PETsys Time-of-Flight PET ASIC


  Figure 1: Detail of test board showing the TOFPET2 ASIC bonded on the board before the application of a protective epoxy layer. A BGA packge version is under development.  


The PETsys High Performance TOFPET2 ASIC is a new 64 channel chip for the readout and digitization of signals from fast photon detectors in applications where a high data rate and fast timing is required. It uses a low threshold for timing and a high threshold for accepting the event. Both thresholds are separately configurable for each channel. Every time one of the 64 channels exceeds the high threshold a record is created giving the channel number, the time and the charge of the event. Activity in one channel does not cause any dead-time on the other channels.
A short description of the ASIC2 can be found here :
A first performance report can be found here:



Main Features

  • Designed in standard CMOS 110 nm technology.
  • Signal amplification and discrimination for each of 64 independent channels.
  • Dual branch analogue interpolation TDCs for each channel. The first branch is used for timing measurement. The second branch can either be used for time-over-threshold (ToT) or charge measurement (ADC).
  • Quad-bufered charge integration for each TDC or ADC in each channel
  • Dynamic range: 1500 pC.
  • SNR 25 dB for Qin=200 fC (about one p. e.) and input capacitance of 320 pF.
  • TDC time binning: 30 ps.
  • Gain adjustment per channel: 1, 1/2, 1/4, 1/8.
  • Supports positive or negative input signal polarity
  • On-chip calibration pulse generator with 6-bit programmable amplitude.
  • Max channel hit rate: 480 kHz.
  • Rejects dark counts without triggering, allowing to handle over 1 MHz of dark counts.
  • Separately configurable thresholds for each channel.
  • Configurable charge integration time up to one microsecond.
  • Fully digital output, 4 LVDS data links double data rate (DDR) compatible.
  • Max output data rate: 2.6 Gb/s.
  • Clock frequency: 200 MHz.
  • Power consumption per channel: 5-8 mW, depending on certain settings.




Figure 2.
Pulse hight spectrum obtained with a radioactive source of 22Na and with a LYSO crystal of 3x3x5 mm3 mounted on a KETEK-PM3325-WB SiPM at 4 V overvoltage and at 20° C. The charge signal is integrated in a time window of 350 ns. The energy resolution at 511 keV is 10.5 % after correction for the SiPM non-linearity.



Figure 3.

Time difference between the two signals from a positron annihilation event. Measured at 20°C with a 22Na point source and two 3x3x5 mm3 LYSO:Ce crystals coupled to two NUV-HD SiPM pixels produced by FBK, and AC coupled tot the ASIC. These SiPM pixels are 4×4 mm2 , and have 40 μm cell pitch.