This work presents the design of a high-bandwidth and high slew rate class-AB amplifier in a linear assisted hybrid converter for envelope tracking (ET) applications. ET has become prevalent for improving the efficiency of RF power amplifiers (PA) in portable devices when transmitting LTE signals. The class-AB amplifier in the hybrid converter provides the AC power to the PA, whereas the DC power is provided by a DC-DC converter. The class-AB amplifier is designed to track the LTE signal envelope, up to 20 MHz in bandwidth. Optimization is required to improve the efficiency of the system. A novel high-speed current-sense block is implemented to accurately sense the output stage currents of the class-AB amplifier. The amplifier is implemented in a 0.5–μ\Ά CMOS process, operates from a 3.6–5.0 V supply and is capable of driving a resistive load range from 20–4 Ω. The class-AB amplifier achieves 80 MHz UGF at a 4 Ω load, consuming roughly 33 mA quiescent current. Simulation results shows the tracking of 20 MHz LTE signals with an RMS error better than −34 dB.