Compact 6.5-28.5 GHz On-Chip Balun With Enhanced Inband Balance Responses

In this letter, a miniaturized on-chip stacked-spiral-coupled (SSC) Marchand balun is proposed with wideband operation, i.e., fractional bandwidth (FBW) >125%. To improve the inband balance responses (i.e., amplitude- and phase-balances), the self-coupled compensation line and center-tapped ground-shield with deep trench are introduced. To verify the mechanism of structures mentioned above, a balun operating from 6.5-28.5 GHz is implemented and fabricated using a 0.13-μm SiGe technology. The measured amplitude-and phase-imbalances of the on-chip balun are ±1 dB and ±1.66°, respectively.