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Hi Jens,
Thank you again for the excellent insight.
We are not doing strict CDS, because of the nature of the CMOS device.
The reset and video levels are sampled and stored at different times
on the device (as in most CMOS imagers). Also, there is only one
output on the device.
As far as acquisition board goes, I think you are exactly right, the
acquisition board may be what is limiting me. I will be moving to a
more sophistiated setup soon.
But does what I see so far at least advance the theory that I'm never
in a shot-noise limited region because at maximum signal, my noise is
only 2.7 times the read noise?
Best regards,
Patrick
Jens Dierks wrote:
> Hi Patrick,
>
> > Ok. I think I'm on to something here ...
> >
> > The read noise is high: about 280 e rms.
>
> Oh, this explains something.
> Sensors normally has to be read out by CDS or dual slope integration
> (weighted dsi is the best), and some sensors can be read without
> destruction of the charges, so noise can be lowered by multiple
> readouts.
> Then there are sensors with charge multiplying processes, but this
> increases the shot noise.
> Timing and correct filtering are important for a low noise readout.
>
>
> > However, I still have high dynamic range: saturation = 500ke. So
> > dynamic range is 20*log(500000/280) = 65dB. Is it strange that I can
> > have both high dynamic range and high read noise? I know the two are
> > somewhat decoupled, because the full well is quite high, but something
> > seems a little off here.
>
> Far off, if you ask me. High dynamic range doesnt increase the readout
> noise in this amount. Sensors with such a high fullwell have sometimes
> two different readout modes, one with a higher v/charge output and
> decreased fullwell - but a slightly lower read-noise, and one with
> the maximum fullwell and somewhat higher readout-noise.
> But the values for good CCDs are somewhere about 5 and 8e_rms,
> dependend on the speed and method of readout, higher than 20e should be
> avoided.
>
> I think you should use a acquisition board, designed or handmade for
> the sensor.
>
> Best regards,
> Jens
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