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Two new millimeter-wave digitally controlled oscillators (DCOs) that achieve a tuning range >10% and fine frequency resolution 1 MHz simultaneously are described. Switched metal capacitors distributed across a passive resonator tune the oscillation frequency. To obtain sub-MHz frequency resolution, tuning step attenuation techniques exploiting an inductor and a transformer are proposed. Two 60-GHz implementations, a fine-resolution inductor-based DCO (L-DCO) and a transformer-coupled DCO (T-DCO), are demonstrated in 90-nm CMOS. The phase noise of both DCOs is lower than -90.5 dBc/Hz at 1-MHz offset across 56-62 GHz. The T-DCO achieves a fine frequency tuning step of 2.5 MHz, whereas the L-DCO tuning step is over one order of magnitude finer at 160 kHz. The L-DCO and T-DCO consume 10 and 12 mA, respectively, from a 1.2-V supply. The size of each DCO core is 0.4 ×0.4 mm2.
Date of Publication: Nov. 2013