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Subject: Simple OTA gain

Date: 08/28/03 at 6:56 AM
Posted by: Jason
E-mail: jason_class[AT55]yahoo.com (replace [AT55] with @ to reply)
Message Posted:

Hello Russ,

I am sorry that I need to bother you again. This is about OTA(Operational tansconductance Amplifier)

I have uploaded the circuit on below page

http://www.geocities.com/jason_class/gain_is.gif

The ratio of M8 to M7 is B, the ratio of M5 to M3 is 1, The ratio of M1 to M2 is 1 and lastly the ratio of M6 to M4 is B.I drew 2 main current path, one is in red and another is in purple.
For the red one, it branch to a green path and join at Vout.
All the 3 paths will join at Vout as seen from the circuit diagram. I do not know if the path I drew is the right ones. SO please correct me if I am wrong.

I do not know how to determine amplification of voltage or current after each transistor. I know that for current mirror mosfet pairs, there is no gain at all. So can I say for M5 and M3 current mirror, there is no gain? The same goes for M4 and M6?

Could enlighthen me how to see the change in gain and using what formula when I
need to analyse the gain at each transistor. I read from text book and it is about using delta I / delta V = gm formula .

Then eventually, what is the total gain and how should I add them together?Please help me to understand in details as I really want to learn the correct way to analyse
such a big circuit.

Can we in a overall perspective, teach me how should I analyse this circuit in depth?

Thank you Russ. I apologise for all inconveniences caused