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?

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    \$\begingroup\$ 1.59 farads seems excessive. \$\endgroup\$ – Andy aka Sep 23 '20 at 11:47
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    \$\begingroup\$ Does it do what you expect in simulation? \$\endgroup\$ – user_1818839 Sep 23 '20 at 12:10
  • \$\begingroup\$ @BrianDrummond I'm sorry, I don't know how to simulate it :( How can I do that? \$\endgroup\$ – Rose Sep 23 '20 at 12:42
  • \$\begingroup\$ @Andyaka thankyou for pointing that out! It should be 1.59uF \$\endgroup\$ – Rose Sep 23 '20 at 12:43
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    \$\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 Sep 23 '20 at 18:59

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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