TikZ-PGF – How to Create Circled Inline Numbers and Letters

Question

Based on Good way to make \textcircled numbers?, is there a simple way to make the circles look exactly the same for numbers and all letters (i.e. size and placement)?

When one inserts an a in the circle, the node is drawn slightly lower than the node for a number.

\documentclass{article}

\usepackage{tikz}
\newcommand*\circled[1]{\tikz[baseline=(char.base)]{
    \node[shape=circle, draw, inner sep=1pt, 
        minimum height=12pt] (char) {#1};}}

\begin{document}
This is \circled{a} \circled{1} balloon.
\end{document}

EDIT

Based on the answer by @koleygr and the post circled letters: same size as uncircled letters, I find this solution the most pleasing and versatile:

\newcommand*{\circled}[2][]{\tikz[baseline=(C.base)]{
    \node[inner sep=0pt] (C) {\vphantom{1g}#2};
    \node[draw, circle, inner sep=3pt, yshift=1pt] 
        at (C.center) {\vphantom{1g}};}}

Answer 1

Edit after accepted:

\documentclass{article}

\makeatletter
\usepackage{tikz}
\usetikzlibrary{calc}
\newcommand*\circled[1]{\tikz[baseline=(char.base)]{
    \node[shape=circle, draw, inner sep=1pt, 
        minimum height={\f@size*1.6},] (char) {\vphantom{WAH1g}#1};}}
\makeatother

\begin{document}
This is \circled{a} \circled{1} balloon.

\noindent\foreach \letter in {A,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P,Q,R,S,T,V,U,W,X,Y,Z,a,b,c,d,e,f,g,h,i,j,k,l,m,n,o,p,q,r,s,t,u,v,w,x,y,z,1,2,3,4,5,6,7,8,9,0,.,/}
{%
\circled{\letter}\space%
}
\end{document}

Output:

Not really perfect because of different base on chars (but it is better from the bellow answer)

Checking the same code in the document environment above with below definition of circled:

As you can see with previous (below) code the sizes change between small and capital letters.

Old answer:

A \vphantom in your definition will help:

\documentclass{article}

\usepackage{tikz}
\newcommand*\circled[1]{\tikz[baseline=(char.base)]{
    \node[shape=circle, draw, inner sep=1pt, 
        minimum height=12pt] (char) {\vphantom{1g}#1};}}

\begin{document}
This is \circled{a} \circled{1} balloon.
\end{document}

Output: