Design Of High-precision Time-interval Measurement Platform Based On FPGA

The time-interval measurement technology plays an indispensable role in various fields,such as positioning and navigation, precision measurement and so on. With the proposedstrategic target of constructing the Oceanic Great Power, the ocean engineering has attractedgreat deal of attention. Ultrasonic flowmeter, which is applied to the field of submarinepipeline liquid flow monitoring, has also become one of the research hotspot on oceantechnology. Moreover, the time-interval measurement technology is justly the soul oftime-difference ultrasonic flowmeter. The accuracy of the time-interval measurement methodlargely determines the measurement accuracy of the ultrasonic flowmeter. Thus, the study andinnovation on the time-interval measurement technology has the theory significance andpractical prospect.Taking the development of time-difference ultrasonic flowmeter as the background, thisdissertation designs a high-precision time-interval measurement platform based on FPGA. Inthis dissertation, some high-precision methods are deeply demonstrated. Basing the principleof time-delay quantization, the tapped delay line method and the cycle delay chain method areinnovatively combined. And then a new time-interval measurement method is proposed inorder to improve the precision and widen the range.This platform consists of signal shaping module and high-precision time-intervalmeasurement module based on FPGA. For the signal shaping module, the comparator chipAD8612with quick conversion speed and high precision is selected which is responsible forthe circuit design for transmit signal and receive signal of the time-difference ultrasonicflowmeter. This circuit realizes the effect that the two signals are converted to continuoushigh-level signals. The high-precision time-interval measurement module based on FPGA isdiscussed as the key part of the platform. Owing to its short delay and strong controllability,FPGA logic element (LE) is innovatively constructed for the delay unit. This process isperformed by some functions in Quartus II software such as Chip Editor, LogicLockBack-Annotation and so on. Consequently, the precision of the platform can reach fewhundred picoseconds. Afterwards, delay units are connected in series and form a delay chain.The specific logic makes the signal circle and vibrate in the delay chain, which effectivelysolves the problem that when the precision is higher the range is much narrower.Finally, the functional verification of the platform is implemented in this dissertation. Onone hand, the actual measurement result shows that the signal shaping module circuit board has a good performance and is able to achieve the design requirements; On the other hand, forthe high-precision time-interval measurement module, the correctness of the logic design istested by SignalTap II, and then the timing simulation is carried out by Modelsim. As a result,the precision of platform can reach600picoseconds, and at the same time the range can reachup to692.115135microseconds.