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Data Sheet

AD7383-4/AD7384-4

MODES OF OPERATION

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Rev. 0 | 19 of 33

The AD7383-4/AD7384-4 have several on-chip configuration regis-

ters 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 com-

ponent from quantization noise and thermal noise (kTC noise) of

the ADC. The AD7383-4/AD7384-4 offer an oversampling function

on-chip with 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 CONFIGURATION1 register.

Normal Averaging Oversampling

Normal averaging oversampling mode is used in applications where

slower output data rates are allowed and where a 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 OSR bits (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. If required, additional resolution can be achieved by con-

figuring the resolution boost bit (RES) in the CONFIGURATION1

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

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

conversion is initiated by the falling edge of CS, and the AD7383-4/

AD7384-4 control all subsequent samples in the oversampling

sequence internally. The sampling rate of the additional n samples

at the device maximum sampling rate is 3 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

SPI frequency required to transmit the data is reduced accordingly.

Figure 29. Normal Averaging Oversampling Operation

Table 12. Normal Averaging Oversampling Mode

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 OS

85.03

85.22

87.00

87.04

4000

001

87.95

88.29

89.50

90.01

1500

010

90.45

91.22

91.76

92.83

750

011

92.67

94.00

93.71

95.50

375

100

94.42

94.67

95.12

97.50

187.5

101

95.27

96.74

95.68

98.32

93.75

110

Invalid

Not applicable

111

Invalid

Not applicable

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