A 24-30-GHz Modified Gilbert-Cell Downconverter With High Linearity and Isolation

This paper introduces a downconverter mixer employing a modified double-balanced Gilbert-cell topology, designed using IHP's 0.13-mu$$ \upmu $$m SiGe BiCMOS technology. Distinct from the conventional topology, a resonator was employed at the emitter of the transconductance stage, which enables the utilization of transconductance stage as an active balun, allowing for direct feeding of the single-ended input without sacrificing the advantageous of the double-balanced topology. The integration of the resonator reduces the amplitude and phase errors within the active balun segment, thereby enhancing port-to-port isolation. The area occupied by the resonator is approximately 1.7 times smaller than that of an RF transformer balun typically employed in conventional double-balanced topologies. The LO and IF differential signals are converted to single-ended ones through transformer baluns for measurement purposes. The frequencies of operation for RF, LO, and IF are 24-30, 18-24, and 6 GHz, respectively. The conversion loss is 7.7 dB at 26 GHz, with port-to-port isolations exceeding 35 dB. The input 1-dB compression point is 5.7 dBm, while the circuit consumes 65-mW power from a 3.3-V voltage supply. Excluding the pads, the active area of the design spans 1 mm2.