D3 sensor efficiency

Started Nov 18, 2007 | Discussions thread
ohyva Veteran Member • Posts: 6,342
Re: A question - Re: Measurement improvement

ejmartin wrote:

ohyva wrote:

Emil, if I understood right you estimate the efficiency of the sensor
indirectly from the noise level estimates.

Yes that's right.

In your opinion, what
could be the effect of possible on-chip digital (i.e. post AD
convertion) noise cancellation like reported to be used in Sony's
sensor - see fig1 in
http://www.sony.net/Products/SC-HP/cx_news/vol50/pdf/imx021.pdf

What is described in the linked document seems to be aimed at
reducing the ADC noise (and the earlier stage seems similar to
Canon's methodology for reducing sensor read noise). Neither would
affect photon shot noise (which is what is used to infer the sensor
efficiency or "gain") unless there were some averaging done over
neighboring pixels. I haven't seen any evidence that there is any
such averaging going on.

The only digital side ADC noise I'm aware of is the quantization noise, which you can reduce only by adding some more quantization steps i.e. increading the bit-depth of the conversion. I'm close sure this is not the case as with ramp type of ADC each additional bit increase the conversion time by a factor of 2.

So the only way in digital domain to reduce the noise I can imagine is to make some inter-pixel manipulation. But like you, I have not more info of what is actually done there in this Sony chip.

What's is you method to eliminate the other noise sources in the data. At least there is besides the photon noise all sort of digital switching introduced noise, dark current noise, analog circuitry noise from apmpifiers and others etc. Some of these are quite independent of the analog signal itself, but some may be dependent on that (like different charge leaks etc.) The CDS method used in Canon cameras (asn something similar digital CDS in Sony sensor) is targeted, by design, to reduce those externally induced signal independent noise sourced (if done right - as if not this may actually double the noise).

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