Digital pressure sensor with filtered frequency output using ring oscillator and mixer

A new temperature insensitive digital pressure-sensing device with filtered frequency output using ring oscillator and mixer is presented. It employs the Micro-Electro Mechanical 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.