Patent
1979-09-04
1981-05-19
Popek, Joseph A.
179 16F, H04M 100
Patent
active
042687233
ABSTRACT:
The loop current (I.sub.X) of a telephone set speech network (1) is automatically initialized at a desired level independent of the central office voltage applied to the input terminals (12, 13) of the set and thus independent of transmission line loop length and other variables. For this purpose, a variable conductance device (20), sush as a Darlington driver (Q1), is connected between the input terminals and the speech network so as to establish a loop current at a circuit node (N1) that is a function of the supply voltage and the conductivity of the device. The loop current is monitored, as by a Schmitt trigger circuit (30), and the conductance of the device (20) is varied accordingly so as to initialize the loop current at the desired level, as by selectively connecting a plurality of resistors (R2 . . . R7) individually and collectively between a base node (26) of the driver (Q1) and the ring lead (17) of the set.
REFERENCES:
patent: 3800095 (1974-03-01), Cowpland
patent: 3906167 (1975-09-01), Baker
patent: 4143247 (1979-03-01), Yoshitoshi et al.
W. F. Chow et al., "MAC-4: A Single-Chip Microcomputer", The Bell System Technical Journal, vol. 58, No. 4, pp. 959-962, Apr. 1979.
Landis J. L.
Popek Joseph A.
Western Electric Company
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