CC2650 ADC minimum sampling rate to sample signal of certain frequency

Xiaoxiao Hou

Other Parts Discussed in Thread: CC2650

Hello,

I am a bit confused about the minimum sampling rate required to correctly sample signal of certain frequency in CC2650 ADC. In Sensor Controller Studio, I fixed the sampling rate at 2kHz by calling function:

adcStartAuxTimer0Trigger(500);

And I tried periodic sine waves of different frequencies: 100Hz, 200Hz, 500Hz, and 1kHz.

It seems ADC with sampling rate fixed at 2kHz is only able to correctly sample sine waves of 100Hz. So the ratio of ADC sampling frequency/signal frequency is 2kHz/100Hz=20. Here shows the figures:

This is sine wave of 100Hz.

This is sine wave of 500Hz:

I am a bit surprised that the ratio is 20. Normally 12-bit ADC takes 14-cycle data conversion and 10-cycle hold time, so according to Nyquist theorem, the minimum ratio should be (10+14)*2=48? Did I make any mistakes here?

Your feedback will be greatly appreciated! Thanks!

Best,

Xiaoxiao

over 8 years ago

0 Eirik V over 8 years ago

TI__Guru 56590 points

Hello Xiaoxiao,
I do not know the details of the ratio you refer to, but I can review the sensor controller code. Did you use the ADC Data Streamer example code?

0 Xiaoxiao Hou over 8 years ago in reply to Eirik V

Intellectual 405 points

Hi Eirik,

Yes I was using ADC data streamer example code. I think my questions is if I set my ADC sampling rate at 2kHz, what is the maximum signal frequency that I can resolve? It seems 100Hz from this example code.

Thanks!

Best,
Xiaoxiao

0 Eirik V over 8 years ago in reply to Xiaoxiao Hou

TI__Guru 56590 points

Hello Xiaoxiao Hou,
This is moving into the signal processing domain. I cannot provide to much help. By looking at your plot for the 500 Hz sampled wave you have 5 samples per period of the sinusoidal shape which should be enough to reconstruct the signal. Check out FIGURE 3-3 here: www.dspguide.com/CH3.PDF

0 Xiaoxiao Hou over 8 years ago in reply to Eirik V

Intellectual 405 points

Hi Eirik,

That makes sense! Thanks so much for your help!

Best,
Xiaoxiao

0 Tarak MAAMMAR over 7 years ago in reply to Xiaoxiao Hou

Expert 1190 points

Hi,
I tried to make a simple ADC program to sample an analog signal. The thing is i can't get correct waves even though i'm trying very low frequency alternative signals (10hz, 20 hz, ...). Can you help to at least identify where the problem is ?

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CC2650 ADC minimum sampling rate to sample signal of certain frequency