Reception band switching circuit with variable attenuation contr

Details Reception band switching circuit with variable attenuation contr Reception band switching circuit with variable attenuation contr

1994-11-18

1996-01-09

Lee, Benny

Wave transmission lines and networks

Coupling networks

Frequency domain filters utilizing only lumped parameters

455266, 4551881, 455340, 4552341, H04B 118, H03H 712

Patent

active

054832098

ABSTRACT:
The invention provides a filter circuit for use in a double-conversion TV tuner exhibiting low diode insertion loss, in which intermodulation distortion does not occur even when an incoming signal has a large amplitude. In the filter circuit according to one preferred embodiment of the invention, there are provided three bandpass filters (BPFs) which allow corresponding RF signals in different frequency bands to pass through them, and six variable attenuation diodes whose impedance is controlled by an AGC voltage applied to an AGC terminal (16). There are also provided switching diodes (20) disposed between an input terminal (1) and the inputs of three BPFs so that the switching diodes (20) select exclusively one of three BPFs so as to apply an RF signal received at the input terminal (1) only to the selected BPF (it will be assumed hereinbelow that the BPF (21) is selected). In this arrangement, not only the impedance of variable attenuation diodes (22, 23) in the selected BPF (21) which provides the extracted RF signal, but the impedance associated with all variable attenuation diodes is controlled by the AGC voltage.

REFERENCES:
patent: 5023939 (1991-06-01), Hori
patent: 5068918 (1991-11-01), Verheijen et al.

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