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AD7380-4

Data Sheet

Rev. 0 | Page 18 of 31

Rolling Average Oversampling

Rolling average oversampling mode can be 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 oversampling bits, OSR (see Table 12).

Table 12 provides the oversampling bit decoding to select the

different oversample rates. The output result is decimated to

16-bit resolution for the AD7380-4. If required, additional

resolution can be achieved by configuring the resolution boost

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

conversion 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

(POR), 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 12. Rolling Average Oversampling Overview

SNR (dB Typical)

Data Output Rate

(kSPS Maximum)

OSR, Bits[2:0]

OS Ratio

2.5 V External Reference

3.3 V External Reference

RES = 0

RES = 1

RES = 0

RES = 1

000

No oversampling

92.5

4000

001

4000

010

95.4

4000

011

95.5

4000

110

Invalid

Not applicable

111

Invalid

Not applicable

INTERNAL

VCC

SDI

SDOA

ACQ

ENABLE OS = 2

ENABLE OS = 4

DON’T CARE

ACQ

...

FIFO

(FIFO1 + FIFO2 +

FIFO3 + FIFO4)/4

(FIFO1 +

FIFO2)/2

(FIFO1 +

FIFO2)/2

(FIFO1 +

FIFO2)/2

tCYC

SDOB

Figure 32. Rolling Average Oversampling Mode Configuration

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