Bias-switching quasi-Doherty-type amplifier for CDMA handset applications

A new approach of "quasi-Doherty" type amplifier based on bias switching has been developed for CDMA handset applications. By dividing the mode of operation according to the output power requirement, the efficiency was optimized in the low-power region while the linearity was improved in the high-power region. In this way, the proposed bias-switching Doherty amplifier could meet the stringent ACPR specification of the CDMA systems over the entire power region while improving the low-power efficiencies. Biasing to the peak amplifier has been switched according the mode of operation for this purpose. Prototype 0.5-W power amplifier module has been designed and fabricated to demonstrate the concept. In the low power mode, PAE of 17% and ACPR of -51.8 dBc were achieved at output power of 16 dBm. In high power mode, PAE of 32% and ACPR of -50 dBc were achieved at output power of 25 dBm.