Data Sheet ADIS16060
Rev. A | Page 9 of 12
THEORY OF OPERATION
The ADIS16060 operates on the principle of a resonator
gyroscope. Two polysilicon sensing structures each contain a
dither frame that is electrostatically driven to resonance. This
generates the necessary velocity element to produce a Coriolis
force while rotating. At two of the outer extremes of each frame,
orthogonal to the dither motion, are movable fingers that are
placed between fixed pickoff fingers to form a capacitive pickoff
structure that senses Coriolis motion.
The resulting signal is fed to a series of gain and demodulation
stages that produce the electrical rate signal output. The rate
signal is then converted to a digital representation of the
output on the SPI pins. The dual-sensor design provides
linear acceleration (vibration, shock) rejection. Fabricating
the sensor with the signal-conditioning electronics preserves
signal integrity in noisy environments.
The electrostatic resonator requires 14 V to 16 V for operation.
Because only 5 V is typically available in most applications, a
charge pump is included on chip. After the demodulation stage,
a single-pole, low-pass filter on the chip is used to limit high
frequency artifacts before final amplification. The frequency
response is dominated by the second low-pass filter, which is
set by adding capacitance across RATE and FILT.
ANALOG-TO-DIGITAL CONVERTER INPUT
Figure 12 shows an equivalent circuit of the input structure of
the ADIS16060 auxiliary ADC.
The two diodes, D1 and D2, provide ESD protection for the
analog inputs, AINx (AIN1 and AIN2). Care must be taken to
ensure that the analog input signal does not exceed the supply
rails by more than 0.3 V, because exceeding this level causes
these diodes to become forward-biased and to start conducting
current. However, these diodes can handle a forward-biased
current of 130 mA maximum. For instance, these conditions
may eventually occur when the input signals exceed either
VCC or GND.
Figure 12. Equivalent Analog Input Circuit
During the acquisition phase, the impedance model for AINx
is a parallel combination of the capacitor CPIN and the network
formed by the series connection of RIN and CIN. CPIN is primarily
the pin capacitance. RIN is typically 600 Ω and is a lumped
component made up of some serial resistors and the on
resistance of the switches. CIN is typically 30 pF and mainly
functions as the ADC sampling capacitor.
During the conversion phase, when the switches are open, the
input impedance is limited to CPIN. RIN and CIN make a 1-pole,
low-pass filter that reduces undesirable aliasing effects and
limits the noise.
When the source impedance of the driving circuit is low, the
ADC input can be driven directly. Large source impedances
significantly affect the ac performance, especially THD. The
dc performances are less sensitive to the input impedance.
RATE SENSITIVE AXIS
Figure 13. Rate Signal Increases with Clockwise Rotation
D1
D2
GND
07103-018
AINx
C
PIN
VDD
R
IN
C
IN
145
8
07103-019
POSITIVE
MEASUREMENT
DIRECTION
RATE
AXIS
LONGITUDINAL
AXIS
LATERAL
AXIS