Hidden Analog Technology at the 2014 ISSCC

At the first International Solid State Circuits Conference (ISSCC), held in Philadelphia in 1954, most of the papers dealt with the properties of these new-fangled transistor things, since most electronic circuits of that era were built using vacuum tubes.

Over the next several years, the topics evolved into ways of using transistors to make circuits, such as amplifiers and oscillators (often the former gave rise to the latter). And as time and technology marched on, digital, analog, and mixed-signal circuits evolved, and gave rise to systems-on-a-chip. The keynote talks evolved too, into broad-ranging discussions of technology's role in society. The conference has come a long way from trying to figure out how transistors work.

The analog technology in this year's ISSCC is all over the place, and sometimes hidden or well disguised.

For example, take a look at the DRAM and non-volatile memory papers. What could be more digital than a memory chip, right?

I was once told that the two most important guys in a memory company are the process guy who can figure out how to make the storage capacitor or floating gate a little bit smaller, and the analog guy who can design one very good sense amp that can accurately discern a 1 from a 0. The guys who put a billion or so of each on a chip are a lot less important.

One of the papers in the 2013 ISSCC demonstrated how important analog technology is on a Flash memory chip. Paper 12.5 “A 128Gb 3b/cell NAND Flash Design Using 20nm Planar-Cell Technology” authored by a team from Micron Technology, described the challenges in using 20-nm floating-gate cells. It turns out that nearby cells in these tiny geometries interfere with nearby cells. Some of this is solved by careful layout (sounds sort of analog-ish, right?). And to get higher density, multiple bits are stored in each cell, three in this case. That means that the cell needs to be programmed to one of eight voltage levels (using DACs and various charge-pumps), then sensed accurately (using a counter-driven DAC and comparator). All those analog circuits need to be built in this 20-nm process, and have temperature compensation to have any chance of working.

Another paper in the same 2013 session was 12.7 “A 45nm 6b/cell Charge-Trapping Flash Memory Using LDPC-Based ECC and Drift-Immune Soft-Sensing Engine” by engineers from Macronix.

This paper describes the techniques used to store six bits per cell (actually arranged in pairs of three bits/per side of each cell, or so they say). They had to measure the threshold for each level in each cell by trial and error (sort of like a successive-approximation A/D) and apply compensation, as well as an encoding scheme to minimize errors, then a parity check for each cell.

Of course, the outside user only sees 0s and 1s go in and come out. Little does he or she know what's going on inside. However, without analog technology, these high-density flash memory chips would not exist. And maybe some of those ideas can be used in your analog system design.

9 comments on “Hidden Analog Technology at the 2014 ISSCC

  1. Steve Taranovich
    January 28, 2014

    You're right Doug, there are so many analog functions inside a “digital” IC that we do not think about. Power management, references, comparators, drivers, etc

  2. Vishal Prajapati
    January 29, 2014

    Thanks for the article Doug. I never knew this much about memory ICs. I thought only one bit is stored in each floating gate. I didn't knew it uses D/A and A/Ds in the memory ICs. I thought analog is being used only for power management in the digital ICs. This article has changed my perspective towards digital ICs.

  3. amrutah
    January 30, 2014

    With all designs ranging in GHZ and the devices getting smaller, the digital binary transitions are no more sharp and follow a transient behaviour giving a analog flavour to the designs.

       @Doug: Any exciting topics in Analog this ISSCC'14?  Looks like the last paper session is dedicated to the Memory…

  4. RedDerek
    January 30, 2014

    I was thinking years ago why a cell had to be 1 or 0. I was thinking along the old logic lines of 1, 0 and high-Z as a base-3 system. Now they are making a cell act as 6 bits? Pretty good. Obviously the analog world had to come into play because of the multiple voltage values.

    Hey, isn't this almost like the old analog shift register? Granted the SR I was talking about a few blogs ago were serial-in, serial-out.

  5. David Maciel Silva
    January 31, 2014

    Exactly Steve,

    Think of a digital integrated circuit that does not have no analog reference is virtually impossible.

    She will always be there have no escape, no digital without any analog?

  6. samicksha
    February 2, 2014

    I guess data converters to connect analog to digital circuits will still remain hot topic with innovation on power efficiency involved.

  7. eafpres
    February 4, 2014

    Hi Doug–very interesting.  I too was not up on the multi-bit per cell approach.  I did find this PR from Intel, where they claim to first sample a 3-bit per cell design in 2010.  So this technology is only about 3 years old, and now already 6-bits.  This started to remind me of quantum computing.  The big deal about quantum computing is the idea of a q-bit, which due to quantum interference, can take on any range of values represented by a superposition of the normal values (so, for 0 and 1, the q-it can act sort of as if it had all values between 0 an 1).  It is this superposition that promises to dramatically speed up some kinds of calculations.  

    Since almost any calculation needs memory in a practical device, I wondered what happens when you get to n-bit per cell memory where n becomes large.  If that memory was also fast, you could possibly get it to behave like q-bits.  It might at least be useful in doing simulations of what quantum comptuers could do.

  8. Netcrawl
    February 4, 2014

    Analog is key, analog is used primarily  in power management, its has a very imporatnt role in digital space, digital won't stand without analog.

  9. Davidled
    February 5, 2014

    I never see only digital circuit. At least wire including PCB wire line, is connected between Digital ICs with Resistor or Cap due to the internal circuit of IC. There is no imagination of any circuit without these components. I think that passive component with wire is required due to the analogy characteristic of IC.

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