Dynamic magnetic information storage or retrieval – General recording or reproducing – Specifics of equalizing
Reexamination Certificate
1994-10-13
2001-06-26
Kim, W. Chris (Department: 2753)
Dynamic magnetic information storage or retrieval
General recording or reproducing
Specifics of equalizing
Reexamination Certificate
active
06252734
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to an arrangement for reproducing an electric signal from a track on a magnetic record carrier, the arrangement including
a magnetic read head for reading from the track an electric signal and for supplying the electric signal to an output,
variable equalizer filter means, having an input coupled to an output of the magnetic read head, a control signal input and an output, the equalizer filter means being adapted to equalize the electric signal read from the track in response to a control signal supplied to its control signal input, and to supply an equalized output signal at its output, and
control signal generator means having an output coupled to the control signal input of the equalizer filter means, the generator means being adapted to generate a control signal and to supply the control signal to its output.
2. Description of the Related Art
Such an arrangement is known from published European Patent Application EP 387,813 A2, corresponding to U.S. Pat. Nos. 5,237,588 and 5,274,512.
In the known arrangement, equalization is realized by varying the filter parameters in response to the control signal supplied to the control signal input, such that the magnitude of the filter response is increased or decreased.
The generation of the control signal in the control signal generator means can be realized in various ways. In the known arrangement, the signal from the equalizer filter means is applied in digital form to a data processing circuit which includes a detection circuit. The detection circuit is adapted to detect the bit error rate in the signal applied to the data processing circuit. A control signal is generated in response to the error rate, which control signal is applied to the control signal input of the equalizer filter means, so as to vary the filter parameters such that the bit error rate is minimized.
The known arrangement has the disadvantage that rather complex circuitry is needed to realize the equalizer filter means and the control signal generator means. The reason is that the known arrangement makes use of equalizer filter means in digital form, so that generating the parameters for the filter in response to the error rate detected requires a complex algorithm.
SUMMARY OF THE INVENTION
The invention has for its object to provide an arrangement for reproducing a digital signal from a track on a magnetic record carrier with simpler circuitry for the realization of the equalizing function. To that purpose, the arrangement according to the invention is characterized in that the equalizer filter means comprise transconductance-capacitor filter means having a tuning signal input for receiving a tuning signal, the transconductance-capacitor filter means having a magnitude characteristic which increases as a function of increasing frequencies in a frequency range below a reference frequency, the control signal input of the the equalizer filter means being coupled to the tuning signal input of the transconductance-capacitor filter means, the transconductance-capacitor filter means further being adapted to control the reference frequency in the filter characteristic in response to the control signal, so as to vary the angle of inclination of the filter curve below the reference frequency.
The invention is based on the following recognition. Investigations have shown that the recording channel exhibits an increased loss towards higher frequencies, which loss occurs, among others, as a result of the properties of the tape that is used, and the quality of the tape-head contact. This loss must be compensated for by the equalizer filter means in order to enable optimal signal reception during reproduction. Transconductance-capacitor filter have appeared to be very useful for that purpose.
Transconductance-capacitor filters are filters of the continuous-time type, and are well known in the art. Reference is made in this respect to a number of publications in the IEEE Journal of solid-state circuits, Vol. 23, no. 3, June 1988, pp. 750-758, no. 4, August 1988, pp. 987-996, Vol. 24, no. 3, pp. 736-743, and the article “Design of continuous-time fully integrated filters: a review”, by R. Schaumann, IEE Proceedings, Vol. 136, Pt.G, no. 4, August 1989, pp. 184-190. Transconductance-capacitor filters (called transc-filters) can be used to implement on-chip analog filters. The time constant of filter sections realized with the transc technique depend strongly on the IC-process-parameters. A variation up to 30% in the time constant is normal. Therefore, these filters must be tuned to the right frequency, which is also called ‘tracking’. This is realized by giving each filter section a tuning control input to which a tuning control signal can be applied. By means of this tuning control signal, the time constant of the filter can be controlled to a required value which is fixed.
In most applications this is a disadvantage, because the filter requires special tracking circuitry.
In the application of the transc-filter in the equalizer filter means, a deliberate use has been made of the variability of the time constant in the transc-filter. In order to compensate for the high frequency loss, the filter should have a filter characteristic which is the inverse of said loss. The filter characteristic therefore exhibits a magnitude characteristic as a function of frequency which increases towards higher frequencies. Preferably, the magnitude characteristic exhibits an exponential behavior. This means that the magnitude of the filter characteristic, expressed in dB, as a function of frequency, plotted on a linear scale, is a more or less straight line with a positive angle for frequencies below the reference frequency. By applying the control signal to the tuning control signal input of the transc-filter, it is possible to vary the time constant and thus the reference frequency of the filter. This results in a sliding of the frequency scale on which the filter characteristic is plotted. As a consequence, this results in a variation of the angle of the more or less straight line, so that an automatic equalization can be realized.
The aforementioned tracking, for stabilizing the filter characteristic to a fixed form, can be realized in various ways. One way is to apply a certain reference voltage to the tuning signal input.
It should be noted that the use of a transc-filter in magnetic disk-drive reproduction channels has been described in the Digest of technical papers for the 1991 IEEE Int. Solid-state circuits conference, paper TP 8.2, pp. 134, 135 and 303. The filter realized is however a fixed low-pass filter for bandlimiting the noise at the output of the magnetic read head amplifier.
REFERENCES:
patent: 4479152 (1984-10-01), Chi
patent: 4564869 (1986-01-01), Baumeister
patent: 4722010 (1988-01-01), Suzuki et al.
patent: 4736257 (1988-04-01), Watanabe et al.
patent: 4945311 (1990-07-01), Smith
patent: 5237588 (1993-08-01), Tanaka et al.
patent: 5274512 (1993-12-01), Tanaka et al.
patent: 0387813 (1990-09-01), None
IEEE Journal of Solid-State Circuits, vol. 23, No. 3, Jun. 1988, pp. 750-758. A 4-MHz CMOS Continuous-Time Filter with On-Chip Automatic Tuning. Krummenacher et al.
IEEE Journal of Solid-State Circuits, vol. 23, No. 4, Aug. 1988, pp. 987-996. Design of a 4-MHz Analog Integrated CMOS Transconductance-C Bandpass Filter. Park et al.
IEEE Journal of Solid-State Circuits, vol. 24, No. 3, Jun. 1989, pp. 736-743. A Micropower CMOS Continuous—Time Low Pass Filter. Kaiser.
IEEE Journal of Solid-State Circuits, vol. 136, Pt. G, No. 4, Aug. 1989, pp. 184-190. Design of Continuous—Time Fully Integrated Filters: A Review. Schuumann.
IEEE Int. Solid-State Circuits Conference, Paper TP 8.2, pp. 134, 135 and 303. 1991. A 15 MHz CMOS Continuous—Time Bessel Filter for Disk Drives. Khoury.
Kahlman Josephus A. H. M.
Rijckaert Albert M. A.
Goodman Edward W.
Kim W. Chris
U.S. Philips Corporation
LandOfFree
Arrangement for reproducing a digital signal from a track on... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Arrangement for reproducing a digital signal from a track on..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Arrangement for reproducing a digital signal from a track on... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2486933