Digital RF Tuning System for Low Power FM Receiver
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Solution Overview
Problem
Existing FM radio and RF receiver technologies face challenges with frequency noise and error amplification due to the use of low frequency reference sources, leading to degraded receiver selectivity and signal-to-noise ratio, and require external components and high power consumption in analog synthesizer and AFC circuit implementations.
Innovation Solution
A digital RF tuning system that uses a digital synthesizer circuit and a digital AFC circuit to generate local oscillator control signals, enabling transient-free switching and eliminating the need for external components by implementing both circuits in the digital domain, with a two-step tuning process involving a synthesizer for coarse tuning and AFC for precise tuning.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If a low frequency reference source (32.768 kHz) is used to minimize power consumption, then power consumption is reduced, but frequency noise and error are multiplied by a large factor resulting in degraded receiver selectivity and signal-to-noise ratio
Solution Approach 1:
The frequency synthesis process is segmented into two distinct stages: a coarse tuning stage using a frequency synthesizer to establish the basic frequency, and a fine tuning stage using an automatic frequency control (AFC) circuit to eliminate remaining frequency errors and noise. This segmentation allows each stage to optimize for its specific function while working together to achieve the overall goal of low power consumption with high frequency accuracy.
Solution Approach 2:
The patent replaces traditional analog AFC circuits with a digital AFC implementation. The digital AFC circuit processes frequency error signals in the digital domain, eliminating the need for analog components such as voltage-controlled oscillators and analog loop filters. This substitution reduces power consumption while maintaining or improving frequency control accuracy.
2Reliability
If analog synthesizer and AFC circuits are used to control LO frequency, then frequency control is achieved, but external components are required and power consumption increases
Solution Approach 1:
The patent replaces analog synthesizer and AFC circuits with digital implementations. The digital synthesizer uses digital signal processing to generate the local oscillator frequency, and the digital AFC circuit uses digital signal processing to correct frequency errors. This eliminates the need for external analog components such as voltage-controlled oscillators, analog loop filters, and external capacitors, while integrating all functionality into the IC.
Solution Approach 2:
The patent merges the synthesizer and AFC circuit functions into a single integrated digital frequency control system. The digital synthesizer and digital AFC circuit work together as a unified system, sharing common digital processing resources and eliminating the need for separate analog component sets. This integration reduces device complexity and eliminates external component requirements.
3Measurement precision
If analog AFC circuit is used for frequency control, then frequency accuracy is improved, but transients and spikes occur when switching from synthesizer circuit
Solution Approach 1:
The patent replaces the analog AFC circuit with a digital AFC circuit that processes frequency error signals in the digital domain. This digital implementation eliminates transient and spike issues during switching from the synthesizer circuit, as digital circuits can be designed to switch cleanly between states without the analog transients that plague analog switching circuits.
Solution Approach 2:
The digital AFC circuit is designed to be pre-configured and ready to accept frequency error signals immediately when switching from the synthesizer circuit. The digital nature of the circuit allows for clean, pre-planned switching sequences that avoid the transient behavior inherent in analog circuits, ensuring stable frequency control from the moment of switching.
Data Source
AI summary
A system for tuning a radio receiver includes a radio receiver configured to provide a downconverted digital error signal, a digital synthesizer circuit configured to generate a first local oscillator control signal, a digital automatic frequency control (AFC) circuit configured to generate a second local oscillator control signal, wherein the digital synthesizer circuit is enabled to generate the first local oscillator control signal when the digital AFC circuit is disabled, the first local oscillator control signal corresponds to an estimate of a desired local oscillator frequency, the digital AFC circuit is enabled to generate the second local oscillator control signal when the digital synthesizer circuit is disabled and the second local oscillator control signal corresponds to the desired local oscillator frequency.