Development of a FPGA-based SoC Instrument for the characterization of High Sensitivity QCM Oscillator Sensors

To characterize the behavior of quartz crystal microbalance (QCM) oscillator sensors, it is not enough to determine their experimental sensitivity, but rather it is essential to study the frequency fluctuations in order to establish the sensor resolution. The development of an FPGA-based system on a chip (SoC) intended to measure the frequency noise and mass resolution of QCM sensors is presented in this paper. The implemented system integrates the frequency measurement and the computation of the Allan deviation and mass resolution of the sensor in a single FPGA. By this way, a reconfigurable and low cost QCM sensor system is obtained working as a standalone measurement instrument. It permits to set the lower limit to the mass variations that can be observed with a sensor in the conditions of the application. A Virtex-4 FPGA from Xilinx was chosen as hardware platform due to its suitable architecture to support SoC and DSP applications. The developed measurement system combines the 32-bit embedded MicroBlazereg soft processor with a specific hardware coprocessor designed to accelerate the computations required for real-time processing. A data flow based on techniques as recursive formulas and jump prediction was proposed in order to reduce the computations and memory requirements of the coprocessor. Also the coprocessor uses a pipeline architecture and time-sharing modules in order to achieve an optimal balance between velocity and area. Finally, the implemented system was validated with a 9 MHz QCM sensor in damping media used for electrochemical applications and the results were compared with a full floating point implementation