Dynamic magnetic information storage or retrieval – General processing of a digital signal – Head amplifier circuit
Reexamination Certificate
1999-02-19
2001-08-28
Faber, Alan T. (Department: 2651)
Dynamic magnetic information storage or retrieval
General processing of a digital signal
Head amplifier circuit
C360S067000, C330S256000
Reexamination Certificate
active
06282038
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to signals read from a data storage medium and, more particularly, to a system and method for estimating an amplitude of a signal read from a data storage medium provided in a disk drive system.
BACKGROUND OF THE INVENTION
Within the disk drive system manufacturing industry, much attention is presently being focused on the performance and reliability of transducers utilized as part of the read/write head. Changes in the operating characteristics of a read transducer, for example, may be indicative of read/write head performance degradation or impending failure of the head. Changes in the amplitude of a readback signal obtained from a particular read/write head, for example, may indicate a possible problem with the read element of that read/write head.
It has been found, for example, that monitoring the amplitude characteristics of a readback signal obtained using a particular read/write head over time may provide insight as to the integrity and operating condition of the read transducer provided on the read/write head. A giant MR (GMR) transducer that is operating in an anomalous manner, by way of example, may produce readback signals of decreasing amplitude over time. The nature and complexity of most read channel designs, however, generally preclude in-situ determination of readback signal characteristics, such as determining, with a high degree of accuracy, readback signal amplitude for a particular read/write head over time.
In a typical read channel design, a variable gain amplifier (VGA) is often employed as the gain element of an automatic gain control (AGC) loop which is used to regulate the amplitude of readback signals provided at the output of the VGA. The AGC loop modifies the gain of the VGA by applying appropriate control signals to the VGA. Although attempts have been made to use VGA control signals for purposes of estimating the amplitude of readback signals input to the VGA, such attempted implementations wholly ignore temperature related factors that adversely affect the accuracy of readback signal amplitude estimates.
There exists a keenly felt need in the disk drive system manufacturing community for an apparatus and method for determining the amplitude of a readback signal obtained from a data storage medium with a high degree of accuracy. There exists a particular need for such an apparatus and method that may be implemented in-situ a read channel. The present invention fulfills these and other needs.
SUMMARY OF THE INVENTION
The present invention is directed to an apparatus and method for estimating an amplitude of a readback signal obtained from a data storage medium and input to a gain modifying amplifier. A method according to the present invention involves sensing an output signal at an output of the amplifier in response to a readback signal applied to an input of the amplifier. A difference signal is produced which is representative of a difference between the amplifier output signal and a reference signal. A compensation signal associated with a temperature coefficient of amplifier gain is generated, and an estimate signal indicative of the amplitude of the readback signal is produced using the compensation signal. The estimate signal is representative of readback signal amplitude when the estimate signal has a magnitude equivalent to that of the difference signal and a polarity opposite that of the difference signal.
Producing the estimate signal may involve adding the estimate signal to the difference signal or subtracting the estimate signal from the difference signal. The reference signal may be representative of a preestablished readback signal amplitude to be maintained at the output of the gain modifying amplifier. The compensation signal has a magnitude which is related to temperature, and is preferably proportional to absolute temperature. Generating the compensation signal may further involve generating a first compensation signal having a magnitude proportional to absolute temperature and generating a second compensation signal having a magnitude independent of temperature. The first and second compensation signals may be selectively used to cancel temperature related gain and polarity variations in the difference signal.
The estimate signal may be a binary estimate signal, and the compensation signal may be a current signal. The difference signal may be applied to a control input of the amplifier so as to equilibrate the amplifier output signal with the reference signal so as to maintain the signal output from the gain modifying amplifier at a predetermined amplitude.
A circuit for estimating an amplitude of a readback signal obtained from a data storage medium includes a gain modifying amplifier having a signal input that receives the readback signal, a signal output, and control inputs that receive an amplifier control signal. The control inputs of the amplifier are coupled to a capacitor, and the amplifier control signal is stored in the capacitor.
The circuit further includes a comparator having inputs coupled to the control inputs of the amplifier via respective resistive elements. A digital-to-analog circuit (DAC) has outputs coupled to the comparator inputs. A temperature compensation circuit is coupled to the comparator inputs and generates a compensation signal associated with a temperature coefficient of amplifier gain. The temperature compensation signal causes a change in voltage across the resistive elements. A logic circuit includes an input coupled to the output of the comparator and an output coupled to an input of the DAC. The logic circuit produces at its output an estimate signal indicative of the amplitude of the readback signal in response to equivalency of voltages at the respective inputs of the comparator. The estimate signal may be a binary signal.
The amplifier, temperature compensation circuit, and comparator preferably have an equivalent temperature profile, and are preferably provided on a common IC substrate. The temperature compensation circuit comprises a current generator and a magnitude control. The temperature compensation circuit may be integral to the amplifier. The gain modifying amplifier may comprise a variable gain amplifier (VGA).
The temperature compensation circuit may generate a first compensation signal having a magnitude proportional to absolute temperature and generate a second compensation signal having a magnitude independent of temperature. The first compensation signal may have a polarity opposite that of the second compensation signal. The first and second compensation signals may be selectively used to cancel temperature related gain and polarity variations in the amplifier control signal. A readback signal amplitude estimating circuit of the present invention may be implemented in a disk drive system or various other types of data storage systems.
The above summary of the present invention is not intended to describe each embodiment or every implementation of the present invention. Advantages and attainments, together with a more complete understanding of the invention, will become apparent and appreciated by referring to the following detailed description and claims taken in conjunction with the accompanying drawings.
REFERENCES:
patent: 4750058 (1988-06-01), Hirt et al.
patent: 5162678 (1992-11-01), Yamasaki
patent: 5321559 (1994-06-01), Nguyen et al.
patent: 5375145 (1994-12-01), Abbott et al.
patent: 5442492 (1995-08-01), Cunningham et al.
patent: 5463603 (1995-10-01), Petersen
patent: 5491447 (1996-02-01), Goetschel et al.
patent: 5519548 (1996-05-01), Liepe et al.
patent: 5572163 (1996-11-01), Kimura et al.
patent: 5631891 (1997-05-01), Moritsugu et al.
patent: 5732055 (1998-03-01), Masaki et al.
patent: 5831781 (1998-11-01), Okamura
patent: 6078455 (2000-06-01), Enarson et al.
patent: 6124998 (2000-09-01), Kanegae
patent: 0521653A2 (1993-01-01), None
patent: 0 521 653 A2 (1993-07-01), None
“Automatic Gain Control with Equalizer”, IBM Technical Disclosure Bulletin, vol. 21, No.9, pp. 3569-3570, Feb. 1979.
Bonaccio Anthony Richard
Philpott Rick Allen
Windler Peter John
Winn Gregory Scott
Faber Alan T.
Hollingsworth Mark A.
International Business Machines - Corporation
LandOfFree
Variable gain amplifier with temperature compensation for... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Variable gain amplifier with temperature compensation for..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Variable gain amplifier with temperature compensation for... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2495319