Front-End Electronics of CXPD for Measuring Transient X-Ray Sources

The low-energy polarization detector (LPD), a payload of the POLAR-2 mission, is a soft X-ray polarization detector with a wide field of view and a large array aimed at measuring X-ray transients. These transients exhibit rapid intensity changes of several orders of magnitude, making it crucial for polarization detectors to have front-end electronics with low dead time, fast readout capabilities, high time resolution, and good energy resolution. In this article, we present the design of the front-end electronics, which consist of a rolling shutter CMOS pixel charge sensor (Topmetal-
$II^{-}$
) and a gas microchannel plate (GMCP) bottom amplifier circuit. Topmetal-
$II^{-}$
’s rolling shutter readout provides fast scanning of large pixel arrays without dead time and acquires 2-D images of photoelectron tracks. Meanwhile, the GMCP’s bottom amplifier circuit measures the energy and time of the X-ray. The front-end electronics are employed by the CubeSat cosmic X-ray polarization detector (CXPD), a proto-flight model of the LPD, achieving a timing resolution of 19 ns, and an energy resolution of 16.5% for linearly polarized X-rays at 8 keV.