Continue to Site

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.

Register Log in

diode connected diode in cmos

Status
Not open for further replies.
C

chang830

Full Member level 5
Joined
Feb 11, 2006
Messages
267
Helped
14
Reputation
28
Reaction score
3
Trophy points
1,298
Activity points
3,424
In cmos design, we always use the diode connected NMOS and pMOS transistors. Why it is called diode conected? Is it because its I-V characteristics like a diode connected bipolar one?I can not see a diode structure from the view of process.


Another question is about the diode in standard cmos process. I need a voltage drop diode in my circuit, I used a diode connected PMOS transistor but I connected the bulk(NWELL) to its drain, then a P+/Nwell diode is developed. I want to know what's the disavantages in using this diode in my design?

Thanks in advance!!!
 

Fisrt, I think for diode connect NMOS Vds has to go above Vth to open the transistor, which is like what we do to make a diode conducted. This is where the diode connected name comes from.

As for your second question, I think there will be no detrimental results. But why don't you use a diode?
 
laglead said:
Fisrt, I think for diode connect NMOS Vds has to go above Vth to open the transistor, which is like what we do to make a diode conducted. This is where the diode connected name comes from.

As for your second question, I think there will be no detrimental results. But why don't you use a diode?
Click to expand...

thanks for the reply. it's helpful to me. As for why not use a diode, because I heared that there is no diode in standard process. The availble diode is to use a CMOS transistor connected as I said before, i.e., connect the bulk to its gain. But I found a diode model in my spice model. But I am not sure how this diode is developed in fabrication, maybe, P+diffusion/nwell. I will replce with this diode in design.
 

At least, I know in UMC process, there are P+/N-well and N+/P-sub diodes.
For low noise concern, P+/N-well is preferred.
 

    C

    chang830

    Points: 2
    Helpful Answer Positive Rating
Status
Not open for further replies.

Similar threads

Part and Inventory Search

Welcome to EDABoard.com

Sponsor

Back
Top