 signal energy. 4.3.8 Mode Switching This switch function routes the signal depending on the modulation and air interface standard being used within the band of interest, for example GSM or UMTS. These band-switching and mode-switching devices need to be efficient (offer low insertion loss). They also need good linearity to preserve the integrity of the amplitude-modulated waveforms used in UMTS/LTE and other third-generation air interfaces and to avoid intermodulation and unwanted harmonics. An increased requirement for linearity implies a larger die size (increased cost) and an increase in insertion loss for these devices. There is therefore both a dollar cost and a performance cost to be considered. These devices are typically GaAs devices, though hybrid CMOS/silicon on sapphire processes are also now available. RF MEMS devices may also provide an alternative option for this function. 4.4 The Impact of Increased RF Integration on Volume Thresholds The power amplifier is presently a separate device not integrated into the RF IC. This is because it is high power (250 milliwatts is equivalent to 24 dBm into 50 ohms). It generates heat. It has to coexist with received radio signals that can be as low as 120 dBm (0.001 of picowatt). It has to be isolated from the other mixed and digital baseband signals on the chip. Single-chip phones may be available within the next two to three years, although some vendors suggest this is significantly overoptimistic. However, the availability of these devices whether sooner or later will increase rather than decrease the volume threshold at which nonstandard RF handset designs become economic. In 2007 most mobile phone designs had the PA, SAW filters and antenna switch (RF front end components) off chip. The VCO (voltage-controlled oscillator) and synthesiser (quite a noisy device) would have been off chip in earlier designs, but by 2007 were generally integrated. As we shall see in Chapter 5 not much has changed in the succeeding five-year period. Partly this is due to the NRE 