A self-test on wafer level for a MEM gyroscope readout based on ΔΣ 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 characterize sensor element and 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 utilizing this modulator is performed in two steps. First, an automatic tuning loop is proposed to configure the collocated feedback and to verify its functionality. In a second step, an offset is added to the settled value of the tuning loop to generate a negative feedback path. The resulting purely electrical ΔΣ modulator structure is utilized to validate the functionality of every single circuit component of the later operated electro-mechanical ΔΣ modulator. Furthermore, it allows the characterization of the bandpass loop filter by observing the ΔΣ modulator output power spectral density.

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