Operation at high frequencies.

[maverikk]

This is rather a silly question. While generating a sinusoidal signal why the shape of the signal gets distorted when I increase the frequency? I am attaching snapshots.  I am using NI PXIe-6366 which has sampling rate 2 MS/s/ch. And I have kept sampling rate as 1Msps while generating the signal. 

The bigger problem that I am facing is that if I transmit this distorted signal, the received signal is even more distorted and I am unable to do the processing required. Its working fine for lower frequencies.

[Kevin_Price · Accepted solution]

How well can you recreate the shape of a sine curve with 5, 4, or ~3 points?  Not very well, as you're seeing.   A typical rule of thumb I've followed is to try to have an output rate that's ~20x the sinusoid waveform frequency when possible.  Then each sine wave is defined with 20 points and starts to show a more realistic sinusoidal shape.  What you can "get away with" depends very much on the system receiving the signal you're generating.

When displaying an AO signal on a LV graph, I often right-click the plot in the graph legend and change the interpolation mode.  There's an option that will make the graph look a bit more like the actual D/A output signal -- it's an instant rise to the sample value followed by a flat hold until the next sample value.

-Kevin P

[RTSLVU]

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@maverikk wrote:

This is rather a silly question. While generating a sinusoidal signal why the shape of the signal gets distorted when I increase the frequency?  

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I know you are not doing audio but this Basics of Digital Audio site will help.

Specially page about Nyquist's Sampling Theorem.