# Tag Info

Accepted

Ripple carry and carry lookahead adders are combinatorial circuits - they do not hold state and they are not clocked. So counting clock cycles is meaningless, unless perhaps you are talking about ...
• 39.6k

### Delay in 4-bit ripple carry adder?

Your analysis of the single full adder is correct as far as it goes, but it is incomplete. The delays you show are all based on the Xi and ...
• 164k

### How do carry save adders work?

But why must it be used to "compute the sum of three or more n-bit numbers" why can't it compute 2 n-bit numbers? The carry save addition of 2 N-bit numbers results in two (N + 1)-bit numbers being ...
• 1,700

You want to take the internal logic for a 4-bit adder with look-ahead carry, such as the 74HC283: and then count up the longest possible gate delay for S2, or bit 1 (I get 6).
• 46.9k
Accepted

We could think of a carry look-ahead adder as made up of two "parts" The part that computes the carry for each bit The part that adds the input bits and the carry for each bit position The ...
• 36
1 vote

Why is the last stage treated like this? Why isn't it treated like the previous stages? The last Carry Look Ahead Adder Block is a ripple carry adder to reduce the complexity of the circuit to save ...
• 2,401
1 vote
Accepted

### CLA Propagate Term: Xor vs Or Gate

For computing the carry propagate term both the expressions Pi = Ai or Bi Pi = Ai xor Bi works since the only difference in the truth tables of XOR and OR is when A=1 and B=1. However in the ...
1 vote

### 8 bit adder with 2 CLA

Get a sheet of grid paper, the bigger the better. Draw out the waveform for all possible inputs of a 4-bit cla and then work through it and calculate the outputs. Write the decimal equivalent on there ...
• 63.3k
1 vote

As you say, there are a lot of references to Carry Look Ahead adder and Prefix adders, such as the the Ladner-Fischer adder and Kogge-Stone adder. How everywhere I looked, it seemed these were shown ...
• 46.9k
1 vote
Accepted

### Delay in 4-bit ripple carry adder?

It took me a while but here's how it is : The first carry and sum will be available after 4.8 us. This should be straight forward. However, for the subsequent stages, you need to keep in mind that ...
• 1,359
1 vote