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Threshold Voltage for NMOS and PMOS transistor

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sykab

sykab

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I want to know if a nmos or pmos transistor are in the saturation region. So vds>vgs-VT. My problem is that I don't know the exact value of VT for nmos and pmos.
I'm using AMS technology 0,35 µm.

Thanks
 

Threshold Voltage

you can just do a dc simulation saving the OP

check the vdsat of the transistor, if Vds is larger, then you are safe in saturation ;-)
 

    sykab

    sykab

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Re: Threshold Voltage

PaloAlto said:
you can just do a dc simulation saving the OP

check the vdsat of the transistor, if Vds is larger, then you are safe in saturation ;-)
Click to expand...

Ok, but I need this information to dimension the transistor, this is, before I do any simulation.

Thanks
 

Re: Threshold Voltage

Vt depends on a lot of factors. In submicron regime, it starts depending on W and L too. So I suggest for the first cut, you can run a simple OP simulation of an nMOS and a pMOS transistor. The OP analysis (atleast in CADENCE) allows you to see the complete operating point analysis of the transistor including all the device capacitances, gm, gds, gmb, vt, ...

You can assume the Vt that you get as the threshold voltage of your transistor and calculate the dimensions required for your particular application. The saturation voltage Vdsat is almost always less that Vgs-Vt. So once you set Vds>Vgs-Vt, Vds would automatically be greater than Vdsat.
 

    sykab

    sykab

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Threshold Voltage

As spminn says, Vth is a technology dependent factor. You either must have the kit from AMS and run sims or have numerical data such as Idsat that allows you to extract the quadratic expression coefficients
 

    sykab

    sykab

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Threshold Voltage

Do DC Operation Point Analysis (suboption in DC analysis options window) then ADE/Results/Print/DC Operation Point and select device. In arised window you are able to see some MOST internal parameters.
The explanation of all parameters you can find by typing "spectre -h bsim3v3" in terminal.
The most interesting of them are: gm, vth, vdsat, ids, gmoverid, region.
Also you can annotate some of them on schematic by ADE/Results/Annotate/DC Operation Point + DC node voltages. Diplayed information depends from design kit.
It's better check that vds>vdsat instead vds>vgs-vth. Because vds>vdsat is valid for all inversion level and vds>vgs-vth only for strong inversion.
P.S. I may make a mistake in names, but I'm sure you will find.
 

    sykab

    sykab

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    V

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Threshold Voltage

The CDS can show all of the parameters around the target transistor in the schematic. You can fool around with the "component display" option.

For 0.35um, the Vds>Vgs-Vth only can give you the ballpark about how the transistor behaves itself. Don't stick to linear/saturation too much. Just look at the gm/ft/current density.
 

    sykab

    sykab

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Threshold Voltage

You got to find it by testing the mos by using it in a simple circuit! But it will be usually in the range of .5 or .6 mV generally! But it varies because of many other paramaters.. So better test your MOS and find out the precise value!
 

    sykab

    sykab

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Re: Threshold Voltage

sykab said:
I want to know if a nmos or pmos transistor are in the saturation region. So vds>vgs-VT. My problem is that I don't know the exact value of VT for nmos and pmos.
I'm using AMS technology 0,35 µm.

Thanks
Click to expand...

Do you know how to connect a nmos or pmos to a diode?
after you do that, make it's current Id equal to 1uA, then the Vgs=Vds will close to threshold voltage.

it is my method to understand the Vth.
 

    sykab

    sykab

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Re: Threshold Voltage

jecyhale said:
sykab said:
I want to know if a nmos or pmos transistor are in the saturation region. So vds>vgs-VT. My problem is that I don't know the exact value of VT for nmos and pmos.
I'm using AMS technology 0,35 µm.

Thanks
Click to expand...

Do you know how to connect a nmos or pmos to a diode?
after you do that, make it's current Id equal to 1uA, then the Vgs=Vds will close to threshold voltage.

it is my method to understand the Vth.
Click to expand...

Yes, I know how to connect a Mos to a diode!
Thanks a lot :).
 

Threshold Voltage

Hi ,
U can run operating point simulation and see .chi file in run directory for all relevant values of transistor.
Even if u have wrongly put the w/l values u will get the Vth values in the .chi file.
Hope this helps
Supreet
 

    sykab

    sykab

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Re: Threshold Voltage

sykab said:
jecyhale said:
sykab said:
I want to know if a nmos or pmos transistor are in the saturation region. So vds>vgs-VT. My problem is that I don't know the exact value of VT for nmos and pmos.
I'm using AMS technology 0,35 µm.

Thanks
Click to expand...

Do you know how to connect a nmos or pmos to a diode?
after you do that, make it's current Id equal to 1uA, then the Vgs=Vds will close to threshold voltage.

it is my method to understand the Vth.
Click to expand...

Yes, I know how to connect a Mos to a diode!
Thanks a lot :).
Click to expand...

Welcome.
I usually set 1uA as the Id, but it will be set as 10 uA for large W/L.
The Vth is the voltage that the MOS can be turned on. So the most important thing is how to define 'turned on'.
Good luck.
 

    sykab

    sykab

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