FIGURE OF MERIT
An important consideration for an equalizer design involves the change in the signal to noise ratio (SNR) introduced by the equalizer. Here the SNR is defined as the peak signal to the rms noise voltage. The figure of merit (FM) of the filter is the ratio of the input to the output SNR expressed in dB. The computation was done numerically with the input signal being Lorentz, the output signal being Van der Maas and the noise power spectral density was taken directly from a disc. The FM as a function of the ratio TM/PW50 is shown in Fig. 3 where TM is one-half the distance between the zero slope points on the Van der Maas (VDM) time function.
Fig. 3. Figure of merit
FILTER DESIGN EXAMPLE
An equalizer to remove intersymbol interference in the time derivative of the slimmed output is now designed to illustrate the ideas discussed thus far. The input signal has a PW50 of about 110 ns and the output VDM frequency function has a cutoff frequency of 12.36 MHz. Initially, the pole locations of the filter were adjusted to equalize the group delay to 10 MHz. This resulted in a time function error (deviation from a constant) of 1.5 ns. Then the zeros were adjusted to minimize the magnitude error. A SPICE analysis of the equalizer showing the input and the output are shown in Fig. 4.
Fig. 4. Spice simulation of example design
During the process of developing this design approach, it became clear that a more appropriate approach would be to specify the objective function in the time domain. This would completely circumvent the need for having precise information about the group delay, for example. Only a modest change is required to change the procedure described here into a time domain design.
Special thanks go to Mr. Don Huber and Dr. Maung Gyi for their significant contributions, and to Mr. Frank Sordello for his support.
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Manuscript received March 23, 1981. Paper 37-8 presented at the 1981 INTERMAG Conference, Grenoble, France, May 12-15. The authors are with the Recording Technology Center, Memorex Corporation, Santa Clara, California 95052.
This Pulse Slimming is another increased productivity example do to using Calculus (level) programming.
visit http://fortranCalculus.info for Match-n-Freq app.
to reproduce the results discussed in this article.