Abstract: A controllable amplifier circuit includes, successively, in a cascode arrangement between a power supply voltage and ground, a control transistor and a field effect amplifier transistor having a control input for applying a gain control signal thereto and a gate input for applying an input signal thereto, respectively, via which control transistor the field effect amplifier transistor supplies an output signal to a signal output of the controllable amplifier circuit. The control transistor varies the working point of the field effect amplifier transistor in the ohmic range in dependence upon the gain control signal, at least in a part of the control range of the gain control signal. The circuit can be used with a low power supply voltage because the controllable amplifier circuit includes a controllable bias circuit which is coupled to the gate input of the field effect amplifier transistor for applying a controllable bias voltage thereto.

Abstract: A method of manufacturing a semiconductor device is set forth to provide a high-frequency bipolar transistor with very fine emitter-base geometry. The method comprises the steps of forming a base region, forming an insulating layer on the base region, and implanting emitter zones and base contact zones in windows in the insulating layer. Only emitter windows are first formed, then the emitter zones are implanted and a masking layer is provided on the insulating layer and in the emitter windows so that the base contact windows can be etched through apertures in the masking layer. The base contact zones are then implanted to the base contact windows.