The design of tetrode transistor amplifiers

The design of tetrode transistor amplifiers encounters problems of the type that occurs with other transistor uses. Desired frequency characteristics, limitations of parasitic elements, and other practical considerations impose constraints on the range of terminations that can be employed. With many transistors, one can terminate a transistor so that it will oscillate without external feedback; this oscillation or other exceedingly sensitive terminations must be avoided. The two-port parameters of the transistor in any orientation in which it is to be used constitute the fixed or given information which is the starting point of the amplifier design. Using this starting point, methods are developed by which one can select, on simple bases, the kinds of terminations that will be suitable. To facilitate the design of amplifiers, a set of charts has been developed from which one can read power gain and input impedance as functions of the load termination. Illustrative tetrode amplifiers are described. These include a common base 20-mc video amplifier, a common-emitter 10-mc video amplifier, an IF amplifier centered at 30 mc, and an IF amplifier centered at 70 mc. Predicted and measured gains are compared.