ADIS16480SLASHPCBZ datasheet(27/40 Pages) AD

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Data Sheet

ADIS16480

Rev. 0 | Page 27 of 40

EXTENDED KALMAN FILTER

ALGORITHM

The extended Kalman filter (EKF) continuously estimates the

state vector, which includes the four elements in a quaternion

orientation array and the bias levels for all three gyroscopes.

Figure 22 illustrates the iterative process used in the EKF, which

uses angular rate measurements (gyroscopes) to predict orienta-

tion updates and then makes corrections using accelerometer

and magnetometer measurements. In addition to continuous

state estimation, the EKF also estimates the error covariance

terms. Using the covariance terms, current orientation, and

gyroscope sensor measurements, the algorithm computes a

Kalman gain that provides a weighting value for each sensor’s

contribution to the state vector. The ADIS16480 has factory

settings for the covariance terms but provides access to them in

the form of user-configuration registers, for fine tuning, based

on application-specific conditions/requirements.

COVARIANCE TERMS

Table 76 through Table 79 provides register information for the

gyroscope noise/RRW process covariance (Q) terms. Table 80

through Table 83 provides register information for the

accelerometer/magnetometer measurement covariance (R)

terms. These covariance terms use the IEEE 32-bit floating-

point format. Each term has two registers, one for the upper

word and one for the lower word.

Table 76. QCVR_NOIS_UPR (Page 3, Base Address = 0x62)

Bits

Description (Default = 0x3727)

[15:0]

Gyroscope noise covariance term, upper word

Table 77. QCVR_NOIS_LWR (Page 3, Base Address = 0x60)

Bits

Description (Default = 0xC5AC)

[15:0]

Gyroscope noise covariance term, lower word

Table 78. QCVR_RRW_UPR (Page 3, Base Address = 0x66)

Bits

Description (Default = 0x2E5B)

[15:0]

Gyroscope rate random walk (RRW) covariance term,

upper word

Table 79. QCVR_RRW_LWR (Page 3, Base Address = 0x64)

Bits

Description (Default = 0xE6FF)

[15:0]

Gyroscope rate random walk (RRW) covariance term,

lower word

Table 80. RCVR_ACC_UPR (Page 3, Base Address = 0x6E)

Bits

Description (Default = 0x3189)

[15:0]

Accelerometer measurement variance term, upper word

Table 81. RCVR_ACC_LWR (Page 3, Base Address = 0x6C)

Bits

Description (Default = 0x705F)

[15:0]

Accelerometer measurement variance term, lower word

Table 82. RCVR_MAG_UPR (Page 3, Base Address = 0x72)

Bits

Description (Default = 0x32AB)

[15:0]

Magnetometer measurement variance term, upper word

Table 83. RCVR_MAG_LWR (Page 3, Base Address = 0x70)

Bits

Description (Default = 0xCC77)

[15:0]

Magnetometer measurement variance term, lower word

CORRECT

PREDICT

GYROSCOPE

Q COVARIANCE

ACCELEROMETERS

MAGNETOMETERS

R COVARIANCE

QUATERNION, BIAS

ERROR COVARIANCE

QUATERNION, BIAS

ERROR COVARIANCE

QUATERNION

EKF PROCESS

Figure 22. EKF Process

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