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Em3rgent0rdr (talk | contribs) →Inaccuracies in non-ideal analog circuits: add cited sentence about 12-bits being practical limit for linearity of DAC due to component matching in 2001. |
Em3rgent0rdr (talk | contribs) →Inaccuracies in non-ideal analog circuits: add about how SAR is commonly used in microcontrollers but suffer from inaccuracies in microcontroller. |
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When implemented as a real analog circuit, circuit inaccuracies and [[Noise (electronics)|noise]] may cause the binary search algorithm to incorrectly remove values it believes {{math|''V''<sub>in</sub>}} cannot be, so a successive-approximation ADC might not output the closest value. It is very important for the DAC to accurately produce all {{math|2<sup>''n''</sup>}} analog values for comparison against the unknown {{math|''V''<sub>in</sub>}} in order to produce a best match estimate. The maximal error can easily exceed several LSBs, especially as the error between the actual and ideal {{math|2<sup>''n''</sup>}} becomes large. Manufacturers may characterize the accuracy using an [[effective number of bits]] (ENOB) smaller than the actual number of output bits.
{{As of|2001}}, the component-matching limitations of the DAC generally limited the linearity to about 12 bits in practical designs and mandated some form of trimming or calibration to achieve the necessary linearity for more than 12 bits.<ref>{{Cite web |date=2001-10-02 |title=Understanding SAR ADCs: Their Architecture and Comparison with Other ADCs |url=https://www.analog.com/en/resources/technical-articles/successive-approximation-registers-sar-and-flash-adcs.html |url-status=live |archive-url=https://web.archive.org/web/20241118075147/https://www.analog.com/en/resources/technical-articles/successive-approximation-registers-sar-and-flash-adcs.html |archive-date=2024-11-18 |access-date=2025-01-03 |website=[[Analog Devices]]}}</ref> {{As of|2012}}, SAR ADCs are limited to 18 bits, while [[Delta-sigma modulation|delta-sigma]] ADCs (which can be 24 bits) are better suited if more than 16 bits are needed.<ref>{{Cite web |date=2012-05-07 |title=Understanding Noise, ENOB, and Effective Resolution in Analog-to-Digital Converters |url=https://www.analog.com/en/resources/technical-articles/noise-enob-and-effective-resoluition-in-analog-to-digital-converter-circuits--maxim-integrated.html |url-status=live |archive-url=https://web.archive.org/web/20240422221715/https://www.analog.com/en/resources/technical-articles/noise-enob-and-effective-resoluition-in-analog-to-digital-converter-circuits--maxim-integrated.html |archive-date=2024-04-22 |access-date=2024-12-28 |website=[[Analog Devices]]}}</ref> SAR ADCs are commonly found on [[microcontrollers]] because they are easy to integrate into a [[Mixed-signal integrated circuit|mixed-signal]] process, but suffer from inaccuracies from the internal reference voltage [[resistor ladder]] and [[Clock signal|clock]] and [[signal noise]] from the rest of the microcontroller, so external ADC chips may provide better accuracy.<ref>{{Cite web |last=Giovino |first=Bill |date=2018-11-21 |title=IoT Microcontrollers Have ADCs, but Know When to Choose and Apply an External ADC |url=https://www.digikey.com/en/articles/iot-microcontrollers-have-adcs-know-when-apply-an-external-adc |url-status=live |archive-url=https://web.archive.org/web/20240624010637/https://www.digikey.com/en/articles/iot-microcontrollers-have-adcs-know-when-apply-an-external-adc |archive-date=2024-06-24 |access-date=2025-01-03 |website=[[DigiKey]]}}</ref>
[[File:ADC animation 20.gif|thumb|alt=Successive approximation animation|Operation of successive-approximation ADC as input voltage falls from 5 to 0 V. Iterations on the ''x'' axis. Approximation value on the ''y'' axis.|right]]
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