Welcome to EDAboard.com

Welcome to our site! EDAboard.com is an international Electronics Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.

transmission gate question

Status
Not open for further replies.

anantha_09

Member level 4
Joined
Jan 28, 2007
Messages
75
Helped
0
Reputation
0
Reaction score
0
Trophy points
1,286
Activity points
1,771
why dont we use only either p or n mos device in Transmission gate

also

why dont we size the p mos and n mos devices in TG unlike we do in cmos devices.
 

forkschgrad

Full Member level 5
Joined
Apr 6, 2007
Messages
271
Helped
18
Reputation
36
Reaction score
8
Trophy points
1,298
Location
Philippines
Activity points
2,363
PMOS transistors are able to pass "0" levels and NMOS are able to pass "1" levels. that config allows for the noninverting propagation of the input signal.
 

satyakumar

Full Member level 3
Joined
May 18, 2006
Messages
186
Helped
20
Reputation
40
Reaction score
11
Trophy points
1,298
Location
Bangalore
Activity points
2,411
Hi,
PMOS effective in passing '1' and NMOS in '0', both combination makes the transfer of data without any degradation, these are used in gating and hence in flip flops etc.
 

lordsathish

Full Member level 5
Joined
Feb 11, 2006
Messages
247
Helped
33
Reputation
66
Reaction score
3
Trophy points
1,298
Location
Asia
Activity points
2,698
Yeah... PMOS can pass a strong one and a NMOS can pass a strong zero...And i am not sure whether we wont size the transistors in transmission gates....as far as i know it should be sized... size it will be uneven resistance for zeros and ones...
 

bg21359

Member level 3
Joined
Mar 1, 2005
Messages
56
Helped
7
Reputation
12
Reaction score
4
Trophy points
1,288
Activity points
1,802
a common way to size transmission gate is to make both pmos and nmos the same size though this will make the rising edge delay and the falling edge delay different, but this is also true for dynamic logic and skewed cmos
 

lordsathish

Full Member level 5
Joined
Feb 11, 2006
Messages
247
Helped
33
Reputation
66
Reaction score
3
Trophy points
1,298
Location
Asia
Activity points
2,698
why do we make both pmos and nmos of same size in transmission gates...?:D:D:D:D:D
 

wangkaust

Newbie level 6
Joined
Sep 23, 2007
Messages
14
Helped
0
Reputation
0
Reaction score
0
Trophy points
1,281
Activity points
1,331
Resistance will be different between high and low signal, if they are different size.
 

msmpy123

Newbie level 4
Joined
Aug 13, 2007
Messages
5
Helped
0
Reputation
0
Reaction score
0
Trophy points
1,281
Activity points
1,311
Hi,
Please go through the details about Transmission gate, How can we size them...
let me know if any thing is unclear!!
 

Joined
Sep 3, 2007
Messages
853
Helped
66
Reputation
132
Reaction score
16
Trophy points
1,298
Activity points
0
I think that the P Mos must be larger (2 times) that N Mos because of the mobility of carriers.
 

salma ali bakr

Advanced Member level 3
Joined
Jan 27, 2006
Messages
971
Helped
104
Reputation
206
Reaction score
21
Trophy points
1,298
Activity points
7,491
this type of implementation of the Transmission Gate (by pmos and nmos) makes it suitable to be used, along with inverters, to build any two-input logic gate...and this is according to Shannon's expansion theorem:

F(A,B) = A F(1,B) + Abar F(0,B)

So if you have 2 transmission gates...the input of one of them would be connected to F(1,B) and its control is A on NMOS and Abar on PMOS...and the input of the other would be F(0,B) and its control is Abar on NMOS and A on PMOS...the output of both is just one wire=> F(A,B)...which takes its value according to the level of A
 

Joined
Sep 3, 2007
Messages
853
Helped
66
Reputation
132
Reaction score
16
Trophy points
1,298
Activity points
0
Hi all,
Salma could you please explain more the tchnique you mensionned coz I couldnt get it. Please if you have material on this matter upload it.
Thanks a lot.
 

salma ali bakr

Advanced Member level 3
Joined
Jan 27, 2006
Messages
971
Helped
104
Reputation
206
Reaction score
21
Trophy points
1,298
Activity points
7,491
I hope these help and explain a little:

Shannon's Expansion states that:

F(A,B)= A F(1,B)+ Abar F(0,B)
 

salma ali bakr

Advanced Member level 3
Joined
Jan 27, 2006
Messages
971
Helped
104
Reputation
206
Reaction score
21
Trophy points
1,298
Activity points
7,491
Thanks a lot...
I'll leave the tech side of me now and go continue with the cooking :D
Heheheee..!
 

ramz

Junior Member level 2
Joined
May 19, 2007
Messages
24
Helped
1
Reputation
2
Reaction score
1
Trophy points
1,283
Activity points
1,410
useful.. material....
 

Status
Not open for further replies.

Part and Inventory Search

Welcome to EDABoard.com

Sponsor

Top