This push push VCO, which is based on a loop ground transmission line, can provide the local signal sources for full band 60-GHz communication systems.
IEEE Task Group 802.15.3c provides allocation for four bands—each with a bandwidth of 2160 MHz. To prevent an image signal or local-oscillator-1 (LO1) leakage signal from being transmitted in the RF bands—and to enable an image-rejection filter to operate around 60 GHz—a sliding intermediate-frequency (IF) range was chosen for the standard. It spans 10,584 to 14,040 MHz. To meet design requirements and enable low-cost transceivers, a single voltage-controlled oscillator (VCO) with a wide frequency-tuning range is required. A 59-GHz push-push VCO has been developed by Hitachi’s Takahiro Nakamura and Toru Masuda together with Katsuyoshi Washio from Tohoku University and Hiroshi Kondoh from EHF Consulting.
Their VCO uses a loop-ground transmission line (LG-TML) with coverage of one-half wavelength at the fundamental frequency and one-quarter wavelength at the second harmonic frequency. Thanks to this transmission line, it is possible to generate both a high-level signal at the second-harmonic frequency and an adequate signal at the fundamental frequency for driving a prescalar. At the same time, the VCO uses the Miller effect of its heterojunction bipolar transistors (HBTs) for wide tuning bandwidth.
The resulting VCO, which is based on 0.18-μm silicon-germanium (SiGe) BiCMOS technology, achieves +1.5 dBm output power while maintaining a 13.9-GHz tuning range (26% of the center oscillation frequency). It exhibits phase noise of -108 dBc/Hz at 1 MHz offset from the carrier while achieving a figure of merit of -189.6 dB. See “A Push-Push VCO with 13.9-GHz Wide Tuning Range Using Loop-Ground Transmission Line for Full-Band 60-GHz Transceiver,” IEEE Journal of Solid-State Circuits, June 2012, p. 1267.