Low-IF Receiver Distortion Waveform Generator for Interference Suppression
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Solution Overview
Problem
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, especially in scenarios with amplitude modulated or bursty signals, and these issues are not adequately addressed by existing compensation techniques.
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 scaled to be subtracted from the signal of interest, using a complex scaling factor to reduce interference, thereby mitigating the effects of second-order and third-order intermodulation products.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If the intermediate frequency is reduced to enable earlier digital conversion and fewer analog components, then receiver integration and cost-effectiveness are improved, but susceptibility to strong-signal interference and varying DC offsets increases
Solution Approach 1:
The patent applies preliminary action by estimating the distortion waveform before it corrupts the desired signal. A distortion waveform generator creates an estimate of the intermodulation products based on the received signal and known non-linear characteristics of the downconverter. This estimated distortion is then subtracted from the downconverted signal to prevent the interference from degrading the desired signal, rather than attempting to remove it after corruption occurs.
Solution Approach 2:
The patent uses copying by creating a replica of the distortion waveform through the distortion waveform generator. This generator produces a copy of what the distortion signal will look like based on the received signal characteristics and modeled non-linear response. This copied distortion estimate is then used to cancel the actual distortion by subtraction, effectively using a synthetic copy to eliminate the real interference.
2Adaptability or versatility
If the antenna filter bandwidth is increased to admit more signals, then receiver versatility is improved, but intermodulation products from unwanted signals increase
Solution Approach 1:
The patent converts the harmful effect of strong interfering signals into a beneficial process. The distortion waveform generator uses the received signal containing the interfering signals to create an estimate of the distortion they will produce. By modeling the non-linear response and generating this distortion estimate, the system transforms the potential harm into useful information that can be subtracted to recover the desired signal.
3Measurement precision
If DC offset compensation techniques are applied to homodyne receivers, then constant DC offset is reduced, but varying DC offset from amplitude modulated or bursty signals remains
Solution Approach 1:
The patent applies dynamics by making the distortion compensation adaptive to changing signal conditions. Rather than using a fixed DC offset compensation value, the distortion waveform generator continuously estimates the distortion based on the current received signal and the modeled non-linear characteristics. This dynamic estimation allows the system to track and compensate for varying DC offsets caused by amplitude modulated or bursty interfering signals, adjusting the compensation in real-time as signal conditions change.
Data Source
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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 (160) 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.