An envelope tracking power amplifier using an adaptive biased envelope amplifier for WCDMA handsets

An envelope tracking power amplifier (ET-PA) using a self-oscillation pulse-width-modulation circuit with an adaptive bias technique is presented. In this technique, the supply voltage to the envelope amplifier is changed depending on the output power level. Since this approach enables the envelope amplifier to change the output power without degrading the signal resolution, the developed ET-PA shows a low adjacent channel leakage power ratio (ACPR) of less than −38 dBc in a wide output power range from 10 to 27 dBm. The ET-PA shows 45.4% overall efficiency at peak output power of 28 dBm. The average efficiency was 29%, which is 2.4 times higher than that of a class-AB PA. The noise power in the receive band (Rx noise) is −136 dBm/Hz at output power of 26 dBm at a frequency of 2.14 GHz.