TABLE OF CONTENTS This chapter illustrates a selection of well-established circuits and data, and comments are reduced to a minimum so as to include the greatest number of useful circuits. The common-emitter and a few other basic amplifier circuits have already been dealt with in Chapter 5. Where several different types of circuits are shown, as for oscillators, practical considerations may dictate the choice of design. For example, a Hartley oscillator uses a tapped coil, but the arrangements for frequency variation may be more convenient than those for a Colpitts oscillator which uses a capacitive tapping. Note that crystal oscillator circuits may have to be modified to take account of the range of drive requirements for crystals of differing frequencies, mode and Q-values. As many variants on basic circuits have been shown as is feasible in the space. Discrete component circuit have been used in order to illustrate the action of each circuit, something that is usually hidden in the depths of the IC versions.
We have looked earlier at the Darlington circuit as an example of a compound transistor circuit that gives an effective multiplication of h fe value. There are some other two-transistor circuits that are still widely used, either in discrete form or incorporated in ICs. One example is the complementary Darlington, using both a NPN and a PNP transistor, sometimes called the Sziklai pair. In this circuit (Figure 7.1), the voltage between base and emitter is just that of a single transistor...
