Messages in this thread | | | From | John Bradford <> | Subject | Re: Want a random entropy source? | Date | Sat, 28 Dec 2002 17:15:46 +0000 (GMT) |
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> > I have never understood how a 16-bit DAC or ADC can have noise above > > 96 dB. Surely _by definition_ a 16-bit DAC or ADC is one that does > > not have noise above that level. > > You're assuming that the ADC input is coupled to a noiseless source. > Most ADCs have a chunk of analogue circuitry just before them which > is a nice source of noise. > > Not only will noise be picked up via disconnected inputs, but it will > also be picked up via the power supply and ground connections to that > analogue circuit. How much of that noise gets into the ADC input is > dependent on the quality, design and physical layout of the analogue > circuit.
Right... So basically it can be claimed to be a 16-bit ADC as long as it is noiseless above 96 dB, when all of the inputs to the ADC are correctly terminated directly at the ADC inputs.
I just think it's funny that loads of "16-bit" soundcards are effectively only 12-bit soundcards :-). Especially as that's about the noise-floor of good quality vinyl :-).
> (As a side note, it's interesting that (what used to be) Crystal > Semiconductor published a large chunk of information on the layout of > boards including the routing of power supplies for combined digital > and analogue circuits (and ADCs fall into that category.))
Good idea - I'd be grateful if more manufacturers would supply a datasheet at all :-).
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