Open Offset Cancellation in Impedance Measurement
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Solution Overview
Problem
Modem-type auto-balancing bridge impedance measurement systems suffer from DC offset errors that affect measurement accuracy, known as open offset, due to the conversion of DC offsets to AC, leading to inaccuracies in impedance values.
Innovation Solution
The method involves applying two or more measurement signals with different phases relative to a local signal to the device under test, measuring the impedance with each signal, and using arithmetic calculations to eliminate the open offset effect, thereby deriving a more accurate impedance value.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a modem-type current-to-voltage converter is used to respond to a broad frequency range, then the frequency response capability is improved, but DC offset errors occur in the phase sensitive detector and integrator which are converted to AC by the vector generator, producing errors in impedance measurement values
Solution Approach 1:
The invention changes the parameter of measurement signal phase by applying two or more measurement signals with different phases (e.g., 0° and 180°) relative to the local signal. By measuring impedance at different phases and combining the results through arithmetic operations, the DC offset error is eliminated while maintaining broad frequency response capability through the modem-type converter
Solution Approach 2:
The invention converts the harmful DC offset error into a beneficial measurement technique. By intentionally applying measurement signals at different phases and using arithmetic combination of the measurements, the previously harmful offset effect is transformed into a solvable mathematical problem that yields more accurate impedance values
Data Source
AI summary
A method for finding the impedance of a device under test using an impedance measuring apparatus having a modem-type auto-balancing bridge, two or more measurement signals, each of which has a different phase with respect to the reference signals supplied to the modem inside said auto-balancing bridge, are applied to a device under test; the impedance of this device under test is measured when each of the measurement signals is applied to the device under test; and the impedance of this device under test is found using the above-mentioned phase and the impedance measurement value of each of these measurements.