High Efficiency Amplifier
Tue, 07/17/2007 - 9:06am
Freescale Semiconductor introduces the Doherty amplifier, which has many characteristics that enable high efficiency. When properly designed, it can deliver efficiency increases of 11 to 14% when compared to standard parallel Class AB amplifiers that are traditionally utilized in wireless base station transmitters. A Doherty amplifier consists of two amplifiers — carrier and peaking — operating under vastly different conditions. The RF power transistors in Doherty amplifiers must provide good output impedance matching under both linear operating conditions in which the RF drive level of the carrier amplifier is “backed off” to ensure high linearity and efficiency, as well as during peak (maximum) signal conditions handled by the peaking amplifier. In creating the seven LDMOS devices, the challenge became optimizing the device structure and output impedance matching to accommodate both types of signal conditions, while also statisfying the needs of the Doherty architecture itself.