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An ASIC Research for Ultrasonic Flow Meters

 

Keywords:ASIC,Ultrasonic Flowmeter,Time Difference Method

An ASIC for ultrasonic flow meter is developed on the basis of transit-time difference.At present,there are two ways to design ultrasonic flow meter, one of which is realized with a large number of distance devices and the other is based on a measuring ASIC.The first plan has many components,complex debugging and low reliability,but the kinds of ASIC for measurement device are few and mostly depending on the high price of imports.Therefore, to design an ASIC for ultrasonic flow meter not only could realize the integration of flow meter.but also could reduce the cost,which is of great significance. All the system level and circuit level analysis and design, the entire system is simulated to meet the requirements by using the Hspice tool. After the completion of layout design, Dracula software tool is used to do the design rules and electrical rules check,during which every design validation has been finished.

Since the 1970s,the ultrasonic flow meter has been widely used as a contact-contact instrument with the rapid development of IC technology.

The chip comprises ultrasonic sensor driving circuit,temperature measurement module,time measurement control module,STOP signal conversion such as modules design.According to the method of time range transform,the logic circuits,triggers,flip-latches and switches are used to control the capacitors to charge in the time measurement control module.
The design transforms the time of ultrasonic propagation into the capacitor’s voltage to achieve a precise time measurement for ultrasonic flow meter.The temperature measurement control module uses a temperature sensor and a precise resistor to compose different discharged loop with a same capacitor.Through measuring the difference time of discharging, it gets the value of the sensors resistor and then gets the fluid’s temperature. The drive module and STOP signal conversion module are sub-frequency,select and comparison circuit based on the transducers’ launched and reception principles.

The ASIC is made in the process of CSMC 0.5um, N-well DPTM standard CMOS. Final testing results show that,the function of time measurement and other miscellaneous function are realized and can reach a certain precision.