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Design >> Mixed-Signal Design >> basic question
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Message started by raja.cedt on Oct 15^th, 2009, 10:56pm

Title: basic question
Post by raja.cedt on Oct 15^th, 2009, 10:56pm

hi every one,
i am new to data converters, so while reading basics i got the following doubts

1.Basically INL indicates deviation from its ideal value so it tells us about distortion and thats it is tough spec in communication, so how about DNL generally in which applications it is Important.

2.I read about parameters SNR, SQNR, SFDR. But whats the significance of these parameters (i have doubt mainly about SFDR)

Thanks for your time.

Title: Re: basic question
Post by loose-electron on Oct 22^nd, 2009, 9:12am

raja -
Its a pretty general question - so I think you need to open the textbooks on this

On SFDR - a good example of where this is important is in DDS systems (direct digital synthesis) - you are trying to create a sine wave out of a DAC and you have a bunch of second order junk in your output.

If the SFDR is 90dB then you can say that your undesired outputs are defined to be 90dB less than the output.

As for the rest, it depends on your application.

DNL and monotonic behavior is is very important in control systems feedback - non-monotonic behavior causes a 180 degree phase flip in a control system application, and DNL erros cause the equivalent of local gain variance in the loop.

Tough to generalize, you need to better define the place the ADC/DAC is getting used.

jerry

Title: Re: basic question
Post by Riad KACED on Oct 22^nd, 2009, 12:32pm

Hi Raja,

The literature is rather rich to answer those questions although some are very academic.

I quite like the data converters book by Franco Maloberti. It does answer all your questions. Besides, things are explained in a very practical way. I really recommand this book although didn't have a real chance to put in practice all what I learnt.

From more a practical point of view, companies like TI, Maxim, NSC ... are all contributing with very handy application notes in the matter. I'm a regular reader of TI's Analog Applications Journal. There is an article that is likely to interest you:
http://focus.ti.com/lit/an/slyt231/slyt231.pdf

Cheers,
Riad.