Block diagram in electrical circuit
\documentclass[margin=3mm]{standalone}
\usepackage{circuitikz}
\usepackage{amsmath} % <---
\newcommand\ds{\displaystyle} % <---
\begin{document}
\begin{circuitikz}[scale=3, european]
\draw (0,1) to [R=$R$] ++ (1,0)
to [L=$L$] ++ (1,0)
to [C=$C$] ++ (1,0)
to [short,i=$i(t)$] ++ (0,-1)
to [twoport,t=\Large $G$,
l={$\xrightarrow[\ds u_e(t)]{}$}] (0,0) % <---
-- (0,1);
\end{circuitikz}
\end{document}
gives:
addendum:
If you like to have circuit's elements on opposite side, than you can write:
\draw (0,1) to [R,a=$R$] ++ (1,0)
to [L,a=$L$] ++ (1,0)
to [C,a=$C$] ++ (1,0)
to [short,i=$i(t)$] ++ (0,-1)
to [twoport,t=\Large $G$,
l={$\xrightarrow[\ds u_e(t)]{}$}] (0,0) % <---
-- (0,1);
or
\draw (0,1) to [R,l_=$R$] ++ (1,0)
to [L,l_=$L$] ++ (1,0)
to [C,l_=$C$] ++ (1,0)
to [short,i=$i(t)$] ++ (0,-1)
to [twoport,t=\Large $G$,
l={$\xrightarrow[\ds u_e(t)]{}$}] (0,0) % <---
-- (0,1);
in both cases the result is the same: