AFC Loop Channel Filtering for Adjacent-Channel Distortion Control

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Solution Overview

Problem

Conventional radio receivers face challenges in efficiently filtering out unwanted channels and reducing noise and distortion due to the placement of automatic frequency control (AFC) circuitry and channel filters, which can lead to frequency response distortion and interference from adjacent channels.

Innovation Solution

Incorporating a channel filter within the AFC loop and utilizing dual feedback loops to remove frequency and phase offsets, allowing for improved signal centering and reduction of undesired channel effects, thereby enhancing noise and distortion reduction.

Engineering Contradictions & Design Principles

VSEngineering 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 may not be frequency centered within the channel filter

Engineering Contradiction:

Improvechannel filtering accuracyVSAvoidfrequency response distortion

Core Design Contradiction:

ReliabilityVSManufacturing precision

Solution Approach 1:

The patent applies preliminary action by performing frequency offset removal through AFC circuitry before the signal enters the channel filter. This preliminary frequency alignment ensures the signal is properly centered within the filter's passband, preventing frequency response distortion while maintaining effective channel selection.

Inventive Principle:

Principle #10Preliminary action

2Reliability

If the AFC circuitry is placed in front of the channel filter, then frequency locking can be achieved, but non-desired channels may influence the AFC circuitry and cause noise or distortion

Engineering Contradiction:

Improvefrequency locking capabilityVSAvoidnoise and distortion from adjacent channels

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

The patent applies the extraction principle by removing harmful adjacent channel signals through the channel filter before they can interfere with the AFC circuitry. The channel filter extracts and eliminates unwanted frequency components, allowing the AFC to operate on a cleaner signal with reduced noise and distortion from adjacent channels.

Inventive Principle:

Principle #2Taking out (Extraction)

3Reliability

If separate dedicated paths are used for AM and FM operation, then each mode can be optimized independently, but the area associated with analog circuitry exceeds that used for digital circuitry

Engineering Contradiction:

Improvereceiver performanceVSAvoidcircuitry area

Core Design Contradiction:

ReliabilityVSArea of stationary object

Solution Approach 1:

The patent applies universality by designing a shared signal processing path that handles both AM and FM operations through common digital circuitry. The same ADC, channel filter, and signal processing blocks serve both modulation modes, eliminating the need for separate dedicated analog paths and significantly reducing overall circuitry area while maintaining optimized performance for each mode through software or control-based configuration.

Inventive Principle:

Principle #6Universality (Multi-functionality)

Data Source

PatentUS7986929B2Providing channel filtering in an automatic frequency control path

Publication Date: 2011.07.26 SKYWORKS SOLUTIONS INC

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.