Diode and Transistor Self-Analogues for Circuit Analysis

A new approach to circuit analysis has been poposed which allows high-frequency circuits to be characterized using simple low-frequency models. 1 With this approach, nanosecond diodes and transistors can be slowed down to audio frequencies and interconnected in audio frequency breadboard models of the high-frequency circuits. Thus, high-frequency circuits can be evaluated and optimized with the convenience afforded by low-frequency breadboard techniques. According to charge-control theory, 2 the frequency and transient responses of diodes and transistors are determined by the charges stored within the devices. Nanosecond diodes and transistors can be slowed down to millisecond models simply by multiplying their stored charge by a factor of 106 or some other convenient value. Charge 487 488 THE BELL SYSTEM TECHNICAL JOURNAL, APRIL 1968 storage in the devices can be classified broadly as terminal voltage dependent (fixed charge in depletion layers) and terminal current dependent (charge in transit). The former can be multiplied by connecting large capacitors between the device terminals, as described by Levine. 3 The latter can be multiplied by using small resistors as current sensors in series with device terminals, and using the voltage developed across these resistors, suitably amplified, to cause charge storage in capacitors connected to the device. 1 Models thus constructed have given excellent results for transistors operated in their active regions.4 The models also give time-scaled storage times when representing diodes or transistors operated in their saturation regions, but the values may be in error by a factor of two or more.