center frequency of Phase noise measurement plot from the output of a NCO is always in Mhz Range while what i expect is GHz range.

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Hi, I was trying to generate a 2.4 GHz sine wave using a NCO. tuning word and sampling time were given for the same. The output from the scope is showing a 2.4Ghz wave (not sinusoidal, but it oval shaped balls). When i connect a phase noise measurement block to the same signal and plot the noise graph, it is showing that center frequency is 13Mhz only. What could be the possible error?
The sampling time given is 2e-10, for 16 bit accumulator size. FTW is 31458 as int16.
Thanks.

Accepted Answer

Gokul Nath S J
Gokul Nath S J on 23 May 2023
Hi Rezim,
The issue you are observing with the oval shaped balls instead of a sinusoidal waveform could be due to some non-ideal effects in your implementation, such as nonlinearity, distortion, or quantization noise. It is also possible that the signal generated by your NCO is not being correctly captured by your oscilloscope.
Regarding the issue of the phase noise measurement block showing a center frequency of only 13 MHz instead of 2.4 GHz, it is possible that the measurement block is not configured correctly or is not designed to measure such high-frequency signals. One possible explanation could be that the measurement block has a limited bandwidth, which could cause it to measure only the low-frequency components of your signal, resulting in a center frequency of only 13 MHz.
It is important to check the configuration and specifications of your measurement block to ensure that it is capable of measuring the frequency range of your signal. Additionally, you may want to consider using a spectrum analyzer or other high-frequency analysis tool to verify the frequency content of your signal.
with regards,
Gokul Nath S J

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