中文摘要：

极弱准直流电流信号测量技术在精密仪器仪表研制过程中有着广泛地应用,其中前置放大器是核心,决定了系统的噪声水平和响应时间常数。在前置放大器的模拟研究中,通过建立电阻直接反馈法和＂T＂型电阻网络反馈法构成前置放大器的电噪声模型,获取了前置放大器在各种情况下的性能参数。模拟结果表明：系统的信噪比与传感器等效电容值成反比,与反馈电容值成正比,且不能笼统地认为电阻直接反馈法和＂T＂型电阻网络反馈法哪种方法更优,应根据具体的情况选用合适的反馈形式。该模拟结果可为极弱电流信号检测器中前置放大器设计提供参考。

英文摘要：

Weak current measurement technique is used in many fields and its development plays an important role in the related fields. Preamplifier for extremely weak current technology,which determines the noise and respond time level,plays a critical role of the entire instrument. Based on the electrical noise model,this subject aims at determining the right feedback resistor way between direct feedback resistor and T feedback resistor network for the preamplifier. From the simulation results,we can conclude that the Signal to Noise Ratio is inverse proportion to the equivalent capacitance of the sensor and direct proportion to feed back capacitance,and neither direct feedback resistor way nor T feedback resistor network way is a omnipotence way for all the circuits. In the actual situation,we must choose the right feedback resistor way for the idiographic situation.