Comb Signal Phase Calibration Using Pilot Tone Across Limited Bandwidth
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Solution Overview
Problem
Existing methods struggle to accurately measure phase relationships between comb teeth of a comb signal using a receiver with a bandwidth less than the total bandwidth of the comb signal, particularly for phase-sensitive characteristics like error-vector-magnitude (EVM) in devices under test (DUTs).
Innovation Solution
A method involving a pilot tone and local oscillator (LO) signal is used to sequentially convert selected comb teeth to an intermediate frequency (IF) channel, allowing for phase measurement and calibration, with phase adjustments applied to ensure accurate phase differences are ascertained and applied to measurements of DUT signals, even when the receiver's bandwidth is insufficient to capture the entire signal spectrum.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a receiver with limited bandwidth is used to measure comb signal phases, then device complexity is reduced, but measurement precision deteriorates because the receiver cannot capture the entire comb signal spectrum
Solution Approach 1:
The comb signal spectrum is divided into multiple segments, each fitting within the receiver's bandwidth. The local oscillator frequency is sequentially adjusted to bring different comb teeth into the receiver's passband, allowing complete spectrum measurement through multiple sequential measurements that are later combined
Solution Approach 2:
A pilot tone is introduced as an intermediary reference signal that mixes with the local oscillator to produce a converted pilot tone. By measuring phase differences of this intermediary signal across different LO frequencies, the system establishes reference phase relationships that enable accurate measurement of the actual comb signal phases
2Adaptability or versatility
If the local oscillator frequency is changed to measure different comb teeth, then the measurement bandwidth coverage is improved, but phase measurement accuracy deteriorates due to LO phase instability between frequency changes
Solution Approach 1:
The system continuously monitors the phase of the converted pilot tone as the local oscillator frequency changes. This feedback information about LO phase drift is used to apply real-time phase corrections to the comb tooth phase measurements, compensating for LO instability and maintaining measurement accuracy across frequency transitions
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 and characterization of phase relationships and phase-sensitive characteristics across the entire bandwidth of comb signals and DUT outputs, overcoming the limitations of receivers with limited bandwidth.
Implementation Method 1
sequentially converting the selected comb teeth to a first intermediate frequency (IF) signal in a first IF channel by mixing the comb 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 phases of selected comb teeth of a comb signal using a local oscillator (LO) signal whose frequency and phase are changed for each sequential measurement, and adjust the measured phases to account for the change of phase in the LO signal from measurement of one selected comb tooth to the next to ascertain reference phase differences between the selected comb teeth. The measured phases of the selected comb teeth are adjusted by applying a phase offset determined from a first phase and a second phase of a pilot tone which are measured using the LO signal, respectively, before and after the frequency and phase of the LO signal change from measurement of one comb tooth to the next. The frequency of the pilot tone is maintained to be substantially the same when measuring the first phase and the second phase of the pilot tone.