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https://designers-guide.org/forum/YaBB.pl Design >> Mixed-Signal Design >> Why is the SNDR of signal-delta ADC is not dominated by mismatch? https://designers-guide.org/forum/YaBB.pl?num=1516522644 Message started by Jacki on Jan 21st, 2018, 12:17am |
Title: Why is the SNDR of signal-delta ADC is not dominated by mismatch? Post by Jacki on 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 |
Title: Re: Why is the SNDR of signal-delta ADC is not dominated by mismatch? Post by sheldon on 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 |
Title: Re: Why is the SNDR of signal-delta ADC is not dominated by mismatch? Post by Jacki on 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. |
Title: Re: Why is the SNDR of signal-delta ADC is not dominated by mismatch? Post by Jacki on 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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