Chopper-Stabilized Wheatstone Bridge Readout for Low-Noise Sensing
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Solution Overview
Problem
Conventional Wheatstone bridge sensor readout channels suffer from noise interference due to biasing signal noise and input-referred amplifier DC offset, leading to performance degradation and increased power consumption, particularly in high-precision applications.
Innovation Solution
A sensor readout system utilizing chopper stabilization and correlated double sampling to modulate and filter signals at the chopping frequency, reducing noise components to the baseband while up-converting the useful signal, 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 IA and the ADC, then the input DC offset and low-frequency input noise are reduced, but the low-pass filter requires a low cut-off frequency which increases the silicon area
Solution Approach 1:
The patent applies periodic chopping action to modulate the biasing signal at a chopping frequency, which periodically switches the signal between two paths. This periodic modulation shifts the noise spectrum away from DC, allowing the low-pass filter to use a higher cut-off frequency while still effectively reducing low-frequency noise and DC offset, thereby reducing the required filter area.
Solution Approach 2:
The patent changes the frequency parameter of the biasing signal by modulating it with a chopping signal. This frequency transformation allows the noise components to be shifted to different frequency ranges, enabling the use of a less stringent low-pass filter with higher cut-off frequency, thus reducing the filter's silicon area while maintaining noise reduction effectiveness.
2Measurement precision
If a low-pass filter with low cut-off frequency is used to attenuate DC offset, then the DC offset is fully attenuated, but additional power consumption is required for buffers or programmable gain amplifiers in front of the ADC
Solution Approach 1:
By applying periodic chopping modulation to the biasing signal before it reaches the Wheatstone bridge, the patent shifts the DC offset and low-frequency noise to the chopping frequency and its harmonics. This allows the system to use a higher cut-off frequency low-pass filter that requires no additional buffers or PGAs, thereby reducing power consumption while maintaining effective DC offset attenuation.
Solution Approach 2:
The patent extracts the DC offset and low-frequency noise components from the baseband by modulating them to the chopping frequency band. This separation allows the useful signal to be processed with a simpler, lower-power filter configuration while the noise components are naturally rejected by the filtering and subsequent demodulation process.
3Device complexity
If the biasing signal noise is not addressed, then the readout channel can be simpler, but the noise in the biasing signal degrades the sensor measurement performance
Solution Approach 1:
The patent converts the harmful noise in the biasing signal into a beneficial effect by modulating the biasing signal with a chopping signal. This modulation shifts the noise spectrum away from DC, and the subsequent low-pass filtering and demodulation process naturally rejects the noise components while recovering the useful sensor signal, thereby improving measurement performance without significantly increasing system complexity.
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
The system effectively eliminates noise components and improves gain accuracy, enabling compact filter designs and reduced power consumption while maintaining signal integrity.
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 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
Implementation Method 3
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 4
a low-pass filter configured to filter the amplified signal with a cutoff frequency of at least 3×fchop (e.g., a cutoff frequency of 3.5×fchop) to generate a filtered signal
Data Source
AI summary
Example embodiments relate to sensor readout systems and sensor readout methods. One example sensor readout system includes a signal generator configured to generate a biasing signal. The sensor readout system also includes a first chopper configured to modulate the biasing signal using a chopping signal with a chopping frequency fchop to generate a modulated biasing signal. Additionally, the sensor readout system includes a Wheatstone bridge circuit that includes resistive branches. At least one of the resistive branches includes an impedance-based sensor. The Wheatstone bridge circuit is configured to receive the modulated biasing signal and to generate a sensing signal based on the modulated biasing signal. Further, the sensor readout system includes a second chopper configured to modulate the sensing signal using the chopping signal with the chopping frequency fchop to generate a modulated sensing signal.