Study of the effect of the low-pass filter time constant on the noise level of quartz-enhanced photoacoustic spectroscopy sensors

Quartz Enhanced Photoacoustic Spectroscopy (QEPAS) is a sensitive trace gas detection technique employing Quartz Tuning Forks (QTF) as sensitive elements. Usually, a transimpedance amplifier is used as QTF front-end electronic, with a 10 MΩ feedback resistor. With a low-pass filter time constant of 100 ms, the thermal noise of the QTF intrinsic resistance (~100 kΩ) represents the main noise contribution. For real-time applications, shorter time constants need to be employed. In this work, we studied different amplifier structures with the aim to reduce the QTF thermal noise and improve the signalto- noise ratio when the QTF is used in QEPAS sensors.