Chopper Circuitry for Intermodulation Distortion Avoidance
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Solution Overview
Problem
Mobile communications devices face challenges in effectively handling intermodulation distortion in receive signals, particularly in translating RF carrier frequencies to intermediate or baseband frequencies, which affects signal quality and accuracy in GPS and data reception.
Innovation Solution
The implementation of a chopper circuitry that includes an I/Q sampler and interchanger to sample and hold I and Q values at a specific sample rate, interchanging I values with Q values, effectively shifting the intermodulation carrier frequency from baseband to intermediate frequency and the receive signal carrier frequency from intermediate to baseband, thereby avoiding intermodulation distortion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional frequency translation is used to convert RF carrier frequency to intermediate frequency, then signal translation is achieved, but intermodulation distortion components remain at baseband and degrade signal quality
Solution Approach 1:
The patent extracts the harmful intermodulation distortion components from the baseband signal by using a chopper circuit that modulates these components to a different frequency range. The chopper circuit samples the I and Q channel signals and swaps their values, effectively moving the intermodulation distortion away from the baseband frequency where it degrades signal quality.
Solution Approach 2:
The patent changes the frequency parameter of the intermodulation distortion components by using a chopper circuit that modulates these components to a different frequency. By sampling at a specific rate and swapping I/Q values, the intermodulation distortion is shifted from baseband to a higher frequency, separating it from the desired signal band.
2Reliability
If direct frequency translation without I/Q swapping is used, then circuit complexity is reduced, but intermodulation distortion cannot be avoided
Solution Approach 1:
The patent employs periodic action through the chopper circuit that samples the I and Q channel signals at a specific sample rate and periodically swaps their values. This periodic swapping action effectively modulates the intermodulation distortion components to a different frequency, achieving distortion avoidance through time-domain modulation rather than complex frequency-domain processing.
3Reliability
If I/Q values are sampled and swapped at high sample rate, then intermodulation distortion is effectively avoided, but processing complexity and power consumption increase
Solution Approach 1:
The patent applies partial action by sampling the I and Q channel signals at a specific sample rate that is sufficient to avoid intermodulation distortion but not excessively high. The chopper circuit performs selective swapping of I/Q values at this optimized sample rate, achieving the necessary distortion avoidance while minimizing unnecessary processing and associated power consumption.
Data Source
AI summary
In accordance with one aspect of the disclosure, apparatus are provided. A filter is provided to receive from an antenna a receive signal of a given type and a low noise amplifier is provided to amplify the received signal. A translator down translates the receive signal carried at a radio frequency to be carried at an intermediate frequency. An I/Q channel separator is provided to separate the receive signal carried at the intermediate frequency into an analog in-phase (I) signal in an I channel and an analog quadrature-phase (Q) in a Q channel. An analog-to-digital (A/D) converter is provided to respectively convert the I signal and the Q signal to digital domain representations of the I signal and the Q signal. An intermodulation (IM) distortion avoider is provided to avoid IM distortion in the receive signal. The IM distortion avoider includes a carrier frequency exchanger to exchange an IM carrier frequency of IM distortion contained in the receive signal with a carrier frequency of the receive signal.