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An 11-bit time-to-digital converter (TDC) with high time resolution implemented in CMOS VLSI is presented. The TDC operates with a wide and clock-adjustable resolution of LSB = 50 ps to 1 ns, and with good power supply, temperature, and environmental effects compensation. The dead time of the measurement is as low as 0.5 μs and the event rate can be as high as 1 MEvents/s. The power dissipation is a function of event rate and clock frequency; the TDC dissipates <10 mW at an event rate of 100 kEvents/s and LSB=100 ps. The TDC was incorporated in a complete time-of-flight (TOF) system on a chip that in addition included front-end analog signal processing. The TOF chip is already flying onboard the HENA (High Energy Neutral Atoms) instrument of the IMAGE NASA mission, launched in 2000, and is part of many other instruments such as particles, X-ray, and the laser altimeter of the Messenger spacecraft.