hybrid cascode

7-16 elektor july/august 1980 21 hybrid cascode It is general knowledge that cascoding two or more transistors creates a new transistor with better characteristics than the individual ones (see figure 1). These include a very slight retroaction from point C ("collector") to point B ("base") and a higher collector impedance, thus a much better approach to current source operation at point C. In the all transistor version of figure 1, the base of T2 will have to be fed a certain voltage with respect to the emitter of T1 — 0.6 volts (D1 in figure 1) at least. If T2 is replaced by an N channel FET, the DC bias of the cascode will be a lot easier to preset —see figure 2. As far as slope is concerned (i.e. the ratio between collector current and base voltage) both versions are equally good.