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 (Q₅) for sinking current from an output node to low potential, a base drive transistor (Q₄) for driving the base of a current sinking pulldown transistor element (Q₅), an input base node (A) of the base drive transistor (Q₄) coupled to receive input signals of high and low level potential, and a voltage clamp network (Q₁,Q₂,Q₃) 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 (R₄,Q₆) is coupled between the input base node (A) and low potential. The resistance (R₄) of the RC network is coupled in series with the voltage clamping network (Q₁,Q₂,Q₃) adding a transient overdrive voltage in series with the clamping voltage at the input base node when the capacitance (R₅) of the RC network (R₄,Q₆) is charging through the resistance (R₄) during transition from low to high level potential at the input. The RC network (R₄,Q₆) and the voltage clamp network (Q₁,Q₂,Q₃) effectively form a Y network with the common branch coupled to the input base node through the resistance (R₄).