The present disclosure relates in general to Diffuse Correlation Spectroscopy system for obtaining an autocorrelation function, and more particular, to a correlator and method for controlling a sampling time period and data length used for calculating an autocorrelation function. The correlator may include, a sampling gate circuit which is open during a variable time period and provides a data sample, a correlation circuit which calculates a correlation function from the data sample provided from the sampling gate circuit, and a parameter determining circuit which determines a sampling time period to be used by the sampling gate circuit based on the correlation function.
