Time-of-flight (TOF) measurement in PET scanners allows a more accurate image reconstruction and/or a lower delivered radiation dose. We are developing a fully custom ASIC to take advantage of the characteristics of the SiGe Bi-CMOS process for timing measurements, integrating a fully-depleted pixel matrix with a low-power BJT-based front-end per channel, integrated on the same 100 um thick die. All the pixels are multiplexed to a single TDC to extract timing information. Each front-end includes a BJT preamplifier with active feedback, a CMOS discriminator and a calibration DAC. A triggered readout logic is included to reduce the data to be read out of the system. The target timing resolution is 30 ps for a 511 keV photon with a 1 pf input capacitance. The front-end has a gain of 95 mV/fC and a rise time of 1 ns. Its low power consumption of 135 uW, makes it possible to stack multiple ASICs on top of each other, in order to increase the detection efficiency. A total of more than 1 million channels will form the complete scanner. A full-featured prototype with a small 10-by-3 pixel matrix has been submitted in April 2017, after a number of smaller prototypes to validate each block. A full-size chip is currently being designed.​