Abstract: To determine the deviation of longitudinal signal components from a predetermined value on a balanced two-wire circuit (A,B), a first voltage is measured between one of the wires (A) and a first reference potential by means of a first voltage measuring means (3), a second voltage is measured between the second wire (B) and a second reference potential by means of a second voltage measuring means (4), and the difference between the first and the second voltage is formed by means of a difference forming means (5), said difference being proportional to the deviation of the longitudinal signal components from the mean value of the first and the second reference potential.

Abstract: In a driving stage for driving the two differential amplifier output stages of a subscriber line interface circuit, the driving stage is adapted to generate four driving currents in dependence on, on the one hand, transversal and longitudinal signals incoming to the driving stage and, on the other hand, a reference current, and to supply these driving currents in pairs to the two inputs of the differential amplifier output stages, all four of the driving currents being larger than zero.

Abstract: An apparatus for automatically switching a load between different supply voltages in dependence on varying voltage demands of the load includes a number of analog series regulators. The supply voltage connection terminals of the series regulators are connected to an individual one of the supply voltages while the output terminals of the series regulators are connected to the load to individually conduct current to/from the load in one and the same direction.