Chopped wave operational amplifier for reducing switch artifacts by using ORL
By introducing an ORL module into the chopper op amp to generate and feedback the regulation voltage, the problem of introducing switching artifacts when the chopper op amp is eliminated is solved, and a lower offset voltage and a smaller noise spectrum is achieved, which improves the accuracy of precision instruments.
Patent Information
- Application Number
- CN202411788941.6
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-12-06
- Publication Date
- 2025-03-18
AI Technical Summary
Chopper op amps introduce switching artifacts when eliminating offsets, resulting in an increase in noise spectrum and affecting the performance of precision instruments.
A chopping operational amplifier including a chopping module, a two-stage amplification module and an ORL module is designed. The ORL module generates a regulation voltage according to the demodulation signal and feeds it back to the first-stage amplification module to reduce the equivalent offset voltage and switching artifacts at the input.
It effectively reduces the amplitude of switching artifacts, improves the accuracy of precision instruments, and achieves lower offset voltage and smaller noise spectrum.
Smart Images
Figure CN119652262A_ABST
Abstract
Description
Technical Field
[0001] The invention belongs to the field of semiconductor analog integrated circuit design, and in particular relates to a chopper operational amplifier which uses ORL to reduce switching artifacts. Background Art
[0002] Zero-drift precision operational amplifiers are designed for small differential input voltage and high output precision. They not only have low input offset voltage, but also high common mode rejection ratio (CMRR), high power supply rejection ratio (PSRR), high open loop gain and low drift over a wide temperature and time range. These features make them very suitable for applications such as low-side current detection and sensor interface, especially with very small differential signals. Common methods for reducing offset of zero-drift precision operational amplifiers include auto-zeroing and chopping.
[0003] Although the internal working principles of auto-zero amplifiers and chopper amplifiers are different, their goals are the same, which is to minimize offset and offset-related errors. However, both methods will introduce some disadvantages when eliminating offsets. For example, although chopping is suitable for amplifiers that work continuously and does not increase the baseband noise density, its modulation principle will modulate the offset voltage to the chopping frequency band to cause ripples, and there will be glitches at the time of switch jumps on the ripples, which is the switching artifact.
[0004] In a chopper, the clock is coupled to the differential input pins through the parasitic capacitance of the chopping switches. When the clock changes state, charges are injected into the differential input pins. These charge injections are converted into output voltage glitches through the finite input source impedance. The size and shape of the glitches depend on the number and matching of the input source impedances and the charge injections at the differential input pins. These output ripples and glitches introduce switching artifacts that contribute to the noise spectrum at the chopping frequency and its multiple integer frequencies. For smaller offset and noise, ways should be found to reduce these switching artifacts. Summary of the invention
[0005] In view of the above-mentioned technical problems, the purpose of the present invention is to propose a chopper operational amplifier that uses ORL to reduce switching artifacts, which is used for preamplification of precision instruments and meters to reduce switching artifacts.
[0006] The technical solution of the present invention is: In a first aspect, the present invention provides a chopper operational amplifier, comprising a chopper module, a two-stage amplification module and an ORL module; The chopper module includes a chopper 1 and a chopper 2; The two-stage amplification module includes a first-stage amplification module and an output-stage amplification module; The input end of the chopper 1 is used to obtain an input signal, and the output end is connected to the input end of the first-stage amplification module, and is used to generate a modulation signal according to the input signal and transmit it to the first-stage amplification module; The output end of the first-stage amplification module is connected to the input end of the second chopper, and is used to generate a first output signal according to the modulation signal and transmit it to the second chopper; The output end of the second chopper is connected to the input end of the output stage amplification module, and is used to generate a demodulation signal according to the first output signal and transmit it to the output stage amplification module; The input end of the ORL module is connected to the output end of the chopper 2, and the output end is connected to the first-stage amplification module, for generating a regulation voltage according to the demodulated signal and feeding the regulation voltage back to the first-stage amplification module.
[0007] The technical effect achieved by the above setting is as follows: After the input signal is modulated by chopper 1, a modulated signal is obtained. The modulated signal passes through the first-stage amplification module to obtain the first output signal OUT1. After OUT1 is demodulated by chopper 2, a demodulated signal is obtained. The demodulated signal passes through the output-stage amplification module to obtain the output signal. The ORL module obtains the adjustment voltage Vint according to the demodulated signal, and Vint is fed back to the first-stage amplification module, thereby reducing the equivalent offset voltage at the input end and reducing the switching artifacts on the offset voltage.
[0008] The role of the ORL module is to suppress the chopper ripple from the input stage. Switching artifacts are an important part of the chopper ripple. The chopper ripple from the input stage is the main source of output ripple. There is no noise aliasing. At the chopping and its harmonics, the ORL acts like a narrow-band notch filter. The width of the ORL notch is determined by the unity gain bandwidth, and the position of the notch is determined by the chopping frequency. Compared with the switched capacitor notch filter or auto-zero, a relatively low chopping frequency can be used, so it is low offset and has no stability problems.
[0009] Further, the ORL module includes a capacitor and an offset reduction loop; One end of the capacitor is connected to the output end of the second chopper, and the other end is connected to the offset reduction loop, and is used to integrate the switching artifacts on the demodulated signal to obtain a square wave and transmit it to the offset reduction loop; The output end of the offset reduction loop is connected to the first-stage amplification module, and is used to generate a regulation voltage Vint according to the square wave, and feed the regulation voltage Vint back to the first-stage amplification module.
[0010] The technical effect achieved by the above setting is as follows: capacitor C integrates the switching artifacts on the demodulated signal to obtain a square wave, which passes through the ORL (offset reduction loop) to obtain a voltage Vint, which is fed back to the first-stage amplifier module to reduce the equivalent offset voltage at the input end while reducing the switching artifacts on the offset voltage.
[0011] Furthermore, an input end of the chopper is connected to an input signal, and an output end of the chopper is connected to a first-stage amplification module, which is used to modulate the input signal to the same frequency as the clock signal to obtain a modulated signal; The second input end of the chopper is connected to the output end of the first stage amplification module, and the output end is connected to the input end of the output stage amplification module and connected to a capacitor, so as to generate a demodulation signal and demodulate the frequency of the first output signal OUT1 from the same frequency as the clock signal to the same frequency as the input signal.
[0012] The two-stage amplification module includes a first-stage amplification module and an output-stage amplification module, which are used to amplify the input signal; The input end of the first-stage amplification module is connected to the input end of the first chopper, and the output end is connected to the input end of the second chopper, and is used to amplify the modulated signal.
[0013] The input end of the output stage amplification module is connected to the output end of the chopper 2, and the output end is connected to the output signal end, for amplifying the demodulated signal; The input end of the ORL module is connected to the capacitor C, and the output end of the ORL module is connected to the first-stage amplifier module, which is used to convert the square wave into a regulation voltage Vint and feed it back to the first-stage amplifier module. This is a negative feedback, which reduces the ripple and switching artifacts in the demodulated signal.
[0014] The first-stage amplifier module is a folded cascode (common term) structure. The access point of Vint in the first-stage amplifier module is the folding point of the folded cascode (common term) structure, which is equivalent to the amplitude of the ripple and switching artifacts generated at the input end, and has the opposite direction. It is negative feedback, which plays a role in suppressing ripples and switching artifacts.
[0015] Furthermore, the chopper operational amplifier also includes a reference for providing a DC voltage bias for each other module to ensure a DC operating point of each other module.
[0016] Furthermore, the chopper operational amplifier also includes an oscillator for generating a clock signal as a switching signal for chopper 1 and chopper 2.
[0017] Furthermore, the chopper operational amplifier is implemented based on CMOS technology.
[0018] The technical effect achieved by the above settings is: based on CMOS technology, it is further expanded on the basis of pure chopping technology and an ORL (offset reduction loop) is added to allow the circuit to achieve lower offset voltage and smaller switching artifacts.
[0019] Furthermore, the chopper operational amplifier further includes a GM amplifier and a second capacitor arranged between the offset reduction loop and the first-stage amplification module; The input end of the GM amplifier is connected to the output end of the offset reduction loop and is also connected to the positive end of the second capacitor, and the output end of the GM amplifier is connected to the first-stage amplification module; The positive end of the second capacitor is connected to the input end of the GM amplifier and the output end of the offset reduction loop, and the negative end of the second capacitor is grounded.
[0020] The technical effect achieved by the above settings: The purpose of adding the GM amplifier and the second capacitor between the ORL (offset reduction loop) and the first-stage amplifier module is to reduce the noise voltage caused by the introduction of the ORL (offset reduction loop) module, so that the 1 / f noise (1 / f noise, also known as flicker noise, is a type of noise whose spectrum density is inversely proportional to the frequency) of the ORL (offset reduction loop) will not affect the input reference noise of the entire circuit. This is because the ORL (offset reduction loop) modulates its own noise to the chopping frequency and then filters it out through the second capacitor. f is the corner frequency (also known as the cutoff frequency) of the MOS tube (metal oxide semiconductor field effect transistor), which refers to the frequency at which the gain of the MOS tube (metal oxide semiconductor field effect transistor) begins to decrease in high-frequency applications. This frequency is an important parameter for evaluating the performance of the MOS tube in high-frequency circuits.
[0021] Reduce the noise voltage introduced by the ORL (offset reduction loop) block so that the 1 / f noise of the ORL (offset reduction loop) does not affect the input referred noise of the entire circuit. This is because the ORL (offset reduction loop) modulates its own noise to the chopping frequency and then filters it out through the second capacitor. As long as the second capacitor is chosen large enough to filter out the modulated 1 / f noise, the amplifier will still maintain its very low 1 / f noise corner.
[0022] As long as the second capacitor is large enough to filter out the modulated 1 / f noise, the amplifier will still maintain its extremely low 1 / f noise corner. The preferred value range of the second capacitor is 1 pF to 1.5 pF, and 1.25 pF is selected in Embodiment 2.
[0023] Further, the offset reduction loop includes a chopper three, a cascode fully differential amplifier and a third capacitor; The input end of the chopper three is connected to a capacitor, and the output end is connected to the input end of the common-source common-gate fully differential amplifier, and is used to modulate a square wave, so that the square wave and the input signal modulated by the first chopper are converted into a modulated signal; The output end of the common-source and common-gate fully differential amplifier serves as the output end of the offset reduction loop; the third capacitor is connected to both ends of the common-source and common-gate fully differential amplifier, and the common-source and common-gate fully differential amplifier and the third capacitor together constitute an integrator, thereby converting the square wave output from the capacitor into a triangular wave whose amplitude is positively correlated with the switching artifact amplitude on the demodulated signal.
[0024] In a second aspect, the present invention provides a preamplifier circuit, comprising the chopper operational amplifier as described in the first aspect.
[0025] Compared with the prior art, the present invention has the following beneficial effects: 1. The present invention designs an ORL (offset reduction loop) module to reduce the switching artifacts on the offset voltage, thereby improving the accuracy.
[0026] 2. The present invention proposes an operational amplifier design method that uses ORL to reduce switching artifacts. This method is based on CMOS technology. According to this method, an average input offset voltage (Vos) of 0.515μV, an input bias current of less than 10pA, and a rail-to-rail input and output voltage range can be obtained. Compared with a pure chopper operational amplifier that does not use ORL, the amplitude of the switching artifact can be reduced to 1 / 4.
[0027] 3. The present invention further expands on the pure chopper amplifier to achieve lower switching artifacts and smaller equivalent input offset voltage. The circuit can utilize the existing common source and common gate amplifier architecture and chopper to achieve low power consumption and low input noise. BRIEF DESCRIPTION OF THE DRAWINGS
[0028] Figure 1 It is a principle block diagram of a chopper operational amplifier that uses ORL to reduce switching artifacts in the present invention; Figure 2 It is a principle block diagram of a preferred technical solution of a chopper operational amplifier that uses ORL to reduce switching artifacts in the present invention; Figure 3 This is a screenshot of the simulation results of the input equivalent offset voltage of the chopper operational amplifier that uses ORL to reduce switching artifacts according to the present invention.
[0029] Figure 4 The schematic diagram of the offset reduction loop of the chopper operational amplifier using ORL to reduce switching artifacts according to the present invention is shown in FIG.
[0030] In the figure: C, capacitor; C2, second capacitor; Cint, third capacitor; Vint, adjustment voltage; Gm1, GM amplifier; OUT1, first output signal. DETAILED DESCRIPTION
[0031] The present invention will be further described below in conjunction with the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present invention, and cannot be used to limit the protection scope of the present invention.
[0032] In the description of this embodiment, it should be noted that if the terms "center", "up", "down", "left", "right", "vertical", "horizontal", "inside", "outside", etc. appear, the orientation or position relationship indicated is based on the orientation or position relationship shown in the accompanying drawings, which is only for the convenience of describing this embodiment and simplifying the description, and does not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on this embodiment. Example 1
[0033] like Figure 1 As shown in FIG. 1 , the low offset operational amplifier for reducing switching artifacts by using ORL is composed of a reference, an oscillator, a chopping module, a two-stage amplification module, and an ORL module.
[0034] The oscillator generates clock signals fCP and fCN as switching signals of chopper 1 and chopper 2; The chopper module includes a chopper 1 and a chopper 2; An input end of the chopper is connected to the input signal, and an output end of the chopper is connected to the first stage amplifier, which is used to modulate the input signal and modulate the signal to the same frequency as the clock signal to obtain a modulated signal; The second input end of the chopper is connected to the output end of the first stage amplification module, and the output end is connected to the input end of the output amplification stage and the capacitor C, which is used to generate a demodulation signal to demodulate the frequency of OUT1 from the same frequency as the clock signal to the same frequency as the input signal.
[0035] The two-stage amplification module includes a first-stage amplification module and an output-stage amplification module, which are used to amplify the input signal; The input end of the first-stage amplification module is connected to the input end of the first chopper, and the output end is connected to the input end of the second chopper, and is used to amplify the modulated signal.
[0036] The input end of the output amplifier module is connected to the output end of the second chopper, and the output end is connected to the output signal end, so as to amplify the demodulated signal; The input end of the ORL module is connected to the capacitor C, and the output end of the ORL module is connected to the first-stage amplifier module, which is used to convert the square wave into a regulation voltage Vint and feed it back to the first-stage amplifier module. This is a negative feedback, which reduces the ripple and switching artifacts in the demodulated signal.
[0037] The input signal is modulated by the chopper 1 to obtain a modulated signal, the modulated signal is passed through the first stage amplification module to obtain a first output signal OUT1, the first output signal OUT1 is demodulated by the chopper 2 to obtain a demodulated signal, and the demodulated signal is passed through the output stage amplification module to obtain an output signal; Capacitor C integrates the switching artifacts on the demodulated signal to obtain a square wave, which passes through the ORL (offset reduction loop) to obtain the regulated voltage Vint. The regulated voltage Vint is fed back to the first-stage amplifier module to reduce the equivalent offset voltage at the input end and the switching artifact on the offset voltage.
[0038] The reference provides DC voltage bias for each module to ensure the DC operating point of each module.
[0039] The oscillator generates clock signals fCP and fCN, which serve as switching signals for chopper 1 and chopper 2. Based on CMOS technology, it is further extended on the basis of pure chopping technology. Adding an ORL (offset reduction loop) allows the circuit to achieve lower offset voltage and smaller switching artifacts.
[0040] Figure 1 The sampling capacitor C in the circuit samples the offset voltage at the input of the output stage amplifier module (that is, the output of chopper 2), feeds it back to the input after passing through the ORL loop, and reduces the equivalent average offset voltage and switching artifacts at the input.
[0041] The role of the ORL module is to suppress the chopper ripple from the input stage. Switching artifacts are an important part of the chopper ripple. The chopper ripple from the input stage is the main source of output ripple. There is no noise aliasing. At the chopping and its harmonics, the ORL acts like a narrow-band notch filter. The width of the ORL notch is determined by the unity gain bandwidth, and the position of the notch is determined by the chopping frequency. Compared with the switched capacitor notch filter or auto-zero, a relatively low chopping frequency can be used, so it is low offset and has no stability problems.
[0042] Specifically, Figure 4 As shown, the structure of the offset reduction loop includes a chopper 3, a cascode fully differential amplifier, and a third capacitor Cint.
[0043] Chopper 3 is used to modulate the square wave so that it and the input signal modulated by chopper 1 are both modulated signals. The common-source common-gate fully differential amplifier and the third capacitor Cint together form an integrator to convert the square wave from capacitor C into a triangular wave whose amplitude is positively correlated with the amplitude of the switching artifact on the demodulated signal. Example 2
[0044] like Figure 2 As shown, based on Example 1, this embodiment adds a GM amplifier Gm1 and a second capacitor between the ORL (offset reduction loop) and the first-stage amplification module, the input end of the GM amplifier Gm1 is connected to the output end of the ORL (offset reduction loop), and is also connected to the positive end of the second capacitor, and the output end of the GM amplifier Gm1 is connected to the first-stage amplification module. The positive end of the second capacitor is connected to the input end of the GM amplifier Gm1, and is also connected to the output end of the ORL (offset reduction loop), and the negative end of the second capacitor is grounded GND8.
[0045] The purpose of adding the GM amplifier Gm1 and the second capacitor between the ORL (offset reduction loop) and the first-stage amplifier module is to reduce the noise voltage caused by the introduction of the ORL (offset reduction loop) module, so that the 1 / f noise of the ORL (offset reduction loop) will not affect the input reference noise of the entire circuit. This is because the ORL (offset reduction loop) will modulate its own noise to the chopping frequency and then filter it out through the second capacitor. As long as a large enough second capacitor is selected to filter out the modulated 1 / f noise, the amplifier will still maintain its extremely low 1 / f noise angle. The preferred value range of the second capacitor is 1pF to 1.5pF. In this embodiment, 1.25pF is selected as the capacitance value of the second capacitor.
[0046] like Figure 3 As shown, the present invention proposes an operational amplifier design method for reducing switching artifacts using ORL, which is implemented based on CMOS technology. According to this method, an average input offset voltage (Vos) of 0.515μV, an input bias current of less than 10pA, and a rail-to-rail input and output voltage range can be obtained. Compared with a pure chopper operational amplifier without ORL, the amplitude of the switching artifact can be reduced to 1 / 4.
[0047] The present invention further expands on the pure chopper amplifier to achieve lower switching artifacts and smaller equivalent input end offset voltage. The circuit can utilize the existing common source and common gate amplifier architecture and chopper to achieve low power consumption, low input noise and other characteristics. Example 3
[0048] This embodiment provides a preamplifier circuit, including the chopper operational amplifier as described in Embodiment 1 or Embodiment 2.
[0049] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features, and in the description of the present invention, "plurality" means two or more, unless otherwise clearly and specifically defined.
[0050] In the present invention, unless otherwise clearly specified and limited, the terms "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.
[0051] In the present invention, unless otherwise clearly specified and limited, a first feature being "above" or "below" a second feature may include that the first and second features are in direct contact, or may include that the first and second features are not in direct contact but are in contact through another feature between them. Moreover, a first feature being "above", "above" and "above" a second feature includes that the first feature is directly above and obliquely above the second feature, or simply indicates that the first feature is higher in level than the second feature. A first feature being "below", "below" and "below" a second feature includes that the first feature is directly above and obliquely above the second feature, or simply indicates that the first feature is lower in level than the second feature.
[0052] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "examples", "specific examples", or "some examples" means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner.
[0053] Although the embodiments of the present invention have been shown and described above, it is to be understood that the above embodiments are exemplary and are not to be construed as limitations on the present invention. A person skilled in the art may change, modify, replace and modify the above embodiments within the scope of the present invention without departing from the principles and intent of the present invention.
Claims
1. A chopper operational amplifier, characterized in that: It includes a chopper module, a two-stage amplifier module and an ORL module; The chopper module includes a chopper 1 and a chopper 2; The two-stage amplification module includes a first-stage amplification module and an output-stage amplification module; The input end of the chopper 1 is used to obtain an input signal, and the output end is connected to the input end of the first-stage amplification module, and is used to generate a modulation signal according to the input signal and transmit it to the first-stage amplification module; The output end of the first-stage amplification module is connected to the input end of the second chopper, and is used to generate a first output signal according to the modulation signal and transmit it to the second chopper; The output end of the second chopper is connected to the input end of the output stage amplification module, and is used to generate a demodulation signal according to the first output signal and transmit it to the output stage amplification module; The input end of the ORL module is connected to the output end of the chopper 2, and the output end is connected to the first-stage amplification module, for generating a regulation voltage according to the demodulated signal and feeding the regulation voltage back to the first-stage amplification module.
2. The chopper operational amplifier according to claim 1, characterized in that: The ORL module includes a capacitor and an offset reduction loop; One end of the capacitor is connected to the output end of the second chopper, and the other end is connected to the offset reduction loop, and is used to integrate the switching artifacts on the demodulated signal to obtain a square wave and transmit it to the offset reduction loop; The output end of the offset reduction loop is connected to the first-stage amplification module, and is used to generate a regulation voltage Vint according to the square wave, and feed the regulation voltage Vint back to the first-stage amplification module.
3. The chopper operational amplifier according to claim 2, characterized in that: An input end of the chopper is connected to an input signal, and an output end of the chopper is connected to a first-stage amplification module, which is used to modulate the input signal to the same frequency as the clock signal to obtain a modulated signal; The input end of the second chopper is connected to the output end of the first-stage amplification module, and the output end of the second chopper is connected to the input end of the output-stage amplification module and is connected to a capacitor, so as to generate a demodulation signal, and demodulate the frequency of the first output signal from the same frequency as the clock signal to the same frequency as the input signal; The two-stage amplification module includes a first-stage amplification module and an output-stage amplification module, which are used to amplify the input signal; The input end of the first-stage amplification module is connected to the input end of the chopper 1, and the output end is connected to the input end of the chopper 2, for amplifying the modulated signal; The input end of the output stage amplification module is connected to the output end of the chopper 2, and the output end is connected to the output signal end, for amplifying the demodulated signal; The input end of the ORL module is connected to the capacitor, and the output end of the ORL module is connected to the first-stage amplifier module, which is used to convert the square wave into a regulation voltage Vint and feed it back to the first-stage amplifier module, thereby reducing the ripple and switching artifacts in the demodulated signal.
4. The chopper operational amplifier according to claim 2, characterized in that: The chopper operational amplifier also includes a reference for providing a DC voltage bias for each of the other modules to ensure the DC operating point of each of the other modules.
5. The chopper operational amplifier according to claim 2, characterized in that: The chopper operational amplifier further comprises an oscillator for generating a clock signal as a switching signal for the first chopper and the second chopper.
6. The chopper operational amplifier according to claim 1, characterized in that: The chopper operational amplifier is implemented based on CMOS technology.
7. The chopper operational amplifier according to claim 2, characterized in that: The chopper operational amplifier also includes a GM amplifier and a second capacitor provided between the offset reduction loop and the first-stage amplification module; The input end of the GM amplifier is connected to the output end of the offset reduction loop and is also connected to the positive end of the second capacitor, and the output end of the GM amplifier is connected to the first-stage amplification module; The positive end of the second capacitor is connected to the input end of the GM amplifier and the output end of the offset reduction loop, and the negative end of the second capacitor is grounded.
8. The chopper operational amplifier according to claim 2, characterized in that: The offset reduction loop includes a chopper three, a cascode fully differential amplifier and a third capacitor; The input end of the chopper three is connected to a capacitor, and the output end is connected to the input end of the common-source common-gate fully differential amplifier, for modulating a square wave; The output end of the common-source and common-gate fully differential amplifier serves as the output end of the offset reduction loop; the third capacitor is connected to both ends of the common-source and common-gate fully differential amplifier, and the common-source and common-gate fully differential amplifier and the third capacitor constitute an integrator, thereby converting the square wave output from the capacitor into a triangular wave whose amplitude is positively correlated with the switching artifact amplitude on the demodulated signal.
9. A preamplifier circuit, characterized in that: It comprises a chopper operational amplifier as described in any one of claims 1 to 8.