A CLOSED-FORM DELAY EXPRESSION FOR DIGITAL BICMOS CIRCUITS WITH HIGH-INJECTION EFFECTS

A non-iterative formula is derived for calculating the delay time of d igital BICMOS circuits with their bipolar transistors operating in hig h-current regime. Effects such as the base transit-time increase of mi nority carriers and the decrease of the current gain of the bipolar tr ansistors are all incorporated in the model. This model can be used to investigate the effects of most device parameters such as transistor sizes and external loading on the performance of the circuits without resorting to any iterative procedures. This simplified model compares well with the original model to 10% over a wide range of operating con ditions, and is especially accurate for situations where base widening affects the bipolar transistors.