Li HAN, Sam Huh, and Neal H. Clinthorne

1
A VLSI Design for Energy Extraction and Pileup
Prevention for High Count-Rate Scintillation
Signals
Li HAN, Sam Huh, and Neal H. Clinthorne Universit
y of Michigan, Ann Arbor, MI, USA
Eq.(6) Digital PPE uses shifter and look-up-table
to calculate energy

• I. Goal and Design Rationale
• Design a Very Large Scale Integration (VLSI) full
  digital processor to recover photon energy
  deposited in a NaI scintillation detector for
  high event rates where multiple scintillation
  pulses overlap.
• Digital solutions offer more flexibility and
  higher noise immunity than digital-analog hybrid
  active pileup prevention energy (PPE) circuits.
• The full digital PPE algorithm and circuit design
  not only increases working frequency up to
  400MHz, but also avoids floating point
  multiplication, which could be implemented by the
  Application Specific Integrated Circuit (ASIC)
  procedure or Field Programmable Gate Arrays
  (FPGA) chip.
• The layout of the chip has been implemented using
  the method of ASIC design flow with the TSMC
  0.18um standard cell CMOS technology on CAD
  system.

III. PPE-CHIP Architecture
II. Methods and Algorithms
Fig.2 PPE-CHIP Architecture and Features

• The active pileup prevention energy (PPE)
  method1
• Integrate the present event dynamically until the
  next is detected.
• Estimate a weighted-value to represent the total
  energy inside the scintillation detector which
  includes both the energy from present event and
  the remnant energy from all the previous events
• Calculate the energy of the latest event by
  subtracting the residual energy, i.e. a
  decay-weighted sum of the previous total energy
  based on the present total energy

Fig.3 Pipelined Energy Extractor with Look up
Table
Fig.1 The full digital PPE Technology acquired
data from 100MHz A/D converter, sampled from NaI
scintillation detector (t 230ns) at at every
10ns (Ts).
Eq.(1) Sampled Data at point n for non-pileup
events
Eq.(2) Sampled Data at point n for pileup events
Fig.4 PPE-CHIP Internal Structure and Virtuoso
CAD Layout
IV. Experimental Results
Eq.(3) The discrete weighted sum Sj and Sj-1 for
the jth, (j-1)th gamma ray
Eq.(4) Variable SEj is 10 times less then Sj
Fig. 5 Comparison of Dynamic and Conventional
Fixed Threshold
Eq.(5) Extract the total energy Ej for the jth
pileup gamma ray
Fig. 6 Comparison of Energy Spectra at Different
Count Rates and Different Methods ,i.e. D-PPE
(l), DLC (m), DI (r)
1Wong, W-H., et al. IEEE Trans. Nucl. Sci,
45(3)898902, 1998
Contact Li HAN (lhan_at_umich.edu)