US 6,487,672 B1 · Digital timing recovery using baud rate sampling

Abstract

A baud rate digital timing recovery circuit for use in the read channel of a storage device controller is able to operate nominally at the baud rate by recognizing and compensating for oversampling and undersampling conditions. The read channel includes a sample rate converter for interpolating between digitally sampled values and a digital timing recovery loop that detects a phase error in the interpolated signal and adjusts the interpolation interval accordingly. An accumulator circuit generates a modulo-TS interpolation interval value, where TS is the sampling period. Detection circuitry detects when the interpolation interval value has wrapped through its maximum value or minimum value and generates an oversampling or undersampling signal in response. The oversampling and underampling signals are received by an elastic buffer. The elastic buffer operates to store extra values that are generated during undersampling conditions and also disregards bogus samples that are generated during oversampling conditions, in response to the undersampling and oversampling signals. A mini-elastic buffer, also responsive to the oversampling and undersampling signals may be employed in the phase detection loop. The system can operate at the nominal baud rate or can operate at a half baud rate with two parallel paths for processing two incoming samples with each clock cycle.

Claims20

Dependent claims

A device for reading information stored on a medium by detecting data from a sequence of discrete time interpolated samples , the interpolated samples generated by interpolating a sequence of discrete time channel samples generated by sampling pulses in a read signal from the medium, the device comprising:

a sampling clock outputting a clock signal with a period of T;
a sampling device, responsive to the sampling clock, receiving as input the read signal and outputting the channel samples;
an interpolated timing recovery circuit receiving as input the channel samples and outputting the interpolated samples, including an accumulator for generating, modulo-T, an interpolation interval value;
an elastic buffer wherein the interpolated samples received from the interpolated timing recovery circuit are stored, and from which the interpolated samples are subsequently read out to a data detector.

1 more element

A method for reading information from a medium at the same baud rate as the information was written to the medium, the information being stored on the medium as an analog signal, the analog signal having associated with it a phase and a baud rate, the method comprising:

reading the analog signal;
sampling the analog signal at a sample rate nominally the analog signal baud rate to generate a digital signal comprising channel samples;
interpolating between channel samples to generate an interpolated signal comprising interpolated samples, in response to an interpolation interval, the interpolation interval value having a minimum and a maximum value;
storing the interpolated samples in an elastic buffer;
passing the interpolated samples from the elastic buffer to a data detector;
detecting when the interpolation interval value has wrapped from its maximum value to or through its minimum value and in response preventing the passing of one interpolated sample from the elastic buffer to the data detector;
and
detecting when the interpolation interval value has wrapped from its minimum value to or through its maximum value and in response storing a channel sample in the elastic buffer in addition to an associated interpolated sample and allowing both the interpolated sample and the channel sample to pass to the data detector.

5 more elements

A read channel for correcting a phase error between a channel signal that is read from a storage medium, the channel signal having been written to the storage medium at a baud rate, comprising:

means for reading the channel signal from the storage medium;
means for sampling the channel signal to generate a sample signal comprising channel samples;
means for detecting a phase error in the sampled signal;
means for generating a modulo-T interpolation interval, where T is proportional to the baud rate;
means for interpolating between channel samples in response to the modulo-T interpolation interval to generate an interpolated signal comprising interpolated samples;
storage means for storing the interpolated samples, wherein the storage means, in response to an indication that the interpolation interval has wrapped from T to 0, treats the interpolated sample associated with such condition as invalid, and wherein the storage means, in response to an indication that the interpolation interval has wrapped from 0 to T, treats the interpolated sample associated with such condition as valid and also stores a sample point associated with such condition as valid.

3 more elements

Dependencies are inferred from the claim text.

Digital timing recovery using baud rate sampling

Life of this patent

Digital timing recovery using baud rate sampling

Life of this patent

Abstract

Claims20