Telecommunications – Receiver or analog modulated signal frequency converter – Frequency or phase modulation
Patent
1988-12-12
1990-04-03
Eisenzopf, Reinhard J.
Telecommunications
Receiver or analog modulated signal frequency converter
Frequency or phase modulation
455213, 455221, H04B 110
Patent
active
049147153
ABSTRACT:
An FM receiving circuit is provided with a front end section operative to select an FM signal from FM broadcasting signals and producing an intermediate frequency signal on the basis of the FM signal, and an audio signal producing section supplied with the intermediate frequency signal for producing audio signals and responsive to a first control signal for eliminating noise components due to a rapid variation in the electric field strength of the FM signal, and the audio signal producing section is associated with a level detecting circuit supplied with an intermediate frequency signal transferred from the audio signal producing section and producing a voltage signal representative of an envelope of the intermediate frequency signal, a low-pass filter circuit providing a time constant for producing the first control signal on the basis of the voltage signal and responsive to a second control signal for variation in the time constant, a high-pass filter circuit operative to differentiate the voltage signal for producing a differential signal, and a rectifier circuit operative to rectify the differential signal for producing the second control signal, so that the audio signal producing section can quickly respond to the first control signal even if the FM signal is rapidly varied in the electric field strength.
REFERENCES:
patent: 4087641 (1978-05-01), Sugai
Eisenzopf Reinhard J.
Kuntz Curtis
NEC Corporation
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