Readout electronics based on the 128-channel chip “Viking” (IDE AS inc., Norway) is considered. The chip “Viking” integrates 128 low noise charge-sensitive preamplifiers with tunable CR-(RC)² shapers, analog memory and multiplexed readout to one output. All modules of readout electronics were designed and produced in KIPT taking into account the published recommendations of IDE AS inc

Kulibaba, V.I.

Maslov, N.I.

Naumov, S.V.

Ovchinnik, V.D.

Prokhorets, I.M.

Наукова електронна бібліотека періодичних видань НАН України (Vernadsky National Library of Ukraine)

READOUT ELECTRONICS FOR MULTICHANNEL DETECTORSV.I. Kulibaba, N.I. Maslov, S.V. Naumov, V.D. Ovchinnik, I.M. ProkhoretsNSC KIPT, Kharkov, Ukrainenaumov@kipt.kharkov.uaReadout  electronics  based  on  the  128-channel  chip  “Viking”  (IDE AS inc.,  Norway)  is  considered.  The  chip “Viking” integrates 128 low noise charge-sensitive preamplifiers with tunable CR-(RC)2 shapers, analog memory and multiplexed readout to one output. All modules of readout electronics were designed and produced in KIPT tak-ing into account the published recommendations of IDE AS inc.PACS number: 29.40.Wk1  INTRODUCTIONThere is a big difficulty or even an impossibility to design  and  implement  conventional  readout  systems based on discrete components as a number of readout channels of a detector grows (i.e. microstrip detectors [1], diode matrixes [2] etc). For example, to build readout electronics for the 128-channel detector one should ap-ply 128 charge sensitive amplifiers, 128 shapers, 128-channel ADC and a lot of additional elements. A size and a power consumption of such a system will surely make it unusable in a real practice. And it is absolutely impossible to design a discrete readout system for the 768-strip  detector.  That  is  the  reason  why  integrated electronics has being actively developed since the end of 80’s. The integrated readout electronics main features are low power consumption, small outlines, low noise (200 e- or less).  These features allow to place readout electronics  near  to  the  detector,  simplify  a  cooling, make  possible  to  reach  a  signal-to-noise  ratio  60  or more.2  MULTICHANNEL READOUT CHIPWe  have  chosen  the  Viking  VA2  chip  (IDE  AS company, Norway) to design our readout system. This chip has such main characteristics: •128 readout channels of analog signals from a detector, each  of  them  includes  charge  sensitive  preamplifier, CR-(RC)2 shaper and analog memory;•integrated multiplexer used to dispatch all 128 analog signal to one output in a sequential readout mode;•built-in test  and control  circuits,  which include input multiplexer  and  shift-register  to  distribute  test  pulses through the chip channels;•externally adjustable peaking time in a range from 0.5 to 2 µs;•noise performance 60е + 11е*pF for a peaking time of 2 µs;•dynamic range no less than 4 MIP for bipolar signals and 8 MIP for a single polarity;•maximal readout rate up to 10 MHz;•contact  pads  have  a  pitch  of  50  µm, that  meets  de-mands of the most popular detector bonding;•available  as  unpacked  dices,  outline  dimensions 6×4 mm.The  structure  of  one  readout  channel  of  VA2  is shown in Fig. 1. This type of readout designs is used of-ten to build as well as sophisticated multichannel and simple single channel preamplifiers.Fig. 1. Structure of one analog readout channel of  VA2 chip.It  integrates  the  charge  sensitive  preamplifier,  the voltage controlled CR-(RC)2 shaper, the analog memory with  the  externally  controlled  track-n-hold  circuitry. This readout system has a big flexibility, that allows to adjust  all  parameters when a maximum of speed or a minimum of noise is required in the experiment. 128 bit shift  register  controls  the  sequential  readout  process. The structure of overall chip is shown in Fig. 2.The next describes the work of the chip. 128 input pads are bonded to corresponding detector pads, from where the analog charge signal comes. After a physical event (a particle detection) each channel collects some charge. Then after the peak of the pulse in the shaper has been reached, an external signal activates the analog memory of the chip, that fixes the peak voltage. Shifting a one bit through the control shift register multiplexes all analog channels outputs sequentially to one output of the chip, i.e. multiplexed readout is achieved. The out-put signal can be processed by a computer to obtain a spectrum. The chip can also work in a single channel mode.  In  this  mode  an  arbitrary  channel  is  selected through the  control  shift  register,  the  analog  memory circuits  are disabled and it  means the chip work as a simple pair of preamplifier-shapers. This mode is very useful for testing purposes and allows to estimate a pure noise performance of the readout system without an in-fluence  of  high  frequency  digital  circuits,  which  are used in a high speed sequential multiplexed readout.3  READOUT ELECTRONICSOur  readout  electronics  system  comprises  hybrid module, repeater module and sequencer (Fig. 3). Hybrid module is designed on a printed circuit board with nick-ВОПРОСЫ АТОМНОЙ НАУКИ И ТЕХНИКИ. 2001. №5.Серия: Ядерно-физические исследования (39), с. 177-179.177el coated copper contact pads, that gives a possibility to bond aluminum or gold conductors with help of ultra-sonic  welding.  The  Viking VA2 chip  is  fixed on the board by a special glue.Fig. 2. Structure of overall VA2 chip.Fig. 3. Experimental setup.The  board  can  provide  a  connection  to  the  chip through a special flat film microcable or through tradi-tional  microwires,  which  are  bonded  to  pads  on  the board by means of ultrasonic welding. The main task of this printed circuit board are to provide an exchange of digital and analog signals between VA2 chip and the re-peater module, to filter power supplies of the chip, to set necessary operation mode of the chip through the con-trol circuits on the board. The form-factor of the PCB allows  to  fix  detectors  in  the  vicinity  of  the  readout chip. The repeater module and the sequencer control the readout process. When an external trigger signal is ac-tive the sequencer generates a sequence of digital TTL signals to control the VA2 chip and the ADC. The cur-rent setup uses the trigger signal from a scintillation de-tector. The sequencer also allows to work with the chip in a manual channel selection, when the chip is set in a single channel mode as described above. The repeater converts digital TTL signals of the sequencer to signals compatible with VA2 CMOS logic levels, amplifies out-put analog signals from VA2 chip, stabilizes power sup-plies  for  the  chip.  It  also  allows  smooth  adjusting  a peaking time of the shaper inside the Viking chip.The analog signal from the repeater module comes to an input of a fast ADC with built-in FIFO memory. The size of the memory should be enough to keep all data from 128 channels of VA2chip. In this setup there are two types of ADC available for use – the CAMAC ВОПРОСЫ АТОМНОЙ НАУКИ И ТЕХНИКИ. 2001. №5.Серия: Ядерно-физические исследования (39), с. 177-179.178ADC or the computer built-in ADC.A maximal possible readout frequency for this sys-tem is 1 MHz, that gives a reaction time less than 130 µs. The time diagram of the readout process is shown in Fig. 4.Fig. 4. Example of sequential readout of one chip.4  RESULTSWe have studied the system to evaluate its operation and quality. Noise performance of readout system was investigated and spectral distributions were obtained to find signal-to-noise ratio, that is an universal parameter of the detection system. All spectra were obtained on a 128 strip  single-side detector  from isotope  sources  of gamma-quanta  241Am for the single channel mode and electrons 90Sr for the total 128 strip readout (multichan-nel mode). Noise performance of the system has been preliminary  calculated  using  formulas  for  the  noise sources definition in the readout electronics [3]. The to-tal  noise  (e- r.m.s)  is 222rla ENCENCENCENC ++= ,  where  ENCa is the amplifier noise, ENCl is the noise of the leakage cur-rent Il of the strip, ENCr is the noise of the parallel com-bination Rp of the feedback resistor of the amplifier and the biasing resistor of the detector. Considering real pa-rameters of the detector to be 1 nA for the leakage cur-rent, 5 pF for the strip capacitance and 18 MOhm for the Rp resistor combination, we can calculate the noise as ENC=320 e- r.m.s,  that  gives  the  signal-to-noise  ratio value 70 for MIP equivalent charge (about 22500 e-).These  spectra  are  shown in  Fig.  5.  The  signal-to-noise ratio for these spectra is more than 60 and fits well our previous calculations. That signal-to-noise ratio im-plies a good possibility to use such systems in a wide range of accurate experiments or technical engineering and designs.5  CONCLUSIONThe system of readout electronics based on the inte-grated chip Viking VA2 was considered. These chips al-low  designers  to  build  high-quality  readout  systems with  small  quantities  of  components  for  multichannel detectors. As an example of such system readout elec-tronics for microstrip detector was considered. It is quite possible  to  design  readout  systems  based  on  Viking chips for use with other types of multichannel detectors, such  as  photodiode  matrixes.  IDE AS  company  pro-duces families of similar integrated multichannel read-out chips with integrated triggering circuits – self-trig-gering chips TA and XA. They allow to design high-speed multichannel readout systems for detectors with-out  external  triggering  components,  also  they  give  a possibility  for  multichannel  or  microstrip  detectors  to operate with gamma-quanta radiation sources in a real multichannel  mode  of  detection,  that  is  not  possible when  using  ordinary  externally  triggered  integrated readout electronics for these detectors, such as VA chips series.020460810012140618022042680305100052000533500405000600057750080850090100 0Number of countsChannels 10023040506070809 0102040608100120140160180Number Of Counts Cluster, mVFig. 5. Example of spectra of gamma-quanta and elec-trons from isotope sources 241Am and 90Sr.REFERENCES1.A.P. de Haas,  P.Kuijer,  V.I.Kulibaba,  N.I.Maslov, V.L.Perevertailo, V.D.Ovchinnik, S.M.Potin, A.F.Staro-dubtsev.  Characteristics  and  radiation  tolerance  of  a double-sided microstrip detector with polysilicon bias-ing resistors //  Problems of Atomic Science and Tech-nology. Issue: Nuclear-Physics Research (36). 2000, v. 2, p. 26-33.2.G.Bochek, V.Kulibaba, N.Maslov, S.Naumov, A.Star-odubtsev.  Silicon  pad  detectors  for  a  simple  tracking system and multiplicity detectors creation //  Problems of  Atomic  Science  and  Technology.  Issue:  Nuclear-Physics Research (37). 2001, v. 1, p. 36-39.3.E.Nygård, P.Aspell, P.Jaron, P.Weilhammer, K.Yosh-ioka. CMOS low noise amplifier for microstrip readout.  Design  and  results.  CERN-PPE/90-142  October  1-st, 1990.ВОПРОСЫ АТОМНОЙ НАУКИ И ТЕХНИКИ. 2001. №5.Серия: Ядерно-физические исследования (39), с. 177-179.179

Readout electronics for multichannel detectors

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Readout electronics for multichannel detectors

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Наукова електронна бібліотека періодичних видань НАН України (Vernadsky National Library of Ukraine)