency of 100Hz, so the overall circuit exhibits good noise performance. Figure 9 The algorithm used is Cadence's built-in FFT analysis algorithm, which shows a total harmonic distortion (THD) of -82.65 dB and an effective number of bits (ENOB) of 12.24 bits.

[0046] As can be seen from the above results, the chopper operational amplifier circuit of the present invention, which is applied to voltage isolation, has high linearity and low distortion while having voltage isolation effect.

[0047] The systems, devices, modules, or units described in the above embodiments can be implemented by computer chips or entities, or by products with certain functions. A typical implementation device is a computer. Specifically, a computer can be, for example, a personal computer, laptop computer, cellular phone, camera phone, smartphone, personal digital assistant, media player, navigation device, email device, game console, tablet computer, wearable device, or any combination of these devices.

[0048] It should also be noted that the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0049] The above embodiments should be understood as illustrative only and not as limiting the scope of protection of the present invention. After reading the description of the present invention, those skilled in the art can make various alterations or modifications to the present invention, and these equivalent changes and modifications also fall within the scope defined by the claims of the present invention.

Claims

1. A chopper operational amplifier circuit applied to voltage isolation, characterized by, Comprise: Transconductance amplifier amp1, amp2, amp3, amp4, amp5, chopper modulation circuit CHIN, CHOUT, CHFB, CHRRL, capacitor Cin1, Cin2, Cfb1, Cfb2, Cs1, Cs2, Cint1, Cint2, Cm1, Cm21a, Cm21b, Cm22a, Cm22b, resistor res1, res2, chopper modulation signal f chop Wherein the input end VIN is connected with the chopper modulation circuit CHIN, the chopper modulation circuit CHIN is connected with the capacitor Cin1 and the capacitor Cin2 respectively, the capacitor Cin1 is connected with the negative pole of the transconductance amplifier amp1, the capacitor Cin2 is connected with the positive pole of the transconductance amplifier amp1, the output end of the transconductance amplifier amp1 is connected with the chopper modulation circuit CHOUT, the chopper modulation circuit CHOUT is connected with the input end of the transconductance amplifier amp2, the output end of the transconductance amplifier amp2 is connected with the transconductance amplifier amp3, the capacitor Cm21a and the capacitor Cm22a are connected with the positive input end and the negative input end of the amp2 from the positive output end of the transconductance amplifier amp3 respectively, the capacitor Cm21b and the capacitor Cm22b are connected with the positive input end and the negative input end of the amp2 from the negative output end of the transconductance amplifier amp3 respectively, the capacitor Cm1 and the capacitor Cm2 are connected with the negative input end and the positive input end of the transconductance amplifier amp2 from the positive output end and the negative output end of the transconductance amplifier amp3 respectively, the output positive and negative ends of the transconductance amplifier amp3 are connected with the chopper modulation circuit CHFB and the capacitor Cfb1, Cfb2 in one way, the capacitor Cfb1 and the capacitor Cfb2 are connected with the capacitor Cin1 and the capacitor Cin2 respectively, and the other way is connected with the capacitor Cs1 and the capacitor Cs2 in turn, and then connected with the chopper modulation circuit CHRRL, the transconductance amplifier amp4, amp5, and then connected with the output end of the transconductance amplifier amp1, the capacitor Cint1 and the capacitor Cint2 are connected across the transconductance amplifier amp4.

2. The chopper operational amplifier circuit for voltage isolation according to claim 1, wherein The chopper modulation circuit Chin is used to modulate the analog input signal of the high voltage end into a voltage signal with a frequency of f chop ; The resistance res1, res2 and capacitor Cin1, Cin2 a high-pass filter, filter out the high voltage end of the DC signal, and play a role in bias resistance, to provide the appropriate static operating point for the transconductance amplifier amp1; The input of the transconductance amplifier amp1 comes from the capacitor Cin1, Cin2 from the high voltage end of the analog AC voltage signal coupled, and the input voltage signal into a current signal; The chopper modulation circuit CHOUT is used to up-convert the AC current signal output from the transconductance amplifier amp1 from a frequency f chop down-convert the analog signal frequency to the high voltage end, and to up-convert the offset voltage V OFFSET of the transconductance amplifier amp1 to a frequency of f chop ; The capacitor Cm1, Cm21, Cm22 around the transconductance amplifier amp2, amp3 form an integral circuit, the current signal from the amp1 output into a voltage signal in the output end, its output size Vout=Vin×(Cfb / Cin); The capacitor Cfb1 / Cin1, Cfb2 / Cin2 is the feedback coefficient of the overall circuit, determines the size of the overall circuit closed loop gain; The capacitances Cs1, Cs2, the chopper modulation circuit CHRRL, the trans-impedance amplifiers amp4, amp5 form a ripple cancellation loop, which finally generates a compensation current Icom with V OFFSET The generated offset current I OFFSET The compensation is performed, which finally plays a role in eliminating the ripple.

3. The chopper operational amplifier circuit for voltage isolation according to claim 1, wherein The isolation input capacitor Cin1, Cin2 will be isolated from the high voltage end and the low voltage end, play a role in protecting the low voltage end, the role of the chopping modulation circuit CHIN is to modulate the input AC signal into high frequency through the capacitor Cin1, Cin2 isolation of the high voltage end of the high common mode voltage on the low voltage end of the impact.

4. The chopper operational amplifier circuit for voltage isolation according to claim 1, wherein The overall structure of the circuit is the three-stage operational amplifier structure of the nested Miller compensation (NMC), the last stage is class-AB output, class-AB output can provide large dynamic current at low static current, enhance the driving ability.

5. The chopper operational amplifier circuit for voltage isolation according to claim 1, wherein The chopping modulation circuit CHIN and the chopping modulation circuit CHUOT respectively play the role of up-conversion and down-conversion, CHIN modulates the alternating current signal to the same frequency f chop The same high frequency, CHOUT modulates the current signal output from the transconductance amplifier amp1 to the same frequency as the input signal of the high voltage end, and modulates the V OFFSET 1 / f noise to high frequency, while playing the role of envelope detector, restoring the waveform of the signal; At the same time, the capacitors Cm1, Cm21, Cm22 form an integration circuit around the transconductance amplifiers amp2, amp3 to present the output current and voltage signal of amp1 at the output end, but due to the offset voltage of the transconductance amplifier and the residual voltage generated in the chopping modulation circuit due to the high chopping frequency, the output end will also present.

6. The chopper operational amplifier circuit for voltage isolation according to claim 2, wherein The input capacitors Cs1, Cs2 of the ripple elimination loop RRL will convert the output end's unbalanced AC current signal I OFFSET coupled to the input end of the chopping modulation circuit CHRRL, which will convert the coupled I OFFSET into a DC signal, and then through the integration circuit formed by the capacitors Cint1, Cint2 around the transconductance amplifier amp4 to be integrated into a voltage signal, and finally through the transconductance amplifier amp5 to convert the voltage signal output from amp4 into a compensation current signal I COM The unbalanced current I OFFSET is compensated, which plays a role in eliminating ripples.

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