RF Synthesizer Loop Filter Design for Minimal OFDM Inter-carrier Interference

Abstract

This paper describes the influence of Radio-Frequency synthesizer loop filter design on OFDM inter-carrier interference. OFDM modulation scheme is very sensitive on carrier phase and frequency variations, resulting on inter-carrier interference leading to incorrect message decoding and the increase of system bit error rate. Radio-Frequency synthesizer has the main role on modulation and demodulation processes of base band IQ signals. The loop filter is one of its building blocks designed for loop stability. It also shapes the phase noise frequency response at the output of the frequency synthesizer. The achieved results are supported by simulation scenarios based on OFDM architecture, including radio-frequency synthesizer topology. The loop filter frequency response, local oscillator phase noise power and bandwidth are configurable. These simulations features allow the design trade-off between synthesizer stability and output phase noise power.