Balanced bridge saw filter

Details Balanced bridge saw filter Balanced bridge saw filter

1994-07-26

1996-04-16

Lee, Benny T.

Wave transmission lines and networks

Coupling networks

Electromechanical filter

333195, 333196, 310313C, 310313D, H03H 964

Patent

active

055086675

ABSTRACT:
The invention relates to a SAW filter comprising a first and second pair of substantially equivalent SAW transducers electrically coupled to form a bridge circuit. Each of the transducers of the first pair of transducers have a center frequency which is slightly different to the center frequency of each of the transducers of the second pair of transducers. The product of the static capacitance of the first pair is the same as the product of the static capacitance of the second pair. In use, signals input to the filter and having a frequency within the passband of the filter are coupled to the output of the bridge circuit via one or other or both arms of the bridge, as in normal bridge circuit operation. However, out of band signals are blocked since all the transducers are equivalent capacitors having the same capacitance (i.e., static capacitance). Thus, transmission of out of band signals through the filter is inhibited by the balanced nature of the bridge.

REFERENCES:
patent: 2922128 (1960-06-01), Weinberg
patent: 3750027 (1973-07-01), Hartmann
patent: 3768047 (1973-10-01), Campbell et al.
patent: 4396851 (1983-08-01), Kishimoto et al.
patent: 4731585 (1988-03-01), Wright
patent: 4785270 (1988-11-01), Kinsman
patent: 5028895 (1991-07-01), Fliegel
patent: 5093638 (1992-03-01), Kinsman et al.
"SAW Planar Network", by Tseng et al., 1974 Ultrasonics Proceedings, pp. 282-285, 1974, New York (no month).
"800-MHz High-Performance SAW Filter Using New Resonant Configuration" by Hikita et al., IEEE Transactions On Microwave Theory and Techniques, vol. 33, No. 6, pp. 510-518, Jun. 1985.
"Miniature SAW Antenna Duplexer for 800-MHz Portable Telephone Used in Cellular Radio Systems" by Hikita et al., IEEE Transactions On Microwave Theory And Techniques, vol. 36, No. 6, 1988, pp. 1048-1056.

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