Generalized Input and Output Equivalent Circuits for Networks with Active Three-Terminal Devices

Any active three-terminal device can be characterized for low-frequency work by means of input and output static characteristic curves. From these curves, the piecewise linear equivalent circuit of the device is then obtained. The active device can be excited by sources connected between each of the three terminals and a reference terminal. Alternately, these sources can be considered to be external Thevenin equivalents between each terminal and the reference terminal. Under this general form of excitation, the complete input and output equivalent circuits, including the effects of terminations, can then be obtained. The results are given in terms of independent sources and hence are easily applicable to any circuit involving active elements.