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Implementing an ADC inside X-i-l-i-n-x C-P-L-D?

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Bus Master

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xilinx delta sigma adc

Hi there,

I'm a novide in VHDL programming. I wonder if i can implement an ADC unit inside a x-i-l-i-n-x C-P-L-D XC9536 or XC95108?

I need multi channel i/ps (12 ch) for atlease 10 bits resolution.

Is this possible?

Any help is highly appreciated.

Yours,
 

Ace-X

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cpld comparator

No! CPLD is fully digital circuit - it has no configurable analog blocks inside. It is possible to use external comparator to build simple delta-sigma ADC. Of course, I think it is not good idea, especially for CPLD! Check this link for more information on how you can use CPLDs:
http://www.xilinx.com/apps/epld.htm#XC9500XL

Also, check PSoC from Cypress - they have configurable analog blocks on-chip.

Ace-X.
 

7rots51

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implementing delta sigma converter xilinx

hi

is it possible to build 16 bit sigma delta ADC at low speed with a part of cpld and a comparator?

please comment on this.
bye
 

Ace-X

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7rots51 said:
is it possible to build 16 bit sigma delta ADC at low speed with a part of cpld and a comparator?
bye
I'm not sure about 16-bit, because the main problem will be selecting very precise resistor and capacitor for external low pass filter. 12 bits ADC looks more real. Check these links for main idea about ADC with programmable logic:
http://www.xilinx.com/xapp/xapp154.pdf
http://www.xilinx.com/xapp/xapp155.pdf

These application notes describe ADC and DAC design with Virtex FPGA, but CPLD's architecture is also suitable for this approach.


Ace-X.
 

padspcb

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Well it all deppends on the speed/precision of conversion.
Obviously the ladder comparator is the best way...
But supose you just want to know battery level or some
other low profile value.
The easyest way is to use a capacitor on the cpld input
and a resistor in series to the voltage source.
You keep the capacitor grounded by setting pin to output and gnd
Then you reset a counter, set pin to input and start counting
until input reaches high level. then you read the count
and you can use some formula to get value=a*count+b
with known cap and resistor, you may get curve.
the highest the input voltage is from digital high level
more linear it will be.
You may also place a resistor to vcc but then you will have 2 curves
but sometimes needed to check for no connected value
This is the method used by pic microcontrolers
hope this helps also
Pads
 

Jaannee

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Analog signal slowly rising is newer good for a cmos-input...
You should better put some sort of comparator inbetween. I´m shure Microchip uses an internal comparator for this application.

But this approach is more straightforward than to build your own sigma/delta-converter!

/Janne
 

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