Chopper Amplifier Circuit for Offset and 1/f Noise Suppression
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Solution Overview
Problem
Designing high gain DC amplifiers that effectively address input offset voltage and 1/f noise is challenging, especially for small input signals, as these unwanted signal components can significantly affect the output, and traditional methods like output filtering can be difficult to implement, particularly in solid-state or integrated circuit implementations.
Innovation Solution
A chopper amplifier system that modulates the input signal into an AC signal, uses a high-pass or band-pass amplification stage to attenuate lower frequency components, and then de-modulates it back to DC, reducing the need for complex output filtering by shifting unwanted signals out of the desired frequency range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a chopper amplifier system modulates the input signal into an AC signal and uses a high-pass or band-pass amplification stage, then the amplification of small signals is improved while the amplification of offset and 1/f noise is minimized, but the device complexity increases due to the modulation and demodulation stages
Solution Approach 1:
The patent applies periodic chopping action by modulating the input signal with a square wave chopper signal at frequency fchop. This periodic modulation shifts the DC and low-frequency signal components to the chopper frequency and its harmonics, enabling the amplification stage to operate at higher frequencies where 1/f noise and offset voltage are significantly reduced. The periodic nature of this modulation is fundamental to the chopper amplifier's ability to separate desired signal from unwanted low-frequency components.
Solution Approach 2:
The patent changes the frequency parameter of the signal by modulating it from DC/low-frequency to the chopper frequency range. This parameter transformation allows the signal to be processed in a frequency range where the amplifier's noise characteristics are superior. The modulation process effectively transforms the signal from a static DC level to a dynamic AC signal at a higher frequency, exploiting the amplifier's frequency-dependent noise behavior.
2Measurement precision
If traditional output filtering is used to remove unwanted signals in DC amplifiers, then the offset voltage and 1/f noise are reduced, but the filter design becomes difficult to implement, particularly in solid state or integrated circuit implementations
Solution Approach 1:
The patent performs preliminary filtering action by using a high-pass or band-pass amplification stage before the output stage. This preliminary frequency-based filtering removes or attenuates low-frequency unwanted components (offset voltage and 1/f noise) before they reach the output. By performing this filtering action early in the signal path rather than relying solely on a complex output filter, the design simplifies the requirements for the final output filter and makes the overall system more manufacturable in integrated circuits.
3Power
If high gain is used to amplify small input signals to desired output level, then the output signal strength is improved, but the unwanted signal components from offset voltage and 1/f noise are also significantly amplified
Solution Approach 1:
The patent extracts the unwanted offset voltage and 1/f noise components from the signal path by modulating the signal to a frequency range where these components are naturally attenuated. The chopper modulation effectively separates the desired signal from the harmful low-frequency components, allowing high gain amplification to be applied selectively to the modulated signal while the offset and noise remain at their original low-frequency positions where they can be filtered out.
Data Source
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AI summary
A chopper amplifier and method of operation are described. The chopper amplifier comprises a first chopper arranged to modulate an input signal using a first chopper signal having a chopper frequency. An amplification stage has an input arranged to receive the chopped signal and an output, and supplies an amplified signal at the output. An output chopper is arranged to integrate the amplified signal using a second chopper signal having the chopper frequency to generate an amplified output signal. The amplification stage is further configured to filter the chopped signal to attenuate signal components having frequencies lower than the chopper frequency.