Self-compensated dual tone multiple frequency generator

Details Self-compensated dual tone multiple frequency generator Self-compensated dual tone multiple frequency generator

1989-03-08

1991-06-25

Ng, Jin F.

Telephonic communications

Supervisory or control line signaling

Substation originated

379256, 364721, H04M 100

Patent

active

050273892

ABSTRACT:
A Dual-Tone Multi-Frequency (DTMF) Generator produces a row and column tone frequency for application to the input of two source follower buffer stages. The outputs of the buffers stages are combined in summation operational amplifier to generate the DTMF Signal. There is a voltage level shift between the input and output terminal of the source followers which can be compensated with a self-compensated circuit. With a perfect match between the compensated signal and the source follower, the operational range of working voltage can be about 1.8V to 5V, and the generator can tolerate threshold voltage variation of the transistors.

REFERENCES:
patent: 3174095 (1965-03-01), Cocker
patent: 4103220 (1978-07-01), Huntley
patent: 4639554 (1987-01-01), Masuda et al.
ERSO Data Book Telecommunication 1988, pp. 87-89 and 61-63.
"Self Stabilizing Voltage Reference", R. Stewart, Technical Notes RCA, TN No. 122, Dec. 29, 1978.

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