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rigomm
Joined: 17 Mar 2010
Posts: 13
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| ADC internal clock sampling frequency |
 Posted: Thu Aug 05, 2010 7:40 am |
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Hello.
I´m using the dspic30f3012 configured to use the Fast RC oscillator and the 16 PLL. Everything works fine but...
I´m trying to figure out what is the "ADC internal clock"
I know that there are several clock sources for the ADC module. I have used the external clock but now I´m using the directive:
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setup_adc( ADC_CLOCK_INTERNAL );
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How can I calculate the sampling rate?
What or where is that ADC_Internal clock?, is a special clock for the ADC, what is the frequency.
I read the data sheet and search in this forum and many others but I couldn't find answers.
I measured the conversion time for my program and the TAD is 208ns!!!
As mentioned above, the main clock is (7,37MHz*16=117.92MHz) FRC.
How con I calculate the sampling rate, where come from this 208ns?
Thank you for any help or hint! |
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PCM programmer
Joined: 06 Sep 2003
Posts: 21708
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rigomm
Joined: 17 Mar 2010
Posts: 13
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| Solved...but |
| Posted: Thu Aug 05, 2010 10:44 pm |
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PCM programmer, than you for your time to reply my message! 
Actually I had already read this file that you kindly addressed to, but I didn't find what I was looking for.
and those documents are intended for a 10bits converter, but anyway, just by adding 2 TAD more it will works for a 12 bits ADC.
However I didn't find any hint about the sampling rate using the internal ADC clock on these pages.
But I found the answer in this other file.
http://techtrain.microchip.com/webseminars/documents/dsPIC12bADC_p1_121604.pdf
Th internal AD clock has a nominal rate of 47KSPS with a nominal Time of conversion of 21us, according to that file.
I hope it helps to somebody else looking for the same data.
By the way, I measured that and I have a conversion time of 32us, so I have 11us more from I don't know where. 
Anyway, I'm keep searching.
Thanks! |
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PCM programmer
Joined: 06 Sep 2003
Posts: 21708
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| Posted: Thu Aug 05, 2010 10:51 pm |
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Look in the Electrical Specifications section in your PIC data sheet.
Look for this parameter in the A/D CONVERSION TIMING REQUIREMENTS table:
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tRC A/D Internal RC Oscillator Period
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It will give the typical oscillator period, in ns. (Also the min and max).
I don't have the data sheet for your PIC with me, but it will probably
have that spec in it. |
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