\node[vdd] (vdd) at (0,0) {};
\draw (vdd) to [ american current source
               , l=$I_{\mathrm{0}}$
               ] ++ (0,-1.25) 
            to [short,-] ++ (0,-0.25) coordinate (x)
            to [short,-] ++ (0,-0.25)
            node [pmos,anchor=source] (m1) {};
\draw (m1.drain) to [short,-] ++ (0,-0.25) coordinate (vss)
                 node[vss] {};

\draw (m1.gate) to [short,-o]  ++ (-0.25,0) node[left] {I};
\draw (x)       to [short,*-o] ++ (1.0,0)   node[right] {O};    

\node[ anchor    = west
     , inner sep = 2pt
     , font      = \footnotesize
     ] () at ($(m1.source)!0.5!(m1.drain)$) {M1};