The SAR500, a calibrated, compensated, high-precision, high-stability and low noise digital oscillatory gyroscope is under development by Sensonor Technologies AS. This gyroscope has a SPI interface and is placed in a rigid customized package of ceramic.
The SAR500 incorporates an analog ASIC and a Butterfly MEMS die. The control of this device is through a digital ASIC or a FPGA. The FPGA or the digital ASIC also incorporates the required functional algorithms for enabling the superior performance of the device. The SAR500 is calibrated at the factory and is also compensated to counter effects of temperature for offering highly precise digital output across a wide range of temperatures. It also exhibits low sensitivity to vibrations and shock due to perfect tuning of detection and excitation frequencies along with perfect electrical and mechanical balancing for the dual masses.
Its signal processing circuits incorporate a complete customized analog ASIC, along with a digital component and is implemented in a structured ASIC or an FPGA. Fifth order delta-sigma ADCs, precision type of low noise charge amplifiers, low pass filters through which signals are fed back and voltage references are included in the analog ASIC. A high resolution and stable implementation of the delta-sigma DACs for detection and excitation feedback and the loop filters is made possible by the digital ASIC. It is also responsible for performing low noise synchronous modulation, in addition to compensating for temperature drift of scale factor and bias. To ensure efficient read out of data and angular rate, the gyro has been configured like a SPI slave.
The sensing element is a system of two similar masses that are suspended using asymmetric springs to pedestals so as to minimize the thermal and mechanical stress. The detection and excitation modes are controlled through closed feedback loops. For perfectly tuning the detection and excitation modes’ resonance frequency, extra pairs of electrodes have been provided.
These additional electrodes are also used for active compensation of the gyroscope’s quadrature offset. A specialized sealed cavity is utilized to contain the vibrating masses inside a low pressure hermetic environment that is required for high-Q factors and low dynamic damping. The selection of crystalline materials for the sensing element structure and complete symmetry of design about the vertical axis has resulted in enhanced stability of the gyroscope.
The important performance features of this device include bias repeatability of 0.1deg/hr, angular random walk of 0.004 deg/sqr(hr) and in-run bias stability of 0.02 deg/hr.