The existing solution for phase-roll compensation in echo cancelers is to use a second-order phase locked loop (PLL) with a cross-coupled structure. In this structure a Hilbert transform is applied to the error signal to estimate the instantaneous phase difference between the actual far echo and the locally estimated one. Simplified echo canceler structures that implement the adaptive-step sign algorithm cannot compensate for phase roll. This is because the Hilbert transform cannot be applied to a signal sampled and quantized with a single-bit A/D converter. A new technique to estimate the instantaneous phase difference in full-duplex data mode is presented. This technique is based on the sign algorithm to avoid the use of the Hilbert transform. This results in a simplified structure for echo cancelers that compensate for phase roll.
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