Local Oscillator Phase Shift Calibration for RF Measurement
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Solution Overview
Problem
Existing frequency-converting measurement techniques fail to accurately characterize devices under test when the local oscillator is stepped in frequency, as they struggle to account for phase shifts caused by the local oscillator frequency synthesis and transmission line effects, requiring complex external reconverting mixers customized for each device.
Innovation Solution
A method that involves measuring RF to IF group delays at multiple local oscillator frequencies, assembling these into a group delay array, integrating to create a phase array, comparing calculated and measured phases, and applying an error correction model to account for local oscillator phase shifts, allowing for characterization without an external reconverting mixer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the local oscillator is stepped in frequency during measurement, then the measurement can cover a wider frequency range, but phase shifts occur at the junction of the device under test due to frequency synthesis and transmission line effects
Solution Approach 1:
The patent applies preliminary action by performing a calibration measurement before the actual device characterization. During calibration, the same measurement setup is used to determine the phase shift behavior of the local oscillator path. This pre-determined phase shift information is then used to correct subsequent measurements, allowing the system to maintain measurement precision even when the local oscillator is stepped in frequency.
2Measurement precision
If an external reconverting mixer is used to solve the phase shift problem, then measurement accuracy is improved, but device complexity and customization requirements increase
Solution Approach 1:
The patent uses copying by creating a virtual model of the phase shift behavior through calibration measurements. Instead of adding physical compensation components like external mixers, the system measures and stores the phase shift characteristics of the local oscillator path, then applies this copied information as a correction factor during device characterization, thereby eliminating the need for additional hardware.
Solution Approach 2:
The patent introduces an intermediary element in the form of a calibration-based phase shift correction model. This intermediary serves as a mathematical bridge between the measured quantities and the desired device characteristics, allowing the system to account for local oscillator phase shifts without requiring direct physical modification of the measurement setup or addition of compensating hardware.
3Measurement precision
If an external reconverting mixer is customized for each device under test, then measurement accuracy is maintained, but ease of operation and measurement efficiency decrease
Solution Approach 1:
The patent applies universality by creating a general calibration procedure that can be used with any frequency-converting device. The calibration process characterizes the measurement setup's phase shift behavior once, and this characterization can then be applied to multiple different devices under test without requiring customization. This makes the measurement system universal and easy to operate across different devices.
Data Source
AI summary
A method is provided that determines a relative phase change of a local oscillator signal. A method of determining a relative phase change of a RF signal is also provided. Generally, the methods described ensure that the effect of a swept local oscillator frequency on the measurements can be identified, particularly quantified. Hence, the effect can be considered in the error correction model applied later such that the measurement equipment can be calibrated appropriately.