Second stage in fully differential output OTA design

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sudeep_

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Hi,

I have a boubt in the second stage of fully differential output OTA. I used PMOS loads, Is it double size needed in the second stage than 1stage of PMOS loads?

Why PMOS loads needed double size than 1st stage?




Thanks!
 

sudeep_ said:
Hi,

I have a boubt in the second stage of fully differential output OTA. I used PMOS loads, Is it double size needed in the second stage than 1stage of PMOS loads?

Why PMOS loads needed double size than 1st stage?




Thanks!
Click to expand...

Hi,

It depends. In order to make your amplifier meet your specs such as gain, the easiest way is by set up the gm for pmos at second stage by 10 times to the pmos at first stage. As the gm increase, the current will also increase. By this you can see that the W/L for pmos at second stage will be larger than the first stage.
 

Thanks for reply, Can you hint me to match the current between the PMOS load and current source biased NMOS at the second stage.

The problems is the currents would not match at the second stge.
 

The small current variation shown in DC run also
 

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