FPGA-Based Self-Calibrating Time-to-Digital Converter for Time-of-Flight Experiments

We describe the architecture of a FPGA-based self-calibrating Time to Digital Converter (TDC), specifically intended to measure the width of an input pulse. The configuration consists of two controllable ring oscillators with a very small difference in their frequencies, wherein this difference determines the achievable resolution. The calibration scheme relies on an accurate pulse-generator or external crystal-oscillator to provide a stable...