Apparatus and method for assisting envelope tracking with transient response in supply voltage for power amplifier

An apparatus, comprising:

• a load coupled between a first voltage rail and a second voltage rail;
• a capacitor;
• an amplifier configured to source or sink current to or from the first voltage rail via the capacitor;
• a first switching device coupled between an output of the amplifier and the second voltage rail, wherein the first switching device is configured to selectively sink current from the first voltage rail via the capacitor to control a supply voltage on the first voltage rail;
• and
• a second switching device coupled between the first voltage rail and the second voltage rail, wherein the second switching device is configured to selectively discharge the capacitor.

A method, comprising:

• sourcing or sinking current to or from a first voltage rail for a load via a first current path including a capacitor to control a supply voltage on the first voltage rail;
• selectively sinking current from the first voltage rail for the load via a second current path including the capacitor to further control the supply voltage on the first voltage rail, wherein the second current path is different than the first current path;
• and
• selectively discharging the capacitor, wherein selectively discharging the capacitor is via a third current path.

An apparatus, comprising:

• a load coupled between a first voltage rail and a second voltage rail;
• a capacitor;
• an amplifier configured to source or sink current to or from the first voltage rail via the capacitor;
• a switching device coupled between the first voltage rail and the second voltage rail, wherein the switching device is configured to selectively discharge the capacitor;
• a measuring device configured to measure a voltage drop across the capacitor;
• and
• a controller configured to turn on the switching device based on the voltage drop across the capacitor.

An apparatus, comprising:

• a load coupled between a first voltage rail and a second voltage rail;
• a capacitor;
• an amplifier configured to source or sink current to or from the first voltage rail via the capacitor;
• a switching device coupled between the first voltage rail and the second voltage rail, wherein the switching device is configured to selectively discharge the capacitor;
• and
• a controller configured to turn on the switching device based on an input signal or a mode change between a first mode of controlling the supply voltage based on an average power of the input signal and a second mode of controlling the supply voltage based on an envelope of the input signal.