Panasonic Presents 14-Megapixel MOS Sensor for Compact Cameras

Over the last year, we've seen the CCD slowly dwindle in D-SLR cameras and be largely replaced by MOS-type sensors. The CCD is now slowly being replaced in compacts too, with MOS sensors gradually gaining ground. Panasonic has been hanging on in there with its CCDs, but has now unveiled a brand new MOS sensor for its compact cameras.

The launch of cameras like the Casio F1 and Sony HX1 has brought all the advantages of MOS-type sensors into the spotlight.

First of all, MOS sensors offer improved light sensitivity. In SLR cameras, this quality has been proven with the arrival of 12-Megapixel CMOS cameras like the Nikon D300 and Sony Alpha 700. In compact cameras, BSI CMOS sensors use an inverted structure to capture more light. In this field, the 10-Megapixel Sony Exmor R, for example, easily beats the 12- and 14-Megapixel CCDs typically found in entry-level models.

For video and general functions, an MOS can read information much more quickly than a CCD. It can, for example, continuously transfer the 60 Megapixels per second required for a Full HD film, whereas CCDs max out at 720 HD at 30 frames per second. An MOS can also handle shooting around ten full-resolution pictures in just one second, equivalent to a read-speed of 100 Megapixels per second!

These burst speeds are regularly used by manufacturers to bring new functions to their cameras, such as High Dynamic Range (HDR), hand-held long exposure, deleting moving objects from a picture and sweep panorama (and even stereoscopic images).

Note that a backlit MOS is a little more complicated (and thus more expensive) to make than a regular front-illuminated MOS sensor.

Playing it safer than Sony

Sony took a very big risk introducing its BSI-type CMOS sensors, as the compacts that featured them had a reduced resolution of 10 Megapixels, all at a time when the market standard was 12 Megapixels (and 14-Megapixel models were already on the horizon). For years, manufacturers had been racing for the biggest number of pixels, so it was difficult to explain to consumers that cutting back to 10 Megapixels on an expensive, high-end model would actually improve picture quality. However, the second generation Exmor R sensor put Sony back into the pixel race, moving resolution back up to 12 Megapixels.

Panasonic yesterday launched its first MOS sensor for compact cameras, after having already used them for several years in its 4/3" cameras. This new sensor isn't quite as daring as Sony's, as it's a classic MOS (the wiring is above the photodiodes) rather than a backlit version, and it has a resolution of 14 Megapixels just like the popular CCD sensors of the moment. Panasonic's MOS also has the same 1/2.33" size as its CCD, effectively making the CCD and MOS perfectly interchangeable, particularly in the brand's marketing spiel.



The diagram above, provided by Panasonic, shows the sensor has a fairly classic structure, with the photodiode underneath the wiring. It does, however, also show Panasonic's Micro Light Tube technology, which is supposed to help ensure the effective transmission of light to the diodes by creating a kind of light-channelling tunnel, and without compromising the upper structure and wiring.

The physicists among you might be scratching your heads right now, though. If the sensor has 14 Megapixels for an overall size of just 4.6 x 6.2 mm, the photo-sensitive site shown in the diagram must measure 1.4 µm across. So if the diagram is to scale, that makes the Micro Light Tube less than 700 nm wide and barely as deep.

At this scale, representing the path of light as a straight line is an oversimplification that simply doesn't wash. Plus, the wavelength of a red photon is around 650 nm, which is almost as wide as the Micro Light Tube itself! Therefore, making a structure of this size with a tube and mirrors that reflect and direct light exactly as shown in the diagram seems rather difficult to us.

We'll have to wait and see the results for ourselves, but, based purely on our high-school physics lessons, we have some serious doubts about the scale and accuracy of this diagram. The upside-down structure of the BSI sensor (with the photodiode on top of the circuit wiring) seemed a little more convincing.

High-speed

The new sensor, known as the Mega MOS, offers the high-speed playback capabilities typical to this type of sensor. In other words, it can handle information very quickly. Image processing therefore has to keep up, and so Panasonic has released a new image processing chip, the Venus Engine FHD, to process the data.

The new sensor and image processor allow for 1080i HD video at 50 half-frames per second, or 720p HD at 50 frames per second (60 in NTSC regions), recorded in the AVCHD format. The burst mode reaches 11 frames per second for 15 pictures in 14-Megapixel resolution, and there's a quick-burst mode at 60 pictures per second in 3.5 Megapixels.

However, the high-speed video mode remains fairly limited. It's only captured in 320 x 240 pixels at a maximum speed of 220 fps. The Casio FH100, for example, captures high-speed video at 240 fps in 448 x 336 pixels and can even reach 1,000 fps in a much-reduced resolution.

Two Panasonic cameras featuring this new sensor are due for launch later this year: one compact and one bridge. Interestingly, the bridge will also be available with a CCD sensor of the same size and the same resolution. A comparison between the two is therefore inevitable, particularly for electronic noise, so we can check just how effective those Micro Light Tubes really are in practice.

> Digital Camera Reviews: Choose the Best Compact Camera

> Buyer's Guides: Our Pick of The Best Products