Archive for Pico Projection

Navdy Launches Pre-Sale Campaign Today

Bring Jet-Fighter Tech to Your Car with NavdyIts LAUNCH Day for Navdy as our presale campaign starts today. You can go to the  Navdy site to see the video.  It was a little over a year ago that Doug Simpson contacted me via this blog asking about how to make a aftermarket heads up display (HUD) for automobiels.     We went through an incubator program called Highway1 sponsored by PCH International that I discussed in my last blog entry.

The picture above is a “fancy marketing image” that tries to simulate what the eye sees (which is impossible to do with a camera as it turns out).   We figures out how to do some pretty interesting stuff and the optics works better than I thought was possible when we started.    The image image focuses beyond the “combiner/lens” to help with the driver seeing the images in the far vision is about 40 times brighter (for use in bright sunlight) than an iPhone while being very efficient.

Navdy Office

Being CTO at a new start-up has kept me away from this blog (a start-up is very time consuming).  We have raise some significant initial venture capital to get the program off the ground and the pre-sale campaign takes it to the next level to get products to market.  In the early days it was just me and Doug but now we have about a dozen people and growing.

Karl

Whatever happened to pico projectors embedding in phones?

iPad smBack around 2007 when I was at Syndiant we started looking at the pico projector market, we talked to many of the major cell phone as well as a number of PC companies and almost everyone had at least an R&D program working on pico projectors.  Additionally there were market forecasts for rapid growth of embedded pico projectors in 2009 and beyond.  This convinced us to develop small liquid crystal on silicon (LCOS) microdisplay for embedded pico projectors.  With so many companies saying they needed pico projectors, it seemed like a good idea at the time.  How could so many people be wrong?

Here we are 6 years later and there are almost no pico projectors embedded in cell phones or much else for that matter.   So what happened?   Well, just about the same time we started working on pico projectors, Apple introduced their first iPhone.    The iPhone overnight roughly tripled the size of the display screen of a smartphone such as a Blackberry.  Furthermore Apple introduced ways to control the screen (pinch/zoom, double clicking to zoom in on a column, etc.) to make better use of what was still a pretty small display.   Then to make matter much worse, Apple introduce the iPad and tablet market took off almost instantaneously.    Today we have larger phones, so called “phablets,” and small tablets filling in just about every size in between.

Additionally I have written about before, the use model for a cell phone pico projector shooting on a wall doesn’t work.   There is very rarely if ever a dark enough place with something that will work well for a screen in a place that is convenient.

I found that to use a pico projector I had to carry a screen (at least a white piece of paper mounted on a stiff board in a plastic sleeve to keep clean and flat) with me.   Then you have the issue of holding the screen up so you can project on it and then find a dark enough place that the image looks good.    By the time you carry a pico projector and screen with you, a thin iPad/tablet works better, you can carry it around the room with ease, and you don’t have to have very dark environment.

The above is the subjective analysis, and the rest of this article will give some more quantitative numbers.

The fundamental problem with a front projector is that it has to compete with ambient light whereas flat panels have screens that absorb generally 91% to 96% of the ambient light (thus they look dark when off).     While display makers market contrast number, these very high contrast numbers assume a totally dark environment, in the real world what counts is the net contrast, that is the contrast factoring in ambient light.

Displaymate has an excellent set of articles (including SmartPhone Brightness Shootout, Mobile Brightness Shootout 2, and Smartphone Shootout 2) on the subject of what they call “Contrast Rating for High Ambient Light” (CRHAL)  which they define as the display brightness per unit area (in candela’s per meter squared, also known as “nits”) of the display divide by the reflectivity of ambient light in percent by the display.

Displaymate’s CRHAL is not a “contrast ratio,” but it gives a good way to compare displays when in reasonable ambient light.  Also important, is that for a front projector it does not take much ambient light to end up dominating the contrast.  For a front projector even dim room light is “high ambient light.”

The total light projected out of a projector is given in lumens so to compare it to a cell phone or tablet we have to know how big the projected image will be and the type of screen.   We can then compute the reflected light in “nits”  which is calculated by the following formula Candelas/meter2 = nits = Gn x (lumens/m2)/PI (where Gn is the gain of the screen and PI = ~3.1416).   If we assume a piece of white paper with a gain of 1 (about right for a piece of good printer paper) then all we have to do is calculate the screen area in meters-square, multiply by the lumens and divide by PI.

A pico projector projecting a 16:9 (HDTV aspect ratio) on a white sheet of notebook paper (with a gain of say 1) results in 8.8-inch by 5-inch image with an area of 0.028 m2 (about the same area as an iPad2 which I will use for comparison).    Plugging a 20 lumen projector in to the equation above with a screen of 0.028 m2 and a gain of 1.0 we get 227 nits.  The problem is that same screen/paper will reflected (diffusing it) about 100% of the ambient light.   Using Displaymate’s CRHAL we get 227/100 = 2.27.

Now compare the pico projector numbers to an iPad2 of the same display area which according to Displaymate has 410 nits and only reflects 8.7% of the ambient light.   The CRHAL for the iPad2 is 410/8.7  = 47.   What really crushes the pico projector by about 20 to 1 with CRHAL metric is that the flat panel display reflects less than 10th of the ambient light where the pico projector’s image has to fight with 100% the ambient light.

In terms of contrast,to get a barely “readable” B&W image, you need at least 1.5:1 contrast (the “white” needs to be 1.5 brighter than the black) and preferably more than 2:1.   To have moderately good (but not great) colors you need 10:1 contrast.

A well lit room has about 100 to 500 lux (see Table 1 at the bottom of this article) and a bright “task area” up to 1500 lux.   If we take 350 lux as a “typical” room then for the sheet of paper screen there are about 10 lumens of ambient light in our 0.028 m2 image from used above.   Thus our 20 lumen projector on top of the 10 lumens of ambient has a contrast ratio of 30/10 or about 3 to 1 which means the colors will be pretty washed out but black on white text will be readable.  To get reasonably good (but not great) colors with a contrast ratio of 10:1 we would need about 80 lumens.   By the same measure, the iPad2 in the same lighting would have a contrast ratio of about 40:1 or over 10x the contrast of a 20 lumen pico projector.   And the brighter the lighting environment the worse the pico projector will compare.    Even if we double or triple the lumens, the pico projector can’t compete.

With the information above, you can plug in whatever numbers you want for brightness and screen size and no matter was reasonable numbers you plug in, you will find that a pico projector can’t compete with a tablet even in moderate lighting conditions.

And all this is before considering the power consumption and space a pico projector would take.   After working on the problem for a number of years it became clear that rather than adding a pico projector with its added battery, they would be better off to just make the display bigger (ala the Galaxy S3 and S4 or even the Note).   The microdisplay devices created would have to look for other markets such as near eye (for example, Google Glass) and automotive Heads Up Display (HUD).

Table 1.  Typical Ambient Lighting Levels (from Displaymate)

Brightness Range

Description

0 lux  –

100 lux  –

500 lux  –

1,000 lux  –

3,000 lux  –

10,000 lux  –

20,000 lux  –

50,000 lux  –

100,000 lux  –

100 lux

500 lux

1,500 lux

5,000 lux

10,000 lux

25,000 lux

50,000 lux

75,000 lux

    120,000 lux

Pitch black to dim interior lightingResidential indoor lighting

Bright indoor lighting:  kitchens, offices, stores

Outdoor lighting in shade or an overcast sky

Shadow cast by a person in direct sunlight

Full daylight not in direct sunlight

Indoor sunlight falling on a desk near a window

Indoor direct sunlight through a window

Outdoor direct sunlight

Extended Temperature Range with LC Based Microdisplays

cookies and freezing

Extreme Car Temperatures

A reader, Doug Atkinson, asked a question about meeting extended temperature ranges with LC based microdisplays, particularly with respect to Kopin.    He asked the classic “car dash in the desert and the trunk in Alaska” question. I thought the answer would have broader interest so I decided to answer it it here.

Kopin wrote a good paper that is available on the subject in 2006 titled “A Normally Black, High Contrast, Wide Symmetrical Viewing Angle AMLCD for Military Head Mounted Displays (HMDs) and Other Viewer Applications”. This paper is the most detailed one readily available describing the how Kopin’s transmissive panels meet the military temperature and shock requirements.  It is not clear that Kopin uses this same technology for their consumer products as this paper is specifically addressing what Kopin did for military products.

With respect to LC microdisplays in general, it should realized that there is not a huge difference in the technical spec’s of the liquid crystals between the LC’s  most small panel microdisplays use and large flat panels in most cases. They often just use different “blends” of the very similar materials. There are some major LC differences including TN (twisted nematic), VAN (vertically aligned nematic), and others.   Field sequential color are biased to wanting faster switching “blends” of the LC.

In general, anywhere a large flat panel LC can go, a microdisplay LC can go. The issue is designing the seals and and other materials/structures to withstand the temperature cycling and mechanical shock which requires testing,  experimentation, and development.

The liquid crystals themselves generally will go through different phases from freezing (which is generally fatal) to heating up to the the “clearing point” where the display stops working (but is generally recoverable).  There is also a different spec for “storage temperature range” versus “operating temperature range.” Generally it is assumed the device only has to work in a temperature range in which a human could survive.

At low temperature the LC gets “sluggish” and does not operate well but this can be cured by various “heater mechanisms” including having heating mechanisms designed into the panel itself.  The liquid crystal blends are often designed/picked to work best at a higher temperature range because it is easier to heat than cool.

Field sequential color LCOS is more affected by temperature change because temperature affects not only the LC characteristics, but the switching speed. Once again, this can be dealt with by designing for the higher temperature range and then heating if necessary.

As far as Kopin’s “brightness” goes (another of Doug’s questions), a big factor is how powerful/bright the back light has to be. The Kopin panel blocks something like 98.5% of the light by their own spec’s. What you can get away with in a military headset is different than what you may accept in a consumer product in terms of size, weight, and power consumption. Brightness in daylight is a well known (inside the industry) issue for Kopin’s transmissive panels and one reason that near eye display makers have sought out LCOS.

[As an aside for completeness about FLC]  Displaytech which was sold the Micron and then sold to Citizen Finetech Miyota and the Kopin bought Forth Dimension Display (FDD) both use Ferro-electric LC (FLC / FLCOS) which does have a pretty dramatically different temperature profile that is very near “freezing” (going into a solid state) a little below 0C which would destroy the device. Displaytech claimed (I don’t know about FDD) that they had extended the low temperature range but I don’t know by how much. The point is that the temperature range of FLC is so different that meeting military spec’s is much more difficult.

Sony and Sumitomo

Sorry for being away from the blog so long.  I had two big “consulting gigs” come in one right after the other and I have been working virtually non-stop for the last 6 weeks.  There has been a lot of news come in that period in the area of displays and lasers and I will try and get caught up on some of it.

Today I would like to talk about Sony and Sumitomo announcement of a 530nm 100mW Green laser with 8% efficiency.  At least on the surface, this appears to be a big improvement what Soraa, Osram, and Nichia have announced to date.   But the big question is whether this really changes anything for pico projectors?

Semiconductor laser diode/True green laser emitting

Sumitomo and Sony 530nm Direct Green Laser Diode

Sony was much quieter than Soraa, OSRAM and Nichia but it certainly should have been expected since they developed blue lasers for blue ray (see for example from 2007 “Sony’s Blue Laser Diodes Down to $8 – PS3 and BD Player Price Cuts Soon?”).  Sumitomo had announce they were working on green laser materials back in 2010 but they were not known as a maker of laser diode end products and were thought to be a material supplier (to Sony as it turns out).

Another company to watch would be Opnext who is a leader in red lasers and announced a blue laser diode back in January 2011. All the green laser diode developments I know of came from “stretching” their blue laser developments to get green.

Certainly the Sony-Sumitomo device looks on the spec’s to be significantly better than other companies’ prior announcements with a 100mW, 530nm wavelength (huge improvement over the others), and 8% efficiency.  When you factor in the luminous efficiency at 530nm, they appear to have about double the lumens/Watt of any other green laser announcement I have seen.

Something else to consider, Sony has long been a manufacture of LCOS devices so I would suspect (I have no inside knowledge) that Sony would be looking to couple this laser with their LCOS developments.  They also have the ability to make some very small pixels from their in high resolution LCOS devices.  But the question is whether they and support field sequential color which it necessary for making small embeddable devices.  It should be noted that Sony has a line of  embedded pico projectors in video cameras that use TI’s DLP®

With all this activity and the seeming much improved spec’s from Sony-Sumitomo does this change everything and will laser projectors soon be everywhere?  Unfortunately, I don’t see this as changing things much, at least in the next year few years.

Now the bad news and just based on what they have said.  A 100mW 530nm green laser only supports about a 20 lumen projector which is pretty dim except for a pretty dark room or a very small image. A projector using an 8% WPE green laser probably does not have net an efficiency advantage (after factoring in all the pro’s and con’s) over a good LED projector with at 20 lumens.  While this might have been an interesting product a couple of years ago, the market has mostly moved on to higher lumen projectors.

And then we have to some questions that were not in the release.  Such as how far away is the Sony-Sumitomo green laser diode is from being a product and how much will it cost. Today a green LED to support a 20 lumen projector probably costs about $2. I think there is a serious question as to whether a ~20 lumen project has a value proposition today even if the lasers were inexpensive by the time you factor in the rest of the projector cost.

My bottom line is that it looks like Sony and Sumitomo have made some great technical progress, but it is does not appear to be enough to have a seriously competitive volume product in the market any time soon.    Anyway, that is the way I see it,

Karl

Soothsayer 7: Microvision’s Obfuscations Causing a Buzzing Sound

Microvision continues to make thinly veiled accusations against this blog in their May 9th, 2012 Company Displayground Blog (quoting directly with my bold emphasis added):

Our shareholders are following the topic of direct green lasers with avid interest and we get a lot of questions from them on price and availability. They have ridden the green laser wave with MicroVision and are understandably anxious for their investment and patience to pay off. There is another group of MicroVision watchers that take an active interest in direct green lasers and for that matter, all things MicroVision and have quite a bit to say. We welcome such interest as we are really proud of what our patented solution can do and the advancements we have made with the PicoP Gen2 display technology. But it does get tiring to have an open mic of misinformation from parties who only seem to have an interest in not seeing Microvision succeed. We try and ignore this contingent just like the best thing to do when a fly is buzzing around your head is to ignore it. Eventually the fly finds something or someone else to buzz around and the problem resolves itself.

Like most things Microvision writes they raise more questions than they answer.  For example, who is this “group” of watchers that “ have quite a bit to say” about green lasers?  As far as I know, this is the only blog regularly writing about green lasers for small projectors.   I guess they feel like I have them surrounded :-).   I would suggest that the real reason they cannot ignore the “buzzing sound” is that is goes contrary to Microvision’s attempts at obfuscation and eventually their investors and analysts ask questions.

I take the most interest went key specs are missing or when states what is at best a half-truth.  From what I read, Microvision obfuscates, uses straw-men, half-truths,  give meaningless ratios of improvements, and state goals/expectations as if they have been met.  They could put this all to rest if they could be specific about what they consider “misinformation” and give direct clear answers.  

$200 Green Laser Clarification:

Microvision’s blog when on to clarify(?) what Microvision’s Lance Even’s was saying green lasers costing nearly $200 that I address in my April 30th blog.  Quoting directly from the Microvision Blog:

The price of direct green lasers is understandably a topic of speculation since the manufacturers of the diodes have not publicly discussed pricing or even the exact timing of commercial availability. We cannot reveal specifics around these issues, but we can and have stated that we expect the prices of direct green lasers to be significantly less than synthetic green lasers which have cost nearly $200.

Microvision, apparently in response to my blog on the “nearly $200” price of DGL clarified that Mr. Evan’s $200 remark was in reference to the synthetic green lasers.   But note it is only an “expectation” (as in some time in the future) that the prices will be lower.

It is also interesting that Microvision is admitting publicly that the lasers were costing them nearly $200 (or maybe more at some point).  You have to wonder why they went to market with the ShowWX using a $200 laser for projector with only 10 to 15 lumens.  Can you imagine what investor reaction would have been back in 2009, 2010, or 2011 if they knew that Microvision was selling a supposedly high volume consumer product with a $200 laser in it?   My speculation is that unless they agreed to pay $200 for the lasers and buy a lot of them, that they would have had no way to build any product and if they couldn’t show (some pun intended) and that would make it impossible to raise money.   To keep investors on the hook, so to speak, they had to use obfuscation about the cost of lasers (some things never seem to change).  The losses on the ShowWx were essentially marketing expenses to raise money from the “shareholders” that were following the company back then.

They seem to have made the calculation that they needed to loose many millions of dollars on the ShowWx product line in order to keep the investor money flowing in.  Now that they consider those losses in the rear view mirror, they are admitting to them.   I wonder when they will come clean on the cost and specs of today’s direct green lasers.

More Half-Truths from Microvision

One more interesting set of half truths from Microvision’s blog:

We are confident that the manufacturers of the direct green lasers will be able to meet the volume requirements as the market demand for direct green lasers grows, and we expect price to fall accordingly.”

The first half-truth is that “manufacturers of the direct green lasers will be able to meet the volume requirements.”  Yes, this is true today, but only because the volumes will be very low.   Among the reasons is that the price of the lasers will be very high and that they are not currently designed into any high volume products.   Secondly, by laws of supply and demand, if the lasers are expensive few will be bought and thus they will meet the volume requirements.  Thirdly, the growth in the market could be very slow so it would be easy to meet what Microvision “expects.”    In short, Microvision like a politician, used a lot of words to give no real information.

What Microvision won’t admit, I suspect because that would be bad for raising money, is that the direct green laser has so far proven difficult to make due to the physics involved.    Certainly very smart and capable people are working on DGL, but they are not ready in the near future for the high volume consumer products.

Soothsayer 6: Microvision’s Lance Evans “Green lasers alone are $200 each now”

First, sorry for being away so long.  Some family and other matters took me a way and I fell out of the habit of posting.  I am going to try to have at least couple of posts up a week.

My “Soothsayer” series started back in December 2011 when Microvision released an 8-K a very trasparent response to this blog.  In Microvision’s Dec. 19th 2011 8-K they stated ““In the coming weeks we intend to provide a series of posts that discuss direct green lasers in more detail, as well as other business updates. Stay tuned!”

Well, it has been 19 weeks since Microvision’s 8K and there has been pretty much silence from them on “more details.”  Microvision has had plenty of opportunities to add “more details” in the last 5 months but has chosen not to.  They say a “slip in Washington is when you accidentally tell the truth” well maybe Microvision did that today.

In a way, Microvision finally broke the silence with an article today in an April 30th Technology Review article with Lance Evans (a director of business development at Microvision) stating, “Green lasers alone are $200 each now.” Remember this is probably for a green laser that supports on the order of a 15 lumen projector and has a wavelength that is too short (too blue) to be used in a typical projector and it not very efficient in terms of lumens per Watt. These are lasers that are a best useable in a car HUD display and not a batter powered cell phone or hand held projector.

Back in December 2011 Microvision’s 8K stated, “DGLs will be much cheaper than synthetic green lasers at introduction.”  How does this fit with DGL’s costing $200 today? 

The article does day that “Evans expects that costs should fall to a tenth of current levels by the end of this year,” but note the word “expects” is corporate speak for “believe, wish, hope, or dream” because you generally can’t hold them legally accountable for an “expectation.”  What other than a wish causes the direct green laser cost road map to drop from $200 now to one-tenth that cost or $20 in less than 7 months?  Are there people lined up to buy lasers first at $200, then $100, then $50 say to support a 15 lumen projector?  None of this makes any business sense.

Even if Mr. Evans “expectations” come true, and DGL drop by 10x in less than 7 months to $20 by the end of the year (really for 2013 production), is this really a viable business?   By comparison, there are 200 lumen LED base projectors on the market today and the cost of the red, green, and blue LEDs combined cost less than $20 today.   For a 15 lumen LED projector today, the LEDs are more like $3 for the RGB set.  For a pico projector to make it into a cell phone, the cost to the cell phone maker of the whole projector including electronics has to be on the order of $25 or less (just ask any cell phone maker, I have asked many).  You can even come close with even a $10 DGL, no less 20, when you factor in the cost of everything it takes to make a projector including optics and electronics.

I’m a long term believer that eventually all projectors and in fact a vast number of other products will be using lasers.   It is just going to take more than 2 year for the brilliant people at the laser manufactures to figure out how to make the direct green lasers at a cost point that will lead to mass adoption.

Soothsayer 5: Thanks for the “Shout Out” on the Microvision Conference Call!

It’s nice to know that a CEO of a public traded company is following my blog.   On today’s Microvision Conference Call (available for a few days) at 34:16 in the call, Microvision CEO, Alexander Tokman, in his closing remarks gave a “shout out” of sorts with,  “The direct green laser is becoming a reality this year and not 2014 as some led you to believe.

As anyone that has followed Microvision or my blog and my comments on direct green lasers the last few months should know, by “some” he means “me.”   First, he has mischaracterized what what has been written.    What I have written is that direct green lasers will not be practical for high volume applications until 2014 or beyond.

As I wrote Microvision’s “Soothsayer(?)” for their “Number One Question” in  response to me in Microvision 8K’s “false soothsayer” comments:

The real question is whether these lasers will be available at a price point, with a wavelength, and an efficiency that is practical.   I don’t doubt that most if not all the companies will be in production with a green laser in 2012, but what constitutes “mass production” is a different matter.   Nichia already has a 510nm green laser in production, for example, and it might be possible to build a heads up display for an automobile with it (albeit a bit expensive for the purpose), but that is clearly impractical in terms of wavelength, efficiency, and cost for building a high volume battery powered projector.   I also question whether they will be bright enough for a volume product other than a HUD.

Instead of addressing the real issues, Microvision has seen fit to play silly word games with the definition of word “commercial.”   “Commercial” simply means that companies will sell a product with a given spec.  It does not mean the that product, in this case a Direct Green Laser will meet the cost and performance requirements for a high volume application.  The reality is that the “commercial” direct green lasers are going to be available in 2012 (and 2013) are going to be way too expensive and with key performance limitations  for any kind of significant volume consumer products.

Now lets look at the math in Microvision’s timeline.  At 15:50 into the conference call Alexander Tokman talks about their commercialization timeline for a consumer product.    He said they hope to have a company committed by “mid year 2012” and that companies will generally take “6 to 18 months” to develop a product.   If you follow Microvision at all, you will note that Mr. Tokman timelines are usually wildly optimistic, but just taken him at his word with a “start” in mid 2012 and more realistically 12 to 18 months to get a product designed and ready for production adds up to products STARTING to be manufactured (not even high volume) in late 2013 to mid 2014 if (and this is a big if) everything goes according to Mr. Tokman’s hopes.

But given Mr. Tokman’s history of over optimism, this would seem to say that he is really talking 2014 or later; oh but wait, he said in the conference call that it was “not 2014 as some led you to believe.”     So which does his mean?

TI DLP® “Diamond” Pixel

Fig. 1 DLP Diamond Pixel (above) compared to test pattern (below)

TI’s DLP® WVGA (848×480) and WXGA (1280×800) microdisplays use what are commonly known as “diamond” pixels.  This article will explain what these pixels look like, their effect on image quality, and the reason behind diamond pixel.

As a side note: all the pictures of projected images were taken on a Qumi 1280×800 projector using the HDMI (digital) input driven at the “native” 1280×800 resolution to try and give the best possible source image.

Diamond Pixel Organization

Fig. 2 Diamond Pixel Column and Row Numbering

Fig. 2 Show how the “diamond pixels” are organized.  The pixels themselves are square, but they are rotated 45 degrees and fit like tiles in a zig-zag arrangement.  The Columns and row numbering are based on how the memory bit (signified by the red dot in Fig. 2) for each pixel is address.  You should notice that the columns numbering is more spread out than the row numbering.  For a WVGA (848×480) there are 608 columns [roughly 848/sqrt(2)] and 684 rows [roughly 480xsqrt(2)].  Note that if you multiple 608 x 864 you will get slightly more than 848×480 so there are roughly the same number “pixels.”  Details on this organization for the WVGA can be found in the DLP® 0.3 WVGA Series 220 DMD data sheet.   For the WXGA (1280×800) there are about 910 columns by 1136 rows (the datasheet is not publicly available).

Image Re-sampling Effect of Diamond Pixels

Fig. 3 Simplified Diamond Pixel Re-sampling

The image quality issues with diamond pixels comes from trying to “re-sample” (remap) the pixels from a normal square grid to the “diamond grid.  Fig. 3 Show shows a simplified example of the problem.  There are two black pixels labeled “A” and “B” shown.  On the left side of the figure, the green grid shows the normal/square array of pixels and it is overlaid with the the diamond grid in red.  As can be seen pixel A straddles/touches pixels 1 through 5 in the diamond grid and pixel B straddles pixels 5 though 11.   There is no really good way to map the pixels.  If you you just mapped to the nearest pixel on the diamond grid, it would cause severe jaggies, so it is best to re-sample/filter the pixels onto the diamond grid.

On the right hand side of Fig. 3, I did a simple weighting of the areas of overlap to remap the pixels.   Notice how the pixels have blurred out.  Also notice that the two black pixels end up mapping into different shapes in on the diamond grid because their relative alignment between the square and diamond grid is different.

TI’s DLP uses more complex algorithms than those used in Fig 3 that attempt to reduce the blurring by sharping (particularly in the horizontal direction) or allowing more jagged artifacts (in the vertical direction).  Any algorithm/filtering/re-sampling by necessity will be a compromise between jagged pixel artifacts and blurring. 

Fig. 4 below shows a close-up of a series of simple test patterns of a checkerboard, horizontal lines, and vertical lines with a picture of the projected image from a test pattern.    The checkerboard is pretty well obliterated in the DLP’s re-sampling process and you see what is known as a classic under-sampling problem where you see the “difference frequency” or a low resolution version of the repeating pattern.  It is also interesting is that the artifacts are different in the horizontal and vertical direction because they use different re-sampling algorithms horizontally and vertically.

Fig. 4 Closeup of Checkerboard, Horizontal Lines, and Vertical Lines compared to test pattern

Fig. 5 below shows more more of the test pattern (click on image to see all the detail – at the end of this article, I have included the whole the test image used so you can duplicate this test).   The longer lines in the test pattern are suppose to be 4 alternating black and white lines.  Where the 4 line pairs cross there are some strange effects (one of which is circled).   On vertical lines or groups of lines there is the occasional “ghost line” (some of which are pointed to with red arrows); these are as a result of the horizontal filtering/re-sampling process.   Vertical lines generally look a little better but they have that ghosts lines (“sharpening halos”) as a result of trying to keep from loosing sharpness.

The vertical re-sampling process (which shows up in horizontal lines) is much simpler and results in more jagged artifacts and less effective resolution.   You can also see in the dot in the letter “i” in the “8 Point Arial” how a single pixel blurs out over multiple pixels in the diamond grid of pixels.  Notice how all the dots in the “i’s” vary (circled in red) and in the Arial 10 point font the dots in the letters “i” even point in different directions.

Fig. 5 Diamond Pixel Projected Image of Center of Test Pattern

Why DLP Uses Diamond Pixel

The “marketing spin” I have heard for the diamond pixel organization is that it can give perceptively better resolution.  But this could only be true if the source image is much higher resolution than the displayed image.  As the pictures above demonstrate, about the worst case image is to drive the Diamond Pixel with its supposed “native” resolution.

At least one real reason that the TI DLP® uses the diamond arrangement is to try and reduce the projector’s thickness.   DLP’s require “off axis illumination” which means the light comes into the mirror array non-perpendicular to the surface.  When the mirror is tilted “on,” the angle of the mirror directs the light toward the projection lens. The current DLP mirrors tilt approximately +/- 12 degrees and they tilt diagonally (at 45 degrees).

Fig. 6 Light Paths for “Square” versus “Diamond” Pixel Arrangement

With normal/square mirror arrays (left half of FIG. 6) this would mean that for light to go out of the projector the light must come from above or below projection lens.  But in order to have the illumination light come from above or below the projection lens would make the projector much thicker.   This was not an issue for DLP in RPTVs or larger data projectors, but with Pico Projectors, customers care a lot about thickness.   The “Diamond Mirror Solution” was to rotate the mirrors so that the light could be in the same plane (right half of Fig. 6) as the projected image.

Conclusions

While the diamond pixels address the thickness issue, they definitely hurt resolution and cause artifacts and a loss of resolution.  The obvious problem is that a single pixel on a rectangular grid will cover part of at least 4 or more pixels on the diamond grid.  So there has to be some scaling/filtering to map the pixels from the rectangular grid onto the diamond grid.   The DLP ASIC tries to combat this blurring in the horizontal direction by filtering and sharpening.  The vertical processing is simpler and results in more jaggies.

Many of the problems with DLP’s diamond pixel are closely related to the resolution problems of Laser beam scanning that I wrote about in a previous article (see: http://www.kguttag.com/2012/01/09/cynics-guild-to-ces-measuring-resolution/).  Namely, it is the problem of trying to re-sample the original image to fit a grid or scanning process that does not match the original image.  Even if the number of “pixels” is the same, the re-sampling process hurts resolution and causes unwanted artifacts (for those engineers in the audience, it is a classic Nyquist sampling issue).

In optical terms DLP optics are “off-axis” which means the illumination of the display is not perpendicular to the imager.  Off-Axis optics are always bigger and their light path takes up more volume.  The diamond rotation keeps this volume from increasing thickness, but still the volume of a DLP optical engine tends to be bigger for the same F-number and Focal Length optics.   In general, DLP “pico projectors tend to have longer throw ratios (longer focal length lenses) and this may be due to trying to keep the optics from becoming larger.

Appendix

Below is the test pattern used to create the images above on a DLP 1280×800 projector.  To use this correctly, you need to drive the HDMI input of the projector at 1280×800.

I have included a similar test pattern for WVGA (848×480) that can be used with the WVGA DLP projectors like the PK201 or  Microvision’s ShowWX/+/HDMI projectors.  Additionally, I have included a 720p (1280×720) version of the test patter in case you come across a 720p projector.

I would like to thank Paul Anderson for taking the picture of the test pattern on his 1280×800 DLP Qumi Projector that I used in this article.

1280×800 Test Pattern:

848×480 Test Pattern:

720P Test Pattern:

Answering Questions on Laser with LCOS and LBS

Syndiant 720p LCOS Panel

I got asked a series of questions by reader “me_wwwing” after the article Laser with LCOS is Focus Free — Yes Really! that I am answering in this post because I thought they would be of general interest.  I did have to edit a few of the questions for clarity but tried to keep the intent as best I could and I have re-ordered the questions to put what I think are the more interesting questions first.   For background for the reader I need to add that from prior questions and comments, I know me_wwwing to be a fan of Microvision’s laser beam scanning (LBS) so that may color some of the questions and the answers.

Q1. Does Syndiant need to use the same lasers as MVIS [Microvision laser beam scanning (LBS)]?

The simple answer is that LCOS panels can use any of the lasers that LBS can use and can use lasers that LBS cannot use.   LBS puts constraints on both Diode Pump Solid State Lasers (DPSS also known as “synthetic” or “frequency doubled) and for direct diode lasers (DGL).

Answer Part 1: DPSS Green Lasers

First, Syndiant makes the LCOS microdisplays and not the entire optical engine.     A panel (LCOS or DLP) optical engine has a wider selection of lasers that it can use both for direct green lasers as well as DPSS green lasers.   So the quick answer is that it can use any of the lasers that a LBS system can use plus it can use laser types and variation that LBS cannot use.

With DPSS green lasers, panels could use the less expensive to make and much more electrically efficient (generally about 2X the efficiency) slower switching lasers.  The slower switching frequency doubled lasers are capable of greater than 12% wall plug efficiency (WPE) with the desirable 532nm wavelength green.   About the best the fast switching frequency double green lasers ever got to was about 6% WPE.

The slower switching DPSS greens are capable of going to very high brightness; they can be over 10 times brighter than today’s Direct Green Diode Lasers (DGL).   Their electrical to lumen efficiency is over 3X the best DGLs today.   And their cost is lower than DGLs.   But the drawbacks to DPSS greens include the size and the small spectral bandwidth that causes higher speckle.

Answer Part 2: Direct Green Diode Lasers (DGL)

It turns out that there are different kinds of direct-diode lasers as well.  Most notably there are “single mode” and “multi-mode” lasers.

LCOS or DLP can use either the single-mode or multi-mode lasers, but lasers LBS can only use single-mode lasers.   Multi-mode lasers change wavelength, phase, and/or optical polarity somewhat randomly.  The rate of mode changing would look like noise in a LBS scanning process so it is unusable in an LBS system, but in a panel (LCOS or DLP) system the hopping simply gets average out as it is faster than the eye can detect.

Since changing wavelength and phase reduces speckle, multimode lasers have less speckle.  It turns out that lasers naturally want to mode hop, so it is easier (cheaper) to make multimode lasers, multimode lasers are more electrically efficient and multi-mode lasers can be made much brighter/more powerful (in fact, as they make the laser cavity bigger to make lasers more powerful it is hard to keep them from mode hopping).  So panel based projectors have a significant advantage in being able to use multi-mode lasers.

Historically, traditional laser uses such as telecom and interferometry, needed single mode lasers.   But the same coherent light for these applications is what causes speckle, so for panel based projectors you want “poor quality” lasers with less coherency and thus speckle.

Q2. How big is Syndiant Controller?

The Syndiant’s 720p ASIC is currently 9mm X 9mm in its current package, but could be put in a significantly smaller package by reducing the pin count for an embedded cell phone.  The current package has a lot of extra pins for supporting a mix of applications that make it bigger.

Q3. What are the dimensions of Syndiant’s PCB?  The new one or the old one to have a starting point.

Syndiant sells the panel and the driver ASIC and not a PCB per say.  Single SYA1231 ASIC for their 720p is currently 9mm x 9mm includes frame buffer memory and ARM CPU and can be put in a smaller package for embedded applications.    So there really isn’t much in the way of board space for the new Syndiant 720p controller.  Basically, it is just one small chip 9mm X 9mm chip and not a “PCB” per say.

Syndiant’s single small ASIC compares extremely favorably to the Microvision 720p board which has 2 custom ASICS (one about ~11mm x 11mm and the other ~10mm x 10mm)  and an Altera FPGA (~6mm x 6mm)  on it.  There is also a 4th I.C. on their board which is an Intersil laser driver (5mm x 5mm).   The  picture below is from www.technogytell.com with my notes added it:

Microvision "720p" Optics and Driver Board

Totalling up the area of Microvision’s two ASICs and FGPA, Syndiant’s current control ASIC takes about 1/3rd the area and 1/3rd the ICs of Microvision’s 3 chip controller.   Also just looking at all the power conversion circuitry required in the Microvision “720p” board suggests that it needs a lot of different voltages with some significant power requirements and all this adds cost, board space, and power.

Q4. What size diagonal lens (encased) does Syndiant’s displays need to cover the diagonal of the display?  A length too would be nice. old specs are ok to start with [assuming laser illumination]

The diagonal of the “active display” of the older SYL2010 was 0.21”.  It had a 5.4 micron (10-6 meter)  pixel such that an 800 pixel high display was 4.3mm.   The lens would need to be a bit thicker than this diagonal.  For a small high volume product the lens would be cut to a more rectangular than circular shape to reduce height.   So the lens could be about 6 mm thick.   The SSTDC SEE100 prototype engine http://www.picoprojector-info.com/laseno-see100-module-photo  engine’s lens with its barrel was non-optimized (circular) and was about 8mm thick and 8mm long.  An optimize rectangular-cut lens could have been about 5mm tall.

There is nothing keeping LCOS with laser illumination from going below 5 micron pitch (they will eventually get to around 3 micron and perhaps less) for its pixels.   At about 5 microns the active display for a 720p would be about 3.6mm tall.  A rectangular cut lens would then be about 4.5mm to 5mm tall or a round lens would be about 7mm tall.

Q5. Does the dichroic color combiner lens need to cover the surface of the Vibrating Despeckle unit [the answer addresses the broader question of the light combining system for LCOS and LBS]?

No, the light is not significantly spread out before the dichroic color combiners in an LCOS system.  Also the alignment of the dichroic mirrors/filters and the lasers is non-critical in an LCOS or DLP optical engine.

In should note, however that the alignment of the lasers and the dichroic combiners is very critical in an LBS design.  You should note in this teardown picture (picture taken from a laserpointerforums) that I have labeled the two ball shaped optics (pointed to in magenta) used to aligned the red and blue lasers and then glued into place.   The need to critically align the lasers adds cost and quality issues into to the manufacturing process.

Microvision ShowWX (WVGA) Optics

 

Q6. What is the power to run the PCB and the light engine on a Syndiant’s Displays? (SVGA and WVGA).

That really is a complex and involved question and depends on a lot of factors including the optical engine design and the target brightness.  I am also assuming that this is with LED illumination.   With LEDs the lumens per Watt of power tends to go down as the projector gets brighter, that is one of the advantages with lasers, namely that efficiency does not go down with power. 

It is helpful to break the power into two part, the panel and controller electronics and then the illumination and optics.   For low lumen (less than 30 lumen) projectors, the power of the display and its control is a significant part of the overall power (and less so at higher brightnesses).

The Syndiant LCOS display and ASIC for the WVGA or SVGA will usually consumed about 0.4W.   Due to a number of design improvements, Syndiant’s 720p panel and ASIC consume less power while have a higher color field rate and better light throughput than the older WVGA and SVGA devices while having about 3X the pixels.

In the low lumen area of 10 to 15 lumens with a small, 0.21” WVGA or SVGA panel optical companies were able to get about 7 to 10 lumens per LED Watt.    With some power conversion overhead and including the panel and ASIC this mean that you could get with LEDs about 12 to 15 lumens for 2W of power.  While this is still not good enough for the very high volume cell phone applications, it compares very favorably to the ShowWX which takes 4+ Watts for about 15 lumens.

With lasers the efficiency depends heavily on the lasers used and is dominated by the green laser efficiency which is pretty poor with today’s DGLs.   With today’s DGL efficiencies, LEDs will produce more lumens per Watt, but this will change in the future as lasers improve.   I fully expect to see eventually over 30 lumens per Watt with DGL and LCOS because today with the current DGL, they would be doing well to get 3 to 5 lumens per Watt .

Q7. What would be the lumen output from Syndiant’s displays using the new lasers that Microvision will use [this question was edited for clarity].

This is not a simple question as the spec’s on the lasers and how they can be driven have not been finalized.   I’m pretty sure the lasers that Microvision was using “lab prototype” lasers at CES that were being “over driven.”  The best I can answer right now is to give some insight into the lumens per watt that can be expected as the lasers are perfected.

To begin with, the optical throughput for a laser/LCOS engine should be in the 30% to 40% range where for LBS the optical throughput is reported to be in the 55% to 60% range.   But note, this is the part of the system were LBS looks best in terms of efficiency, but this does not tell the whole story.

Where LBS looses in terms of efficiency is in the drive and control of the laser and the MEM’s mirror.    The Microvision MEM’s mirror alone (not including the ASICs and FPGA’s) at WVGA has been reported to take about 0.4 Watts.   Syndiant’s new 720p LCOS Microdisplay and ASIC combined will take less than that.   Then you have all the power of the 2 ASIC’s and the FPGA that the Microvision 720p board requires.    So LCOS starts with a big lead in terms of power just in power of the display and control.

Then we have biggest power wasters for LBS, that of having to analog modulate the laser drive power.   First you have the fact that each pixel in the laser beam scanning process must be analog modulated at very high speed and high speed analog modulation wastes power.

Additionally, most people are not aware that the laser beam also has to be modulated due to the varying speed of the laser sweep.   If you think about it the laser beam horizontal sweep has to accelerate from zero to the maximum speed at the center of the screen and then decelerate to stop at the far side before returning.  To make a solid image appear uniform, the laser drive has to be constantly varying (for a “solid white” image the drive approximates a sine wave).  See such as the Microvision White Paper (a figure from which is copied below) and the excerpt (copied below) from the Microvision patent application”Apparatus and Method for Interpolating the Intensities of Scanned Pixels“:

From US Patent Application 20090213040

Q7. What is the power to run the PCB and the light engine on a Syndiant’s Displays? (SVGA and WVGA).

That really is a complex and involved question and depends on a lot of factors including the optical engine design and the target brightness.  I am also assuming that this is with LED illumination.   With LEDs the lumens per Watt of power tends to go down as the projector gets brighter, that is one of the advantages with lasers, namely that efficiency does not go down with power.

The LCOS display and ASIC for the WVGA or SVGA will usually consume less than ess than 0.4W.   Due to a number of design improvements, Syndiant’s 720p panel and ASIC consume less power while have a higher color field rate and better light throughput than the older WVGA and SVGA devices while having about 2X to 3X the pixels.

In the low lumen area of 10 to 15 lumens with a small, 0.21” WVGA or SVGA panel optical companies were able to get about 7 to 10 lumens per LED Watt.    With some power conversion overhead and including the panel and ASIC this mean that you could get with LEDs about 12 to 15 lumens for 2W of power.  While this is still not good enough for the very high volume cell phone applications, it compares very favorably to the ShowWX which takes 4+ Watts for about 15 lumens.

Q8. Which VGA display panel is best suited for the cell phone market?

I don’t know that there is a “best.”  Right now about the only reasonably high volume embedded panel is the color filter LCOS one by Himax that is used in cell phones for the India and China market.   The performance of these engines is too poor to be used in “first world” markets.   I think many of them are also less than VGA resolution.   They are typically about 5 to 10 lumens with pretty poor color and contrast and use very cheap but relatively large optics.

Personally, I don’t see a big “first world” need for a VGA or WVGA display.   Why bother projecting an image that lower in resolution than the cell phone’s display?   I think the big market will be to projector resolutions that are at least 720p

Q9. Does Syndiant plan on building the Light Engine?

I can’t comment on Syndiant’s future plans, but Syndiant’s business model has been to be a panel supplier.    There are very large number of good optical engine companies in the world so I don’t know why Syndiant would want to change.

Q10. Is Syndiant depending on someone else to make the Light Engine and Syndiant only sell the display panel?

Syndiant makes the panel and for use by many companies.   This allows different companies to make different products aimed at different markets.

Q11. Does Syndiant’s displays need a Vibrating Despeckle unit with DGLs?

It depends on the DGLs.  With the multimode DGLs you can drive them in such a way as to induce more mode-hopping to reduce speckle.   I would expect the there will not be despeckling required with volume production DGLs.

Q12. Does the light coming off the Vibrating Despeckle unit need to cover the homoginizer [a reference to the 3 year old SSTDC optical engine that used a vibrating despeckler]?

In the old SSTDC design with a vibrating despeckler, the light was partly spread before going to the despeckling mirror but not as large as the homoginizer.

 

Laser with LCOS is Focus Free — Yes Really!

Focus Free LCOS+Laser Projection (click for larger image)

Yes, when LCOS panels are used with lasers they can be “Focus Free.”   I have found that even very technical people have a hard time believing this as it goes against one’s everyday experience dealing with “normal” light and lenses.    People assume that the main function of a lens is to “focus light.”  After all, people are used to having to focus a camera lens or with a projector using lamps or LED light.

The optical physics of why it is focus free would take a long technical discussion, but it has to do with the laser light being effectively infinite f-number.  It is analogous to stopping a camera down to a high f-number where the depth of focus become very large.

Hopefully, “seeing is believing.”  I have uploaded a couple of still pictures (click on images for larger versions) and a short YouTube video demonstrating the focus free nature of the a Laseno Projector (sold in the U.S. as the AAXA L2).  This projector used a SYL2010 SVGA (800×600) LCOS plane with a 5.4 micron pixel pitch and 0.21″ diagonal.

For the top picture in this article, I projected the image the ceiling and some crown molding in my house.  This ceiling has lots of angle and different depths to it and with the crown molding in the way there is some obvious depth differences. Of course with the Laseno/AAXA L2 projector, there is no focusing necessary.

Projected at and angle to demonstrate focus free

Projected at and angle to demonstrate focus free (click on image)

For the picture on the left, I projected the image at a skewed angle from the side to cause a range of depths to be displayed.  The problem you have is that while the projected image is focus free, when the laser light hits the screen it looses it high f-number characteristics and thus the camera needs to focus.   By projecting the image on a flat piece of paper and shooting the picture straight onto the piece of paper I was able to focus the camera while demonstrating the focus free nature of the projector.

But perhaps the best way to demonstrate the focus free nature of a laser/LCOS projector is with a video.  I shot a short ~1 minute video where I mounted the projector on a little dolly and pulled it back away from the screen.  There was some shaking as I moved the projector so I stopped occasionally as I moved it it back so you could see it was still in focus.   I zoomed with the video camera in so you could see the detail in the video image.   Note that the camera’s exposures was locked/fixed on the starting frame, so as the image gets larger, it becomes darker by the ratio of the area so as the projector pull back the video gets a little dark.

I would recommend watching the video at 720p and in full screen to see how the focus is maintained.

Focus Free Video Demonstration

Other Information on the Images

The ~2 year old Laseno projector I used for these pictures has a fixed focus lens.   The image become well focused about 8″ from the projector to infinity.

The Laseno projection lens is not of high quality and you will see some serious chroma aberrations in picture as well as some spots having some blur due to the quality of the lens.  Additionally the projector has “100% offset” meaning that it projects through only the top half of the projection lens so that the projector will project upward from a flat surface without having a keystone effect.  Because of the offset projection, the image is best at the bottom of the image (which is from the center of the lens) at the chroma aberrations (color separation) become progressively worst toward the time.

You definitely will see laser speckle in the images.  The despeckle design was low cost and done over 3 years ago and it uses frequency doubled green lasers which inherently have a high amount of speckle.  Most people who have seen the AAXA L1/L2 “live and compared it to the ShowWX have said that the speckle with the Laseno/AAXA L1/L2  is less than that of Microvision’s ShowWX.