ADIS16080 Analog Devices, Inc., ADIS16080 Datasheet - Page 11

• Manufacturer Part Number: ADIS16080
• Description: ?80?/sec Yaw Rate Gyroscope With Spi
• Manufacturer: Analog Devices, Inc.

THEORY OF OPERATION
The ADIS16080 operates on the principle of a resonator
gyroscope. Two polysilicon sensing structures each contain a
dither frame that is electrostatically driven to resonance. This
produces 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 rejects external g forces and vibration. 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,
there is a single-pole, low-pass filter included on-chip that is used
to limit high frequency artifacts before final amplification. The
frequency response is dominated by the second low-pass filter,
which is set at 40 Hz. For additional bandwidth reduction
options, see the Setting Bandwidth section.
SUPPLY AND COMMON CONSIDERATIONS
Power supply noise and transient behaviors can influence the
accuracy and stability of any sensor-based measurement system.
When considering the power supply for the ADIS16080, it is
important to understand that the ADIS16080 provides 0.2 μF of
decoupling capacitance on the V
of noise present in the system power supply, the ADIS16080
may not require any additional decoupling capacitance for this
supply. The analog supply, V
V
receiving the digital output data. V
down-stream logic power supply and supports standard 3.3 V
and 5 V logic families. The V
decoupling capacitors.
INCREASING MEASUREMENT RANGE
The full-scale measurement range of the ADIS16080 is increased
by placing an external resistor between the RATE pin and FILT
pin, which results in a parallel connection with the internal
180 kΩ, 1% resistor. For example, a 330 kΩ external resistor
gives ~50% increase in the full-scale range. This is effective for
up to a 4× increase in the full-scale range (minimum value of
the parallel resistor allowed is 45 kΩ). The internal circuitry
headroom requirements prevent further increase in the linear
full-scale output range. The trade-offs associated with increas-
ing the full-scale range are potential increase in output null drift
(as much as 2°/sec over temperature) and introducing initial
null bias errors that must be calibrated.
DRIVE
, are segmented to allow multiple logic levels to be used in
CC
DRIVE
, and the digital drive supply,
CC
supply does not have internal
DRIVE
pin. Depending on the level
is intended for the
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SETTING BANDWIDTH
An external capacitor can be used in combination with an on-
chip resistor to create a low-pass filter to limit the bandwidth of
the ADIS16080 rate response.
The −3 dB frequency is defined as
where:
R
manufacturing to 180 kΩ ± 1%.
C
Any external resistor applied between the RATE pin and the
FILT pin results in
where R
With C
is obtained based upon an internal 0.022 μF capacitor
implemented on-chip.
SELF-TEST FUNCTION
The ADIS16080 includes a self-test feature that actuates each of
the sensing structures and associated electronics in the same
manner as if subjected to an angular rate. It provides a simple
method for exercising the mechanical structure of the sensor,
along with the entire signal processing circuit. It is activated by
standard logic high levels applied to Input ST1, Input ST2, or
both. ST1 causes a change in the digital output equivalent to
typically −540 LSB, and ST2 causes an opposite +540 LSB change.
The self-test response follows the viscosity temperature dependence
of the package atmosphere, approximately 0.25%/°C. Activating
both ST1 and ST2 simultaneously is not damaging. Because ST1
and ST2 are not necessarily closely matched, actuating both
simultaneously can result in an apparent null bias shift.
CONTINUOUS SELF-TEST
As an additional failure detection measure, a power-on self-test
can be performed. However, some applications warrant a
continuous self-test while sensing rate.
RATE SENSITIVE AXIS
OUT
OUT
LONGITUDINAL
is the internal impedance that was trimmed during
is the external capacitance across the RATE and FILT pins.
R
f
OUT
OUT
OUT
EXT
AXIS
Figure 20. Rate Signal Increases with Clockwise Rotation
=
=
= 0 μF, a default −3 dB frequency response of 40 Hz
is the external resistor.
1/
1
(
180
LATERAL
(
2
AXIS
×
RATE
kΩ
AXIS
π
×
×
R
4 5
R
OUT
EXT
8
×
) (
/
(
C
180
OUT
kΩ
+
0.022
RATE OUT
RATE IN
+
R
EXT
μF
)
)
)
ADIS16080
0 LSB
4095 LSB
CLOCK-WISE
ROTATION