Mixed analog digital secondary channel FSK modem
US5214641A · kind A · utility
Assignee
Inventors
Key dates
| Filing date | Sep 9, 1991 |
| Grant date | May 25, 1993 |
| Priority date | — |
| Expiry date | Sep 9, 2011 |
Classification
- Technology area (CPC H)Electricity
- CPC primaryH04L5/06
- WIPO fieldTelecommunications
- WIPO sectorElectrical engineering
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…
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.