Variable Impedance Sensing With Offset-Compensated Matching
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Solution Overview
Problem
Conventional variable impedance sense (VIS) circuits face accuracy limitations due to input offset voltages, which increase errors as supply voltage decreases, and fail to differentiate between positive and negative offsets, leading to unacceptably inaccurate impedance matching.
Innovation Solution
The proposed VIS circuit includes an offset detection mechanism that detects and compensates for inherent input offsets by modifying the digital code values based on the polarity of the offset, using a counter circuit to adjust the impedance settings accordingly, thereby reducing worst-case errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional VIS circuits are used for impedance matching, then the circuit structure is simple, but the measurement precision deteriorates due to input offset voltages
Solution Approach 1:
The patent applies preliminary action by detecting and storing the offset voltage value before performing the main impedance measurement. The offset detection is performed in advance during an initialization phase, and the stored offset value is then used to compensate for errors in subsequent measurements. This allows the system to eliminate systematic errors without adding complexity to the core measurement process.
Solution Approach 2:
The patent changes the measurement parameter by introducing offset compensation through digital code adjustment. Instead of directly measuring impedance, the system measures the offset voltage, converts it to a digital code, and uses this code to adjust subsequent impedance measurements. This parameter transformation enables accurate compensation while maintaining circuit simplicity.
2Measurement precision
If offset compensation is implemented in VIS circuits, then the measurement precision improves, but the device complexity increases due to additional circuit components
Solution Approach 1:
The patent achieves multi-functionality by using the same comparator and ADC circuitry for both offset detection and impedance measurement. The comparator serves dual purposes: first for detecting offset voltage, then for measuring impedance. This universal use of existing components provides offset compensation functionality without requiring additional dedicated hardware, thus avoiding increased device complexity.
Solution Approach 2:
The patent uses copying by creating a duplicate measurement path where the offset detection process mirrors the impedance measurement process. The same circuit topology and measurement methodology are used for both functions, allowing the system to leverage the existing measurement infrastructure for offset compensation without adding complex new circuitry.
3Use of energy by moving object
If supply voltage is reduced to save power, then the use of energy decreases, but the measurement precision deteriorates due to increased offset voltage impact
Solution Approach 1:
The patent implements feedback by continuously monitoring the offset voltage and using this information to adjust the impedance measurement in real-time. The offset detection creates a feedback loop where the measured offset is used to compensate for errors in subsequent measurements. This feedback mechanism maintains measurement precision even when supply voltage is reduced, as the system adaptively corrects for the increased offset impact.
Solution Approach 2:
The patent combines multiple measurement techniques into a composite approach: it integrates offset voltage detection, digital code conversion, and impedance measurement into a unified system. This composite methodology allows the system to simultaneously achieve low power consumption and high measurement precision by leveraging the strengths of each component technique.
Data Source
AI summary
A variable impedance sense (VIS) circuit (600) can detect and store an input offset value inherent in a sensing loop (620 and/or 622). According to a detected input offset polarity, a resulting impedance matching binary code can be adjusted to compensate for error that can be introduced by the input offset. The binary code can also be adjusted to compensate for additional error that can be introduced by dropping a least significant bit (LSB) of the code to reduce noise effects caused by the switching of the LSB.