This paper presents the design and evaluation of a linear 3.3 V SiGe power amplifier (PA) for 3G and 4G femtocells with 18 dBm modulated output power at 2140 MHz. Different biasing schemes to achieve high linearity with low standby current were studied. The ACPR linearity performance with WCDMA (3G) and LTE (4G) downlink signals were compared, and differences analysed and explained.