so did i get it right that every dds chip needs an external reference clock generated by a quarz oscillator or something? there's no dds chip with an internal reference clock?
A crystal and a pair of ceramic capacitors should set you back by no more than 50 cents, so what's not to like about the standard solution?
Nothing i just wanted to know...
Correct. None of them have a built-in reference clock.
I stand partially corrected. There is one part I know of, the ADuC7129, which is technically an ARM7 microcontroller of ours, but it has a built in DDS and a built-in oscillator. However, reading the brief section on it's DDS, it only has a register to set the output frequency and another register for a phase offset and that's it.
ADuC7129 still needs a crystal or external clock, no?
It does not. From page 49 of the datasheet:
"The ADuC7128/ADuC7129 integrate a 32.768 kHz oscillator, a clock divider, and a PLL. The PLL locks onto a multiple (1275) of the internal oscillator to provide a stable 41.78 MHz clock for the system. The core can operate at this frequency, or at binary submultiples of it, to allow power saving. The default core clock is the PLL clock divided by 8 (CD = 3) or 5.2 MHz."
However, if I read a bit more in the datasheet this internal 32.768kHz oscillator has a tolerance of +/-3%. If you want a more accurate clock, then page 49 also mentions how you can connect an external crystal or other oscillator to the part.
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