drain bias in more detail the high efficiency power amplifier 630 amplifies the rf signal using the amplitude component linearly amplified by the linear amplitude amplifier 611 of the bias modulator 610 as the drain bias voltage and using the current generated by the switching regulator 615 as the drain bias current when the bias modulator of the eer power transmitter controls the input bias voltage of the switching regulator based on the magnitude of the amplitude component the performance change is now illustrated fig7 a and 7b are graphs showing the performance change of an eer power transmitter according to an exemplary embodiment of the present invention herein to examine the performance change it is assumed that the eer power transmitter uses a mobile wimax amplitude signal of the institute of electrical and electronics engineers ieee 802 16e standard with a 10 mhz band and that the peak to average power ratio papr is 8 db with a crest factor reduction cfr adopted fig7 a shows the output current of the bias modulator when a constant bias voltage is applied to the switching regulator and fig7 b shows the output current of the bias modulator when the bias voltage of the switching regulator is controlled based on the magnitude of the amplitude component according to an exemplary embodiment of the present invention when the bias modulator supplies the two step bias voltage of zero 0 and vds to the switching regulator according to the magnitude of the amplitude signal the.