Multiplex communications – Wide area network – Packet switching
Patent
1991-09-09
1993-05-25
Olms, Douglas W.
Multiplex communications
Wide area network
Packet switching
370121, 375 8, 375 17, 375 60, 375 91, 455 43, H04J 100, H04L 2732
Patent
active
052146413
ABSTRACT:
A secondary channel FSK modem for use with primary channel QAM modems is described. The present invention is a fully integrated 75 bps narrowband secondary channel FSK modem which may be utilized with a primary channel QAM modem at data rates up to 19.2 kbps. The present invention applies switched capacitor circuits to implement band split filters and FSK transmitters. A micro-digital signal processor is implemented to realize the FSK receiver to achieve higher performance, long-term stability and versatility. The present invention provides 40 Hz separation of two carrier frequencies to improve bandwidth efficiency. In operation, an FSK modulator is combined with a highpass filter and delay equalizer to separate a section of the main channel bandwidth for use with the secondary channel. The FSK signal and QAM signal are then summed and provided to a smoothing filter for transmission line output. For receiving, an anti-alias filter recovers the received line signal and couples the signal to a highpass filter and bandpass filter. The highpass filter signal is delay equalized and coupled to a smoothing filter to obtain the main channel output. The bandpass filter is coupled through an A/D converter and to a micro-digital signal processor to recover the FSK data.
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Chen Ching-Siang
White Bert
Hsu Alpus H.
Olms Douglas W.
Silicon Systems Inc.
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