Impedance Analyzer Calibration Using Switching Circuitry
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Solution Overview
Problem
Conventional microcontroller-based impedance analyzers face accuracy issues at higher frequencies due to non-ideal operational amplifier performance, which affects the consistency of impedance measurements.
Innovation Solution
A microcontroller-based impedance analyzer that uses a square wave stimulus and additional calibration structures to account for non-idealities, employing a switching circuit to selectively couple calibration impedances and the device under test, and processor circuitry to sample and analyze signals to provide accurate impedance measurements across a wide range of frequencies.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional operational amplifiers are used in microcontroller-based impedance analyzers, then cost is reduced and integration is simplified, but measurement accuracy deteriorates at higher frequencies due to non-ideal op amp performance
Solution Approach 1:
The patent applies preliminary calibration actions before actual measurements. Two calibration impedances (ZCAL1 and ZCAL2) are measured first to determine correction factors that compensate for op amp non-idealities. These pre-determined factors are then used to correct subsequent DUT measurements, allowing accurate high-frequency measurements with low-cost op amps.
Solution Approach 2:
The patent changes the measurement parameters by introducing frequency-dependent correction factors derived from calibration measurements. Instead of relying on the op amp to maintain ideal performance across frequencies, the system measures the actual frequency response through calibration and applies mathematical corrections to compensate for deviations, thereby maintaining measurement accuracy across a wide frequency range.
2Measurement precision
If additional calibration structures and switching circuitry are added to compensate for op amp non-idealities, then measurement accuracy improves, but device complexity increases
Solution Approach 1:
The switching circuitry serves multiple functions: it selects between DUT and calibration impedances, enables calibration mode operation, and facilitates automatic correction factor determination. This multi-functionality reduces the need for separate dedicated calibration circuits, thereby limiting the increase in overall device complexity while achieving improved measurement accuracy.
Solution Approach 2:
The system performs self-calibration by automatically measuring the known calibration impedances, computing the correction factors, and applying them to subsequent measurements. This self-service approach eliminates the need for manual calibration procedures and external calibration equipment, reducing operational complexity despite the added circuit elements.
Data Source
AI summary
A circuit for measuring an impedance of a device under test (DUT). The circuit includes: (i) circuitry for generating a stimulus wave at a stimulus frequency; (ii) an amplifier circuit coupled to the DUT to present a response signal from the DUT in response to the stimulus wave; (iii) switching circuitry for selectively coupling, between the stimulus wave and an input to the amplifier, either the DUT, a first calibration impedance, or a second calibration impedance. With the switching functionality, calibrations are performed so to provide a measure of impedance of the DUT in response to the plural calibrations.