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channel length and cascode maximum gain point

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GSarris

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Hello i have designed a cascode opamp and i have one question. I use the 0.18um process and when i increase my channel length (starting from the minimum length) the maximum output gain occurs for a lower Vin. Do you have any ideas why that should happen? Shouldn't that occur for higher Vin, since the threshold voltage of the transistors increases with incresing channel length? What do i get wrong? thank you in advance
George
 

dick_freebird

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Is VIN also affecting your bias current and making the
FETs more saturated at lower VIN -> lower Ibias?
 

GSarris

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Here is my entire schematic. PLease look it and tell me if you have any idea.
Thank you in advacne! cascode_0.18u.png
 

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