90 Degree Hybrid-Coupler Based Phase-Interpolation Phase-Shifter for Phase-Array Applications at W-Band and Beyond
In the proposed phase shifter, a 90 degree-hybrid performs I/Q phase splitting and phase interpolation to synthesize all four quadrant phases after amplitude weighting made by VGAs. In such way, by designing the weighting amplifiers with a matched impedance, the I/Q accuracy and thereby accuracy of phase interpolation is not sensitive to the amplifier loading. In contrast, the conventional phase shifters where the quadrature network precedes active amplifiers suffers from a loading effect from amplifiers, hence I/Q accuracy degrades. All building blocks in the proposed system can be cascaded with a matched low impedance to make less vulnerable to parasitic capacitance effect, suitable for mm-Wave applications. The idea is verified by designing a Phase Shifter achieving low RMS phase error (<5 degrees over 92-100 GHz) for 5-bit phase solution, gain 5-9.5 dB and saturated output power -3 dBm at 94 GHz in 0.13 micrometers SiGe BiCMOS technology.
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