Has any one heard of OTA (operational transcunductance amplifier)?
would you mind giving me some links of technical information about that .

 

I've heard of them, but never had occasion to use one. Walter Jung in his classic work has a chapter on them.

http://www.amazon.com/Op-Amp-Cookbook-3rd-Walter-Jung/dp/0138896011

 

See the attached datasheets and apps for the National CA3080 (now made by Rochester) or the LM13700.

 

Thank to both of you.
I am going to work with that for the first time.