A 14.5Gb/s, 2.75pJ/bit, Direct-Digital, Star-QAM Modulator and Co-Designed Frequency Multiplier Operating at 140GHz

This article presents a direct-digital, Star-QAM modulator with frequency up-conversion (×2). A push-push frequency doubler (PPFD) with integrated common node (CN) switches generates 2nd harmonic amplitude shift keying (H-ASK) modulation, uniquely affording constant load impedance. Four PPFDs, (i) fed by using half-quadrature phase shift network (HQ-PSN), (ii) applied with suitable binary data sequence (Dbits), and (iii) combined their in-phase and quadrature waveforms, enable Star-QAM at the output, accompanied with frequency ×2. This circuit exhibits a conversion loss of 9.7 dB and maximum output power (Pout,2f) = -5 dBm at 140 GHz. It also shows a maximum data rate of 14.5 Gb/s by using Star-QAM, having an error vector magnitude (EVM) of -13 dB without external pulse shaping (PS) and equalization (EQ). Implemented in Global Foundries (GF) 90 nm Silicon Germanium BiCMOS technology, it occupies only 0.8 mm² of active chip area, consumes 40 mW of DC power with a bit-efficiency of 2.75 pJ/bit, which exhibits significant advancement in compact, multi-functional, and high-data-rate modulator design.