ADC research trends: Migration to CMOS


Figure 1. Scientific “market share” trend for CMOS ADCs.

CMOS TAKE-OVER: I don’t think it will surprise anyone to learn that most experimental ADC implementations are nowadays done in CMOS. Figure 1 shows how the fraction of CMOS ADCs has increased in the scientific output. Last year (2011), over 98% of all papers in the mainstream sources were about A/D-converters implemented in CMOS. While experimental ADC research used to involve bipolar/BiCMOS designs as well, it is now completely dominated by CMOS.

CMOS ADCs were a significant part of the research field already in the early days. There is some transient noise in the beginning, due to the few papers published each year. Knowing the total paper count per year from a previous post, we can see that the curve is stable for all years having a total paper count above 10.

Figure 2 displays the evolution of ADC implementation papers grouped by device type. The taxonomy used here is simplified to {Bipolar, BiCMOS, CMOS, Other}, where the “Other” category includes various FET variations that are not complementary MOS (e.g., JFET or NFET), together with CCD, TFT, optoelectronic and quantum devices. In some papers it was not possible to determine which device type was used (n/a). Figure 3 illustrates the scientific “market share” trends for CMOS/Bipolar/BiCMOS ADCs. The underlying data is the same as in Fig. 2.

I realize that there might be specialized conferences or workshops where you may still find a bipolar ADC, but the graphs are representative of the journals and conferences where the vast majority of IC implementations are reported – including BCTM (IEEE Bipolar/BiCMOS Circuits and Technology Meeting) and CSIC (Annual IEEE Compound Semiconductor Integrated Circuit Symposium).

So, what do you think about the future of bipolar and BiCMOS ADCs? Do they have a place in the future? Is there any application or performance spec where they are the better alternative? Is there any relevant research left to do? My impression is that commercial ADC parts still use at least BiCMOS process options more often than scientific designs do. Why is that? Will they too migrate to 100% CMOS?

In an upcoming related post I hope to look at CMOS scaling and node adoption.

Figure 2. Evolution of paper count per device type.

Figure 3. Evolution of scientific “market share” per device type.

FootnoteS

Data for 2012 was excluded from the graphs since the year is not yet complete. This far, 100% of the surveyed 2012 papers have treated CMOS ADCs.

The term “paper” or “ADC paper” used in this post (and many others) refers to an implementation type of paper, where a measured IC implementation is reported. Simulation-only, and theoretical papers are not included in the survey.

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4 responses to “ADC research trends: Migration to CMOS

  1. George Storm

    I think one clue might be to look at publications by origin – the publication rate of manufacturers of ADCs seems to have been tailing off over the years (unless I am missing something, it now looks to average less than one/year per major supplier). The other issue is that leading-edge C-MOS is both “fashionable” and the area where the issues are changing, so it is the “natural” place for papers to appear.
    However, I suspect that bipolar (mostly within BiCMOS these days) still gives better trades-off for speed /precision until supplies are below about 1-Volt.

  2. It is mostly the fraction of papers from industry that has diminished, even if the absolute numbers also have decreased. I have discussed that previously here.

    If I divide the data set into “Industrial” and “Academic” and replot Fig. 3 above for each category separately, the “Industrial” plot looks very similar to Fig. 3 above, but with a boosted bipolar share. This is because (as you perhaps suspected) nearly all bipolar papers originate from industry. Thus the negative trend for bipolar ADCs in Fig. 3 is almost entirely defined by the “industrial” sub-community itself migrating from bipolar ADCs to other options. Not primarily because it is loosing shares in the overall paper count, even though that will further accentuate the trend.

    Regarding BiCMOS, the trends within both subsets have been an almost constant, but slowly decreasing percentage for the last 15-20 years. Eyeballing it, the average percentage drop per year is similar in both subsets, although the percentage of BiCMOS papers within the industrial subset remains approximately twice as large over time as the percentage among academic contributions. The diminishing share of BiCMOS ADCs in Fig. 3 is therefore primarily because both sub-communities are migrating from BiCMOS research. Since – as you also suggested – BiCMOS has a stronger position within the industrial sub-community, the trend is further accentuated by its reduced scientific output.

    So, as far as I can tell from the data, there is/has been an actual migration from bipolar/BiCMOS to CMOS across both academic and industrial contributors. In fact, the academic community has already embraced CMOS wholeheartedly since well over two decades, so the trends we still observe are mainly a reflection of the ongoing migration to CMOS within the industrial research community.

  3. Pingback: ADC performance evolution: Low-voltage operation – part 1 | Converter Passion

  4. Pingback: ADC performance evolution: Low-voltage operation – part 2 | Converter Passion

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