ADIS16490BMLZ datasheet(13/38 Pages) AD

13 / 38 page

ADIS16490

Data Sheet

Rev. 0 | Page 12 of 37

THEORY OF OPERATION

The ADIS16490 is an autonomous sensor system that starts up

on its own when it has a valid power supply. After running through

its initialization process, it begins sampling, processing, and

loading calibrated sensor data into the output registers, which

are accessible using the SPI port.

INERTIAL SENSOR SIGNAL CHAIN

Figure 22 provides the basic signal chain for the inertial sensors

in the ADIS16490, which processes data at a rate of 4250 SPS

when using the internal sample clock. Using one of the external

clock options in FNCTIO_CTRL[7:4] (see Table 131) can

provide some flexibility in selecting this rate.

MEMS

SENSORS

CALIBRATION

FILTERING

OUTPUT

DATA

REGISTERS

Figure 22. Signal Processing Diagram, Inertial Sensors

Gyroscope Data Sampling

The ADIS16490 produces angular rate measurements around

three orthogonal axes (x, y, and z). Figure 23 shows the basic

signal flow for the production of x-axis gyroscope data (same as

y-axis and z-axis). This signal chain contains two digital MEMS

gyroscopes (XG1 and XG2), which have their own ADC and sample

clocks (fSGX1 and fSGX2 = 4100 Hz that produce data independently

from each other. The sensor to sensor tolerance on this sample rate

is ±200 SPS. Processing this data starts with combining (summa-

tion and rescale) the most recent sample from each gyroscope

together by using an independent sample master frequency (fSM)

clock (fSM = 4250 Hz, see Figure 23), which drives the rest of the

digital signal processing (calibration, alignment, and filtering)

for the gyroscopes and accelerometers.

MEMS

GYROSCOPE

XG1

MEMS

GYROSCOPE

XG2

X-AXIS

RATE DATA

SAMPLE 1

X-AXIS

ANGULAR RATE

DATA PROCESSING

fSM = 4250Hz

X-AXIS

RATE DATA

SAMPLE 2

fSGX2 = 4100Hz

fSGX1 = 4100Hz

ADC

Figure 23. Gyroscope Data Sampling

Accelerometer Data Sampling

The ADIS16490 produces linear acceleration measurements

along the same orthogonal axes (x, y, and z) as the gyroscopes,

using the same clock (fSM, see Figure 23 and Figure 24) that

triggers data acquisition and subsequent processing of the

gyroscope data.

ACCELEROMETER

X-AXIS

MEMS

X-AXIS

ACCELERATION

DATA PROCESSING

fSM = 4250SPS

ADC

Figure 24. Accelerometer Data Sampling

External Clock Options

The ADIS16490 offers two modes of operation to control data

production with an external clock: sync mode and pulse per

second (PPS) mode. In sync mode, the external clock directly

controls the data sampling and production clock (fSM in Figure 23

and Figure 24). In PPS mode, users can provide a lower input

clock rate (1 Hz to 128 Hz) and use a scale factor (SYNC_SCALE

processing rate that is between 3000 Hz and 4250 Hz for best

performance.

Inertial Sensor Calibration

The calibration function for the gyroscopes and the

accelerometers has two components: factory calibration and

user calibration (see Figure 25).

FROM

SENSORS

FILTERING

FACTORY

CALIBRATION

USER

CALIBRATION

Figure 25. Gyroscope Calibration Processing

Gyroscope Factory Calibration

Gyroscope factory calibration applies the following correction

formula to the data of each gyroscope:



















































































(1)

where:

ωXC, ωYC, and ωZC are the postcalibration gyroscope data.

m11, m12, m13, m21, m22, m23, m31, m32, and m33 are the scale and

alignment correction factors.

ωX, ωY, and ωZ are the precalibration gyroscope data.

bX, bY, and bZ are the bias correction factors.

g11, g12, g13, g21, g22, g23, g31, g32, and g33 are the linear g correction

factors.

a'X, a'Y, and a'Z are the postcalibration accelerometer data.

All the correction factors in each matrix/array are derived from

direct observation of the response of each gyroscope to a variety

of rotation rates at multiple temperatures across the calibration

temperature range (−40°C ≤ TC ≤ +85°C). These correction

factors are stored in the flash memory bank, but they are not

available for observation. CONFIG[7] provides an on/off control

for the linear g compensation (see Table 135). See Figure 43 for

more details on the user calibration options that are available

for the gyroscopes.

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