Electric lamp and discharge devices: systems – Plural power supplies – Plural cathode and/or anode load device
Reexamination Certificate
2001-04-19
2003-03-11
Wong, Don (Department: 2821)
Electric lamp and discharge devices: systems
Plural power supplies
Plural cathode and/or anode load device
C347S237000, C347S238000
Reexamination Certificate
active
06531826
ABSTRACT:
TECHNICAL FIELD
The present invention relates to generally a self-scanning light-emitting device, particularly to a self-scanning light-emitting device whose amount of light may be corrected.
BACKGROUND ART
A light-emitting device in which a plurality of light-emitting elements are arrayed on the same substrate is utilized as a light source of a printer, in combination with a driver circuit. The inventors of the present invention have interested in a three-terminal light-emitting thyristor having a pnpn-structure as an element of the light-emitting device, and have already filed several patent applications (see Japanese Patent Publication Nos. 1-238962, 2-14584, 292650, and 2-92651.) These publications have disclosed that a self-scanning function for light-emitting elements may be implemented, and further have disclosed that such selfscanning light-emitting device has a simple and compact structure for a light source of a printer, and has smaller arranging pitch of thyristors.
The inventors have further provided a self-scanning light-emitting device having such structure that an array of light-emitting thyristors having transfer function is separated from an array of light-emitting thyristors having writable function (see Japanese Patent Publication No. 2-263668.)
Referring to
FIG. 1
, there is shown an equivalent circuit diagram of a fundamental structure of this self-scanning light-emitting device. According to this structure, the device comprises transfer elements T
1
, T
2
, T
3
. . . and writable light-emitting elements L
1
, L
2
, L
3
. . . , these elements consisting of three-terminal light-emitting thyristors. The structure of the portion of an array of transfer elements includes diode D
1
, D
2
, D
3
. . . as means for electrically connecting the gate electrodes of the neighboring transfer elements to each other. V
GK
is a power supply (normally
5
volts), and is connected to all of the gate electrodes G
1
, G
2
, G
3
. . . of the transfer elements via a load resistor R
L
, respectively. Respective gate electrodes G
1
, G
2
, G
3
. . . are correspondingly connected to the gate electrodes of the writable light-emitting elements L
1
, L
2
, L
3
. . . . A start pulse &phgr;
s
is applied to the gate electrode of the transfer element T
1
, transfer clock pulses &phgr;
1
and &phgr;
2
are alternately applied to all of the anode electrodes of the transfer elements, and a write signal &phgr;
I
is applied to all of the anode electrodes of the light-emitting elements. The self-scanning light-emitting device shown in
FIG. 1
is a cathode common type, because all of the cathodes of the transfer elements and the light-emitting elements are commonly connected to the ground.
Referring to
FIG. 2
, there are shown respective wave shapes of the start pulse &phgr;
s
, the transfer clock pulses &phgr;
1
, &phgr;
2
, and the write pulse signal &phgr;
I
. The ratio (i.e., duty ratio) between the time duration of high level and that of low level in each of clock pulses &phgr;
1
and &phgr;
2
is substantially 1 to 1.
The operation of this self-scanning light-emitting device will now be described briefly. Assume that as the transfer clock &phgr;
1
is driven to a high level, the transfer element T
2
is now turned on. At this time, the voltage of the gate electrode G
2
is dropped to a level near zero volts from 5 volts. The effect of this voltage drop is transferred to the gate electrode G
3
via the diode D
2
to cause the voltage of the gate electrode G
3
to set about 1 volt which is a forward rise voltage (equal to the diffusion potential) of the diode D
2
. On the other hand, the diode D
1
is reverse-biased so that the potential is not conducted to the gate G
1
, then the potential of the gate electrode G
1
remaining at 5 volts. The turn on voltage of the light-emitting thyristor is approximated to a gate electrode potential+a diffusion potential of PN junction (about 1 volt.) Therefore, if a high level of a next transfer clock pulse &phgr;
2
is set to the voltage larger than about 2 volts (which is required to turnon the transfer element T
3
) and smaller than about 4 volts (which is required to turn on the transfer element T
5
), then only the transfer element T
3
is turned on and other transfer elements remain off-state, respectively. As a result of which, on-state is transferred from T
2
to T
3
. In this manner, on-state of transfer elements are sequentially transferred by means of two-phase clock pulses.
The start pulse &phgr;
s
works for starting the transfer operation described above. When the start pulse &phgr;
s
is driven to a low level (about 0 volt) and the transfer clock pulse &phgr;
2
is driven to a high level (about 2-4 volts) at the same time, the transfer element T
1
is turned on. Just after that, the start pulse &phgr;
s
is returned to a high level.
Assuming that the transfer element T
2
is in the on-state, the voltage of the gate electrode G
2
is lowered to almost zero volt. Consequently, if the voltage of the write signal &phgr;
I
is higher than the diffusion potential (about 1 volt) of the PN junction, the light-emitting element L
2
may be turned into an on-state (a light-emitting state).
On the other hand, the voltage of the gate electrode G
1
, is about 5 volts, and the voltage of the gate electrode G
3
is about 1 volt. Consequently, the write voltage of the light-emitting element L
1
is about 6 volts, and the write voltage of the light-emitting element L
3
is about 2 volts. It follows from this that the voltage of the write signal &phgr;
I
which can write into only the light-emitting element L
2
is in a range of about 1-2 volts. When the light-emitting element L
2
is turned on, that is, in the light-emitting state, the amount of light thereof is determined by the write signal &phgr;
I
. Accordingly, the light-emitting elements may emit light at any desired amount of light. In order to transfer on-state to the next element, it is necessary to first turn off the element in on-state by temporarily dropping the voltage of the write signal &phgr;
I
down to zero volts.
The self-scanning light-emitting device described above may be fabricated by arranging a plurality of luminescent chips each thereof is for example 600 dpi (dots per inch)/128 light-emitting elements and has a length of about 5.4 mm. These luminescent chips may be obtained by dicing a wafer in which a plurality of chips are fabricated. While the distribution of amounts of light of light-emitting elements in one chip is small, the distribution of amounts of light among chips is large. Referring to
FIGS. 3A and 3B
, there is shown an example of the distribution of amounts of light in a wafer.
FIG. 3A
shows a plan view a three-inch wafer
10
, wherein an x-y coordinate system is designated. The light-emitting elements are arranged in a direction of x-axis, and the length of one luminescent chip is about 5.4 mm.
FIG. 3B
shows the distribution of amounts of light at locations in the x-y coordinate system. It should be noted in
FIG. 3B
that the amount of light is normalized by an average value within a wafer. In
FIG. 3B
, four distributions of amounts of light are shown, with y-locations being different (i.e., y=0, 0.5, 1.0, and 1.35 inches).
It is apparent from
FIG. 3B
that each distribution of amounts of light in a chip is within the deviation of at most ±0.5% except chips around the extreme peripheral part of a wafer, but the average values of amounts of light in respective chips on a wafer are distributed in a range of the deviation of about 6%, because the amounts of light in a wafer are distributed like the shape of the bottom of a pan as shown in FIG.
3
B. It has been noted that another wafers have distributions similar to that of
FIG. 3B
, and average values of amounts of light are varied among wafers. In this manner, while the amounts of light are distributed in a small range in a chip, the average values of amount of light of respective chips in a wafer are distributed broadly.
Therefore, a self-scanning light-emitting device having a
Kusuda Yukihisa
Ohno Seiji
Yamashita Ken
Yoshida Harunobu
Nippon Sheet Glass Co. Ltd.
RatnerPrestia
Tran Thuy Vinh
Wong Don
LandOfFree
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