Question

Introducing Schottky diode between base and collector of TTL output transistor:

• A. Increases speed by inhibiting saturation
• B. Decreases speed by inhibiting saturation
• C. Increases fan-out by enabling saturation
• D. Increases speed by enabling saturation

Hint:

Schottky TTL = Fast switching by preventing deep saturation of output transistors.

Answer 1

The Correct Option is A

In TTL (Transistor-Transistor Logic) circuits, speed is a critical factor. When a transistor reaches saturation, it takes more time to switch off, slowing down circuit performance. To address this, a Schottky diode is used between the base and collector of the output transistor.

A Schottky diode has a lower forward voltage drop compared to a regular diode, which helps prevent the transistor from going into deep saturation. This is known as a Schottky-clamped transistor. By inhibiting saturation, the turn-off time of the transistor is reduced, effectively increasing the speed of the circuit.

• With the Schottky diode in place, if the transistor begins to saturate, the diode conducts, diverting excess base current and preventing full saturation.
• This reduces the time taken for the transistor to recover from saturation (turn-off delay), thus increasing the overall speed of the TTL circuit without compromising performance.

Thus, the introduction of a Schottky diode between the base and collector increases the speed of the TTL output transistor by inhibiting its saturation.