A novel frequency measurement technique for quartz microbalance systems and other resonator-based sensor systems

This paper describes the operation and design of a simple, low cost period counting system based on a D flip-flop mixer, directly applicable to quartz microbalances and quartz resonator-based sensors. The architecture of the period counting system is based on measuring the period of a low frequency difference signal obtained by subtracting a high stability reference frequency from the unknown frequency to be measured. An analysis of miscount errors caused by phase jitter in the input signals, when the period counting system is used as a quartz resonator based high temperature pressure sensor, is presented. We present a model that predicts miscount rates and discusses design rules to avoid phase jitter induced miscounts. The frequency measurement system was implemented using Peregrine´s 0.5 micron silicon-on-insulator (SOI) UTSi^® process. The integrated system was successfully tested and its functionality verified at 180°C ambient temperature. This circuit, implemented as a low power, ultrahigh resolution, frequency measurement circuit, can facilitate the production of inexpensive, high accuracy battery powered sensors.