Hi every scientist
I am doing a design for an oscillator circuit, and I need an OTA ( Operational Transconductance Amplifier ) with " negative transconductance for active component in my circuit.
In many papers, the author using OPA660 but when I simulated it in PSpice, the transconductance always positive. I think the author maybe use the old version of OPA660, and it is not available now.
So, does anyone know the about the OTA with negative transconductance? Please give me a recommendation.
Best regards and thanks so much for those who reading my question ^^
Dear Prof.Josef Punčochář
You mean positive feedback for circuit or for this device ?
Actually, I just follow to this paper.
Or a more modern concept :-)
https://www.researchgate.net/publication/51873514_Development_of_a_Mass_Sensitive_Quartz_Crystal_Microbalance_QCM-Based_DNA_Biosensor_Using_a_50_MHz_Electronic_Oscillator_Circuit
Article Development of a Mass Sensitive Quartz Crystal Microbalance ...
Dear Prof. Josef Punčochář
Thanks so much for your shared file
In the later paper you have sent. The circuit was designed by Miller topology, and the author did not show how to simulate or any graph from Pspice. He/Shi just show the final circuit.
I have already referred to these reference topology of Mille, all of these show that OPA660 have negative transconductance ( that means gf < 0, if Prof have free time, please see me attached paper). I try to simulate OPA660 in Pspice but my gf >0 always.
That's is my problems. Anyway I really wanna say thank you for your warmly consultant.
If I successfully simulate OPA660 in Pspice, everything will clear for me.
Unfortunately, it is not marked the arrow convention (for currents) either in the article or the datasheet of OPA660! That is bad situation! You have to think about it well. I think it is something great mistake.
See a convention in attachement below, OPA 660 is diamond transistor (plus buffer).
Dear Nhan Dinh Ngo, You write:
"I think this value is constant only for DC analysis
however in case of AC voltage, the value of transconductance will be a function of frequency".
The answer is hidden in the picture.
But OPA660 is very old circuit, You must see some modern - AD844? Or OPA860.
Josef
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