How many MOS transistors are required to implement full adder?

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alpeshchokshi

Full Member level 2
how many min. no. of MOS transistors are required to implement full adder???

xstal

Full Member level 2
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.:|

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

Arturi

Member level 2
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

Newbie level 6
Re: INTERVIEW QUESTION

min num of 28 transistors are required to omplement fulla dder

alpeshchokshi

Full Member level 2
Re: INTERVIEW QUESTION

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

Jyotshna Mamillapalli

Junior Member level 3
Re: INTERVIEW QUESTION

Try with pass transistors
For sum you need 6 transistors

bhanuriramesh

Newbie level 6
Re: INTERVIEW QUESTION

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

Jyotshna Mamillapalli

Junior Member level 3
Re: INTERVIEW QUESTION

can u explain how do we acheive using 28 transistors?

Zeng Jie-jun

Junior Member level 3
Re: INTERVIEW QUESTION

See Picture.

smalldog

Junior Member level 2
Re: INTERVIEW QUESTION

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

xstal

Full Member level 2
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

Full Member level 3
INTERVIEW QUESTION

full custom design

sumit_techkgp

Full Member level 2
INTERVIEW QUESTION

It depends on your delay and power requirement
Sumit

Mehdikhantan

Newbie level 3
14 of the cmoses are enough
See the picture attached

subbuindia

Member level 5
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

Newbie level 3
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

Mehdikhantan

Newbie level 3
see this one
it works with 10 T

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