PACIFIC: Silicon photomultiplier readout ASIC for the LHCb upgrade

PACIFIC is a 64 channel mixed-signal ASIC designed for the readout of the Scintillating Fibre (SciFi) Tracker developed for the LHCb upgrade in 2018/19. The SciFi Tracker uses as active material 250 μm scintillating fibres, stacked in 6 layer mats and sensed by custom designed 128 channel silicon photomultiplier (SiPM) arrays. It will be comprised of 12 planes, each covering an area of 5×6 m
²
. PACIFIC is connected directly to the SiPM arrays without any interface components, using a current conveyor to acquire the current pulses coming from these sensors. The following stage is a fast shaper with a fully configurable double pole-zero cancellation scheme, which reduces the pulse width and thus the spillover. Subsequently, the signal is accumulated with a gated integrator, using two interleaved units to maximize the integration time. Finally, the digitization is performed with a 2 bit non-linear flash ADC, bundling together the data from two channels and outputting them through a serializer at 160 Mbps. Altogether, the target power consumption is 10 mW per channel. Several prototypes have been produced using IBM and TSMC CMOS 130 nm process technology, including a full size prototype.