Materials Are Precious To Linearity

When sizing up components for linearity performance, switches and attenuators can't be ignored. A great deal of research in recent years on microelectromechanical- systems (MEMS) devices for use as switches, for example, has been for reaching improved levels of linearity in digitally modulated communications systems. Recognizing the key link between materials and linearity, Peregrine Semiconductor Corp. developed their patented silicon-on-insulator UltraCMOS technology in which silicon CMOS devices are fabricated on insulating sapphire substrates. As mentioned earlier, the choice of materials for electronic components can largely determine the expected linearity performance, and this choice of silicon-on-sapphire (SOS) materials helps eliminate voltage-dependent parasitic bulk capacitances that can lead to nonlinearities.

As an example, the firm's model PE42440 single-pole, four-throw (SP4T) 50-ohm switch is based on the UltraCMOS SOS technology, also drawing from the company's HaRP technology to achieve high linearity from 50 MHz to 3 GHz. Ideal for transceivers, the reflective switch has low insertion loss of 0.45 dB and isolation of 34 dB at 1 GHz. But it is in the area of IIP3 performance where this device shines, with performance of +67 dBm. The IIP2 performance is even more impressive, at +96 dBm. These values are across the full frequency range, since the switches are tested with two +18-dBm input tones 1 MHz apart and swept across the full frequency range. The PE42440 SP4T switch has a 2-s switching time and is supplied in a 16-lead 3 x 3 mm QFN package.