use circuitikz picture inside tikzpicture

In block scheme I like to add a node with call out shape, which contain details of electronic circuit. This electronic circuit is easy to draw with circutikz package. Here is my attempt to achieve this goal:

documentclass[tikz,border=3mm]{standalone}
    usetikzlibrary{positioning,%
                    shapes,shapes.callouts%
                    }
    usepackage{fouriernc}
    usepackage[scaled=0.83]{helvet}
    usepackage[scaled=0.82]{luximono}
    usepackage{marvosym,pifont}

    usepackage[T1]{fontenc}
    usepackage[utf8]{inputenc}
%---------------------------------------------------------------%
usepackage[european,siunitx]{circuitikz}
usepackage{siunitx}
sisetup{detect-family,
     color = teal!40!black}
%---------------------------------------------------------------%
    begin{document}
begin{tikzpicture}
coordinate (a) at (0,0);
coordinate (b) at (4,0);
draw (1,-0.1) -- (1,0.1);
draw (2,-0.1) -- (2,0.1);
draw (3,-0.1) -- (3,0.1);
    draw[ultra thick,*-*] (a) -- (b);
node[shape=rectangle callout,
      draw, rounded corners,
      callout pointer width=3.3 mm,
      callout pointer shorten=-2mm,
      font=sffamilyfootnotesize,
      align=center,
      callout absolute pointer={(b)},
      scale=0.5] at ([xshift=19mm,yshift=3mm] b)
    {termination circuit
    begin{circuitikz}[sharp corners]
draw[ultra thick, blue] plot[smooth,domain=-0.25*pi:-0.75*pi, samples=36] (0.25*pi+x,{-1*sin(2*x r)});
draw[ultra thick, red]  plot[smooth,domain=-0.25*pi:-0.75*pi, samples=36] (0.25*pi+x,{+1*sin(2*x r)});
draw[ultra thick, red]  plot[smooth,domain=-0.75*pi:-1.25*pi, samples=36] (0.25*pi+x,{+1*sin(2*x r)});
draw[ultra thick, blue] plot[smooth,domain=-0.75*pi:-1.25*pi, samples=36] (0.25*pi+x,{-1*sin(2*x r)});
draw   (0,3)   node[right] {SI{+5}{V}}
    to [R=$R_s$,o-] (0,+1)  node[right] {A}
    to [R=$R_k$,*-*] (0,-1) node[right] {B}
    to [R=$R_s$, -o] (0,-3)
                node[right] {SI{0}{V}};
    end{circuitikz}
    };
node[shape=rectangle callout,
      draw, rounded corners,
      callout pointer width=3.3 mm, 
      callout pointer shorten=-2mm,
      font=sffamilyfootnotesize, 
      align=center,
      callout absolute pointer={(a)},
      scale=0.5] at ([xshift=-19mm,yshift=3mm] a)
    {termination circuit
    begin{circuitikz}[sharp corners]
draw[ultra thick, blue] plot[smooth,domain=-0.25*pi:-0.75*pi, samples=36] (0.25*pi+x,{-1*sin(2*x r)});
draw[ultra thick, red]  plot[smooth,domain=-0.25*pi:-0.75*pi, samples=36] (0.25*pi+x,{+1*sin(2*x r)});
draw[ultra thick, red]  plot[smooth,domain=-0.75*pi:-1.25*pi, samples=36] (0.25*pi+x,{+1*sin(2*x r)});
draw[ultra thick, blue] plot[smooth,domain=-0.75*pi:-1.25*pi, samples=36] (0.25*pi+x,{-1*sin(2*x r)});
draw   (0,3)   node[right] {SI{+5}{V}}
    to [R=$R_s$,o-] (0,+1)  node[right] {A}
    to [R=$R_k$,*-*] (0,-1) node[right] {B}
    to [R=$R_s$, -o] (0,-3)
                node[right] {SI{0}{V}};
    end{circuitikz}
    };
end{tikzpicture}
    end{document}

Questions:

• why both nodes are not the same (as I expected);

• why I receive error “unknown function ‘south (in south east)’ if I use for positioning of node possibilities offered by positioning library?

  node[shape=rectangle callout,
  draw, rounded corners,
  callout pointer width=3.3 mm,
  callout pointer shorten=-2mm,
  font=sffamilyfootnotesize,
  align=center,
  callout absolute pointer={(a)},
  scale=0.5,
  above left=-19mm and 3mm of a] {content of node};

Edit: I correct a bit my preamble where by mistake I had usepackage{circuitikz} twice. The second one should be siunitx wit added setup. I like to have labels of resistors in sans sheriff font, but this hasn’t happen. I do not knoe why not, but this is not a issue of this questionseparate question.