Compact Series Power Combining Using Subquarter-Wavelength Baluns in Silicon Germanium at 120 GHz

This paper presents an explicit analysis of the bandwidth and port imbalance of a subquarter-wavelength transmission-line (t-line) transformer and verifies this with the design of a two-stage D-band power amplifier (PA). Series power combining techniques incorporate both stacked heterojunction bipolar transistors (HBTs) and power combining using an 8-way sub-quarter-wavelength t-line transformer above 100 GHz. The extremely compact power combining methodology leads to a small die area of 0.62 mm
²
and a record 254-mW/mm
²
output power per unit die area. The PA has been fabricated in a 90-nm silicon germanium BiCMOS technology and produces more than 21-dBm output power over the frequency range of 114-130 GHz with a peak output power of 160 mW ≈ 22 dBm at 120 GHz and a 3-dB small-signal bandwidth of 35 GHz. This output power is 32% higher than the highest prior art, while the chip area is 77% smaller.