RF-PAs in 4G LTE mobile devices handle modulated signals with high peak-to-average power ratios (PAPRs) while maintaining linearity and power efficiency. Envelope-tracking technology increases the efficiency of an RF-PA by modulating its supply voltage proportionally to the RF signals. The function of an envelope-tracking supply modulator (ETSM) is to track the envelope information and provide the same output voltage to the RF-PA. Figure 2.3.1 shows a conventional hybrid ETSM, which is comprised of a linear amplifier (LA) and a hysteresis-controlled switching regulator (SWR). Since the ETSM is mainly battery-powered, an additional SWR is required. This paper presents a single-inductor dual-output (SIDO) converter that removes both SWRs, as illustrated in Fig. 2.3.2, to speed up the performance of the ETSM. In the past, a cross-regulation (CR) effect was recognized as one the most critical drawbacks in the conventional design with single-inductor multiple-output (SIMO) converters, and numerous research papers have attempted to suppress CR [1,2]. In this paper, however, the proposed ETSM design, driven by the LA, makes effective use of the CR effect for achieving faster and efficient envelope tracking. Results show that, at a switching frequency of 2MHz, the proposed ETSM can deliver up to 2W of average output power with an efficiency of 82%.