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Feed-Forward Adaptive Equalization

IP.com Disclosure Number: IPCOM000060489D
Original Publication Date: 1986-Apr-01
Included in the Prior Art Database: 2005-Mar-08
Document File: 2 page(s) / 31K

Publishing Venue

IBM

Related People

Schneider, RC: AUTHOR [+2]

Abstract

A method of adaptive equalization is described that compensates for variations in the high frequency components of a tape or disk read signal. Unlike many known methods of adaptive equalization, the adjustment is made without the need for detected data or a known training sequence. As shown in Fig. 1, the read signal passes through an amplifier, fixed equalizer and automatic gain control (AGC) circuit. This is conventional and well known. The signals at point A (the output of AGCl) are of the same uniform amplitude. However, their shape may be different, indicating too much or too little compensation. Fig. 2 shows two read signals, with the one at the right having too little compensation.

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Feed-Forward Adaptive Equalization

A method of adaptive equalization is described that compensates for variations in the high frequency components of a tape or disk read signal. Unlike many known methods of adaptive equalization, the adjustment is made without the need for detected data or a known training sequence. As shown in Fig. 1, the read signal passes through an amplifier, fixed equalizer and automatic gain control (AGC) circuit. This is conventional and well known. The signals at point A (the output of AGCl) are of the same uniform amplitude. However, their shape may be different, indicating too much or too little compensation. Fig. 2 shows two read signals, with the one at the right having too little compensation. Both signals have the same amplitude, but the second derivative of the undercompensated pulse has lower amplitude than the pulse that is properly compensated. The variable equalizer is of the form: 1-KFS2 The use of a second automatic gain control stage (AGC2) in the second derivative (S2) path will compensate for the variation in the second derivative amplitude as the high frequency components vary. Thus, a much more uniform equalized signal will result. Adjustment could be made during a low frequency start burst or during random data.

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