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Passive RLC Implementation of an Equalizer for Digital Magnetic Recording

IP.com Disclosure Number: IPCOM000036695D
Original Publication Date: 1989-Oct-01
Included in the Prior Art Database: 2005-Jan-29
Document File: 5 page(s) / 116K

Publishing Venue

IBM

Related People

Dolivo, F: AUTHOR [+3]

Abstract

The proposed implementation of the digital magnetic recording equalizer makes use of a network built with passive components. These components are resistors (R), capacitors (C), and inductors (L); thus, the resulting networks are called RLC networks.

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Passive RLC Implementation of an Equalizer for Digital Magnetic Recording

The proposed implementation of the digital magnetic recording equalizer makes use of a network built with passive components. These components are resistors (R), capacitors (C), and inductors (L); thus, the resulting networks are called RLC networks.

There are various reasons for using RLC networks. A prime consideration is their effectiveness over a wide range of frequencies; the signal bandwidth of recording systems ranges typically from close to DC to tens of MHz. Other considerations include their low cost and moderate complexity. These assets are very important if one plans to use these filters in a competitive product.

The RLC networks realize a given voltage transfer function. This prescribed transfer function is determined by requiring that the required wave shape appears at the detector. We are assuming that the read signal is passing through a LOWPASS filter with a fixed cutoff frequency and that its characteristic is taken into account when determining the required equalizer transfer function.

The prescribed equalizer transfer function can be decomposed into individual second-order transfer functions. Each of these transfer functions can be implemented separately when they are decoupled by means of suitable buffer amplifiers. These second-order transfer functions are of the general biquadratic form shown in Fig. 1 below.

(Image Omitted)

In Fig. 1, K is some gain factor. The finite real constants K, a, c, d, and e satisfy K > 0,

a + 0 or 1,

c > 0,

_

d*d

e > --- > 0,

_

4 and b may be zero, positive or negative. The constants determine the network transfer function. Depending on the coefficients a, b, and c, T(s) in Fig. 1 may be classified as shown in Fig. 2.

(Image Omitted)

.

The proposed complete implementation of the digital magnetic recording equalizer makes use of three filter sections. Two of these sections, namely, the ALLPASS and NOTCH sections, are second-order networks which form the actual equalizer; the third section corresponds to the above-mentioned LOWPASS section of higher order. The three sections are described in Fig. 2.

1

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The LOWPASS section is an equally terminated seventh-order Butterworth lowpass filter which e...