AFC Loop Channel Filtering for Adjacent-Channel Distortion
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Solution Overview
Problem
Conventional radio receivers with analog circuitry face challenges in efficiently filtering out unwanted channels, leading to frequency response distortion and noise due to the placement of channel filters and automatic frequency control (AFC) circuitry in the signal processing path, which can be influenced by adjacent channels.
Innovation Solution
Incorporating a channel filter within the AFC loop, with dual feedback paths to remove frequency and phase offsets, allowing for improved signal centering within the channel filter and reducing distortion, and using digital signal processing for channel filtering and AFC functions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the channel filter is placed ahead of the AFC circuitry, then the desired channel can be filtered before frequency control, but frequency response distortion occurs because the incoming signal is not frequency centered within the channel filter
Solution Approach 1:
The patent applies preliminary action by performing frequency offset removal and signal centering before the channel filtering operation. The AFC circuitry pre-processes the signal to center it at the desired frequency, ensuring that when the channel filter subsequently processes the signal, it operates on a properly centered input, thereby avoiding frequency response distortion while maintaining effective channel separation
2Reliability
If the AFC circuitry is placed in front of the channel filter, then frequency control can be applied first, but non-desired channels influence the AFC circuitry causing noise or distortion
Solution Approach 1:
The patent implements feedback by placing the channel filter within the AFC loop, where the filtered signal is fed back to the AFC circuitry. This allows the AFC to operate on a signal that has already had unwanted channels removed, preventing adjacent channel interference from corrupting the frequency control process. The feedback mechanism ensures that only the desired channel information is used for frequency offset detection and correction
3Area of stationary object
If digital circuitry is used instead of analog circuitry, then area and cost are reduced, but processing complexities require significant digital processing to match analog receiver performance
Solution Approach 1:
The patent merges the channel filtering function with the AFC loop structure, combining two separate signal processing functions into an integrated system. This integration allows the digital channel filter to work synergistically with the digital AFC circuitry, where the filter cleans up the signal for the AFC and the AFC provides frequency tracking for the filter, thereby reducing overall processing complexity compared to implementing these as separate, independent digital processing stages
Data Source
AI summary
In one embodiment, the present invention includes a method for filtering an incoming signal in a channel filter of an automatic frequency control (AFC) loop to obtain a filtered incoming signal, generating a frequency offset from the filtered incoming signal in the AFC loop, removing the frequency offset from the incoming signal to obtain an adjusted signal, and providing the adjusted signal to an input of the channel filter.