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AD7721:  CMOS, 12-/16-Bit, 312.5 kHz/468.75 kHz Sigma-Delta ADC

Product Details

The AD7721 is a complete low power, 12-/16-bit, sigma-delta ADC. The part operates from a +5 V supply and accepts a differential input of 0 V to 2.5 V or ±1.25 V. The analog input is continuously sampled by an analog modulator at twice the clock frequency eliminating the need for external sample-and-hold circuitry. The modulator output is processed by two finite impulse response (FIR) digital filters in series. The on-chip filtering reduces the external antialias requirements to first order in most cases. Settling time for a step input is 218.4 µs while the group delay for the filter is 109.2 µs when the master clock equals 15 MHz.

The AD7721 can be operated with input bandwidths up to 229.2 kHz. The corresponding output word rate is 468.75 kHz. The part can be operated with lower clock frequencies also. The sample rate, filter corner frequency, settling time, group delay and output word rate will be reduced also, as these are proportional to the external clock frequency. The maximum clock frequencies in parallel mode and serial mode are 10 MHz and 15 MHz respectively.

Use of a single bit DAC in the modulator guarantees excellent linearity and dc accuracy. Endpoint accuracy is ensured by on-chip calibration of offset and gain. This calibration procedure minimizes the part’s zero-scale and full-scale errors.

The output data is accessed from the output register through a serial or parallel port. This offers easy, high speed interfacing to modern microcontrollers and digital signal processors. The serial interface operates in internal clocking (master) mode, the AD7721 providing the serial clock.

CMOS construction ensures low power dissipation while a power-down mode reduces the power consumption to only 100 µW.


  • 16-Bit Sigma-Delta ADC
  • 468.75 kHz Output Word Rate (OWR)
  • No Missing Codes
  • Low-Pass Digital Filter
  • High Speed Serial Interface
  • Linear Phase
  • 229.2 kHz Input Bandwidth
  • Power Supplies: AVDD, DVDD: +5 V ± 5%
  • Standby Mode (70 µW)
  • Parallel Mode (12-Bit/312.5 kHz OWR)

Functional Block Diagram for AD7721


Title Content Type File Type
AD7721: CMOS 16-Bit, 468.75 kHz, Sigma-Delta ADC Data Sheet (Rev A, 12/1997) (pdf, 259 kB) Data Sheets PDF
AN-311: How to Reliably Protect CMOS Circuits Against Power Supply Overvoltaging  (pdf, 217 kB) 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
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
Circuit Suggestions Using Features and Functionality of New Sigma-Delta ADCs 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
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

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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Price, packaging, availability

AD7721 Model Options
Model Package Pins Temp.
Price*(100-499) Price*1000 pcs RoHS View PCN/ PDN Check Inventory/
AD7721AR Status: Production 28 ld SOIC - Wide 28 Ind Tube, 27 $14.36 $12.22 N  Material Info PCN Purchase
AD7721ARZ Status: Production 28 ld SOIC - Wide 28 Ind Tube, 27 $13.09 $11.13 Y  Material Info PCN Purchase
AD7721ARZ-REEL Status: Production 28 ld SOIC - Wide 28 Ind Reel, 1000 - $11.13 Y  Material Info PCN Purchase
Price Table Help

The USA list pricing shown is for BUDGETARY USE ONLY, shown in United States dollars (FOB USA per unit for the stated volume), and is subject to change. International prices may differ due to local duties, taxes, fees and exchange rates. For volume-specific price or delivery quotes, please contact your local Analog Devices, Inc. sales office or authorized distributor. Pricing displayed for Evaluation Boards and Kits is based on 1-piece pricing.

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