Readback waveform oversampling method and apparatus
A read channel is configured to obtain an analog readback waveform from a magnetic recording medium of a disk drive at a sampling rate of one sample per one written bit. A buffer is coupled the read channel. Circuitry is configured to inject a plurality of different phase offsets into the read channel for each of a plurality of revolutions of the medium. The circuitry is also configured to store, in a buffer, an amplitude of the readback waveform for each of the different phase offsets. The circuitry is further configured to generate an oversampled readback waveform using the amplitudes stored in the buffer.
1. A method, comprising:
obtaining, via a read channel of a disk drive, a readback waveform from a magnetic recording medium at a sampling rate of one sample per one written bit;
for each of a plurality of revolutions of the medium, injecting a plurality of different phase offsets into the read channel;
storing, in a buffer, a waveform defined by an amplitude of sub-waveforms each associated with one of the different phase offsets; and
generating an oversampled readback waveform using the amplitudes stored in the buffer.
2. The method of claim 1 , wherein the phase offsets range from about −50% to about +50% relative to a nominal phase of the readback waveform.
3. The method of claim 1 , wherein:
obtaining the readback waveform comprises recovering a written-in phase from a preamble of the readback waveform; and
injecting the phase offsets comprises injecting positive phase offsets and negative phase offsets into the read channel relative to the written-in phase.
4. The method of claim 1 , wherein the readback waveform is oversampled by a factor ranging from 2 to 32.
5. An apparatus, comprising:
a read channel configured to obtain an analog readback waveform from a magnetic recording medium of a disk drive at a sampling rate of one sample per one written bit;
a buffer coupled the read channel; and
circuitry configured to:
for each of a plurality of revolutions of the medium, inject a plurality of different phase offsets into the read channel;
store, in a buffer, an amplitude of the readback waveform for each of the different phase offsets; and
generate an oversampled readback waveform using the amplitudes stored in the buffer.
6. The apparatus of claim 5 , wherein the circuitry comprises:
a timing recovery block coupled to an analog-digital-converter (ADC) of the read channel; and
a phase injection block coupled to the timing recovery block;
wherein the timing recover block is configured to inject the different phase offsets into the ADC in response to phase offset values received from the phase injection block.
7. The apparatus of claim 5 , wherein the phase offsets range from about −50% to about +50% relative to a nominal phase of the readback waveform.
8. The apparatus of claim 5 , wherein the timing recovery block is configured to:
recover a written-in phase from a preamble of the readback waveform; and
inject positive phase offsets and negative phase offsets into the ADC relative to the written-in phase.
9. The apparatus of claim 5 , wherein the readback waveform is oversampled by a factor ranging from 2 to 32.
10. The apparatus of claim 5 , wherein the circuitry comprises a processor configured to measure a metric or a phenomenon of disk drive operation that requires sampling of the readback waveform at the oversampling rate.
11. The apparatus of claim 5 , wherein the disk drive is a heat-assisted magnetic recording (HAMR) disk drive.