An efficient SiGe double-balanced mixer with a differential rat-race coupler

This paper describes an efficient, fully differential mixer intended to be used in a 77-GHz frequency-modulated continuous wave radar transceiver, which is realized in a Silicon-Germanium bipolar technology. The double-balanced mixer is equipped with a differential rat-race coupler, which uses a differential transmission line with a circumference of only one wavelength and provides an LO-RF isolation better than 30 dB over a wide frequency range. The mixer draws a very low quiescent current of 7.5 μA from a supply voltage of 3.3V. The measured voltage conversion loss is 0.5 dB and 0.3 dB at an LO power of 0dBm and 2 dBm, respectively. The measured input referred 1-dB compression point is -3dBm at an LO power of 0dBm and -2.2dBm if the LO power is increased to 2 dBm.