CMOS Switches Offer High Performance in Low Power, Wideband Applications

High performance RF switches are among the key building blocks required in modern wireless communication systems. Switches that provide low insertion loss, high isolation between ports, low distortion and low current consumption are much sought after for high frequency applications such as phase shifters, switchable filters, transmitters and receivers for radar systems—ranging from large installations to anti-collision radar in cars—and communication systems from base stations to cell phones. Traditionally, only a few processes were available for developing good wideband/RF switches. Gallium arsenide (GaAs) FETs, PIN diodes and electromechanical relays have dominated the market, but standard CMOS is now making its mark. GaAs has been popular because of its low on resistance, low off capacitance and high linearity at high frequencies. As CMOS process geometries continue to shrink, the performance of CMOS switches has increased to the point that they have broken the 1 GHz barrier, and are now able to compete with GaAs switches. Designed to maximize bandwidth while maintaining low cost, CMOS switches offer an alternative to expensive GaAs switches in low cost, low power applications. This article explains the key specifications associated with wideband switches, traditional methods used for wideband switching, and the benefits of CMOS switch technology. It also shows how new CMOS switches can outperform GaAs switches in low power, high frequency applications. This should convince you that CMOS wideband switches are ideal solutions for applications such as cable modems, MRI scanners, xDSL modems, next-generation cordless phones, and applications in the aviation industry that require an operating frequency up to 1 GHz and beyond.