Baseband injection provides a useful approach for use in linearizing power amplifiers. The challenge is the determination of the required baseband signal. In  a generalized formulation quantifying the baseband voltage signal, injected at the output bias port, to linearize the device behavior was introduced. This envelope domain based solution requires the determination of only a small number of linearizing coefficients. More importantly these coefficients should be stimulus, hence bandwidth independent. This property has been experimentally investigated using a 10W Cree GaN HEMT device under a 3-tone modulated stimulus at 1.5dB of compression. It will be shown that the linearization coefficients were invariant when varying the modulation bandwidth from 2MHz to 20MHz.