“Soothsayer” Part 3 – Where Does the LBS Power Go?

In my last blog I wrote about the power measurements on the ShowWX and a number of people asking “where did the all the ShowWX’s power go?”

Microvision wants you to think that they just point the lasers directly at their mirror and with next to no power loss the laser light is steered onto the screen, but the truth is anything but this.  It turns out that there is considerable electronics consuming power to control the mirror and lasers and are significant light loosing optics required to make it work.    In this blog, I we will take a peek behind the Microvision curtain.

First, Microvision has not published specifications on the power consumption of their mirror or other chips in their system.   Second, I did opened a ShowWX to take a peek inside (see above), but I didn’t rip it apart to measure the current for each of the components.   It was clear with 5W of power consumption and the very poor image (more on that in the next installment) that it wasn’t going to be a serious competitor to Syndiant, so there was no point in our spending the time and effort to do a detailed power evaluation.   Even with these caveats, it is possible to get a reasonable understanding of the power consumption issues associated with laser beam scanning with the available information.

So per the above my number are not going to be “perfect” but I do believe them to be reasonable estimates.   Microvision could clear this all up by publishing their actual numbers instead of their usual hand waving like “making a 40% improvement” without saying what part of the total power was improved by 40% and what was the starting point.   I would welcome Microvision’s corrections with their actual numbers.    Personally, I think it is the case that Microvision feels “it is better to remain silent and be thought a fool, than to open your mouth and remove all doubt.”

Above is figure 28 from patent application 20110234919  by Microvision.   This block diagram outlines the major electronic components that would be required in a ShowWX (or ShowWX plus).  As seen from the picture of the opened projector and in Fig. 28 below, there are a lot of components each of which is consuming power.   Fig. 28 also gives some idea as to the complexity in driving a LBS.    And the picture of the inside of the ShowWX demonstrates that all this takes up a lot of space (note there is a two PC board “sandwich” with all the circuitry inside the ShowWX).

Some people have made the point that the ShowWX is a standalone projector and that the power would go down a lot if it was embedded.    In reality, there is not much from Fig. 28 that would go away.   The “media module” in the ShowWX is only an analog RGB to digital converter and for WVGA resolution this should consume about 0.2 Watts.  The battery and some of the power management might be reduced which might save another 0.2W to 0.5W.  There might be a few other things but most of the rest of Fig. 28 would have to be there for an embedded LBS projector.  So maybe out of the 5.5 Watts the ShowWX consumes, at the very most 1W might not be needed with embedding.  That still leaves around 4.5W if this was to be embedded which is way too high for any realistic volume cell phone application.

Let’s start with the beam scanning mirror in the lower right of Fig. 28.   To make the mirror scan the laser beam even roughly correctly requires actively driving mirror.   The shorter the throw angle or the higher the resolution, the more the power goes up.  Based off a published paper by Microvision from a few years back and datasheets from other makers of 1-D beam scanning mirrors, the power consumption of the Microvision mirror is about 0.3W to 0.5W (not exactly nothing).  There are “free oscillating” mirrors that consume much less power but these don’t produce a good scan for making a projector.

Next in Fig. 28 there is the DSP and MEMs ASIC.  The problem is that the mirror naturally wants to oscillate in a squiggly sinusoidal Lissajous pattern (see for example Microvision patent application 20090213040 ) which isn’t very good for generating video image.  To somewhat straighten out the Lissajous pattern (it still is not nice straight lines — more on that next time) takes power going to the mirror and power to constantly be calculating and correcting the scanning process.   The correction of the scanning process with the DSP and/or ASIC plus losses in the drive circuitry is probably taking about 0.5W.    So with the mirror itself and the drive circuitry and control of the mirror alone there is about 0.75W 1W being used.

The next big block in Fig. 28 is the “Video Control Module” (VCM) which is where most of the power is going.  Note that the HSYNC, VSYNC, and STATUS signals go from the MEMs Control Module to the VCM.   The reason is that the incoming image has to be stored and processed and distorted to match the scan process of the MEMs mirror.   Even with the active drive, the MEMs mirror does not move the laser beam in nice straight lines at a uniform speed.   In fact it moves in curves at a non-uniform speed and the VCM’s job is to re-shape/transform the image so that after it goes through the MEMs scanning it looks similar to the original image.

The VCM takes the digitized RGB data and stores it in the SDRAM.  I then processes/scales/transforms the image base on the distortion of the MEMs scanning process.  It then feeds the reprocessed image to the laser drivers.  All the read and writing to the DRAM and the processing by the ASIC/FPGA takes power, probably on the order of another 0.5W.

Next comes the power taken in driving the lasers.  To make a LBS system work, the laser beam has to be modulated (intensity changed) at high speeds which consumes significant power.   The lasers drivers are either analog (which consumes power) or have to be very high speed switching digital (which also consumes power) to give the various intensity levels for an image.  Even when displaying “black” this circuitry has to be “idling” to be ready to turn on in a few nanoseconds and is consuming power.   Likely 30% to 50% of the power going to the laser is being consumed in the laser drivers.

[Update 2011-12-22: The optics below show a polarization based combiner from the Microvision application.  My understanding is that Microvision currently is using dichroic mirrors instead of beam splitters for parts 610 and 612 and a total internal reflectance prism in place of beam splitter 614 to first reflect the light into the mirror and then let it pass out of the projector.  The light throughput for the dichroic mirror based combiner optics including the MEMs mirror is suppose to be about 60% which is the same number I used in the laser power calculations]

Now let’s get to the optics.  I have show below Figures 20 which is a simplified diagram and Figure 6 showing an optical module from the patent application.  To hear Microvision talk about it, you would think that only DLP and LCOS require optics and have losses from the optics.

The lasers 204, 206, and 208 have to have their beam shaped by lenses.  602, 604 and 606 each of which is probably losing about 1% of the light.   Then note that in order to combine them in a single beam, they have to go through mirror 608 and beam splitters 610, and 612.  There is roughly a 5% light loss in the mirror 5% to 10% in going through each beam splitter (note some lasers go through more than one beam splitter in the combiner).   Then you have the beam splitter 614 with another 5% to 10% loss, the quarter wave plate 2002 and another 2 to 4% loss that directs the laser light the MEMs mirror 616 which has about a 15% reflectivity loss, then back through the beam splitter with another 5% to 10% loss.   Taking all the optical losses together and only about 50% to 65% of the light from the lasers is going to make it out.

Finally, we have the losses from converting electrical energy to light energy in the lasers.   The frequency doubled lasers were reportedly getting about 6% WPE.    There is a lot of complicated math involving the wavelengths of the light the efficiency of the lasers for which I will use a spreadsheet to calculate the result assuming the lasers used by Microvision and about a 60% optical throughput from the optics.   The lasers themselves are taking on the order of 0.7 Watts.   remember that this number has to multiplied by about 1.3 to 1.5 to include the drivers for the lasers.  So the lasers and drivers alone are consuming about 0.9W to 1W.

Add it all up, subtract off the little bit from the batter circuit and the video-in chip and there is about 4 to 5 Watts being used by the LBS including its electronics.  Microvision can hand wave about saving 40% here and 20% there, but the problem is they have to save about 80% everywhere to get their power down to their “goal” of 1W.

Appendix:

Below is a figure taken from “Scanned Laser Pico projectors: Seeing the Big Picture (with a Small Device)” that shows a more simplified diagram than the one in Fig. 28 above.

Below is a top view of the inside of the ShowWX.

A typical Analog Devices analog RGB to Digital RGB converter AD9883A and it will take about 0.2W for WVGA resolution.

http://www.analog.com/static/imported-files/data_sheets/AD9883A.pdf

For anyone interested, I have added a picture showing the hottest point on the case.  It was roughly just above the large ASIC/FPGA in the picture above:

8 comments

  1. Mike Takeda says:

    Hi Karl

    Thank you for convincing analysis. I think it is mostly right!

    I wish you could make apple to apple comparison between flying spot vs. LCOS quantitatively.

    I know some disadvantages by LCOS + LD.
    – Need more complicated optics, DOA….etc correct?
    – LCD only works as a modulation SHUTTER which makes light loss
    – LCOS size decises pixel #,so there is trade-off of size and pixel # so that you want to embed modules onto Smart phones.etc.
    – It does not maintains focus-free in slanted cases.
    – Need field sequencial machanism with motor and wheel.
    – Higher LD peak power with lower duty.

    Mike

    • admin says:

      Mike,

      I hope to get to all this eventually, but it will take some time to write it all up and I will try and give you some quick responses below. See if I have answered you questions. There are definitely pros and cons to each technology. When analyzing power, you have to look at the whole system power before and after the light source.

      The optics are “different” but not necessarily more or less complicated, particularly when both use lasers. Both systems have to combine the R, G, and B into a single light source. Both need a beam splitter to direct the light toward the panel/mirror and then back out through a 90 (or close to 90) degree angle. Both have some beam shaping optics. Note that with LBS the alignment of the laser beam is much more critical than it is with LCOS. LCOS has to do a bit more to spread the light from a laser. LCOS also needs a projection lens; with lasers the projection lens is simple small and cheap (gets back to the optical properties of laser light) but it is more complex with LEDs. But if you look at the optics diagrams side by side there are not a lot of big differences.

      While LCOS does modulate the light that goes out, LBS has to (analog at hundreds of Megahertz or extremely high speed digitally) modulate the power driving the laser which can be very inefficient. In both cases there is “power wasted” but in different parts of the system. Note also that if you have “typical dark scenes” panels (DLP and LCOS) can dynamically change the light source power during dark scenes and save much of the power in a typical movie.

      LCOS has a lot of room to go in making the pixel smaller. It has some significant advantages over DLP in this regard. Certainly it is not a problem for making HD resolutions in a cell phone.

      If LCOS or DLP uses laser illumination, then they are focus free. It would take a lot to explain why (and it is another thing I hope to write up), but the AAXA L1 certainly was focus free and it used a Syndiant LCOS panel and lasers. I have demonstrated this many times in pubic. This is one of the many misconceptions that has be promulgated by the LBS companies, particularly Microvision.

      In pico projectors there is not a “motor and wheel” for sequential. It is all done by switching the LEDs or lasers.

      The difference in duty cycle between field sequential color and LBS is not as big as you would think. You have to look at all the factors. Once again this will take a while to explain and I hope to get to it.

      • Mike Takeda says:

        Karl

        Oh, I made a mistake that LCOS systems do not need wheel.etc if using 3 lasers or LEDs, but one white LED system needs wheel.etc.

        I agree with you that we need more data as apple to apple.

        Mike

        • admin says:

          I don’t think anyone is using a color wheel and white LEDs. There are companies using “white” (really blue LEDs with a phosphor to give more colors) with color filter LCOS for the very low end, low color quality products.

  2. Paul Cunningham says:

    Hi Karl,

    I’m just wondering why you have spent so much time on your personal blog, to make your point about LBS (Microvision in particular), when you said there was no point in even spending the time doing power measurements because they were not in the same league as your panel method? 
    I mean, why bother with this? I presume you will not allow this post on your blog, but the question needs to be addressed at some stage as I’m sure you must realize that you may as well rename your domain http://www.reasonswhymicrovisiondoesntwork.com instead of kguttag.com…
    If I employ your services as CES 2012, how do I know you will spend your time telling my clients about MY product, and not use it as another opportunity to rubbish LBS?

    Paul

    • admin says:

      Paul,

      I certainly understand that I am spending more time on Microvision than they probably deserve and frankly when I started this blog I wasn’t planning on spending so much time on them. I was trying to paint an accurate picture of the state of Green Lasers and unfortunately for Microvision and its fans, that runs afoul of the myths and innuendos they have been promulgating. When Microvision release and 8-K and Blog to “correct” what “false soothsayers” (clearly a veiled reference to me unless you know of a lot of other people that had been writing about green lasers availability) which questioned my integrity, I decided that it was only fair to show their past history of predictions.

      And besides, the weeks before Christmas are usually slow news weeks and nothing drives readership like a little controversy. There is a difference in what makes for an interesting blog and what makes sense to do as part of a company. Also, I happen to know a lot of the problems with LBS and have some pictures so it is easy stuff to write.

      As far as “leagues” go, show me any brand name company using Microvision’s products. They are ridiculously too expensive for their intended markets and their performance. Other than having spent an enormous amount of money promoting their concept, they are not really a factor in the market. I would have liked to have done a tear down power analysis of the ShowWX to show where all the power went with more precision, but like I wrote, it wasn’t worth the effort. The ShowWX consumes over 5W for just 10 lumens of output and the ShowWX+ is about 5W for about 15 lumens and they are not much more than bare bonds projectors. Anybody with a little technical ability can measure these facts. They are miles away from the “goals” they have been talking about for years. The burden of proof should be on Microvision to say how they are going to get the power into a rational range for embedding. What I tried to show is that they have been misleading people about their power consumption not once or twice but for many years.

      I understand that the LBS concept sounds simple and sounds like it would be really efficient, but I happen to have looked at it more detail than the casual investor, market analyst or person just following the technology and know better, or else Microvision is really dumb to have spent $400M to date and still be wasting 5W in the ShowWX — tell me which is it? I don’t think Microvision has dump technical people, the problem is that LBS is not the panacea that it is being made out to be by those working in LBS.

      If there is any worry in the pico projector industry it is that Microvision is going to burn a big ($400M+) hole in the ground and bring disrepute to the whole concept of pico projectors. They are also implying things about green lasers that the laser companies are not committed to doing and the laser companies are afraid they will be blamed for not delivering on promises they never made.

      I’m different from the other analysts and market reporters out there in that I am not out to make everybody happy and give “everyone a trophy.” Most analysts/reporters want to please all the companies in a market so they can sell their services, reports, and/or advertising. This certainly has a place, but I feel my place is to critically analyze what is going on. So if a company is to hire me, I don’t see my job, as many consultants do, to tell you how great and wonderful you are, but rather to tell you what your strengths and weaknesses are relative to the competition. I will try and give you an accurate picture of the market.

      So what you see as “trashing Microvision” I see as correcting the misleading information they have put out. I would welcome your finding factual errors with what I wrote. By taking a stand on the state of direct green lasers in 2012, you and others will have a way to judge my credibility versus Microvision’s. I expect that 2012 will validate what I have been reporting on green lasers.

      So what do you think. Do you think I am not telling the truth about the ShowWx’s power consumption. Do you think I am being too pessimistic about direct green lasers? What is it specifically you disagree with me about other than I should not pick on Microvision?

      Also, can you tell me why you care? If I am really a nobody with no credibility, how can it hurt Microvision? And you may notice that I let your comments go through exactly as you wrote them.

  3. JW says:

    Your original write up citing all the optics in the patent drawing are off. They do “shoot the beams directly” onto the MEMS. There is no polarization, and only dichro’s to combine. The patent shows cubes and a bunch of early conception, nothing like the final product ; )

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