A 45 Gb/s D-band Hybrid Star-QAM-OOK Transmitter Using a Quad-Harmonic Modulator with Constant Impedance Balanced Architecture in 90nm SiGe BiCMOS

This work presents D-band reconfigurable Quadrature Second Harmonic modulator. The proposed modulator features a quadrature frequency doubler with integrated shunt switches at the common-emitter node, and with balanced switching mechanism inspired by photonic interferometer, enabling reconfigurable 4-APSK (Star QAM) and OOK modulation. The design maintains a nearly constant input impedance and output with less than 1% mismatch across all modulation states, ensuring robust performance for next-generation scalable arrays and short-range high-speed connectivity. Developed using a 90 nm SiGe BiCMOS process and heterogeneously integrated with a fused silica antenna, the modulator achieves data rates of up to 45 Gb/s with a BER better than 10−6 across a 28% bandwidth spanning 126 GHz to 160 GHz, supporting a range of 20-30 cm. The chip occupies an area of 1.2 mm × 1.7 mm, consumes an average of 100 mW DC power, and delivers -3 dBm Psat with spectral efficiency of 3.3 pJ/bit.