This is the specifications that must be met: "Design a charge amplifier for a piezoelectric sensor that has 500 pF capacitance. It should pass frequencies from 0.05 to 100 Hz so that it can detect carotid pulses, and it should not drift into saturation."

This is the values that I was able to solve:


The resulting circuit looks like this:


I based it on a circuit I saw on the internet but I'm not sure. Was I able to do it correctly?

  • 2
    \$\begingroup\$ 1.59 farads seems excessive. \$\endgroup\$
    – Andy aka
    Commented Sep 23, 2020 at 11:47
  • 1
    \$\begingroup\$ Does it do what you expect in simulation? \$\endgroup\$
    – user16324
    Commented Sep 23, 2020 at 12:10
  • \$\begingroup\$ @BrianDrummond I'm sorry, I don't know how to simulate it :( How can I do that? \$\endgroup\$
    – Rose
    Commented Sep 23, 2020 at 12:42
  • \$\begingroup\$ @Andyaka thankyou for pointing that out! It should be 1.59uF \$\endgroup\$
    – Rose
    Commented Sep 23, 2020 at 12:43
  • 1
    \$\begingroup\$ There are several quality resources on the design of signal condition circuits for piezoelectric sensors online. See Signal Conditioning Piezoelectric Sensors from TI, Signal Conditioning for Shock Sensors (AN4708) from STM, and Interfacing Piezo Film to Electronics for in depth design information. \$\endgroup\$
    – Ben Longo
    Commented Sep 23, 2020 at 18:59

1 Answer 1


This circuit does not amplify.

At best, the ratio of input delta_voltage to output delta_voltage, in absence of that first large capacitor (1.59F), will be

  • 500 pF / 31uF or 1/60,000

If you need that feedback time constant, then use 10Meg Ohm, and 31nF.


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