Broadband Voltage Current Probe Calibration Using Intermediate Loads
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Broadband voltage/current (VI) probes experience significant measurement errors and reduced unit-to-unit repeatability, especially near open and short circuit stages, leading to inaccuracies in impedance measurements and performance degradation at high frequencies.
Innovation Solution
A calibration method involving the use of two known loads (Load 1 and Load 2) instead of traditional open and short circuits, allowing for the determination of open circuit (ZOC) and short circuit (ZSC) impedances, which are then used to calculate calibration coefficients, thereby reducing errors and enhancing accuracy across the Smith chart.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional open and short circuit calibration stages are used, then calibration can be performed, but measurement errors are significantly magnified near open and short locations on the Smith chart
Solution Approach 1:
The patent introduces intermediate calibration loads (e.g., 16 ohm and 300 ohm loads) that serve as mediators between the extreme open and short circuit conditions. These intermediate loads provide stable, well-defined impedance points that avoid the measurement errors associated with direct open/short calibration, while still enabling full Smith chart coverage through mathematical transformation of the calibration coefficients.
2Adaptability or versatility
If open and short circuit calibrations are performed, then calibration coefficients can be determined, but unit-to-unit repeatability degrades at high frequencies
Solution Approach 1:
The patent changes the calibration parameters from extreme conditions (open/short circuits) to intermediate, well-defined impedance values (e.g., 16 ohm and 300 ohm loads). This parameter change results in more stable calibration coefficients that maintain unit-to-unit repeatability at high frequencies while still providing comprehensive Smith chart coverage through the calibration transformation.
3Quantity of substance
If calibration equipment performs measurements into short and open load conditions, then calibration data can be obtained, but signal to noise ratio is poor and performance is distorted
Solution Approach 1:
The patent converts the harmful effect of poor signal-to-noise ratio in open/short conditions by avoiding those extreme conditions entirely. Instead, it uses intermediate loads that provide strong, clean signals with excellent signal-to-noise ratios, thereby eliminating measurement distortion while still obtaining all necessary calibration data through mathematical transformation.
Data Source
AI summary
A calibration method for performing open circuit and closed circuit calibrations of a voltage/current (VI) probe. In one implementation the method may involve inserting a VI probe into a circuit including a first known load (Load 1) and a applying a first signal to the circuit. A first raw impedance (ZRAW1) may be measured using the Load 1. The VI probe may then be inserted into the circuit along with a second known load (Load 2) in place of the Load 1, and a second signal may be applied to the circuit. A second raw impedance (ZRAW2) may then be measured using the Load 2. A fixed reference impedance (ZR50) may then be defined. The first and second raw impedances, and the fixed reference impedance, may then be used in determining an open circuit impedance (ZOC) and a short circuit impedance (ZSC). The ZOC and ZSC impedances may then be used to determine a plurality of calibration coefficients for the VI probe.