Design Of Quartz Crystal Microbalance Frequency Measuring System Based On FPGA

Quartz Crystal Microbalance (QCM) sensor is developed gradually since 1959 as a modem trace material detection and analysis technology. Because of its high sensitivity, high selectivity, reusable, easy to operate, and other advantages, QCM sensor is widely used in physical, chemical, biological, food industry, environmental science, clinic medicine, and other fields.However, the fundamental frequency of most existing QCM sensors is mostly in the level of 5?10MHz. In order to improve the sensitivity of QCM, it is important to design a high fundamental frequency QCM. The frequency temperature drift impact accuracy of QCM measurement, using dual quartz crystal differential frequency measurement method, the elimination of environmental temperature to the single channel QCM measurement frequency temperature drift.This topic design a QCM frequency measurement system for dual channel. Firstly, it is designed that a QCM oscillating circuit for dual channel. QCM oscillating circuit consists of two-stage OPA660 wide bandwidth operational transconductance amplifier, can make oscillation for QCM of fundamental frequency about 40MHz. The circuit can operate well in gas and liquid, the Allan variance of output frequency in gas is better than 5x 10-9@ls, it is provided as the stable source of oscillation frequency for the measurement system. Secondly, a dual frequency count system based on the Field Programmable Gate Array (FPGA) is designed to synchronous measure the output frequency of the dual channels QCM oscillating circuit. Frequency count implement with common cycle frequency measurement method. At the same time, a high stability and constant temperature crystal oscillator, the Allan variance is better than 2.3×10-9@ls, is used as time gate to improve the counting deviation. Thirdly, a PC frequency display and storage system based on Lab VIEW is designed. It can control the frequency counting system online, and display the measurement results of two channels on time. At the same time, it can store the measurement results for the subsequent analysis. Finally, sets up the experimental system and tests. Through the analysis of experimental data, the system basically achieve the desired objectives, provide a reference for the application of QCM measurement.