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An interpolative-phase-tuning (IPT) technique is proposed to tune the frequency of millimeter-wave (MMW) LC-based ring oscillators without using varactor. As a key feature, the tradeoff between tank Q and tuning range of the proposed IPT oscillators is independent of the operation frequency, which makes the IPT technique suitable for applications at MMW frequencies. Moreover, the IPT oscillators can achieve larger frequency tuning range and much better phase accuracy over the tuning range as compared to the conventional gm-coupled LC oscillators for multiphase generation. Two IPT oscillator prototypes are designed and implemented in a 0.13-μm CMOS process. The first one operates at 50 GHz with eight output phases and measures phase noise of -103.7 dBc/Hz at 1-MHz offset and -127.8 dBc/Hz at 10-MHz offset, tuning range of 6.8%, and figure of merit (FOM) of 186.4 dB while occupying chip area of 0.36 mm2. The second prototype oscillates at 60 GHz with four output phases and measures phase noise of -95.5 dBc/Hz at 1-MHz offset, -120.6 dBc/Hz at 10-MHz offset, tuning range of 9%, and FOM of 180.6 dB with chip area of 0.2 mm2.