Diode operation of a transistor in functional blocks

Many functional blocks have a basic double-diffused three-layer n-p-n or p-n-p structure to permit the incorporation of transistors. If diodes are also to be incorporated in the block, it is often more convenient to connect the transistor structure already present as a diode so that "batch" processing can be used. There are five different ways to connect a transistor as a diode, either by opening certain electrodes or by short-circuiting a pair of electrodes. The different connections are compared both analytically and experimentally on the basis of forward voltage drop, recovery time and reverse characteristics. It is found that the shorted collector -base connection has the shortest recovery time, comparable to fast computer diodes, and a lower forward voltage drop than the open collector diode connection. The performance is almost equivalent to a diode with a metallic contact in place of the collector. The shorted emitter-base connection has the lowest forward voltage drop. There is good agreement between theory and experiments. The applications of this analysis to the design and fabrication of a high-speed nonsaturated diode-emitter follower AND gate functional block will be illustrated.