ADIS16COM1SLASHPCBZ datasheet(17/37 Pages) AD

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Preliminary Technical Data

ADIS16000/ADIS16229

Rev. PrA | Page 17 of 37

Real-Time Mode

Set REC_CTRL1[1:0] = 11 to place the device into real-time mode.

In this mode, the device samples only one axis, at a rate of

5 kSPS, and provides data on its output register at the SR0

sample rate setting in AVG_CNT[3:0] (see Table 28). Select the

axis of measurement in this mode by reading its assigned register.

For example, select the x-axis by reading X_BUF, using DIN =

0x1400. See Table 59 or Table 60 for more information on the

x_BUF registers. No other ADIS16229 nodes will be able to

communicate with the ADIS16000 when one of them is in real-

time mode.

SPECTRAL RECORD PRODUCTION

The ADIS16229 produces a spectral record by taking a time

record of data on both axes, then scaling, windowing, and

performing an FFT process on each time record. This process

repeats for a programmable number of FFT averages, with the FFT

result of each cycle accumulating in the data buffer. After com-

pleting the selected number of cycles, the FFT averaging process

completes by scaling the data buffer contents. Then the data

buffer contents are available to the SPI and output data registers.

SAMPLE RATE/FILTERING

The sample rate for each axis is 20 kSPS. The internal ADC

samples both axes in a time-interleaving pattern (x1, y1, x2,

y2…) that provides even distribution of data across the data

record. The averaging/decimating filter provides a control for

the final sample rate in the time record. By averaging and

decimating the time domain data, this filter provides the ability

to focus the spectral record on lower bandwidths, which produces

finer frequency resolution in each FFT frequency bin. AVG_CNT

(see Table 28) provides the setting for the four different sample

rate options in REC_CTRL1[11:8] (SRx, see Table 27). All four

options are available when using the manual FFT, automatic

FFT, and manual time capture modes. When more than one

sample rate option is enabled while the device is in one of the

manual modes, the device produces a spectral record for one

SRx at a time, starting with the lowest number. After completing

the spectral record for one SRx option, the device waits for

another start command before producing a spectral record for

the next SRx option that is enabled in REC_CTRL1[11:8]. When

more than one sample rate option is enabled while the device is in

the automatic FFT mode, the device produces a spectral record

for one SRx option, and then waits for the next automatic trigger,

which occurs based on the UPDAT_INT and INT_SCL registers.

See Figure 17 for more details on how multiple SRx options

influence data collection and spectral record production. When

in real-time mode, the output data rate reflects the SR0 setting.

Table 29 provides a list of SRx settings available in the AVG_CNT

bin widths, bandwidth, and estimated total noise. Note that each

SRx setting also has associated range settings in the REC_CTRL2

shown in the FFT_AVG1 and FFT_AVG2 registers (see Table 34

and Table 35, respectively).

Table 28. AVG_CNT

Page 1-6, Low Byte Address = 0x32, Read/Write

Bits

Description (Default = 0x9630)

[15:12]

Sample Rate Option 3, binary (0 to 10),

SR3 option sample rate = 20,000 ÷ 2AVG_CNT[15:12]

[11:8]

Sample Rate Option 2, binary (0 to 10),

SR2 option sample rate = 20,000 ÷ 2AVG_CNT[11:8]

[7:4]

Sample Rate Option 1, binary (0 to 10),

SR1 option sample rate = 20,000 ÷ 2AVG_CNT[7:4]

[3:0]

Sample Rate Option 0, binary (0 to 10),

SR0 option sample rate = 20,000 ÷ 2AVG_CNT[3:0]

Table 29. Sample Rate Settings and Filter Performance

SRx

Option

Sample

Rate, fS

(SPS)

Bin

Width

(Hz)

Bandwidth

(Hz)

Peak Noise

per Bin

(mg)

20,000

39.1

10,000

5.18

10,000

19.5

5,000

3.66

5,000

9.8

2,500

2.59

2,500

4.9

1,250

1.83

1,250

2.4

625

1.29

625

1.2

313

0.91

313

0.6

156

0.65

156

0.3

0.46

0.2

0.32

0.1

0.23

0.0

0.16

Figure 16. Signal Flow Diagram, REC_CTRL1[1:0] = 00 or 01, FFT Analysis Modes

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