Compact Multifunctional 180° Hybrid-Based 300-GHz Subharmonic I/Q Downconversion Resistive Mixers in 130-nm SiGe Process

In this letter, a compact multifunctional 180° hybrid suitable for subharmonic in-phase/quadrature (I/Q) mixers is proposed. To feed LO and RF signals at different frequencies and distribute dc supply, the hybrid combines an out-of-phase dual balun, two in-phase power dividers based on T-junction and coupled lines, and four zero-ohm transmission lines (ZTLs) into a single passive component. Chip size, insertion loss, and bandwidth can all be improved by reducing the number of passive components cascaded in the circuit. The proposed hybrid’s footprint is further minimized by employing redundant line and compensation capacitor techniques. In a 130-nm SiGe BiCMOS technology, two proof-of-concept subharmonic I/Q downconversion resistive mixers with/without an on-chip LO quadrupler are implemented. Both mixers feature wideband HBT-based IF amplifiers and emitter followers, which eliminate the need for dc-blocking capacitors that constrict the IF bandwidth. The mixer, without an integrated LO multiplier, occupies an area of
$0.685\times 0.692\,\,{\mathrm{ mm}}^{2}$
and achieves a measured conversion gain of approximately 0 dB from 255 to 310 GHz. The mixer with an on-chip LO quadrupler exhibits a conversion gain of approximately −1 dB from 270 to 300 GHz and a 3-dB IF bandwidth from 0.01 to 7 GHz. Additionally, the measured image rejection ratio (IRR) is greater than 20 dB within the operating frequencies.