Tuesday, January 06, 2009

Two Patents Came Late

Two patent came late for the last week patent review. One of them is Forza's US7471231 differential dual slope ADC - easily understandable for the picture below:

The differential approach is said to enable a more consistent switching point, allowing the amplifier to be linear over a larger part of its range. It's probably true, but at the expense of added area and power consumption. Also, the PREAMP block should have an wide common mode range and good high-frequency common mode rejection, which might increase power even more.

Altasens' application US20080316342 looks quite obvious to me. It talks about gain control with fine steps. The gain control is split between analog and digital. The analog gain provides coarse gain steps and the digital gain provide finer gain steps between adjacent coarse analog gain values. Since analog gain can suffer from low precision, on-chip calibration is implemented to calibrate the analog and digital gain.
If granted, it would become quite broad and strong patent, but to me it seems obvious and I think there would be some prior art, even though I can not point to it specifically.


  1. Forza is lucky. Pls look into earlier Aptina patent US6885331 Fig.6. Isn't it the same? Diff comparator, diff ramp, a CB switch ...

  2. Yes, you are right. Forza has enough small differences to pass a patent examiner, but I doubt its patent would stand in court.

  3. The Forza patent was published during 10/08 (at the 18 month point). It is still undergoing examination. I couldn't find any reference to prior art whatsoever. I doubt this one makes it through the examination process with its claims intact.

    This seems like a lot of overhead. What applications do you guys think this design is good for?


  4. Well.. Looks to me like 6,885,331 is mostly about the ramp generator and the capacitors used to make it, and 7,471,231 is about the details other than the ramp generator for dual slope operation. I am not going identify myself because this discussion should not appear in any hypothetical future court case. But since I know all the very talented people involved, all I can say is that I did not see any conflict between the patents during my brief look at each one. Of course they both describe approaches for column parallel ADC so they have that in common.

    Anyone who does not know what these designs are good for has not been paying attention to some of the most aggressive and successful chip designers in the world.

  5. To rj: Forza patent has been granted, that is, it has passed the examination already. I think the patent examiner mostly checked the claims and saw no overlap at the claims level.

    To Anonymous: True, the patent scopes are different. However, in terms of prior art, Micron's Fig. 6 clearly shows the same principle as Forza's patent. So, I think that if these two patents ever meet in the court, many of Forza's claims would be invalidated, but few might still stand.

  6. For better or worse, I have had significant experience in the patent arena. '331 fig 6 is quite different from '231's figure, even to an untrained eye. Just count the number of caps and where the ramp generator ties in. In any case, no need to get hung up on the figures. Just read the claims, word for word since every word counts. If there are two identical claims then there is a problem, if not, then pretty much the examiner's decision is a good one. (Obviousness issues aside - and that is a hard row to hoe).

    There has been a steady evolution in column-parallel ADC design for speed, power and accuracy. Since these guys all used to work together in the glory days, it is no surprise that the inventions share many common traits.

    Also, if '231 is viewed as an improvement over something basic in '331 but still uses things claimed in '331 then there could be an infringement issue for products using '231 but that does not invalidate '231.
    For example, if someone used the ramp generator of '331 but added a switch or changed the timing to improve performance, then they could have a valid patent whose use would still require a license from the holder of '331.

    I don't think '231 has that issue but I have not looked at the two patents side by side, claim by claim, word for word.

    Sorry, still should remain anonymous but you all know who this is.

  7. Interesting discussion. I had not intended to take it that far, but let's try it, just for fun. Forza patent claim #1 says:

    1. An analog to digital converter system, comprising: a signal sampling line; a reset sampling line; a ramping circuit, creating a first ramp that changes value between a first voltage value and a second voltage value, in a first direction and creating a second ramp that changes value in an opposite direction to said first ramp, and coupled to said reset sampling line; and a logic element, creating a digital value based on a difference between said signal and reset values and based on an intersection between said first and second ramping portions.

    Don't you think that this Forza claim should be rejected due to the lack of novelty, based prior art on Fig. 6 in Micron's patent?

  8. Hard to say because Fig 6 does not show any ramping up and down signals. It is also hard to say what the examiner would have said if they had cited '331 that issued almost 2 yrs prior to their filing. But '331 is about the ramp generator as evidenced by the chosen title and the claims. '231 does not address the ramp generator in any particular detail.

    Without taking away anything from the technical innovation of '331, I think '231 stands on its own. I love claims 12 and 13 for example even if claim 1 is a little broad.

    You all need to stop thinking like engineers and start thinking like patent attorneys and juries. It is a totally different world.

  9. > You all need to stop thinking like engineers and start thinking like patent attorneys and juries. It is a totally different world.

    I have yet to see two patent attorneys that think alike. Or, may be, they just talk differently. And juries often make paradoxical decisions, you are right. So, I use my common sense comparing these two patents and I'm sure there would be a bunch of patent lawyers which agrees with me and another bunch which disagrees.


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