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Why is the SNDR of signal-delta ADC is not dominated by mismatch? (Read 662 times)
Jacki
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Why is the SNDR of signal-delta ADC is not dominated by mismatch?
Jan 21st, 2018, 12:17am
 
Hello,

   Recently I read some documents about SAR-ADC and sigma-delta ADC. I find for SAR-ADC if mismatch calibration is not used, the SNDR is limited by mismatch, and it is hard for SAR-ADC to reach more than 12 bits. But for sigma-delta ADC, as I remembered, its SNDR is not dominated by mismatch, in other words, mismatch is not a big impact on the SNDR. Could anybody explain the reason for me, is it right for both CT-sigma-delta ADC and SC-sigma-delta ADC?
   Thank you very much.
   Jacki
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sheldon
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Re: Why is the SNDR of signal-delta ADC is not dominated by mismatch?
Reply #1 - Jan 21st, 2018, 8:25pm
 
Jacki,

   It depends on the architecture of the Delta-Sigma ADC architecture.
Traditionally, the Delta-Sigma ADC uses a 1 bit DAC and a 1-bit DAC does
not have mismatch. However, it is very hard to achieve high dynamic
range using a 1-bit DAC. To achieve high dynamic range, multi-bit DACs
are used. When multi-bit DACs are used, special techniques are required
to reduce the impact of mismatch: element rotation, data-weighted
averaging, ... So to achieve high dynamic range, special methods are
required for Delta-Sigma converters.

                                                                         Sheldon  
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Jacki
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Re: Why is the SNDR of signal-delta ADC is not dominated by mismatch?
Reply #2 - Jan 22nd, 2018, 10:22pm
 
Hi Sheldon,

   Thank you very much for your reply. I am new to sigma-delta ADC, want to learn this charming structure.
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Jacki
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Re: Why is the SNDR of signal-delta ADC is not dominated by mismatch?
Reply #3 - Mar 20th, 2018, 1:44am
 
Hi Sheldon,

   About the multi-bit DAC, normally if we use binary DAC, the linearity is good. If we use the thermometer coded to binary DAC, I think we almost can guarantee the linearity of the multi-bit DAC, am I right?
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