Design And Development Of Ultra Weak Signal Processing Circuit For Space Ionization Radiation Measurement

The space radiation environment is one of the important factors to influence high reliability,lifetime of spacecraft and astronaut health in space exploration activities. On-orbit monitoringequipment for space radiation dose is very important to research and explore space radiationenvironment. An ultra weak signal measurement device and a current generator have been designedand developed for space dosimeter in this paper.In order to measure high dynamic weak output current of space dosimeter, a measurement moduleis designed for the very weak current measurement with multi stage amplification. It includes I-Vconverter, amplifier stage circuit, zero correct circuit and low pass filter for measuring the currentfrom10pA to10uA. A complete analysis of this current measurement module with respect to itscircuit structure is given. With respect to noise, Dc drift, leakage currents, the signal protectiontechnology and shielding technology are applied. The whole actual circuit is finished using highprecision electrometer amplifier. Results shown that, the current of measuring range is from10pA to10μA. The resolution is10-13A, it has fast response, time low excursion, low power and small volumeand so on.In order to test and correct the measuring instrument of weak current detection, a high accuracycurrent generator has been developed for the generation of very small currents (below100pA) basedon operational amplifiers. It has been built using op amps, resistors, constant voltage and standardresistance values to gain weak current output with V-I converter. A negative feedback adjustmentcircuit is designed to eliminate the output current changing with the load. The effects of strayimpedances on the behavior of the current source are taken into account and the techniques necessaryto achieve an optimum stable performance. Experiments show that the micro-current source is tableand reliable; the output current range of circuit is100pA-10μA.The research work mainly embodies in the two aspects as follows:1. A weak current measurement circuit has been developed using operational amplifiers withmulti-level amplification. The circuit can measure the current from10pA to10μA, the signalprotection technology and shielding technology are used in the circuit. 2. A high-accuracy current source has been developed for the generation of very small currents(100pA-10uA) based on operational amplifiers. Negative feedback circuit, shielding and filtering areapplied.