  The cotangent bundle $T^*X$ to a complex manifold $X$ is classically endowed
with the sheaf of $\cor$-algebras $\W[T^*X]$ of deformation quantization, where
$\cor\eqdot \W[\rmptt]$ is a subfield of $\C[[\hbar,\opb{\hbar}]$. Here, we
construct a new sheaf of $\cor$-algebras $\TW[T^*X]$ which contains $\W[T^*X]$
as a subalgebra and an extra central parameter $t$. We give the symbol calculus
for this algebra and prove that quantized symplectic transformations operate on
it. If $P$ is any section of order zero of $\W[T^*X]$, we show that
$\exp(t\opb{\hbar} P)$ is well defined in $\TW[T^*X]$.
