Electronics > Projects, Designs, and Technical Stuff

Charge Amplifier - Spice vs. App Note

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sdouble:

--- Quote from: geo_leeman on April 24, 2019, 11:10:54 pm ---
--- Quote from: sdouble on April 24, 2019, 08:38:28 pm ---your Cc is far too high.
i should be in the (tens to hundreds of) pF range

--- End quote ---
Actually assuming Cc to be zero, the other cap is the sensor/transducer capacitance.

--- End quote ---
yep, my bad.
Are you sure that it is of 20 uF ? That seems rather high.

geo_leeman:
In this case it is, just was working with some "nice" values for simulation. Real sensor is a plate about 10" in diameter.

sdouble:
a plate is not capacitive.
are there 2 parallel plates ?

Zero999:

--- Quote from: geo_leeman on April 22, 2019, 03:10:27 am --- I made up a quick spreadsheet and modeled the circuit in LTSpice (granted, with a different opamp, but with high GBP and FET input) and my numbers don't quite agree.
--- End quote ---
For future reference, use LTSpice's UniversalOpamp model and set the gain, roll-off, input impedances to the same as the real op-amp you intend to use. It's not perfect, but better than using a random op-amp model, substantially different to the op-amp you're going to use.

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