A bit of a puzzler here:

According to Mr Gauweiler, whose case is being brought
by a constitutional expert, Karl Albrecht Schlachtschneider, a
bundestag vote on the charter, rather than a vote by the people,
contravenes Germany’s ”basic law” or constitution.

"The
bundestag cannot give away to the EU more rights than it has itself.
Such a far-reaching constitutional law can only be based on a
referendum of the German people," he said yesterday in a statement,
which he claimed had the backing of many other MPs.

Prof
Schlachtschneider has be reported as saying that the EU charter goes
beyond the limits set by Germany’s constitutional court in a
ground-breaking 1993 ruling on the institution’s Maastricht treaty.

The
German government, has ruled out a referendum, arguing that Germany’s
basic law does not allow for one. Referenda are banned in Germany due
to the perception that they allowed Hitler to change the law in his
quest for power.

I’m not sure I have this quite right. So a referendum would be illegal under the Basic Law, and so would the Bundestag simply voting it through be illegal under that same law. So how can they sign it at all?