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An improved equal precision frequency measurement method is presented for acquisition of frequency signal output from high sensitivity scalar atomic magnetometers. The frequency range to be measured is from 75 kHz to 350 kHz with a resolution better than 0.01 Hz, and the sampling rate should be at least 10 Hz. To meet the requirements on dynamic ra...
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... In [14,15], Polish scholars used the TDC method in FPGA to realize the measurement of frequencies up to 200 MHz, and the maximum frequency measurement error within 1 s is 2.4 Hz. In [16], Y.H Ge et al. used the TDC-GP22 chip to achieve an extended measurement of ±1 counting error. Under the condition of a sampling rate of 10 Hz, the frequency measurement resolution is smaller than 0.01 Hz. ...
Frequency-modulated (FM) signals are widely used in sensing, measurement, and signal detection due to their strong anti-interference and easy transmission characteristics. Although the high-precision measurement methods for static signals are quite complete, the high-precision measurement methods for dynamic FM signals still need to be studied, and the measurement accuracy in the high-sampling system still has room for improvement. Traditionally, the equal-precision measurement method is widely applied in most scenarios. However, its accuracy is limited by the quantization error of ±1 word and the sampling gate time, making it difficult to improve the frequency measurement accuracy while ensuring a high sampling rate at the same time. In this paper, a high-precision feedback frequency measurement system with the capability to eliminate the quantization error of ±1 word is proposed. The proposed system consists of two stages, the rough measurement stage based on the equal-precision measurement method and the precise measurement stage based on the negative feedback tracking architecture using the phase–frequency detector (PFD) and direct digital synthesizer (DDS). The effectiveness and feasibility of the system are verified by both simulation and experiment. At the sampling rate of 2 kHz, the frequency measurement accuracy is improved by more than 30 dB.
... Based on it, several ( í µí± ) identical equal precision frequency measurement units are implemented on FPGA to improve the accuracy of frequency measurement to 1/í µí± of the original method [15]. A method using FPGA and TDC for high precision frequency measurement was first proposed in [16] which further improve the accuracy of frequency measurement by several orders of magnitude. ...
... This paper presents a novel method of frequency measurement using FPGA and TDC. Instead of measuring more precise counting values of equalprecision frequency measurement [16], this method obtains the converted frequency indirectly by accurately measuring the time of multiple measured signal cycles. It has better accuracy performance than previous works according to the error analysis. ...
... The principle of the method using FPGA and TDC proposed in [16] is shown in Fig. 1(b). The measured signal í µí± í µí± of this method is expressed as: ...
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 ±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.
