Abstract: Electronic gain control is achieved by means of a differential controller in combination with a multistage, feedback amplifier. Both the input impedance and the output impedance have a low ohmic value, so that the influence of parasitic capacitances in the differential controller on the bandwidth is significantly reduced.

Abstract: Broadband control amplifier having a wide control range and comprising a differential amplifier in the negative feedback loop. An auxiliary coupling is provided in the feedback loop having a transfer factor which renders the open loop gain independent of the signal distribution in the differential amplifier. The control amplifier can, for example, be used as an input amplifier in a receiver for optical fibre systems, to compensate for the length and temperature-dependent attenuation of the optical link.

Abstract: An optical receiver comprises a photodiode (1) which is connected to a biasing circuit (2), and also to the output (14) of the receiver via the series arrangement formed by a preamplifier (3), a control amplifier 4 and an output amplifier (5), the output of the receiver being connected to the control input 10 of the control amplifier (4) via a detector (6) and a differential amplifier (9). The control amplifier (4) is what is commonly referred to as a differential controller, in which alternating current and direct current are processed in the same manner. As a consequence thereof, it is possible to determine the optical input level of the receiver continuously at the output of the control amplifier by means of a simple ammeter (8).

Abstract: The invention relates to a differential controller comprising two transistors connected as a long-tailed pair with the base circuits of the transistors including resistors whose values are equal to the bulk resistances of the two transistors. The collector circuits of the two transistors include means for injecting currents into said resistors, which currents are proportional to the collector currents of the two transistors.