Features and Benefits
- 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)
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.
Product Lifecycle Production
At least one model within this product family is in production and available for purchase. The product is appropriate for new designs but newer alternatives may exist.
Documentation & Resources
AN-202: An IC Amplifier User’s Guide to Decoupling, Grounding, and Making Things Go Right for a Change (Rev. B)2/14/2015
AN-389: Using Sigma-Delta Converters-Part 22/14/2015
AN-388: Using Sigma-Delta Converters-Part 12/14/2015
AN-311: How to Reliably Protect CMOS Circuits Against Power Supply Overvoltaging3/8/2008
AN-397: Electrically Induced Damage to Standard Linear Integrated Circuits:11/18/2002
AN-283: Sigma-Delta ADCs and DACs9/24/2002
Designing Power Supplies for High Speed ADC2/1/2012
Delta-Sigma Rocks RF, As ADC Designers Jump On Jitter1/12/2006
Part 2: Circuit Suggestions Using Features and Functionality of New Sigma-Delta ADCs6/1/2002
Part 1: Circuit Suggestions Using Features and Functionality of New Sigma-Delta ADCs10/1/2001
Tools & Simulations
ADI has always placed the highest emphasis on delivering products that meet the maximum levels of quality and reliability. We achieve this by incorporating quality and reliability checks in every scope of product and process design, and in the manufacturing process as well. "Zero defects" for shipped products is always our goal.
Sample & Buy
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