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A third harmonic enhanced technique is proposed to implement a broadband and low-phase-noise CMOS frequency tripler. It nonlinearly combines a pair of differential fundamental signals to generate deep cuts at the peaks of the fundamental waveform, resulting in a strong third harmonic frequency output. This mechanism has inherent suppression on the fundamental and the other harmonics so that only a low-Q high-pass filter on the lossy silicon substrate is applied at the output to further reject the fundamental and the second harmonic frequencies, in contrast to the high-Q filters used in most of the previous tripler designs. The fabricated circuit using 0.18 m CMOS technology is compact and has an input frequency range from 1.7 GHz to 2.25 GHz, or an output frequency range from 5.1 GHz to 6.75 GHz, resulting in about 28% frequency bandwidth. The optimum conversion loss from the tripler is 5.6 dB (27.5% efficiency) at an input power of 2 dBm. The suppressions for the fundamental, second and fourth harmonics in the measurement are better than 11 dB, 9 dB, and 20 dB within an input power range from 2 dBm to 7 dBm.