Novel RF switch concepts for differential wireless communications frontends

This paper presents two novel switch configurations for differential-mode circuits that clear the path to fully differential frontends. Both concepts exploit the effect of mode-blocking circuits to enhance their isolation capability far beyond the blocking values of standard transistor switches or p-i-n diodes when being shut off. As a result, the new switch concepts offer higher performance with respect to standard unbalanced structures without requiring twice the effort as differential components often do. Both structures feature different advantages, making them interesting solutions for applications both in the RX and TX paths. The simple and low-loss Z-SPST switch with series switch elements shows superior isolation with respect to unbalanced switches over a wide frequency range. On the other hand, the X-SPST switch with cross-coupled semiconductor switches offers low loss when on, extremely high small-band isolation, and can carry more power than standard semiconductor switches in use. It is also capable of extremely high isolation in a narrow bandwidth. Two novel switches realized with standard SMD components showed an improvement of isolation from 13 dB to more than 20 dB, while losses increased from 0.45 to 0.50 dB and 0.55 dB at 2 GHz, respectively