Chopper-Stabilized Wheatstone Bridge Readout With Relaxed Low-Pass Filtering
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Solution Overview
Problem
Conventional Wheatstone bridge sensor readout channels face challenges with noise in the biasing signal, requiring bulky low-pass filters and additional power consumption due to chopper stabilization, which complicates precision and increases size constraints.
Innovation Solution
A sensor readout system that includes a first and second chopper to modulate the biasing and sensing signals, respectively, with a chopping frequency, followed by amplification, low-pass filtering with a cutoff frequency of at least 3×fchop, and correlated double sampling to eliminate noise components, allowing for relaxed low-pass filtration and reduced power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If chopper stabilization is implemented in the readout channel for both the instrumentation amplifier and the ADC, then the input DC offset and low-frequency noise are reduced, but the device complexity and power consumption increase
Solution Approach 1:
The patent combines the chopper stabilization functions for both the instrumentation amplifier and ADC into a single shared chopper circuit. This merging approach reduces the overall device complexity and component count while maintaining the noise reduction benefits for both stages, directly addressing the contradiction between measurement precision improvement and device complexity increase
Solution Approach 2:
The shared chopper circuit serves multiple functions: it performs stabilization for the instrumentation amplifier, stabilization for the ADC, and signal modulation for both stages. This multi-functionality reduces the total number of separate stabilization circuits needed, thereby reducing device complexity while maintaining measurement precision
2Measurement precision
If a low-cut-off frequency low-pass filter is used after the instrumentation amplifier, then the filtered signal quality is improved, but the filter size and power consumption increase
Solution Approach 1:
The patent changes the operating parameters of the low-pass filter by setting its cut-off frequency to at least 3 times the chopping frequency (fcut-off ≥ 3 × fchop). This parameter change allows the filter to achieve adequate signal quality without requiring a excessively low cut-off frequency, thereby reducing the filter size and associated power consumption while maintaining acceptable filtered signal quality
Solution Approach 2:
The patent applies preliminary chopper stabilization before the low-pass filter to reduce low-frequency noise and DC offset. This preliminary anti-action reduces the burden on the subsequent low-pass filter, allowing it to operate with a higher cut-off frequency and smaller size while still achieving the desired signal quality
3Measurement precision
If buffers or programmable gain amplifiers are added in front of the ADC, then the signal conditioning is improved, but the overall power consumption increases
Solution Approach 1:
The patent extracts and removes unnecessary buffers and programmable gain amplifiers from the readout channel by relying on the chopper stabilization and optimized low-pass filter design. This elimination of redundant components reduces power consumption while maintaining adequate signal conditioning through the essential chopper and filter stages
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 stabilizes the instrumentation amplifier, reduces noise, and improves gain accuracy while minimizing the need for bulky filters and buffers, leading to a more compact and power-efficient sensor readout channel.
Implementation Method 1
a first chopper configured to modulate the biasing signal using a chopping signal with a chopping frequency fchop to generate a modulated biasing signal
Implementation Method 2
a second chopper configured to modulate the sensing signal using the chopping signal with the chopping frequency fchop to generate a modulated sensing signal
Implementation Method 3
a low-pass filter configured to filter the amplified signal with a cutoff frequency of at least 3×fchop to generate a filtered signal
Implementation Method 4
a Wheatstone bridge circuit comprising resistive branches, at least one of the resistive branches comprises an impedance-based sensor, the Wheatstone bridge circuit being configured to receive the modulated biasing signal and to generate a sensing signal based on the modulated biasing signal
Data Source
Figure 1
Figure 2
Figure 3A~3B
AI summary
A sensor readout system (100) is provided. The sensor readout system (100) comprises a signal generator (101) configured to generate a biasing signal (102), a first chopper (103) configured to modulate the biasing signal (102) using a chopping signal (117) with a chopping frequency fchop to generate a modulated biasing signal (104) . It also comprises a Wheatstone bridge circuit (105) comprising four resistive branches (R1, R2, R3, R4), at least one of the four resistive branches comprises an impedance-based sensor (Rs1, Rs2, Rs3). The Wheatstone bridge circuit (105) is configured to receive the modulated biasing signal (104) and to generate a sensing signal (106) based on the modulated biasing signal (104). A second chopper (107) is configured to modulate the sensing signal (106) using the chopping signal (117) with the chopping frequency fchop to generate a modulated sensing signal (108) .