Totem-pole output behavior in TTL A TTL totem-pole output stage is designed so that the two output transistors:

Introduction / Context:
Totem-pole outputs provide active pull-up and active pull-down for fast edges and strong drive. Correct operation requires preventing simultaneous conduction of the pull-up and pull-down devices, which would short VCC to GND.

Given Data / Assumptions:

• Classic TTL totem-pole uses two bipolar transistors in a stacked arrangement.
• Internal steering and diode networks manage transitions.
• Goal: minimize propagation delay while avoiding shoot-through.

Concept / Approach:
Designers bias and steer base currents to ensure break-before-make behavior: when the pull-down turns on, the pull-up is off, and vice versa. This reduces transient crowbar current and heat, improving reliability and power efficiency.

Step-by-Step Solution:

Verification / Alternative check:
Timing waveforms in TTL datasheets show minimal overlap currents; internal diode clamps and bias networks enforce non-overlap.

Why Other Options Are Wrong:

• Always on together: would short supply and ground.
• Phase splitting/voltage regulation: not the purpose of the TTL output stage.

Common Pitfalls:
Assuming minor overlap is acceptable; while some transient current exists, the design strives to keep it minimal.

Final Answer:
are never on together