Miscellaneous active electrical nonlinear devices – circuits – and – Specific identifiable device – circuit – or system – Unwanted signal suppression
Reexamination Certificate
2000-06-22
2001-07-03
Le, Dinh T. (Department: 2816)
Miscellaneous active electrical nonlinear devices, circuits, and
Specific identifiable device, circuit, or system
Unwanted signal suppression
C327S063000, C360S065000
Reexamination Certificate
active
06255898
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a noise eliminating circuit, and more particularly, to a noise eliminating circuit for eliminating noise (i.e., thermal asperity) in an amplification circuit that is produced when a magneto resistive (MR) head contacts a hard disk, which amplifies reproduction signals of the hard disk.
In a conventional hard disk device, heat is produced when an MR head contacts a hard disk while reading data. This increases the resistance of the MR head and results in a reproduction signal ST that includes low frequency noise, which is referred to as thermal asperity (TA), as shown in FIG.
1
.
FIG. 2
is a schematic block diagram showing a first prior art thermal asperity compensating circuit
81
, which eliminates thermal asperity. The compensating circuit
81
, which is connected between a first read amplifier
82
and a second read amplifier
83
, includes a capacitor C, a resistor R, and a switch SW. The compensating circuit
81
functions as a bypass filter. When thermal asperity is detected, the switch SW is activated and the compensating circuit
81
eliminates the thermal asperity.
FIG. 3
is a schematic block diagram showing a second prior art thermal asperity compensating circuit
84
. The compensating circuit
84
is connected between a first read amplifier
82
and a second read amplifier
83
and includes a delay circuit
85
, an envelope waveform generating circuit
86
, a low-pass filter
87
, and an operational amplifier circuit
88
.
An amplified reproduction signal generated by the first read amplifier
82
is delayed by the delay circuit
85
and then provided to the operational amplifier circuit
88
. The amplified reproduction signal is also provided to the operational amplifier circuit
88
via the envelope waveform generating circuit
86
and the low-pass filter
87
.
When thermal asperity is included in the amplified reproduction signal output by the first read amplifier
82
, the thermal asperity component is provided to the operational amplifier circuit
88
via the envelope waveform generating circuit
86
and the low-pass filter
87
. The operational amplifier circuit
88
detects this noise and then removes the thermal asperity component from the amplified reproduction signal provided by the delay circuit
85
and generates an amplified reproduction signal from which the thermal asperity is eliminated.
The first read amplifiers
82
located upstream of the thermal asperity compensating circuits
81
,
84
also amplify the thermal asperity component. Accordingly, the first read amplifier
82
may be saturated by the thermal asperity component. A circuit for preventing saturation may be provided in the first read amplifier
82
. This would, however, complicate the circuit configuration of the first read amplifier
82
. Further, after eliminating thermal asperity, a relatively long time would be necessary to terminate the saturated state. In other words, a certain length of time would be necessary for the first read amplifier
82
to start functioning normally again.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a noise eliminating circuit that eliminates noise components without saturating the amplification circuit when noise is produced.
To achieve the above object, the present invention provides a noise eliminating circuit for eliminating noise from an input signal. The noise eliminating circuit includes a differential amplifier for receiving the input signal and a feedback signal and generating a differential amplified signal. A detection circuit is connected to the differential amplifier for detecting noise included in the differential amplified signal and generating a control signal. The control signal is activated when the noise is detected. A feedback circuit is connected to the differential amplifier and the detection circuit for cutting off the differential amplified signal in accordance with a first cutoff frequency when the control signal is deactivated, and cutting off the differential amplified signal in accordance with a second cutoff frequency, which includes the frequency of the noise, when the control signal is activated.
Another aspect of the present invention provides an amplification circuit for amplifying a reproduction signal read from a magnetic recording medium using a magneto resistive head. The amplification circuit includes a differential amplifier for receiving the reproduction signal and a feedback signal and generating a differential amplified signal. A detection circuit is connected to the differential amplifier for detecting thermal asperity noise included in the differential amplified signal and generating a control signal. The control signal is activated when the noise is detected. A feedback circuit is connected to the differential amplifier and the detection circuit for cutting off the differential amplified signal in accordance with a first cutoff frequency when the control signal is deactivated, and cutting off the differential amplified signal in accordance with a second cutoff frequency, which includes the frequency of the thermal asperity noise, when the control signal is activated.
A further aspect of the present invention provides a magnetic recording device including a magneto resistive head for generating a reproduction signal in accordance with polarity changes of a magnetic recording medium, and an amplification circuit connected to the magneto resistive head for amplifying the reproduction signal. The amplification circuit includes a differential amplifier for receiving the reproduction signal and a feedback signal and generating a differential amplified signal. A detection circuit is connected to the differential amplifier for detecting thermal asperity noise included in the differential amplified signal and generating a control signal. The control signal is activated when the noise is detected. A feedback circuit is connected to the differential amplifier and the detection circuit for cutting off the differential amplified signal in accordance with a first cutoff frequency when the control signal is deactivated, and cutting off the differential amplified signal in accordance with a second cutoff frequency, which includes the frequency of the thermal asperity noise, when the control signal is activated.
Other aspects and advantages of the present invention will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.
REFERENCES:
patent: 5418660 (1995-05-01), Sato et al.
patent: 5801896 (1998-09-01), Freitas
patent: 6151400 (2000-11-01), Seligman
Kawai Takumi
Ono Akihiko
Arent Fox Kintner & Plotkin & Kahn, PLLC
Fujitsu Limited
Le Dinh T.
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