Design of 32-channel TDC Based on Single FPGA for {\mu}SR Spectrometer at CSNS

TL;DR

This paper presents a 32-channel FPGA-based TDC for {}SR spectrometers at CSNS, achieving high precision, flexible configuration, and efficient data transmission for material microstructure studies.

Contribution

The design introduces a multi-channel, high-precision TDC with real-time configurability and calibration, tailored for {}SR spectrometer applications.

Findings

FWHM precision better than 273 ps per channel

Deep hit-buffer capacity up to 512 signals

Linear response with low temperature sensitivity

Abstract

Muon Spin Rotation, Relaxation and Resonance ({\mu}SR) technology has an irreplaceable role in studying the microstructure and properties of materials, especially micro-magnetic properties. An experimental muon source is being built in China Spallation Neutron Source (CSNS) now. At the same time, a 128-channel {\mu}SR spectrometer as China's first {\mu}SR spectrometer is being developed. The time spectrum of {\mu}SR can be obtained by fitting the curve of positron count rate with time. This paper presents a 32-channel Time-to-Digital Converter (TDC) implemented in a Xilinx Virtex-6 Field Programmable Gate Array (FPGA) for measuring the positron's flight time of {\mu}SR Spectrometer. Signal of each channel is sampled by 16 equidistant shifted-phase 200 MHz sampling clocks, so the TDC bin size is 312.5ps. The measuring range is up to 327us. This TDC has the ability to store multiple hit signals in a short time with a deep hit-buffer up to 512. Time tag is added to each data to record the moment when the data was detected. Programmable time window and channel shielding give the flexibility to choose the time range and channels of interest. The delay of each channel can be calibrated. The data is transmitted to data acquisition system (DAQ) through Gigabit Ethernet. TDC and control logic are configured in real time by DAQ. The results of test show that the Full Width at Half Maximum (FWHM) precision of single channel is better than 273 ps with a low sensitivity to temperature and the linearity is pretty well.