What improvements can be added?
Specially the decoration item.
MWE
\documentclass{article}
\usepackage{circuitikz}
\usetikzlibrary{shapes,arrows}
\usetikzlibrary{decorations.pathreplacing}
\begin{document}
\begin{circuitikz}[american voltages,scale=2]
\draw (0,0) node op amp,scale=1.5{};
\draw (amp.+) to [short,-*] ++(0,0) node[ground]{};
\draw (amp.-) to [R=\SI{$R_1$}{\ohm},-o] ++(-2,0) to [V=\SI{1}{V}] ++(0,-2) node[ground]{};
\draw (amp.out) to [short] ++(1,0) to [R=\SI{$R_l$}{\ohm}] ++(0,-2) node[ground]{};
\draw (amp.-) to [short,*-] ++(0,1) to [R=\SI{$R_2$}{\ohm}] ++(2,0) to [short,-*] ++(0,-1.37);
\draw (-2.25,-0.2) node [1] {}
node[right,blue] {$i_P=i_N=0,A$};
\draw [decorate,thick,decoration={brace,amplitude=5pt,raise=1ex,mirror},color=blue]
(-0.85,0.4) -- (-0.85,-0.4) node[midway,yshift=0em,xshift=-4.5em]{{$v_P=v_N=0,V$}};
\end{circuitikz}
\end{document}

