A Self-Test on Wafer Level for a MEM Gyroscope Readout Based on $\Delta \Sigma$ Modulation

This paper presents the implementation of a self-test for a gyroscope readout based on electro-mechanical ΔΣ modulation. Commonly, sensor element and readout ASIC are fabricated on separate wafers. Therefore, the ability to separately characterize the sensor element and the ASIC before packaging is desirable in order to reduce unnecessary expense. For the proposed self-test, a charge integrator with collocated detection and feedback is configured to generate an additional feedback path, which is used to operate a purely electrical ΔΣ modulator on wafer level. The self-test is performed in two steps. First, an automatic compensation controller configures the collocated force-feedback and thereby verifies its functionality. In a second step, an offset is added to the settled value of the controller to generate a negative feedback path to the input of the readout interface. The resulting purely electrical ΔΣ modulator is utilized to validate the functionality of every single circuit component of the later operated electro-mechanical ΔΣ modulator. The proposed self-test makes use of the already available hardware and therefore avoids an additional hardware overhead. Numerical simulations are performed to verify the proposed compensation controller concept as well as the selftest itself. The simulation results of the self-test are confirmed by measurements.