For example, when the converter is configured with a
2.5V reference and placed in a gain setting of 2, the
typical input voltage range is 1.25V to 3.75V (common-
mode voltage = 2.5V). However, an input range of 0V to
2.5V (common-mode voltage = 1.25V) or 2.5V to 5V
(common-mode voltage = 3.75V) would also cover the
converter’s full-scale range.
DATA
RATE FREQUENCY
(HZ)
-3DB
EFFECTIVE RESOLUTION (BITS RMS)
(HZ)
G = 1
G = 2
G = 4
G = 8
G = 16
10
25
30
50
60
2.62
6.55
7.86
13.1
15.7
26.2
65.5
20
19
19
17
17
15
12
20
19
19
17
17
15
12
20
19
18
17
17
15
12
19
18
18
17
16
15
12
18
18
17
16
16
15
12
100
250
Voltage Span—This is simply the magnitude of the typical
analog input voltage range. For example, when the converter
is configured with a 2.5V reference and placed in a gain
setting of 2, the input voltage span is 2.5V.
TABLE III. Effective Resolution vs Data Rate and Gain
Setting. (Turbo Mode Rate of 1 and a 1MHz
clock.)
Least Significant Bit (LSB) Weight—This is the theoreti-
cal amount of voltage that the differential voltage at the
analog input would have to change in order to observe a
change in the output data of one least significant bit. It is
computed as follows:
DEFINITION OF TERMS
An attempt has been made to be consistent with the termi-
nology used in this data sheet. In that regard, the definition
of each term is given as follows:
Full−Scale Range
LSB Weight =
Analog Input Differential Voltage—For an analog signal
that is fully differential, the voltage range can be compared
to that of an instrumentation amplifier. For example, if both
analog inputs of the ADS1212 are at 2.5V, then the differ-
ential voltage is 0V. If one is at 0V and the other at 5V, then
the differential voltage magnitude is 5V. But, this is the case
regardless of which input is at 0V and which is at 5V, while
the digital output result is quite different.
2N
where N is the number of bits in the digital output.
Effective Resolution—The effective resolution of the
ADS1212/13 in a particular configuration can be expressed
in two different units: bits rms (referenced to output) and
microvolts rms (referenced to input). Computed directly
from the converter’s output data, each is a statistical calcu-
lation based on a given number of results. Knowing one, the
other can be computed as follows:
The analog input differential voltage is given by the follow-
ing equation: AINP – AINN. Thus, a positive digital output is
produced whenever the analog input differential voltage is
positive, while a negative digital output is produced when-
ever the differential is negative.
10V
PGA
ER in Vrms
20 • log
− 1.76
For example, when the converter is configured with a 2.5V
reference and placed in a gain setting of 2, the positive full-
scale output is produced when the analog input differential
is 2.5V. The negative full-scale output is produced when the
differential is –2.5V. In each case, the actual input voltages
must remain within the AGND to AVDD range (see Table I).
ER in bits rms =
6.02
10V
PGA
ER in Vrms =
6.02 • ER in bits rms + 1.76
Actual Analog Input Voltage—The voltage at any one
analog input relative to AGND.
20
10
Full-Scale Range (FSR)—As with most A/D converters,
the full-scale range of the ADS1212/13 is defined as the
“input” which produces the positive full-scale digital output
minus the “input” which produces the negative full-scale
digital output.
The 10V figure in each calculation represents the full-scale
range of the ADS1212/13 in a gain setting of 1. This means
that both units are absolute expressions of resolution—the
performance in different configurations can be directly com-
pared regardless of the units. Comparing the resolution of
different gain settings expressed in bits rms requires ac-
counting for the PGA setting.
For example, when the converter is configured with a 2.5V
reference and is placed in a gain setting of 2, the full-scale
range is: [2.5V (positive full scale) minus –2.5V (negative
full scale)] = 5V.
Main Controller—A generic term for the external micro-
controller, microprocessor, or digital signal processor which
is controlling the operation of the ADS1212/13 and receiv-
ing the output data.
Typical Analog Input Voltage Range—This term de-
scribes the actual voltage range of the analog inputs which
will cover the converter’s full-scale range, assuming that
each input has a common-mode voltage that is greater than
REFIN/PGA and smaller than (AVDD – REFIN/PGA).
ADS1212, 1213
10
SBAS064A
BB [ BURR-BROWN CORPORATION ]
