FM Receiver Bandwidth Control for Interference and Distortion
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Solution Overview
Problem
Conventional FM receivers face challenges in accurately differentiating between adjacent-channel interference and noise, leading to inadequate removal of interference and increased audio distortion, particularly in weak electric field states and during high modulation.
Innovation Solution
An FM receiver with a bandwidth controller that selectively uses a fluctuation component signal in weak electric field states and a detection output signal in stronger states to adjust the bandpass filter bandwidth, minimizing false detections and optimizing interference removal and audio quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If the bandwidth of the band-pass filter is reduced to remove adjacent-channel interference, then adjacent-channel interference is reduced, but audio distortion increases when the FM signal is highly modulated
Solution Approach 1:
The patent implements dynamic bandwidth control of the band-pass filter based on detected signal conditions. The system automatically adjusts the filter bandwidth between a narrow bandwidth (for interference rejection) and a wide bandwidth (for preserving audio quality) according to the modulation state and signal strength, resolving the contradiction between interference removal and audio fidelity
Solution Approach 2:
The system changes the bandwidth parameter of the band-pass filter dynamically based on detected signal characteristics. By monitoring the modulation state and electric field strength, the system adjusts the filter bandwidth parameter to optimize both interference rejection and audio quality under different operating conditions
2Object-affected harmful factors
If the bandwidth is reduced in weak electric field states to remove interference, then adjacent-channel interference is reduced, but false detection of noise as interference occurs, increasing audio distortion
Solution Approach 1:
The system uses feedback from the detection circuit to monitor signal characteristics and distinguish between actual adjacent-channel interference and noise. By analyzing the detected output signal and electric field strength, the system provides feedback to the bandwidth controller to make informed decisions about bandwidth adjustment, preventing false detection and unnecessary bandwidth reduction
Solution Approach 2:
The system performs preliminary detection and analysis of the signal state before adjusting the bandwidth. By detecting the electric field strength and analyzing signal characteristics in advance, the system determines whether the high-frequency components are due to actual interference or noise, preventing premature bandwidth reduction that would cause audio distortion
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach allows for accurate differentiation and effective removal of adjacent-channel interference while minimizing audio distortion, improving overall audio quality by dynamically adjusting the bandpass filter bandwidth based on signal strength and modulation state.
Implementation Method 1
a bandpass filter for allowing a transmission bandwidth to be variably set, and transmitting the received target FM signal that has been converted to the intermediate signal
Implementation Method 2
An RF (radio frequency) signal received by an antenna 2 is mixed with a first local oscillation signal in a first mixer circuit 4. The target reception signal is subjected to frequency conversion in order to obtain a first intermediate signal SIF1 having a predetermined intermediate frequency fIF1
Implementation Method 3
SIF2 is then subjected to FM detection using a detection circuit 10, and an extracted detection output signal SOUT is outputted
Data Source
AI summary
An FM receiver that is suitable for reducing a transmission bandwidth WF of a bandpass filter to remove adjacent-channel interference, and increasing WF to prevent audio distortion. A detection output signal SOUT is inputted to an HPF 122 when a reception electric field strength signal SM-DC indicates an intermediate or stronger electric field. In a weak electric field, an AC component signal SM-AC, which is extracted from an intermediate signal SIF1 prior to detection and which has fewer high-pass noise components than SOUT, is inputted to the HPF 122. A control circuit 120 detects a case as an adjacent-channel interference state when a large amount of high-pass components passes through the HPF 122, and reduces WF of an IFBPF 70 in order to remove adjacent-channel interference. When a small amount of high-pass components is transmitted, WF is increased in order to minimize audio distortion.