TTL output stage design – totem-pole configuration: In transistor–transistor logic (TTL) with a totem-pole output stage, how are the two output transistors intentionally operated to prevent shoot-through and minimize power dissipation while delivering fast edges to the load?

Introduction / Context:
The TTL totem-pole output is a classic push-pull arrangement that provides both strong sourcing and sinking capability. Correct timing inside the gate ensures the upper and lower transistors do not conduct simultaneously. This avoids shoot-through current from VCC to ground, protects the device, and maintains sharp rise/fall times for digital signals driving typical CMOS/TTL inputs.

Given Data / Assumptions:

• Standard TTL gate with a totem-pole (push-pull) output stage.
• Goal: fast transitions with low static power.
• Load is a typical high-impedance logic input plus stray capacitance.

Concept / Approach:
In a push-pull totem-pole, one transistor sources current to drive a HIGH, and the other sinks current to drive a LOW. If both turned on together, a direct current path would exist from VCC through the upper device to the lower device to ground (shoot-through). TTL internal drive networks and brief dead-time ensure complementary action so only one device is on at a time, greatly reducing dissipation and noise.

Step-by-Step Solution:
Recognize push-pull topology: one device pulls up, the other pulls down.During a LOW→HIGH transition, the lower device turns off before the upper device turns fully on (dead-time).During a HIGH→LOW transition, the upper device turns off before the lower device turns on.Therefore, the intended behavior is that both devices are never on together.

Verification / Alternative check:
Datasheets specify low ICC during static states and show fast edges; observing with a current probe confirms no sustained shoot-through during transitions.

Why Other Options Are Wrong:
Always on together causes shoot-through and heat.

Phase-splitting and voltage regulation are not the primary function of the TTL totem-pole.

“Always alternating at 50% duty cycle” is irrelevant to logic output behavior.

Common Pitfalls:
Assuming both devices conduct during switching; while momentary overlap can occur in poorly designed stages, proper TTL design minimizes it.

Final Answer:
never on together