Multichannel FPGA based MVT system for high precision time (20 ps RMS) and charge measurement

In this article it is presented an FPGA based Multi-Voltage Threshold (MVT) system which allows of sampling fast signals (1–2 ns rising and falling edge) in both voltage and time domain. It is possible to achieve a precision of time measurement of 20 ps RMS and reconstruct charge of signals, using a simple approach, with deviation from real value smaller than 10%. Utilization of the differential inputs of an FPGA chip as comparators together with an implementation of a TDC inside an FPGA allowed us to achieve a compact multi-channel system characterized by low power consumption and low production costs. This paper describes realization and functioning of the system comprising 192-channel TDC board and a four mezzanine cards which split incoming signals and discriminate them. The boards have been used to validate a newly developed Time-of-Flight Positron Emission Tomography system based on plastic scintillators. The achieved full system time resolution of σ(TOF) ≈68 ps is by factor of two better with respect to the current TOF-PET systems.