ADIS16IMU5SLASHPCBZ datasheet(17/46 Pages) AD

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Data Sheet

ADIS16575/ADIS16576/ADIS16577

THEORY OF OPERATION

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INTRODUCTION

Upon power-up or reset, with all control registers set to their

factory defaults, the IMU automatically starts continuous sampling,

processing, and loading of calibrated sensor data into the output

registers at a rate of 2000 SPS. If the SYNC_4KHZ mode is

enabled (controlled by MSC_CTRL, Bit 11, Table 120), an internal

sampling rate of 4000 SPS is available. During the initial power-on

or after a reset, the IMU performs a series of diagnostic tests,

including sensor-level self tests and cyclic redundancy check (CRC)

computations of the program memory that is loaded from the flash

into random access memory (RAM), ensuring the integrity of the

system before beginning data sampling and processing.

INERTIAL SENSOR SIGNAL CHAIN

Figure 41 shows the basic signal chain for the inertial sensors

in the IMU. When operating in internal clock mode (the factory

default setting, see Register MSC_CTRL, Bits [3:2], Table 120), the

nominal output data rate (ODR) is 2000 SPS.

Figure 41. Signal Processing Diagram, Inertial Sensors

Gyroscope Data Sampling

The three gyroscopes produce angular rate measurements around

three mutually orthogonal axes (x, y, and z). Figure 42 shows

the data sampling plan for each gyroscope when the ADIS16575/

ADIS16576/ADIS16577 operate in internal clock mode (default, see

an analog-to-digital converter (ADC) and sample clock (fSG) that

drives data sampling at a fixed rate, based on the gyroscope reso-

nator (nominally 4 kHz). The ADC output is fed into the cascaded,

integrator-comb (CIC) interpolator, which synchronizes with the IMU

sample clock. The interpolation filter enables all inertial sensor

measurements to be captured synchronously.

Figure 42. Gyroscope Data Sampling

Accelerometer Data Sampling

The three accelerometers produce linear acceleration measure-

ments along the same mutually orthogonal axes (x, y, and z)

as the gyroscopes. Figure 43 shows the data sampling plan for

each accelerometer when the ADIS16575/ADIS16576/ADIS16577

operate in internal clock mode (default, see Register MSC_CTRL,

Bits[3:2] in Table 120). Like the gyroscopes, each accelerometer

is equipped with an ADC and a sample clock that drives data

sampling at a fixed rate. The ADC output is fed into the CIC

interpolator, which synchronizes with the IMU sample clock. The

interpolation filter enables all inertial sensor measurements to be

captured synchronously.

Figure 43. Accelerometer Data Sampling

External Clock Options

The ADIS16575/ADIS16576/ADIS16577 provide three different

modes of operation that support these devices using an external

clock to control the internal processing rate (fSM in Figure 42 and

Figure 43) through the SYNC pin. The MSC_CTRL register (see

Table 120) provides the configuration options for these external

clock modes in Bits[3:2].

Inertial Sensor Calibration

The inertial sensor calibration function for the gyroscopes and the

accelerometers has two components: factory calibration and user

calibration (see Figure 41).

The factory calibration of the gyroscope applies the following cor-

rection formulas to the data of each gyroscope:

ωXCωYCωZC = m11m12m13

m21m22m23

m31m32m33 ×

ωXωYωZ + bXbYbZ

where:

ωXC, ωYC, and ωZC are the gyroscope outputs (post calibration).

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

alignment correction.

ωX, ωY, and ωZ are the gyroscope outputs (precalibration).

bX, bY, and bZ provide bias correction.

All of the correction factors in this relationship come from direct

observation of the response of each gyroscope at multiple tempera-

tures over the calibration temperature range (−40°C ≤ TC ≤ +85°C).

These correction factors are stored in the flash memory bank, but

these factors are not available for observation or configuration. See

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