Simple Sensor Design Tweak

[Jonathan Wienke]

I don't know much about electronics, but wouldn't it be easier to just record the the times it takes for the individual pixels to fill up. If every pixel would be configured so that when full, release charge.

This approach has some merit, but each pixel on the sensor would require its own counting circuit and RAM storage (8 bits would be nice) that would increment each time the detector reached a preset voltage limit and had its charge dumped. Then along with the analog charge level, the counter bits could be read and combined with the A/D converter output to increase the resolution of the output. The only issues would be that the RAM cells and counter circuitry would take much more room on the chip than the photodetectors, and the data lines to read each pixel value would go from 1 analog to 1 analog + 8 binary. My approach would be much easier to fabricate, as only 2 additional components (1 resistor, and 1 transistor to connect and disconnect it from the detector) and 1 additional signal line (the resistor connect/disconnect signal) would be required.

[32BT]

I'm a complete nitwit regarding electronic engineering, but the little information I do think I understand leads me to believe that a CCD is charged before exposure and that the actual exposure is supposed to generate a current (not a charge) which is what is detected and converted to a digital signal.

So I think of a PhotoDetector site as a continuously charged capacitor which generates current (discharges) on exposure. If this is indeed the case then I presume the resistor idea should be redesigned to work as expected?

But more importantly: why would you want to create non-linear behavior? Does the dynamic range increase really weight up against the colorinfidelities?

[thierrylegros396]

Changing the bias was one of my solutions to create HDR sensor ( tread posted last month ).
Jonathan and others were not convinced at that time.

Sure it is a good solution, but practically it's not so simple, because for each cell, charge and capacitor are very small.
But for manufacturers like Canon, it would be possible.

So, I hope it will be THE next big improvement !

[Ray]

I tend to think that the guys in the research laboratories at Kodak or Canon have already thought of such ideas as this and not implemented them because of some serious trade-off in performance that is too difficult or expensive to work around.

But it's fun to get at least some insight into the issues.

[Ray]

While it's possible that the researchers in Kodak, Sony or Canon laboratories have considered this idea, it's also possible that they haven't.

Yes. I'd have to agree that's possible. I think researchers sometimes get so far advanced in their field that they lose sight of the fundamentals.

I have no way of gauging whether this applies in this instance. Electronics is not my forte.