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ADIS16362

Rev. 0 | Page 13 of 20

Internal Sample Rate

The SMPL_PRD register provides discrete sample rate settings

using the bit assignments in Table 18 and the following equation:

tS = tB × (NS + 1)

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

149 SPS.

Table 18. SMPL_PRD Bit Descriptions

Bit

Description (Default = 0x0001)

[15:8]

Not used

[7]

Time base (tB)

0 = 0.61035 ms, 1 = 18.921 ms

[6:0]

Increment setting (NS)

Internal sample period = tS = tB × (NS + 1)

The default sample rate setting of 819.2 SPS preserves the sensor

bandwidth and 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 the reduced rates.

Power Management

Setting SMPL_PRD ≥ 0x0A also sets the sensor to low power

mode. For systems that require lower power dissipation, in-

system characterization helps users to quantify the associated

performance trade-offs. In addition to sensor performance, this

mode affects SPI data rates (see Table 2). Set SLP_CNT[8] = 1

(DIN = 0xBB01) to start the indefinite sleep mode, which

requires a CS assertion (high to low), reset, or power cycle to

wake up. Use SLP_CNT[7:0] to put the device into sleep mode

for a specified period. For example, SLP_CNT[7:0] = 0x64

(DIN = 0xBA64) puts the ADIS16362 to sleep for 50 sec.

Table 19. SLP_CNT Bit Descriptions

Bit

Description

[15:9]

Not used

[8]

Indefinite sleep mode; set to 1

[7:0]

Programmable sleep time bits, 0.5 sec/LSB

Digital Filtering

A programmable low-pass filter can provide additional noise

reduction on the inertial sensor outputs. This filter contains two

cascaded averaging filters that provide a Bartlett window, FIR filter

response (see Figure 14). For example, set SENS_AVG[2:0] = 100

(DIN = 0xB804) to set each stage to 16 taps. When used with the

default sample rate of 819.2 SPS, this value reduces the sensor

bandwidth to approximately 16 Hz.

–20

–40

–60

–80

–100

–120

–140

0.001

0.01

0.1

FREQUENCY (Ratio)

N = 2

N = 4

N = 16

N = 64

Figure 14. Bartlett Window, FIR Filter Frequency Response

(Phase Delay = N Samples)

Dynamic Range

The SENS_AVG[10:8] bits provide three dynamic range settings

for this gyroscope. The lower dynamic range settings (±75°/sec

and ±150°/sec) limit the minimum filter tap sizes to maintain

resolution. For example, set SENS_AVG[10:8] = 010 (DIN =

0xB902) for a measurement range of ±150°/sec. Because this

setting can influence the filter settings, program SENS_AVG[10:8]

and then SENS_AVG[2:0] if more filtering is required.

Table 20. SENS_AVG Bit Descriptions

Bit

Description

[15:11]

Not used

[10:8]

Measurement range (sensitivity) selection

100 = ±300°/sec (default condition)

010 = ±150°/sec, filter taps ≥ 4 (Bits[2:0] ≥ 0x02)

001 = ±75°/sec, filter taps ≥ 16 (Bits[2:0] ≥ 0x04)

[7:3]

Not used

[2:0]

Number of taps in each stage, N = 2M

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