Electrical computers: arithmetic processing and calculating – Electrical analog calculating computer – Particular function performed
Reexamination Certificate
1998-06-19
2001-11-06
Mai, Tan V. (Department: 2121)
Electrical computers: arithmetic processing and calculating
Electrical analog calculating computer
Particular function performed
Reexamination Certificate
active
06314444
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to improvement in electronic filters, and more particularly, but not by way of limitation, to improvement in electronic filters that are suitable in sampled communication channels such as in digital magnetic recording disk drive read channels.
BACKGROUND OF THE INVENTION
One type of signal processing typically associated with high-density magnetic recording channels is the time-domain equalization. Such equalization is used to reshape a readback signal received by the channel to an approximation of a desired target waveform in the time domain, such as used in a Partial Response, Maximum Likelihood (PRML) detection read channel (see the paper “A PRML System for Digital Magnetic Recording” by R. D. Cidecian et al., IEEE Journal on Selected Areas in Communication, vol.10, no.1 January 1992). As will be recognized, reshaping the readback signal allows intersymbol interference (ISI) to be reduced and controlled, facilitating reliable sequential decoding of the digital information stored on disk.
Basic instrument for time-domain equalization in magnetic recording channels is the transversal equalizer, be it in a digital implementation (see U.S. Pat. No. 5,422,760, issued Jun. 6, 1995, entitled “Disk Drive Method Using Zoned Data Recording and PRML Sampling Data Detection with Digital Adaptive Equalization” filed Aug. 17, 1994 by Abbott et al.) or in analog implementation. The analog transversal equalizer, in turn, can be implemented either in discrete-time version, on samplers or in a continuous-time version. A continuous-time implementation is described in U.S. Pat. No. 5,592,340, issued Jan. 7, 1997, entitled “Communication Channel with Adaptive Analog Transversal Equalizer” filed Sep. 21, 1994 by Minuhin et al.
Transversal equalizers may be Finite Impulse Response (FIR) filtering devices or Infinite Impulse Response (IIR) filtering devices like the ones described in the above-identified Minuhin et al. '340 patent. A recent paper by V. Minuhin et al. “Adaptive, Analog, Continuous-Time Time-Domain Equalization for Sampled Channels in Digital Magnetic Recording” IEEE Transactions on Magnetics, September 1997, shows that IIR filters outperforms FIR filters not only as a practical device, but also theoretically.
The Minuhin et al. paper refers to the particular equalizer described as a Generalized Transversal Equalizer (GTE), to distinguish it from well known analog transversal equalizers. A need exists for an improved filtering system for a communication channel, and particularly for magnetic recording channel by making it simpler and more economical in manufacturing; reduce its size and power dissipation.
The present invention provides a solution to this and other problems, and offers other advantages over the prior art.
SUMMARY OF THE INVENTION
The present invention relates to GTE equalizers which solve the above-mentioned problem by further reduction of complexity, size and cost of the most component-intense blocks of GTE equalizers. In particular, the analog filter-delay elements have been reduced to a second order of filter-delay design. Despite the low order of the filter-delay elements, sufficient values of delays required for proper operations of the GTE equalizer are provided. The filter-delay elements are realized in integral implementation as just one biquad (i.e., an active filter section with second order denominator and numerator) with only two transconductor elements and two small integrated capacitors per section. In contrast, prior art filters required higher order filter-delay elements having at least two biquads per section. For example, the above-identified Minuhin et al. '340 patent describes sixth order filter delay elements.
In accordance with one embodiment of the invention, a second order filter-delay element for use in a generalized analog transversal equalizer is described which provides phase and group delay responses equivalent to low-pass filters of third and fourth order. In addition, the filter-delay element provides sufficient values of delays required for proper operations of the analog generalized transversal equalizer despite having a low order.
In accordance with another embodiment of the invention, a method of generating the lower order filter-delay element is described. The method includes decomposing denominators of an original low-pass transfer function into two polynomial multiplicands. Subsequently, one polynomial multiplicand is moved from a denominator into a numerator. A sign of members with odd degree of complex frequencies is changed in the numerator. Then, coefficients of polynomial in the numerator are adjusted to achieve zeros of transformed transfer function that are mirror-reflected images relative to complex frequency axis of poles created by the moved polynomial multiplicand in the original low-pass transfer function. Finally, a lower order filter-delay element is generated based on the transformed transfer function.
Also, a circuit embodying an active C-transconductor realization of a second order filter-delay element for use in a generalized analog transversal equalizer with a transfer function designed as a result of performing the method is described. The circuit includes a biquad C-transconductor circuit with at least two excitation nodes and an input voltage buffer with two complimentary outputs. An adjustment mechanism is used to change a ratio of two signals provided by the two complimentary outputs at input excitation nodes of the C-transconductor circuit to obtain required coefficients of a numerator of a transfer function to realize desired zeros of the transformed transfer function.
These and various other features as well as advantages which characterize the present invention will be apparent upon reading of the following detailed description and review of the associated drawings.
REFERENCES:
patent: 5168461 (1992-12-01), Wu et al.
patent: 5325322 (1994-06-01), Bailey et al.
patent: 5422760 (1995-06-01), Abbott et al.
patent: 5592340 (1997-01-01), Minuhin et al.
patent: 5650954 (1997-07-01), Minuhin
D.S. Humpherys, “Equiripple Network Approximations Using Iteration Techniques,” Proceedings of National Electronics Conference, pp. 753-758, (Jun. 19, 1964).
R.D. Cideciyan, Francois Dolivo, Reto Hermann, Walter Hirt, And Wolfgang Schott, “A PRML System for Digital Magnetic Recording,” IEEE Journal on Selected Areas of Communications, vol. 10 (No. 1), pp. 38-56, (Jan. 19, 1992).
K. Parsi, N. Rao, R. Burns, A. Chaiken, M. Chambers, R. Cheug, B. Forni, D. Harnishfeger, C. Jam, S. Kaylor, M. Pennell, J. Perez, M. Rohrbaugh, M. Ross, G. Stuhlmiller, N. Weiner, “TP 4.3: A 200Mb/s PRML Read/Write Channel IC,” 1996 IEEE International Solid-State Circuits Conference, pp. 66-67, (Feb. 8, 1996).
V. Minuhin And V. Kovner, “Adaptive, Analog, Continuous-Time Time-Domain Equalization for Sampled Channels in Digital Magnetic Recording,” IEEE Transaction on Magnetics, vol. 33, (No. 5), pp. 2782-2784, (Sep. 19, 1997).
K. Parsi, R. Burns, A. Chaiken, M. Chambers, B. Forni, D. Harnishfeger, S. Kaylor, M. Pennell, J. Perez, N. Rao, M. Rohrbaugh, M. Ross, G. Stuhlmiller, “A PRML Read/Write Channel IC Using Analog Signal Processing for 200 Mb/s HDD,” 1996 IEEE Journal of Solid-State Circuits, vol. 31 (No. 11), pp. 1817-1830, (Nov. 1996).
R. Alini, G. Betti, R. Castello, F. Heydari, G. Maguie, L. Fredrickson, L. Volz, D. Stone, “SA 19.3: A 200MSample/s Trellis-Coded PRML Read/Write Channel with Digital Servo,” 1997 IEEE International Solid-State Circuits Conference, pp. 318-319 and 246-247, (Feb. 8, 1997).
Minuhin Vadim B.
Rub Bernardo
Cesari Kirk A.
Mai Tan V.
Seagate Technology LLC
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