Spectral Stitching for Wider-Band Vector Signal Analysis
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Solution Overview
Problem
Current methods for increasing instantaneous bandwidth in RF vector signal analyzers and generators face limitations due to the scalability issues of quadrature mixing and inaccuracies in time-interleaving techniques, while existing solutions either introduce errors or fail to preserve dynamic range.
Innovation Solution
The method of spectral stitching, which involves using multiple vector signal analyzers to process overlapping frequency bands, digitizing, interpolating, frequency-shifting, filtering, and adjusting gain and phase to combine the bands into a composite signal with unity frequency response, effectively increasing bandwidth without sacrificing dynamic range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If quadrature mixing is used to double bandwidth, then instantaneous bandwidth is increased, but DC leakage spur and image spur are created
Solution Approach 1:
The patent divides the frequency band into multiple sub-bands using bandpass filters, with each sub-band processed by a separate ADC. This segmentation approach avoids the DC leakage and image spur problems inherent in quadrature mixing by eliminating the mixing process entirely, while still achieving bandwidth extension through parallel processing of multiple frequency segments.
2Speed
If time-interleaving is used to increase sample rate, then instantaneous bandwidth is increased, but dynamic range is reduced due to timing inaccuracies and magnitude/phase differences
Solution Approach 1:
Each ADC is assigned to process a specific frequency sub-band with dedicated bandpass filtering, allowing each converter to operate optimally within its local frequency range. This local specialization maintains high dynamic range for each sub-band while the aggregate system achieves extended bandwidth, avoiding the timing and phase synchronization issues that plague time-interleaved systems.
3Speed
If multiple ADCs are used to achieve larger bandwidth, then instantaneous bandwidth is increased, but device complexity increases
Solution Approach 1:
The patent employs multiple identical ADC units, each performing the same function of digitizing its assigned sub-band. This universal approach allows the system to scale bandwidth by simply adding more of the same proven converter modules rather than requiring complex custom-designed high-speed converters, thereby managing device complexity through replication of standardized components.
Data Source
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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.