An active differential broad-band phase splitter for quadrature-modulator applications

Area-efficient single-ended-to-differential phase-splitter (balun) integration is difficult for frequencies below 6 GHz. Few broad-band solutions are available, and those given in the literature often introduce quite high amplitude and/or phase errors to differential signaling. In this paper, a cascade of differential pairs is shown always to outperform any single-stage solution, and the measurement data for a two-amplifier prototype are supplied to support the theory. The prototype circuit was realized on 0.8-mum SiGe as a 2.5-V RF integrated circuit measuring 1.2times1.2 mm2including pads. The measured gain error is better than -1 dB up to 4.6 GHz, while phase difference is between 179.7deg-180.9deg in 0.6-4.1 GHz. The application of the realized phase splitter in a broad-band quadrature modulator is discussed