A novel AGC scheme for QAM demodulator applications

The performance of traditional approaches of automatic gain control (AGC) will be seriously degraded by intersymbol interference (ISI). This could result in slow convergence and possible instability problems. In this paper, we propose an equalizer-based AGC scheme to overcome the ISI interference and it uses the error signal of the equalizer output to control the AGC loop direction. Simulation results demonstrate good acquisition and tracking performances of the new scheme under large ISI circumstances. Our equalizer-based AGC is already silicon-proven for the application of QAM demodulator using charter 0.25 um cell libraries.