Research Of An ASIC For Ultrasonic Flowmeter

Since the 1970s, the ultrasonic flowmeter has been widely used as a non-contacted instrument with the rapid development of IC technology. At present, there are two ways to design ultrasonic flowmeter, one of which is realized with a large number of discrete devices, and the other is based on a measuring ASIC. The first plan has many components, complex debugging and low reliability. The kinds of ASIC for measurement are few and mostly depend on imports on a high price. Therefore, to design an ASIC for ultrasonic flowmeter not only could realize the integration of flowmeter, but also could reduce the cost, which is of great significance.In the thesis, an ASIC for ultrasonic flowmeter is designed based on the principle of time difference. The chip comprises ultrasonic sensor driver circuit, time measurement control, temperature measurement control, 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 flowmeter. 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 different time of discharge, it gets the value of the sensor's 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 transducer's launch and reception principles.At 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.The ASIC is made in the process of CSMC 0.5μm, N-well DPTM standard CMOS. Final testing results show that, the function of time measurement and other assistant function are realized and can reach a certain precision. The thesis analyzes the shortage of the chip and its reason is given in the end.