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Questions tagged [carry-look-ahead]

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CLA Propagate Term: Xor vs Or Gate

Okay say I have to use a CLA adder to implement the addition of two 2-bit numbers, X = x1x0, Y = y1y0. And say I have to write down the logical expression for the final carry-out. So C1 or the first ...
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143 views

carry look ahead adder

An N-bit carry lookahead adder, where N is a multiple of 4, employs ICs 74181 (4 bit ALU) and 74182 ( 4 bit carry lookahead generator). The minimum addition time using the best architecture for this ...
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1answer
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Trouble with 8-bit Carry Lookahead Adder in Verilog

I'm new to Verilog programming. I'm trying to work up to a 64-bit CLA by building a 4-bit CLA, then an 8-bit (out of 2 instances of a 4-bit), then a 16-bit (out of 2 instances of the 8-bit one). I'll ...
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1answer
2k views

Time complexity of carry look ahead adder

How is the time complexity of carry look ahead adder O(log n)? Can you explain in terms of gate delays?
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1answer
545 views

Carry-lookahead adder in VLSI, Static VS Dynamic?

I study one course about VLSI. in adder lecture my profesor talk about Adders. in Carry-lookahead adder first talk about static version, as follows: at next we start about dynamic version of CLA and ...
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1answer
433 views

8 bit adder with 2 CLA

I need to make an 8 bit adder with 2 4-bit look ahead adders.I spent a lot of time reading about it and I think I get the gist of how it works, but I can't seem to get this. I spent a lot of time ...
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1answer
773 views

calculate clock cycle of ripple Carry and lookahead adder

How would you find the number of clock cycles it takes to produce sum, the carry out, and overflow flag using ripple carry or lookahead adder. Can someone please explain me how would we go on finding ...
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1answer
155 views

Arithmetic Circuits (ADDERS!)

I usually only become a passive reader in this forum, but today I decided to ask my first question. How many logic gates required for a 4-bit Carry Look Ahead adder and Prefix adder? I know that ...
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1answer
252 views

Carry look ahead adder with 2-input gates?

I would like to make a 8 bit adder, with carry look ahead, but i only have 2-input logic gates. All I've heard about use some at least 4-input gates. Or do I need to use a totally different method, ...
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1answer
5k views

How to find gate delay for 4-bit look-ahead carry adder?

How can I find Gate Delay for bit 1 of the sum by a 4-bit look-ahead carry adder?
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2answers
9k views

Delay in 4-bit ripple carry adder?

In pic below I have drawn a full adder and mentioned their delays, please help me to verify my answer.
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1answer
6k views

How do carry save adders work?

I thought I understood the concept but wikipedia has confused me. There are two outputs because one's for a partial sum and one's the carry bits. But why must it be used to "compute the sum of three ...
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0answers
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How to compare carry-lookahead and ripple-carry adders?

I am a bit stuck with the concept of carry-lookahead adder so I'd like to compare it with another concept I'm more familiar with: the ripple-carry adder. I'm trying to make some basic math comparison ...
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1answer
155 views

Design of an adder circuit

I have a adder circuit consisting of carry look ahead adders. However, I am not allowed to use the generate function to determine the sum of the two numbers. I am allowed to use basic logic operations(...
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1answer
3k views

Multiply 4 Digit Binary Number By 3 - Circuit

I want to find a way to multiply a 4 digit binary number by 3. I have this circuit that doing this process and I don't understand how it works. To multiply a number by 2 I need to shift the digits ...
2
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1answer
31k views

How to calculate Gate Delays in normal Adders and Carry Look Ahead Adders

In my textbook the gate delays for the n-bit ripple adder is given as \$ 2n \$ for \$c_n\$ bits and \$ 2n-1 \$ for \$ s_n-1 \$ for the circuit as shown below: But, for a 4-bit Carry Look Ahead Adder ...
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1answer
6k views

Carry Look ahead adder Propagate & Generate Outputs

I am taking comp architecture course, and we are given a task to write 32 bit look-ahead adder in VHDL. Instructor provided the instruction and diagram. While reading, Wikipedia article, I stumbled on ...
3
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1answer
704 views

Carry-lookahead adder - what happens to carry bit?

I recreated and trying to understand for the sake of fun and learning the circuit that can be seen here on second page: Link . This is basically a 4-bit carry-lookahead adder, but there is one thing ...
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2answers
592 views

Why does design_vision compile my carry-lookahead adder into a ripple-carry adder?

At my school we have Synopsis "design_vision" in the computer labs. I don't know how to use any of the features so to me it's just a schematic-drawing tool. Out of curiosity, I hand-coded in Verilog ...
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2answers
4k views

How to determine if a Carry Look Ahead Adder Overflows

I am implementing a 32 bit CLA Adder like how a 16 bit adder is implemented in Wikipedia Problem is how do I determine if the block overflows? I will need the carry into bit 32 (which is now in the ...
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1answer
3k views

Whats the difference with Carry Look Ahead Generator & Block Carry Look Ahead Generaor

Whats the difference between this 2 CLAG (Carry Look Ahead Generator) CLAG Block CLAG I mean, the way Carries of 1st 3 bits are the same and the last carry is actually \$G*\$? The difference is use ...
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1answer
3k views

Carry look ahead adder/subtractor & Overflow, Negative Bits

I am suppose to design a carry look ahead adder with ... Input flag bits E (Enable) S (Subtraction) Output The usual sum & carry out O (Overflow) N (Negative) Z (Zero) But the question is ...
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1answer
5k views

How does this carry look ahead block work?

This is a carry look ahead adder : This adder is known to calculate one or more carry bits before the sum. From the figure we see that carry look ahead block calculates the carry C1,C2,C3,C4 . But i ...