Thanks dear echo47;
I understand its role for modifying transfer characteristics.
but what about turn-off delay?
I read in TI TTL Databook [volume2] that this circuit reduce turn-off time Q6.
when we ignore it's role about modifying transfer characteristics,
and compare it's effect for reduction of turn-off delay time,
which one is better, simple resistor or this circuit?
i think, one simple resistor is better.
because it clamp Q6-base to ground.
but in this config. as Vbe going below 0.6-0.7 both of transistor going to off state.
Am i right?