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Data Sheet

AD7383-4/AD7384-4

MODES OF OPERATION

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Rev. 0 | 20 of 33

Rolling Average Oversampling

Rolling average oversampling mode is used in applications where

higher output data rates are required and where a higher SNR

or dynamic range is desirable. Rolling averaging involves taking a

number of samples, adding them together, and dividing the result

by the number of samples taken. This result is then output from

the device. The sample data is not cleared when the process

completes. The rolling oversampling mode uses a first in, first

out (FIFO) buffer of the most recent samples in the averaging

calculation, allowing the ADC throughput rate and output data rate

to stay the same.

Rolling average oversampling mode is configured by setting the

OS_MODE bit to Logic 1 and having a valid nonzero value in the

OSR bits. The oversampling ratio of the digital filter is controlled

using the OSR bits (see Table 13).

Table 13 provides the oversampling bit decoding to select the

different oversample rates. The output result is decimated to 16-bit

resolution for the AD7383-4 and 14-bit for the AD7384-4. Additional

resolution can be achieved by configuring the RES bit in the

CONFIGURATION1 register. See the Resolution Boost section for

further details.

In rolling average oversampling mode, all ADC conversions are

controlled and initiated by the falling edge of CS. When a conver-

sion is complete, the result is loaded into the FIFO. The FIFO

length is 8, regardless of the oversampling ratio set. The FIFO

is filled on the first conversion after a power-on reset on the first

conversion after a software controlled hard or soft reset. A new

conversion result is shifted into the FIFO on completion of every

ADC conversion regardless of the status of the OSR bits and the

OS_MODE bit. This conversion allows a seamless transition from

no oversampling to rolling average oversampling, or different rolling

average oversampling ratios without waiting for the FIFO to fill.

The number of samples, n, defined by the OSR bits are taken from

the FIFO, added together and the result is divided by n.

Table 13. Rolling Average Oversampling Overview

OSR, Bits[2:0]

Oversampling Ratio

AD7383-4 SNR (dB Typical)

Data Output Rate (kSPS Maximum)

2.5 V Reference

3.3 V Reference

RES = 0

RES = 1

RES = 0

RES = 1

000

No oversampling

85.14

85.21

87.02

87.03

4000

001

87.05

87.42

88.55

89.02

4000

010

89.76

90.27

91.00

91.85

4000

011

92.22

93.25

93.23

94.78

4000

110

Invalid

Not applicable

111

Invalid

Not applicable

Figure 30. Rolling Average Oversampling Mode Configuration

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