Device for varying the cutoff frequency of a low-pass filter

Details Device for varying the cutoff frequency of a low-pass filter Device for varying the cutoff frequency of a low-pass filter

1997-07-25

1999-11-30

Bost, Dwayne D.

Telecommunications

Receiver or analog modulated signal frequency converter

Local control of receiver operation

455307, 455340, 455297, 455296, H04B 106

Patent

active

059958170

ABSTRACT:
For eliminating the emphasis given an audio signal in the transmitter, an audio signal processor of an audio device (e.g., a car radio) contains a low-pass filter. In order to attenuate the spurious higher-frequency signal fractions in case of poor reception and accordingly low received field strength, the cutoff frequency of the low-pass filter is shifted in the direction of lower frequencies in accordance with a received field strength signal when the field strength becomes lower. In order to avoid external adjusting components and save pins on the IC chip, the field strength signal is supplied to an analog-to-digital converter and the latter supplies a digital signal to a low-pass filter whose cutoff frequency is variable. For this purpose the low-pass filter contains a number of integrated components one of which is connected or disconnected by a digit place of the digital signal in each case.

REFERENCES:
patent: 3760287 (1973-09-01), Harris
patent: 4368355 (1983-01-01), Ichikawa
patent: 5287556 (1994-02-01), Cahill
patent: 5673003 (1997-09-01), Zocher
patent: 5758276 (1998-05-01), Shirakawa et al.
patent: 5758296 (1998-05-01), Nakamura
patent: 5809399 (1998-09-01), Tuutijarvi et al.

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