Modem comprising saw filters having opposite bassband delay char

Details Modem comprising saw filters having opposite bassband delay char Modem comprising saw filters having opposite bassband delay char

1991-02-26

1993-07-27

Chin, Stephen

Pulse or digital communications

Repeaters

Testing

375 96, 375 39, H04B 138

Patent

active

052316475

ABSTRACT:
In a modem device comprising (a) a first surface acoustic wave (SAW) rolloff filter circuit (51) having a first passband delay characteristic for primarily band-limiting into an output signal of a modulator device a multivalued quadrature amplitude modulated signal derived from input digital signal sequences and (b) a second surface acoustic wave rolloff filter circuit (52) having a second passband delay characteristic for rolloff waveform shaping an input signal of a demodulator device into a rolloff waveform shaped signal which is used in producing output digital signal sequences of the demodulator device, the second passband delay characteristic is selected as an inverse characteristic of the first passband delay characteristic. The first and the second passband delay characteristics have first and second ripple amplitudes. Preferably, the first and the second ripple amplitudes are given opposite polarities. More preferably, the second ripple amplitude is substantially equal to the first ripple amplitude. It is possible to use the first and the second surface acoustic wave rolloff filter circuits either separately in the modulator and the demodulator devices, or in between the modulator and the demodulator devices, or only in the modulator or the demodulator device.

REFERENCES:
patent: 4751478 (1988-06-01), Yoshida
patent: 4881049 (1989-11-01), Yagi
patent: 4890316 (1989-12-01), Walsh et al.
patent: 5048054 (1991-09-01), Eyuboglu et al.
patent: 5057786 (1991-10-01), Yoshikawa

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