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Croaker Senior Member Offline Posts: 235	size of quantization levels Feb 05^th, 2007, 12:23pm Is there any standard for determining the LSB size? The two definitions I see are: Vfs/2^N or Vfs/(2^N-1) Is any one better than the other?
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Vabzter Junior Member Offline Posts: 26 Sweden	Re: size of quantization levels Reply #1 - Feb 27^th, 2007, 3:17am Hi, I was going through this paper which highlights major parameters of DAC..Hope this answes your question http://grouper.ieee.org/groups/1658/NextMeetingArchive/061030DAPONTE/imeko_IWADC... BR Vabzter
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ywguo Community Fellow Offline Posts: 943 Shanghai, PRC	Re: size of quantization levels Reply #2 - Feb 27^th, 2007, 6:32pm I prefer Vfs/2^N for ADC. I read that paper. What's the definitioin of 1's complement? Why are they named 2's complement and 1's complement respectively? Thanks Yawei
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Croaker Senior Member Offline Posts: 235	Re: size of quantization levels Reply #3 - Feb 28^th, 2007, 10:32am You can find discussions on 1s and 2s complement in any digital electronics book. They are used for representing negative numbers. http://en.wikipedia.org/wiki/Two's_complement
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Croaker

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Re: size of quantization levels
Reply #4 - Feb 28^th, 2007, 10:34am

Vabzter wrote on Feb 27^th, 2007, 3:17am:

Hi,
I was going through this paper which highlights major parameters of DAC..Hope this answes your question

http://grouper.ieee.org/groups/1658/NextMeetingArchive/061030DAPONTE/imeko_IWADC...

BR
Vabzter

Not really. They are using Vref/2^N. The difference between the two standards that I see are Vref/2^N means your full-scale output is one LSB less than Vref and Vref/(2^N - 1) allows the full-scale output to be equal to Vref. Also, the LSB sizes are slightly different.

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ywguo

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Shanghai, PRC

Re: size of quantization levels
Reply #5 - Feb 28^th, 2007, 6:27pm

Hi, Croaker,

Let's discuss it with an N-bit flash ADC. It needs 2^N comparators and references. Normally the references are generated using a resistor ladder, which is tied between the positive reference (ref+) and the negative reference (ref-). If the resitive ladder is composed of 2^N resistors of equal resistance, the most negative reference tied to one of the comparators is V_ref-. The most positive reference tied to one of the comparators is (V_ref+-V_ref-)�(1-1/2^N)+V_ref-. Then one LSB is equal to (V_ref+-V_ref-)�(1/2^N). However, if the resistive ladder is composed of (2^N-1) resistors of equal resistance, the most positive reference tied to one of the comparators is V_ref+. The one LSB is equal to (V_ref+-V_ref-)�(2^N-1). I think it depends on your choice.

Best regards,
Yawei

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