\documentclass[12pt,border=1pt,crop,multi=false,tikz,class=scrartcl]{standalone}
\usepackage{setspace}
\usepackage{circuitikz} 
\usetikzlibrary{arrows,shapes,calc,positioning,fit,decorations.markings}

\begin{document}
\begin{circuitikz}
	\draw
		(3,.5) node [op amp] (opamp) {} 
		(0,0) node [ground] {} to [C, l=C] (0,2)  to[short, -*] (1,2)
		node [above] {6} 
		(1,2) ǀ- (opamp.-)
		(1,2) to [R, l=R] (4.5,2) to [short, -*] (4.5,.5) node[above right] {$c$}
		(opamp.out) to[short,-o] ++(1.5,0) node[above] {V$_o$}
		(4.5,.5) to [R, l=R$_1$, -*] (4.5,-1.5) node[right] {$a$}
		(4.5,-1.5) to [R, l=R$_2$] ++(0,-2) node[ground]{}
		(opamp.+) -- ++(-1,0) ǀ- (4.5,-1.5)
	;
\end{circuitikz}
\end{document}