Two oscillators resonate with the same crystal and one is offset. Possible?

[neazoi]

DDS is as stable as the source, its direct frequency division through a phase increment latch, plus a digital to analog conversion in cases where a sine wave output is desired.

Two DDS dividers running from the same source would track exactly.
If the obtainable DDS frequency increments were 1 Hz, you could generate two frequencies 1Hz apart very easily.

Is this also the case with microcontrollers when used as DDS? (i.e microcontroller produces a square wave by switching on and off a pin).
If so, two microcontrollers could be driven by the same external oscillator, or the same microcontroller can output two outputs with different division ratio and so different frequencies.
Will these frequencies exactly track each other?

 

[Warpspeed]

Will these frequencies exactly track each other?

In theory yes, but the reason application specific DDS chips are used in frequency synthesizers is that its a lot easier to get the speed and fine frequency resolution with some very fast counters and adders, than to try to write a software program, unless the output frequencies you require are very low.

Usually a micro-controller just reads a keyboard, or a shaft encoder, and drives a digital frequency readout, with perhaps a few memories and other features.
All the DDS frequency generation is done in a special purpose chip, the micro-controller just loads the required frequency into the DDS chip, and away it goes....

Something like this perhaps:
70 Mhz output max, with 40 milli Hertz resolution.
32 bit programming word.
https://www.analog.com/en/products/...hesis-modulators/ad9851.html#product-overview

That is just an example, there are plenty of similar devices out there.

Two of these, and a simple low end micro-controller to do the housekeeping.

 

[volker@muehlhaus]

Is this also the case with microcontrollers when used as DDS? (i.e microcontroller produces a square wave by switching on and off a pin).

Then you must be careful with interrupts that change the timing in the main code.