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Making sure a MOS cascode doesnt collapse over corners

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manrajgujral

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Hi,

So I need to make sure a MOS Cascode along with other devices in one (vertical) arm of the circuit lying between VDD and GND doesn't collapse under all corners.
For this i usually make sure the VDS (or the VCE in Biploar) doesnt go below say 250mV (or about 300mV in Biploar) in a nominal run, say a dc sweep over temperature.

I see there is a device thats showing a VDS of about 100mV in that nominal run and i need to increase that drop, i am assuming that i increase the channel resistance , or the on-resistance. The current would remain the same in that arm (controlled by some active device in the signal path and not the cascodes) and therefore i can see it will not affect the operation of the circuit.

So I either increase the Length , or decrease the Width depending on other aspects such as noise and area etc. but essentially that's what I am thinking of doing. Varying L and W to increase the on-resistance to get a higher drop. - yes that will push some other device doen in the chain but that's a secondary concern.

My question is , is that what you guys recommend? or are there another ways to ensure the cascodes don't crash over corners?

Thanks
 

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