v =

B

1

-

x

A

·

s =

N

(x

)

-

i

x

2

N

i =1

1

N

å

E =

N

log s :

-

2 N

0

s

24 : s

0

Analysis Mode

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3.2

Measurement Modes

Raw: In this measurement, codes are read from the installed ADS device and displayed. No processing or

analysis is done on the sample stream. Data can be displayed as hexadecimal codes, decimal codes, or

volts.

Voltage is calculated according to Equation 3:

Where:

•

A is the converter gain (64 for the ADS1131 and 128 for the ADS1231)

•

v

•

x is the ADC decimal code

•

B is the number of converter bits, 2

(3)

v

The voltage display is autoranging. All ranges are shown with six significant figures having three decimal

places. The ranges are given in Table 4.

Table 4. Voltage Display Ranges

VOLTAGE RANGE

DISPLAY SUFFIX

Nanovolts

< 1μV

n

Microvolts

< 1mV

u

Millivolts

< 1V

m

Volts

≥ 1V

V

RMS noise: In this mode, a number of codes are read from the installed ADS device, and an RMS noise

calculation is performed on them using the standard-deviation formula (given in Equation 4):

(4)

The result can be displayed as decimal codes, volts, or an effective number of bits (ENOB). For decimal

codes, s

is converted to a voltage as in raw mode.

ENOB: E is calculated using Equation 5:

(5)

Where N is the maximum number of available bits (18 for the ADS1131 and 24 for the ADS1231).

The zero case is needed when a string of equal codes is read. This can happen when the converter is

clipping.

This measurement requires a number of codes to be read before a calculation can be made. Therefore,

event happens when the mode is first entered, when the converter configuration changes, or when NEW

BLOCK is pressed.

The number of codes used in the calculation is selected in Configuration mode; 50 codes are used in

laboratory characterization, so this value is the default.

Peak-to-peak noise: In this mode, a number of codes are collected, and the absolute value of the

difference between the minimum and maximum is calculated. The result can be displayed in decimal or

hexadecimal codes, volts, or noise-free bits (ENOB). Volts are calculated as in raw mode; ENOB is

calculated in the same way as in RMS mode.

12

ADS1131REF and ADS1231REF

SBAU175A

– July 2010 – Revised August 2011

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