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3-Phase AD9834 - Phase Accumulation Error

Question asked by NickB91 on Jan 15, 2016
Latest reply on Jan 27, 2016 by NickB91

Hi,

 

I am designing a 3-phase voltage source using 3x AD9834 chips that are on individual PCB's. They are all individually clocked on their own PCB's using a 1MHz Crystal Oscillator. (So not sharing a clock source)

 

When looking at the outputs, the frequencies are all exactly 50Hz (In the order of 50.000 accuracy), which is great.

 

My problem is if I for example, look at two phases together on an oscilloscope, they move away from each other and accumulate a continuously increasing phase error (approximately 0.036 Degrees per second) which is very considerate and a big problem for my application.

 

Why would this be happening? Are the AD9834 IC's known to have this error? Is it due to them not running off of the same oscillator?

 

I assume it is the AD9834's themselves leading to this problem but I am not sure how to fix it - I will try and run them off the same clock as a last resort but its tricky in my current situation of surface mount accessibility.

 

Any ideas would be greatly appreciated! Thanks.

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