Design of a Low-Noise, High-Quality Variable Gain Pre-Amplifier for Acoustic Applications

This paper presents the design of a low-noise, high-quality pre-amplifier optimized for an acoustic application related to high frequency underwater imaging. The proposed low-noise pre-amplifier (LNA) design is focused on amplifying low-power signals while maintaining a minimal signal-to-noise ratio (SNR) degradation. Noise reduction is achieved through careful selection of components, configurations, and operating points within the operational bandwidth. Key design goals, including impedance matching, variable gain (20-80 dB using 0-5 VDC control signal), a central frequency of 400 kHz, and a 10 kHz bandwidth, are met. The proposed pre-amplifier features a two-stage, adjustable gain of 80 dB, followed by a four-stage, 8^th order filter using a multiple feedback topology. This design demonstrates significant improvements, achieving an input-referred voltage noise of 0.488nVrms /√Hz, a bandwidth of 9.8 kHz, and a quality factor of 41, surpassing conventional LNA designs.