Combined crystal and LC filter

Details Combined crystal and LC filter Combined crystal and LC filter

1995-05-12

1996-08-06

Lee, Benny

Wave transmission lines and networks

Coupling networks

Electromechanical filter

333175, 333188, 330306, H03H 900

Patent

active

055437567

ABSTRACT:
A circuit for an intermediate frequency filter combines a variable bandwidth series resonant filter circuit and a parallel resonant filter circuit. A variable output impedance drives the filter and a variable input impedance amplifier buffers the output of the filter. The output impedance of the driver is made to track the input impedance of the output buffer. Changes in the gain of the filter with respect to bandwidth are relatively small. The noise figure of the filter remains low. The circuit is not operated in the non-linear region of the crystal because relatively low drive currents are needed at narrow bandwidths so that the crystal is not overdriven. The LC filter tunes out the stray capacitance from the load of the crystal filter.

REFERENCES:
patent: 3633134 (1972-01-01), Barrows et al.
patent: 3727154 (1973-04-01), Dailing et al.
patent: 4489264 (1991-01-01), Ohto
patent: 4568886 (1986-02-01), English
patent: 4600903 (1986-07-01), Temer
patent: 5072200 (1991-12-01), Ranky
patent: 5162759 (1992-11-01), Yajima
patent: 5229735 (1993-07-01), Quan
patent: 5319327 (1994-06-01), Konig

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