[...]... junction in breakdown is used as a voltage reference called a “zener diode.” If current is limited, the junction recovers when the reverse voltage is reduced Designers use these zeners for a wide variety of clipping and protection circuits Transistors are designed to operate over a range of voltages without breakdown occuring In bipolar transistors, higher breakdown voltages are achieved by reducing collector... (1.48) and where ND is the base doping, donors per cm3 Equation 1.47 describes the collector current as a function of base to emitter voltage It is an important equation, widely used in bipolar circuit design 1.5.2 Base Current Bipolar transistors are current gain devices The collector current is a multiple of the base current The current gain β = Ic /Ib varies over a wide range for transistors produced . Corp. Practices and Pitfalls Analog BiCMOS DESIGN