An Interface IC For Capacitive Accelerometer

Due to the limitation on the manufacturing technology, the sensors and interfacecircuits of the domestic MEMS accelerometers are still manufactured separately,especially for the accelerometers with high precision and large dynamic range which areapplied in the area of industry and military. The sensors generally processed by bulksilicon technology, and the interface circuit by surface silicon processing technology. Thecomplete accelerometer assembled through a secondary integration technology (PCB orhybrid).Because of the small size of the MEMS sensor, the output signal is weak. Theinterface circuit must have a higher degree of sensitivity and integration. Improve thesignal detection sensitivity generally requires the lock-in amplifier technology, i.e. thesignal modulation in a high-frequency signal before transmission processing, in order toavoid the DC drift and low frequency noise problems. The final signal can be rebuildedby a synchronous demodulator.There are two circuit topologies generally used by MEMS differential capacitiveaccelerometer. One is named open-loop structure which has good robustness, but lesslinear dynamic range. The other is closed-loop force feedback structure, better linearitydynamic range, but the circuit structure is relatively complex and requires careful stabilityproblems.In this paper, we design an interface IC for a bulk silicon differential capacitiveacceleration sensor. The main contents of this paper are:1. Analysis the principle of capacitive accelerometer, the physical model of thedifferential capacitive acceleration sensor, sensor-related characteristics of themathematical description of the closed-loop force feedback structure differentialcapacitive accelerometer system principle, composed of circuit module.2. The design ideas, structure and working principle of an interface IC based on abipolar process. This IC is designed for closed loop feedback structure differentialcapacitive accelerometer.3. The IC layout design implementation.4. Tested results, including the characteristics of circuit and co-sensor, for analysisand comparison.