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High-Gain Low-Noise Pre-Amplifier and Narrow Band-Pass Filter for Photoacoustic Spectrometer

Sapna, P. Bhaskar, Parvathi C. S., Immanuel J

In this paper an attempt is made to design and develop a high-gain low-noise pre-amplifier and a narrow band-pass filter for photoacoustic spectrometer (PAS). A two-stage pre-amplifier with the gain of 1000 and a second order state variable narrow band-pass filter are designed and fabricated. The pre-amplifier and narrow band-pass filter circuits are designed with a low-noise op-amp (LM308). This arrangement improves the sensitivity and signal-to-noise ratio of the photoacoustic (PA) signal. The frequency response of the PA cell is studied with carbon-black and liquid crystal samples. The resonant frequency of the PA cell was found at 345Hz. The performance of the system is tested in both the presence and absence of modulated laser beam applied on the sample, and it is found that the signal quality has been improved with the pre-amplifier and narrow band-pass filter designed for the present study.