Multimode 2.4 GHz CMOS power amplifier with gain control for efficiency enhancement at power backoff

In this paper, a power amplifier (PA) with gain control is presented for 2.4 GHz applications. The power gain can be digitally controlled in six steps by the combination of three bits. This technique was used to control power gain and to achieve an improvement in efficiency at power backoff. The design was implemented using a 0.13 µm CMOS technology and is able to deliver a variable power gain between 26.5 dB and 35.9 dB and a peak power-added efficiency (PAE) of 38 % with a 1.8 V power supply. The power consumption of the PA is reduced from 225 mW in the highest-gain mode to 179 mW for the lowest-gain, allowing an enhanced efficiency when maximum gain is not required for transmission.