Miscellaneous active electrical nonlinear devices – circuits – and – Specific signal discriminating without subsequent control – By amplitude
Reexamination Certificate
1999-04-27
2001-07-24
Lam, Tuan T. (Department: 2816)
Miscellaneous active electrical nonlinear devices, circuits, and
Specific signal discriminating without subsequent control
By amplitude
C327S178000, C327S179000
Reexamination Certificate
active
06265905
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
The present application is related to U.S. patent application Ser. No. 09/300,564, entitled “A Quasi-Current Sensing Input Impedance Controlled Preamplifier for Magnetoresistive Elements,” filed on the same day and assigned to same Assignee as the present application.
FIELD OF THE INVENTION
The present invention relates to signal processing in a data storage device and more particularly to a method and system for providing a quasi-voltage sensing preamplifier having controlled input impedance.
BACKGROUND OF THE INVENTION
Magnetic recording media, such as disks are widely used for storing data. In order to write to or read form such recording media, storage devices such as disk drives are typically used. Storage devices typically include heads for reading from and/or writing to the recording media. A head is typically attached to a slider, which holds the head above the recording media. The slider is attached to a suspension, which supports the slider above the recording media. The slider is coupled to an actuator arm which moves the head, slider, and suspension across the recording media.
Currently magnetoresistive (MR) heads are increasingly popular for use in read heads. A MR head includes a MR sensor, which has a resistance that varies with an applied magnetic field. The MR sensor may be an anisotropic magnetoresistance (AMR) sensor or a giant magnetoresistance (GMR) sensor. In order to use the MR sensor, The MR sensor is coupled with electronics, which drive the MR sensor and read the signal from the MR sensor. The electronics are coupled with the MR sensor using a wire interconnect.
The signal from the MR sensor can be read by sensing the voltage across the MR sensor. In order to do so, a conventional voltage-sensing preamplifier (conventional VS preamplifier) is used. Typically, an input of the conventional VS preamplifier is coupled with the interconnect. Voltage from the interconnect is provided to input devices in the conventional VS and amplified by a gain stage in the conventional VS. The input devices typically include transistors. The amplified signal is then provided either as a single ended or differential signal to the remainder of the electronics.
Although the combination of the MR sensor, the interconnect, and the conventional VS preamplifier is capable of reading data on recording media, one of ordinary skill in the art will readily recognize that the ability of the storage device to read at higher data rates is limited. Previously, limitations in the bandwidth of the storage device were due to other portions of the electronics. However, improvements in other portions of the electronics have increased the bandwidths of these components of the storage device. As a result, the bandwidth for the storage device has increased. As the data rate increased, the interface between the MR sensor, the interconnect, and the conventional VS preamplifier has become of increasing importance in constraining the bandwidth of the storage device. In particular, the useful bandwidth of the conventional VS preamplifier as used in the storage device is limited. Thus, the ability of the storage device to read at higher data rates is also limited.
Conventional methods for addressing the limited bandwidth of the conventional VS preamplifier also have drawbacks. One reason for the limited bandwidth of the conventional VS preamplifier is the impedance mismatch between the MR sensor, a characteristic impedance of the interconnect, and the input impedance of the conventional VS preamplifier. The MR sensor has a resistance which can vary on the order of two or three to one. The interconnect typically has a relatively low characteristic impedance, generally on the order of fifty ohms. The characteristic impedance of the interconnect also changes. Different heads may be used in the storage device. These heads occupy different positions within the storage device. In order to reach these heads, the interconnects may have different lengths or shapes. Furthermore, the interconnect typically twists and bends during use, thereby changing the characteristic impedance of the interconnect. The conventional VS preamplifier has a very high input impedance, much more than the characteristic impedance of the interconnect. Thus, the input impedance of the conventional VS preamplifier does not match the characteristic impedance of the interconnect.
In the conventional VS preamplifiers the mismatch between the impedances of MR sensor, the characteristic impedance of the interconnect, and the input of the conventional VS preamplifier is partially addressed by providing a resistor coupled with input devices of the conventional VS preamplifier. The resistor is coupled in parallel with the bases of the transistors used as the input devices. This lowers the input impedance of the conventional VS preamplifier. However, one of ordinary skill in the art will readily recognize that the resistor causes increased signal attenuation, which is undesirable. Consequently, such a method may not be desirable in the conventional VS preamplifier.
Accordingly, what is needed is a system and method for improving the bandwidth of the conventional VS preamplifier and, therefore, the data rate for the storage device. The present invention addresses such a need.
SUMMARY OF THE INVENTION
The present invention provides a method and system for providing a voltage-sensing preamplifier for use with a magnetoresistive sensor. The method comprises providing a gain stage and providing a control circuit coupled with the gain stage. In a system aspect, the present invention includes a gain stage and a control circuit. The gain stage includes at least one input device that is coupled with the magnetoresistive sensor. The at least one input device has a first input impedance. The control circuit is coupled to the at least one input device of the gain stage. The control circuit provides at least one signal to the at least one input device. The at least one signal controls the first input impedance of the at least one input device to control a second input impedance of the voltage-sensing preamplifier.
According to the system and method disclosed herein, the present invention provides a voltage-sensing preamplifier having a controllable input impedance. The input impedance of the voltage-sensing preamplifier can, therefore, be substantially matched to a desired valued. For example, the input impedance of the voltage-sensing preamplifier can be substantially matched to a characteristic impedance of an interconnect. Similarly, the input impedance of the voltage-sensing preamplifier can be controlled to be close enough to the characteristic impedance of the interconnect that bandwidth requirements can be satisfied. Thus, the operational bandwidth of the voltage-sensing preamplifier can be increased, allowing for greater ability to read the magnetoresistive sensor at higher data rates.
REFERENCES:
patent: 4223274 (1980-09-01), Paulke et al.
patent: 4510460 (1985-04-01), Tamura
patent: 4816772 (1989-03-01), Klotz
patent: 5442321 (1995-08-01), Bayruns et al.
patent: 5559460 (1996-09-01), Cunningham
patent: 5757230 (1998-05-01), Mangelsdorf
patent: 5859739 (1999-01-01), Cunningham et al.
Chung Paul Wingshing
Jove Stephen Alan
Bluestone Randall J.
International Business Machines - Corporation
Lam Tuan T.
Nguyen Hiep
Sawyer Law Group LLP
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