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Design >> Mixed-Signal Design >> Why ADC output mid-code is not 2^(N-1)?
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Message started by seetoo on Apr 29^th, 2009, 12:23am

Title: Why ADC output mid-code is not 2^(N-1)?
Post by seetoo on Apr 29^th, 2009, 12:23am

Testing my 10bit pipelined ADC,(SMIC 0.18 process)

when diff input both connect dc commen input voltage(0.9V), the output code is not 511.
and the output code in 3 Evaluation Board is different respectively(1# is 485,2# is 540, 3# is 604).

It may because offset of opamp ,but should not so large(about 50mV).

So ,what else may cause the code excursion?

Title: Re: Why ADC output mid-code is not 2^(N-1)?
Post by Berti on Apr 29^th, 2009, 5:47am

Hi Seetoo,

Apart from the large offset the ADC performance is ok (INL, DNL)?

Cheers

Title: Re: Why ADC output mid-code is not 2^(N-1)?
Post by Andrew Beckett on May 1^st, 2009, 5:21am

There are a lot of possible causes I can think of, but I think the first thing is to see what the overall transfer function is - effectively what the INL and DNL is, as Berti suggests.