High efficiency 450W asymmetric three-device Doherty amplifier with digital feedback predistortion

Abstract

An asymmetric Doherty power amplifier based upon a three-device architecture for improved efficiency performance under extended power backoff operation is presented. The topology provides significant advantages in easing input/output matching constraints inherent in asymmetric Doherty amplifiers where the asymmetry necessitates unequal device geometries for the peaking and carrier sub-amplifier circuits. Excellent high efficiency performance (45% @ 8 dB power back-off) is demonstrated by implementing the Doherty amplifier using an advanced prototype LDMOS device technology developed at Freescale Semiconductor. The amplifier achieves a saturated output power greater than 450W at 2.14 GHz when biased with a 28V supply. When driven with a single carrier W-CDMA signal, an efficiency of 45% is achieved at 8 dB power back-off. Moreover, when linearized with a digital feedback pre-distorter the amplifier achieves an ACPR better than −55 dB.