\begin{circuitikz}[scale = 0.7, transform shape]

  
%  \draw[help lines] (0,0) grid (8,6);
%  \foreach \x in {0,...,14} \draw (\x,-1) node {\x};
%  \foreach \x in {0,...,7} \draw (-1,\x) node {\x};

  % uref
  \draw(1,1) to[V_<=\large{16V}, l^=\large{$U_{ref}$}] (1,5);
  \draw(1,3) -- (1,-0.1) node[rground]{};

  % op, refpunkt ist der ausgang
  \draw(13,1) node[en amp, anchor=out] (op) {};
  \draw(op.+) -| (10,-0.1) node[rground]{};
  \draw(op.-) -| (10,3) to (10.5,3) to[R=$R_{gk}$, a=1$k\Omega$] (12.5,3) -| (op.out);
  % ausgangsbeschaltung
  \draw(op.out) to[short,-o] (13.5,1){};
  \draw[-{Triangle[scale=2.5, length=2, width=2]}](13.5,0.8) -- (13.5,0.2);
  \draw(14,0.5) node[]{\Large{$U_a$}};
  \draw (13.5,0) to[short,o-] (13.5,-0.1) node[rground]{};
  
  \ctikzset{label/align = rotate}
  \draw(3,4) to[R=$2\cdot R_0$, a=2$k\Omega$] (3,6);
  \draw(5,4) to[R=$4\cdot R_0$, a=4$k\Omega$] (5,6);
  \draw(7,4) to[R=$8\cdot R_0$, a=8$k\Omega$] (7,6);
  \draw(9,4) to[R=$16\cdot R_0$, a=16$k\Omega$] (9,6) to (1,6) to (1,5);
  \ctikzset{label/align = straight}

  \draw(3,4) node[spdt,xscale=-1, yscale=-1, anchor=in, rotate=90] (z3) {};
  \draw(5,4) node[spdt,xscale=1, yscale=-1, anchor=in, rotate=90] (z2) {};
  \draw(7,4) node[spdt,xscale=-1, yscale=-1, anchor=in, rotate=90] (z1) {};
  \draw(9,4) node[spdt,xscale=1, yscale=-1, anchor=in, rotate=90] (z0) {};

  \draw(z3.out 1) |- (op.-);
  \draw(z2.out 2) |- (op.-);
  \draw(z1.out 1) |- (op.-);
  \draw(z0.out 2) |- (op.-);

  \draw(z3.out 2) node[rground]{};
  \draw(z2.out 1) node[rground]{};
  \draw(z1.out 2) node[rground]{};
  \draw(z0.out 1) node[rground]{};

  \pause
  % U_d
  %\draw(op.out) to[short,-o] (13.5,1){};
  \draw[color=blue,-{Triangle[scale=2.5, length=2, width=2]}](10,0.75) -- (10,1.25);
  \draw(9.8,1) node[color=blue,anchor=east]{\Large{$U_d \approx 0V$}};

  \pause
  \draw[color=blue,-{Triangle[scale=2.5, length=2, width=2]}](6,0.5) -- (6,1.25);
  \draw(6,0.5) node[color=blue, anchor=north]{\large{Potential $\approx$ 0V}};

  \pause
  \draw[color=blue,-{Triangle[scale=2.5, length=2, width=2]}](12.5,4) -- (10.5,4);
  \draw(11.5,4) node[color=blue, anchor=south]{\Large{$U_a$}};

  % stroeme durch widerstaende
  \pause
  \draw (3,4.1) to [color=red,short,i_=\large{$i_3=8mA$}] (3,4);
  \pause
  \draw (7,4.1) to [color=red,short,i_=\large{$i_1=2mA$}] (7,4);

  % gesamtstrom
  \pause
  \draw (10,2.2) to [color=red,short,i_=\Large{${i_{ges}}$}] (10,2.2);
  \pause
  \draw (13,2.2) to [color=red,short,i^=\Large{${i_{ges}}$=10mA}] (13,2.1);

  % spannung
  \pause
  \draw(11.7,4.4) node[color=blue, anchor=west]{\Large{=-10V}};
  
  %\draw(5,4) to[nos=$z_2$] (5,2) |- (op.-);
  %\draw(7,4) to[nos=$z_1$] (7,2) |- (op.-);
  %\draw(9,4) to[nos=$z_0$] (9,2) |- (op.-);
  
 
  % ausgang
  %\draw(op.out) to[short,-o] (op.out){};
  %\draw(8.5,0.5) node[]{\Large{$U_a$}};
  %\draw[-{Triangle[scale=2.5, length=2, width=2]}](8,0.8) -- (8,0.2);
%  \draw(8,-0.2) to[short,->] (8,-0.8);
  %\draw (8,0) to[short,o-] (8,-0.2) node[rground]{};
  
\end{circuitikz}
