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

This article presents a direct-digital, Star-QAM modulator with frequency up-conversion (x2). A push-push frequency doubler (PPFD) with integrated common node (CN) switches generates <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$2^{\text{nd}}$</tex> harmonic amplitude shift keying (H-ASK) modulation, uniquely affording constant load impedance. Four PPFDs, (i) fed by using half-quadrature phase shift network (HQPSN), (ii) applied with suitable binary data sequence (<tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$D_{\text{bits}}$</tex>), and (iii) combined their in-phase and quadrature waveforms, enable Star-QAM at the output, accompanied with frequency <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\times 2$</tex>. This circuit exhibits a conversion loss of 9.7 dB and maximum output power <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\left(\mathrm{P}_{\text{out},2\mathrm{f}}\right)=-5 \text{dBm}$</tex> 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 <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\text{mm}^{2}$</tex> of active chip area, consumes 40 mW of DC power with a bitefficiency of 2.75 pJ/bit, which exhibits significant advancement in compact, multi-functional, and high-data-rate modulator design.