TOFPET ASIC for PET applications

Abstract

A 64-channel ASIC for Time-of-Flight Positron Emission Tomography (TOF PET) imaging has been designed and simulated. The circuit is optimized for the readout of signals produced by the scintillation of a L(Y)SO crystal optically coupled to a silicon photomultiplier (SiPM). Developed in the framework of the EndoTOFPET-US collaboration [1], the ASIC is integrated in the external PET plate and performs timing, digitization and data transmission for 511 keV and lower-energy events due to Compton scattering.Multi-event buffering capability allows event rates up to 100 kHz per channel. The channel cell includes a low input impedance low-noise current conveyor and two trans-impedance amplifier branches separately optimized for energy and time resolution. Two voltage mode discriminators generate respectively a fast trigger for accurate timing and a signal for time-over-threshold calculation, used for charge measurement. The digitization of these signals is done by two low-power TDCs, providing coarse and fine time stamps that are saved into a local register and later managed by a global controller, which builds-up the 40-bit event data and runs the interface with the data acquisition back-end.Running at 160 MHz the chip yields a 50 ps time binning and dissipates 7 mW per channel (simulated for 40 kHz event rate p/channel) for high capacitance photodetectors (9 mm 2 active area Silicon Photomultiplier with 320 pF terminal capacitance). The minimum SNR of 23.5 dB expected with this capacitance should allow triggering on the first photoelectron to achieve the envisaged timing performance for a TOF-PET system.

Validation of a highly integrated SiPM readout system with a TOF-PET demonstrator

“…The cooled air flows over the copper plates of the DMs and stabilizes the temperature of the DMs to (19.0 ± 0.5) °C. The readout electronics is based on the TOF-PET Application Specific Integrated Circuit (ASIC) [2,3]. TOFPET ASIC is a low-noise and low-power 64-channel mixed-mode chip with fully digital output designed in 130 nm CMOS technology for SiPM readout, developed in the framework of the EndoTOFPET-US project [3].…”

“…The fine time measurement uses a set of four Time to Analogue Converters (TAC) and an ADC as described in [2]. The TDCs are calibrated using a procedure that consists of triggering the TDCs with test pulses synchronous to the system clock and varying the test pulse delay in fine steps to obtain the TDC response curve.…”

Asymmetric Data Acquisition System for an endoscopic PET-US detector

“…MPPC arrays readout is performed by means of a low power, low noise and high bandwidth ASIC with 64-channels implemented by the consortium [8][9]. The ASIC is able to trigger on the first photoelectron, while rejecting dark counts (L0-Plate Trigger Stage), at a maximum rate of 160 Kevents/s per channel.…”

“…Given the risk of using a novel technology for MPPCs readout, two different ASICs have been independently implemented by the collaboration: TOFPET ASIC [8] and STiC ASIC [9]. The STiC and TOFPET ASICs will be used to assemble two versions of the external plate, dedicated to prostate and pancreatic cancer detection respectively.…”

“…For the external plate case, they specify the amplification gain of the signals produced by the photodetectors as well as the thresholds used in time and energy measurements [8][9]. For the internal probe, this set of parameters specifies key characteristics such as the channel masking profile (DCR reduction), smart reset frequency (dead time reduction), or time and energy thresholds [13].…”