ADIS16305

Rev. 0 | Page 13 of 20

CALIBRATION

Manual Bias Calibration

The bias offset registers in Table 16 and Table 17 provide a manual

adjustment function for the output of each sensor. For example,

if GYRO_OFF = 0x1FF6 (DIN = 0x9B1F, 0x9AF6), the GYRO_OUT

offset shifts by −10 LSBs, or −0.125°/sec.

Table 16. GYRO_OFF Bit Descriptions

Bits

Description (Default = 0x0000)

[15:13]

Not used.

[12:0]

Data bits. Twos complement, 0.0125°/sec per LSB.

Typical adjustment range = ±50°/sec.

Table 17. XACCL_OFF, YACCL_OFF, ZACCL_OFF

Bit Descriptions

Bits

Description (Default = 0x0000)

[15:12]

Not used.

[11:0]

Data bits. Twos complement, 0.6 mg/LSB. Typical

adjustment range = ±1.22 g.

Frame Alignment

The PITCH_OFF and ROLL_OFF registers (see Table 18) provide

the angular orientation difference between the inertial frame

(internal) and the external frame (package). They follow the same

orientation as PITCH_OUT and ROLL_OUT, as shown in Figure 14.

Table 18. PITCH_OFF, ROLL_OFF Bit Descriptions

Bits

Description

[15:10]

Not used.

[9:0]

Data bits. Twos complement, 0.014°/LSB.

Gyroscope Automatic Bias Null Calibration

Set GLOB_CMD[0] = 1 (DIN = 0xBE01) to execute the automatic

bias null calibration function. This function measures the

gyroscope output register and then loads the gyroscope offset

register with the opposite value to provide a quick bias calibration.

All sensor data is then reset to 0, and the flash memory is updated

automatically within 50 ms (see Table 19).

Gyroscope Precision Automatic Bias Null Calibration

Set GLOB_CMD[4] = 1 (DIN = 0xBE10) to execute the precision

automatic bias null calibration function. This function takes the

sensor offline for 30 sec while it collects a set of data and calculates

more accurate bias correction factors for each gyroscope. After

this function is executed, the newly calculated correction factor

is loaded into the gyroscope offset registers, all sensor data is

reset to 0, and the flash memory is updated automatically within

50 ms (see Table 19).

Restoring Factory Calibration

Set GLOB_CMD[1] = 1 (DIN = 0xBE02) to execute the factory

calibration restore function. This function resets each user calibration

register to 0x0000 (see Table 16 and Table 17), resets all sensor

data to 0, and automatically updates the flash memory within

50 ms (see Table 19).

Linear Acceleration Bias Compensation (Gyroscope)

Set MSC_CTRL[7] = 1 (DIN = 0xB486) to enable correction for

low frequency acceleration influences on gyroscope bias. Note

that the DIN sequence also preserves the factory default condition

for the data-ready function (see Table 24).

OPERATIONAL CONTROL

Global Commands

The GLOB_CMD register provides trigger bits for several useful

functions. Setting the assigned bit to 1 starts each operation,

which returns the bit to 0 after completion. For example, set

GLOB_CMD[7] = 1 (DIN = 0xBE80) to execute a software reset,

which stops the sensor operation and runs the device through

its start-up sequence. This sequence includes loading the control

registers with their respective flash memory locations prior to

producing new data. Reading the GLOB_CMD register

(DIN = 0x3E00) starts the burst read sequence.

Table 19. GLOB_CMD Bit Descriptions

Bit(s)

Description

[15:8]

Not used

[7]

Software reset command

[6:5]

Not used

[4]

Precision autonull command

[3]

Flash update command

[2]

Auxiliary DAC data latch

[1]

Factory calibration restore command

[0]

Autonull command

Internal Sample Rate

The SMPL_PRD register provides discrete sample rate settings

using the bit assignments in Table 20 and the following equation:

For example, when SMPL_PRD[7:0] = 0x0A, the sample rate is

149 SPS.

Table 20. SMPL_PRD Bit Descriptions

Bit(s)

Description (Default = 0x0001)

[15:8]

Not used

[7]

0 = 0.61035 ms, 1 = 18.921 ms

[6:0]

The default sample rate setting of 819.2 SPS provides optimal

performance. For systems that value slower sample rates, keep the

internal sample rate at 819.2 SPS. Use the programmable filter

(SENS_AVG) to reduce the bandwidth, which helps to prevent

aliasing. The data-ready function (MSC_CTRL) can drive an

interrupt routine that uses a counter to help ensure data coherence

at reduced rates.