Design of a rail-to-rail, low output impedance class AB power amplifier for envelope tracking of polar modulators

This paper presents the design of a class-AB power amplifier suitable for envelope modulator of polar power amplifiers. Polar modulation is one of the most popular RF power amplifier efficiency enhancement techniques. Class-AB power amplifier is a main building block of hybrid switching envelope modulator which is known as linear and efficient envelope modulator architecture. Design of high DC gain, wide bandwidth, low output impedance class-AB is important in the design of HSEM. In this paper the design of a class-AB PA suitable for 10 MHz OFDM signals will be discussed in a 0.18 μm CMOS technology. The class-AB PA has approximately 94 dB DC gain, 704 MHz unity gain bandwidth and 0.25 unity gain negative feedback output impedance at 20MHz.