Evaluating Power Amplifier Performance for LTE and 802.11ac Designs

The wireless market’s insatiable demand for more bandwidth and faster data speeds is placing increased performance requirements on the components used in the RF front end of wireless devices, especially smartphones. New wireless standards such as LTE and 802.11ac employ advanced modulation schemes and signal processing to meet these performance demands, but these sophisticated techniques place stringent linearity and efficiency requirements on the RF PA.

PA component manufacturers are employing digital predistortion (DPD) and envelope tracking (ET) to manage PA linearity and efficiency, respectively, but DPD and ET are challenging to implement, test and optimize. Designers must have practical and reliable techniques to evaluate and manage these features under a wide range of potential operating conditions, before manufacture, to ensure that their PAs perform as intended and integrate properly with other components used in the transceiver.

The purposes of this paper are to highlight the implications LTE and 802.11ac have on PA designs; explain the use of DPD and ET to manage linearity and efficiency; and discuss three measurements that can be used to evaluate and optimize PAs that use these technologies. The measurements include error vector magnitude (EVM) and spectrum mask for 802.11ac PAs and adjacent channel leakage power ratio (ACLR) for LTE PAs.