A time and frequency measurement method based on delay-chain technique

The short time-interval and frequency measurement are main research projects in the measurement of time and frequency. Traditional measurement methods include direct counting, analog interpolating, time-to-voltage conversion, time vernier and time-to-digital conversion. However these methods are all complicated and the instruments based on these methods are expensive. A novel method for short time-interval and frequency measurement based on delay-chain technique is presented in this paper. This method utilizes measured short time-interval or measured frequency signal to generate count gate. A delay-chain is used to delay reference frequency signal orderly. So a group of signals with phase-shifting evenly in a period of reference frequency signal are generated, and are counted respectively under the same count gate. With the average of the counts as the count of reference frequency, the decimal counting error is reduced and measurement accuracy is improved. The measurement resolution of this method for short time-interval and measurement accuracy for frequency are equal to the measurement results under condition of increasing frequency of reference frequency signal by the times of the number of delay unit in a delay-chain. An experiment demonstrates the resolution of short time-interval measurement and the accuracy of frequency measurement could be 100 ps and respectively and the theoretical measurement resolution and accuracy could be higher. Although it needs more delay units and counters in order to achieve high-accuracy measurement, this is not a problem because new device has been used, such as FPGA. This method is suitable for high-accuracy and low-cost measurement..