一种低频低噪声前置放大器的设计

Design of a low noise preamplifier for low frequency

针对甚低频、超低频通信中存在的微弱信号难以检测问题,设计了一种低频低噪声前置放大器。首先建立了放大器噪声模型并对噪声特性、噪声匹配进行分析,然后详细阐述了低噪声放大器电路中晶体管的选择、直流工作点的设置、负反馈网络的设置、阻容元件的选择、输入阻抗匹配等设计要点,并提出一种多层屏蔽设计方法。通过仿真对低噪声放大器电路进行测试与分析,结果表明在1 kHz~1 MHz下电压增益可达38 dB,1 kHz时等效输入噪声为0.99nV/√Hz,噪声系数达到0.73 dB,噪声性能大大提高,且信号失真较小,满足了低噪声放大器噪声系数小、增益大、输入端良好匹配的性能设计要求,可以实现甚低频、超低频远距离通信中对微弱信号的有效接收。

In order to solve the problem that weak signal is difficult to detect in very low frequency and ultra-low frequency communication, a low noise preamplifier for low frequency is designed. Firstly, the noise model of amplifier is established and the noise sources and noise matching are analyzed, then the design points of the low noise amplifier circuit are described in detail, and a multi-layer shielding design method is proposed. Through simulation and experimental measurement, it is concluded that at 1 kHz~1 MHz, the voltage gain can reach 38 dB, at 1 kHz, the equivalent input noise is 0.99nV/√Hz, the noise coefficient reaches 0.76 dB. The noise performance is greatly improved, it can meet the performance design requirements of low noise amplifier and can realize the effective reception of weak signal in VLF and VLF long-distance communication.