Comment by alok-g
20 hours ago
I used to be a display architect about 15 years back (for Qualcomm mirasol, et al), so my knowledge of the specifics / numbers is outdated. Sharing what I know.
High pixel density displays have disproportionately higher display refresh power (not just proportional to the total number of pixels as the column lines capacitances need to be driven again for writing each row of pixels). This was an important concern as high pixel densities were coming along.
Display needs fast refreshing not just because pixel would lose charge, but because the a refresh can be visible or result in flicker. Some pixels tech require flipping polarity on each refresh but the curves are not exactly symmetric between polarities, and further, this can vary across the panel. A fast enough refresh hides the mismatch.
Since you are knowledgable about this, do you have any idea what happened to Mirasol technology? I was fascinated by those colour e-paper like displays, and disappointed when plans to manufacture it was shelved. Then I learnt Apple purchased it but it looks more like a patent padding purchase than for tech development as nothing has come out of it form Apple too. Is it in some way still being developed or parts of its research tech being used in display development?
Being a key technology architect for it (not the core inventor), I know all about it, and then some more!
I cannot however talk publicly about it. :-(
It has been a disappointment for me as well. I had worked on it for nearly eight years. The idea was so interesting--using thin-film interference for creating images is akin to shaping Newton's rings into arbitrary images, something which even Newton would not have imagined! The demos and comparisons we had shown to various industry leaders and sometimes publicly were often instantly compelling. The people/engineers in the team were mostly the best I have ever worked with, and with whom I still maintain a great connection. But unfortunately, there were problems (not saying how much tech how much people) that were recognized by some but never got (timely) addressed. And a tech like it does not exist till date.
I do not think anything on it is being developed further.
The earliest of the patents would have expired by now.
Liquavista, Pixtronics, etc., have been alternative display technologies that also ultimately didn't make the impact desired, AFAIK.
Meanwhile, LCDs developed high pixel densities (which led to pressures on mirasol tech too), Plasma got sidelined. EInk displays have since then made good progress, though, in my opinion, are still far from colors and speeds that mirasol had. And of course, OLED, Quantum dots, ...
My fantasy display would be some kind of reflective-mode display that can passively show static images like e-ink, have partial updates like MIP LCD in wearables, response times like modern LCD and AMOLED, and "super-real" contrast/gain.
I.e. actually do wavelength conversion to not just reflect a narrow-pass filtered version of the ambient light, but convert that broad spectrum energy into the desired visuals, so it isn't always inherently dimmer than the environment. I can only imagine this being either:
1. some wild materials science stuff that manages interference
2. some wild materials science stuff that controls multi-photon fluorescence
3. some wild materials science stuff to fuse photoelectric and electroemissive functions in the same panel. i.e. not really passive but extremely low loss active system to double-convert the ambient light that can follow the power curve of available light
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What's interesting about these newer 1Hz claims is that they're basically trying to sidestep the exact problems you mention
Correct.
I myself have been privy to similar R&D going on for more than a decade.
> the column lines capacitances need to be driven again for writing each row of pixels
Not my field so please forgive a possibly obvious question: That seems true regardless of the pixel count (?), so for that process why wouldn't power also be proportional to the pixel count?
I notice I'm saying 'pixel count' and you are saying 'pixel density'; does it have something to do with their proximity to each other?
Total column line capacitance is impacted by the number of pixels hanging onto it as each transistor (going to the pixel capacitance) adds some parasitic capacitance of its own. Hope that answers your question. You are right in the sense that a part of the total column capacitance would depend on just the length and width of it, irrespective of the number of pixels hanging onto it.
I had back then developed what was perhaps the most sophisticated system-level model for display power, including refresh, illumination, etc., and it included all those terms for capacitance, a simplified transistor model, pixel model, etc.
I did not carefully distinguish pixel density vs. pixel count while writing my previous comments here, just to keep it simple. You can perhaps imagine that increasing display size without changing pixel count can lead to higher active pixel area percentage, which in turn would lead to better light generation/transmission/reflection efficiency. There are multiple initially counter-intuitive couplings like that. So it ultimately comes down to mathematical modeling, and the scaling laws / derivatives depend on the actual numbers chosen.
Addition:
Another important point -- Column line capacitances do not necessarily need full refresh going from one row of the pixels to the next, as the image would typically have vertical correlations. Not mentioning this is another simplification I made in my previous comments. My detailed power model included this as well -- so it could calculate energy spent for writing a specific image, a random image, a statistically typical image, etc.