Question

The main disadvantage of Manchester carry chain is ___________

(a) Ripple factor

(b) Propagation delay

(c) Capacitive load

(d) Both propagation delay and capacitive load

The question was asked by my school principal while I was bunking the class.

This key question is from 4-Bit Parallel Adder/Subtractor in chapter Arithmetic Circuits of Digital Circuits

Answer 1

Correct choice is (d) Both propagation delay and capacitive load

To elaborate: Propagation delay is the measure of time taken by the output to go to the next state when the input is altered. One of the major downsides of the Manchester carry chain is that the capacitive load of all of these outputs, together with the resistance of the transistors causes the propagation delay to increase much more quickly than a regular carry lookahead.