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INA821: small signal response close to maximum frequency

Philip Egger
Prodigy 30 points
Part Number: INA821
Other Parts Discussed in Thread: INA103

I plan to use the INA821 with a gain of 10 up to a frequency of 1MHz.

According to the Gain vs Frequency plot [Figure 21] I'd get a small dampening but not more.

On the other hand, a large Signal with 1MHz will be almost nonexistent at the output according to Figure 40.

In what manner will a for example 100mV signal be affected?

 

Kind regards

  • 0
    Guru 140200 points
    Hi Phil,

    the 970kHz bandwidth specification at a gain of 10 in figure 22 is a small signal specification. The large-signal frequency response in figure 40, on the other hand, is a large signal specification, where also the finite slew rate of INA821 comes into play.

    Take care, only because the INA821 has a 970kHz bandwidth at a gain of 10 does not mean that it can properly handle signals in this frequency range. First, this is only valid for sine waves but not for signals with arbitrary shape and, second, the INA821 is producing lots of distortion at this frequency. This can be seen from figure 41 of datasheet.

    Allow the instrumentation amplifier to have some gain reserve of factor 10 or even more to make it properly work and to keep the signal distortion low. So, If your signal bandwidth is actually 1MHz and you need a gain of 10 you might better look for a faster intrumentation amplifier.

    Kai
  • 0 in reply to kai klaas69
    TI__Genius 10850 points

     Phil,

    Kai is correct.

    I would recommend you build this schematic in our Spice simulator (TINA). We model these conditions allowing you to see the effects of your input / gain.

    Please download the simulator here: http://www.ti.com/tool/TINA-TI

    Please download the INA821 model here: http://www.ti.com/product/INA821/toolssoftware

    If you have any questions, share your TINA circuit for us to evaluate.

    -Tamara

  • 0 in reply to Tamara M Alani
    Prodigy 30 points

    Thank you both very much for your help!

     

    You are in fact both right, and I found the mistake I made. I’m having a mixed signal as an Input. The steepest edges have a ΔV of 150mV at a Δt of 700ns. With a Gain of 10 this would require a slew rate of just over 2,1V/µs with the INA821 having a max of 2V/µs.

    As predicted by you the signal was badly deformed. I found the INA103 to be an better alternative (15V/µs) But the signal is still slightly deformed. I know that the INA series is not meant for real high-speed operations but is there an alternative with a slightly higher bandwidth?

     

    Kind regards

     

    Phil