A Study of SiGe HBT Signal Sources in the 220–330-GHz Range Sorin P . V oinigescu, Senior Member , IEEE

Abstract

The paper presents design optimization strategies and a comparison of the performance of SiGe HBT fundamental and push–push Colpitts and Colpitts–Cla pp voltage-controlled oscilla- tors (VCOs), with and without doublers and buffers, as possible so- lutions for efficient milliwatt-level, low-noise signal sources at sub- millimeter-wave frequencies. Th e fundamental frequency Colpitts VCO covers a 12% tuning range between 218 and 246 GHz (the highest for SiGe HBTs) with up to 3.6-dBm output power and 0.8% ef ficiency. The 300-GHz signal source, consisting of a Col- pitts–Clapp VCO followed by a buffer ampli fier and a doubler, shows 1.7-dBm output power around 290 GHz, 101-dBc/Hz phase noise at 10-MHz offset, 7.5% tuning range, and 0.4% ef fi- ciency. Finally, the push-push Colpitts–Clapp VCO exhibits the highest operation frequency, from 309 to 325 GHz, but with re- duced ef ficiency of only 0.07% and 5% tuning range. It was con- cluded that the differential cascode buffer placed between the VCO and doubler was instrumental in achieving the best phase noise and output power with good ef ficiency and without compromisin g tuning range.