| Electronics > Projects, Designs, and Technical Stuff |
| Can 768kHz-capable AK449X DACs run at 512kHz? |
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| SiliconWizard:
AFAIK, the modulator usually runs at the master clock frequency. I haven't looked at the DS in details, but I don't think it has an internal PLL allowing it to clock the modulator at a higher frequency than the master clock. Please correct though if I missed it. |
| phofman:
--- Quote from: moffy on June 01, 2020, 02:51:51 pm ---Normally the output antialias filter should be 1/2 the sampling or less frequency, as you suspect. --- End quote --- That is why I am interested in the actual sampling frequency, after digital oversampling in the DAC, to make sure my analog LP filter will have enough attenuation at sampling frequency/2 (the nyquist) while not affecting the usable frequency range (defined by the steep digital filter in the oversampler = slightly below fs/2). Thanks a lot for your patience. Pavel. |
| phofman:
--- Quote from: SiliconWizard on June 01, 2020, 03:05:30 pm ---AFAIK, the modulator usually runs at the master clock frequency. I haven't looked at the DS in details, but I don't think it has an internal PLL allowing it to clock the modulator at a higher frequency than the master clock. Please correct though if I missed it. --- End quote --- That would be good, the planned master clock is in all cases at least 32MHz, giving the analog active LPF enough room between cutoff at 260kHz and nyquist at 16MHz. Thanks, Pavel. |
| SiliconWizard:
--- Quote from: phofman on June 01, 2020, 03:41:39 pm --- --- Quote from: SiliconWizard on June 01, 2020, 03:05:30 pm ---AFAIK, the modulator usually runs at the master clock frequency. I haven't looked at the DS in details, but I don't think it has an internal PLL allowing it to clock the modulator at a higher frequency than the master clock. Please correct though if I missed it. --- End quote --- That would be good, the planned master clock is in all cases at least 32MHz, giving the analog active LPF enough room between cutoff at 260kHz and nyquist at 16MHz. --- End quote --- To me that's usually how that works. The "fs" factor is the oversampling factor - which itself defines the ratio between the frequency at which the modulator runs, and the sample rate. As you can see (or already know), a typical sigma-delta modulator needs to run at a much higher frequency than the sampling rate to get "good" performance. OTOH, a sigma-delta DAC is pretty much entirely digital - and these days, running @32MHz is not that big a deal. So that's still a very efficient way of implementing DACs. |
| moffy:
learnt something about sigma/delta dacs vs SAR. :P |
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