Solution 1:

(i) To determine the critical voltages for the basic TTL inverter shown.

VIL = VBE,O(FA) - VCE,I(SAT) = 0.7 - 0.2 = 0.5V

VIH = VBE,O(SAT) - VCE,I(SAT) = 0.8 - 0.2 = 0.6V

VOL = VCE,O(SAT) = 0.2V

VOH = VCC = 5V

Voltage Transfer Characteristics:

(ii) Simulation using spice: