A temperature compensation subsystem for an IMEMS CMOS pressure sensor

Piezoresistive CMOS-MEMS pressure sensor with ring oscillator readout including ΣΔ analog-to-digital converter on-chip

“…FREQUENCY-TO-DIGITAL CONVERSION As shown above the output from the integrated sensor is a frequency modulated signal which needs to be converted into a digital representation. By examining the equation describing an FM-signal it is obvious that the accumulated phase represents the integral of the baseband signal which in this case is the sensed pressure: (8) where , the instantaneous angle, is given by (9) By quantizing the accumulated phase and performing firstorder differentiation on the quantized phase, the system is equivalent to a first-order continuous-time -modulator referred to as the Frequency Delta-Sigma Modulator (FDSM) [2], [3]. The block diagram of the FDSM is illustrated in Fig.…”

“…By calculating the difference between Equation (4) and (5) we get (6) The value of is typically 138.1 for p-MOS devices compared to -13. 8 for n-MOS devices at room temperature. Placing p-MOS transistors on the diaphragm will therefore exhibit a significantly higher sensitivity to shear stress, than for an n-MOS transistor.…”

“…Placing p-MOS transistors on the diaphragm will therefore exhibit a significantly higher sensitivity to shear stress, than for an n-MOS transistor. The temperature dependency of can be eliminated by adding a temperature compensation subsystem, as explained in [8].…”