SamPic0: A 16-channel, 10-GSPS WTDC digitizer chip for picosecond time tagging

SamPic0 is a Waveform Time to Digital Converter (WTDC) multichannel chip providing outstanding time measurement capabilities. It makes use of the AMS 0.18-μm CMOS technology. One of its specificities stands in its capacity to directly measure the arrival time of fast analog signals without the need of any external discriminator. Each of its 16 channels associates a traditional DLL-based TDC providing a raw time based on a counter and a DLL associated with an ultra-fast 64-cell deep analogue memory (bandwidth > 1.5 GHz, sampling frequency > 10GS/s) allowing fine timing extraction as well as other parameters of the pulse like charge, pulse width or rise-time. Each channel also integrates a discriminator that can self-trigger the channel independently or allows it to participate to a more complex trigger embedded on-chip. External trigger is also available. After triggering, analogue data is also digitized on-chip by massively parallel low-power 11-bit Wilkinson ADCs running at 1.3 GHz and only data corresponding to a predetermined region of interest is then transferred towards the acquisition system. Dead-time is thus limited to 1.6 μs for an 11-bit conversion and is as low as 400 ns for a 9-bit conversion which already provides an excellent time precision. Contrasting with the existing fast sampler chips usually designed for all-purpose applications and requiring external electronics to be used for performing accurate timing measurements, the SAMPIC0 chip presented here has been specifically designed for the latter type of application. Although the SAMPIC0 chip was originally thought as a technological demonstrator, its readout has been structured for low dead-time applications and its design thus permits an easy integration in medium size acquisition systems. Such a set of boards and DAQ system has already been developed with the primary goal of evaluating the chip performances, but it is also usable to take data with detectors in a real environment. This setup, including a powerful software with an original interactive graphical interface, has permitted the characterization of the SAMPIC0 chip, and the measurements of its time resolution which is as good as 14 ps rms without any time correction. This value is decreased in the range of 3 to 4 ps rms after a simple correction, itself based on a very simple calibration. This calibration remains very stable with time and can thus be stored on-board. This paper will present the new WTDC concept, the chip architecture, the existing set of boards and DAQ system and will give report of the latest measurements of the chip performances. It will also present the modifications and additions to the design of the second version of the chip, which should be submitted in 2014.