Highly efficient power amplifier for CDMA base stations using Doherty configuration

We have extended the classical Doherty amplifier to support CDMA base station power amplifiers that require high efficiency and good linearity. At first, we have estimated three transistors, Motorola´s MRF21085, MRF5S21090 and MRF5P21180 LDMOS´s, to confirm the suitability for Doherty operation. Since the MRF21085 transistor is not suitable, we have excluded it. Two 2.14GHz high power Doherty amplifiers are implemented using two MRF5S21090 and a MRF5P21180, respectively, and are optimized at 40W for high efficiency and good linearity using IS95A 8FA CDMA signal. The performances of the Doherty amplifiers are compared with a conventional balanced class AB amplifier using two MRF5S21090. At 40W average output power, the MRF5S21090 and MRF5P21180 Doherty amplifiers deliver the efficiencies of 34.8% and 40.0%, which represent 11.2% and 16.4% enhancements, respectively, compared to the conventional amplifier. The linearities of all the amplifiers are adjusted to about -31dBc.