Other Parts Discussed in Thread: TLV2771, TLV6741
I am looking for an appropriate charge amplifier for a Piezo sensor.
The sensor is a PVDF foil, metallized with gold with a size of ~5x5mm2.
The thickness is 28µm (also available are 52µm and 110µm, but I guess we will use the 28µm one for reasons of flexibility).
The foil specifications are as follows:
Approximate Piezo Coefficients:
d31 = -5 to -6, d32 = -4 to -5, d33 = -28 to -32,
Di-electric Constant (Relative permittivity):
So the capacity of the sensor is roughly ~100pF.
The foil will be incorporated into an artificial finger, basically a silicone form of a real finger, to sense the vibrations which are formed when the finger is rubbed across a surface.
The electrodes are glued to the sensor. The amplifier can be located the closest roughly 5 to 10 cm away from the sensor.
The frequencies of interest, and mainly generated, are between 10 to 2000Hz.
The amplitude of the vibrations, responsible for the induced strain in the foil, will be small however I don’t know how small.
So unfortunately I am not yet sure about the generated voltages but I guess they could be in the mV range.
For a start I thought to connect the amplifier (about which I hope to gather some information here) to a USB oscilloscope (Picoscope 2206) with Input characteristics
BNC, 1 MΩ ±1% ∥13 pF ±1 p
This is a 8bit System with a 50Mhz bandwidth.
However the goal is to connect it to an accurate AD converter and connect it to the PC without the use of this oscilloscope.
In the TI Application report: Signal Conditioning Piezoelectric sensors, the OP Amp TLV2771 is used for a moderate amount of amplification.
There is a post by Mandar Kothavade: selecting opamp for sensing piezo generated voltages.
Where his piezo has capacitance near about 5nF and it generates voltage waveforms of frequency around 500kHz in the range -5mV to 5mV. and he asks for a opamp which should be able to sense this voltage and amplify it in the voltage range 0-3V.
The suggestions was to use the OPA2301.
However this might be mainly due to the high frequeny demand!?
I am also interested in how to dimension the feedback resistor and capacitance, as for expected small input voltages from the piezo and the desired low frequency cut off of about 10Hz i wonder wheter this can be realized with one amplifier stage or not?
Unfortunately have a confined knowledge when it comes to electronics and so I would be very thankful for any suggestions concerning an approriate amplifier model and tips on the required crcuit!
Thanks a lot to everyone in advance!