  We have studied the weak decay constants and the Isgur-Wise form factor of
the B and D mesons in the heavy quark limit, by employing a relativistic quark
confinement model. It is an attempt to improve our previous work within the
same line of thinking, but by incorporating a couple of novel aspects. First,
the infrared behavior of the heavy quark is considered by modifying its
conventional propagator in terms of a single parameter $\nu$. Second, the mass
difference of the heavy meson and heavy quark: $E=m_H-M_Q$ has been included.
It is found that the weak decay constants depend strongly on the mass
difference E with a relatively mild $\nu$ dependence. As for the Isgur-Wise
function it is controlled more sensitively by the infrared parameter $\nu$,
leading to its suppression at maximum meson recoil.
