Implementation of Time to Digital Converter on FPGA for high-resolution-performance in Particle Therapy applications

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Time-to-digital converters (TDCs) are essential for precise time measurements in several domains. FPGA-based TDCs are a flexible, low-cost, highly customizable alternative. We have implemented an FPGA-based TDC based on a tapped delay line architecture, targeting the latest device families of AMD, to measure single particle transit times in a silicon sensor with a <30ps resolution at Particle Therapy clinical rate (average rate of 1e7-1e9 pps). This is highly needed for new in-vivo online treatment verification techniques, e.g. Prompt Gamma Timing. The TDC design relies on carry-logic blocks to introduce a small delay, and latch-based observation points placed at regular intervals along the chain to sample the signal at discrete time steps. Manufacturing process variations are addressed by acting directly on placement and routing. A synchronous counter is enabled to extend the measurement range. Experimental validation confirmed an average of 5.8 ps with an uncertainty of 30 ps..

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