A Novel AGC Scheme for DFE Read Channels

The problem of automatic gain control (AGC) for DFE (decision feedback equalization) read channels is addressed. We analyze an existing AGC algorithm that uses slicer input for deriving the gain error signal and show that it suffers from ambiguity in the control direction of AGC loop due to the presence of feedback equalizer. This could result in slow convergence and possible instability problems. A new AGC scheme has been proposed to overcome this ambiguity and it uses the sign of the forward equalizer output instead of slicer input to control the AGC loop direction. Simulation results show good acquisition and tracking performances of the new scheme under noisy circumstances.