Electric circuit on presentation

Question

I am working on presentation and I searched for best way to draw electrical circuits and found out it is in LaTeX. I worked a little bit in LaTeX, but not enough to draw these, so if there is anyone who would help me I would be very grateful. BTW, I need to recreate these circuits:

Answer 1

Here's the first circuit, I'll leave the second as an exercise for the reader :).

\documentclass[border=20, tikz]{standalone}
\usepackage{circuitikz}
\usetikzlibrary{calc}
\begin{document}
    \begin{tikzpicture}
        \draw (0, 0) to[L, l=\(L_1\)] (0, 4);
        \draw (2, 0) to[C, l=\(C_1\), *-*] (2, 4);
        \draw (2, 4) to[R, l=\(R_1\), *-*] (4, 4);
        \draw (4, 0) to[C, l=\(C_2\), *-*] (4, 4);
        \draw (6, 0) to[R, l=\(R_2\), *-] (6, 2);
        \draw[fill=black] (6, 2) to[diode, l=\(D_1\), -*] (6, 4);
        \draw (8, 0) to[R, l=\(R_3\), *-] (8, 2);
        \draw[fill=black] (8, 4) to[diode, l=\(D_2\), *-] (8, 2);
        \node[op amp, xscale=-1, yscale=-1] (opamp) at (14, 2) {};
        \draw ($(opamp.out) + (-1, 0)$) to[short, *-] (opamp.out);
        \draw ($(opamp.out) + (-1, 0)$) -- ($(opamp.out) + (-1, 1.5)$);
        \draw ($(opamp.out) + (-1, 0)$) -- ($(opamp.out) + (-1, -1.5)$);
        \coordinate (opamp plus) at (opamp.+);
        \coordinate (opamp minus) at (opamp.-);  %  - sign in opamp.- causes errors with the |- notation
        \draw (opamp plus) -- (opamp plus|-(0, 3.5));
        \draw ($(opamp.out) + (-1, 1.5)$) to[R, n=R4, -*] (opamp plus|-(0, 3.5));
        \node[below] at (R4.s) {\(R_4\)};  % want name to appear below below
        \draw (opamp minus) -- (opamp minus|-(0, 0.5));
        \draw ($(opamp.out) + (-1, -1.5)$) to[R, l=\(R_5\), -*] (opamp minus|-(0, 0.5));
        \draw (0, 4) -- (2, 4);
        \draw (4, 4) -- (opamp plus|-(0, 4));
        \draw (15.2, 4) -- (opamp plus);
        \draw (0, 0) -- (8, 0);
        \draw (8, 0) to[R, l=\(R_6\)] (opamp minus|-(0, 0));
        \draw (15.2, 0) -- (opamp minus);
        \node[ground] at (8, 0);
    \end{tikzpicture}
\end{document}