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Non-Biased Pulse Write With Buried Servo

IP.com Disclosure Number: IPCOM000050549D
Original Publication Date: 1982-Nov-01
Included in the Prior Art Database: 2005-Feb-10
Document File: 4 page(s) / 54K

Publishing Venue

IBM

Related People

Haynes, MK: AUTHOR

Abstract

A method of writing is described that is compatible with buried servo, which overwrites effectively and which does not require AC bias recording of data.

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Non-Biased Pulse Write With Buried Servo

A method of writing is described that is compatible with buried servo, which overwrites effectively and which does not require AC bias recording of data.

Buried servo systems have been previously described with a biased pulse write method which is compatible. The need for AC bias, however, is an impediment to the use of buried servo at high data rates since the bias, at from 4 to 8 times the data clock frequency, may be at a higher frequency than can be used conveniently with present circuits, heads and semiconductor devices. An alternative write method which does not require AC bias is therefore desirable.

The AC bias has several important functions in the biased pulse write method, but the most important is to assure overwrite-erasure of old data with new. When a string of NRZ (non return to zero recording) zeros occurs, the high- pass filtered write current will have no energy which could overwrite or erase old data hence, the need for AC bias. An essential ingredient of the technique described herein is use of an encoding scheme such that pulses are recorded during every bit period, with polarity or phase relationships which convey the information content, so that overwrite erasure is ensured regardless of the data content.

Another function of AC bias in the biased pulse write is to reduce the amplitude of data signal components at or near the servo frequencies by supplying most of the writing energy needed to record on the medium. An important ingredient of this invention is that the encoding scheme, like the FM (frequency modulation) method which it resembles in some ways, has no DC component and rolls off at the low end so that the energy content of random data at or near the servo frequencies is greatly reduced below that of an NRZI (non return to zero change on ones recording) coded waveform.

Another function of AC bias in bias pulse write is believed to be to supply high frequency energy to the head during writing so that the servo signals can be read without loss. With bias pulse write, the servo output signals increase by about 20 percent due to the presence of the AC bias. With many pulse recording schemes which have been tested, the servo output decreases by as much as 50 percent during writing due to the presence of writing pulses' An important ingredient of this technique is that the encoded and filtered write pulses supplied to the head operate, like an AC bias, so as to increase the servo output by about the same 20%. While an increase is not necessary, it is desirable to avoid a decrease during writing.

Although the encoding method reduces data components near the servos in random data, specific data patterns may contain a great deal of energy in that region of the spectrum. It is therefore necessary, as in biased pulse write, to use a high-pass filter to physically reduce the energy level at the low end so as to avoid interference with the servos. Again, as in biased pul...