A high efficiency 250W LDMOS amplifier for polar transmitter at 940MHz

A high efficiency wideband code-division multiple access (W-CDMA) base station amplifier using LDMOS is presented in the 900MHz to 980MHz band. LDMOS has widely demonstrated its ability to work efficiently within Doherty structure at attractive cost, and it is shown that it can also be used together a drain modulated system. The transistor is in inverted class F, and in a polar transmitter topology: at medium and high power, the amplitude control is done through the Vdd modulator and the phase control through the RF input: at low power, RF input is modulated in phase and amplitude, which avoids the problems linked to a pure Envelope Elimination and Restoration (EER) systems. With appropriate optimization of transistor, 65% efficiency can be achieved at 8dB Output Back Off (OBO) from max power over the 900MHz-980MHz band with 16.5dB Gain, and more than 67% efficiency can be reached at 6.5dB OBO.