A variable negative resistance VCO suitable for measuring quartz crystal microbalance

This paper present a design circuit CMOS in 0.5um to detected QCM resonant frequency and QCM peak current for calculate mass weight of load on QCM surface. The QCM resonant frequency was changed by mass on QCM surface and QCM peak current depended on QCM resonant frequency. The differential of QCM resonant frequency (Δf) between QCM unloaded and QCM with loaded on surface can use for calculate mass on QCM surface by relationship between Δf and Δm. The measurement of QCM resonant frequency and QCM impedance used VCO sine wave to generate frequency for QCM and sweep frequency for detected QCM resonant frequency. The QCM was used value at 10MHz so the VCO frequency output will sweep frequency around 10MHz for detected QCM frequency output. After that measure the QCM current to detect QCM peak current and counter frequency from VCO between QCM unloaded and QCM with loaded on surface.