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Maxim > Design Support > Technical Documents > Application Notes > Amplifier and Comparator Circuits > APP 1127
Maxim > Design Support > Technical Documents > Application Notes > Sensors > APP 1127
Keywords: thermal sensor, temperature sensor, piezoelectric, high-impedance input, high-Z buffer
amplifier, temp sensor, piezo, charge amplifier, high-pass filter, noise rejection, common-mode rejection,
CMR, differential to single-ended, signal conditioning,
APPLICATION NOTE 1127
Amplifier Provides Signal Conditioning for
Piezofilm Sensor
Jun 26, 2002
Abstract: Described circuit provides a thermal output from a piezofilm transducer. The circuit is a high-
input-impedance differential charge amplifier using three op amps in a somewhat classical
instrumentation amplifier configuration. The differential stage rejects resistor-generated thermal noise,
and acts as a first-order high-pass filter. Choice of component values is discussed, and some typical
valuese are suggested. Alternate configurations are suggested for overcoming some typical circuit
limitations.
Piezoelectric films (piezofilms, or piezo-films) can convert signals in a variety of ways: electrical to
mechanical (e.g., a loudspeaker), mechanical to electrical (microphone), and thermal to electrical
(temperature sensor). In the circuit of Figure 1, the piezofilm element performs thermal to electrical and
mechanical to electrical conversions. It is intended to act as a temperature sensor and only incidentally
acts as a microphone.
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