How to design composite Cascode OTA...

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shady205

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Hello friends...

Is anyone aware of this architecture composite cascode OTA..(Actually i'm using two stage with first stage as composite cascode and 2nd stage as common source stage..)

I want to design it ..but lil confused how to start the design...

my requirements are 120dB gain and UGB > 1MHz and max power consumption of

the ota is 7.5uA with a supply of 1.8V


Advanced Thanks and Best Regards

Shady205
 

You need more constraints. If they are not set make
them up. You need to know the load, else you
can't realistically set the current in the output (M12).
I'm showing my lack of knowledge here: why the
composite transistors?
Anyway, GBW is set by Gm of input stage and Cc
(to first order) so give the input stage half your current, figure out the Gm you get from M3/M4
given other constraints (offset, noise). Set their
size, set Cc (add an R in series equal to 1/Gm12).
 

As nowatt said, you need more constraints. Then design it step by step.
Composite transistors here can enlarge the output resistance with a factor gm*ro at the price of its gm.
 

The Load of the above mentioned schematic is 250f & 500f .

The ICMR range is 625mV ~ 725mV
 

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