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AD7711A:  CMOS, 24-Bit Sigma-Delta, Signal Conditioning ADC with RTD Current Source

Product Details

The AD7711A is a complete analog front end for low-frequency measurement applications. The device accepts low level signals directly from a transducer and outputs a serial digital word. It employs a sigma-delta conversion technique to realize up to 24 bits of no missing codes performance. The input signal is applied to a proprietary programmable gain front end based around an analog modulator. The modulator output is processed by an on-chip digital filter. The first notch of this digital filter can be programmed via the on-chip control register allowing adjustment of the filter cutoff and settling time.

The part features two differential analog inputs and a differential reference input. Normally, one of the channels will be used as the main channel with the second channel used as an auxiliary input to periodically measure a second voltage. It can be operated from a single supply (by tying the VSS pin to AGND) provided that the input signals on the analog inputs are more positive than -30 mV. By taking the VSS pin negative, the part can convert signals down to -VREF on its inputs. The part also provides a 400 µA current source that can be used to provide excitation for RTD transducers. The AD7711A thus performs all signal conditioning and conversion for a single or dual channel system.

The AD7711A is ideal for use in smart, microcontroller based systems. Input channel selection, gain settings and signal polarity can be configured in software using the bidirectional serial port. The AD7711A contains self-calibration, system calibration and background calibration options and also allows the user to read and write the on-chip calibration registers.

CMOS construction ensures low power dissipation, and a software programmable power-down mode reduces the standby power consumption to only 7 mW typical. The part is available in a 24-pin, 0.3 inch-wide, hermetic dual-in-line package (Cerdip) as well as a 24-lead small outline (SOIC) package.


  • Charge Balancing ADC
    - 24 Bits No Missing Codes
    - ±0.0015% Nonlinearity
  • 2-Channel Programmable Gain Front End
    - Gains from 1 to 128
    - Differential Inputs
  • Ability to Read/Write Calibration Coefficients
  • Low-Pass Filter with Programmable Filter Cutoffs
  • Bidirectional Microcontroller Serial Interface
  • Internal/External Reference Option
  • Single- or Dual-Supply Operation
  • Low Power (25 mW typ) with Power-Down Mode (7 mW typ)

Functional Block Diagram for AD7711A


For purchasing, please refer to the AD7711 site.


Title Content Type File Type
AD7711A: LC2MOS, Signal Conditioning ADC with RTD Current Source Data Sheet  (Rev D, 02/2004) (pdf, 323 kB) Data Sheets PDF
AN-311: How to Reliably Protect CMOS Circuits Against Power Supply Overvoltaging  (pdf, 217 kB) Application Notes PDF
AN-607: Selecting a Low Bandwidth (<15 kSPS) Sigma-Delta ADC  (pdf, 222 kB) Application Notes PDF
AN-615: Peak-to-Peak Resolution Versus Effective Resolution  (pdf, 70 kB)
This application note describes effective resolution and peak-to-peak resolution and highlights the difference between these two specifications.
Application Notes PDF
AN-397: Electrically Induced Damage to Standard Linear Integrated Circuits:  (pdf, 149 kB)
The Most Common Causes and the Associated Fixes to Prevent Reoccurrence
Application Notes PDF
AN-202: An IC Amplifier User’s Guide to Decoupling, Grounding, and Making Things Go Right for a Change  (pdf, 76 kB) Application Notes PDF
AN-389: Using Sigma-Delta Converters-Part 2  (pdf, 590 kB)
When to Use/How to Use Sigma-Delta ADCs; Continuation of Part 1 Discussion.
Application Notes PDF
AN-388: Using Sigma-Delta Converters-Part 1  (pdf, 590 kB)
When to Use/How to Use Sigma-Delta ADCs
Application Notes PDF
AN-283: Sigma-Delta ADCs and DACs  (pdf, 1699 kB)
Overview of Sigma-Delta Concepts: Oversampling, Noise Shaping Using the Sigma-Delta Modulator, Digital Filtering and Decimation.
Application Notes PDF
AN-406: 06: Using the AD771X Family of 24-Bit Sigma-Delta A/D Converters  (pdf, 187 kB) Application Notes PDF
MS-2210: Designing Power Supplies for High Speed ADC  (pdf, 327 kB) Technical Articles PDF
Delta-Sigma Rocks RF, As ADC Designers Jump On Jitter
(Electronic Design, 1/12/06)
Technical Articles HTML
Designing and Applying Remote Field Instruments
by Albert O' Grady and Jim Ryan, Analog Devices B.V.
...Good things can come in small packages because of on-chip capabilities
(Control Engineering, September 1998)
Technical Articles HTML
Circuit Suggestions Using Features and Functionality of New Sigma-Delta ADCs Technical Articles HTML
Ask the Applications Engineer-27: What problems am I most likely to run into when instrumenting an industrial system?
(Analog Dialogue, Vol. 33, No. 2, February, 1999)
Analog Dialogue HTML
RAQs index Rarely Asked Questions HTML
Glossary of EE Terms Glossary HTML

Design Tools,Models,Drivers & Software

Title Content Type File Type
Sigma-Delta ADC Tutorial
An interactive illustration showing the behavior of an idealized sigma-delta A/D converter.
Utilities and Conversions HTML
AD7711A Code Examples Code Examples HTML

Evaluation Kits & Symbols & Footprints

Symbols and Footprints— Analog Devices offers Symbols & Footprints which are compatible with a large set of today’s CAD systems for broader and easier support.

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