question about comparator

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admiral_v

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why in this comparator out voltage is between -vdd and +vdd While we expect 0-vdd
 

The circuit does not have a positive supply called +vdd. Then its output cannot be a positive voltage.
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Meaned to say "the circuit has only positive Vdd and can't have negative output"?

There may be some negative voltage peaks by capacitive crosstalk, bad hardly to full inverted Vdd level.
 

Before I posted I wrote that the circuit was missing a negative supply due to the arrows on the transistor "emitters". Then I realized the transistors are Mosfets and the arrows on Mosfets sources are in the opposite direction with the opposite polarity to emitters on transistors. So I corrected by saying the positive supply is missing.
 

Apparently you don't understand the meaning of a differential voltage probe V(out+,out-1).
 

That is because you are testing differential output. When Vout+ = 2.5V and Vout- = 0V, your simulation result gives 2.5V and when Vout+ = 0V and Vout- = 2.5V, your simulation result gives -2.5V.

Xiahan
 

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