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Circuit for Identifying Frequency of a Message

IP.com Disclosure Number: IPCOM000082323D
Original Publication Date: 1974-Nov-01
Included in the Prior Art Database: 2005-Feb-28
Document File: 2 page(s) / 30K

Publishing Venue

IBM

Related People

Leavitt, BE: AUTHOR

Abstract

The circuit of the drawing produces a signal at an output 2 to identify that a message has one of several preselected frequencies. An oscillator 3 runs at a suitably higher frequency than the frequency of a message, so that the number of pulses from the oscillator 3 during the period of a synch pulse for the message identifies the message frequency.

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Circuit for Identifying Frequency of a Message

The circuit of the drawing produces a signal at an output 2 to identify that a message has one of several preselected frequencies. An oscillator 3 runs at a suitably higher frequency than the frequency of a message, so that the number of pulses from the oscillator 3 during the period of a synch pulse for the message identifies the message frequency.

A circuit 4 includes a counter that counts the pulses of oscillator 3 during such a period. Circuit 4 also includes a decoder that produces outputs 5, 6, 7 that identify the count for particular frequencies that are to be detected.

A circuit 8 receives the synch pulses of the message waveform and produces signals to start, stop, and reset the counter at transitions of the synch pulses, and signals that identify these times for three successive counting periods.

The other components of the drawing detect one of the selected frequencies and illustrate the circuits for detecting other frequencies. At the end of the first counting period, a timing signal FIRST COUNT controls AND gate 9 to set a signal from circuit 4 into a latch 10.

At the end of a second counting period a signal SECOND COUNT controls AND gate 12 to set the second output of circuit 4 into a latch 13. This signal also controls AND gate 14 to transmit a signal through OR gate 15 to output 2, if the first and the second outputs of circuit 4 agree.

At the end of a third counting period, a signal THIRD COUNT contr...