Norwood, Mass., USA: To minimise the influence of linear shock and vibration, Analog Devices developed a gyroscope that’s actually four gyros connected in two differential pairs. The ADXRS800, fashioned with the differential quad beam architecture, will target automotive electronic stability control applications.
“Each pair of devices works in antiphase,” says Christoph Wagner, marketing manager for Active Safety. “\\[In normal operation,\\] one moves to the left and one to the right. If the gyro is subject to excessive acceleration, such as when the underside of the car is hit by a stone, both devices move to the left, so the signals are combined differentially.”
Though it improves the signal-to-noise ratio only slightly, shock and vibration performance improves significantly. Sensitivity to linear acceleration is specified at only 0.03°/s/g and vibration rectification is only 0.0002°/s/g2, much better than previous generations of the product.
Wagner also points out that although the MEMS structure is four times the size of a single gyro, it will not increase the size of the overall device package.
The ADXRS800 includes on-chip temperature compensation, which according to Wagner, was not possible in past generations of the device. It performs linearly over the range -40 to +105°C, with temperature compensation data stored on-chip. Previous gyros were just analogue sensors with no digital memory available to store the calibration data. As a result, compensation had to be done by a separate microcontroller on the customer’s side, which is now eliminated. Devices specified up to +125°C are available on request.
A fully-integrated continuous self-test architecture improves functional safety. The electromechanical system’s integrity is checked by applying a high-frequency electrostatic force to the sense structure. This simulates a real input rate at a frequency outside the baseband—the self-test processing is thus completely separate from the baseband signal processing.
The quad gyro, which draws 6mA under normal operation, offers a measurement range of ±300°/s at a resolution of 80 LSB/°/s.