fix: correct a node name

changes nothing

Final.tex

@@ -90,7 +90,7 @@ amplification is depicted below.
     (OA.out) to ++(0, 0) coordinate (OUT) to (FB)
     (OUT) to [short, *-o] ++(0.5,0) node [right=0.2cm]{$v_{out}$};
     \node (v_p) [above=0cm] at (OA.+) {$v_p$};
-    \node (v_p) [below=0cm] at (OA.-) {$v_n$};
+    \node (v_n) [below=0cm] at (OA.-) {$v_n$};
     ;
 \end{circuitikz}
 \end{figure}