ADC Designs Including Delta-Sigma

I recently interviewed a candidate who listed having worked in an ADC group at Analog Devices.  Wanting to ask a technical question on a topic he would/should know, I noticed that I wasn’t sure exactly how an ADC works.  So, I thought up three solutions before asking the question, but still wondered how ADC’s work fast enough for applications like audio.  I’m familiar with the ramp and counter method used in microcontrollers from having used them.  The successive approximation method is also a straightforward and fairly good solution, but even that takes 24 cycles for audio quality ADC.  Next, I reinvented multistage subranging ADC as a way to expand flash ADC.  While trying to figure out what my invention was called, I stumbled across another really cool ADC that I would never have thought of.  The operation of most ADC’s can be explained to anyone because they don’t require special knowledge to understand, but delta-sigma ADC’s are completely based on frequency-domain thinking.  Learning about them helped improve my understanding of DSP and control theory.

Here’s a good discussion of various ADC’s:
http://www.analog.com/library/analogDialogue/archives/39-06/architecture.html

Read all 3 parts of this post.  Part 1 helps understand what the modulator does.  Part 2 makes Nyquist simpler than ever before.  Part 3 gives insight into how the noise shaping really works.
http://skywired.net/blog/tutorials/how-delta-sigma-works/

I like this one because it explains how you extract 16 bits of width out of just 64 samples.
http://www.triadsemi.com/2007/01/25/how-to-design-a-16-bit-sigma-delta-analog-to-digital-converter/

And once you understand all that, you’ll appreciate this piece on upsampling in CD players
http://www.simaudio.com/pdf/Upsampling.pdf
but don’t buy one because it’s all overpriced.  Advertising the $1.25 DAC http://www.ti.com/product/pcm1748 in a CD player as “Burr Brown” brand is like restaurants labeling their bacon “applewood smoked”.

One thought on “ADC Designs Including Delta-Sigma

  1. Actually, I can imagine that delta-sigma converters were probably covered in one lecture in some class. But in college, there were three other classes to worry about, homework and more. Now, I can spend all the time I need, a few hours, a day, reading up on the topic until I understood it more deeply. Another problem with college is that many classes are prerequisites for each other. You need fundamentals of math to understand engineering classes, but the math classes don’t make sense until the classes with the applications. Sometimes it helps to take one class, the next, and then go back and retake the first one. But teaching myself one topic after another, in depth, seems to work best.

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