Browse Prior Art Database

Digital Multifrequency Receiver and Detector

IP.com Disclosure Number: IPCOM000081891D
Original Publication Date: 1974-Aug-01
Included in the Prior Art Database: 2005-Feb-28
Document File: 3 page(s) / 48K

Publishing Venue

IBM

Related People

Adams, RL: AUTHOR

Abstract

This multifrequency receiver permits the use of various algorithms in distinguishing between valid signals such as telephone "AB signals" and noise.

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Digital Multifrequency Receiver and Detector

This multifrequency receiver permits the use of various algorithms in distinguishing between valid signals such as telephone "AB signals" and noise.

By circuitry not shown in the figure, the input signal from the telephone line is fed through an amplifier with automatic gain control and a high-impedance input, yielding the sum of the two A,B tones or voice. This signal is divided into two channels by high and low-pass filters, separating the low-frequency pulses (the A frequency group) from the high-frequency group, the B frequencies. For this purpose, the low-pass filter can pass all frequencies below 1 kilohertz and the high-frequency filter can pass all those above 1 kilohertz. The respective channels then include saturated amplifiers to form pulse trains from the positive half-waves of their respective signal trains.

The logic will determine the frequency by measuring the duration between successive pulses. Each duration will be referred to as a sample, where a sample may be one, or by the addition of suitable counter circuitry, some fixed number of full or half-waves, of the signal of interest.

In the figure, the portion of the frequency discriminating circuitry for the low- frequency pulse train is shown since, except for the counter stepping rate, the low and high-frequency circuitries are identical. The shaped pulse train is fed by line 10 through circuitry 12, 14 which provides a synchronized sequence of pulses ("P", "Q" and "R" in that order).

P updates counter 16 in accordance with an algorithm based on a comparison of the present decoded output with previous decoded output.

Q updates register 18 for future compares.

R resets counter...