High performance MEMS accelerometer and gyro with a unique SMD and digital interface

High performance inertial sensors based on Micro-Electro-Mechanical Systems (MEMS) have been progressively replacing quartz accelerometers, mechanical gyroscopes (gyros) and even Fiber Optic Gyros in navigation and positioning systems, at least in the less demanding applications. But until now, the IMU/INS system manufacturers usually had to interface two different types of sensors, with different communication protocols (Analog or SPI/
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IC or RS for digital), two different type of packages, that were often bulky metal housing with pins or connectors and not compatible with standard Surface Mountable Device (SMD) assembly, and two sets of passive components. This was resulting on a complex and expensive integration and still rather large Inertial Measurement Units (IMU). In this paper, we present a technical approach selected to achieve higher performances SMD MEMS accelerometer and gyro sensors built with the same package and the same digital SPI interface to reduce the bill of material and simplify the sensor integration and thus reduce the effort and duration of the development of MEMS IMUs. It is based on a generic Sigma-Delta closed-loop capacitive MEMS architecture for both the accelerometer and the gyro combined with a hermetic J-lead ceramic package compatible with SMT assembly.