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some question about sar adc

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iiiiisland

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hi
i generally have two questions about a 10bit sar adc

1. is offset cancellation essential when designing the comparator of the adc
using the archetecture of a preamp with latch?

2. is it need trimming or calibration to design a 10bit sar adc?

if the offset of the comparator must be cancelled, do you have any good ideas to elliminate this offset? i mean some good archetecture to share. or the preamp shoule be designed with two amp?


do anybody have some paper to illustrate the split of the cap array of dac in detail?
pls share with me


thank you all

best regards to you
island
 

ashish_chauhan

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Yes it is essential to cancel the offset of camparator in a SAR-ADC.

Since you are using a capcitive DAC you can go for shorting of input and output of comp in the discharge cyle of DAC.
 

iiiiisland

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thank ashish_chauhan for your advice!

you said to shorten the input and output of the comparator to eliminate offset. but my comparator is a combination of a preamp and a latch. whether should i shorten the output of the preamp or the output of the latch to the input end ?

thank you
 

linxiang0431

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Before design i think you'd better calculate the gain issue of the comparator due to the accuracy requirement and when done, you need just short the input and output of preamp regardless the offset caused by latch.
 

paley

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1.it is essential to cancel the offset of camparator in a SAR-ADC
2.it's not need calibration in a 10bit sar adc
 

fredflinstone

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iiiiisland said:
hi
i generally have two questions about a 10bit sar adc

1. is offset cancellation essential when designing the comparator of the adc
using the archetecture of a preamp with latch?

2. is it need trimming or calibration to design a 10bit sar adc?

if the offset of the comparator must be cancelled, do you have any good ideas to elliminate this offset? i mean some good archetecture to share. or the preamp shoule be designed with two amp?


do anybody have some paper to illustrate the split of the cap array of dac in detail?
pls share with me


thank you all

best regards to you
island
The preamp will help in reducing the latch offset. But the preamp itself will have offset and hence that has to be cancelled. And you need not calibrate the capacitor DAC to get 10 bits ..

There is a good paper on Comparator Offset cancellation by C.Enz.

https://www.edaboard.com/viewtopic.php?p=539992#539992

It will help you in designing offset cancellation schemes.
 

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