Digital Pressure Sensor with Filtered Frequency Output Using Ring Oscillator and Mixer

James Yang1,  Zhiping Yu1,  Litian Liu1,  Zhaohua Zhang1,  Roy Liu2,  Yafei Bi2
1Institute of Microelectronics, Tsinghua University, Beijing 100084, P.R. China, 2Lionax Technology USA Corporation


A new temperature insensitive digital pressure-sensing device with filtered frequency output using ring oscillator and mixer is presented. It employs the Micro-ElectroMechanical Systems (MEMS) technologies to form pressure sensing using PMOS ring oscillators to generate frequency which depends on the pressure-induced stress. The digital pressure sensor has several advantages. One of them is the very low temperature coefficient and simple fabrication process. Another one is to convert the analog measurement of pressures into the frequency measurement. Compared to a direct pressure measurement, it is much more convenient and easier to conduct the frequency measurement with digital circuits. Since the ring resonators are exposed to the change of the pressure, the structure is significantly simplified as no shielding protections of the sensor from the pressure are required.