Amplifiers – With semiconductor amplifying device – Including field effect transistor
Reexamination Certificate
2000-02-28
2001-04-17
Pascal, Robert (Department: 2817)
Amplifiers
With semiconductor amplifying device
Including field effect transistor
C330S253000, C360S067000, C029S603060
Reexamination Certificate
active
06218903
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a very-small-signal amplifier apparatus and a magnetic disk storage apparatus using the same. More specifically, the invention relates to a magnetic disk storage apparatus such as a hard disk drive and, particularly, to a technology that can be effectively utilized for amplifying very small signals by using a magnetoresistance effect element (MR) head as a read head and, particularly, to a technology that can be effectively utilized for amplifying very small signals by using a composite head including a magnetoresistance effect element as the read head and an inductive head as a write head.
A read amplifier for MR head constituted by CMOS (complementary MOS) has been disclosed in IEEE Journal of Solid State Circuits, Vol. 29, No. 12, December, 1994, pp. 1589-1595. According to the read amplifier disclosed in the above-mentioned literature, a bias current is supplied to an MR head through an amplifier MOSFET to generate a read current that varies depending upon a change in the magnetoresistance.
SUMMARY OF THE INVENTION
The above-mentioned read amplifier has an advantage that it can be operated on a single power source such as of 5 V (volt) while supplying a bias current to an MR head as described above to generate a read current that varies depending upon a change in the magnetoresistance thereof. When a read signal is obtained in the form of a current signal as described above, an inductance component of the wiring connecting the MR head to the read amplifier is contained in the current signal that is to be amplified. The results in a problem that the gain decreases at high frequencies. In a hard disk storage apparatus, there is a tendency to increase the recording density in order to increase the storage capacity. Accordingly, the frequency of the signal that is to be read spreads over a wide band up to high frequencies. Therefore, the above-mentioned current sensing system is no longer suited for increasing the density of recording.
As a sensing system adapted for increasing the storage density, there can be effectively employed a voltage sensing system which obtains a change in the magnetoresistance as a voltage signal. The MR head is operated in a state where an operation bias current is supplied, and a voltage signal obtained there is as small as, for example, about 20 mV inclusive of a DC component. Even though such a small voltage signal is supplied across the gate and the source of an amplifier MOSFET, the voltage across the gate and the source is not sufficient to operate the MOSFET and cannot be amplified. It can, therefore, be conceivable to use a level-shifting circuit such as a diode, and add a DC voltage produced by a level-shifting circuit to the above-mentioned voltage signal in order to apply it across the gate and the source of the amplifier MOSFET. In such a case, however, the circuit elements such as a diode for effecting the level-shifting operation and the resistive element themselves may be sources of noise. Such noise components mix into a small voltage signal generated depending upon a change in the magnetoresistance of the MR head, producing another problem in that a desired S/N ratio is not obtained.
In order to solve this problem, it can be considered to employ two power-source circuits of positive polarity and negative polarity to use a negative voltage for the bias circuit on the source side of the amplifier MOSFET and to use a positive potential for the load circuit provided on the drain side. By using the two power sources of positive and negative polarities, a bias voltage is maintained that is necessary to operate the amplifier MOSFET and a voltage signal generated by the MR head is supplied as it is to the gate, thereby making it possible to ensure the above-mentioned S/N ratio. This, however, requires complex power-source circuits for generating a positive voltage and a negative voltage, making it difficult to decrease the size of the device and to lower the cost of production.
When a positive power source is used, a neutral point voltage can be applied to an end of the MR head, thereby generating a very small signal from the other end thereof, and ensuring a bias voltage necessary to operate the amplifier MOSFET. In general, however, the ground potential is applied to the magnetic disk in order to discharge static electricity that is generated due to air friction or the like when it rotates at a high speed. When the above-mentioned neutral point voltage is applied to the MR head, a discharge phenomenon may take place since the MR head and the magnetic disk are at different potentials. In order to prevent this discharge phenomenon between the MR head and the magnetic disk, it is generally considered convenient to apply the ground potential to an end of the MR head, thereby matching the potential of the magnetic disk that is at the ground potential of the circuit.
An object of the present invention is to provide a very-small-signal amplifier capable of amplifying very small signals of up to high frequencies with high sensitivity, while simplifying the circuit structure. Another object of the present invention is to provide a magnetic disk storage apparatus which realizes read operation over a wide band of up to high frequencies with high sensitivity, while simplifying the circuit. These and other objects as well as novel features of the present invention will be more apparent from the description of the specification and the accompanying drawings.
An outline of a representative aspect of the invention disclosed in this application will be briefly described. A modified differential circuit includes a first transistor of a first conductivity type and a second transistor of a second conductivity type each having a control terminal, a terminal of the input side and a terminal of the output side, wherein the terminals of the input side are connected in common, and a current is allowed to flow depending upon a voltage difference applied across the control terminals, and wherein a very small voltage signal generated by an input signal source means is applied to the control terminal of the first transistor, a bias voltage is applied to the control terminal of the second transistor, and an amplified signal corresponding to the very small voltage signal generated by the input signal source means is generated from the terminal on the output side of the second transistor.
Another representative aspect of the invention disclosed in this application will be briefly described below. A magnetic disk storage apparatus includes a disk-like magnetic storage medium to which a first potential for discharging static electricity that is generated due to rotational operation is applied, and a read head of a magnetoresistance effect element, to whose one end the first potential is applied and which outputs a read signal from the other end thereof, wherein use is made of a modified differential circuit including a first transistor of a first conductivity type and a second transistor of a second conductivity type each having a control terminal, a terminal of the input side and a terminal of the output side, the terminals of the input side being connected in common, and wherein a very small voltage signal generated by the read head is applied to the control terminal of the first transistor, a bias voltage is applied to the control terminal of the second transistor, and a signal amplified from the very small voltage signal generated by the read head is generated from the terminal of the output side of the second transistor.
REFERENCES:
patent: 4881043 (1989-11-01), Jason
patent: 5323278 (1994-06-01), Contreras et al.
patent: 5430584 (1995-07-01), Petersen
patent: 5711063 (1998-01-01), Budde et al.
patent: 5712739 (1998-01-01), Nakamura et al.
H.W. Klein et al, “A 0.8nV/Hz CMOS Preamplifier for Magneto-Resistive Read Elements”, IEEE Journal of Solid-State Circuits, vol. 29, No. 2, Dec. 1994, pp. 1589-1595.
Hashimoto Takashi
Hatanaka Noriaki
Mochizuki Tatsuo
Nagaya Yuji
Sonoyama Katsuya
Hitachi , Ltd.
Mattingly Stanger & Malur, P.C.
Nguyen Patricia
Pascal Robert
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