Comparison between Analog and Digital Time and Frequency Measurement Techniques

Along with the accuracy enhancement of different kinds of frequency standards, more demands are made on the measurement precision. In time and frequency measurement instruments, both digital and analog processing techniques and circuits are used widely. The paper focuses primarily on the limitations of the technology and the principle in the use of the analog and the digital measurement approaches. Based on the principle of the conventional method measuring the period of frequency difference between the reference and the measured frequency standards, the analog and the digital measurement techniques are compared in actual realization, configuration, precision and error sources etc. A number of experiments indicate that the precision of the analog method is as high as 10-13/tau and the precision of the digital method about 10-12/tau or lower. Furthermore, the digital scheme in TTL circuits has great influence of trigger error and quantified error on measurement result; while in ECL circuits, trigger error is held down and the precision is greatly enhanced. Moreover, this paper proposes some improvement step. One had better appropriately combine ultra-high speed devices with the digital method to obtain a high precision frequency measurement device.