PETsys TOFPET2 ASIC

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. Standard it is provided as BGA package.

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 :

TOFPET2 a high-performance ASIC for time and amplitude measurements of SiPM signals in time-of-flight applications

A performance report can be found here:

Experimental characterization of the PETsys TOFPET2 ASIC

For the ASIC2 Data Sheet : see the documentation section.

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.
On-chip calibration pulse generator with 6-bit programmable amplitude.
Max channel hit rate: 600 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 two microseconds.
Fully digital output, 4 LVDS data links double data rate (DDR) compatible.
Max output data rate: 3.2 Gb/s.
Clock frequency: 200 MHz.
Power consumption per channel: 8.2 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 15°C with a 22Na point source and two 2x2x3 mm3 LYSO:Ce crystals coupled to two Hamamatsu S13361-30361-3050AE MPPC arrays.

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