Contributed by Dick James
Recently we got our hands on a Sony MP-CL1 mobile projector, or as they are more commonly known these days, a pico-projector. It’s a pretty compact device being a tad under 6” long, a tad over 3” wide, and a tad over ½” thick (145 x 77 x 13 mm), and weighs in at 210 gm (~7.4 oz.), so it will definitely fit in all but the smallest purses, or make a hefty shirt-pocket full.
The unit has a 16x9, 1920x720 display, with a claimed contrast ratio of 80,000:1 and a full colour palette, generated with a laser light source capable of cranking out 32 lumens (good for a 40-inch display in a darkened room). Connection is by HDMI and USB ports and WiFi (IEEE 802.11 a/b/g/n), and it retails for $350 US on Amazon and elsewhere.
Now that we’ve covered the specs, what do we find inside? It has a fairly solid aluminum chassis, and a battery that Sony says is large enough to charge up your phone in an emergency.
The projector sub-assembly lies next to the battery, and with the lid off we can see the optical engine sitting at an angle in the sub-frame.
It appears that the projector itself is a unit from Microvsion:
They have a technology they call PicoP® Display, which uses laser beam scanning (LBS); red, blue and green lasers combine to give the full range of colours, and a patented MEMS scanner crates the image. Other pico-projectors using the LBS engine include the Celluon Pico-Pro and the Sharp RoBoHon phone.
If we flip the unit around and take a look at the front, we can see the MEMs itself;
At the right are the wire bonds connecting it to the flex tape, and in the centre is the micromirror of the MEMS unit, connected to, and surrounded by, an oval coil which is suspended laterally by a thin microwire. Within the oval is the (almost) circular mirror suspended vertically by a wider torsion bar. With the two axes allowing the mirror to move in the x- and y-directions, we can get the raster pattern necessary to make the image, as shown in this Microvision schematic:
The colour modulation to create the image is done by tweaking the brightness and timing of the three lasers.
The MEMS itself is actually a good-sized silicon die – I make it ~4.5 x 7.3 mm, and the mirror itself ~1.1 x 1.2 mm. Another feature of note is tucked in the top right corner:
Which is where STMicroelectronics come in – they clearly make the MEMS die for the Microvision module. This is the second time recently that we’ve seen ST micromirrors in products, we blogged about the Intel RealSense camera back in July. This one is different, though, the RealSense MEMS is an electrostatic scanning mirror that only scans in one direction, whereas the Microvision device is a dual-axis electromagnetic scanning mirror.
The comb structures that convert the electrostatic signal to torsional rotation are clearly visible on either side of the mirror disc.
If we take a closer look at the 2-axis mirror from the Sony projector, we can see a coil is formed on the front of the oval silicon substrate, and other electromagnetic moldings are on the back of the structure.
Clearly a sophisticated piece of MEMS design, and very different from the Texas Instrument DLP projectors we have seen, which use arrays of individual micromirrors to create the pixels in the display.
In terms of the potential for pico-projectors, TechNavio predicts a CAGR of 33% over the next three years for the different technologies, including liquid crystal on silicon (LCoS), digital light processing (DLP), laser beam steering (LBS) and holographic laser projection (HLP). So even though LBS systems are just a part of that growth, it bodes well for the micromirror business, and STMicroelectronics will no doubt be a force in that space!