  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.
