Computer-Networks

Question 813

Which of the following has lowest propagation delay?

A	ECL
B	TTL
C	PMOS
D	CMOS

Computer-NetworksEthernetNieLit STA 2016 March 2016

Question 813 Explanation:

● Propagation Delay: It represents the transition time which elapses when the input level changes. The delay which occurs for the output to make its transition is the propagation delay.
● Characteristics of TTL logic:
○ Power dissipation is usually 10 mW per gate.
○ Propagation delays are 10 ns when driving a 15 pF/400 ohm load.
○ Voltage levels range from 0 to Vcc where Vcc is typically 4.75V – 5.25V. Voltage range 0V – 0.8V creates logic level 0. Voltage range 2V – Vcc creates logic level 1.
● Characteristics of Emitter Coupled Logic (ECL)
● The storage time is eliminated as the transistors are used in difference amplifier mode and are never driven into saturation.
● It is the fastest logic family and has the lowest propagation delay.

Correct Answer: A

Question 813 Explanation:

● Propagation Delay: It represents the transition time which elapses when the input level changes. The delay which occurs for the output to make its transition is the propagation delay.
● Characteristics of TTL logic:
○ Power dissipation is usually 10 mW per gate.
○ Propagation delays are 10 ns when driving a 15 pF/400 ohm load.
○ Voltage levels range from 0 to Vcc where Vcc is typically 4.75V – 5.25V. Voltage range 0V – 0.8V creates logic level 0. Voltage range 2V – Vcc creates logic level 1.
● Characteristics of Emitter Coupled Logic (ECL)
● The storage time is eliminated as the transistors are used in difference amplifier mode and are never driven into saturation.
● It is the fastest logic family and has the lowest propagation delay.