This paper describes a 2.5G cellular transceiver with standard DigRF interface, implemented in a low-cost 0.13µm CMOS process. This is the first CMOS single-chip, polar closed-loop transmitter, excluding the power amplifier (PA). This transmitter achieves an efficiency of 26% in EDGE mode by linearizing a saturated PA in a closed-loop feedback system. This is much higher than the typical 15-to-18% efficiency of systems using a linear PA [1]. Typical high-band/ low-band performance of −62/−64dBc in 30kHz for 400kHz offset spectral mask and 1.4/1.7% EVM in EDGE mode are significantly better than those reported earlier [1–3]. Using a low-noise quadrature mixer topology, the receiver, including T/R switch and SAW filters, achieves a sensitivity of −110dBm. The RF solution, consisting of PAs in a multi-chip integrated antenna switch module, SAW filters with integrated matching components and the transceiver, shown in Fig. 6.1.1, is the smallest form factor available in the market today.