e approach promises overall reductions in DC power drain and heat dissipation and cost and board real estate but will need to be optimised for any or all of the process choices. However, even if this broadband PA problem can be solved, within the foreseeable future each full-duplex band requires an individual duplexer. Connecting one broadband PA to multiple duplexers is a lossy proposition with complex circuitry. To match a good broadband PA, a switched (or tuneable) duplexer is required. 5.5.5 Path Switching and Multiplexing Unlike power amplifiers that drive current into a low impedance, switches must tolerate high power in a 50-ohm system. If connected to an antenna with impedance other than 50 ohms the voltage will be even higher, commonly above 20 Vpk. The switch is in the area of highest 23 This is an area where recent progress has been made. Multiband power amplifiers are now available that cover 1710 to 1980 MHz, a bandwidth of 13%. Making Telecoms Work Table 5.5 Power-handling requirements. Reproduced with permission of Peregrine Semiconductor24 System Average Operating VPK @ Standard Power Peak Power VSWRs Two Tone CDMA2000 WCDMA 802.11g VHF 2-way "Maximum average power at antenna in a 50-ohm system per the system specification. b At angle that produces the highest voltage. Assumes crest factor reduction. voltage and has the most severe power-handling and linearity requirements with a need to have an IP3 of >70 dBm. Table 5.5 gives typical power-handling requirements. Low-voltage FETS can be 'stacked' in series for high-voltage handling in the OFF condition, but this requires a low loss insulating substrate, either GaAs or silicon on sapphire. Apart from power handling, switches must be highly linear and have low insertion loss. Switch losses have more than halved over the past five years that has allowed for higher throw counts and cascaded switches but substantial performance improvements are still needed due to the steadily increasing throw count of the antenna side switch, the addition of a PA side