Digital Auto Balance Bridge for AC Impedance Measurement
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Solution Overview
Problem
Analog-based auto balance bridge techniques for precision AC impedance measurements are limited in accurately determining impedance due to issues with stray capacitances and require complex additional circuitry for variable loop gain bandwidth, leading to calibration and noise challenges.
Innovation Solution
A digital AC impedance measurement system utilizing digital controllers, D/A converters, and A/D converters to apply and monitor voltages, maintaining a virtual ground at one terminal, thereby eliminating stray capacitance effects and allowing adjustable loop gain bandwidth through digital parameter adjustments.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If analog-based auto balance bridge technique is used, then measurement precision is improved by eliminating stray capacitance effects, but device complexity increases due to requirement for additional circuitry for variable loop gain bandwidth
Solution Approach 1:
The patent replaces the analog feedback loop with a digital feedback loop. The digital controller performs the feedback function through software algorithms rather than analog circuitry, eliminating the need for additional analog components while maintaining the virtual ground effect and measurement precision.
Solution Approach 2:
The patent changes the implementation domain from analog to digital, allowing loop gain bandwidth to be adjusted through digital parameter modification rather than physical circuit changes. This enables variable loop gain bandwidth through software control, reducing hardware complexity.
2Measurement precision
If analog feedback loop is used to zero out voltage at second terminal, then measurement precision is improved by eliminating stray capacitances, but reliability deteriorates due to calibration and noise challenges
Solution Approach 1:
The patent substitutes the analog feedback mechanism with a digital one. The digital controller processes signals through ADC converters and applies feedback through DAC converters, eliminating analog noise and calibration issues while maintaining the virtual ground effect for precise measurements.
Solution Approach 2:
The patent creates a digital copy of the feedback function rather than using the physical analog feedback path. The digital controller replicates the feedback control algorithm in software, providing a cleaner signal path free from analog noise and calibration drift.
3Device complexity
If digital controller with D/A and A/D converters is used, then device complexity is reduced by eliminating additional circuitry, but measurement precision may be affected by conversion accuracy
Solution Approach 1:
The patent replaces complex analog circuitry with digital conversion components. The digital controller with ADC and DAC converters provides precise control and measurement through digital signal processing, achieving both simplified circuitry and maintained precision through high-resolution conversions.
Data Source
AI summary
An AC impedance measurement system is used for measuring the impedance of a DUT. A measured voltage is applied to a first DUT terminal by a first digital to analog converter, the voltage appearing at the second terminal of the DUT is monitored through an analog to digital converter and forced by a second digital to analog converter to a desired negligible value, and a digital controller determines the impedance of the DUT from the measured voltage and the current necessary to force the voltage appearing at the second terminal to the desired negligible value.