Spectral Stitching Using Pilot Tone Phase Correction
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Solution Overview
Problem
Existing measurement systems with limited bandwidth struggle to accurately measure periodically modulated signals and their output, particularly in characterizing phase-sensitive characteristics like error-vector-magnitude (EVM), due to spectral regrowth and phase shifts during downconversion.
Innovation Solution
The method involves sequential downconversion of signal portions using varying local oscillator frequencies, with a pilot tone to measure and adjust phases, allowing phase-adjusted measurements across the entire spectrum, even when the measurement device's bandwidth is less than the signal's bandwidth, by stitching together overlapping portions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a receiver with limited bandwidth is used to measure signals, then the measurement device is more practical and cost-effective, but the complete signal spectrum cannot be measured
Solution Approach 1:
The patent divides the wideband signal spectrum into multiple narrower frequency segments that can be sequentially measured by a limited-bandwidth receiver. Each segment is downconverted to a different intermediate frequency (IF) range using multiple LO frequencies, allowing the receiver to capture the entire spectrum through sequential measurements rather than requiring simultaneous wideband capture.
2Quantity of substance
If sequential downconversion with multiple LO frequencies is performed to measure wideband signals, then complete spectrum measurement is achieved, but phase measurement accuracy deteriorates due to phase shifts
Solution Approach 1:
The patent introduces a pilot tone as an intermediary reference signal that is processed through the same downconversion path as the actual signal. By measuring the phase of the pilot tone at each LO frequency and using it to compensate for phase shifts in the signal measurements, the system eliminates the harmful phase effects while maintaining accurate phase measurement capability.
3Measurement precision
If the measurement bandwidth is increased to cover the entire signal spectrum, then complete signal characterization is possible, but the measurement device becomes more complex and expensive
Solution Approach 1:
The patent employs periodic sequential measurement cycles where the receiver systematically tunes through multiple LO frequencies to capture different segments of the signal spectrum. Each cycle measures a specific frequency segment, and by repeating this process across all required LO frequencies, the complete spectrum is characterized over time rather than requiring simultaneous wideband measurement capability.
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 accurate measurement of amplitude and phase across the entire signal spectrum, including phase-sensitive characteristics, even when the measurement device's bandwidth is limited, by correcting for phase shifts and reconstructing the full signal spectrum.
Implementation Method 1
converting portions of the output signal spectrum down to an intermediate frequency (IF) signal in a first IF channel by mixing the output signal with a local oscillator (LO) signal
Implementation Method 2
mixing the pilot tone with the LO signal to produce a converted pilot tone in a second IF channel
Data Source
AI summary
A system and method sequentially measure the amplitude and phase of an output signal of a device under test in each of two or more frequency ranges which together span the output signal spectrum, using a local oscillator (LO) signal whose frequency changes for each measurement. The measured phase of the output signal is adjusted for at least one of the frequency ranges to account for a change of phase in the LO signal from measurement of one frequency range to another frequency range, including applying to the measured phase a phase offset determined by measuring the phase of a pilot tone using the LO signal before and after the frequency of the LO signal changes from measurement of one frequency range to another. The phase-adjusted measurements of the output signal in the two or more frequency ranges are stitched together to determine the amplitude and phase of the output signal across the output signal spectrum.