Elecrtical and Computer Enginnering, Isfahan University of Technology
In this paper a two-phase supply modulator suitable for envelope tracking power amplifier is presented. The designed supply modulator has the linear assisted switching architecture. Two-phase architecture is used in order to reduce the output switching ripples. The proposed architecture uses hysteretic control instead of pulse width modulation (PWM) which significantly reduces the circuit complexity. Moreover, fewer number of external R and C elements are used which leads to simpler architecture in comparison with reported two-phase PWM supply modulators. The proposed envelope modulator is evaluated with 0.18 µm CMOS technology. The results show that the designed two-phase modulator improves the output switching noise ripples and consequently enhances the overall linearity of the modulator compared to the single-phase case. The overall efficiency of the two-phase envelope modulator is 72.5% with 80 MHz switching frequency for a one-tone 5 MHz envelope signals at 27.4 dBm output power. The RMS output voltage ripples is less than 7.2 mV in a wide range of input signal amplitude while a SFDR of 50.4dB is achieved.