Multi-Channel Receiver AFC Using Per-Signal Frequency Offsets
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Solution Overview
Problem
Traditional automatic frequency control (AFC) methods for multi-channel receivers fail to accurately correct frequency offsets across different signals, leading to inefficiencies, increased costs, and user experience issues like audio muting due to the need for external tuner adjustments and complex calibration.
Innovation Solution
The implementation of an AFC system that maintains separate frequency offset values for each signal, allowing individual demodulators to correct their respective signals independently, eliminating the need for tuner center frequency adjustments and enabling universal compatibility with various tuner types.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional AFC correction methods are used with a single reference signal, then frequency offset correction is achieved for that signal, but other signals with different offsets remain uncorrected and require additional corrections
Solution Approach 1:
The patent divides the frequency offset correction into separate segments for each signal source (satellite signals and terrestrial signals). Each signal type maintains its own frequency offset measurements and corrections rather than using a single unified reference. This segmentation allows each signal to be corrected independently according to its specific offset characteristics.
Solution Approach 2:
The patent applies different frequency offset correction characteristics to different signal sources. Satellite signals receive corrections based on satellite-specific offset measurements, while terrestrial signals receive corrections based on terrestrial-specific measurements. This local quality approach ensures each signal type is corrected with the appropriate offset values for its specific characteristics.
2Measurement precision
If the tuner center frequency is externally controlled to correct frequency offsets, then frequency correction is achieved, but device complexity increases and calibration of switched capacitor network is required
Solution Approach 1:
The patent extracts the frequency offset correction function from the tuner center frequency control and implements it separately through frequency offset values that are applied to the demodulator. This separation removes the need for external tuner control and eliminates the complexity of calibrating switched capacitor networks, while still achieving accurate frequency offset correction for each signal.
3Device complexity
If a single frequency tuner is used for multiple signals, then receiver cost and footprint are reduced, but frequency offset correction becomes problematic when switching between signals with different offsets
Solution Approach 1:
The patent performs preliminary frequency offset measurements and corrections for each signal source before switching occurs. Frequency offset values are pre-calculated and stored for both satellite and terrestrial signals, so when switching between signal sources, the appropriate offset values are already available immediately, preventing audio muting and ensuring continuous signal reception.
4Ease of manufacture
If inexpensive oscillators are used in the frequency tuner, then receiver cost is reduced, but frequency accuracy decreases due to crystal oscillator variations and temperature sensitivity
Solution Approach 1:
The patent implements feedback through continuous frequency offset measurements for each signal source. The system constantly monitors the actual frequency offsets of satellite and terrestrial signals and uses this feedback information to adjust and apply appropriate correction values, compensating for oscillator variations and temperature effects without requiring expensive high-precision oscillators.
Data Source
AI summary
Systems and methods for performing automatic frequency control are provided. Instead of relying on individual frequency tuners for each channel of a multi-channel receiver system, the present subject matter uses a single frequency tuner for receiving each channel of the multi-channel receiver system. A locked demodulator may be designated as a reference demodulator and frequency offset values associated with the reference demodulator may be applied to other demodulators of the multi-channel receiver. These frequency offset values may be used by individual demodulators of each channel for correcting corresponding frequency offsets.