ABSTRACT
This chapter is dedicated to a unique configuration of the field effect transistor — a diode connected transistor. The ideal conventional p-n junction diode is shown in Figure 8.1a. Ideally, if the potential at point A, VA, is greater than the potential at point B, VB , such that VA−VB > VT , the threshold voltage of the diode, there is a flow of current from A to B. On the other hand, if VA−VB < VT , there is no current from A to B as illustrated by Figure 8.1d. In other words the diode can be considered to be a circuit element which permits current flow in just one direction — from the p-side to the n-side — if the potential drop from p to n is greater than the threshold voltage of the diode. On the other hand, if the diode is reverse biased with the potential at point B being greater than the potential at point A, no current flow, except for a small leakage current, is allowed. This is exactly what a diode connected transistor achieves. This configuration is given importance because of its particular usefulness as a biasing element in large area electronic systems and is the main focus of this chapter.
