A circuit includes a first Viterbi detector configured to generate a first estimate signal based on an equalized signal. The first estimate signal includes preliminary non-return-to-zero data estimates. A first filter is configured to generate a first filtered signal based on a preliminary decision signal. The preliminary decision signal is generated based on the first estimate signal. A second Viterbi detector is in communication with the first Viterbi detector. The second Viterbi detector is configured to generate a final decision signal based on a sum of (i) a delayed version of the equalized signal, and (ii) the first filtered signal, wherein the final decision signal comprises final non-return-to-zero estimates.