FORSTERKARE MED VARIABEL FORSTERKNING.

摘要

A novel structure of an operational amplifier with a feedback differential amplifier connected between the operational amplifier output and input and with a feedforward differential amplifier connected between signal input and the input of the operational amplifier, results in a circuit gain which is the ratio of the gains of the two differential amplifiers. Temperature variations are cancelled because gain is a ratio of similar transistor differential pairs. Current sources placed in the emitter circuit of each differential pair provide gain control. Compression results when the current source of the feedback differential pair is varied in proportion to the amplitude of the alternating output signal, while maintaining the current source of the feed-forward differential pair constant. Expansion is achieved by varying the current source of the feed-forward differential pair in proportion to the amplitude of the alternating input signal while maintaining the current source of the feedback differential pair at a constant level.