[MOVED] resistor with mosfet

[paramis]

Hi all,
I need a resistance (R=4Kohm),I want to use of Tr insted of R.
How can i made a constance resistance with mosfet that R=4k?

 

[crutschow]

Re: resistor with mosfet

Why not just use a 4k resistor?

 

[paramis]

Re: resistor with mosfet

because I want to draw layout and resistor need a big area but tr need small area.

 

[rahdirs]

Re: resistor with mosfet

I am not exactly sure,but if you use the formula for Ron,
Tox = 4E-9 m from PSpice model of TSMC's 180nm MOSFET process(change Tox according to your model)
E0=8.85E-12 F/m ,Er=3.97 ,Cox=E0*Er/tox
Cox=8.784E-3F/m²
For a NMOS: un = 670 cm^2/(V*s)
For a PMOS: up = 250 cm^2/(V*s)

Using NMOS, unCox = 0.067*(8.784E-3) = 0.5885E-3
Ron = 1/unCox(W/L)(Vgs-Vth)
4E3 = E3/0.588*(W/L)(Vgs-Vth)
(W/L)(Vgs-Vth) = 1/4*0.588 = 0.4248.

if you use (Vgs-Vth)=0.424,Vgs = 0.824.
You get (W/L)=1

By,the way i never saw one using MOSFET as 4K resistor

 

[tpetar]

Re: resistor with mosfet

because I want to draw layout and resistor need a big area but tr need small area.

How do you mean resistor need big area?

You can use SMD resistors.

https://smtsharing.blogspot.com/2012/08/smd-and-component-package.html

What power for that resistor you need, you didnt specify that ? Also there is stronger resistors in SMD case.

Resistor in 2512 can have 2W power.

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Bourns High Power Resistors
http://www.bourns.com/ProductLine.aspx?name=pulse_power_resistors