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Operational amplifiers for usage in GIC

TMishonov137
on Feb 15, 2021

Dear AD Engineers,

In order to construct device for measurements in condensed matter physics we analyze different filters.

We search a modern operational amplifier for usage in Generalized Impedance Converter (GIC).

Looking in AD collection of dual operational amplifiers, we found the following models to have application in GIC topologies (as filters) in their specifications: AD712, OP275, OP285, AD8542

Particularly in OP285/OP275 we read the following sentence:

“The closely matched and uniform ac characteristics of the OP285 make it ideal for use in GIC (Generalized Impedance Converter) and FDNR (Frequency Dependent Negative Resistor) filter applications.”

Our question is -- which are the most important parameters of an operational amplifier that makes it ideal or at least suitable in GIC and FDNR filter applications?

For example:

“The AD712 is ideally suited to drive high speed ADCs because it offers both wide bandwidth and high open-loop gain.”

and

“The circuit in Figure 46 uses a 100 Ω isolation resistor that enables the amplifier to drive capacitive loads exceeding 1500 pF; the resistor effectively isolates the high frequency feedback from the load and stabilizes the circuit.”

or

“Thus designed, the AD712 settles to ±0.01%, with a 10 V output step, in under 1 μs, while retaining the ability to drive a 250 pF load capacitance when operating as a unity-gain follower.”

Also, could you please point out at least one modern (introduced in the last 10 years) operational amplifier for such usage?

The newest of the mentioned operational amplifiers above was launched in 2003 according to its first documentation revision.

Thank you in advance for the cooperation.

Truly yours,

Todor Mishonov

  • 0
    •  Analog Employees 
    on Feb 17, 2021 7:00 AM 2 months ago

    Hi Todo Mishonov,

    Choosing a suitable op amp for a GIC and FDNR application would highly depend on what cut-off frequency you're targeting. May I know what your target frequency is? The stopband attenuation? But answering your question, I would be inclined to say that the gain bandwidth product, slew rate, and THD+N of the amplifier are the ones to look out for in this type of application.

    In the mean time, you could look at the ADA4610. Its a new amplifier and has a much higher gain bandwidth product and slew rate than the ones you've listed.

    Thanks,

    Donnie

  • 0 on Feb 19, 2021 3:33 PM 1 month ago in reply to dcruz

    Dear Donnie,

    Thank you for the clarifying discussion.

    We are not targeting any specific frequency, rather we have frequency interval 10-100 kHz in which according to our scientific project nanovolts need to be measured. After a broad-band-low-noise pre-amplifier, we wish to apply a high-Q resonance filter. Then the signal will be amplified again before being applied to a lock-in voltmeter. Thank you for the suggestion to use ADA4610, we will repeat our experiment with this OpAmp. Please find in the following link the current version of our manuscript, which is not a secret.

    https://drive.google.com/file/d/1l6gU-ApJ1TK2nhfXasjEMfplO7brqrHc/view?usp=sharing

    Moreover, we could appreciate if a peer review journal can address to EngineerZone for professional refereeing; university teachers are often not familiar with the latest development of commercial OpAmps. At the moment we will appreciate every comment you might have concerning our manuscript.

    With regards,

    Todor Mishonov