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I want to design a lowpass filter-4th order Bessel, so two Sallen-Key low-pass circuits in cascade with a cutoff frequency of 200Hz. I need to choose the op amps for it.

I have these 3 op amps to choose from:

  • MCP6004
  • TL084
  • LM324

A quick google search tells me that MCP6004 is best used for analog filters and the TL084 for AC-DC conversions which is a thing I will plan to do.

I tried to find data sheets for TL084 and all I found was this.

enter image description here

There's like a TL084A,B,C and beyond so I'm not even sure what I am looking at, all I know is that I have can have a TL084. I don't know what the B and C versions are.

In the very top left of that link Ihave the main features that I think are valid for all models of TL084, it has a very high slew rate. I tested that in LTspice and compared it to LM324 and the results show me that when I put a square wave input at a TL084 op amp I get a square wave but when I do it to a LM324 I get a trapezoid. Because my circuit has a cutoff frequency of 200 Hz I think that any ampop unity-gain bandwidth can do well here, so I will perhaps exclude the LM324.

For the MCP6004 I got its sheet and found this:

enter image description here

All the input bias currents and input voltage offset are very low.

For the TL084 I got confused reading the sheet.

enter image description here

I found this in page 16. I'mnot sure if that is for the TL084 as in the image it has a X in it. If that's the case then the input bias currents and input voltage offset are also very low.

What should I choose?

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    \$\begingroup\$ I dont understand why this question is closed, he clearly is asking for help to understand what parameters he should look at for his filter. This is not off topic. \$\endgroup\$
    – Linkyyy
    Commented Nov 2, 2021 at 16:39
  • \$\begingroup\$ You choose based on the expected performance of your circuit. You haven't stated that at all. Noise, offsets, out-of-band performance, power rail versatility, temperature range, overall gain, input impedance, output drive capability, slew rate and probably some more things that just are not covered in this: lowpass filter-4th order Bessel. Next asking someone to choose based on 3 offerings means that you are presuming one of the 3 is the overall best choice in all op-amps in the world. This will outdate answers rapidly. Not accepting answers is also something you should look at. \$\endgroup\$
    – Andy aka
    Commented Nov 2, 2021 at 17:36

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