Adaptive Interpolation for Reducing Signal Spurs in Oscilloscopes
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Real-time oscilloscopes employing bandwidth extension schemes face challenges due to hardware and software filter imperfections, leading to signal crossover and aliasing issues that limit the use of maximum theoretical bandwidth, causing spurs and reducing the accuracy of frequency representation.
Innovation Solution
The implementation of adaptive upsampling using FIR taps derived from the impulse responses of both low and high-frequency channels during calibration, which sets software imperfections to match hardware imperfections, effectively canceling out spurs and improving frequency accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If maximum theoretical bandwidth is used by setting fS=fLO, then bandwidth extension is achieved, but hardware and software filter imperfections cause signal crossover and aliasing leading to spurs and reduced frequency accuracy
Solution Approach 1:
The patent converts the harmful effects of hardware filter imperfections and software interpolation errors into beneficial canceling spurs. By deliberately designing the software interpolation filter to create spurs at the same frequency and amplitude as the hardware-induced spurs, but with opposite phase, the two error sources cancel each other out. This transforms what would normally be detrimental artifacts into a mechanism for improving measurement precision while maintaining maximum bandwidth extension.
2Speed
If narrow cross-over regions are used between adjacent bands, then maximum available bandwidth is utilized, but large group delay variations and filter imperfections cause signal degradation
Solution Approach 1:
The patent accepts the inevitable signal degradation from narrow cross-over regions and hardware filter imperfections, then converts these harmful effects into beneficial outcomes through deliberate spur generation and cancellation. The software filter is designed to generate spurs that match the frequency and amplitude characteristics of the hardware-induced degradation, allowing cancellation of the negative effects while maintaining high bandwidth utilization.
Solution Approach 2:
The patent changes the parameters of the software interpolation filter to deliberately create spurs at specific frequencies and amplitudes that match the hardware imperfections. By adjusting the filter coefficients and design parameters, the software-induced spurs are tuned to cancel the hardware-induced spurs, transforming fixed hardware limitations into adjustable parameters that can be compensated in real-time.
3Device complexity
If finite-length linear digital filters are used for upsampling, then computational complexity is reduced, but the filters cannot leave the original frequency 100% intact and create 0% spur when frequency is nearly equal to Nyquist
Solution Approach 1:
The patent accepts that finite-length linear digital filters inherently create spurs when upsampling near-Nyquist frequencies, rather than attempting to eliminate them. Instead, the filter design deliberately generates spurs that match the characteristics of hardware-induced spurs, enabling cancellation. This approach maintains computational simplicity while improving frequency representation accuracy through the cancellation mechanism.
Data Source
AI summary
A method and apparatus for acquiring an analog signal. The method of the invention comprising the steps of acquiring a first portion of the analog signal by a first channel, the first portion of the analog signal spanning a first bandwidth range, and acquiring a second portion of the analog signal by a second channel, the second portion of the analog signal spanning a second bandwidth range adjacent the first bandwidth range. At least one spur in the signal acquired by the first channel corresponding to a portion of the analog signal that should have properly been acquired by the second channel is offset with an opposite spur in the second channel.