Development of signal processing system of avalanche photo diode for space observations by Astro-H
Development of signal processing system of avalanche photo diode for space observations by Astro-H
复制标题
Astro-H空间观测雪崩光电二极管信号处理系统的开发
DOI：
10.1016/j.nima.2012.03.022
复制
发表时间：
2012
期刊：
影响因子：
--
通讯作者：
et al
中科院分区：
文献类型：
--
作者：
M.Ohno;et al
Astro-H是日本第六个X射线空间观测站，将于2014年发射。Astro-H的两个机载仪器，硬X射线成像仪和软伽马射线探测器被许多大型锗酸铋（Bi 4Ge 3 O 12; BGO）闪烁器包围。最佳的闪烁光读出系统是必不可少的，以减少背景信号，并实现高性能的主探测器，因为大多数的伽马射线从主探测器的视场外或内部产生的放射性同位素，由于激活可以消除反符合技术使用BGO信号。我们采用雪崩光电二极管（APD）的光传感器的这些BGO探测器，因为它们的紧凑性和高的量子效率，使它很容易设计这样的大数量的BGO探测器系统。对于APD的信号处理，由于航天器上电路实现面积的限制，使用现场可编程门阵列（FPGA）上的数字滤波器和其他触发逻辑来代替离散模拟电路。为了有效地观测，我们必须利用数字滤波来获得尽可能低的反符合信号阈值。此外，这种反重合信号应在5μs内送到主探测器，使其及时否决模数转换。考虑到这一要求和FPGA逻辑规模的限制，我们采用了两种滤波器，即精度系数仅为2bit的8延迟抽头滤波器和精度系数为8bit的16延迟抽头滤波器。前一种简单滤波后的数据在轨道上快速提供反符合信号，后一种滤波在数据下行后进行详细分析。
Astro-H is the sixth Japanese X-ray space observatory which will be launched in 2014. Two of onboard instruments of Astro-H, Hard X-ray Imager and Soft Gamma-ray Detector are surrounded by many number of large Bismuth Germanate (Bi4Ge3O12; BGO) scintillators. Optimum readout system of scintillation lights from these BGOs are essential to reduce the background signals and achieve high performance for main detectors because most of gamma-rays from out of field-of-view of main detectors or radio-isotopes produced inside them due to activation can be eliminated by anti-coincidence technique using BGO signals. We apply Avalanche Photo Diode (APD) for light sensor of these BGO detectors since their compactness and high quantum efficiency make it easy to design such large number of BGO detector system. For signal processing from APDs, digital filter and other trigger logics on the Field-Programmable Gate Array (FPGA) is used instead of discrete analog circuits due to limitation of circuit implementation area on spacecraft. For efficient observations, we have to achieve as low threshold of anti-coincidence signal as possible by utilizing the digital filtering. In addition, such anti-coincident signals should be sent to the main detector within 5μs to make it in time to veto the A–D conversion. Considering this requirement and constraint from logic size of FPGA, we adopt two types of filter, 8 delay taps filter with only 2 bit precision coefficient and 16 delay taps filter with 8 bit precision coefficient. The data after former simple filter provides anti-coincidence signal quickly in orbit, and the latter filter is used for detail analysis after the data is down-linked.