Impedance Calibration Using Frequency-Dependent Error Models
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Solution Overview
Problem
Conventional impedance measurement devices face challenges in accurate calibration, especially at low impedances and high frequencies, due to systematic errors and the lack of fully characterized impedance standards, leading to unreliable and non-traceable measurements.
Innovation Solution
A calibration procedure that uses low-value resistors and short standards to perform full impedance calibration directly at the device connectors, incorporating a multiplexer for automatic selection of calibration standards and accounting for frequency-dependent behavior, allowing for reliable and repeatable measurements across a wide range of impedances and frequencies.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional factory pre-calibration and short-compensation methods are used, then calibration is simple and quick, but measurement accuracy deteriorates at low impedances and high frequencies
Solution Approach 1:
The patent performs preliminary determination of frequency-dependent impedance characteristics of calibration standards before actual measurements. This preliminary characterization enables the system to compensate for systematic errors in advance, allowing accurate measurements at low impedances and high frequencies without requiring complex real-time calibration procedures.
Solution Approach 2:
The patent changes the approach from using fixed impedance standards to using standards with known frequency-dependent impedance characteristics. By incorporating the frequency dependence parameter into the calibration model, the system can accurately characterize systematic errors across the entire frequency range, resolving the contradiction between simple calibration and accurate measurement.
2Measurement precision
If fully characterized impedance standards are used, then absolute traceable calibration is achieved, but such standards are not available for low value resistors
Solution Approach 1:
The patent changes the requirements for calibration standards from needing full impedance characterization to only requiring known frequency-dependent impedance characteristics. This parameter relaxation enables the use of readily available low value resistors while still achieving absolute traceable calibration through the frequency-dependent error model.
Solution Approach 2:
The patent introduces an intermediary mathematical model that relates the partially known impedance characteristics of available standards to the full error characterization needed for accurate measurements. This intermediary model enables calibration accuracy equivalent to fully characterized standards while using readily available components.
3Ease of manufacture
If relative response calibration is performed, then calibration can be done with available standards, but traceable absolute results cannot be obtained
Solution Approach 1:
The patent transforms the calibration approach from relative response comparison to absolute error characterization by incorporating frequency-dependent impedance parameters. This enables the use of available standards while achieving traceable absolute results through the mathematical relationship established in the error model.
Data Source
AI summary
A method of calibrating an impedance measurement device for measuring DUT impedance includes performing short calibration measurements using a short calibration standard to obtain short raw data; performing first shunt calibration measurements using a first shunt calibration standard to obtain first raw data, the first shunt calibration standard having known first resistance and unknown first inductance; performing second shunt calibration measurements using a second shunt calibration standard to obtain second raw data, the second shunt calibration standard having known second resistance and unknown second inductance; determining first and second complex impedances of the first and second shunt calibration standards by calculating the first and second inductances using the short, first and second raw data applied to a specific error model; and determining general error coefficients for an error model using the first and second complex impedances and the first and second raw data applied to a one-port calibration procedure.