Amplifier (buffer) with a "down" node

Question

How can I draw an amplifier with a down node? On the manual are shown different types of amplifiers: fd op amp (2 in - 2 out), plain amp (2 in - 1 up - 1 out) etc. I need just an "hybrid" amp: I need it to have just 1 in and 1 out (like the buffer), but I need it to have a down node too. How can I solve this problem?

If i use "buffer" class, i get 1 in - 1 out, but i don't have access to the "down" pin. Thanks in advance.

This is my actual work

\begin{circuitikz}[american voltages]
\draw
(0,0) node[buffer] (opamp) {}
(opamp.in) to [short, -o] ++(-2,0) coordinate (Ai)
(opamp.out) to [short, -o] ++ (2,0) coordinate (Ao);
\end{circuitikz}

If i use (opamp.down) it doens't work.

Answer 1

In a recent circuititz (version 1.0 or above) you have two possibilities:

\documentclass[border=10pt]{standalone}
\usepackage[siunitx, RPvoltages]{circuitikz}
%\usepackage[siunitx, RPvoltages]{circuitikzgit}
\begin{document}
\begin{circuitikz}
    \draw (0,0) node[plain mono amp](A){} (A.down) -- ++(0,-0.5);
    \draw (3,0) node[muxdemux, 
        muxdemux def={NL=1, NR=1, NB=1, w=3, Lh=3, Rh=0, square pins=1}] {}; 
\end{circuitikz}
\end{document}

which gives:

Notice that amplifiers are not path-type components, but node-type ones. It is very important to grasp the difference, because it's one of the basic points in circuitikz...