Need help with transconductance operational amplifier

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Discussion Overview

The discussion centers around the use of an operational transconductance amplifier (OTA) as a voltage-controlled current source, specifically focusing on the connection and configuration needed to output an AC current in response to an AC voltage. Participants inquire about adjusting the gain or transconductance (gm) and seek guidance on practical implementation.

Discussion Character

  • Technical explanation
  • Homework-related

Main Points Raised

  • One participant asks how to connect an OTA to function as a voltage-controlled current source and requests guidance on adjusting the gain or transconductance.
  • Another participant inquires about the specific application for which the OTA is intended.
  • Questions are raised regarding the input voltage range and the required output current range.
  • A later reply suggests connecting the input voltage to the non-inverting input and the output current to the inverting input to create a negative feedback loop, which regulates the output current based on the input voltage.
  • It is mentioned that the gain or transconductance can be adjusted by changing the feedback resistor value, with higher values resulting in higher gain or transconductance.
  • Participants are directed to refer to the OPA860 datasheet for specific guidance on using the device as a voltage-controlled current source and for formulas related to transconductance calculations.

Areas of Agreement / Disagreement

The discussion does not present a consensus, as participants are still exploring different aspects of the configuration and application of the OTA. Multiple viewpoints and questions remain unresolved.

Contextual Notes

Participants have not specified the exact input voltage range or output current range needed, which may affect the implementation details. There is also a reliance on the datasheet for specific guidance, indicating that further clarification may be necessary.

riie
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Hi all,

Does anyone know how do I connect an OTA if I want to use it as a voltage-controlled current source, meaning that it will ouput an AC current when i supplied an AC voltage?
Any guide I can refer to?

And how do I adjust the gain or transconductance, gm?

For example, OPA860 with pinout E,C,B, Iq.
http://www.ti.com/lit/ds/symlink/opa860.pdf

Thanks!
 
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anyone?
 
Hi. You pdf seems to provide a lot of information. What application are you hoping to use this for?
 
What is your input voltage range and what output current range do you need?
 


Hello,

To use an OTA as a voltage-controlled current source, you will need to connect the input voltage to the non-inverting input and the output current to the inverting input. This will create a negative feedback loop, which will regulate the output current based on the input voltage. The gain or transconductance can be adjusted by changing the value of the feedback resistor. A higher value feedback resistor will result in a higher gain or transconductance, while a lower value will result in a lower gain or transconductance.

As for a guide, I recommend referring to the datasheet for the specific OTA you are using. In this case, the OPA860 datasheet you provided has a section on using the device as a voltage-controlled current source. It also includes a formula for calculating the transconductance based on the feedback resistor value. Additionally, there are many online resources and tutorials available on using OTAs as voltage-controlled current sources that you may find helpful.

I hope this helps. Good luck with your project!
 

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