THEORY OF OPERATION
The ADS1210 and ADS1211 are precision, high dynamic
range, self-calibrating, 24-bit, delta-sigma A/D converters
capable of achieving very high resolution digital results.
Each contains a programmable gain amplifier (PGA); a
second-order delta-sigma modulator; a programmable digi-
tal filter; a microcontroller including the Instruction, Com-
mand and Calibration registers; a serial interface; a clock
generator circuit; and an internal 2.5V reference. The
ADS1211 includes a 4-channel input multiplexer.
In order to provide low system noise, common-mode rejec-
tion of 115dB and excellent power supply rejection, the
design topology is based on a fully differential switched
capacitor architecture. Turbo Mode, a unique feature of the
ADS1210/11, can be used to boost the sampling rate of the
input capacitor, which is normally 19.5kHz with a 10MHz
clock. By programming the Command Register, the sam-
pling rate can be increased to 39kHz, 78kHz, 156kHz, or
312kHz. Each increase in sample rate results in an increase
in performance when maintaining the same output data rate.
The programmable gain amplifier (PGA) of the ADS1210/
11 can be set to a gain of 1, 2, 4, 8 or 16—substantially
increasing the dynamic range of the converter and simplify-
ing the interface to the more common transducers (see Table
I). This gain is implemented by increasing the number of
samples taken by the input capacitor from 19.5kHz for a
gain of 1 to 312kHz for a gain of 16. Since the Turbo Mode
and PGA functions are both implemented by varying the
sampling frequency of the input capacitor, the combination
of PGA gain and Turbo Mode Rate is limited to 16 (see
Table II). For example, when using a Turbo Mode Rate of
8 (156kHz at 10MHz), the maximum PGA gain setting is 2.
ANALOG
INPUT
(1)
FULL-
SCALE
RANGE
(V)
10
5
2.5
1.25
0.625
EXAMPLE
VOLTAGE
RANGE
(3)
(V)
0
1.25
1.88
2.19
2.34
to
to
to
to
to
5
3.75
3.13
2.81
2.66
ANALOG INPUT
UTILIZING V
BIAS(1,2)
FULL-
SCALE
RANGE
(V)
40
20
10
5
2.5
EXAMPLE
VOLTAGE
RANGE
(3)
(V)
±10
±5
±2.5
±1.25
±0.625
The output data rate of the ADS1210/11 can be varied from
a few hertz to as much as 15,625kHz, trading off lower
resolution results for higher data rates. In addition, the data
rate determines the first null of the digital filter and sets the
–3dB point of the input bandwidth (see the Digital Filter
section). Changing the data rate of the ADS1210/11 does not
result in a change in the sampling rate of the input capacitor.
The data rate effectively sets the number of samples which
are used by the digital filter to obtain each conversion result.
A lower data rate results in higher resolution, lower input
bandwidth, and different notch frequencies than a higher
data rate. It does not result in any change in input impedance
or modulator frequency, or any appreciable change in power
consumption.
The ADS1210/11 also includes complete on-board calibra-
tion that can correct for internal offset and gain errors or
limited external system errors. Internal calibration can be
run when needed, or automatically and continuously in the
background. System calibration can be run as needed and the
appropriate input voltages must be provided to the ADS1210/
11. For this reason, there is no continuous System Calibra-
tion Mode. The calibration registers are fully readable and
writable. This feature allows for switching between various
configurations—different data rates, Turbo Mode Rates, and
gain settings—without re-calibrating.
The various settings, rates, modes, and registers of the
ADS1210/11 are read or written via a synchronous serial
interface. This interface can operate in either a self-clocked
mode (Master Mode) or an externally clocked mode (Slave
Mode). In the Master Mode, the serial clock (SCLK) fre-
quency is one-half of the ADS1210/11 X
IN
clock frequency.
This is an important consideration for many systems and
may determine the maximum ADS1210/11 clock that can be
used.
The high resolution and flexibility of the ADS1210/11 allow
these converters to fill a wide variety of A/D conversion
tasks. In order to ensure that a particular configuration will
meet the design goals, there are several important items
which must be considered. These include (but are certainly
not limited to) the needed resolution, required linearity,
desired input bandwidth, power consumption goal, and sen-
sor output voltage.
The remainder of this data sheet discusses the operation of
the ADS1210/11 in detail. In order to allow for easier
comparison of different configurations, “effective resolu-
tion” is used as the figure of merit for most tables and
graphs. For example, Table III shows a comparison between
data rate (and –3dB input bandwidth) versus PGA setting at
a Turbo Mode Rate of 1 and a clock rate of 10MHz. See the
Definition of Terms section for a definition of effective
resolution.
GAIN
SETTING
1
2
4
8
16
NOTE: (1) With a 2.5V reference, such as the internal reference. (2) This
example utilizes the circuit in Figure 12. Other input ranges are possible. (3)
The ADS1210/11 allows common-mode voltage as long as the absolute
input voltage on A
IN
P or A
IN
N does not go below AGND or above AV
DD
.
TABLE I. Full-Scale Range vs PGA Setting.
TURBO MODE RATE
1
2
4
8
16
AVAILABLE PGA SETTINGS
1, 2, 4, 8, 16
1, 2, 4, 8
1, 2, 4
1, 2
1
TABLE II. Available PGA Settings vs Turbo Mode Rate.
®
9
ADS1210, 1211
BURR-BROWN [ BURR-BROWN CORPORATION ]
