GATE CSE 1998 | Question: 1.15

Question

The threshold level for logic 1 in the TTL family is

• A. any voltage above 2.5 V

• B. any voltage between 0.8 V and 5.0 V

• C. any voltage below 5.0 V

• D. any voltage below V$_{cc}$ but above 2.8 V

Answer 1

(D) any voltage below Vcc ( ≈ 5 V) but above 2.8 V 
Transistor transistor logic (TTL) was designed that any input from 0.8 volts to 0 volts is considered a logic 0, and any input from 2.6 to 5.0 volts is considered a logic 1. See the following Wikipedia page for more information 
http://en.wikipedia.org/wiki/Transistor_...