Selective RF circuit with varactor tuned and switched bandpass f

Details Selective RF circuit with varactor tuned and switched bandpass f Selective RF circuit with varactor tuned and switched bandpass f

1995-08-17

1998-05-12

Eisenzopf, Reinhard J.

Telecommunications

Receiver or analog modulated signal frequency converter

Local control of receiver operation

4551804, 4551912, 4551882, 333174, 334 15, H04B 118, H03H 700, H03H 512

Patent

active

057521794

ABSTRACT:
A selective RF circuit for a double conversion tuner includes three sections: low and mid band double tuned bandpass sections and a high band double tuned bandpass section. Each section includes tuning varactors and one or more coupling varactors. The varactors are operated in a first tuning mode for exhibiting a variable capacitance and in a second mode for presenting a substantial low impedance across their terminals. A microprocessor controlled circuit arrangement applies DC potentials to the tuning and coupling varactors and to two pairs of switching diodes simultaneously for selecting and tuning the desired bandpass section. The varactors in each bandpass section are complemented with fixed capacitors selected so that the product of the loaded Q and the coupling factor of any active double tuned bandpass filter is maintained substantially equal to unity over the entire tuning range.

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