Masanori Ohno (Hiroshima Univ.) Development of Digital Signal Processing System of Avalanche Photodiodes for Space Observations by Astro-H Masanori Ohno (Hiroshima Univ.) Kunihiro Goto, Yoshitaka Hanabata, Hiromitsu Takahashi, Yasushi Fukazawa (Hiroshima U.), Hiroyasu Tajima (Nagoya U. STE), Yoshino, Masao Yoshino, Tatsuhiko Saito, Haruki Mizoma, Takeshi Namamori, Jun Kataoka (Waseda U.), Shunsuke Torii, Makoto Sasano, Hideki Uchiyama, Kazuhiro Nakazawa, (Univ. of Tokyo), Shin Watanabe, Motohide Kokubun, Masayuki Ohta, Tamotsu Sato, Tadayuki Takahashi (ISAS/JAXA), and the ASTRO-H HXI/SGD team Dec. 6, 2011 HSTD-8 Symposium

The ASTRO-H Mission ASTRO-H is Japanese 6th series of X-ray observatory. It is scheduled to be launched in 2014 with an H-II A rocket. Scientific instruments Soft X-ray Spectrometer (SXS) Soft X-ray telescope + X-ray calolimetor Soft X-ray Imager (SXI) Soft X-ray telescope + CCD Hard X-ray Imager (HXI) Hard X-ray telescope + hard X-ray imager Soft Gamma-ray Detector (SGD) Narrow field-of-view Compton camera SGD 14 m ! SGD HXI 1000 HXI Energy resolution (eV) 100 SXI Total length : 14 m Weight : 2.7 t Largest scale satellite for Japan SXS 1 0.1 1 10 100 Energy range (keV) Dec. 6, 2011 HSTD-8 Symposium

Hard X-ray Imager (HXI) telescope Hard X-ray imaging in 5 – 80 keV energy band with very high sensitivity. (better than Suzaku/HXD by >2 order of magnitude) Camera part Double Side Si Strip (Hayashi’s talk) (4 layers, E< 25 keV) CdTe Double Side Strip (1 layer) Hard X-ray imaging with 12 m focal length Fine position resolution (250 um) High detection efficiency up to 80 keV Low detector background by BGO active shield Hard X-ray Imager (HXI Dec. 6, 2011 HSTD-8 Symposium

Soft Gamma-ray Detector (SGD) new concept of soft gamma-ray (10 — 600 keV) detector with Very low background = narrow field-of-view Compton camera Multi-layer Si/CdTe Compton camera - pixel-type Si detector (32 layers) (Hayashi’s talk) - pixel-type CdTe detector (8+2 layers bottom/ side) ~10 cm ~12 cm Detector background can be reduced by constraint photon direction based on Compton kinematics BGO shield detectors - Passive Shield for cosmic-ray particles - Active shield for gamma-rays from out-of-FoV or radio-activated detector materials Very important to reduce background for both HXI and SGD Dec. 6, 2011 HSTD-8 Symposium

BGO Readout System HXI and SGD has the same concept of BGO readout system APD Processing and Management Unit (APMU) to S/C BGO APD S Analog +ADC Data/ CMD 300-400 V CSA FPGA MIO MDE …. HV-APD SpW 9BGOs+11APDs for HXI 25BGOs+25APDs for SGD HXI and SGD are new detector for space application  there are many requirements and constraints for APMU logic design (About APD/CSA  Saito’s talk) Dec. 6, 2011 HSTD-8 Symposium

Requirements for readout logic Timing diagram of main detector signal It takes about 100 us to finish A/D conversion in the main detector of HXI/SGD We should veto A/D conversion for the events simultaneously detected by BGO shield detectors. (These events can be regarded as background events.) Otherwise, we loss much observation time ! slow fast trig 1-3us hold >5us ADC on <100us Requirements from main detectors Timing diagram of BGO signal Veto signal (Fast BGO) must be sent to main detector before A/D conversion starts (within 5 us) BGO signal <5us Fast BGO Dec. 6, 2011 HSTD-8 Symposium

Design limitation from Space detector Power budget 　Power resource : Solar paddle Only 5.3 W is allocated for BGO signal processing Maximum performance by Minimum resources Saving the space 　Only 6cmx10cm space is allowed to 14 ch analog/ADC processing (for SGD) No space to implement many discrete analog circuit  We apply the digital filter to process BGO signal Rad-Hard There are not so many choices of devices with radiation tolerance.  FPGA: ACTEL RT series is commonly used  1MHz sampling ADC (ADC128S102) is applied for BGO signal processing RT AX 2000S for HXI/SGD (2,000,0000 gate) We developed optimized digital filter for BGO signal processing on limited sample number of ADC and gate number of FPGA. Dec. 6, 2011 HSTD-8 Symposium

Design of the digital filter In the digital filter, sampled, discrete-time signals are summed after some mathematical operations and we obtain filtered signals like analog filter. Example of BPF (100-200 kHz) freq. response for some delay units Delay Delay Delay Input Delay 2 4 8 16 32 operations output Sum transmittance For example, we can construct band pass filter (BPF) with any frequency response; Larger number of delay units Better precision of coefficient 0 100 200 300 400 500 Realize expected frequency response Frequency (kHz) Design policy of digital filter for HXI/SGD BGO signal processing Search optimum frequency of pass band Number of delay units and precision of coefficient Dec. 6, 2011 HSTD-8 Symposium

Design of the digital filter 1. Optimum BPF pass band Comparison of power spectrum density of BGO+APD signal and noise comp. BGO+APD with 137Cs signal -20℃ -5℃ power >300 kHz Signal component is not so evident (10 % of S/N ratio) BGO+APD w/o source (noise) -20℃ -5℃ >500 kHz Nyquist frequency for 1 MHz sampling 500 1000 Frequency (kHz) BPF lower than 300 kHz range is suitable for BGO+APD signal Dec. 6, 2011 HSTD-8 Symposium

Design of the digital filter 2 Design of the digital filter 2. delay units and precision of coefficient 100-300 kHz BPF response for various delay units 100-300 kHz BPF response for various precision of coefficient Delay 4 Delay 8 Delay 16 Delay 32 20-bit decimal 8-bit signed integer Multiples of 2 2-bit signed integer 100 200 300 400 500 100 200 300 400 500 Frequency (kHz) Frequency (kHz) Two types of digital filter for HXI/SGD BGO signal processing A: 8 delay units with 2-bit precision coefficient  quick trigger generation for on-line veto to main detector B: 16 delay units with 8-bit precision coefficient  generate hit pattern and histogram for more detail analysis in off-line Dec. 6, 2011 HSTD-8 Symposium

Optimization of digital filter parameters Detail parameters of digital filter (16 delay/8-bit) are tuned using 1cm3 BGO and analog/digital circuit with somewhat equivalent design to flight model (Bread Board Model) APMU BBM 390 V Analog +ADC BBM CSA Data BGO APD FPGA PC 1cm3 BGO+APD HV-APD APMU BBM Take waveform via BBM CSA and APMU and save in the PC Filter with various digital filter parameters using digital filter software and make histogram Dec. 6, 2011 HSTD-8 Symposium

Optimization of digital filter parameters 241Am 60 keV spectrum No filter analog shaper (ORTEC571) Optimized digital filter Threshold (keV) No filter 37.1 Analog shaper 25.9 Optimized digital filter (50-80 Hz BPF) 30.5 10 20 30 40 50 60 70 80 Energy (keV) We optimize the digital filter under very limited resource condition (1MHz sampling ADC and 16 delay/8-bit coefficient filter).  Our filter can improve the threshold of BGO signal compared with no filter case by 18 %. Dec. 6, 2011 HSTD-8 Symposium

Feedback analog parameters HXI/SGD BGO signal processing system has analog shaping circuit (Saito’s talk) Optimization of digital filter is affected by analog shaping parameters 137Cs spectrum using 8cm x 8cm x 4cm BGO Analog shaper No digital filter Digital filter Analog Parameter Optimized Digital Filter freq. Threshold (keV) CR-RC (1.1 us) 50—80 kHz 60.6 CR-RC(1.1us; CR through) 60—90 kHz 61.5 CR-RC (1.0 us) 60—70 kHz 62.7 CR-RC (1.2 us) 61.4 Twin-T 30—85 kHz 63.9 Energy (keV) Analog shaper (CP4417) 65.7 Combination of analog/digital filter optimization achieves comparable/better threshold than analog shaping amp Dec. 6, 2011 HSTD-8 Symposium

End-to-end test Performance test using bread board model from BGO to APMU BGO readout system (1ch readout) : almost all component is consist of BBM BBM APMU 370 V Analog +ADC BBM CSA Data BGO APD FPGA PC BGO (8x8x4 cm3) Pre-FM APD BBM HV-APD HV control From APMU preliminary 1ch BGO readout system works and 137Cs spectrum is obtained. Preliminary results show that threshold is 66.4 keV End-to-end setup HV is not BBM (CP6671) Analog shaper Dec. 6, 2011 HSTD-8 Symposium

Summary We developed digital signal processing system of APD for space observations by ASTRO-H mission Digital filter is applied to achieve high performance under condition of limited circuit implementation space Two types digital filter are designed considering requirement and constraint of logic size and power budget. 1) simple 8 delays/2-bit precision coefficient filter to satisfy requirement of quick trigger generation within 5 us 2) 16 delays/8-bit precision coefficient filter to achieve low energy threshold Optimize 16 delays/8-bit filter combining analog circuit parameters  Achieve comparable/better threshold than analog shaping amp. End-to-end performance test is now ongoing Dec. 6, 2011 HSTD-8 Symposium

Feedback analog parameters HXI/SGD BGO signal processing system has analog shaping circuit (Saito’s talk) Digital filter optimization is affected by analog shaping parameters 137Cs spectrum using 8cm x 8cm x 4cm BGO Analog shaper No digital filter Digital filter Analog Parameter Optimized Digital Filter freq. Threshold (keV) CR-RC (1.1 us) 50—80 kHz 60.6 CR-RC(1.1us; no CR) 60—90 kHz 61.5 CR-RC (1.0 us) 60—70 kHz 62.7 CR-RC (1.2 us) 61.4 Twin-T 30—85 kHz 63.9 Energy (keV) Analog shaper (CP4417) 65.7 Combination of analog/digital filter optimization achieve comparable/better threshold than analog shaping amp Dec. 6, 2011 HSTD-8 Symposium

Quick Trigger Generation Simple filter (8 delay/2-bit precision coeff.) is required to generate a trigger signal within 5 us to veto A/D conversion of main detector BGO input signal Filter coefficient: (-1,0,1,0,0,0,0,0) Trigger signal after simple filter <5us Simple filter can generate a trigger within 5 us for normal amplitude of signal. Need to study lower limit of signal amplitude (trigger is delayed in low signal). Dec. 6, 2011 HSTD-8 Symposium

Block Diagram of SGD Electronics Dec. 6, 2011 HSTD-8 Symposium