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Design >> Mixed-Signal Design >> SAR ADC noise and comparator resolution
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Message started by vodka69 on Jul 17^th, 2014, 5:48pm

Title: SAR ADC noise and comparator resolution
Post by vodka69 on Jul 17^th, 2014, 5:48pm

For SAR ADC, how to decide the minimum resolution of the comparator? How to tackle the noise in the design? Thanks

Title: Re: SAR ADC noise and comparator resolution
Post by RobG on Jul 18^th, 2014, 11:20am

Well, it has to be less than 1/2 LSB, hopefully you can make it 1/10 LSB and let the quantization noise dominate.

Title: Re: SAR ADC noise and comparator resolution
Post by eternity on Jul 22^nd, 2014, 8:13am

Adding to the comment above, if you are going for differential architecture, the minimum resolution of comparator can be doubled which relaxes the design limits relatively.

Regarding more stuffs on noise specfications of comparator or in general regarding SAR ADCs, please refer to the online PhD(free edition) by Pascal Meinerzhagen. He had probably covered all the aspects to its maximum.

Eternity

Title: Re: SAR ADC noise and comparator resolution
Post by jockeymonto on Jul 23^rd, 2014, 6:36am

Hi, The above two comments are very useful. Generally you would start with the required resolution of you analog input to the ADC. By that I mean what is the amplitude difference between two adjacent sampled inputs which you want your ADC to allot two different adjacent digital codes. Obviously this determines the ADC resolution or the required LSB. Say this required resolution or LSB is around 2mV. The ADC required resolution is then obviously 9 bits. Generally the resolution of an ADC should be such that it makes quantization error (plus minus half an LSB) of ADC insignificant so that we can accommodate the inaccuracies introduced by other circuit elements in the ADC like the comparator. So unless I know what is your required analog resolution, I can't say anything about comparator resolution. Pick an ADC with LSB 10 times lower than the required analog resolution; resolution of comparator will then be LSB of the picked ADC.