The patent badge is an abbreviated version of the USPTO patent document. The patent badge does contain a link to the full patent document.
The patent badge is an abbreviated version of the USPTO patent document. The patent badge covers the following: Patent number, Date patent was issued, Date patent was filed, Title of the patent, Applicant, Inventor, Assignee, Attorney firm, Primary examiner, Assistant examiner, CPCs, and Abstract. The patent badge does contain a link to the full patent document (in Adobe Acrobat format, aka pdf). To download or print any patent click here.
Patent No.:
Date of Patent:
May. 25, 1993
Filed:
Sep. 09, 1991
Ching-Siang Chen, Irvine, CA (US);
Bert White, Irvine, CA (US);
Silicon Systems, Inc., Tustin, CA (US);
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.