A 45Gb/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 a 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 and output impedance across all modulation states, minimizing Error Vector Magnitude (EVM) variation over the bandwidth and enabling robust performance for next-generation short-range high-speed connectivity. Developed using a 90 nm SiGe BiCMOS process and heterogeneously integrated with a fused silica antenna, the modulator achieves a data rate of up to 45 Gb/s with EVM better than -19 dB and less than ± 1.6 dB variation across a 20% bandwidth spanning 132 GHz to 158 GHz. The chip occupies an area of 1.1 mm×1.75 mm, consumes an average PDC of 100 mW, and delivers -3.6 dBm Psat with a spectral efficiency of 3.3 pJ/bit.