Abstract:

A highprerformance preamplifier and data acquisition system was designed to measure the ultralow and fastchanging current in the quadrupole mass spectrometer. The system uses a composite transimpedance preamplifier, a 4thorder active lowpass analog filter and a successive approximation analogtodigital converter. The realtime control and highspeed largecapacity FIFO data buffer of the data acquisition are implemented with the fieldprogrammable gate assay logic. By analyzing the impact of the gain and the bandwidth on the signaltonoise ratio(SNR) and the full width at half maximum(FWHM), the suitable gain and bandwidth were selected. Experimental results indicat that in the highrate scanning, 30 kHz bandwidth improves SNR and doesn't effect FWHM and signal intenssity. With the increase of the gain, the SNR increases. As the gain increases from 106 to 108 V/A, the FWHM increases from 0.52 to 0.6. When the gain increases to 109 V/A, the FWHM increases to 2 because of low bandwidth of the preamplifier. In lowrate scanning, as the bandwidlth need is low, 109 V/A gain enhances the SNR while mainfaining the FWHM of 0.2.

Key words: technology of instrument and meter, quadrupole mass spectrometer, preamplifier, fieldprogrammable gate array, data acquisition