Phase AF CCD Die Shot

Back in 2014 we were investigating the AF/Lens system at NikonHacker. To understand the operation of phase AF, some efforts were put into the AF sensor itself. There were leaked D1X schematics indicating 3 linear CCDs made by Sony (ILX105 and ILX107) are incorporated into the MultiCAM-1300. In the old days, a single chip could not handle that many segments of linear pixels on a single die, so that the light path had to be split and focused onto multiple chips. The same is done on MultiCAM-2000 which uses 3 chips as well.

Then from the D200 until D90, a single chip ILX148 is used to handle all 11 focus points in the new CAM-1000 AF system. Some teardown serves as great resources even showing a die photo of that sensor. Missing in between was the D70’s CAM-900. Later I came across a cheap working sensor stripped from a broken D70 and decided to take a look.

Front

Back

The entire module came in with dust, clearly from a broken camera fall onto the ground. I tore the 2 duct tap covering the slit between the chip and plastic optical assembly. The opening is a metal mask outlying the light transmission boundaries of 5 focus points.

Then I use a knife to peer off the glue on the sides, exposing the reddish epoxy adhesion between the chip carrier and the optical module. A gentle pull separated them apart.

The Sensor

Sensor Die

Now the AF CCD is exposed! You could see a total of 12 linear CCD segments forming 6 pairs.

Let’s look at the back side of the optical assembly to understand why.

Lenslet

It appears each focus point has a pair of microlenses. The center cross-type use 2 linear segments in perpendicular, thus 4 lenslets. That gives you total of 6 pairs.

To illustrate how this works, I cover the focus plane with a scratching paper and point its front toward a light bulb. And here’s the image.

Segment-Image

The pattern matches the layout of linear CCD.

Now we could mimic a high contrast target by covering 2 focus points in half with a sticker.

You could see the 2 lenslets forms a copy of 2 high-contrast edges in the 2 segments.

When this is relayed from a photographic lens, the distance between the 2 high-contrast edges will vary depending on the defocus value. The firmware A then uses some sort of cross-correlation algorithm to determine that distance. The distance is then compared against the calibrated value to get the actual defocus amount used to drive the lens AF motor.

So far that’s for the working principle for the phase AF optics. There’s a lot need to dig into the ASM codes of firmware A, and the electronic interface between the AF CCD and the MCU running the codes. Here I decided to desolder the CCD from the flex board. The CCD is packaged inside a CLCC and the contacts form a L-shape covering both side and bottom. It turned out the heat from soldering iron disassociates the wires from flexible board before melting the solder on the bottom. All the contact pads on the flexible board are destroyed.

The backside of the CLCC package has following marking.

20140906_205726

It’s a Sony ILX127AA linear CCD.  405 R9KK is the product batch code. “405” indicates it’s made in the 5th week of 2004, around the time of D70 and D70s.

The schematics can be obtained from wiring trace. In the diagram below, VREF is probably 3.3V based on the trace. SD0~3 and STB formed a simple parallel command interface. CLK is the master clock input. The analog output of pixel intensity is on Vout synchronized to SYNC.

image

Now we could dig into the image sensor die using a microscope. I took more than 50 shot and stitched using a panoramic software. The CCD was manufactured using a very old process node, probably larger than 1 micron.

ILX127AA

Click for Large View

The charge transfer is based on 2-phase CCD. The total number of pixels is around 996. Considering the metal masked pixels, this number reduces to 912. Thus MultiCam-900 make sense. The greenish regions are the actual photodiodes. The photon generated charge is then transferred to the shaded region on the left or to the top. The charge is then clocked and shifted out to the output amplifier. The three long segments are continuous with dummy pixels in between two correlated pixel regions. The six shorter ones form the left, center and right focus points are broken into two due to the long segments. Thus each shorter one has its own amplifier. The CCD integrates all the input command decoder/segment select/CCD driver logic on chip, as indicated by the vertical grid of synthesized transistors and their metal interconnect wires.

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3 Responses to Phase AF CCD Die Shot

  1. Pingback: Weekly Nikon news flash #448 | Nikon Rumors

  2. Thanks. Nikon D100, Fujifilm FinePix S2 Pro, Fujifilm FinePix S3 Pro, Fujifilm FinePix S3 Pro UVIR, Kodak Professional DCS Pro 14n, Kodak Professional DCS Pro SLR/n also using Nikon Multi-CAM 900 autofocus system.

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