Originally Posted by Carl_Huff
Much noise and nuisance presented here because I had not posted distortion and noise plots for the AP20.
Thanks Carl. Your status and that of Datasat went up good few notches in my book
Using that data we can then repeat the earlier comparison we did.
Your measurements of THD+N:
TI's bench testing of the same DAC:
A quick point that has escaped some on this forum. It is not the cost of the raw DAC chips that is most important when designing a new product as they have become a commodity. It's how they are used that is most important in determining the fidelity of the finished good.
Great point and indeed, I made the same earlier that in-circuit performance is very different than bench performance by chip company where lab grade power supply and clock sources are used with no other high-speed signals whaling around.
Summarizing, the spurious distortion products went up from -110 db in TI testing to roughly -90db in AP-20. Assuming the distortion product as the floor of our performance, we are looking at 15 bits in your machine vs 18 bits TI's workbench.
For reference, this is the Benchmark DAC1 again:
Its spurs are at -120 db or a whopping 30 db better than measured AP-20! Man, these guys know how to grind down distortion!
BTW, the vertical scale is squashed so much in your graphs. Assuming you didn't do that to hide the variations, it would be great to have the graphs in proper aspect ratio. I had to really squint to read the -90db number
For now, it seems that your noise figures are much better than Roger's testing showed. I do not expect a device with -100db noise figure to have the kind of hiss he heard. What was the test fixture there? Just the AP's input load? If so, what load was used? Either way, your potential customers have something to celebrate there
Also, is the first THD+N Digital Out measurement correct? I don't see the signal that was used to drive the unit. Seems like the input was off in that test even though it says it was at full scale like the analog out above? [EDIT: never mind, I was looking at one graph, and reading the title of another
I got a kick out of digital out noise test. Looks like there is dither noise at 24-bit resolution which is what I had suggested it would do in that front
. At any rate, it is an uninteresting graph otherwise as in digital domain, we don't worry about noise.
Again, thanks a bunch for the information.