ES310627A1 - Improvements in electronic circuits having variable gain or attenuation - Google Patents

Abstract

A gain control circuit comprises a pair of transistors T1, T2 with their emitters connected together and to earth via a path Zoo of infinite impedance at signal frequency, a control voltage V being applied between the bases of the two transistors and a bias network R3, R4 connected to the base of the first, T2. The signal is fed to the base of the second transistor T1, the base of the first being earthed via an impedance, i.e. capacitor C 22 , of low value for signal frequency each collector is connected to an H.T. supply via a load resistor R, the output being derived from one or other of the collectors. To avoid distortion when one of the transistors is biased near cut-off, a pair of such circuits may be used (Figs. 5, 6, not shown), the second transistors in each being driven in push-pull by the signal and the collectors being suitably cross-connected in pairs. The common emitter impedance Zoo may comprise a further transistor (Fig. 7, not shown), while the bias networks may include temperature-sensitive resistors to provide temperature compensation (Fig. 8, not shown). It is stated in the Specification that the arrangement may be used as a modulator or for the purpose of frequency changing.