Modulation schemes employed in long-term-evolution advanced (LTE-A) services for higher data-rate with high peak-to-average power ratios (PAPR) are becoming more complicated, which degrades the efficiency of RF power amplifiers (PA). Envelope-tracking modulators (ETM) have been proposed to improve the PA efficiency and linearity by dynamically adjusting the supply voltage of the RF PA according to the envelope of the transmitted signal.