In the illustrated embodiment, the DC path filter 103 includes a shunt capacitor 127 and a series inductor 128. Additionally, the AC path filter 104 includes a first series inductor 131, a second series inductor 132, a first shunt capacitor 135, and a second shunt capacitor 136. Although example implementations of a DC path filter and an AC path filter are depicted in FIG. 3A, the teachings herein are applicable to DC path filters and AC path filters implemented in a wide variety of ways. Accordingly, other implementations of filters can be used in accordance with the teachings herein.

In certain implementations, one or more components of a filter are controllable (for instance, digitally programmable and/or analog-tuned) to provide enhanced flexibility and/or configurability. For example, in the illustrated embodiment, the first shunt capacitor 135 and the second shunt capacitor 136 are controllable. Although two examples of controllable filter components are shown, other filter components can additionally or alternatively be implemented to be controllable.

FIG. 3B is a schematic diagram of another embodiment of an envelope tracking system 150 for a power amplifier 101. The envelope tracking system 150 of FIG. 3B is similar to the envelope tracking system 140 of FIG. 3A, except that the envelope tracking system 150 includes a different implementation of an AC path filter 144.