Average Power Tracking (APT)

The primary metric that APT aims to improve. PAE measures the net efficiency of a power amplifier by accounting for the RF drive power:

• Formula: PAE = (Pout_RF - Pin_RF) / Pdc
• APT Impact: By reducing the DC supply voltage (Pdc) during low-power transmissions, APT directly increases PAE compared to a fixed-supply PA.

The DC-DC converter that executes the APT voltage commands. In an APT system, the modulator's slew rate and bandwidth requirements are relaxed compared to ET. It only needs to change voltage between transmission slots, not within a symbol period, allowing for a simpler, lower-cost buck converter design.

A baseband signal processing technique often paired with APT. CFR reduces the Peak-to-Average Power Ratio (PAPR) of the transmitted signal before it reaches the PA. This prevents infrequent high-power peaks from forcing the APT system to use a higher average voltage than necessary, further optimizing efficiency.

A critical challenge in Envelope Tracking that is not required in APT. In ET, the RF signal path and the dynamic supply voltage path must be synchronized to the nanosecond at the transistor drain. APT's slow, slot-based voltage changes eliminate this complex timing alignment problem entirely.

The linearization technique used alongside APT. While APT changes the PA's operating point, it introduces supply-dependent AM/AM and AM/PM distortion. A DPD system must characterize and invert these nonlinearities to maintain signal quality. The DPD model complexity increases when moving from APT to ET.