For Class-E1 EDGE polar transmitters, we proposed a 4-W master-slave switching amplitude modulator (MS-SAM) for both high efficiency and wide bandwidth. It consists of a combination of two step-down modules with different switching frequencies and different switch sizes. The master module was designed for wide bandwidth and the slave module for high efficiency. The paper also presents a new current-sensing circuit based on a sample-and-hold circuit operable under a high switching frequency (> 40 MHz). We showed the topologies and operating principles. The chip was fabricated in a standard 0.35-mu m CMOS process with an area of 6.45 mm(2). The MS-SAM could drive the amplifiers of up to 4-W RF power in the experiment. We obtained an efficiency of 89%, and the converter's bandwidth was wide enough to meet the EDGE spectral requirements.