In this letter, a wide tuning range W-band phase-locked loop (PLL) in 90 nm CMOS is presented. A novel frequency tripling topology with a single cross-coupled pair and a dual tank is proposed for the voltage-controlled oscillator (VCO) to achieve wide tuning characteristics under low power consumption. The locking range of the PLL at the fundamental tone is 25.4–29.7 GHz, and an excellent tuning range at the third harmonic frequency up to 12.9 GHz (from 76.2 to 89.1 GHz, 15.6%) is obtained. Under a 1.2 V supply voltage $({\rm P}_{\rm diss}=62.4 {\rm mW})$ , the measured closed-loop phase noise of the PLL is $-$ 83.5 dBc/Hz at 78.34 GHz. To the best of our knowledge, the achieved turning range is the highest currently reported for the PLLs operating in a similar frequency range in CMOS technology.