Miscellaneous active electrical nonlinear devices – circuits – and – Gating – Utilizing three or more electrode solid-state device
Reexamination Certificate
2002-08-07
2004-01-27
Tran, Toan (Department: 2816)
Miscellaneous active electrical nonlinear devices, circuits, and
Gating
Utilizing three or more electrode solid-state device
C327S588000, C327S110000
Reexamination Certificate
active
06683487
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The present invention relates to a current driver circuit in which data for a magnetic signal from a write current pre-amplifier is written to a magnetic storing device such as a magnetic disk driven by a hard disk drive (HDD) or a floppy disk drive (FDD).
FIG. 9
is a circuit view showing a conventional current driver circuit. In
FIG. 9
, Tr
1
and Tr
2
indicate current drivers including P-channel metal oxide semiconductor (PMOS) transistors respectively. Tr
3
and Tr
4
indicate current receivers including N-channel metal oxide semiconductor (NMOS) transistors respectively. Tr
5
to Tr
8
indicate NMOS transistors, respectively. WH indicates a write head for producing a magnetic signal from a write current. CS indicates a current source for supplying a reference current Iref. A voltage of a high voltage source is applied to gates of the current receivers Tr
3
and Tr
4
and the transistor Tr
7
through the current source CS so as to turn on the current receivers Tr
3
and Tr
4
and the transistor Tr
7
.
FIG. 10
is a timing chart showing an operation of the circuit.
Next, an operation of the conventional current driver circuit will be described below.
The conventional current driver circuit is shown in
FIG. 9
as an example of writing data with a magnetic signal onto a magnetic disk driven by an HDD or the like. Each of the current drivers Tr
1
and Tr
2
functions as a switch. When a gate terminal A of the current driver Tr
1
is set to a low level of V
11
, the current driver Tr
1
is turned on. When a gate terminal B of the current driver Tr
2
is set to a low level of V
11
, the current driver Tr
2
is turned on. A current mirror circuit includes the current receivers Tr
3
and Tr
4
and the transistor Tr
7
. In cases where a high voltage of Vh
2
is applied to a gate terminal of the transistor Tr
8
, the transistor Tr
8
is turned on, and the current mirror circuit functions as a current source circuit. When the transistor Tr
5
or Tr
6
is turned on, the current mirror circuit functions as a current source circuit. That is, a switching of the current source circuit occurs in the current receivers Tr
3
and Tr
4
according to the on-off of the transistor Tr
5
or Tr
6
.
The gate terminals A and B of the current drivers and gate terminals C and D of the transistor Tr
5
or Tr
6
are set to levels respectively as shown in the flow chart of FIG.
10
. In a time period T
1
, the current driver Tr
1
and the transistor Tr
6
are turned on. Therefore, when the current receiver Tr
4
is turned on in the switching operation, a write current Iwc flows through the write head WH in a right direction in FIG.
9
. Also, in a time period T
2
, the current driver Tr
2
and the transistor Tr
5
are turned on. Therefore, when the current receiver Tr
3
is turned on in the switching operation, a write current Iwc flows through the write head WH in a left direction in FIG.
9
. The write head WH is formed of a coil. Therefore, a magnetic field is induced in the write head WH due to the write current Iwc flowing through the write head WH, the direction of the magnetic field is changed according to the change of the flow direction of the write current, and a magnetic signal is produced. The write head WH is disposed near to a magnetic disk (not shown), and data of the magnetic signal is written to the magnetic disk.
The current drivers Tr
1
and Tr
2
and the current receivers Tr
3
and Tr
4
are disposed in the inside of an integrated circuit, and the current drivers Tr
1
and Tr
2
and the current receivers Tr
3
and Tr
4
are connected with external devices (for example, the write head WH) through pins of the integrated circuit. Also, the write head WH is connected with pins of the integrated circuit through inter-connectors.
Recently, a data transfer rate of the magnetic signal has been increased more and more in case of the use of the HDD or the like. To write data of the magnetic signal in the magnetic disk at a high transfer rate, it is required to rapidly change the flow direction of the write current Iwc. Therefore, to heighten the data transfer rate, it is required to shorten both a rise time Tr and a fall time Tf of the write current Iwc. Because an operation frequency has been recently increased, current driving performance of the transistors is temporarily increased during a flow direction changing operation of the write current Iwc. Therefore, the rise time Tr and the fall time Tf of the write current Iwc can be shortened. However, in cases where the impedance matching between the write head WH and a group of pins of the integrated circuit connected with the write head WH is not obtained, energy of the current generated in the integrated circuit is not perfectly consumed as the write current Iwc, and energy not consumed is returned to a current supply end as a reflected component. The returning of the reflected component is called an undershoot phenomenon.
FIG. 11
shows a waveform view showing the undershoot phenomenon. In cases where a degree of the “undershoot” in the phenomenon exceeds a certain level, the magnetic field is not sufficiently induced to write data of the magnetic signal in the magnetic disk. As a result, when the data is read out from the magnetic disk, there is high probability that a reading-out error occurs. Therefore, to heighten the data transfer rate, it is required to solve the problem of the returning of the reflected component, and the impedance matching between the write head WH and the group of pins of the integrated circuit connected with the write head WH is necessary in the current driver circuit.
In the conventional current driver circuit shown in
FIG. 9
, current flows through the current driver Tr
1
or Tr
2
functioning as an MOS transistor switch, the write head WH and the line of the current source circuit (that is, a group of the current receiver Tr
3
and the transistor Tr
5
or a group of the current receiver Tr
4
and the transistor Tr
6
) in that order. An output impedance of the current driver Tr
1
or Tr
2
is equal to 1/(&bgr;×(Vgs−Vth)), and an input impedance of the current source circuit is equal to 1/(&lgr;×Id). Here, Id denotes a drain current. Vgs denotes a difference in voltage between a gate and a source of the current driver Tr
1
or Tr
2
. Vth denotes a threshold voltage of the current driver Tr
1
or Tr
2
. &bgr; and &lgr; are described later. Though the output impedance of the current driver Tr
1
or Tr
2
and the input impedance of the current source circuit depend on process and bias conditions, the input impedance of the current source circuit is considerably higher than the output impedance of the switch.
An example of an output impedance of the MOS transistor switch and an example of the input impedance of the current source circuit are described. An output resistance of the MOS transistor switch is expressed by Rout(SF), and an input resistance of the current source circuit is expressed by Rin(CS).
Rout(
SF
)=1/(&bgr;×(
Vgs−Vth
))=1/(
k
×(
W/L
)×(
Vgs−Vth
))
k=&mgr;n×Cox=&mgr;n×∈ox/tox
Here, W denotes a gate width, L denotes a gate length, &mgr;n denotes a mobility of electrons, Cox denotes a fixed capacitance of an oxide film (SiO
2
), ∈ox denotes a dielectric constant of the oxide film, and tox denotes a thickness of the oxide film. In the 0.25 &mgr;m process, &mgr;n=0.05 m
2
/(V*s), ∈ox=34.5 pF/m and tox=6 nm are satisfied. Therefore, k=290 &mgr;A /V
2
is obtained. In cases where W=500&mgr;m and L=0.25 &mgr;m are satisfied, W/L=2000 is obtained. When the write current Iwc set to 50 mA, Vgs set to 2.5 V and Vth set to 0.7 V are satisfied, Rout(SF)=1.4&OHgr; is obtained.
Rin
(
CS
)=1/(&lgr;×
Iwc
))
&lgr;=(1/2
L
){square root over ( )} (2
∈s
/(
q×Nimp×
(
Vds−Veff+&phgr;o
)))
Here, ∈s denotes a dielectric constant of silicon, q denotes an electric ch
Takeuchi Toru
Umeyama Takehiko
Leydig Voit & Mayer LTD
Mitsubishi Denki & Kabushiki Kaisha
Tran Toan
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