Technical question: Readout noise

Hi!

I have read that at a high readout speed there is more readout noise. At
it decreases with decreasing readout speed.
But what is the origin of respectively the reason for readout noise?

Does it have something to do with the capacitors of the register of a
CCD-chip where the pixels are being read from?

Thank you for your answers!

David

David Yasli wrote:
Hi!

I have read that at a high readout speed there is more readout noise. At
it decreases with decreasing readout speed.
But what is the origin of respectively the reason for readout noise?

Does it have something to do with the capacitors of the register of a
CCD-chip where the pixels are being read from?

No.
It's noise converting the stored charge from the readout pixel into
a voltage at the output pin of the chip.
If you are only reading out at 50Khz, compared to 5Mhz "normal", then
you can ignore all output noise that's over 50Khz (or so.).
If reading out at 5Mhz, you get all the high frequency noise too.

On Fri, 09 Apr 2004 14:00:58 +0200, David Yasli wrote:

I have read that at a high readout speed there is more readout noise. At
it decreases with decreasing readout speed.
But what is the origin of respectively the reason for readout noise?

The readout noise comes from several sources. One component is thermal noise in
the output amplifier. The thermal characteristics of the amplifier depend in
part on the readout rate- this is the only fundamental reason that increased
readout rates produce increased readout noise, and in general, this is a small
effect. Readout noise also consists of quantization noise, which is an
uncertainty associated with converting from analog to digital. In principle
there is no readout rate effect here, but in practice many converters produce a
more accurate output if they are given longer to settle. Another component of
readout noise occurs as the result of timing errors in the correlated double
sampling logic. This involves integration, and if there is any variation in the
timing of the reset and charge signals, it will show up as noise. As you read
faster and faster, those signals become shorter and shorter. At high speeds,
even a few picoseconds of timing jitter will introduce significant readout
noise.

_________________________________________________

Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com