Development of a novel high-performance readout circuit for alpha and beta energy spectrum measurement

A novel high-performance readout circuit with multi-Junction field-effect transistors (Multi-JFETs) and high-speed integrated operational amplifiers as the core was designed. By coupling the circuit to a large area passivated ion injection planar silicon (PIPS) detector, excellent alpha and beta energy spectrum can be obtained. Therefore, it can be applied to radon monitor, radioactive aerosol monitor and other equipment to achieve high precision information on radioactive substances in the environment. The input stage of the circuit adopts the parallel structure of JFETs to achieve the matching between the amplifier circuit with the detector junction capacitance. The bias circuit adopts JFETs to form a constant current source while using the gate-source self-biased parallel structure to obtain large transconductance gain and good amplification linearity. The main amplifier circuit adopts a high-speed and low-noise operational amplifier with the advantages of high open-loop gain and stable quiescent point. The performance of this readout circuit was tested, in which the rise time of the signal is 35 ns, the sensitivity of charge-voltage conversion is better than 0.979 mV/fC when the input capacitance is less than 100 pF, and the equivalent noise charge is 1.55 fC, noise slope is 0.00366 fC/pF. By coupling the readout circuit to a PIPS detector with a sensitive area of 450 mm(2), the signal-to-noise ratio of the output signal is 116 : 1 for the Am-241 alpha source and 20 : 1 for the Sr-90-Y-90 beta particles. The energy spectrum measurement of the Pu-238 source was performed, providing FWHM is 16.90 keV@5499 keV.