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Problem about Inverting signals inside FPGA.

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EDA_hg81

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inverting fpga

My situation is as following:
Have to use Virtex E to drive a sensor with 5V TTL logic.
I used NC7ST04 inverter as a level shifter.
https://images.elektroda.net/66_1226541807.jpg
Inside FPGA I wrote code as:
Code:
Signal_out <= not ( signal );
Based on above way, after two inverting the signal is going to be changed to 5V TTL with the same rising and falling edges as inside LVTTL logic.
But the problem is the signal output from FPGA is totally wrong, the voltage is inverted but with a -3.3V offset as in the figure 2th.

https://images.elektroda.net/51_1226541772.jpg

I used the same ground reference measure those two signals.

What is the problem?
Thank you for your suggestions.
 

yego

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Pretty odd indeed.
How about checking your .ucf file if the output has been properly defined with a suitable standard ?
or perhaps you simply mixed up your scope leads ?
 

    EDA_hg81

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EDA_hg81

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When I switched the proram, I didn't change the probe.

It is so confused.
 

EDA_hg81

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I tried use the component INV.

the same result.

So sad.:cry:
 

benradu

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Check your channel 1 setting (on the scope). I believe you have coupling set to AC instead of DC.
 

    EDA_hg81

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EDA_hg81

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yes.

you are so right.

my setting was AC coupling.

Thank you so much.
 

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