Dual tone multifrequency generator

Details Dual tone multifrequency generator Dual tone multifrequency generator

1977-07-15

1978-08-29

Claffy, Kathleen H.

Oscillators

Relaxation oscillators

331179, H04Q 912

Patent

active

041105680

ABSTRACT:
A DTMF generator includes a high gain differential amplifier having a noninverting input, an inverting input, and an output. A first audio oscillator connects to the inverting input of the amplifier via a first series of frequency determining components. A second audio oscillator connects to the amplifier output via a second series of frequency determining components. The noninverting input of the amplifier connects to ground. A plurality of SPST switches interconnects the first and second frequency determining components, such that when any particular switch is closed, a unique feedback path is established from the amplifier output to the inverting input. This causes a ground potential to exist at the contacts of the particular closed switch thereby forcing both oscillators to turn on.

REFERENCES:
patent: 3424870 (1969-01-01), Breeden
patent: 3699477 (1972-10-01), McKell
Electronic Design, No. 24, Nov. 22, 1970, p. 60, "Ideas for Design".

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