NTT DoCoMo has developed a prototype multi-band power amplifier that accommodates eight frequency bands between 700 MHz and 2.5 GHz. As a result, a not-too-big mobile phone that works across frequencies — including LTE, W-CDMA and GSM — could be developed.
DoCoMo’s amplifier does its magic by employing matching circuits whose frequency characteristics are controlled by multiple semiconductor switches according to the required frequency band.
Standard mobile phones use a separate single-band amplifier for each band, hence a device that could work across various networks inevitably increases in size to accommodate new frequency bands.
And for the record, power amplifiers are used in mobile phones to increase signal power up to levels required for wireless communication.