Sense/drive architecture for CMOS-MEMS accelerometers with relaxation oscillator and TDC

This paper reports a mixed-signal architecture for capacitive accelerometers conditioning based on capacitance ratio to frequency conversion and high-precision digital frequency demodulation with coarse-fine time-to-digital converter (TDC) and delay-locked loop (DLL). Furthermore, the front-end has a capability to apply pulse-controlled electrostatic actuation which can be used for the accelerometer self-test or for closed-loop operation if an external digital feedback controller is added. Since the design is dominated by standard digital circuitry, the presented concept allows rapid prototyping, what is especially important in case of microsensors monolithically integrated in advanced CMOS processes where classic analog circuits are difficult to scale-down.