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.

Transistors in Weak Inversion

Status
Not open for further replies.

taik

Member level 3
Joined
Oct 22, 2007
Messages
58
Helped
1
Reputation
2
Reaction score
0
Trophy points
1,286
Activity points
1,604
For transistors in weak inversion, Rds=Va/Id where Va is the early voltage.

Does it mean we have to characterise the Va for transistors of different W? Va seems to be different for different W.

For e.g in designing a MOS Load Common Source amplifier where gain is Gm * Rds. I would need to find the required Rds of each transistor.

Also, in Spectre, when you do a Print->DC Operating Points, in the list of outputs displayed, is Ron = Rds?
 

Yeah, Va is related with W. And the Ron in spectre result is the Rds!

Added after 11 minutes:

I also wanna get help with the topic:
I'm designing a bandgap with subthreshold transistors. I find the Ids=W/L*Id0*exp(Vgs/(VT*n)) not accurately right for a mid-area exits between strong-inversion and weak invesion. So my bandgap has a poor PSRR(30db). Can any bro. give me a help. Thanks!
 

so if i have a targetted Rds and Id, i would have to find the W that corresponds to the Va that I need?
 

can any tell me the value of vgs in weak inversion mode??
 

can any tell me the value of vgs in weak inversion mode??
when Vgs < Vth, NMOS is in weak inversion & you will still get some current when you have a voltage difference between Drain and Source. Sub threshold currents flow in the weak inversion region.

You can calculate Vth easily for a known impurity concentration(Na) & Cox.
Vth = VFB + 2φf -(Qb/Cox) - (Qox/Cox)
 

Status
Not open for further replies.

Similar threads

Part and Inventory Search

Welcome to EDABoard.com

Sponsor

Back
Top