Asynchronous/synchronous gain control for interpolated timing recovery

Abstract

A sampled amplitude read channel is disclosed for reading data recorded on a disk storage medium by asynchronously sampling an analog read signal, equalizing the asynchronous sample values according to a desired partial response, and interpolating the equalized sample values to generate synchronous sample values substantially synchronized to a baud rate of the recorded data. The read channel further comprises a gain control circuit which generates a gain error for adjusting the amplitude of the analog read signal to a nominal value through a variable gain amplifier (VGA). During acquisition, the gain error is computed from the asynchronous sample values at the output of the sampling device in order to avoid the delay associated with the discrete equalizer filter and the timing recovery interpolation filter. This decreases the acquisition time and the corresponding length of the acquisition preamble, thereby reserving more area on the disk to record user data. After acquisition and while tracking the random user data, the gain control loop is reconfigured to generate the gain error according to using the synchronous, interpolated sample values output by the timing recovery circuit.