GB1476909A - Compensating circuit for electronic switches - Google Patents

Abstract

1476909 Gating circuits INTERNATIONAL STANDARD ELECTRIC CORP 15 April 1975 [22 April 1974 (2)] 15425/75 Heading H3T 15 April In a circuit for compensating for the resistance of an electronic switch RON, e.g. in a telephone exchange equipment, the switch is connected in series with a controllable negative resistance -R, a resistor RM and a voltage source W and the control signal for the negative resistance is derived by measuring the voltage across resistor RM. As described the voltage across this resistor is compared with the voltage of an A.C. source W in a comparator V which produces an error signal to adjust - R until the two voltages are equal. Speech currents may be coupled into the switch by transformers which are by-passed by circuits T11, T12 at the frequency of source W. The source W is similarly by-passed by circuit T2 at speech frequencies. In a modification, Fig. 3 (not shown), a D.C. source (G) is used in place of source W. A pair of circuits of either type may be employed in a balanced arrangement, Figs. 2, 4 (not shown), or in an alternative balanced arrangement, Fig. 5, a first negative resistance - R1 may be controlled in dependance on a comparison between the voltage of the source G<SP>1</SP> and that across the resistor RM and a second negative resistance - R2 may be controlled in dependance on the voltage between points B, D by a second comparator AS. A suitable form of negative resistance is disclosed, Figs. 6, 7 (not shown).