Method for tuning the input stage of a receiver to a desired rec

Details Method for tuning the input stage of a receiver to a desired rec Method for tuning the input stage of a receiver to a desired rec

1981-11-12

1985-04-16

Murray, Richard

Facsimile and static presentation processing

Facsimile

Specific signal processing circuitry

455186, H04N 544

Patent

active

045119236

ABSTRACT:
A tuning signal having a duty cycle representing a transmission frequency to be received is converted by a D/A converter to a tuning voltage which in turn is applied to a voltage variable tuning capacitance in the receiver input stage. To avoid the effects of ripple on the tuning voltage, the instantaneous d.c. level of the tuning voltage is stored on a capacitor during the tuning operation. On completion of tuning, the tuning voltage is disconnected and the stored capacitor voltage is applied to the tuning capacitance, thereby eliminating the unwanted ripple voltage. The tuning voltage produced by the D/A converter as well as that stored by the storage capacitor, are connected to the input of a voltage follower amplifier whose output is connected to the tuning capacitance. The amplifier design is such that when its input and output voltages are equal, its quiescent current is small whereas when its input and output voltages differ a current source is switched to provide a large output current. Thus, the tuning voltage applied to the tuning capacitance rapidly follows changes in the input tuning signal.

REFERENCES:
patent: 4004231 (1977-01-01), Elshuber et al.
patent: 4031549 (1977-06-01), Rast et al.
patent: 4159487 (1979-06-01), Elshuber et al.
patent: 4198605 (1980-04-01), Yamashita et al.
patent: 4200841 (1980-04-01), Nagata et al.
patent: 4291414 (1981-09-01), Kimura
patent: 4301540 (1981-11-01), Sato et al.
IEEE Transactions on Consumer Electronics, vol. CE-26, No. 1, Feb. 1980, pp. 20-26, vol. CE-25, No. 4, Aug. 1979, pp. 621-622.

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