Format efficient timing acquisition for magnetic recording read channels

Abstract

A timing recovery circuit for magnetic recording applications that use preamble synchronization bits. The timing recovery circuit uses a modified digital phase lock loop having a digital rotator. An analog to digital converter (ADC) receives an analog input and provides ADC digital samples to the digital rotator. In order to compensate for analog delay and slewing, it is noted that changing the sampling point in the ADC is equivalent to introducing a phase change in the output. This phase change can be introduced much faster digitally, using a digital rotator, for example, than through changing the analog sampling points. The digital rotator snaps to an initial phase estimate almost instantly as compared to the time required to change the ADC sampling points. As the ADC slews to the initial phase estimate, the digital rotator derotates in step until the ADC reaches the initial phase estimate.