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Signal superposition on received signal from CC2400

Other Parts Discussed in Thread: CC2400


I performed tests with a CC2400. I injected on its digital I/O a square signal which is half of the programmed bitrate. On the edges of the signal, I can identify a superposition of a sinusoid which frequency's is the double of the deviation. Here is a screenshot of the oscilloscope.

Is it normal ? Is there a problem with my design ?

If it's normal, why do we get this kind of signal ? Thank you for your answers.


  • Clement, 

    It looks like "ringing" or some other test and equipment error not the part itself.

    Can you post a little image of how you measured this graph, where you inject what signals and how it was measured. Maybe a picture of your setup.


  • Hello,

    thank you for considering my questions. I'm sorry but I can't post this kind of picture because of confidentiality reasons. But I can explain how the measure has been performed.

    First, I inject a square signal at 250kHz on the pin 29 of the CC2400. It's amplitude is 3V (DVDD = 3.3V). The measured signal is obtained after decoding over the air. We have a receiver which is synchronized at the chip's frequency decoding NRZ signal. This decoder is plugged to the oscilloscope. when there is nothing connected to the IO pin, the decoder "sees" a sinusoid at a frequency which is twice the deviation frequency.

    Thank you.