In one embodiment, an MLS DC-to-DC converter generates two or more MLS voltages for a modulator that controls a power amplifier supply voltage, and a DC voltage that controls the power amplifier supply voltage through a DC path that bypasses the modulator. Additionally, the regulation of the DC voltage is different from the regulation of the MLS voltages. For example, the regulation period and/or non-overlap period used for regulation can be different for the DC voltage relative to the MLS voltages. Thus, pulse-width modulator (PWM) sequence can be different for the DC path versus the AC path.

FIG. 12 is a schematic diagram of one example of MLS envelope tracking for a continuous wave signal. The example shown is for a continuous wave signal having a frequency of about 100 MHz and a corresponding period of about 10 ns. Examples of suitable MLS voltage levels for the signal are shown.

FIG. 13 is a schematic diagram of one example of envelope frequency distribution for various signal waveforms. For each type of signal waveform, the graph depicts the percentage of DC envelope energy, AC envelope energy less than 1 MHz, and AC envelope energy greater than 1 MHz. Providing both an AC path through a modulator output filter and a separate DC path that bypasses the modulator provides enhanced efficiency for a variety of types of RF signal waveforms.

Some of the embodiments described above have provided examples in connection with mobile devices. However, the principles and advantages of the embodiments can be used for any other systems or apparatus that have needs for envelope tracking.