A multi-level envelope tracker can suffer from degraded efficiency when both DC and AC currents for a power amplifier supply voltage are circulated through switches of the MLS modulator and/or a common filter. For example, power losses are incurred in the DC resistance of the modulator's switches and/or the filter's inductors.

Although the DC resistance of the switches can be implemented to be low (for instance, a small percentage of the power amplifier's DC load), implementing the switches in this manner results in relatively large layout and/or significant switching losses. For instance, when a desired source impedance is about 0.2 Ohm, the switches of the MLS modulator can be constrained to achieve less than 0.2 Ohm of on-state resistance, which can result in a relatively large switch layout.

Multi-level envelope tracking systems with separate DC and AC paths are provided. In certain embodiments, an envelope tracking system for generating a power amplifier supply voltage for a power amplifier is provided. The envelope tracking system includes an MLS DC-to-DC converter that outputs multiple regulated voltages, an MLS modulator that controls selection of the regulated voltages over time based on an envelope signal corresponding to an envelope of the RF signal amplified by the power amplifier, an AC path filter coupled between an output of the MLS modulator and the power amplifier supply voltage, and a DC path filter coupled between a DC voltage and the power amplifier supply voltage.