Improving a frequency measurement circuit for high-accuracy QCM sensors

This paper presents the design of a FPGA-based digital counter for the measurement of the oscillation frequency of Quartz Crystal Microbalance (QCM) sensors. This work is part of a bigger project focused on the development of a standalone QCM system for the analysis and characterization of organic coatings. The method used to implement the digital counter is the direct frequency measurement. Therefore, special attention is paid in the design of the time-base generator. Measurement errors due to the drift of the system oscillator are discussed, and several solutions are proposed taking advantage of the embedded DLL circuits available in the FPGAs. The designed digital counter is implemented and tested using the Xilinxpsilas Spartan XC3S200 FPGA.