GB1048100A - A circuit arrangement for reducing the error in step-by-step pilot-controlled level regulation devices in telecommunication transmission systems - Google Patents

Abstract

1,048,100. Automatic volume control. TELEFUNKEN PATENTVERWERTUNGS G.m.b.H. March 3, 1964 [March 14, 1963; Dec. 5, 1963], No. 8900/64. Heading H4R. In a pilot controlled automatic volume control system, particularly for multi-channel carrier systems, e.g. of Specification 1,009,064; in which variations of the pilot signal level from a standard level in one direction or the other are detected by a respective one of two voltage discriminator two-state devices, e.g. Schmitt triggers, which control the stepping direction of a gain adjusting device including a thermistor, the effects of the back-lash, or hysteresis, in the operating potential of the voltage discriminator two-state device is reduced by feeding them via a temperature compensated comparison amplifier of relatively high gain. Fig. 1 shows an embodiment in which the rectified pilot voltage, applied to terminal Up, is compared with the voltage developed across Zener diode D 1 to control the input voltage to the low and high level voltage discriminator Schmitt trigger stages ST 1 and ST 2 . The arrangement is independent of temperature if the temperature coefficient of transistor Ts 1 is equal and opposite to that of diode D1. Alternatively the Zener diode may be connected in the base circuit of one of a pair of transistors connected as a differential amplifier with the rectified pilot signal applied to the base of the other transistor, Fig. 2 (not shown). An additional diode may be connected in one or the other base circuits of the differential amplifier to compensate the temperature coefficient of the pilot rectifying diode, Figs. 3 and 4 (not shown).