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How many MOS transistors are required to implement full adder?

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xstal

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Re: INTERVIEW QUESTION

Refer Kang or Rabey, The logic is implemented such that the carry logic is reused in sum logic. Hence the number of transistors are minimum.:|

Added after 33 minutes:

Refer Kang, The logic is implemented such that the carry logic is reused in sum logic. Hence the number of transistors are minimum.:|
 

Arturi

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Re: INTERVIEW QUESTION

A full adder has 2 XORs, 2 ANDs and 1 OR gate.

Each XOR has 2 ANDs and 1 OR and 2 INVs

So we have a total of 6 ANDs and 3 ORs and 2 INVs

ANDs and ORs use 6 transistors in CMOS, INVs use 2 transistors

So, 6*(6+3) + 2*(2) = 54 + 4 = 58 Tranistors

Hope I got that right!

:)

cheers
 

bhanuriramesh

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Re: INTERVIEW QUESTION

min num of 28 transistors are required to omplement fulla dder
 

alpeshchokshi

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Re: INTERVIEW QUESTION

can you explain me how u reached to the 28 no. transistors????
 

Jyotshna Mamillapalli

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Re: INTERVIEW QUESTION

Try with pass transistors
For sum you need 6 transistors
 

bhanuriramesh

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Re: INTERVIEW QUESTION

we cant implement a fulladder sum with 6 transistor....
min num of transistors req r 28.........................
 

Jyotshna Mamillapalli

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Re: INTERVIEW QUESTION

can u explain how do we acheive using 28 transistors?
 

Zeng Jie-jun

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Re: INTERVIEW QUESTION

See Picture.
 

smalldog

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Re: INTERVIEW QUESTION

What kind of job interview were you done for this questin? Layout position, or designer, or system manager
 

xstal

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Re: INTERVIEW QUESTION

Hi,
28 transistor solution is the optimum. This is the same solution that I suggested (refer Kang). It is reusing the carry logic to obtain sum.
 

cnspy

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INTERVIEW QUESTION

full custom design
 

sumit_techkgp

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INTERVIEW QUESTION

It depends on your delay and power requirement
Sumit
 

Mehdikhantan

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14 of the cmoses are enough
See the picture attached
 

subbuindia

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14 of the cmoses are enough
See the picture attached

Hi friend....

Can you explain how this circuit gets the outputs of full adder? Of course, I didn't check all conditions. Suppose I take A=0, B=0 and C=1. Accroding to this inputs we have to get the carry output is 0. But, in this circuit we get, 1.

Even, Why you are using A xor B as input for carry output?
 

Mehdikhantan

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Hi friend....

Can you explain how this circuit gets the outputs of full adder? Of course, I didn't check all conditions. Suppose I take A=0, B=0 and C=1. Accroding to this inputs we have to get the carry output is 0. But, in this circuit we get, 1.

Even, Why you are using A xor B as input for carry output?
oh
excuse me
there is a mistake in the picture
A XNOR B Is correct
try that;)
 

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