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Question about ADC frontends...

Question asked by mdot on Jul 5, 2011
Latest reply on Jul 11, 2011 by mdot



Not even sure if this is the right forum to ask this question. If not, just point me in the right direction and I'll ask it there.


But, since it has to do with me interfacing to a SigmaDSP, I figured I start here.


After using the evaluation board for the ADAU1701 for a few months now, I've decided that I want to base my little project prototype on either the AD1940 or AD1941 and use a AD1938 CODEC as the analog interface. I figured the easiest way to get up and running would be to base the prototype PCB on one of the evaulation boards, that brought up a few questions:


1.) In the datasheet for the AD1940 evaluation boards, it says that the actual board architechture is four layers with dedicated ground and power planes. Of course, four layer boards can get pretty expensive for prototyping. My question is, does anyone know what the affect on performance would/could by using a two layer PCB instead?


I'm sure there is some app note, or article addressing this line of questions, I just haven't found anything that is both "on subject" and "up-to-date".


2.) The evaluation board has mix of different capacitor with different chemistries. How does one go about deciding which chemistries are used where, in the analog input buffer? Also, why is it that it seems electrolytic caps are only used either as the first component on an analog input, or the last component of an analog output?


3.) Does anyone have any suggestions of how to possibly reduce some of the component count of the ADC frontend without completely ruining soudn quality? Is there such a thing as an ADC frontend IC for audio?


I think that's all I have for now, as if that's not enought, if anyone has any input or, has some references that could point me to, it would be greatly appreciated.


Eventhough I have a degree in Electrical Engineering, I have been writing software since I graduated from college. So, I have never had to design a circuit this complex. This little project is really showing me the difference between what I learned in school and "the real world" of circuit design. *laffs*