Mike28
Newbie level 1
So I am trying to design an OTA to meet the following specs:
![Specs.png Specs.png](https://www.edaboard.com/data/attachments/52/52371-b02b9fe1a5c6f7c99e97fad41bf41289.jpg)
Plus the following constraints:
The maximum allowed transistor width is W=100um.
The maximum allowed transistor length is L=20um.
The maximum allowed capacitance (if you use Miller compensation) is Cc=2pF.
The supplies are Vss=0 & Vdd=1.8V.
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I decided to go with the typical 2 stage miller OTA:
![Circuit.png Circuit.png](https://www.edaboard.com/data/attachments/52/52372-b32d0305ff4bae7a06e9cc3acb4200a0.jpg)
and the best result I got was (while meeting the specs) GBW = 20 MHZ.
______________________________________________________________________________
NOTE: I checked few posts in the forum, and I saw a lot of designers suggest using the RFC OTA. I checked it and its design seems to be 10 times harder than the Miller OTA (I am still new to the analog design :grin![Smile :) :)](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)
![Specs.png Specs.png](https://www.edaboard.com/data/attachments/52/52371-b02b9fe1a5c6f7c99e97fad41bf41289.jpg)
Plus the following constraints:
The maximum allowed transistor width is W=100um.
The maximum allowed transistor length is L=20um.
The maximum allowed capacitance (if you use Miller compensation) is Cc=2pF.
The supplies are Vss=0 & Vdd=1.8V.
______________________________________________________________________________
I decided to go with the typical 2 stage miller OTA:
![Circuit.png Circuit.png](https://www.edaboard.com/data/attachments/52/52372-b32d0305ff4bae7a06e9cc3acb4200a0.jpg)
and the best result I got was (while meeting the specs) GBW = 20 MHZ.
______________________________________________________________________________
- Is the miller OTA suitable for this design problem?
- Is there any rule of thumb on choosing the transistor's W and L?
- What is the maximum GBW that I can achieve while meeting the specs? (this will help decide if my design was okay, at least.)
NOTE: I checked few posts in the forum, and I saw a lot of designers suggest using the RFC OTA. I checked it and its design seems to be 10 times harder than the Miller OTA (I am still new to the analog design :grin
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