FM Receiver Tracking Filter with Feedforward Frequency Control
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional FM receivers face limitations in trade-offs between selectivity, sensitivity, stability, and other performance indicators due to increasing station density and changing receiving conditions, leading to increased adjacent channel captures and reduced performance, especially in mobile operations.
Innovation Solution
The introduction of a second FM demodulator for feedforward tracking control of the center frequency of the first narrow-band FM tracking filter, allowing for separation of signal selection and filter tracking functions, thereby providing an extra degree of freedom in design and optimizing both demodulators independently for improved performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If the bandwidth of the first narrow-band FM tracking filter is decreased to improve selectivity and suppress adjacent channel interference, then selectivity and adjacent channel suppression are improved, but delay in frequency tracking increases and higher modulation frequencies are deteriorated
Solution Approach 1:
The patent divides the frequency tracking function into two separate paths: a feedback path using the first FM demodulator for stability, and a feedforward path using the second FM demodulator for rapid response. This segmentation allows the filter bandwidth to be narrowed for better selectivity while the feedforward path compensates for tracking delays, resolving the contradiction between selectivity and tracking speed.
Solution Approach 2:
The second FM demodulator performs preliminary frequency detection before the signal passes through the narrow-band filter. By anticipating frequency changes through the feedforward path, the system prepares tracking adjustments in advance, reducing the effective tracking delay that would otherwise result from using only a narrow filter bandwidth.
2Object-affected harmful factors
If the center frequency of the first narrow-band FM tracking filter is dynamically tracked to improve selectivity, then selectivity and sensitivity are improved, but stability and distortion factors deteriorate
Solution Approach 1:
The patent segments the frequency tracking control into two independent control loops: a feedback loop that ensures stability by comparing actual frequency with reference, and a feedforward loop that improves interference rejection by anticipating frequency changes. This segmentation allows dynamic tracking for better selectivity while maintaining overall system stability through the balanced operation of both loops.
Solution Approach 2:
The patent employs dual feedback mechanisms: the first FM demodulator provides feedback for stability control, while the second FM demodulator provides feedforward feedback for interference suppression. This dual feedback system allows the filter to dynamically track frequency for improved selectivity while the balanced feedback loops maintain receiver stability and minimize distortion.
3Adaptability or versatility
If conventional detector module circuitry is added to change signal transmission characteristic in response to receiving states, then limited improvement in specific receiving states is achieved, but device complexity and sources of instability increase
Solution Approach 1:
The second FM demodulator serves multiple functions simultaneously: it provides feedforward frequency tracking control to the first filter, serves as a detector for receiving state assessment, and generates control signals for adapting signal transmission characteristics. This multi-functionality achieves receiving condition adaptation without adding separate detector module circuitry, thereby avoiding increased device complexity and instability sources.
Data Source
AI summary
FM receiver including an RF input circuit followed by a tunable mixer stage for frequency conversion of an RF FM signal into an IF FM signal, which is coupled to an FM input of a first narrow-band IF filter. The center frequency of the first narrow-band IF filter is controlled to vary in dependence on the IF FM signal. The first narrow-band IF filter is subsequently coupled to a first FM demodulator and a first LF signal processing unit. To increase the receiver's selectivity and sensitivity without adversely affecting tracking stability, the FM input of a first narrow-band IF filter is coupled through a second FM demodulator to a control input of said first narrow-band FM tracking filter for a feed forward tracking control of the center frequency of said first narrow-band FM tracking filter with the momentary frequency of the IF FM signal.