Question I spoke to you briefly this morning regarding selecting an ADC for a new instrument we are developing, I have looked on the AD website but there is no parameter search that I could find for ADC's.The main parameters I require are as follows :-1. Resolution >= 14 bits, parallel output 2. Conversion time < 2us. 3. DNL < 1 lsb 4. Snap shot operation (Not continuos sampling) Optional features 1. Internal reference 2. Internal sample & hold Answer Up until fairly recently, the only way to get 14 bit resolution with conversion time of >2us was to use a sigma delta architecture or to use a very high speed pipeline architecture ADC with throughput rates in the 10MHz region (See AD7721 and AD9260 for examples of sigma delta parts and AD9240, AD9243 for examples of high speed pipeline devices). It is quite possible to get pipeline ADCs with throughput rates up to the high 10s of MHz range at 12 resolution ( see the AD9224 and AD9226 for example) but to get the conversion time, i.e. the time between applying the signal and obtaining a result as opposed the time between successive conversions, down to below 2us for 14bit resolution is pretty difficult. The AD7863 which Irfan suggests comes close but the conversion time is nearer 5 or 6 us and as you say it's dual where only a single is required. From the sound of your spec, what you really want is a Successive Approximation Register (SAR) ADC where you can hit the Convert Start signal asynchronously and get a result back within the specified time. Current Successive Approximation devices are just not fast enough to meet this spec. In fact the closest you can get with currently release parts from ADI is the AD7851, 14 bit single converter with a conversion time of 2.78us At Analog Devices we are working on improving the speed of SAR ADCs with a new high speed low power SAR core and we have had significant success in achieving high speed operation (>1us) at 10 and 12bit resolution. It's much harder to maintain this speed up to 14 bit resolution but one of our new (soon to be released) ADC pushes the envelope out slightly and achieves the 2us conversion time (quite a feat for a SAR converter). The product is the AD7899 which is as yet unreleased. It is scheduled for general release at the end of July and Samples will be available from Impact at that time.

AD7899 - CS and RD tied permanently low

Question Can the CS and RD inputs be tied permanently low in single device designs. Answer The AD7899 needs to see an edge on the RD signal to clock out the data. This can be achieved by either using one signal to drive CS and RD, or hold CS low and pulse RD. You will also notice the example of where the EOC signal can be used as the RD input as per page 11 of the datasheet EOC Mode.

English

Forums
Popular Forums
Product Forums
View All
Application Forums
Design Center Forums
Learn
Highlighted Webinar

Fast-Track Certification: Leveraging IC Safety App Notes for Functional Safety Designs
Stop guessing, start certifying. Learn how to use IC safety application notes to streamline your FMEDA and meet IEC 61508 and ISO 13849 standards with...
Places
Libraries
Upcoming Learning & Events
View All Webinars
Community Hub
Challenge Yourself!
View All
What's Brewing
View All
Places
Resources
View All
ContentZone
Visit ContentZone
Search content by industry or technology.

Blogs

Technical Articles

Tutorials

Videos

Webinars

Your ADI content all in one place.
View ContentZone
The Latest Read

Clock Tree Design and Why “PLL Locked” Is Not Enough
In high-performance RF systems, clocking architecture is a foundational element that directly governs signal integrity, synchronization, and overall system...

New Release

Signal Chain Designer: DC Error Simulation
This video covers the DC error calculation capabilities of Signal Chain Designer. DC error is unique in that often requires calibration and has so many...

Recent Technical Insights

The Right Switch-Mode Power Supply Control Scheme
This article compares three switch-mode power supply control schemescurrent-mode control, voltage-mode control, and hysteretic-mode control to guide engineers...

EngineerZone

Precision ADCs

Log In

User
Site
Search

OR

Ask a Question

Data Converters

Precision ADCs

Documents AD7899: FAQ

Q&A
File Uploads
FAQs/Docs
Help Articles
Members
Tags
Cancel

Products Mentioned

AD7899 Production
The AD7899 is a fast, low power, 14-bit A/D converter that operates from a single +5 V supply. The part contains a 2.0 Âµs successive approximation ADC...
Datasheet
AD7899 on Analog.com

Table of Contents