Monthly Archives: January 2011

The mother of all ADC FOM


– “We all love figures-of-merit – that’s why there are so many of them.”

ADC measurement

Well … in reality there are only one or two that have reached canonical status, while the rest have found marginal use independently of their qualities (or possible lack thereof). Nevertheless, they are out there, and to bring some order in the flora and also to prepare the way for future analog-to-digital converter (ADC) FOM proposals and a better discussion of the topic, I will follow in the footsteps of another Swede – Carl Linnaeus – and try to develop some classification of the FOM species. In order to do that, I’d like to introduce you to “The Mother of All FOM” (TMAF):

F = K \times{P}^{\alpha_P}\times{f}^{\alpha_f}\times{V}^{\alpha_V}\times{A}^{\alpha_A}\times{L}^{\alpha_L}\times{D}^{\alpha_D}\times{2}^{\alpha_B B}

TMAF is a generic FOM expression that is explained in more detail on the page ‘A generic ADC FOM’ [1], which also explains the mapping between the linear form F (above) and the logarithmic form G

G = X_{dB}+M_0+M+ \dfrac{20}{\alpha_B}\times[\alpha_P\times\log{P}+\alpha_f\times\log{f}+...\\ +\alpha_V\times\log{V}+\alpha_A\times\log{A}+\alpha_L\times\log{L}+\alpha_D\times\log{D}]

A long list of generic sub-expressions (FOM classes) are found on the page named ‘Generic ADC FOM classes’ [2], together with examples of explicit FOM expressions found in the literature. Here, I’ll just give one example by looking at the generic sub-expression for the “A-class” FOM (for lack of better nomenclature):

F_{A} = \dfrac{P}{2^{B} f}

With B = ENOB , and f = f_s , we get the expression for the “ISSCC FOM”, the most commonly used ADC FOM today:

F_{A1} = \dfrac{P}{2^{ENOB} f_{s}}

By setting B = ENOB @ DC , and f = \min \left \{ 2\times ERBW, f_{s}\right \} , we get the inverted expression for the “ITRS FOM”, which is used e.g., in [3]

F_{A2} = \dfrac{P}{2^{ENOB @ DC} \min{\left\{2\times ERBW, f_{s}\right\}}}

Read more in [1], and see more examples in [2]. The introduction of a generic FOM and generic FOM classes allows the similarities and differences between figures of merit to be analyzed in a more systematic way. It’s a first attempt to define a common language and classification so we can actually compare and discuss the strengths and weaknesses of different FOM – a discussion that I believe is much needed.

Why?

Stay tuned, and you will find out …

References

[1] B. E. Jonsson, “A generic ADC FOM”, Converter Passion blog, On-line, https://converterpassion.wordpress.com/a-generic-adc-fom/, Jan., 2011.

[2] B. E. Jonsson, “Generic ADC FOM classes”, Converter Passion blog, On-line, https://converterpassion.wordpress.com/generic-adc-fom-classes/, Jan., 2011.

[3] System drivers, International Technology Review for Semiconductors, 2009 Update, On-line, http://www.itrs.net

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The global ADC “FOM-o-meter”


Living in a FOM-centric world of ADC design? Wondering who’s got the current world record, and what it is? And what about that other FOM they’re sometimes using – who can possibly keep track of the state-of-the-art of both?

Well … say hello to the Converter Passion global “FOM-o-meterwhich is here to help in a FOM-crazed scientific environment. With the global FOM-o-meter you can always check the current state-of-the-art with respect to A/D-converter figures-of-merit (FOM) whenever you need to know. You’ll get the source citation and the numeric value. The reading is based on massive amounts of data, and continuously updated with the latest publications.

My intention is to make ADC figures-of-merit one of the main Converter Passion topics this spring, and perhaps throughout the year – depending on your response. From numerous private conversations with conference delegates, colleagues, and clients I have concluded that there is a rich flora of opinions, and you will have plenty of opportunity to have your say here on the blog.

As a little warm up exercise, the global FOM-o-meter is hereby introduced as a service to CP readers. It’s a ‘static page’ (as opposed to a blog post) in WordPress lingo, so I’ve put it in the INFO menu above, and in the PAGES link list in the sidebar. The FOM-o-meter v1.0 monitors the following two figures of merit:

F_{A1} = \dfrac{P}{2^{ENOB} f_s}

F_{B1} = \dfrac{P}{2^{2 ENOB} f_s}

They are probably familiar to many of you, but we’ll take a closer look at both of them in posts to come, so don’t worry if they are new to you. Current data covers 1974 – March 2010, but is soon to be updated to present day. Having processed the 1400+ documents from 1974 to March 2010, I have to admit that I was a bit tired of reading scientific papers on analog-to-digital converters. That’s why there’s almost a year until first update. But my brain is now fully recovered, and you should expect several updates per year.

Now, go ahead and check out who’s got the world record

Trying to keep warm


Staying indoors to keep warm

Here in Sweden we’ve just had the coldest December since 1800-something, and most of us are just trying to keep warm. Well … at least I do. Even with the “heat wave” (–4°C) we’re currently experiencing I still prefer the sweet warmth of the house. And then, of course, my boss (that’s me) is keeping me pinned down at the office desk with work, work, and more work. Right now I’m pushing myself to produce at least one, and hopefully two manuscripts to submit for review to the 2011 IMEKO IWADC conference. There’s still one more week before the closing date, so if you haven’t submitted anything yet you may want to give it a try yourself. Surely you have some good ideas that haven’t yet been published. Keep us posted about your progress!

I don’t know about you, but I’m one of those that actually enjoy writing scientific papers. And right now in freezing cold Scandinavia, the thought of going to the warm and beautiful Italy in the summer is a major source of additional inspiration for writing 😉

Faithful blog visitors have probably been staring at those Water-on-Insulator crystals for a while now, wondering when or perhaps if this blog is ever going to return to the narrow path of data converters again. Have faith! As soon as the manuscripts are in – possibly even sooner – I’ll be back with a post opening up the topic of ADC figures-of-merit (FOM). Lots of potential for interesting discussions, don’t you think? Now you have a few days to prepare your mind …