Anomalous behavior of transistor-transistor logic circuits with totem-pole output

The response of transistor-transistor logic (TTL) gates, with totem-pole output, for input conditions which are in the logically undefined region, is studied experimentally and analytically. The phase splitter and the totem-pole configuration in these circuits are such that they exhibit Schmitt trigger action due to positive feedback over a range of input conditions. This anomalous behavior results in hysteresis loops in the static input, output and transfer characteristics of these gates. Analytical procedures are followed to determine the magnitude of the hysteresis width as well as the actual static input and transfer characteristics. Experimental observations show that the hysteresis width has increased as the circuits were modified from one generation to the other for better speed.