ADAQ7980 datasheet(32/45 Pages) AD

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Data Sheet

ADAQ4381-4

ADC MODES OF OPERATION

analog.com

Rev. 0 | 32 of 45

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 required. 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, which allows 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 11).

Table 11 provides the oversampling bit decoding to select the

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

resolution for the ADAQ4381-4. If additional resolution is required,

then this can be achieved by configuring the resolution boost bit in

the Configuration1 Register. For more details, see the Resolution

Boost section.

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 (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 11. Rolling Average Oversampling Overview, G = 1

OSR [2:0]

OS Ratio

SNR (dB typical)

Data Output Rate (kSPS max)

RES = 0

RES = 1

000

No OS

85.0

4000

001

85.0

87.1

4000

010

85.1

90.0

4000

011

85.4

92.4

4000

110

Invalid

N/A1

111

Invalid

N/A1

1 N/A means not applicable.

Figure 67. Rolling Average Oversampling Mode Operation

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