My brain hurts. :-)
Winsor
Long Beach, California, USA
On / June 27, 2007 CE, at 5:15 AM, Tim Hughes wrote:
> Winsor,
> There is what is called quantization noise which adds to the
> sensor noise and is A/D bit
> depth dependent. In a good design the sensor noise is a lot bigger
> than quantization noise, so A/D
> resolution then adds very little quantization noise , exactly as
> you suggest.
>
> Generally random noise adds as RMS quantities, so quantization
> noise is a small effect,provided
> sensor noise is greater than the A/D LSB by about a factor of 3x
> (at >3x the quantization adds <
> ~10% to sensor noise) . So ideally you want the A/D to have 2-3
> bits more resolution than the
> sensor dynamic range,and having a convertor noise level itself of
> less than 0.5LSB, so that it
> then does not contribute significantly to the sensor's inherent
> noise limit.
>
> Take the hypothetical extreme case of the sensor having a much
> wider dynamic range than the A/D
> bit depth (!) and the A/d having converter noise less than 0.5LSB,
> then the noise would be solely
> limited by quantization noise of A/D. Say we then had a sensor
> voltage that is sitting at the edge
> of any A/D bit transition: a 12 bit A/D quantization noise floor
> would then be worse than the
> 16bit A/D noise floor by about 16x (4bits). In reality the higher
> resolution A/D likely has more
> noise above it's quantization limit, so the difference would be
> smaller.
>
> Tim Hughes
==============================================
List usage info: http://www.zuikoholic.com
List nannies: olympusadmin@xxxxxxxxxx
==============================================
|