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I want to purchase AD 844 current feed back operational amplifier, I have done simulation of a circuit which involves AD 844. Now  I want to design that circuit but I am not sure How to feed current as an input in AD844.

AD844 require current as an input but I am not aware of a device which can give output as current so tell me from where I can get this current.

In my project I have to relate this current with frequency so I need an IC which can convert frequency to current but this current should be an AC current because the circuit which i am using (with AD844) cannot run on DC as it has some capacitor circuitry involved.

  • Hi Divya,

    The AD844 does not necessarily require a current input. It may be operated in the same way as a conventional (that is, voltage feedback) op amp, but it has different internal architecture than the conventional, so instead of generating an error voltage internally, it generates an error current. Do keep in mind that there are some special considerations that need to be kept in mind because its transfer function will also be different from the conventional amp. There is a very good document on current feedback amplifiers, MT-057 which you might find an interesting read.

    I would like to clarify your application though. You require an IC that can convert frequency to some sort of current, which will then be received by the AD844, correct? Or were you planning to use the AD844 for the conversion? Would you be willing to share your schematic?


  • Thanks for your reply Kris. I will read MT-057 attached by you and yes absolutely right I want some IC which can convert frequency to some sort of current and this current should be AC current. So if you encounter with this sort of IC please Let me know.

    and i am attaching the paper which involves the circuitry which i am using in my project(Page 4 of pdf). You can see it and give your suggestions.

  • IT is rather simple to make a voltage to current converter:

    When a 1 volt AC input is provided across a 1K resistor to pin 2 it will generate a 1 mA current against the zero volt of the input; roughly though, because of the imput impedance of about 50 ohms. But you get the idea.

    This way I myself have tested the basic I/V use of the AD844 in a configuration where it has the reference resistor on pin 5 (that prrovides the I/V amplification) and no feedback from pin 6.

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