四极质谱检测中复合放大器的低噪声高带宽设计

四极质谱峰信号是10-11A到10-6A级的微弱电流，并且快速变化，所以在大动态范围内实现低噪声和高带宽是设计关键。设计一种开环增益(ac)可调整的同相输入复合跨阻抗放大器，分析ac对信号和噪声的作用。在较低放大倍率时，改变ac后同相输入复合放大器会降低自身产生的噪声，实现低噪声；在较高放大倍率时，改变ac后同相输入复合放大器能扩展被极高阻值的反馈电阻和寄生电容降低的信号带宽。实验结果表明：与反相输入复合放大器相比，同相输入复合放大器在106-107V/A放大时能降低5-30%噪声，在108V/A放大时扩展带宽1.8倍并提高10-15%质谱峰强度，提高了质谱峰的信噪比。

Low-noise and wide-band design of composite preamplifier in the Quadrupole mass spectrometer

Concerning the preamplifier to measure the ultra low current in the Quadrupole mass spectrometer, low noise and wide bandwidth is the key to this system as the current is from 10-11A to 10-6A and varies quickly. So we design the Non-inverting input composite preamplifier (NIICP), and analyze the open-loop gain (ac) to optimize the frequency response of signal and noise. In the lower magnification, the circuit optimizes ac to reduce intrinsic noise. In the higher magnification, the circuit optimizes ac to recover high frequency signal which is damped down by the low pass transfer function of the large feedback resistance and parasitic capacitance. Compared with inverting input composite preamplifier (IICP) in the commercial Quadrupole mass spectrometer, experimental results indicate that NIICP reduces 5-30% in the 106-107V/A magnification, expands signal bandwidth 1.8 times and increases 10-15% MS peak signal amplitude in the 108 V/A magnification, improves the SNR of MS peaks detection.