Low-IF Receiver Distortion Cancellation for Strong-Signal Interference
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Solution Overview
Problem
Radio receivers, particularly homodyne and low-IF receivers, are susceptible to interference from strong interfering signals due to non-linear distortion, which causes varying DC offsets and intermodulation products that are difficult to compensate using existing methods.
Innovation Solution
The implementation of a distortion waveform generator that approximates the non-linear response characteristics of the downconverter circuit, allowing for the estimation and filtering of distortion waveforms, which are then sampled and subtracted from the signal of interest using a scaling factor to reduce interference, effectively addressing both square-law and cubic term non-linearities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If the number of tuned circuits is reduced to minimize circuitry, then device integration and cost are improved, but susceptibility to strong interfering signals worsens
Solution Approach 1:
The patent creates a copy of the interfering signal path by generating a distortion waveform that replicates the non-linear distortion effects. This copied distortion waveform is then used to cancel the actual interference through subtraction, allowing the receiver to compensate for strong signal interference without requiring additional tuned circuits.
Solution Approach 2:
The patent converts the harmful non-linear distortion effects into a useful cancellation mechanism. By modeling and generating the distortion waveform that causes interference, the system can then subtract this modeled distortion from the received signal, transforming the harmful non-linearity into a beneficial cancellation tool.
2Reliability
If DC offset compensation methods are used to compensate for varying DC offsets, then signal quality is improved, but the complexity of compensation increases
Solution Approach 1:
The patent employs feedback by continuously monitoring the received signal and adjusting the distortion waveform generation to match the actual interference conditions. The distortion waveform generator adapts to varying DC offsets and interference patterns, providing dynamic compensation without requiring complex manual adjustment mechanisms.
Solution Approach 2:
The system performs self-compensation by automatically generating and subtracting distortion waveforms based on the received signal characteristics. The distortion waveform generator operates autonomously to model and cancel interference, reducing the need for external compensation mechanisms and simplifying the overall system.
3Object-affected harmful factors
If second-order intermodulation products are suppressed using balanced circuit structures, then interference from strong signals is reduced, but cubic term interference remains
Solution Approach 1:
The patent addresses different orders of non-linearity by changing the parameters of the distortion waveform generator to model both second-order (square-law) and third-order (cubic) distortion terms. This allows the system to compensate for multiple types of interference simultaneously by adjusting the distortion model parameters to match the actual interference characteristics.
Data Source
AI summary
Circuits and methods are disclosed for compensating for received signal distortion caused by non-linearities in the receiver circuitry. An exemplary receiver circuit includes a distortion waveform generator configured to approximate one or more non-linear response characteristics of a downconverter circuit used to downconvert the received radio frequency signal. The estimated distortion waveform thus produced is filtered, using a filter or filters substantially similar to those used for filtering an intermediate frequency signal that includes the desired signal and non-linear distortion products caused by strong interfering signals. The filtered estimated distortion waveform and the intermediate frequency are sampled, to obtain a sampled distortion signal and a sampled signal of interest. The sampled distortion signal is scaled, and subtracted from the sampled signal of interest to obtain reduced-interference signal samples. In some embodiments, the scaling factor is determined by correlating the sampled signal of interest with the sampled distortion signal.