For the analysis of micro signal amplification and extraction, low noise measurement system is often the first stage of processing.The key part is the preamplifier, and noise becomes the important restraint factor, which determines the precision of the system.This paper introduces the design of a preamplifier circuit applied to low frequency micro signal detection.The circuit is composed of two stages, the first stage using discrete component design, and the second stage using a low noise integrated components design.The simulation results show that the voltage gain of the circuit is 80 dB, and its bandwidth is 300 kHz.The noise level of the amplifier is excellent and is better than the commercial amplifier.The circuit has the advantages of simple structure, and easy to realize.It is suitable for low frequency micro signal amplifier.%对于微弱信号的提取和放大分析，低噪声测量系统往往是分析处理的第一个阶段，其中关键的部分是前置放大器，而噪声成为重要的制约因素，它决定了整个系统的精度。介绍了一种低噪声前置放大电路的设计，该电路由两级构成：第一级使用分立元件设计，第二级使用低噪集成元器件设计。通过仿真表明，电路实现了电压增益80 dB，电路的带宽为300 kHz，电路的噪声性较商用放大器更优异。该电路结构简单，易于实现，适用于低频微信号的放大。
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