| Charge Amplifier |
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EXPLANATION A piezoelectric transducer has very high DC Output Impedance and appears as a Voltage Source in series with a Capacitor . A charge amplifier therefore needs to have a very high Input Impedance at DC. DESIGN Charge amplifiers are usually constructed using Op Amp s with a Feedback capacitor. They thus act in a similar manner to an Integrator . Since the transducer acts in a similar manner to a Differentiator , the two transfer functions cancel and the output voltage is proportional to the charge produced by the transducer. Stray capacitance at the input to the amplifier is not detrimental to operation because this capacitance is always at a Virtual Ground . APPLICATIONS
PRECAUTIONS Cable from the transducer to the amplifier should not be subject to vibration as extra charges can be generated by friction and lead to unwanted noise output. EXTERNAL LINKS
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