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.

CMOS transmission gate

Status
Not open for further replies.

firsttimedesigning

Full Member level 1
Joined
Jul 4, 2007
Messages
97
Helped
1
Reputation
2
Reaction score
1
Trophy points
1,288
Activity points
2,241
cmos imelt

i am having trouble to figure out how to design a CMOS transmission gate. I dont know what voltage should i put for +Vcc and -Vcc. I have tried several different values, 1,2 and etc. However, Cadence Spectre always gives me a warning message that says the "the bulk drain junction current exceeds 'imelt'...". I want to know what is the value of imelt. Also is there an equation for the bulk drain junction current? Finally, what value of Vcc should i use to prevent the junction current exceed imelt? thanks in advance.
 

srieda

Full Member level 2
Joined
Dec 24, 2006
Messages
147
Helped
20
Reputation
40
Reaction score
3
Trophy points
1,298
Location
India
Activity points
2,111
cmos transmission gate

1st question : What are the transistors you are using - high voltage or low voltage?
2nd question : why should you connect nmos bulk and gate to -vcc?? cant you just ground them?
3rd point : Your transmission gate is in off condition as pointed to in the diagram, is this what u want?
 

firsttimedesigning

Full Member level 1
Joined
Jul 4, 2007
Messages
97
Helped
1
Reputation
2
Reaction score
1
Trophy points
1,288
Activity points
2,241
Thank you for replying.
1st question: I am sorry but I dont know what is a high voltage transistor or low voltage transistor. I have never heard of those terms before.

2nd question: I connected bulk to -5V because I want the negative voltage to be able to pass the switch. If I connect the bulk to the ground, then the lowest voltage this switch can pass is -0.7V. Also -Vcc is not -5V, rather it's the voltage that is supposed to turn on or off the switch. I apologize for the confusion.

3rd question: Everytime I simulate it, the transistor breaks down because vgs and vgd of the NMOS transistor has exceeded the oxide breakdown voltage. So I dont even know if this switch is in off condition.

I like to know at what Vcc voltage will turn on this switch and what Vcc voltage will turn off this switch.

Thanks in advance
 

tandy

Newbie level 6
Joined
May 26, 2009
Messages
11
Helped
4
Reputation
8
Reaction score
4
Trophy points
1,283
Location
Macao. SAR, china
Activity points
1,336
1. different technologies provide the transistors in different operation voltage. eg. H35B4D3 for 0.35um Process can both provide the standard low voltage transistor (3.3V) and also provide the high voltage transistor that can operated in 20V or even 50V.
2. if you use dual supply, it is ok for the connection.
3. for your case, i advice you use high voltage transistor. but you should confirm your current technology is available for high voltage design first.
regardings
 

checkmate

Advanced Member level 3
Joined
Feb 25, 2004
Messages
833
Helped
178
Reputation
356
Reaction score
125
Trophy points
1,323
Location
Toilet Seat
Activity points
7,815
We need to know the range of voltages you are trying to pass.
If it includes the negative range, are you sure that your process has triple well capabilities to support it?
 

Milad-D

Full Member level 3
Joined
Jan 13, 2011
Messages
170
Helped
59
Reputation
118
Reaction score
57
Trophy points
1,308
Location
Netherlands
Activity points
2,189
In the nmos transistor, there is a diode between drain and bulk.( p on the bulk and n on the drain) and vice versafor the pmos transistor. You should be always cautious about not to forward bias these diodes. Because it produce a lot of current which can exceed imelt please check that.
 

Status
Not open for further replies.

Similar threads

Part and Inventory Search

Welcome to EDABoard.com

Sponsor

Top