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Data Sheet

AD7380-4

Rev. 0 | Page 17 of 31

MODES OF OPERATION

The AD7380-4 has several on-chip configuration registers for

controlling the operational mode of the device.

OVERSAMPLING

Oversampling is a common method used in analog electronics

to improve the accuracy of the ADC result. Multiple samples of

the analog input are captured and averaged to reduce the noise

component from quantization noise and thermal noise (kTC

noise) of the ADC. The AD7380-4 offers an oversampling

function on-chip. The AD7380-4 has two user configurable

oversampling modes: normal averaging and rolling average.

The oversampling functionality is configured by programming

the OS_MODE bit and OSR bits in the Configuration 1

Normal Averaging Oversampling

Normal averaging oversampling mode can be used in

applications where slower output data rates are allowed and

where higher SNR or dynamic range is desirable. Normal

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 cleared when the process completes.

Normal averaging oversampling mode is configured by setting

the OS_MODE bit to Logic 0 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. If required, additional resolution can be

achieved by configuring the resolution boost bit (RES) in the

Configuration 1 register. See the Resolution Boost section for

further details.

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

and added together, and the result is divided by n. The initial

ADC conversion is initiated by the falling edge of CS and the

AD7380-4 controls all subsequent samples in the oversampling

sequence internally. The sampling rate of the additional n

samples at the device maximum sampling rate is 4 MSPS. The

data is ready for readback on the next serial interface access.

After the averaging technique is applied, the sample data used

in the calculation is discarded. This process is repeated every

time the application needs a new conversion result and is

initiated by the next falling edge of CS.

As the output data rate is reduced by the oversampling ratio,

the serial peripheral interface (SPI) frequency required to

transmit the data is reduced accordingly.

Table 11. Normal Averaging Oversampling Overview

SNR (dB Typical)

OSR, Bits[2:0]

OS Ratio

2.5 V External Reference

3.3 V External Reference

Data Output Rate

RES = 0

RES = 1

RES = 0

RES = 1

(kSPS Maximum)

000

No OS

90.8

92.5

4000

001

95.5

1500

010

96.5

95.2

98.2

750

011

95.8

99.2

96.3

100.5

375

100

96.3

100.4

96.8

101.2

187.5

101

101.2

102.2

93.75

110

Invalid

Not applicable

111

Invalid

Not applicable

SDOA

INTERNAL

ACQ

DON’T CARE

t0 RESULT

ACQ

DON’T CARE

CONVERT START AT

t0 RESULT

SDOB

Figure 31. Normal Averaging Oversampling Operation

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