ADIS16480

Data Sheet

Rev. 0 | Page 24 of 40

DIGITAL SIGNAL PROCESSING

GYROSCOPES/ACCELEROMETERS

Figure 20 provides a block diagram for all of the components

and settings that influence the frequency response for the

accelerometers and gyroscopes. The sample rate for each

accelerometer and gyroscope is 9.84 kHz. Each sensor has

its own averaging/decimation filter stage, which reduces the

update rate to 2.46 kSPS. When using the external clock option

(FNCTIO_CTRL[7:4], see Table 149), the input clock drives a

4-sample burst at a sample rate of 9.84 kSPS, which feeds into

the 4× averaging/decimation filter. This results in a data rate

that is equal to the input clock frequency. Note that the

sensitivity to coning and sculling depends on the sample

rate. At 2.46 kHz, the sensitivity is very low, but can become

influential at lower sample rates. For best performance when

using an external clock, use the maximum input frequency

of 2.4 kHz.

AVERAGING/DECIMATION FILTER

The DEC_RATE register (see Table 67) provides user control

for the final filter stage (see Figure 20), which averages and

decimates the accelerometers, gyroscopes, delta angle, and delta

velocity data. Note that the orientation outputs do not go through

an averaging stage, prior to decimation. The output sample rate is

equal to 2460/(DEC_RATE + 1). When using the external clock

option (FNCTIO_CTRL[7:4], see Table 149), replace the 2460

number in this relationship, with the input clock frequency. For

example, turn to Page 3 (DIN = 0x8003), and set DEC_RATE =

0x18 (DIN = 0x8C18, then DIN = 0x8D00) to reduce the output

sample rate to 98.4 SPS (2460 ÷ 25).

Table 67. DEC_RATE (Page 3, Base Address = 0x0C)

Bits

Description (Default = 0x0000)

[15:11]

Don’t care

[10:0]

Decimation rate, binary format, maximum = 2047

See Figure 20 for impact on sample rate

MAGNETOMETER/BAROMETER

When using the internal sampling clock, the magnetometer

output registers (xMAGN_OUT) update at a rate of 102.5 SPS

and the barometer output registers (BAROM_xxx) update at a

rate of 51.25 SPS. When using the external clock, the magne-

tometers update at a rate of 1/24th of the input clock frequency

and the barometers update at a rate that is 1/48th of the input

clock frequency. The update rates for the magnetometer and

barometers do not change with the DEC_RATE register

settings. SYS_E_FLAG[9:8] (see Table 59) offer new data bits

for these registers and the SEQ_CNT register provides a counter

function to help determine when there is new data in the

magnetometer and barometer registers. When SEQ_CNT =

0x0001, there is new data in the magnetometer and barometer

output registers. The SEQ_CNT register can be useful during

initialization to help synchronize read loops for new data in

both magnetometer and barometer outputs. When beginning a

continuous read loop, read SEQ_CNT, then subtract this value

from the maximum value shown (range) in Table 68 to calculate

the number of internal sample cycles until both magnetometer

and barometer data is new.

Table 68. SEQ_CNT (Page 0, Base Address = 0x06)

Bits

Description

[15:11]

Don’t care

[6:0]

Binary counter: range = 1 to 48/(DEC_RATE + 1)

MEMS

SENSOR

330Hz

÷4

GYROSCOPE

2-POLE: 404Hz, 757Hz

ACCELEROMETER

1-POLE: 330Hz

4×

AVERAGE

DECIMATION

FILTER

1

4

4

INTERNAL

CLOCK

9.84kHz

DIOx

OPTIONAL INPUT CLOCK

FNCTIO_CTRL[7] = 1

NOTES

1. WHEN FNCTIO_CTRL[7] = 1, EACH CLOCK PULSE ON THE DESIGNATED DIOx LINE (FNCTIO_CTRL[5:4]) STARTS A 4-SAMPLE BURST,

AT A SAMPLE RATE OF 9.84kHz. THESE FOUR SAMPLES FEED INTO THE 4x AVERAGE/DECIMATION FILTER, WHICH PRODUCES A

DATA RATE THAT IS EQUAL TO THE INPUT CLOCK FREQUENCY.

ORIENTATION

÷D

÷D

1

D

D

FIR

EKF

FILTER

BANK

AVERAGE/DECIMATION

FILTER

D = DEC_RATE[10:0] + 1

SELECTABLE

FIR FILTER BANK

FILTR_BNK_0

FILTR_BNK_1

Figure 20. Sampling and Frequency Response Block Diagram