constant current vdsat values of PMOS and NMOS

[lhlbluesky]

mosfet vdsat

for smic 0.18 um technology, what's the proper value of vdsat for pmos and nmos?
100~200mv is ok?
if vdsat is too large or small, what's the influence?
if vdsat is less than 50mv, what's the problem? can it affect corner analysis?

 

[chungming]

mosfet model vdsat

The Vds ≥ Vgs-Vth if MOSFET operate in saturation region.
You should choose a proper operation point, by doing that you need to specify Vgs voltage.
So the Vdsat = Vgs-Vth, this is the small vds vaule for MOSFET operating in saturation region.

If vdsat is too large, the voltage swing will be reduced.
If vdsat is too small, the Vgs-Vth value is small too, the Ids is also small.
May be the current driving ability is not sufficient to the desired Specs(like GBW of opamp.....).
You can look some analog design book, like sansen, razavi, gray........

 

[lhlbluesky]

does vdsat of a mosfet depend on the vgs

any other reason?pls?

 

[ch1k0]

vdsat for 0.18 um technology

vdsat 150mV ok, large gm for current Id. vdsat 50mV is weak inversion, model is not good.
weak inversion good for very low power, low speed.

 

[quaternion]

vdsat from simulation

vdsat 150mV ok, large gm for current Id. vdsat 50mV is weak inversion, model is not good.
weak inversion good for very low power, low speed.

Are these values valid also for 0.13 um technology ?

 

[ashish_chauhan]

mos vdsat 0.25 v

I will agree with CH1K0...

50mv is too low... it directly says MOS is in subthreshold...

you can chaeck thisin the OP analysis results...

 

[ch1k0]

typical values of vdsat in nmos

vdsat 150mV ok, large gm for current Id. vdsat 50mV is weak inversion, model is not good.
weak inversion good for very low power, low speed.

Are these values valid also for 0.13 um technology ?

any CMOS technology...

Saturation in subthr is ~125mV , Vdsat ~150mV is moderate inversion, Vgs-Vth ~ 200mV for this Vdsat. Run simulation see this you clear.

 

[lhlbluesky]

vdsat is the 200mv vgs vt

if vdsat is 70mv in 0.18um technology,what's the problem that may induce,pls?

when i simulate in different corner for ac and tran analysis,it seems that there is no problem;ok?

 

[analog_prodigy]

vdsat mosfet

If Vdsat is very low say around 50mv, we cann't assure the proper operation of mosfet in saturation after fabrication (because of weak inversion)

And also it depends on speed/power applicaion.

If it is for speed, vdsat should be more and if u want high gain, it should be less.

 

[rajanarender_suram]

operating point vdsat

if vdsat is 70mv in 0.18um technology,what's the problem that may induce,pls?

when i simulate in different corner for ac and tran analysis,it seems that there is no problem;ok?

it may be ok for corner analysis but

if vdsat is Low than the following effects occur
1) S/N will be worse.
2) mathing between the transistors with low Vdsat will be bad
3) speed of the transistor decreases

 

[quaternion]

gm simulation cmos id vdsat

Well!

What are the parameters that control Vdsat?

What I know that it varies with: (Vgs - Vth) , Size , Current(which depend on Vds,..) ,.. ?

 

[saralari]

Re: about vdsat

0.1 to 0.25 is well

 

[Loktik_Vitalij]

Re: about vdsat

What values of VGS are commonly used?
At the higher end, we know that we never want to enter the high-current or velocity-saturation region. We stay away from the transition point to velocity saturation. It is about 0.5 V however, for present day technologies. At the low-current end, we do not want to use the weak-inversion current region either. The absolute values of the currents and of the transconductances become so small
that the noise becomes exceedingly large. Moreover, only low speeds can be obtained. There are some applications where low signal-to-noise ratios and low speed are no problem. Examples are biomedical applications and biotelemetry. In most other applications however, we need better noise performance and higher speeds. Therefore, we do want to work close to weak inversion but not in it. Typical values are VGS−VT values between 0.15 and 0.2 V.