A Novel MMIC Interface for RF-DACs with Integrated Bias Tee, Balun, and Quadrature Splitter for Multi-Gigabit Satellite Transmitters

The direct RF sampling digital-to-analog converter (RF-DAC) is a key enabler for highperformance integrated transceivers. In this work, we present a novel MMIC-based interface for interfacing a digitally modulated intermediate frequency (<tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$F_{c}=3.5$</tex> GHz) signal from a differential RF-DAC to an IQ upconverter for Ka-band downlink data transmission. The proposed MMIC integrates a balun (balanced-tounbalanced conversion), quadrature hybrid (quadrature phase splitting), and DC biasing, providing a compact (<tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\sim 50 \%$</tex> size reduction), cost-effective (<tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\sim 50 \%$</tex> cost reduction), and production-friendly solution. Electromagnetic (EM) simulations demonstrate amplitude and phase imbalances within 1 dB and 6° respectively, isolation between RF and DC ports better than <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$45 \text{dB}, \text{DC}$</tex> current handling up to 130 mA, and balanced port return loss <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$&lt;-12 \text{dB}$</tex> over a wide frequency band from <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$2.4-4.6 \text{GHz}$</tex>. The final MMIC implementation achieves a compact die size of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$4.1 \text{mm} \times 2.9 \text{mm}$</tex>. To the best of our knowledge, this is the first reported design integrating all three critical functionalities into a single MMIC solution, making it a strong candidate for highperformance multi-gigabits satellite transmitters.