Multi-mode loop adaptation scheme for high-density data recording channel

A method for determining the binary sequence of a sampled digital waveform in a high density recording channel, the method comprising the steps of:

• receiving a data sequence with a sequence identifier of a circuit, the data sequence including at least one of a first data sequence and a second data sequence having a fewer number of signal levels than the first data sequence;
• alternately receiving a first data detector output from a first data detector and a second data detector output from a second data detector with a first multiplexer of the circuit;
• and
• changing the first multiplexer between a first mode and a second mode with the sequence identifier based on whether the data sequence is the first data sequence or the second data sequence.

A circuit for a high-density data recording channel, the circuit comprising:

• a 3-level slicer that generates a first data detector output;
• a Viterbi detector that is adapted to generate a second data detector output;
• an automatic gain control loop;
• a phase-locked loop;
• a first multiplexer that changes between a first mode and a second mode to alternately receive the first data detector output and the second data detector output, wherein an output of the first multiplexer proceeds to the automatic gain control loop;
• a second multiplexer that changes between the first mode and the second mode to alternately receive the first data detector output and the second data detector output, wherein an output of the second multiplexer proceeds to the phase-locked loop;
• and
• a sequence identifier that receives a data sequence including at least one of a VFO data sequence and a random data sequence that includes a greater number of signal levels than the VFO data sequence, the sequence identifier changing the first multiplexer between the first mode and the second mode and the second multiplexer between the first mode and the second mode based on whether the data sequence is the VFO data sequence or the random data sequence.