Logic Families and Their Characteristics - Technical MCQs

Q1:

What is unique about TTL devices such as the 74SXX?

A These devices use Schottky transistors and diodes to prevent them from going into saturation; this results in faster turn-on and turn-off times, which translates into higher frequency operation.

B The gate transistors are silicon (S), and the gates therefore have lower values of leakage current.

C The S denotes the fact that a single gate is present in the IC rather than the usual package of 2–6 gates.

D The S denotes a slow version of the device, which is a consequence of its higher power rating.

ANS:A - These devices use Schottky transistors and diodes to prevent them from going into saturation; this results in faster turn-on and turn-off times, which translates into higher frequency operation.

Schottky diode is made up of metal and semiconductor junction, hence it will have low forward knee voltage compared to PN junction diode.

It has less RC constant because of size, and it has larger current density carrying capacity hence it is faster device and hence mainly used in RF applications.