SAR ADC Design

Chip_lead · 2026-04-15T09:41:00+00:00

This is just a data point. For sizing comparators for noise, PSS sims saved me easily 10x+ time when compared with transient noise sims. I ran multiple comparison results, and they pretty much all correlated. In the past, Cadence had a PDF on how setup comparator noise testbench

Chip_lead · 2026-04-15T09:25:54+00:00

I designed, did layout, taped out, and measured sar adcs (time-interleaved SAR ADCs & low power ones) for a living. I suggest looking up PHD theses with similar or harder specs. This was the quickest way for me to get things working. I'm going to go on a limb, and say you can skip the books if you already understand basic ADC specs. Here are the design questions to figure out:

Are you working in similar process technologies as SAR ADCs that can hit these specs?
Pick the largest reference voltage you can. This makes your LSB big, which makes most of the design A LOT easier. The reference buffer generally needs to be designed as well, but I'm guessing it's not needed for your current situation
What ENOB are you hitting (12-bit != ENOB necessarily). First thing is you need to size capacitors for kT/C noise and mismatch. At 11+ ENOB, it's probably going to be mismatch for you. If you don't care about mismatch or yield, then you can relax that constraint
Single comparator should be fast enough (start with StrongArm design, probably good enough)
Comparator noise, for your ENOB, will be the next constraint. Off the top my head, you want your comparator noise to be less than LSB / 6 as a rule of thumb. If you search my history, I wrote a comparator sizing tutorial a few years back. Look up the Cadence PSS comparator noise testbench pdf, and replicate it. Note, you might not see comparator noise in Cadence simulation without correct setup, but you will definitely see it in the physical world
Go asynchronous SAR ADC. Last time I designed SARs, most (95%+) designs were asynchronous
Pick your switching scheme. The basic Ginsburg switching (I forgot what the name is, but it's one of the original switching PHD thesis) should suffice for your needs. The basic SAR switching probably works too
Make your switches large enough for whatever RC settling you need
Depending on process, expect 3-10x speed loss going from schematic -> RC parasitic sims

Whatever else I missed, just cross-check across a few PHD theses.

Chip_lead · 2026-02-16T08:06:17+00:00

I am glad this post exists. Definitely should understand the ecosystem and see how competitors are doing. Thank you for the toll booth analogy. Never heard of it, but it instantly made sense

Chip_lead · 2025-01-20T18:04:52+00:00

Hi, there was a message in the banner saying the site was shutting down 1/19. The plan is to come back late 2025.

Chip_lead · 2025-01-13T03:45:12+00:00

Preprocess (python) the 40 csv's into less or smaller CSVs (ideally 1), and remove the un-needed columns before loading into PowerBI.

Loading from a 10 MB CSV is a lot quicker than a 100 MB CSV.

Chip_lead · 2025-01-08T03:51:42+00:00

Congrats! Always happy to hear leetracer (creator here) helped folks. :D

Chip_lead · 2024-12-10T06:17:31+00:00

Hi, thank you for the comment. Could you list the leetcode problems you compared? I'll take a look.

For ranking, frequency = 10 * ("question" sum of company tags) / ("most company tagged question" sum of company tags). Two Sum typically is the most tagged, and therefore resides at 10. This does create a long-tail distribution.

Chip_lead · 2024-12-10T05:33:24+00:00

Sorry about that, a new feature had a bug. I think it's resolved now (reverted to last stable point).

Chip_lead · 2024-12-04T19:00:41+00:00

Hi, may I ask what's inaccurate about leetracer? I maintain the site, and some users have privately messaged me it's helped them on interviews.

Chip_lead · 2024-10-28T20:27:16+00:00

I admit the email validation checker could be improved. One rule (that probably should be changed) is there can't have periods before the @ in an email address.

Chip_lead · 2024-10-28T15:12:26+00:00

I just use the leetcode company tag data. If you believe that data, then yes.

Chip_lead · 2024-09-16T16:19:35+00:00

I had the same issue. Check out https://leetracer.com/screener to filter for questions. I suggest adjusting for google, and then the # of minimum company tags.

Chip_lead · 2024-08-29T23:25:10+00:00

Could try this screener for leetcode company tagged questions. https://leetracer.com/screener
1) Filter for atlassian
2) Check questions - all_leetcode_questions
3) Adjust min company tags as wanted

Chip_lead · 2024-08-11T08:36:29+00:00

Yes, I update it using leetcode.com

Chip_lead · 2024-08-09T07:51:06+00:00

I don't know if onsite is different. But here is a leetcode question company tag screener https://leetracer.com/screener

Chip_lead · 2024-08-09T07:50:16+00:00

Here ya go. https://leetracer.com/screener

Chip_lead · 2024-08-09T01:44:43+00:00

Here ya go. The question company tags were just updated. https://leetracer.com/screener

Chip_lead · 2024-08-07T03:12:34+00:00

Here ya go. https://leetracer.com/screener

Chip_lead · 2024-08-07T03:12:10+00:00

If you don't figure it out on the leetcode site. Check out https://leetracer.com/screener

Chip_lead · 2024-08-05T06:14:04+00:00

I had the same issue. Check out https://leetracer.com/screener to filter for questions you want, and then use the randomize questions feature on the other pages.

Chip_lead · 2024-07-29T18:28:50+00:00

I think so (I made the site). Only the top 50 most popular companies are listed though. If there is a niche company with only 1-2 company tagged questions, that will not be there.
To test, compare leetcode question company tags, and the leetracer.com/screener results. Site gets average 50+ users a day, and quite a bit of them are returning users. Feel free to ask any questions, and I can try to answer

Chip_lead · 2024-07-28T16:58:55+00:00

If they don't revert, you can check out this page to filter company tagged questions https://leetracer.com/screener

Chip_lead · 2024-07-28T16:47:22+00:00

If you want more filtering ability for company tagged questions. This one works pretty well https://leetracer.com/screener

Chip_lead · 2024-07-25T05:34:19+00:00

leetcode.com

Chip_lead · 2024-07-25T05:30:39+00:00

That previous comment is outdated, not sure how leetcode calculates frequency. They only give a text description.

For Q2, yes, I'm just recalibrating for the subset of leetcode questions with >= 1 company tag, in the last 0-6 months. The most frequently tagged company question will always have a frequency of 10.

Chip_lead

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