Stereo Signal Processing Circuit Adjacent Interference Detection
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
In radio receivers, especially during FM broadcasting, adjacent interference can degrade the signal-to-noise ratio, leading to a decrease in stereo signal quality and sometimes necessitating a switch to monophonic playback when the signal level of the narrow band signal is reduced.
Innovation Solution
A stereo signal processing circuit with an adjacent interference detecting unit that compares wide band and narrow band signal levels, triggering attenuation of the L−R signal and conversion to monophonic playback when the narrow band signal level falls below a certain threshold, while maintaining a high signal level for the desired station, thereby reducing noise and preserving the signal-to-noise ratio.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the narrow band signal level is reduced to switch to monophonic playback, then the signal-to-noise ratio is improved, but the stereo signal quality is degraded
Solution Approach 1:
The patent changes the threshold parameter for switching between stereo and monophonic playback based on detected adjacent interference levels. When adjacent interference is detected, the threshold signal level for switching to monophonic playback is raised, allowing stereo playback to continue at lower signal levels where it would normally switch to monophonic. This dynamic parameter adjustment resolves the contradiction by adapting the switching criterion to current interference conditions.
Solution Approach 2:
The patent implements dynamic switching between stereo and monophonic playback modes based on real-time detection of adjacent interference and signal level. The system continuously monitors signal conditions and adjusts the playback mode accordingly, rather than using a fixed threshold. This dynamic approach allows the system to maintain stereo playback longer under adjacent interference conditions while still switching to monophonic when necessary, resolving the contradiction between maintaining stereo quality and ensuring adequate signal-to-noise ratio.
2Reliability
If the L−R signal is attenuated to reduce noise, then the signal-to-noise ratio is improved, but the stereo signal level is reduced
Solution Approach 1:
The patent adjusts the attenuation parameter of the L−R signal based on the detected adjacent interference level and narrow band signal level. When adjacent interference is detected, the attenuation is applied at a higher threshold signal level, meaning the L−R signal is attenuated less aggressively compared to normal operation. This dynamic parameter adjustment allows the system to reduce noise through attenuation while preserving more of the stereo signal level than would be the case with fixed threshold attenuation.
3Duration of action of stationary object
If the threshold signal level for monophonic switching is lowered, then stereo playback is maintained longer, but the noise level increases
Solution Approach 1:
The patent employs feedback through an adjacent interference detecting unit that continuously monitors the received signal for adjacent channel interference. Based on this feedback, the system dynamically adjusts the threshold signal level for switching from stereo to monophonic playback. When adjacent interference is detected, the threshold is raised, which triggers the switch to monophonic playback at a higher signal level, thereby preventing noise degradation that would occur if stereo playback were maintained at lower signal levels under interference conditions.
Solution Approach 2:
The patent implements dynamic adjustment of the switching threshold based on real-time detection of adjacent interference conditions. Rather than using a fixed threshold, the system adapts the threshold signal level for monophonic switching according to the detected interference level. This dynamic approach allows the system to extend stereo playback duration when conditions permit while automatically switching to monophonic playback at appropriate moments to avoid excessive noise, thus resolving the contradiction between playback duration and noise level.
Data Source
AI summary
A noise level of an output signal is maintained low. An adjacent interference detecting unit compares a signal level of a wide band signal which is a desired station signal of a relatively wide band and a signal level of a narrow band signal which is a desired station signal of a relatively narrow band, and judges that adjacent interference has occurred when the signal level of the narrow band signal is less than or equal to a predetermined level even though the signal level of the wide band signal is greater than or equal to a predetermined level. A variable amplifier (36) attenuates an L−R signal and forms a monophonic signal when the signal level of the narrow band signal is lower than a predetermined level. With this process, when there is adjacent interference, a signal level of the narrow band signal at which the attenuating unit starts attenuating the L−R signal is changed to a relatively high value.