Switched-Resistor Sensor Bridge for Low-Power Sensing
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Solution Overview
Problem
Conventional Wheatstone bridge configurations for sensor electronics face challenges in achieving low-voltage and low-power consumption characteristics, leading to high noise, nonlinearities, and increased power consumption, which are unsuitable for portable and wireless applications.
Innovation Solution
A switched-resistor sensor bridge (SRSB) that converts resistive variations into time or frequency signals, eliminating the need for high excitation voltages and amplification stages, and reducing current consumption to μAmps, while maintaining sensitivity and linearity comparable to Wheatstone bridges.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If Wheatstone bridge configuration is used with high excitation voltages and amplification stages to improve sensitivity, then sensitivity is improved, but power consumption increases and noise is introduced
Solution Approach 1:
The patent replaces the conventional voltage-based Wheatstone bridge measurement system with a frequency-based measurement system. The sensor resistance variations are converted to frequency variations through an oscillator circuit, eliminating the need for high-voltage excitation and analog amplification stages. This substitution of measurement domain (from voltage to frequency) resolves the contradiction by achieving high sensitivity through frequency counting while maintaining low power consumption at the sensor interface.
2Measurement precision
If Wheatstone bridge configuration is used with amplification stages to improve sensitivity, then sensitivity is improved, but noise and nonlinearities increase
Solution Approach 1:
The patent eliminates analog amplification stages by substituting the voltage measurement approach with a frequency measurement approach. The oscillator converts sensor resistance changes directly to frequency changes, which are then counted digitally. This avoids the noise and nonlinearities introduced by analog amplifiers while maintaining high sensitivity through precise frequency counting.
Solution Approach 2:
The oscillator circuit serves as an intermediary device that converts sensor resistance variations into frequency variations. This intermediary transformation allows the sensor signal to be measured in the frequency domain rather than the voltage domain, avoiding the need for noisy analog amplification while preserving sensitivity through the oscillator's frequency response to resistance changes.
3Measurement precision
If conventional Wheatstone bridge is used, then sensitivity can be improved with high excitation voltages, but the system cannot achieve low-voltage operation
Solution Approach 1:
The patent substitutes the high-voltage excitation requirement with a low-voltage oscillator-based frequency measurement system. The oscillator is driven by low voltage but produces a frequency output that is highly sensitive to sensor resistance changes. This allows the system to operate at low voltage levels while maintaining high sensitivity through frequency counting rather than voltage measurement.
4Measurement precision
If Wheatstone bridge configuration is used, then sensitivity can be enhanced, but device complexity increases due to amplification and filtering stages
Solution Approach 1:
The patent replaces the complex analog signal conditioning chain (amplifiers, filters, ADCs) with a simpler frequency-based measurement system. The oscillator directly converts resistance changes to frequency changes, and a simple digital counter measures the frequency. This substitution dramatically reduces circuit complexity while maintaining or improving sensitivity through the frequency domain measurement approach.
Data Source
AI summary
A sensing bridge includes first and second branches in parallel, the first branch including a first resistor in series with a first switch, the second branch including a second resistor in series with a second switch. Resistances of the resistors vary with a sensed physical variable. The branches switch between first and second phases, with the first switch closed and the second switch open during the first phase, and the first switch open and the second switch closed during the second phase. A reference block generates a control signal from the resistance of the variable resistors during the first and second phases. An oscillator generates an oscillating signal during the first and second phases from the variable sense current during the first and second phases. Processing circuitry determines a value of the sensed physical value from an algebraic combination of the oscillating signal during the first and second phases.