TTL current sinking circuit with transient performance enhancement during output transition from high to low

摘要

A transient voltage difference circuit is coupled into a TTL current sinking output circuit for transient performance enhancement during transition from high to low level potential at the output. The TTL output circuit includes a pulldown transistor element for sinking current from an output node to low potential, a base drive transistor for driving the base of a current sinking pulldown transistor element, an input base node of the base drive transistor coupled to receive input signals of high and low level potential, and a voltage clamp network coupled between the input base node and low potential for maintaining a potential level at the input base node sufficient to turn on the base drive transistor. An RC network is coupled between the input base node and low potential. The resistance of the RC network is coupled in series with the voltage clamping network adding a transient overdrive voltage in series with the clamping voltage at the input base node when the capacitance of the RC network is charging through the resistance during transition from low to high level potential at the input. The RC network and the voltage clamp network effectively form a Y network with the common branch coupled to the input base node through the resistance.