Overdrive Voltage ???? please help me

[pelo]

overdrive voltage

Hi,
i have to design a Folded cascode OTA and i want to know what overdrive voltage i have to choise for NMOS and for PMOS.

Vcc = 5v
Ibias=1mA

Other question, for a suplly voltage of 5V what input and output swing i have to take???

Thanx by advance!

 

[pkalavakuru]

overdrive voltage 0.1

Hey..

Find out DC operrating point of OTA..take Common mode Voltage (for you its 2.5v) and dc simulation...

Input swing depends on what type of Differential pair u use and try to know what type of output swing u need ..i mean do u need rail torail ?

start tlike this then u 'll come near to ur goal..

best regards

 

[lianghuamo]

overdrive voltage for pmos

I think the overdrive voltage is mainly dependented by the Vth and the transistor where it is used. I think 10-30% of Vth is good for current mirrors and 8-20% for cascode transistors.

 

[Material]

overdrive voltage 5v

First Vov will not precisely predict the performance of circuit in short channel.

Now circuit designers use Gm/Id or Vdsat intead of Vov.

Big Vdsat will be good for matching.
Small Vdsat will bring big Gm/Id, and is good for power efficient.

For present design, the Vdsat is chosen below 0.2V, or 0.1V depending on your application and process.

 

[ppenday]

overdrive voltage should be greater than 100mV for transistors to operate in saturation region. usually designers keep overdrive volatge around 150mV for safer side.

 

[pelo]

For example, in my Folded cascode, my input pair is a PMOS, i have to take Vov =0.15 (0.2) for all the transistors? for the input pair, the current mirror and the cascode??

And, with a folded cascode what is the best output swing i sould take?
For Vcc = 5V,??
For Vcc = 1.6??

Thanks