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Alan Walsh

The Mystery of SAR ADC Power Specifications

Alan Walsh
Netcrawl
Netcrawl
9/16/2013 9:20:46 AM
User Rank
Master
Re: Datasheets are guides, not facts
@Albing you're right experience is great plus, experience is a great teacher, gaining knowledge from work experience is probably the best teaching tool, it widen and deepen your knowledge. It provide you the ability to spot the problem quickly and solve it faster. I know people who made good things from their experience, for them experience is much better than learning inside classroom.

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goafrit2
goafrit2
9/16/2013 8:57:50 AM
User Rank
Master
Re: Datasheets are guides, not facts
>> Where you don't know or don't have the experience, you need to enlist the help of an applications engineer from the company that made the IC

That is wisdom. However, mastering that skill is important. Maybe, universities must be brought in line to teach and educate students on how to read and understand datasheets. Nonetheless, the key factor here is giving students skill sets to make sense of the numbers and that will come via having practical experience in making and building things

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B_Albing
B_Albing
8/23/2013 4:45:47 PM
User Rank
Editor
Re: Datasheets are guides, not facts
@goafrit2 - I would agree that the data sheet just provides guidance. You need to have the good judgment + experience to know what to do with the info provided. Where you don't know or don't have the experience, you need to enlist the help of an applications engineer from the company that made the IC.

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Netcrawl
Netcrawl
8/19/2013 6:54:46 AM
User Rank
Master
Re: Experience matters
@Fasmicro Yes I agree it's still a mystery but we can solve this mystery, we only need to get the whole picture, we need to fully understand SAR ADC, their architecture and their comparison with other ADCs, I think experience is key here, it give engineers a huge advantages and tool in tackling specific problems. How can you solve the mystery If you don't understand SAR ADC specifications?  

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fasmicro
fasmicro
8/18/2013 2:43:31 PM
User Rank
Master
Experience matters
It could be a "mystery" in SAR ADC because you have this system that needs a lot of digiatl parts to get the final bit sequence. It is the same thing with cyclic or algorithmic ADC where you need solid high performing digital systems to get the bits.  But experience engineers have ways of looking at the power budgets in block-by-block level and come up a fairly good accurate budget. SAR is a tough ADC to make and it is becoming popular with MEMS analog front ends since it offers some good tradeoffs in bits and size. Cyclic does better but you need a huge budget on digital units.

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goafrit2
goafrit2
8/18/2013 2:16:25 PM
User Rank
Master
Datasheets are guides, not facts
>> It is a mystery to me why some data sheets don't take all the specs into consideration when stating a requirement as important as power consumption

My understanding of many datasheet is that you get a guidance from them and not necessarily the facts or hard numbers. You must test the products to get your own metrics. It is hyper commercial marketing. People quote 18 bits chip when the ENOB, DNR and INR are not even up to the performance of 14 bits. They call it "marketing bits". It is not a new thing - just the reflection of the influence of Wall Streets to sell more stuffs by public firms.

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More Blogs from Alan Walsh
A poorly designed reference circuit can cause serious conversion errors. The most common manifestation of a reference issue is repeated or “stuck” codes from the ADC
Once the drive capability has been determined, we must ensure that the noise from the reference circuit does not affect the ADC’s performance.
The voltage reference may integrate a buffer that has sufficient drive current. Otherwise, a suitable op amp can be used as a buffer.
The overall precision of a high-resolution, successive-approximation ADC depends on the accuracy, stability, and drive capability of its voltage reference.
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