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In this paper, a Distributed Active Transformer (DAT) is used to implement a fully-integrated RF power amplifier (PA) for the extended GSM-band and LTE band VIII in a standard 90 nm CMOS process. The DAT allows the designer to integrate both the input and output matching networks as the power combining itself on the same silicon die. The PA delivers up to 29.4 dBm of RF power with 28.4% drain efficiency and a power added efficiency (PAE) of 25.8% by using a 2 V supply voltage. The PA is measured for both GSM-signals and LTE-signals. For GSM, the maximum output power is 29.1 dBm. The corresponding output spectrum at 400 kHz and 600 kHz frequency offset is -68 dBc and -70 dBc and meets the spectral mask requirements. The Power versus Time (PvT) measurement shows that the time domain constraints are met. When applying a LTE-signal with 10 MHz bandwidth and a PAPR of 6.92 dB to the RF PA, the designed PA meets the EVM specification at 25 dBm average output power with 15% PAE.