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s
N
+
1
N
ȍ
N
i
+
1
(x
i
*
x)
2
Ǹ
E +
NJ
24
*
log
2
s
N
: s
N
0
0
24 : s
N
0
0
Analysis Mode
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V
REF
is adjustable from Configuration mode. By default, it is 5V.
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 < 1 μ V n
Microvolts < 1mV u
Millivolts < 1V m
Volts ≥ 1V V
RMS noise: In this mode, a number of codes are read from the ADS1232, and an RMS noise calculation
is performed on them, using the standard-deviation formula in
Equation 4 :
(4)
The result can be displayed as decimal codes, volts, or effective bits (ENOB). For decimal codes, s
N
is
displayed directly. (Hexadecimal is not available since s
N
is generally fractional.) For volts, s
N
is converted
to a voltage as in raw mode.
ENOB: E is calculated using Equation 5 :
(5)
The zero case is needed when a string of equal codes is read. This event can happen when the converter
is clipping.
This measurement requires a number of codes to be read before a calculation can be made. Therefore,
during the first run, the display shows the word
GOT
followed by the number of samples collected. This
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.
The number of codes used in the calculation is selectable in Configuration mode.
Averaged: In this mode, a number of codes are collected, and the average is calculated. The result can
be displayed in decimal codes or volts. (Hexadecimal is not available because the result may be
fractional.) Volts are calculated as in raw mode.
The number of codes used in the calculation is selectable in Configuration mode.
3.3 Progress Graph
The row of apostrophes at the top of the display are used to indicate measurement progress. In Raw
mode, the apostrophe moves across the display when data is being received from the converter. The
apostrophe moves once for every eight samples collected from the ADC.
In block collection modes, the apostrophes form a bar graph. As the collection of a block proceeds, the
bar graph increases. When the bar graph reaches all the way to the right, the new result is generated and
collection restarts.
12 ADS1232REF User ' s Guide SBAU120B – November 2005 – Revised July 2011
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