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How do I calculate the output frequency of my analog output (DAC) device?


Jeffrey
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Most think of the "Update rate" specification in the data sheet or manual of your selected analog output device as your maximum output frequency rate and that is not the case. Your update rate is basically how many data points per second the DAC device can output.

To properly calculate your "Output frequency" you will need to know your update rate, and how many samples per second you want to send out. You can then plug them into the formula below to derive your answer.

Output Frequency = Update Rate / Samples per waveform

Ex: 1,000,000 S/sec ÷ 1,000  = 1000 S/sec

The one thing to keep in mind is the quality of your output signal. Every sample point represents a point on your waveform. So if we used a 1000 Hz sinewave as an example and you were to calculate your output frequency using the formula above you would have 1000 points per cycle which is a good representation of the waveform. The more data points the better.

Now let’s say that your maximum update rate is only 10,000 S/sec. In order for you to achieve a 1000 S/sec output frequency you must lower your samples/sec to 10 S/sec which greatly affects the resolution of your waveform.

The images below are a representation of what the two output signals would look like. Both waveforms are outputting 1000 S/sec but as you can see the one on the right with only 10 S/sec of data points is greatly effected and results in a poor quality waveform. 

image.png.a7c908eaa442c5cb9844d45164a2ecc7.png

So as a rule of thumb the more sample points per cycle and the highest sample rate possible will result in the best output waveform. 

 

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