Browse Prior Art Database

Adaptive DC Restoration

IP.com Disclosure Number: IPCOM000079162D
Original Publication Date: 1973-May-01
Included in the Prior Art Database: 2005-Feb-26
Document File: 3 page(s) / 42K

Publishing Venue

IBM

Related People

Ottesen, HH: AUTHOR [+2]

Abstract

In reading digital signals from a magnetic record medium, the so-called baseline of the readback signals may be shifted. Such shifting can be caused by data patterns, implementation of readback apparatus, and other causes of frequency distortion in AC-coupled readback apparatus.

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Adaptive DC Restoration

In reading digital signals from a magnetic record medium, the so-called baseline of the readback signals may be shifted. Such shifting can be caused by data patterns, implementation of readback apparatus, and other causes of frequency distortion in AC-coupled readback apparatus.

DC restoration circuits have been used to reestablish the baseline by so- called DC clamping action. Most DC restoration circuits respond to an input signal having a constant-amplitude level or envelope. In signals being recovered from magnetic media, as well as other signal sources, such input signals may have a varying amplitude. In magnetic recording, this is particularly true during signal dropouts. In digital communications, it can occur during fade-outs caused by atmospheric conditions, for example. Accordingly, it is desirable to have a DC restoration circuit for restoring the baseline of an input signal, which adapts to input signal amplitude variations.

This adaption is accomplished by adding full-wave rectifier 10 and low-pass filter 11, to make slicer 12 adaptive in a usual DC restoration circuit arrangement. Such a circuit includes high-pass filter 13 transferring the input signal through current summer 14 to an output terminal. Slicer 12 supplies the other input to summer 14.

Slicer 12 takes the DC restored output signal and effectively digitizes the amplitude on a dynamic basis; then passes the digitized signal through low-pass filter 15 to the current summer 14. The low-pass filter 15 accentuates the low-frequency aspect of the slicing operation such that baseline is appropriately restored. The RC time constants for the high-pass and low-pass filter are equal. A general discussion of DC restoration is found in a book by Lucky, Salz, and Weldon, PRINCIPLES OF DATA COMMUNICATION, Page 186 et seq,
McGraw-Hill, 1968.

Adaptive slicer 12 includes a pair of switching comparators 20 and 21 which differ...