A differential frequency detector using single PLL for sensing a dual-channel quartz crystal microbalance in liquids

In this paper, we propose a differential frequency detector, composed only one PLL, used for sensing a dual-channel quartz crystal microbalance (QCM) in liquid environment. The differential circuit topology can eliminate the loading effect of the sensing interface and also provide a better immunity to noise due to degraded Q factor. This detector uses a dual-channel QCM to detect the biological reactant by counting the frequency difference between two channels. The two frequencies are locked alternatively and amplified by only one PLL. The QCM detector was fabricated in 0.35μm CMOS technology and measured to have a small frequency variation <; 0.13 ppm from 30~50.