THE BLACK BOX APPROACH TO HIGH FREQUENCY TRANSISTOR CIRCUIT DESIGN,

The transistor is considered as a black box and its parameters measured at the intended frequency of operation. The advantages of this approach are considered here. Having decided upon this method of representation, the next step is to determine which of the two-port parameters are to be measured. The choice of parameters to be measured is discussed. The application of the black box technique to the design of oscillators and i-f amplifiers is also discussed. In oscillator design, the use of matrix techniques allows the designer to combine the reactive effects of the transistor with the frequency determining elements of the oscillator, to determine the starting conditions and frequency of oscillation. As an illustration, the design of a 3 Mc oscillator is described. In the design of i-f amplifiers, matrix methods can be applied to the evaluation of unilateralizing techniques it is shown that the type of neutralization used will have a considerable effect upon the gain and stability of the amplifier. Comparison of the neutralizing schemes is given over the frequency range from 30 Mc to 80 Mc when the type 3N25 tetrode is used. Once the parameters of the neutralized transistor are computed, the interstage coupling networks can be designed using techniques described elsewhere. The design of an i-f amplifier centered at 60 Mc, using type 3N25 tetrodes, is described. Author