An improved frequency meter for atomic magnetometer based on accurate time measurement

An improved frequency measurement method using FPGA and TDC (time-to-digital converter) is proposed, and its error analysis is carried out. Instead of measuring more precise counting values of equal-precision frequency measurement, this method obtains the converted frequency indirectly by accurately measuring the time of multiple measured signal cycles. It significantly improves the accuracy of the frequency meter in atomic magnetometer. The method is capable of eliminating the (2)1 error of reference signal counting of equal precision frequency measurement method, as well as avoiding the limitation that the measurement range of TDC cannot reach 0. With this method, a prototype of the frequency meter is implemented with very small size. Tests show that the prototype achieved 0.0042 Hz precision and 0.00056 Hz standard deviation in the frequency range of 70 kHz to 350 kHz at the output rate of 10 Hz.