A sampler adapted to a one-dimension slow-varying signal, including: a signal preprocessing unit configured to preprocess an input signal; a slope-controllable sawtooth wave signal generating unit configured to generate a slope-controllable sawtooth wave signal and perform zero-resetting; a signal comparing unit configured to compare the preprocessed input signal from the signal preprocessing unit with the sawtooth wave signal and to output a pulse signal to the generating unit and a signal outputting unit when the preprocessed input signal is equal to the sawtooth wave signal; a counting unit configured to count a number of clock signals while the sawtooth wave signal generating unit is generating the sawtooth wave signal and to transmit the counted number to the signal outputting unit; the signal outputting unit configured to, upon receipt of the pulse signal output from the signal comparing unit, output the number counted by the counting unit at the moment.