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8.3 Micromachined Gyroscopes 205
Voltage
multiplier
Velocity amp
Trim
and
test
Rate
Drivers sensor
Regulators
Coriolis
amp
Output
Demodulator Bias
References
Temperature
(a)
Inner frame
Resonating mass
Mass drive direction
Springs
Coriolis sense fingers
(b)
Figure 8.29 (a) Die photo of the surface-micromachined gyroscope from Analog Devices with
the interface and control electronics integrated on the same chip. It contains two identical
mechanical structures to achieve differential sensing. (b) Schematic drawing of one of the two
identical gyroscope elements. (Courtesy Analog Devices, Inc. Picture taken from ADI Web site,
http://www.analog.com.)
to +85°C and is available in a space-saving 32-pin Ball Grid Array surface-mount
package measuring 7 × 7 × 3 mm. Both are priced at approximately $30 per unit in
thousand-piece quantities. Because the internal resonators require 14V to 16V for
proper operation, ADI includes on-chip charge pumps to boost an applied TTL-
level voltage. Both the ADXRS150 and ADXRS300 are essentially z-axis gyro-
scopes based on the principle of resonant-tuning-fork gyroscopes. In these systems,
two polysilicon sensing structures each contain a so-called dither frame that is
driven electrostatically to resonance. Interestingly, the gyroscope includes two iden-
tical structures to enable differential sensing in order to reject environmental shock
and vibration. Figure 8.29(b) shows one structure schematically.
A rotation about the z-axis, normal to the plane of the chip, produces a Coriolis
force that displaces the inner frame perpendicular to the vibratory motion. This
Coriolis motion is detected by a series of capacitive pick-off structures on the edges