Telephonic communications – Substation or terminal circuitry – Sidetone control or hybrid circuit
Patent
1990-05-08
1993-03-02
Dwyer, James L.
Telephonic communications
Substation or terminal circuitry
Sidetone control or hybrid circuit
379387, 379361, 379395, H04M 100
Patent
active
051916061
ABSTRACT:
An electrical telephone speech network is disclosed in which the transmitting and the receiving amplifiers are serially connected so as to reduce the minimum working current of the whole speech network. As a result, a telephone set in the network can operate properly with a much lower line current, and more extension telephones can be connected parallelly with the speech network. Further, a bias switching circuit is matched with the speech network. Thus, in pulse dialing mode, the line voltage drop of the network loop during "make" status is automatically decreased so that a pulse dialing signal received by the exchange can be more accurate. At the same time, in DTMF dialing mode, the voltage drop of the telephone set is automatically increased, for the purpose of providing a larger AC signal dynamic range to enable a telephone set to deliver a large DTMF signal and operate with a lower line current. Also, owing to direct coupling for feeding DTMF sidetones, the subscriber receives a signal with the least distortion and most stable DTMF sidetone volume.
REFERENCES:
patent: 4406926 (1983-09-01), Duncan
patent: 4442322 (1984-04-01), Grantland
patent: 4496799 (1985-01-01), Kingen et al.
patent: 4507619 (1985-03-01), Dykstra et al.
patent: 4508938 (1985-04-01), Bench et al.
patent: 4550226 (1985-10-01), Teater
patent: 4598255 (1986-07-01), Hong
patent: 4640993 (1987-02-01), Whittaker
patent: 4713629 (1987-12-01), Segal
Augustus Jhancy
Dwyer James L.
Industrial Technology Research Institute
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