Electric lamp and discharge devices: systems – Plural power supplies – Plural cathode and/or anode load device
Reexamination Certificate
2001-08-01
2003-05-27
Phan, Tho (Department: 2821)
Electric lamp and discharge devices: systems
Plural power supplies
Plural cathode and/or anode load device
C345S076000, C345S078000
Reexamination Certificate
active
06570338
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an electro-luminescence display (ELD), and more particularly to a driving circuit for driving electro-luminescence cells arranged on an electro-luminescence panel in a matrix type.
2. Description of the Related Art
Generally, an electro-luminescence (EL) panel converts an electrical signal into light energy to thereby display a picture corresponding to video signals (or image signals). Such an EL panel includes EL cells arranged at intersections between gate lines and data lines. Each of the EL cells responds to a pixel signal from the data line to generate a light corresponding to a magnitude of the pixel signal.
In order to stably apply a pixel signal to each EL cell, the EL panel has cell-driving circuits scanned sequentially line-by-line. Each of the EL cell-driving circuits responds to a control signal at the gate line to sample a pixel signal at the data line and then holds the sampled pixel signal during the next frame interval, to thereby stably apply the pixel signal to the EL cell.
As shown in
FIG. 1
, a conventional EL cell-driving circuit for carrying out such sampling and holding operations of a pixel signal includes a first PMOS thin film transistor (TET) MP
1
connected between an EL cell ELC and a first node Ni. A gate of the first PMOS TFT MP
1
is connected to a second node N
2
, and the EL cell ELC is also connected to ground. A second PMOS TFT MP
2
is connected between the second node N
2
and the EL cell ELC, and is connected at its gate to a gate line GL. A capacitor C
1
is connected between the first and second nodes N
1
and N
2
.
The capacitor C
1
charges a voltage of a pixel signal when the pixel signal is applied from a data line DL and applies the charged pixel voltage to gate electrodes of the first PMOS TFT MP
1
. The first PMOS TET MP
1
is turned on by the pixel voltage charged in the capacitor C
1
, thereby allowing a supply voltage VDD applied, via the first node Ni, from a voltage supply line VDDL to be supplied to the EL cell ELC.
At this time, the first PMOS TFT MP
1
varies its channel width depending on a voltage level of the pixel signal to control a current amount applied to the EL cell ELC. Then, the EL cell ELC generates a light corresponding to the current amount applied from the first PMOS TFT MP
1
. The second PMOS TET MP
2
responds to a gate signal GLS, as shown in
FIG. 2
, applied from the gate line GL to selectively connect the second node N
2
to the EL cell ELC.
More specifically, the second PMOS TFT MP
2
connects the second node N
2
to the EL cell ELC at a time interval when the gate signal GLS is enabled at a low logic, thereby allowing the pixel signal to be charged in the capacitor C
1
. In other words, the second PMOS TFT MP
2
forms a current path of the capacitor C
1
at a time interval when the gate signal GLS at the gate line GL is enabled. The capacitor C
1
charges the pixel signal in the enabling interval of the gate signal GLS, thereby allowing the gate electrode of the first PMOS TFT MP
1
to have a lower voltage than the drain electrode by a voltage level of the charged pixel signal. Accordingly, a channel width of the first PMOS TFT MP
1
is controlled in accordance with a voltage level of the pixel signal to determine a current amount flowing from the first node N
1
into the EL cell ELC.
The conventional EL cell driving circuit further includes a third PMOS TFT MP
3
, connected between the data line DL and the first node N
1
, responding to a gate signal at the gate line GL, and a fourth PMOS TFT MP
4
, connected between the voltage supply line VDDL and the first node N
1
, responding to an inverted gate signal /GLS from a gate bar line /GL.
The third PMOS TFT MP
3
is turned on at a time interval when a low logic of gate signal is applied from the gate line GL, thereby connecting the capacitor C
1
, coupled to the first node N
1
and the source electrode of the first PMOS TFT MP
1
, to the data line DL. In other words, the third PMOS TFT MP
3
responds to a low logic of gate signal GLS to send a pixel signal at the data line DL to the first node N
1
. to the data line DL. In other words, the third PMOS TFT M
3
responds to a low logic of gate signal GLS to send a pixel signal at the data line DL to the first node N
1
.
As a result, the third PMOS TFT MP
3
is turned on during a time interval when a gate signal at the gate line GL remains at a low logic, thereby charging a pixel signal into the capacitor C
1
connected between the first and second nodes N
1
and N
2
. The fourth PMOS TET MP
4
is turned on in a time interval when a low logic of inverted gate signal /GLS from the gate bar line /GL is applied to the gate electrode thereof, thereby connecting the first node N
1
, to which the capacitor C
1
and the source electrode of the first PMOS TFT MP
1
are connected, to the voltage supply line VDDL.
At a time interval when the fourth PMOS TET MP
4
has been turned on, a supply voltage VDD at the voltage supply line VDDL is applied, via the first node N
1
and the first PMOS TFT MP
1
, to the EL cell ELC. Thus, the EL cell ELC generates a light of a quantity according to a voltage level of the pixel signal.
In the conventional EL cell driving circuit, a maximum current amount (i.e., a current margin of a pixel signal) required for obtaining a maximum brightness is small. For this reason, a current difference between gray scale levels of a video signal is approximately several &mgr;A. if a current difference between gray scale levels is set to several &mgr;A, a data driver integrated circuit (IC) chip must have the ability to control current at a range of several &mgr;A accurately. However, it is very difficult to manufacture a data driver IC chip capable of controlling a current at a range of several &mgr;A accurately. As a result, the conventional EL cell driving circuit has problems with driving the conventional EL panel to accurately display a gray scale of a picture.
SUMMARY OF THE INVENTION
The present invention provides a driving circuit for an electro-luminescence cell that increases a current difference of a pixel signal for identifying gray scale levels.
The present invention also provides an electro-luminescence panel that more accurately displays a gray scale of a picture.
In the electro-luminescence (EL) panel according to the present invention, the driving circuit for an electro-luminescence (EL) cell includes an EL cell; a supply is circuit selectively applying current to the EL cell based on a pixel signal from a data line; and a control circuit controlling current flow from the supplying circuit to the EL cell such that an amount of current for discriminating between gray scale levels is approximately tens of micro-amps.
According to an embodiment of the present invention, the supplying circuit includes a first transistor connected between the EL cell and a voltage supply line, and the control circuit includes a second transistor connected between the data line and the voltage supply line such that the first and second transistors form a current mirror. In a preferred embodiment, the second transistor has a channel width of 3 to 20 times greater than a channel width of the first transistor.
REFERENCES:
patent: 5302966 (1994-04-01), Stewart
patent: 5386179 (1995-01-01), Sato
patent: 5684365 (1997-11-01), Tang et al.
patent: 5748026 (1998-05-01), Maekawa et al.
patent: 5786796 (1998-07-01), Takayama et al.
patent: 6229506 (2001-05-01), Dawson et al.
patent: 6380688 (2002-04-01), Bae et al.
LG.Philips LCD Co. , Ltd.
Phan Tho
LandOfFree
Driving circuit for electro-luminescence cell does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Driving circuit for electro-luminescence cell, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Driving circuit for electro-luminescence cell will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3032540