Design of a Low Noise Signal Amplifier for Sensor Signal Amplification

This paper presents the design of a low noise signal amplifier (LNA) with active filtering using operational amplifier suitable for sensor applications. Since the sensor output is a small signal of low amplitude comparable to that of noise signal, an efficient amplifier capable of reducing the noise interaction is required. Here three different types of op-amps based on BJT, FET and CMOS circuits are used in the design of LNA and a comparative study is performed. The amplifier circuit is designed in LTSpice XVII and three types of simulation are carried out to access the performance of the amplifier. First the transient response is performed to ensure the linearity in amplification. Then, the AC analysis is carried out that resulted in a gain of 47 dB in all amplifiers and bandwidth of 3.65 kHz, 39.26 kHz and 69.03 kHz are resulted in BJT, FET and CMOS based op-amp circuits respectively. Finally the noise analysis is executed that resulted in a noise voltage density of $17\ \mu\mathrm{V}/\surd{}\text{Hz}$ (1 Hz–10 kHz), $9\ \mu\mathrm{V}/\surd{}\text{Hz}$ (1 Hz–100 kHz) and $5.5\ \mu\mathrm{V}/\surd{}\text{Hz}$ (1Hz–10 MHz) respectively in the BJT, FET and CMOS based LNA circuits. The simulation results clearly prove that the proposed LNA could be used for sensor signal amplification at different frequencies ranging from 1Hz to 10 MHz.