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This paper presents a novel wideband voltage-controlled oscillator (VCO) and a tunable power amplifier (PA) for multi-band transceivers. The proposed oscillator has a core VCO and a tuning-range extension circuit, which consists of an injection-locked frequency divider (ILFD), and flip flop dividers. The 2-stage differential ILFD can generate quadrature outputs, and it realizes 2, 3, 4, and 6 of divide ratio with very wide output frequency range. In the measurement result, the VCO achieves 9.3 MHz-to-5.7 GHz (199%) of continuous frequency tuning range with -210 dBc/Hz of FoMT, which is implemented by using a 90 nm CMOS process. The proposed tunable PA realizes an output impedance tuning from 0.9 GHz to 3.0 GHz so that external isolators following PAs can be eliminated. The tunable PA employs resistive feedback and a parallel resonance consisting of an inductor and a tunable capacitor array. The PA is implemented by using a 0.18 Â¿m CMOS process. Over all of the frequency range, the PA realizes output return loss S22 of smaller than -10 dB, power gain of larger than 16 dB, output 1-dB compression point of larger than 17 dBm, and power added efficiency (PAE) at 1-dB compression point of larger than 10 %.