Heterodyne Phase Shift Measurement for Amplifier Error Cancellation
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Solution Overview
Problem
Existing methods for measuring phase shifts in periodically excited physical systems face challenges due to high excitation frequencies and low response intensities, which often require amplification, leading to additional phase shifts that complicate the measurement process.
Innovation Solution
A heterodyne phase shift measurement system that generates coherent excitation and local oscillator signals, mixes them with a physical system's response, and uses a computational element to adjust frequencies such that the difference frequency's sign changes, allowing for the subtraction and halving of phase shifts to isolate the system's phase shift from other components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If amplification is applied to increase response intensity for measurement, then the response signal becomes detectable, but additional phase shift is introduced that complicates the measurement
Solution Approach 1:
The patent applies preliminary anti-action by measuring the phase shift at two different frequency offsets (positive and negative) and then subtracting the measurements to cancel out the spurious phase shift introduced by amplification. This pre-compensates for the harmful effect before final calculation, allowing amplification to be used without compromising measurement accuracy.
Solution Approach 2:
The patent changes the frequency offset parameter from a single value to two symmetric values (±Δf). By varying this parameter and measuring at multiple points, the system can distinguish between the physical system's phase shift and the spurious phase shift from amplification, resolving the contradiction between needing amplification and maintaining measurement accuracy.
2Speed
If high excitation frequency is used to study the physical system, then the system's dynamic properties can be measured, but direct phase shift measurement becomes unfeasible
Solution Approach 1:
The patent introduces an intermediary local oscillator signal at frequency f_LO that mixes with the high-frequency response signal. This down-converts the high-frequency phase shift information to a lower intermediate frequency that can be measured directly, making high-frequency system characterization feasible without direct high-speed phase measurement equipment.
Solution Approach 2:
The patent replaces direct electrical phase measurement at high frequency with a heterodyne mixing process. Instead of directly measuring phase at the high excitation frequency, the system uses frequency mixing to translate the phase information to a measurable intermediate frequency, substituting a more practical measurement approach.
3Ease of operation
If heterodyne detection is used to measure phase shift at lower frequency, then measurement becomes feasible, but additional phase shift from circuit components must be distinguished from the physical system's phase shift
Solution Approach 1:
The patent uses periodic action by measuring at two symmetric frequency offsets (±Δf) and then subtracting the results. This periodic variation in measurement conditions allows the spurious phase shift from circuit components to be identified and eliminated, improving precision while maintaining the ease of heterodyne detection.
Solution Approach 2:
The patent implements a feedback-like approach by using the measurement at one frequency offset to correct the measurement at the other offset. The subtraction of the two measurements creates a self-correcting mechanism that eliminates the influence of circuit component phase shifts, ensuring accurate measurement of the physical system's phase shift.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach enables precise measurement of phase shifts independent of phase shifts introduced by circuit components, improving measurement accuracy by canceling out additional phase shifts caused by amplification and other system components.
Implementation Method 1
the response signal is, in turn, mixed by a mixer with a local oscillator signal, to produce an output signal
Data Source
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AI summary
In one embodiment, a frequency generator produces an excitation signal, a local oscillator signal, and a reference signal at a difference frequency of the excitation signal and local oscillator signal. The excitation signal is applied to a physical system to pro¬ duce a response signal, which is mixed with the local oscillator signal. A filter selects a difference frequency component. The frequencies of the excitation signal and/or local oscillator signal are varied, such that the magnitude of the difference frequency is con¬ stant, but a sign of the difference frequency changes from positive to negative. The phase shift of the difference frequency component, with respect to the reference signal, at each of the two signs of the difference frequency, is measured. The measured phase shift at the negative sign is subtracted from the measured phase shift at the positive sign, and the difference is divided in half, to produce a result.