SC1869 Thermal Noise, Residual IM’s and Spurs

Abstract: In Frequency Division Duplexing (FDD) systems where the transmitter and receiver are active at the same time, transmit noise, residual IM’s and spurs are critical impairments that must be properly addressed. The most challenging condition occurs when the transmitter operates at maximum power while the receiver demodulates at its sensitivity level (lowest possible signal level that meets the baseband SNR requirement to resolve the signal). One of the duplexer roles is to reduce the transmitter leakage into the receiver band and prevent receiver desensitization. Therefore, it is important to reduce levels of PA emissions into the receiver band in order to reduce the cost/size of the duplexer.This application note describes the transmitter impairments, strategies to reduce those impairments and the effect of those reductions on the rest of the system. A linearized PA lineup using Scintera’s SC1869 RF PA linearizer is provided with measurements. The SC1869 reduces close-in IM products while meeting standard/regulatory requirements and also offers a small footprint and compelling price point making it ideal for small cell applications.