why diode didn't block 12mV?

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EDA_hg81

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The attachment is my simulation figure.

The question is when the Vss is 3.3V the voltage at “in2” node is 12mV, but why voltage at "out" node is 12mV too?

I think diode is going to block this 12mV and voltage at “out” node should be 0V.

So many thinks for any ideas.
[/i]
 

Just a guess:

With no load across the output, no current can flow so no voltage can be dropped.
Try adding a high value resistor (1MΩ) from the output to ground and see what happens.

Brian.
 

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    EDA_hg81

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it is working now. the output is 420uV when Vss is 3.3V.

Thank you so much.

If i replaced 1n4005 diode with in4148, I got the follow messange:

"breakdown current increased to 3.86635E-10 to resolve incompatability with specified saturation current"

what is the reason for this?

Thanks
 

That's a simulator complaint, your current in breakdown
can't possibly be less than your reverse saturation current
and it's just informing you that it doesn't like insane model
card inputs.
 

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    EDA_hg81

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