Design Of Multi-channel Charge Sensitive Amplification System For In-situ Space Plasma Measurement

The space plasma is widely distributed in the entire solar-terrestrial space.It is an important object of space physics and space weather detection and research,and it can also cause the charge and discharge of spacecraft surface.Therefore the detection of space plasma parameters is of great significance to space science and aerospace engineering.For in-situ space plasma detection instruments,microchannel plate is often used to amplify ions or electrons,the output charge signal of which is weak and is difficult to be measured by the general electronic circuit directly,so it must be preprocessed by the low-noise charge sensitive amplification system.The traditional charge sensitive amplifacation chip usually has single channel,which requires several independent chips in multi-channel detection,thus greatly increasing the size of the circuit.In addition,it is impossible to adjust the threshold voltage when the instrument is in orbit because of the need to adjust the threshold parameters by external electron components.With the development of the research on the characteristics of space plasma,more and more technical requirements are put forward for the charge sensitive amplifacation system.Based on this situation,the miniaturization,multi-channel and flexible configuration of digital interface of charge sensitive amplifacation system has become the new requirements of its design.In this paper,the working principle of in-situ space plasma detection system and charge sensitive amplifacation system is studied and analyzed.Based on the actual requirements of the above,a multi-channel charge sensitive amplifacation system for in-situ space plasma detection is designed.The charge sensitive amplifacation system is composed of 8 independent channels,and every single channel includes charge-sensitive pre-amplifier,filter-shaping-amplify circuit,pulse amplitude discrimination circuit and DA conversion module.Through the selection of high performance chip and the rational design of PCB layout,good noise characteristics and small circuit size are obtained;Through the reasonable design of circuit parameters,large input dynamic range and high charge sensitivity are realized;In addition,through the cooperation of DA converter and discriminating circuit,the digital interface control of the amplification system is realized,so that the threshold voltage of on-orbit detection instrument is able to be adjusted flexibly.Through practical test,the highest operating frequency of this circuit is about10MHz,and the charge sensitivity can achieve about 1.2×10¹²V/C when the dynamic input range 5f C?1.6p C.The total output voltage noise at 10MHz is 1.1×10^-7,the input equivalent noise is,and the input equivalent charge noise is7.48×10^-18Coulombs RMS,which shows excellent noise characteristics of the circuit.In addition,the rising time of the output signal is about 10ns?15ns,the range of the output voltage pulse is about 0?2V,and the minimum power consumption of each channel is 47m W,which shows that the performance of the circuit is fine.Compared with the traditional charge sensitive amplification chip,the charge sensitive amplification system has the advantages of multi-channel,small size,low noise and flexible configuration of digital interface,which is conducive to the realization of high angle resolution,on-orbit adjustment of threshold parameters and miniaturization of electronics design for the in-situ space plasma detection instrument.The circuit can also be applied to other instruments which need charge sensitive amplification.The space environment adaptability?total dose,single particle,etc.?of the system is to be designed and evaluated further to provide design input for on-orbit applications.