A 220 to 260 GHz Ultra-Compact, Calibration-Free 5-bit Phase Shifter with 1.8 Degrees RMS Phase Error in 9HP SiGe Process

This paper presents a precise, calibration-free 220-to-260-GHz 5-bit phase shifter based on a passive trombone line topology, implemented with reverse-saturation-mode NPN bipolar junction transistors (BJTs). Reverse-saturation-mode NPN BJT exhibits a significantly smaller R_ON*C_OFF product and a higher off-state quality factor compared to conventional forward-saturation-mode NPN BJT, enabling the design of a low-loss, high-resolution phase shifter above 200 GHz. The prototype IC is fabricated in a Globalfoundries 9HP SiGe process and occupies only 0.033 mm2. The phase control operates in 11.25-degree steps over 360 degrees at 240 GHz, with an average insertion loss of 14 dB and a DC power consumption of 12 mW. The measured mean RMS phase and gain errors at 240 GHz are 1.8 degrees and 0.74 dB, respectively, without calibration over 14 samples.