Vector Signal Generator Spectral Stitching for Wider Instantaneous Bandwidth
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Solution Overview
Problem
Current methods for increasing instantaneous bandwidth in vector signal generators and analyzers, such as time-interleaving and quadrature mixing, face limitations including inaccuracies, scalability issues, and image rejection problems, and are unable to achieve larger bandwidths without sacrificing dynamic range or introducing errors.
Innovation Solution
The spectral stitching method processes digital signals through multiple parallel processing paths, each handling a frequency band with a center frequency offset, which are phase-locked and time-synchronized, allowing for frequency-shifting, filtering, and gain/phase adjustments to combine the bands into an aggregate frequency band with continuous coverage, using digital half-band filters and vector signal generators.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If time-interleaving is used to increase bandwidth, then instantaneous bandwidth is improved, but measurement precision and reliability deteriorate due to time alignment inaccuracies and magnitude/phase differences between ADCs
Solution Approach 1:
The aggregate frequency band is divided into multiple frequency bands, each handled by a separate vector signal analyzer with its own ADC. Each analyzer processes a specific frequency band independently, avoiding the time alignment issues inherent in time-interleaving while collectively covering the full bandwidth through spectral stitching.
Solution Approach 2:
The invention transitions from time-domain interleaving to frequency-domain parallel processing. Instead of staggering ADC samples in time, the system uses multiple ADCs to simultaneously capture different frequency bands, then stitches the spectra together in the frequency domain to achieve extended bandwidth without compromising precision.
2Speed
If quadrature mixing is used to double bandwidth, then instantaneous bandwidth is improved, but image rejection problems and DC leakage spurs occur
Solution Approach 1:
The system segments the frequency spectrum into multiple bands and processes each band separately with dedicated vector signal analyzers. This avoids the image frequency problems of quadrature mixing by directly sampling each band without frequency translation, eliminating DC leakage and image spurs while achieving bandwidth extension through parallel spectral coverage.
3Speed
If ADC sample rate is increased to achieve larger bandwidth, then instantaneous bandwidth is improved, but device complexity and cost increase
Solution Approach 1:
The total bandwidth requirement is segmented across multiple vector signal analyzers, each handling a portion of the aggregate band. This allows the use of lower sample rate ADCs in each device compared to a single high-speed ADC, reducing the converter rate requirements and associated complexity while achieving the same total instantaneous bandwidth through parallel operation.
Data Source
AI summary
Embodiments are described of devices and methods for processing a signal using a plurality of vector signal generators (VSGs). A digital signal may be provided to a plurality of signal paths, each of which may process a respective frequency band of the signal, the respective frequency bands having regions of overlap. The gain and phase of each signal path may be adjusted such that continuity of phase and magnitude are preserved through the regions of overlap. The adjustment of gain and phase may be accomplished by a complex multiply with a complex calibration constant. The calibration constant may be determined for each signal path by comparing the gain and phase of one or more calibration tones generated within each region of overlap. Each signal path may comprise a VSG to convert the respective signal to an analog signal, which may be combined to obtain a composite signal.