ADS1210/11高精度24位模拟数字转换器详解及应用

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ADS1210和ADS1211是一款高性能的24位模拟到数字转换器（ADC），专为伺服控制器和其他需要精确信号处理的应用设计。这些器件的特点包括： 1. **高分辨率**：作为delta-sigma A/D转换器，ADS1210和ADS1211提供卓越的24位分辨率，确保了极高的数据精度。在低频下（10Hz），它们能够实现23位的有效分辨率，而在1kHz时仍能保持20位。 2. **宽动态范围**：由于采用了delta-sigma架构，这两款芯片能处理非常宽广的电压输入范围，保证了信号不失真，即使在极端条件下也能提供稳定的性能。 3. **灵活接口**：ADS1210采用灵活的SPI兼容SSl接口，支持2-wire模式，简化了系统集成，降低了布线复杂性。 4. **可编程增益放大器**：内置可编程增益放大器允许用户根据应用需求调整输入信号的放大倍数，增强了信号的处理能力。 5. **高切-off频率**：15.6kHz的可编程截止频率使得这些设备适用于高频信号处理，减少了滤波器的需求。 6. **内部/外部参考**：支持内部或外部参考电压，增加了设计灵活性，用户可以根据需要选择更稳定的基准源。 7. **自校准功能**：ADS1211内含4通道多路复用器，提供更高的并行性，同时具备on-chip自校准功能，确保长期稳定性和准确性。 8. **Turbomodule模式**：独特的Turbomodule模式在1kHz采样率下保持20位有效分辨率，这是一种高效的数据处理技术，提高了转换效率。 9. **低噪声输入放大器**：在10Hz以下的转换速率，低噪声输入放大器确保了极高的信噪比，这对于需要极高精度的测量应用至关重要。总结来说，ADS1210和ADS1211是理想的解决方案，适合需要高精度、宽动态范围和灵活接口的工业控制应用，如伺服驱动、传感器数据采集等。其高性能和易用性使其成为众多工程师首选的A/D转换器。

ADS1210, ADS1211

SBAS034B

www.ti.com

ANALOG ANALOG INPUT

INPUT

(1)

UTILIZING V

BIAS

(1,2)

FULL- EXAMPLE FULL- EXAMPLE

SCALE VOLTAGE SCALE VOLTAGE

GAIN RANGE RANGE

(3)

RANGE RANGE

(3)

SETTING (V) (V) (V) (V)

1 10 0 to 5 40 ±10

2 5 1.25 to 3.75 20 ±5

4 2.5 1.88 to 3.13 10 ±2.5

8 1.25 2.19 to 2.81 5 ±1.25

16 0.625 2.34 to 2.66 2.5 ±0.625

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

P or A

N does not go below AGND or above AV

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.

TABLE I. Full-Scale Range vs PGA Setting.

TURBO MODE RATE AVAILABLE PGA SETTINGS

1 1, 2, 4, 8, 16

2 1, 2, 4, 8

4 1, 2, 4

8 1, 2

16 1

TABLE II. Available PGA Settings vs Turbo Mode Rate.

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

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.

ADS1210, ADS1211

SBAS034B

www.ti.com

DATA -3DB

RATE FREQUENCY

(HZ) (HZ) G = 1 G = 2 G = 4 G = 8 G = 16

10 2.62 21.5 21.0 21.0 21.0 20.0

25 6.55 20.5 20.5 20.5 20.0 19.5

30 7.86 20.5 20.5 20.5 20.0 19.5

50 13.1 20.0 20.0 20.0 19.5 19.0

60 15.7 19.5 19.5 19.5 19.0 19.0

100 26.2 18.0 18.0 18.0 18.0 18.0

250 65.5 15.0 15.0 15.0 15.0 15.0

500 131 12.5 12.5 12.5 12.5 12.5

1000 262 10.0 10.5 10.0 10.0 10.0

EFFECTIVE RESOLUTION (BITS RMS)

TABLE III. Effective Resolution vs Data Rate and Gain

Setting. (Turbo Mode Rate of 1 and a 10MHz

clock.)

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:

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 ADS1210 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.

The analog input differential voltage is given by the follow-

ing equation: A

P – A

N. 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.

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 AV

range (see Table I).

Actual Analog Input Voltage—The voltage at any one

analog input relative to AGND.

Full-Scale Range (FSR)—As with most A/D converters,

the full-scale range of the ADS1210/11 is defined as the

“input” which produces the positive full-scale digital output

minus the “input” which produces the negative full-scale

digital output.

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.

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

REF

/PGA and smaller than (AV

– REF

/PGA).

LSB Weight =

Full−Scale Range

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. However, an input range of

0V to 2.5V or 2.5V to 5V would also cover the converter’s

full-scale range.

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.

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:

where N is the number of bits in the digital output.

Effective Resolution—The effective resolution of the

ADS1210/11 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 10V figure in each calculation represents the full-scale

range of the ADS1210/11 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.

Main Controller—A generic term for the external

microcontroller, microprocessor, or digital signal processor

which is controlling the operation of the ADS1210/11 and

receiving the output data.

ER in bits rms =

20•log

10V

PGA









ER in Vrms













−1.76

6.02

ER in Vrms =

10V

PGA









6.02•ER in bits rms +1.76









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