Typically, millimeter-wave applications in the 75-to-100-GHz W-band requiring active devices have been considered the territory of III-V compound semiconductor technology. With fT/fMAX frequencies above 150 GHz, however, newer silicon- germanium (SiGe) processes can compete for those applications. W-band radar and radio transceivers require a phase-locked loop (PLL) in which the most critical components are the voltage- controlled oscillator (VCO) and frequency divider. The design of 77-to-106-GHz Colpitts VCOs, which are fabricated in two generations of SiGe BiCMOS technology, has been proposed by Sean T. Nicolson, Kenneth H.K. Yau, Keith W. Tang, and Sorin P. Voinigescu from the University of Toronto in conjunction with ST Microelectronics' (Crolles, France) Pascal Chevalier, Alain Chantre, and Bernard Sautreuil.

As the integration of W-band circuits rises, high-yield processes must be developed. An understanding of circuit scaling between successive SiGe technology generations also is essential. Colpitts oscillators can be employed to monitor the W-band noise performance of SiGe heterojunction bipolar transistors (HBTs). Comparing the phase noise and output power of a VCO fabricated on several wafer splits allows the relative performance of the HBTs to be deduced.

Measurements show a 106-GHz VCO operating from 2.5 V with phase noise of -101.3 dBc/Hz at 1-MHz offset, which delivers +2.5 dBm of differential output power at +25C with operation verified up to +125C. Using 130- nm MOSFETs, a BiCMOS VCO with a differential MOS-HBT cascode output buffer delivers +10.5 dBm of output power at 87 GHz. See "Design and Scaling of W-Band SiGe BiCMOS VCOs," IEEE Journal of Solid-State Circuits, Sept. 2007, p. 1821.