> > It's (my initial statement you disagree with) hardly an > over-simplification, > > in fact, it is about as complete and accurate as you can get. > It is a plain > > and simple fact that a dynamic range of 5000:1 requires 13 bits > to represent > > that full dynamic range. Again, 1 is the first discernable > signal (as in > > the noise floor), and since you can only measure in increments > OF the noise > > floor...a dynamic range of 5000:1 simply means you can have > every integer > > value from 1 to 5000...and to represent every integer value > from 1 to 5000, > > you need 13 bits. > > Perhaps this can be made clearer by bringing back a concrete example > (similar to one which I think Austin used earlier in this thread). > > Suppose that the output of the CCD analog stage swings from -2.5 to +2.5 > volts, and that there is 0.001 volts of noise. If you install an > analog-to-digital convertor to sample signals from this system, there is a > lower limit to the step size that you should choose. There is no > advantage > to choosing a step size smaller than the noise level of 0.001 volt. Why? > Because when you measure the voltage and get a result x, any value in the > range, you really don't know the actual value. You measured the > signal plus > noise. The signal could have been anything between (x + 0.0005) and (x + > 0.0005). So the optimum "granularity" is a sampling system with (2.5 - > (-2.5))/0.001 = 5000 steps. You could use a system with fewer > steps, but it > would not be optimal. It would not encode all the information. > If you used > a system with more than 5000 steps you would not be measuring with more > accuracy, you would just be building in excess complexity and expense. > > The dynamic range of this system is 5000:1. You would need a 13 bit > converter to represent 5000 discrete steps, since 2^13 = 8192 (more than > enough) but 2^12 = 4096 (not enough).
Hi Julian, Aside from your known sign switch in the tolerance (+- .0005v), perfectly described and perfectly correct. Regards, Austin ---------------------------------------------------------------------------------------- Unsubscribe by mail to [EMAIL PROTECTED], with 'unsubscribe filmscanners' or 'unsubscribe filmscanners_digest' (as appropriate) in the message title or body