Magnetic recording medium evaluation apparatus and evaluation method
View Patent ↗This invention provides a magnetic recording medium evaluation apparatus and evaluation method which yield results having good correlation with error rate measurements even when comparing media with different structures. Signals from a function generator are recorded in a magnetic recording medium. The recording signals are also passed through a first digital filter to obtain ideal restored signals. Reproduced signals from the magnetic recording medium are sampled in synchronization with the output from the function generator, and the discrete signals are passed through a second digital filter to obtain restored signals. The outputs from the first and second digital filters are input to an operational amplifier, and the difference between the restored signals and the ideal restored signals is taken for each sampling of the recording signals. The signal-to-noise ratio of the ideal restored signal to the average of the absolute value of this difference is used to evaluate signal quality.
1. An apparatus for evaluation of a magnetic recording medium, the apparatus comprising:
a spin stand which rotates the magnetic recording medium;
a magnetic recording/reproduction head;
a mechanism to position the magnetic recording/reproduction head above the magnetic recording medium;
a signal generator for generating square-wave signals at an arbitrary frequency f s ;
a recording circuit which processes the square-wave signals at frequency f s for recording on the magnetic recording medium using the magnetic recording/reproduction head;
a spectrum analyzer which performs frequency analysis of reproduced signals y k reproduced by the magnetic recording/reproduction head, and generates a power spectrum of the waveform of the reproduced signals y k ;
storage means for storing a function E f relating to frequency, which is calculated in advance; and
calculating means for calculating, for the power spectrum generated by the spectrum analyzer, a signal-to-noise ratio by taking as the denominator a value obtained by adding values obtained by multiplying each frequency component of the power spectrum by the square of the function E f , excluding the vicinities of the frequency f s and harmonics thereof, and as the numerator a value of the power spectrum at the frequency f s multiplied by the square of the value of the function E f at the frequency f s .
2. The apparatus according to claim 1 , wherein the function E f is obtained, when the relationship between the recording signals x n and signals to be restored z n is expressed by z n =Σc nk x k and the relationship between the reproduced signals y k and the recording signals x n is expressed by y n =Σa nk x k , by calculating a matrix B which has b nk as components and which is an inverse matrix B=A −1 of a square matrix A the components of which are the coefficients a nk , multiplying from the right a matrix C the components of which are the coefficients c nk by a matrix B=A −1 to determine a matrix D=CA −1 , and by performing a discrete Fourier transform on the series e m =d m+k,k satisfying z′ n =Σe n−k y k for signals to be restored z′ n expressed by z′ n =Σd nk y k from the components d nk of the matrix D and the reproduced signals y k .
3. The apparatus according to claim 2 , wherein the signal intensities are measured when signals are recorded at at least two linear recording densities and reproduced, and the coefficients a nk are estimated based on the differences in the reproduced signal intensities at the linear recording densities.
4. The apparatus according to claim 1 , wherein the recording circuit comprises a digital to analog converter.
5. The apparatus according to claim 1 , wherein the storage means and the calculating means are implemented in software running on a microcomputer.
6. A method for evaluation of a magnetic recording medium, the method comprising the steps of:
rotating a magnetic recording medium;
positioning a magnetic recording/reproduction head above the magnetic recording medium;
generating square-wave signals at an arbitrary frequency f s ;
processing the square-wave signals at frequency f s for recording on the magnetic recording medium using the magnetic recording/reproduction head;
performing frequency analysis of reproduced signals y k reproduced from the magnetic recording medium by the magnetic recording/reproduction head, and generating the power spectrum of the waveform of the reproduced signals y k ;
storing a function E f relating to frequency, which is calculated in advance; and
calculating, for the power spectrum, a signal-to-noise ratio by taking as the denominator a value obtained by adding values obtained by multiplying each frequency component of the power spectrum by the square of the function E f , excluding the vicinities of the frequency f s and harmonics thereof, and as the numerator a value of the power spectrum at the frequency f s multiplied by the square of the value of the function E f at the frequency f s .
7. The method according to claim 6 , wherein the function E f is obtained, when the relationship between the recording signals x n and signals to be restored z n is expressed by z n =Σc nk x k , and the relationship between the reproduced signals y k and the recording signals x n is expressed by y n =Σa nk x k , by calculating a matrix B which has b nk as components and which is an inverse matrix B=A −1 of a square matrix A the components of which are the coefficients a nk , multiplying from the right a matrix C the components of which are coefficients c nk by a matrix B=A −1 to determine a matrix D=CA −1 , and by performing a discrete Fourier transform on the series e m =d m+k,k satisfying z′ n =Σe n−k y k for signals to be restored z′ n expressed by z′ n =Σd nk y k from the components d nk of the matrix D and the reproduced signals y k .
8. The method according to claim 7 , wherein the signal intensities are measured when signals are recorded at least two linear recording densities and reproduced, and the coefficients a nk are estimated based on the differences in the reproduced signal intensities at the linear recording densities.
9. The method according to claim 6 , wherein the step of processing the square-wave signals at frequency f s for recording comprises a digital to analog conversation.