Novel Design of a Wideband Low-Noise Amplifier with Adjustable Gain for Underwater Applications

Low-noise amplifiers (LNAs) are designed to amplify only the desired signal while minimizing noise, making them essential for applications requiring precise signal detection, processing in low SNR and high-sensitivity environments. This paper presents a novel LNA design aimed at enhancing signal reception in underwater imaging and communication applications. The proposed design achieves a wideband amplifier with specific parameters: a variable gain range of 40 dB to 80 dB, a broad 30 kHz bandwidth centered at 20 kHz, and a low input-referred voltage noise density of 0.1 μV/√ Hz. The proposed design employs a two-stage amplification approach, first stage with a fixed 40 dB gain and a variable gain in the second stage, reaching up to 80 dB. An initial filter stage reduces out-of-band noise to improve signal quality. This paper also provides a comprehensive analysis of the selection of low-noise op-amps, passive components, filter topologies, and preamplifier configurations. Extensive simulations confirm the effectiveness of the proposed design in significantly enhancing signal reception for underwater applications.