From: Ray Fischer on
John Sheehy <JPS(a)no.komm> wrote:
>rfischer(a)sonic.net (Ray Fischer) wrote in
>
>> You really are being an idiot since I never said otherwise. I said
>> that people don't care about noise PER SENSOR AREA. Of course noise
>> counts as detailed reviews on DPReview show. People DON'T care about
>> noise per sensor area.
>
>Well, they should, if they have in mind a camera with a certain sized
>sensor, which people often do.

Don't try to feed me bullshit in order to justify your weak argument.

--
Ray Fischer
rfischer(a)sonic.net

From: Bob Newman on
On 22 Jul, 05:29, ejmartin <ejm_60...(a)yahoo.com> wrote:
> On Jul 21, 6:52 pm, ejmartin <ejm_60...(a)yahoo.com> wrote:
>
>
>
>
>
> > On Jul 21, 2:24 pm, Bob Newman <bob.csx...(a)gmail.com> wrote:
>
> > > On 21 Jul, 16:39, ejmartin <ejm_60...(a)yahoo.com> wrote:
>
> > > > On Jul 21, 8:04 am, Bob Newman <bob.csx...(a)gmail.com> wrote:
>
> > > > > On 20 Jul, 23:45, ejmartin <ejm_60...(a)yahoo.com> wrote:
>
> > > > What puzzles me about your analysis is that you get the input-referred
> > > > read noise proportional to the sensel capacitance, with no appreciable
> > > > dependence of the front end noise Nf on sensel size;
> > > Yes
> > > > I would think
> > > > also that the FWC is also proportional to the sensel capacitance.
> > > > Then the DR per pixel is totally independent of the capacitance of the
> > > > sensel, which doesn't seem right to me.
>
> > > Why should it not be? What we have done is a simple scale, and none of
> > > the noise sources (or significant ones) appears to be dimension
> > > related.> Moreover, it predicts DR/area
> > > > actually goes up in inverse proportion to the pixel spacing, which
> > > > also seems a bit goofy.
>
> > > Whether it's goofy or not just depends on your preconceptions. If you
> > > look at it another way, we're reading through a greater number of
> > > 'channels', why should that not cause less noise? Also, it also seems
> > > to work in the limit, the one electron pixel, which requires little
> > > pixel DR (note to self: have a look at the DR in a dynamic RAM cell)
> > > to produce an image with zero read noise. Remember also that we're
> > > talking here only about the read noise, shot noise controlled DR is of
> > > course smaller per pixel and the same per area.
> > > Still, if you don't believe it, find the hole in the reasoning.
>
> > OK, I found an interesting recent article by James Janesick etal
>
> >http://www.laserfocusworld.com/display_article/332970/12/none/none/Fe...
>
> > where they say that
>
> > "Fundamentally, CMOS read noise is limited by random telegraph signal
> > (RTS) noise and background flicker noise associated with surface
> > states in output metal-oxide-semiconductor field-effect-transistor
> > (MOSFET) pixel amplifiers. These noise sources can be reduced
> > considerably with the old CCD invention of using buried channel
> > MOSFETs to curtail bias-current surface interaction. This technology
> > will undoubtedly produce a subelectron noise floor in the very near
> > future, thus surpassing CCD read noise."
>
> A couple more references:
>
> www.imagesensors.org/Past%20Workshops/2007%20Workshop/2007%20Papers/0...
That's a great reference. A bit more work on this, and we'll know a
lot more about it.
> www-isl.stanford.edu/~abbas/group/papers_and_pub/1_f_noise.pdf- Hide quoted text -
>
> - Show quoted text -
Meanwhile, from one of your references in the first post:
"The white noise in terms of electrons at the CCD sense node is
equivalent to the white noise in volts, defined above, divided by the
product of amplifier sensitivity and output gain, as follows:

Nwhite (rms electrons) = (4kTBRout)1/2 / Samp • Aamp
In the above equation, S is the amplifier sensitivity and A represents
the amplifier gain. The sensitivity value is a function of the
fundamental electron charge and the CCD sense capacitance and is
expressed in units of volts per electron."

I think that just about confirms my input referred noise theory. The
real issue now is the importance of the other noise sources at current
sensor dimensions. Ultimately, when these become dominant, there will
be a point of diminishing returns. We just don't know where it is
yet.

From: ejmartin on
On Jul 23, 7:42 am, Bob Newman <bob.csx...(a)gmail.com> wrote:
> On 22 Jul, 05:29, ejmartin <ejm_60...(a)yahoo.com> wrote:
>
> > On Jul 21, 6:52 pm, ejmartin <ejm_60...(a)yahoo.com> wrote:
>
> > > On Jul 21, 2:24 pm, Bob Newman <bob.csx...(a)gmail.com> wrote:
>
> > > > On 21 Jul, 16:39, ejmartin <ejm_60...(a)yahoo.com> wrote:
>
> > > > > On Jul 21, 8:04 am, Bob Newman <bob.csx...(a)gmail.com> wrote:
>
> > > > > > On 20 Jul, 23:45, ejmartin <ejm_60...(a)yahoo.com> wrote:
>
> > > > > What puzzles me about your analysis is that you get the input-referred
> > > > > read noise proportional to the sensel capacitance, with no appreciable
> > > > > dependence of the front end noise Nf on sensel size;
> > > > Yes
> > > > > I would think
> > > > > also that the FWC is also proportional to the sensel capacitance.
> > > > > Then the DR per pixel is totally independent of the capacitance of the
> > > > > sensel, which doesn't seem right to me.
>
> > > > Why should it not be? What we have done is a simple scale, and none of
> > > > the noise sources (or significant ones) appears to be dimension
> > > > related.> Moreover, it predicts DR/area
> > > > > actually goes up in inverse proportion to the pixel spacing, which
> > > > > also seems a bit goofy.
>
> > > > Whether it's goofy or not just depends on your preconceptions. If you
> > > > look at it another way, we're reading through a greater number of
> > > > 'channels', why should that not cause less noise? Also, it also seems
> > > > to work in the limit, the one electron pixel, which requires little
> > > > pixel DR (note to self: have a look at the DR in a dynamic RAM cell)
> > > > to produce an image with zero read noise. Remember also that we're
> > > > talking here only about the read noise, shot noise controlled DR is of
> > > > course smaller per pixel and the same per area.
> > > > Still, if you don't believe it, find the hole in the reasoning.
>
> > > OK, I found an interesting recent article by James Janesick etal
>
> > >http://www.laserfocusworld.com/display_article/332970/12/none/none/Fe....
>
> > > where they say that
>
> > > "Fundamentally, CMOS read noise is limited by random telegraph signal
> > > (RTS) noise and background flicker noise associated with surface
> > > states in output metal-oxide-semiconductor field-effect-transistor
> > > (MOSFET) pixel amplifiers. These noise sources can be reduced
> > > considerably with the old CCD invention of using buried channel
> > > MOSFETs to curtail bias-current surface interaction. This technology
> > > will undoubtedly produce a subelectron noise floor in the very near
> > > future, thus surpassing CCD read noise."
>
> > A couple more references:
>
> >www.imagesensors.org/Past%20Workshops/2007%20Workshop/2007%20Papers/0...
>
> That's a great reference. A bit more work on this, and we'll know a
> lot more about it.> www-isl.stanford.edu/~abbas/group/papers_and_pub/1_f_noise.pdf- Hide quoted text -
>
> > - Show quoted text -
>
> Meanwhile, from one of your references in the first post:
> "The white noise in terms of electrons at the CCD sense node is
> equivalent to the white noise in volts, defined above, divided by the
> product of amplifier sensitivity and output gain, as follows:
>
> Nwhite (rms electrons) = (4kTBRout)1/2 / Samp • Aamp
> In the above equation, S is the amplifier sensitivity and A represents
> the amplifier gain. The sensitivity value is a function of the
> fundamental electron charge and the CCD sense capacitance and is
> expressed in units of volts per electron."
>
> I think that just about confirms my input referred noise theory. The
> real issue now is the importance of the other noise sources at current
> sensor dimensions. Ultimately, when these become dominant, there will
> be a point of diminishing returns. We just don't know where it is
> yet.

Yes, after skimming these various articles it sounds as though you
have the right model for that particular noise contribution, and the
question is now a practical one about the magnitudes of other noise
sources which provide a cutoff on the scaling behavior wrt pixel
size. Some of those seem to be dependent on materials aspects like
impurities. There are a few more articles about prototype devices and
modelling noise sources at Eric Fossum's website

http://imagesensors.org/Past%20Workshops/Past%20Workshops.htm

It seems that 2 e- is about the limit of current prototype devices,
and pixel sizes are edging toward 1µ but with more noise (see Micron's
blurb in the 2007 workshop for the latter, and another article in the
2007 workshop for the former, achieved by massive column-parallel
readout). So perhaps current cameras are not close to fundamental
limits.

It does however seem to be the case that the best Canon can achieve
with their current approach (and what they're willing to spend on fab
costs per chip) is ~4 e- for read noise, a figure that has been rather
constant since the 20D over a range of pixel sizes from 8.2µ (1D2) to
5.7µ (40D) but we'll see what transpires with the impending small-
pixel, small-sensor offerings that are supposedly imminent.
From: ejmartin on
BTW, something puzzles me -- if the cutoff is imposed by 1/f type
noise sources, won't those be decreased by reading out the pixel
faster? Which confuses me, I've always understood that read noise is
reduced by slower readout (or was that a limitation of ADC's?), and is
counter to the efforts to reduce read noise by using column parallel
readouts that increase read times.
From: Bob Newman on
On 23 Jul, 16:05, ejmartin <ejm_60...(a)yahoo.com> wrote:
> BTW, something puzzles me -- if the cutoff is imposed by 1/f type
> noise sources, won't those be decreased by reading out the pixel
> faster? Which confuses me, I've always understood that read noise is
> reduced by slower readout (or was that a limitation of ADC's?), and is
> counter to the efforts to reduce read noise by using column parallel
> readouts that increase read times.
I think that there are two effects working against each other. High
speed will limit 1/f noise, but capture chains tend to perform worse
at high speed. The problem tends to be 'settling time'. Every stage
has a limited output current and some capacitance. If you want to
achieve a good sample, you need to sample it when that capacitance is
fully charged. Push too much against the speed limits, or cut the
drive current too much, and you tend to sample while it's still
charging, and then you get jitter noise, due to irregularities in the
sampling period. This is why, I suspect, the D3 A to D chain is so
massively overspecified (one of those six AFE chips provides
sufficient bandwidth according to the specs). The best answer would be
to use a very high specced, high drive sample and hold (which actually
determines the read time), which can capture the sample in a very
small window, and thus minimise 1/f noise, followed by a nice
leisurely ADC. I suspect that is what Sony is doing, and possibly
Canon too. The two papers I've seen (on the D10 sensor and the 52MPix
showcase) have on sensor sample and hold. I think the real advantage
of the Sony column ADC architecture is not mainly noise, but cost. The
very low spec ADC's can be integrated quite easily onto the sensor
chip, and it saves a costly AFE off chip. Higher spec ADC's would
require a costly BiCMOS process, which might not be available on CIS
lines.