FPGA Central

Hi,

I have trouble with the F2812 ADC, I use a ezdsp2812 with a custom mad
extension board.

I feed the ADC input directly (no R-C) from a classical 1 amp (AD8029) 2
Sallen-key lowpass filter, with all unused ADC pin tied to AGND.
The output of the filter look ok on the scope but the ADC reading ar
weird.

0V -> 6DC
1.34 -> EE4
1.72V -> F1C

I have 1 ADC Chanel with no filter for debug but the reading ar
similarity, no change if I put this pin to Agnd either.


But if I unplug my extension card and short VREFLO to agnd and directl
feed the signal I got reading that make sense but with a lot more noise.

Someone have a Idea will I have those troubles, do I need to put a passiv
R-C lowpass at the output of my filter ?

Thx
Eric

thales2 wrote:

> Hi,
>
> I have trouble with the F2812 ADC, I use a ezdsp2812 with a custom made
> extension board.

The ADC of TMS28xx is just an MCU ADC. It really takes nothing special
to make it work.
Your problems are likely to be a combination of the trivial hardware and
software mistakes. I have no doubts that I could fix it in 10 minutes;
but I am not going to do that for free.


Vladimir Vassilevsky
DSP and Mixed Signal Design Consultant
http://www.abvolt.com

Vladimir Vassilevsky wrote:
>