  The spin-orbit coupling (SOC) can mediate electric-dipole spin resonance
(EDSR) in an a.c. electric field. In this letter, the EDSR is essentially
understood as an spin precession under an effective a.c. magnetic field induced
by the SOC in the reference frame, which is exactly following the classical
trajectory of the electron and obtained by applying a quantum linear coordinate
transformation. With this observation for one-dimensional (1D) case, we find a
upper limit for the spin-flipping speed in the EDSR-based control of spin,
which is given by the accessible data from the current experiment. For
two-dimensional case, the azimuthal dependence of the effective magnetic field
can be used to measure the ratio of the Rashba and Dresselhause SOC strengths.
