HK1141357B - Apparatus and methods of generating a test pattern of data, analysing a test pattern of data, and testing a data storage disk medium and/or a read/write head - Google Patents

Abstract

There is disclosed apparatus and methods of generating a test pattern of data, analysing a test pattern of data, and testing a data storage disk medium and/or a read/write head. In a preferred embodiment there is disclosed a method of generating a test pattern of data to be written to a data storage disk medium (4) for testing. The method comprises: rotating the disk (4); detecting fluctuations in the speed of rotation of the disk (4); producing a reference clock signal (53) in accordance with said fluctuations so as to be synchronised with the rotation of the disk (4); and, generating a test pattern of data (58) using said reference clock signal (53) as a timing reference.

Description

Apparatus and method for generating, analyzing data test patterns and testing data storage disk media and/or read/write heads

Technical Field

The present invention relates to apparatus and methods for generating, analyzing data test patterns and testing data storage disk media and/or read/write heads.

Background

In embodiments, the present invention relates generally to head media (head media) testing apparatus, such as "spin stand" or "dynamic electronic testing machines" as are well known in the art. In the art, "spinstands" were first developed in development as application tools that enable the performance of various components of a disk drive (e.g., heads, disks, and tracks) to be evaluated and optimized. It is common today to use spinstands in the field of disk drive manufacturing to test each read/write head or disk produced before it is assembled in a disk drive unit.

A typical spinstand includes a spindle driven by a motor on which a disk to be tested may be mounted and rotated, and a head holding and positioning loading mechanism for holding and positioning the head of the read/write head to be tested. The spinstand also includes a spinstand controller under the control of which the head "flies" over the surface of the disk as it rotates so that test data can be written to or read from the disk using the head. When testing using a spinstand, the head is first placed over a track of the disk and test data is written to the track. The test data is then read back by the head, measured and analyzed, after which the results are displayed to the user. Various parameters that control the writing and/or reading back of data can be controlled and varied in the spinstand, allowing the performance and characteristics of the head or disk to be studied under various conditions. A computer or similar processing device is typically provided to perform the various tests performed on the spinstand and to analyze and display the results of the various measurements performed on the spinstand. In addition, measurements made with the spinstand can be analyzed and displayed using dedicated parametric measurement electronics, spectrum analyzers, or oscilloscopes. This allows a series of tests to be performed including, for example, so-called Bit Error Rate (BER) bathtub curves (bathtubs), track squeeze (track squeeze), track center, read/write offset (read/write offset), overwrite (overwrite), etc.

Errors in testing may result from fluctuations in the rotational speed of the disk. A high precision motor is typically used to drive the spindle and thus the disk attached to the spindle into rotation. However, the motor speed can only be controlled within certain tolerances, which results in undesirable fluctuations in the disk rotational speed. Such fluctuations distort the test data pattern both when written to and when read back from the disk. For highly accurate tests, this distortion can cause serious problems in the testing process.

Disclosure of Invention

According to a first aspect of the present invention there is provided a method of generating a test pattern of data to be written to a data storage disk medium for testing, the method comprising: rotating the magnetic disk; detecting fluctuations in the rotational speed of the disk; generating a reference clock signal in accordance with the fluctuations so as to be synchronized with the disk rotation; and generating a data test pattern using the reference clock signal as a timing reference.

By generating a clock signal synchronized with the rotation of the disk and using it to generate a data test pattern, it is possible to generate a test pattern that accounts for or allows for fluctuations in the rotation of the disk so that it is spatially correct relative to the surface of the disk when the test pattern is written to the disk. This means that the data can be read back and the resulting signal will be a more realistic reproduction of the original data test pattern.

For example, in the case of writing a test frequency into a certain track on a disk, in the prior art, the test frequency actually appearing on the disk will deviate to some extent along the track, which means that the recovered frequency will also be expanded, resulting in a reduction in signal measurement accuracy. In contrast, the present invention enables the frequency to be modulated to accommodate rotational errors of the disk, making the frequency pattern written on the disk more spatially accurate and thus the spread of the signal read back from the disk smaller. This means that it becomes simpler to detect the frequency in the readback signal, since the frequency energy will be more sharply concentrated at the correct frequency and less spread.

In a preferred embodiment, the step of detecting fluctuations comprises: detecting a plurality of marks rotating synchronously with the magnetic disk; and generating a clock signal corresponding to the detected movement of the mark, the clock signal being used to generate a reference clock signal. Such a configuration provides a preferred method of measuring fluctuations in disk rotation so that a reference clock signal can be generated. These marks may be optical marks that are read using laser interferometry. The optical markers may be attached to the disk itself or to the spindle or any other part that rotates with the disk. Alternatively, the labels may be magnetic labels located on the disc that are magnetically detectable. It is generally preferred to provide a plurality of marks to enable fluctuations in the rotation of the disk to be determined with a higher resolution.

In a preferred embodiment, the method comprises taking the clock signal as an input to a phase locked loop which is used to generate said reference clock signal. This provides a simple way of generating the reference clock signal. The use of a phase-locked loop enables the generation of a reference signal adapted to the application according to well-known operating principles of phase-locked loops.

In one embodiment, the method includes generating, by an oscillator, an oscillating clock signal; rotating the disk using a motor locked to the oscillating clock signal; and generating a reference clock signal using the oscillating clock signal, the oscillating clock signal being modulated in accordance with fluctuations in the rotational speed of the disk during generation of the reference clock signal. In fact, in this embodiment, an oscillator is used to generate a reference clock and clock the motor. If separate clocks are used, thermal drift can cause clock-to-clock drift, which can introduce phase errors into the patterns written to the disk. An advantage of sharing one clock is that the error can be substantially eliminated.

The method can comprise the following steps: rotating the magnetic disk; detecting fluctuations in the rotational speed of the disk; generating a reference clock signal in accordance with the fluctuations so as to be synchronized with the disk rotation; reading a data test pattern from a disk to provide a test data signal; and analyzing the test data signal using the reference clock signal as a timing reference. This configuration provides a preferred phase-locked loop architecture. A 1/N counter means that the reference clock signal may be at a different frequency than the clock signal.

According to a second aspect of the present invention there is provided a method of analysing a test pattern of data read from a data storage disk medium, the method comprising: rotating the magnetic disk; detecting fluctuations in the rotational speed of the disk; generating a reference clock signal in accordance with the fluctuation so as to be synchronized with the rotation of the magnetic disk; reading a data test pattern from a disk to provide a test data signal; and analyzing the test data signal using the reference clock signal as a timing reference.

By generating a reference clock signal synchronized with the disk rotation and using it to analyze the test data signal, fluctuations in disk rotation can be taken into account when reading back the data. This makes analyzing the data easier and improves the accuracy of the results.

For example, when a test frequency is written to a track on a disk, in the prior art, the recovered test signal read from the disk is distorted due to disk rotation fluctuations, which means that the recovered frequency will undergo frequency spreading (frequency spread), thereby making signal measurement difficult. In contrast, this aspect of the invention enables the recovered data test signal to be demodulated by disk rotation errors, discarding fluctuations in disk rotational speed, so that analysis of the signal read back from the disk is less affected by frequency dispersion. This means that it is simpler to detect frequencies from the readback signal, since the frequency energy is more strongly concentrated at the correct frequency and the frequency spread is reduced.

The analyzing step includes performing a spectral analysis on the test data signal. As will be discussed below, the configuration of the present invention has particular advantages when used for narrow band measurement testing.

The step of spectral analysis comprises converting said test data signal to an intermediate frequency by mixing said test data signal with a sinusoidal signal generated using said reference clock as a timing reference. This configuration supports more accurate superheterodyne operation on the data signal as part of the spectral analysis test and normalizes the spectrum analyzer for disk speed.

The spectral analysis step may include: an analog-to-digital converter clocked with a reference clock samples and digitizes the test data signal. This enables the spectrum analyzer to be normalized to disk speed. Such an arrangement may also be applied to a spectrum analyzer that digitally performs part or all of the spectrum analysis.

According to a third aspect of the present invention there is provided a method of testing at least one data storage disk medium and a read/write head, the method comprising: rotating the magnetic disk; detecting a rotational speed fluctuation of the magnetic disk; generating a reference clock signal from the fluctuations so as to be synchronized with the disk rotation; generating a data test pattern using the reference clock signal as a timing reference; writing a data test pattern to the disk with the head; reading a data test pattern from the disk by the head to provide a test data signal; and analyzing the test data signal using the reference clock signal as a timing reference.

Using both methods described above provides a more accurate test method. The reference clock signal is used when generating a data pattern to be written to the disk to compensate for disk rotation fluctuations and analyzing the data signal read back from the disk to compensate for disk rotation fluctuations.

In one embodiment, the method comprises: 1) rotating the disk with the motor locked to the oscillator clock signal; 2) providing a reference clock signal by an oscillator clock signal, and modulating the oscillator clock signal according to the fluctuation of the rotation speed of the magnetic disk in the generation process of the reference clock signal; wherein the same oscillator clock signal is used in steps 1) and 2). In this configuration, a single oscillator clock is used as a reference for the entire test apparatus instead of providing separate oscillator clocks in the respective apparatuses. This avoids the thermal drift effect that would normally occur between two separate clocks over time, thereby avoiding a source of error entering the system when data is written to disk and when data is read back and analyzed from disk.

According to a fourth aspect of the present invention there is provided apparatus for generating a data test pattern to be written to a data storage disk medium for testing, the apparatus comprising: a spindle for rotating the magnetic disk; a detector for detecting fluctuations in the rotational speed of the magnetic disk; a processor for generating a reference clock signal in accordance with the fluctuations so as to be synchronized with disk rotation; and a pattern generator for generating a data test pattern using the reference clock signal as the timing reference.

According to a fifth aspect of the present invention there is provided apparatus for analysing a test pattern of data read from a data storage disk medium, the apparatus comprising: a spindle for rotating the magnetic disk; a detector for detecting fluctuations in the rotational speed of the magnetic disk; a processor for generating a reference clock signal in accordance with the fluctuations so as to be synchronized with disk rotation; a controller for reading a data test pattern from the disk to provide a test data signal; and an analyzer for analyzing the test data signal using the reference clock signal as a timing reference.

According to a sixth aspect of the present invention there is provided apparatus for testing at least one data storage disk medium and a read/write head, the apparatus comprising: a spindle for rotating the magnetic disk; a detector for detecting fluctuations in the rotational speed of the magnetic disk; a processor for generating a reference clock signal in accordance with the fluctuations so as to be synchronized with disk rotation; a pattern generator for generating a data test signal using the reference clock signal as the timing reference; a controller for writing a test pattern of data to the disk using the head and subsequently reading test data from the disk by the head to provide a test data signal; and an analyzer for analyzing the test data signal using the reference clock signal as a timing reference.

Embodiments of the present invention will now be described with reference to the accompanying drawings, which are illustrative.

Drawings

FIG. 1 shows an example of a spinstand according to an embodiment of the invention.

Figure 2 shows an example of a spectrum analyser for use with the spinstand of figure 1.

Detailed Description

Referring to figure 1, a spinstand 1 comprises an air spindle 2 driven by a motor 3 on which a disk 4 is mounted. The spinstand 1 further comprises a loading mechanism (not shown) for holding the head gimbal assembly 5 and positioning the read/write head 6 of the head gimbal assembly 5 over the surface of the disk 4 so that data can be written to or read from tracks on the surface of the disk 4. The spinstands described above are of the type known.

The spinstand 1 has a laser coding system 7 associated with its spindle 2 so that the position of the spindle 2 can be accurately determined. The principles of the laser coding system 7 are well known in the art and will not be described in detail here. In particular, suitable laser encoding systems 7 have been developed for use with servo track writing devices that maintain the servo tracks being written successively in the correct phase with respect to each other with the necessary high degree of accuracy. In short, an encoder scale 7a is provided on the spindle at the end opposite to the end having the magnetic disk 4. The scale 7a comprises a diffraction grating, i.e. a series of black to white transitions arranged in a ring coaxial with the axis of the spindle 2. Preferably, thousands of such transitions, or millions, are provided along the ring. Preferably, the transitions occur at equal angular intervals along the ring.

A grating interferometer 7b is mounted on the spinstand 1 for reading the scale 7a on the spindle 2. The interferometer 7b has a laser (not specifically shown) directed at the scale 7a, enabling a detector (not specifically shown) in the interferometer 7b to detect transitions of the scale 7a as the scale 7a passes the laser as the transitions in the scale 7a move past the laser. In this way, the laser coding system 7 generates a raw coded signal 51 that is used to measure the detected scale 7 a.

The raw encoded signal 51 is passed to optical timing clock electronics 8 which processes the raw encoded signal 51 to produce a processed encoded signal in the form of a clock signal 52, the edges of the clock signal 52 corresponding to the detected transitions on the scale 7 a.

It should be noted that other arrangements for measuring fluctuations in disk rotation are possible. For example, the scale 7 may be attached to the disk 4 or any other part that rotates with the disk 4, rather than to the spindle 2. The use of optical markers is not essential. Magnetic labels may also be used. Magnetic marks may be formed on the surface of the magnetic disk 4.

The clock signal 52 is fed back to the Phase Locked Loop (PLL)10, and the Phase Locked Loop (PLL)10 generates as its output a reference clock signal 53. One skilled in the relevant art will appreciate that there are a variety of ways to implement a phase-locked loop. Only one method is described in detail below.

The phase locked loop 10 typically extracts phase information from the clock signal 52 and uses the phase information to modulate an oscillator clock signal 54 from the crystal 11 to generate a reference clock signal 53. The reference clock signal 53 is implemented as a negative feedback loop feedback. In this example, the reference clock signal 53 is first divided by the 1/N counter 12 to provide a divided reference signal 55. Such division reduces the frequency to a position close to the clock signal 52. The clock signal 52 and the divided reference signal 55 are fed back to the phase detector 13, which determines the phase difference between the two. At the detector output 56, the phase difference is represented as a dc level. Optionally, filtering it by a filter 14 may improve the performance of the phase locked loop 10, as is known in the art. The filtered signal 57 is provided to the vector modulator 15 as a control signal. Vector modulator 15 has as a first input filtered signal 57. The crystal oscillator 11 generates an oscillator clock signal 54 which is also fed back to the vector modulator 15. The vector modulator 15 serves to modulate the phase of the input oscillator signal 54 such that the phase difference between the divided reference clock signal 55 and the clock signal 52 taken from the motor 3 is reduced to or close to 0.

Thus, the reference clock signal 53 is modulated to be generated so as to be synchronized with the rotation of the magnetic disk 4, taking into account the fluctuation in the rotation of the magnetic disk 4.

A number of standard tests performed by spinstands today require the use of narrow band power measurements. One of the tests is the so-called "overwrite" test. The test comprises writing a test data pattern having a first frequency to a track on the disk 4 by means of the read/write head 6, followed by overwriting the first pattern with a second test data pattern having a different frequency. The track is then read back by the head 6 and the acquired signal is analysed to measure the residual signal energy at the first frequency in the overwrite pattern. This is done with a narrow band measurement system centered on the first frequency. It is generally desirable that the narrow band measurement system is operable over a wide frequency range with good resolution so that different data pattern frequencies can be used with sufficient flexibility in testing. In practice, signal analysis is often performed using a tuned spectrum analyzer or similar device.

Since the residual signal energy of the first frequency mode is generally relatively low, it is desirable to use a measurement system with a high dynamic range in detecting and measuring the signal. This means that the spectrum analyzer needs to have a low Resolution Bandwidth (RBW) for this purpose. For example, next generation spinstands provide for RBW to be reduced to 10 kHz. However, due to fluctuations in the speed of the motor when writing test data and when reading back test data, the frequency content of the final data signal read by the head is distorted and spread. For example, a typical motor speed error is 0.001%, and the worst case is a test signal frequency error of 0.002% (i.e., an error of 0.001% for the write mode and an error of 0.001% for the read back mode). When this error is applied to a write frequency signal with a typical frequency of 500MHz, the read back frequency deviation will be greater than ± 10kHz in the worst case. Therefore, it is increasingly difficult to realize a sufficiently narrow RBW capable of picking up a low-level signal and capable of handling possible frequency dispersion. Also, the problem is becoming more severe because the trend in the art is: the signal-to-noise ratio of modern heads 6 is becoming lower, which means that the bandwidth of the narrow-band filter in the spectrum analyzer needs to be further reduced. Furthermore, next generation spinstand devices are expected to handle write frequencies up to 2.5 GHz. The standard techniques are becoming inadequate.

In other types of spinstand testing, similar or identical problems caused by the speed of the spindle are increasing.

In one embodiment, reference clock signal 53 is fed back to pattern generator 16 and used as a timing reference to generate data test pattern 58. The data test pattern 58 is then written to the disk 4 by the head 6. The spatial spread of the data test pattern written to the disk 4 due to fluctuations in the rotation of the disk 4 is thereby reduced. Thus, in performing, for example, the above-described overlay test, the technique of generating the data test pattern 58 may be applied to write a first frequency pattern of test data and/or a second frequency pattern of test data to the disk 4 to mitigate the problems of write frequency distortion and spread.

Fluctuations in the rotation of the disk 4 also affect the fidelity of the test data signal 59 (also referred to as the head signal 59) read back with the head 6. To reduce its effect, in one embodiment, the test data signal 59 is analyzed using the reference clock signal 53 as a timing reference so that the test data signal 59 is demodulated with the reference clock signal 53. Thus, when the overwrite test is performed again, a spectral analysis is performed on the test data signal 59 using this technique of analysing the test data signal 59 to detect the residual signal energy of the first frequency pattern of the overwritten test data, thereby further mitigating distortion and spread problems of the write frequency when it is read back from the disk 4.

Fig. 2 shows an example of an apparatus 20 for performing spectral analysis on a test data signal 59. The spectrum analyzer 20 includes an input stage that operates according to the "superheterodyne" principle. The test data measured by the head 6 is here mixed with a selected frequency sine wave 60 to frequency shift the frequency of interest to an Intermediate Frequency (IF). In this example, the adjustable synthesizer 21 is used to generate the desired frequency 60. The measurement data signal 59 and the generated frequency 60 are fed to the mixer 22 where the signals are mixed to shift the frequency of interest to an intermediate frequency. Alternatively, the tunable synthesizer may be linked to a frequency scanner for spectral analysis over a frequency range of interest.

The shifted test data signal 61 is filtered by intermediate frequency filter 23 to remove unwanted heterodyne frequencies. The filtered signal 62 is then sampled and digitized by an analog-to-digital converter (ADC). The clock 24 of the ADC 24 is derived from the reference clock signal 53. The reference clock signal 53 is fed back to the ADC clock synthesizer 25, which generates a clock signal for the ADC 24 based on the reference clock signal 53 as a timing reference. Thus, the reference clock signal 53 clocks the ADC 24 so that the sampling signal 64 generated by the ADC 24 removes frequency dispersion due to fluctuations in the rotation of the disk 4.

The sampled signal 64 is then passed to a Digital Signal Processing (DSP) system 30. A first-in-first-out buffer 31(FIFO) serves as an input stage of the DSP system 30 and receives the sampled signal 64. Preferably, the FIFO 31 has protection for crossing asynchronous clock domains, so that the DSP system 30 performing the processing is clocked at a higher frequency than the sampling frequency of the ADC 24, thereby improving the delay time of the analyzer 20. The DSP system 30 also includes a digital down converter 32 that receives the sampled signal 64 from the FIFO32 and then down converts the sampled signal 64 to the baseband signal 65. The baseband signal 65 passes through a low pass filter 33 that operates as an RBW filter. From there, the filtered signal 66 is passed to the power detector 34, which measures the power in the signal 66 so that it can be recorded or displayed to a user.

Since the ADC sampling clock 63 is obtained from the reference clock signal 53 using the rotation speed bar value of the disk 4, the sampling signal 64 generated by the ADC 24 eliminates the frequency dispersion caused by the fluctuation in the rotation of the disk 4. This means that the spectrum analyzer 20 becomes normalized to the disk speed.

However, there are other ways to normalize the spectrum analyzer 20 with respect to disk speed. For example, rather than derive the ADC sampling clock 63 from the reference clock signal 53, the superheterodyne frequency 60 may be derived from the reference clock signal 53. This also has the effect of the sampling signal 64 generated by the ADC 24 removing the frequency spread caused by the fluctuations in the rotation of the disk 4 and normalising the spectrum analyser 20 to the disk speed.

In addition, referring to FIG. 1, the motor controller 40, which controls the rotation of the disk 4, is clocked or locked by the same oscillator 11 that clocks the PLL 10. In this way, a single oscillator clock 54 serves as a reference for the entire test apparatus 1, 20 rather than having separate oscillator clocks in the apparatus, respectively. This avoids thermal drift between the two separate clocks, thus avoiding a source of error entering the system, both when writing data to the disk data 4 and when reading back and analyzing data from the disk 4.

These are merely some examples of how reference clock signal 53 may be used as a timing reference to analyze test data signal 59. Other forms are possible depending on the application.

The embodiments of the present invention will be described with particular reference to the examples shown in the drawings. It is to be understood that variations and modifications can be made to the described examples within the scope of the invention.

Claims (12)

1. A method of testing at least one of a data storage disk medium and a read/write head, the method comprising:

rotating the magnetic disk;

detecting fluctuations in the rotational speed of the magnetic disk;

generating a reference clock signal in accordance with the fluctuations so as to be synchronized with the disk rotation;

generating a data test pattern having a test frequency using the reference clock signal as a timing reference;

writing the data test pattern to the disk using the read/write head;

reading the data test pattern from the disk using the read/write head to provide a test data signal; and

the test data signal is analyzed using a reference clock signal as a timing reference to measure the narrowband power of the test data signal.

2. The method of claim 1, wherein the step of detecting fluctuations comprises:

detecting a plurality of marks rotating synchronously with the magnetic disk;

a clock signal corresponding to the detected movement of the mark is generated, which is used to generate a reference clock signal.

3. A method according to claim 2, characterized in that the method comprises: the clock signal is provided as an input to a phase locked loop that is used to generate the reference clock signal.

4. A method according to any of claims 1-3, wherein the step of analyzing comprises performing a spectral analysis on said test data signal.

5. The method of claim 4 wherein said step of spectrally analyzing comprises: the test data signal is converted to an intermediate frequency by mixing the test data signal with a sinusoidal signal generated using the reference clock signal as a timing reference.

6. The method of claim 4 wherein said step of spectrally analyzing comprises: the test data signal is sampled and digitized using an analog-to-digital converter clocked by the reference clock signal.

7. An apparatus for testing at least one of a data storage disk medium and a read/write head, the apparatus comprising:

a spindle for rotating the magnetic disk;

a detector for detecting fluctuations in the rotational speed of the magnetic disk;

a processor for generating a reference clock signal in accordance with the fluctuations so as to be synchronized with the rotation of the magnetic disk;

a pattern generator that generates a data test pattern having a test frequency using the reference clock signal as a timing reference;

a controller that writes a test pattern of data to the magnetic disk using the read/write head and subsequently reads test data from the magnetic disk using the read/write head to provide a test data signal; and

a spectrum analyzer for analyzing the test data signal using the reference clock signal as a timing reference to measure the narrowband power of the test data signal.

8. The apparatus of claim 7, comprising:

a plurality of marks rotating in synchronization with the magnetic disk, the read/write head for reading the marks;

a decoder for generating a clock signal corresponding to the movement of the read mark, the clock signal being used to generate the reference clock signal.

9. The apparatus of claim 8, comprising a phase locked loop receiving as an input a clock signal, the phase locked loop being configured to generate the reference clock signal.

10. The apparatus according to any one of claims 7-9, comprising:

an oscillator for generating an oscillating clock signal;

a motor for rotating the magnetic disk and locked with the oscillation clock signal;

the processor generates a reference clock signal using an oscillating clock signal modulated according to fluctuations in the rotational speed of the magnetic disk, and the motor and the processor use the same oscillating clock signal.

11. The apparatus of any of claims 7-9, wherein the analyzer comprises a mixer to convert the test data signal to an intermediate frequency by mixing the test data signal with a sinusoidal signal generated using the reference clock signal as a timing reference.

12. An apparatus according to any one of claims 7 to 9, wherein the analyser comprises an analogue to digital converter clocked by the reference clock signal and arranged to sample and digitise the test data signal.