A Low Power CMOS Hybrid Coupler with Tunable Operating Frequency

This paper presents a low power lumped-element 3-dB coupler operating at different frequencies for application in multi-standard systems. The coupler is designed based on a method in which the return loss and isolation can be improved by adjusting the components quality factors. To this end, we use a tunable inductor, capable of generating adjustable inductor and negative resistance, in the coupler topology. By tuning the inductance and its quality factor independently, we achieve a hybrid coupler with low return loss and high isolation operating at different center frequencies. Moreover, the negative resistance, generated by the tunable inductor, compensates circuit losses that results in substantial improvement in the coupler insertion loss. The coupler was simulated via 0.18μm CMOS technology with 1.8V supply. Electromagnetic simulation results show that the coupler is capable of operating at the center frequency range of 2.4 GHz - 4.2 GHz with both return loss and isolation less than -25dB. Furthermore, the worst case insertion loss of 0.61dB and the best case insertion loss of 0.05dB are obtained, by using the negative resistance. The power dissipation and the output referred noise voltage of the coupler are less than 7mW and 2.5 nV/√Hz respectively, across the entire frequency tuning range.