Abstract: A zero equalization capacitor is connected to a first input of the comparator K, and at the beginning of the equalization phase, a voltage value of zero is placed at both comparator inputs, and a feedback network RN is connected between the comparator output and the capacitor, whereby the capacitor is charged to such a degree that the output signal of the comparator arrives at the decision threshold between the equality or inequality of the comparator inputs.

Abstract: A digital-analog converter functioning according to the .mu.-law wherein a sequence control receives an input digital signal and controls the position of a plurality of switches so as to selectively apply positive or negative voltages to a main resistor network and an auxiliary resistor network and further controls the plurality of switches in such networks for either grounding or connecting to an operational amplifier the outputs of said main and auxiliary resistor networks so as to produce an analog output signal. The invention is useful in time division multiplex telephone systems with digital subscriber stations, for example.

Abstract: An integrated circuit construction for a telephone subscriber station having a microphone amplifier and a receiving audio amplifier is described. An impedance bridge replaces the conventionally used hybrid transformer. The aforementioned amplifiers are constructed in integrated circuit form as differential amplifiers, which are excited in parallel by separate reference voltages produced from two constant currents generated in a common source.