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OPA191: High pass filter with cutoff frequency <1Hz

Joel Herminjard
Prodigy 80 points

Part Number: OPA191

For a new design, I have to include the measurement of the sonde pressure level (frequency range between 2 - 250 Hz).
The output of the microphone is modulated on a DC component (around 13 VDC).

Before the AD converter I have to remove the DC component. For that I use an active high pass filter.
The cutoff frequency of the filter is <1Hz.

I have a problem of wave on the output of the filter.
Because the values of the capacitor and of the resistor are quiet high (1uF for the capacitor), do they have some precaution to take ?
For example, is it possible to use a ceramic capacitor X7R ?
We often use NOP or COG for filter but the value are too low with this technology.
The used amplifier (OPA191) has a low bias of 5pF. Do you think it could be a problem ?

Any hint will be appreciate.

  • 0
    TI__Guru 64495 points

    Hello Joel,

    Could you elaborate on what you mean by:  "I have a problem of wave on the output of the filter"?

    Are you saying the output of the active filter is oscillating?  If so, please send us the exact circuit schematic and we'll take a look.

    When designing with active filters C0G/NP0 are the preferred dielectrics but as you've noted these won't be available in large values such as 1uF.

    Not sure what you mean by the low bias of 5pF.  Are you referring to the input capacitance?