X- and K_u-Band SiGe-HBT Voltage-Controlled Ring Oscillators for Cryogenic Applications

The theory, design, and implementation of emitter-coupled logic (ECL)-based voltage-controlled ring oscillators (R-VCOs) operating at X- and text{K}_{text {u}} -bands for cryogenic applications are presented. Five- and seven-stage R-VCOs were fabricated in a 130-nm SiGe:C BiCMOS process technology. They provide differential multi-phased local oscillator (LO) signals with a maximum time resolution of 5.4 ps and can operate at both room temperature (RT) and cryogenic temperature (CT). For designing under cryogenic conditions (6 K), the compact model HICUM/L2 was extended, and the corresponding model parameters were extracted at CTs. The implemented 5-/7-stage R-VCOs offer an adjustable frequency range of 9.7-16.5 GHz (52%) and 8.4-13.3 GHz (45%), respectively, with a maximum core power dissipation of 153 and 165 mW. At 6 K, the frequency of operation can be increased up to 18 GHz, while the power dissipation increases by only 30 mW. The R-VCOs occupy a very compact active area of 0.04 and 0.12 mm2. The phase noise of the R-VCOs at 16.5/13 GHz at an offset frequency of 10-MHz is -106.3/-107.3 dBc/Hz. They provide up to -6 dBm of saturated differential output power. To the best of our knowledge, this is the first time an hetero-junction bipolar transistor (HBT)-based 5-/7-stage R-VCO is being presented at X- and text{K}_{text {u}} -band that can operate under cryogenic conditions.