Dynamic magnetic information storage or retrieval – Monitoring or testing the progress of recording
Reexamination Certificate
1998-05-15
2001-07-03
Neal, Regina Y. (Department: 2651)
Dynamic magnetic information storage or retrieval
Monitoring or testing the progress of recording
C360S046000, C327S310000, C327S311000
Reexamination Certificate
active
06256157
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates in general to noise suppression, and more particularly to a method and apparatus for removing noise spikes from an input transducer (head) in a storage system.
2. Description of Related Art
Magnetic data is increasingly stored at higher and higher densities which in turn require increases in the sensitivity of the transducers (heads) used to read the recorded signals. Noise reduction and cancellation likewise becomes more important as sensitivity of the heads increases. Recently, a previously unreported phenomenon associated with data readback has been identified that detrimentally affects the error rate in a data storage system. Errors in data readback have been identified to be caused by very sharp spikes at the input (channel) preamplifier. The sharp spikes are of electrical origin and have been observed in systems using MR heads. The spikes which can be considered to be impulse noise are very narrow in width and broad in spectral content, can be of either polarity and are distributed over a wide range in amplitude.
The effect of the sharp spikes in the input channel signal is randomly dispersed single bit errors. This effect is intermittent and can degrade the soft error rate to unacceptable levels. In fact, spikes above a certain amplitude have sufficient energy in the bandwidth of the recording channel to interfere with detection of the media signal. The precise origin of these spikes is not well understood. It appears that they can occur in the absence a recording signal or MR bias current, but appear to require media/head contact and their relative motion.
FIG. 8
illustrates a graph
800
of a set of noise spikes
802
detected on a DC erased track with an oscilloscope set to persistence mode and a positive trigger level. Note that the noise spikes
802
are identical in structure, i.e., they have substantially the same pulse width
810
, but vary greatly in amplitude
812
.
As a result of such phenomenon, a number of tracks on head arrays may suffer seriously degraded error rates. Problem tracks are randomly distributed on heads, and the problem is intermittent with random increase and decreases in the occurrence of the phenomenon. In addition, problem tracks have shown noise spikes with some media and not with others.
FIG. 9
illustrates a graph
900
of an noise spike
910
corrupting a channel signal
920
in a low end system. As in the high end, the noise spikes
910
are identical in structure, but vary greatly in amplitude. Here too the noise spikes
910
may be found to have a positive and negative (not shown) polarity and to be intermittent.
Since noise spikes are not written to the tape during the recording process, data integrity is not in question. Typical error correction schemes normally can handle single bit randomly distributed errors in readback. However, there are times when the density of errors is so great that data rereads would be required, which would degrade performance. In a worst case, heads or drives may have to be replaced in the field to attempt to eliminate the problem.
It can be seen then that there is a need for an improvement to prevent errors if and when the spikes occur.
SUMMARY OF THE INVENTION
To overcome the limitations in the prior art described above, and to overcome other limitations that will become apparent upon reading and understanding the present specification, the present invention discloses a method and apparatus for removing electrical noise spikes from a signal containing information such as a signal read from the media in a data storage device.
The present invention protects a data storage system, such as a tape or disk drive, from a degraded soft error rate due to electrical spikes in the signals coming from the head.
A method in accordance with the principles of the present invention includes extracting the high frequency component of the noise spike above a normal high frequency cutoff for the system, generating a cancellation signal for the low frequency component of the noise spike using the high frequency component and combining the cancellation signal with the appropriately delayed input signal to remove or reduce the noise spike in the input signal. The cancellation signal may be generated with the opposite polarity from the noise spike or it may be inverted after it is generated so that it can be summed with the raw input signal. A cancellation signal with the same polarity of the noise spike may be used to drive a differential amplifier along with the raw input signal to subtract the cancellation signal.
The invention can be embodied in analog or digital circuitry or a combination thereof. The circuitry is designed to identify the time that a spike occurs along with the amplitude and polarity of the spike which are then used as parameters in generating the cancellation signal.
One embodiment in accordance with the present invention includes a high pass filter, a mixer and circuitry for combining a cancellation signal and the raw signal. The high pass filter removes the low frequency component of the raw signal which is a composite of the information signal and a noise spike. The noise spike has a spectral content above the normal operating frequency bandwidth of the system. Output from the high pass filter determines the timing of the spike. The mixer regenerates the low frequency portion of the noise spike by mixing the output of the high pass filter with an internally generated signal (such as a sinusoidal wave) selected to generate a spectral component (a lower sideband) which can either be used as the cancellation signal or from which the cancellation signal is derived by further processing such as amplitude adjustment. The cancellation signal is the reconstruction of the low frequency component of the spike in the normal operating bandwidth. The mixer acts to shift the frequencies in the high frequency portion of the noise spike downward while preserving the timing and amplitude information. Any standard frequency shifting components or apparatus, whether analog or digital, can be used to achieve this downward shift if the timing and amplitude information is preserved. There will typically be other higher frequency spectral components in the output of the mixer, but since these are above the normal frequency cutoff of the system, they can be removed by a low pass filter. A differential amplifier or other combining device is used to combine the delayed raw input signal and the cancellation signal to obtain the adjusted signal in which the noise signal has been removed or subtracted from the information signal. The raw input signal is delayed to match the delay introduced by the circuitry which generates the cancellation signal.
Although the invention is well suited for use in data storage systems, it can be applied in any signal processing application subject to similar noise spikes whose spectra similarly overlap the input band of the system.
REFERENCES:
patent: 4204170 (1980-05-01), Kage
patent: 4254483 (1981-03-01), Vidovic
patent: 4317142 (1982-02-01), Wray
patent: 4342059 (1982-07-01), Wray
patent: 4591710 (1986-05-01), Komadina et al.
patent: 4914398 (1990-04-01), Jove et al.
patent: 4931743 (1990-06-01), Fukuda et al.
patent: 4994767 (1991-02-01), Hawkes
patent: 5446539 (1995-08-01), Minakawa
patent: 5625320 (1997-04-01), Hagerty
Biskeborn Robert G.
Christensen Eric R.
Seagle David J.
Altera Law Group LLC
International Business Machines - Corporation
Neal Regina Y.
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