Hi,
I have a problem in that I need to calculate the S-Plane TF for a bandpass filter that has a charge input from an accelerometer. The simple circuit is as follows.
-----------------C1uF--------------------------- R475----------------- | | | | q_in R1M R1M C220nF C10nF q_out | | | |
------------------------------------------------------------------------------
And a copy just in case it does not line up right!
-----------------C1uF--------------------------- R475-------------------------- | | | | q_in R1M R1M C220nF C10nF q_out | | | |
------------------------------------------------------------------------------
Where q_in is the input from the accelerometer (at 17.5pC per g). The q_out then goes to an op amp charge amplifier where it is 'converted' to a voltage by a 4.7nF feedback capacitor so that Vout of charge amp = q_out/4.7nF
The question is how do I relate q_in to q_out as an S-Plane transfer function, as I need to know the frequency response of this circuit as it is compensated for later in the signal path, and also for a test calculation. SPICE simulations have been done for the whole circuit, and this circuit section has a high pass cutoff of ~1Hz and low pass of ~1450Hz. Why does it appear that the R1M, C1uF and R1M form the high pass, and C220nF, R475 and C10nF form the low pass part?
I know that for charge analysis in the S-plane, R -> SR and C -> 1/C, but I can not work this out.
I hope someone can shed some light.
Thanks,
Lee.