Chopper Amplifier Sampling to Cut Filter Size and Power
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Solution Overview
Problem
Existing chopper-based stabilization methods for instrumentation amplifiers require bulky low-pass filters and additional power-consuming components, such as buffers or programmable gain amplifiers, to achieve high-precision signal processing, which increases size and power consumption.
Innovation Solution
The method involves modulating the analog signal with a chopping signal, amplifying, low-pass filtering to include harmonics, and performing correlated double sampling to eliminate DC offset and low-frequency noise, allowing for relaxed filtering requirements and reduced power consumption by sub-sampling at the chopping frequency, thereby eliminating the need for bulky filters and additional amplifiers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a low-pass filter with low cut-off frequency is used to attenuate DC offset and noise, then the filtering performance is improved, but the filter size increases significantly
Solution Approach 1:
The patent changes the operating parameters by using sub-sampling at the chopping frequency to shift the signal spectrum, allowing a high-pass filter to replace the traditional low-pass filter. This parameter change in filtering approach enables compact filter design while maintaining effective noise and offset attenuation.
Solution Approach 2:
The patent substitutes the traditional mechanical low-pass filter system with a digital signal processing approach using sub-sampling and correlated double sampling. This replacement eliminates the need for bulky analog low-pass filters while achieving equivalent or superior filtering performance through digital correlation techniques.
2Measurement precision
If buffers or programmable gain amplifiers are added to improve signal precision before ADC, then the measurement precision is improved, but the power consumption increases
Solution Approach 1:
The patent extracts and eliminates unnecessary intermediate buffering and amplification stages by implementing correlated double sampling directly on the sub-sampled signal. This removal of redundant components reduces power consumption while maintaining signal precision through the correlation-based noise rejection technique.
Solution Approach 2:
The system performs self-service by using the chopping frequency itself as the sub-sampling rate, allowing the signal processing to be self-sufficient without requiring additional powered components. The correlated double sampling operation leverages the existing chopping signal to achieve noise rejection without external amplification.
3Measurement precision
If correlated double sampling is performed by subtracting samples at chopping frequency, then DC offset and low-frequency noise are eliminated, but the signal processing complexity increases
Solution Approach 1:
The patent employs periodic action by sub-sampling at the chopping frequency and performing correlated double sampling on periodic samples. This periodic sampling approach simplifies the processing complexity by leveraging the regular timing structure of the chopping signal, making the correlation operation straightforward and efficient.
Solution Approach 2:
The patent applies preliminary action by performing sub-sampling at the chopping frequency before the correlated double sampling operation. This preliminary step organizes the signal into regularly spaced samples that are ready for correlation, reducing the overall processing complexity compared to continuous sampling and filtering approaches.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach improves gain accuracy, reduces noise components, and decreases overall power consumption while enabling compact filter designs, facilitating more efficient analog-to-digital conversion.
Implementation Method 1
the input signal may be first multiplied by a chopping signal, then may be amplified and may be multiplied again by a similar switching function
Implementation Method 2
the DC offset may be converted into an HF component at the output and may be fully attenuated by the low-pass filter (LPF)
Implementation Method 3
performing correlated double sampling operation by subtracting the samples at the chopping frequency. The subtraction may eliminate the input-referred amplifier DC offset and/or low-frequency noise components
Data Source
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AI summary
A method (100) for processing an analog signal is provided. The method comprises the steps of modulating (101) the analog signal using a chopping signal with a chopping frequency fchop to generate a modulated signal, amplifying (102) the modulated signal to generate an amplified signal, low-pass filtering (103) the amplified signal to generate a filtered signal comprising at least one harmonic of the modulated signal, and sub-sampling (104) the filtered signal and performing correlated double sampling operation by subtracting the samples at the chopping frequency.