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Timing Tank Mechanical Filter for Digital Subscriber Transmission System,
FUJITSU LTD KAWASAKI (JAPAN)
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This paper describes the design methods and the experimental results of the timing tank mechanical filter. The composite longitudinal mode transducer was made into a sandwich structure by affixing a constant modules alloy plate to each electrode surface of the piezoelectric ceramic plate. The equivalent electrical circuit constants and the suppression of spurious responses due to the third order longitudinal mode of the transducer were analyzed. The dimensions of the experimental filter were 20L x 12W x 5H mm, the some sizes as a 14-pin dip IC. The center frequency of the filter is 200 kHz and it has low insertion loss of 0.5 to 0.7 dB and a bandwidth of 2.1 to 2.4 kHz 3 dB. The IO phase differences at the center frequency was about 40 degrees. The inclination of the phase was as small as 0.07 to 0.08 degHz and the phase linearity was excellent. The attenuation band has 30 dB or more attenuation over the wide range from 0 to 1.5 MHz to improve the signal to noise ratio of the equipment.
APPROVED FOR PUBLIC RELEASE