Practice question · True or false
A ripple-carry adder's delay grows with the number of bits because each stage waits for the carry from the one below it.
Hints
- Where does stage k get its carry from?
- The dependency chain is the whole width.
Show the answer
True
Why
True. The carry propagates serially, so a 64-bit ripple-carry adder is 64 gate delays deep and the adder sets the processor's critical path. Carry-lookahead computes the carries in parallel from generate and propagate signals, trading a great many more gates for logarithmic depth.
Practise Adders, Multiplexers, and Decoders
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