Product

Overview

Online

Documentation

Design

Resources

Discussion

Sample

& Buy

Data Sheet

ADIS16488A

Rev. C | Page 21 of 35

DIGITAL SIGNAL PROCESSING

GYROSCOPES/ACCELEROMETERS

Figure 20 providesa signal flowdiagramforall of the compo-

nents and settings that influence the frequency responsefor

the accelerometers and gyroscopes. The sampleratefor each

accelerometer and gyroscopeis 9.84 kHz. Each sensor has

its own averaging/decimation filter stage, which reduces the

update rateto 2.46 kSPS. When usingthe external clockoption

(FNCTIO_CTRL[7:4], see Table 118), the input clockdrives a

four-sample burst at a sample rateof 9.84 kSPS, which feeds

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

rate that is equal to the input clockfrequency.

AVERAGING/DECIMATIONFILTER

The DEC_RATEregister (seeTable 56)providesusercontrol for

the final filter stage(seeFigure20), which averagesand decimates

the accelerometers, gyroscopes, delta angle,anddeltavelocity data.

The output samplerateis equal to2460/(DEC_RATE+1).

When using theexternal clockoption(FNCTIO_CTRL[7:4], see

Table 118), replace the 2460number in thisrelationship withthe

input clockfrequency. Forexample, turnto Page3 (DIN= 0x8003),

and set DEC_RATE=0x18 (DIN= 0x8C18, thenDIN= 0x8D00)

to reduce the output sample rateto 98.4 SPS (2460 ÷ 25).

Table 56. DEC_RATE (Page3, 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 (x_MAGN_OUT)updateat a rate of 102.5 SPS

and the barometer output registers (BAROM_xxx)updateat a

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

ometersupdateat a rateof 1/24th of the input clock frequency

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

clock frequency.

The update rates for themagnetometer and barometers do not

change withtheDEC_RATEregister settings.SYS_E_FLAG[9:8]

(see Table 48)offers new data indicator bits thatindicate fresh,

unreaddatais in the x_MAGN_OUT and BAROM_xxx registers.

The SEQ_CNT register provides a counterfunction to help

determine when there is new data in the magnetometer and

barometerregisters.

When SEQ_CNT = 0x0001, there is new data in the magne-

tometer and barometer output registers. During initialization, the

SEQ_CNT register helpsto synchronize read loopsfor new data in

both magnetometerand barometer outputs.When beginning a

continuousreadloop, readSEQ_CNT,then subtract this value

from the maximumvalue shown (range)in Table 57 to predict

the number of internal samplecycles until both magnetometer

and barometerregisterscontain new data samples.

Table 57. SEQ_CNT (Page0, 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

SELECTABLE

FIR FILTER BANK

FILTR_BNK_0

FILTR_BNK_1

AVERAGE/DECIMATION FILTER

D = DEC_RATE[10:0] + 1

1

4

4

÷D

1

D

D

FIR

FILTER

BANK

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.

Figure 20. Sampling and Frequency Response Signal Flow