ADIS16080

Rev. 0 | Page 11 of 16

THEORY OF OPERATION

The ADIS16080 operates on the principle of a resonator gyro.

Two polysilicon sensing structures each contain a dither frame,

which is electrostatically driven to resonance. This produces the

necessary velocity element to produce a Coriolis force during

angular rate. 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

noise present in the system power supply, the ADIS16080 may not

require any additional decoupling capacitance for this supply.

segmented to allow multiple logic levels to be used in receiving the

power supply and supports standard 3.3 V and 5 V logic families.

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 require-

ments prevent further increase in the linear full-scale output range.

The trade-offs associated with increasing 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.

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

(

)

(

)

μF

0.022

π

2

1/

+

×

×

×

=

OUT

OUT

OUT

C

R

f

during manufacturing to 180 kΩ ± 1%.

Any external resistor applied between the RATE pin and the

FILT pin results in

(

) (

)

EXT

EXT

OUT

R

R

R

+

×

=

kΩ

180

/

kΩ

180

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 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 inputs ST1, 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, power-on self test

can be performed. However, some applications can warrant

continuous self test while sensing rate.

RATE SENSITIVE AXIS

This is a z-axis rate-sensing device that is also called a yaw rate

sensor. It produces a positive going output voltage for clockwise

rotation about the axis normal to the package top, that is,

clockwise when looking down at the package lid.

2.5V

RATE

AXIS

RATE

RATE IN

GND

4.75V

0.25V

LATERAL AXIS

A1

LONGITUDINAL

AXIS

Figure 19. Rate Signal Increases with Clockwise Rotation