1. Field of the Invention
The present invention relates to a voltage current conversion device used in a light emitting device such as an exposing apparatus of an electrophotographing system and a display device, and in particular, it relates to a voltage current conversion device preferably disposed in a signal transfer channel for providing a video signal which is a voltage signal to each pixel as a current signal.
2. Related Background Art
As a light emitting device, a display device will be cited as an example. In recent years, in general, an organic electroluminescence (EL) display device, which is one of the Trendy flat display panels, includes a display device of the type in which luminous brightness of an organic EL element disposed in each pixel as a light emitting element is decided by a current value provided in a data signal source. In this type, a voltage current conversion device is disposed in the data signal source and a video signal which is a voltage signal is required to be converted into a current signal. As the voltage current conversion device, for example, its circuit constitution is illustrated in FIG. 9 of Japanese Patent Application Laid-Open No. 2002-40074.
In
In the device of
However, in case the device of
To solve such a problem, first, the present inventor invented a voltage current conversion device of the circuit constitution as shown in
The operation of the device of
First, in a time t1, control signals S2 and S3 become a high level H, and the second transistor T2 and the third transistor T3 turn on. In this manner, the gate potential VG(T1) of the first transistor T1 is pre-charged by the first potential source V1.
Next, in a time t2, the control signal S3 of the gate of the third transistor T3 becomes a low level L, so that the third transistor T3 turns off and the first transistor T1 is applied with a self-bias toward a turn-on voltage, and discharges by drawing a gentle curve. In this manner, the VG(T1) discharges toward the third potential V3 until it becomes the threshold value Vth of the transistor T1 by taking a sufficient time. Here, Va′=Vth.
After the completion of the self-bias period, in a time t3, the control signal S2 becomes L, and the second transistor T2 turns off, and further, in a time t4, the control signal S1 becomes H, and the input control transistor T0 turns on. As a result, the gate of the first transistor T1 becomes a potential Vb′. Here, the Vb′ is a sum of the threshold value Vth of the first transistor T1 and the capacitor split voltages Vc of C1 and C2 of the input voltage Vin. In a time t5, the control signal S1 becomes L and the input control transistor T0 turns off.
In an appropriate time subsequent to the time t5, the control signal S6 becomes H, and the sixth transistor T6 turns on as occasion arises, and the output current Iout corresponding to the gate potential VG(T1) of the first transistor T1 which is set at the time t4 to t5 through the sixth transistor T6 and the first transistor T1 is obtained.
The voltage current conversion device of
However, in the voltage current conversion device of
An object of the present invention is to provide a voltage current conversion device, in which an output current can be drawn as unlimitedly as possible to 0 in case a voltage current conversion characteristic is uniform, and an input voltage Vin is 0.
Another object of the present invention is to provide a voltage current conversion device, comprising:
a voltage/current conversion transistor comprising a gate for receiving a voltage signal inputted from an input terminal, a drain for outputting a current signal from an output terminal and a source;
a gate potential setting circuit for setting the gate of the voltage/current conversion transistor to a predetermined first potential; and
a source potential setting circuit including a setting transistor for setting the source of the voltage/current conversion transistor to a predetermined second potential,
wherein the second potential is different from the potential of the terminal coupled to the gate of the voltage/current conversion transistor through a storage capacitor.
According to the present invention, even in case the self-bias period of the voltage/current conversion transistor which decides an output current is a short period of time, the output current can be almost completely shut off for the zero setting of an input voltage. Consequently, even in case an element reacting to a micro current is current-driven, a definite operation stop of the element can be realized. Further, in case a plurality of voltage current conversion devices of the present invention are used in parallel in the display device and the like, an uniform voltage current conversion characteristic can be obtained without being affected by the irregularity of the threshold value of the transistor.
A circuit constitution of a preferred embodiment of the voltage current conversion device of the present invention is shown in
The voltage current conversion device of
a voltage/current conversion transistor T1 comprising a gate for receiving a voltage signal inputted from an input terminal Vin, a drain for outputting a current signal from an output terminal Iout and a source;
gate potential setting circuits T2, T3 and T7 for setting the gate of the voltage/current conversion transistor T1 to a predetermined first potential V1; and
source potential setting circuits V2, T4, T5 and V3 including a setting transistor T4 for setting the source of the voltage/current conversion transistor T1 to a predetermined second potential V2,
wherein the second potential V2 is different from the potential V3 of the terminal coupled to the gate of the voltage/current conversion transistor T1 through a storage capacitor C2.
In the device of
Further, the gate potential setting circuit may preferably include a transistor T2, which connects the gate and the drain of the voltage/current conversion transistor T1.
Further, the source potential setting circuit may preferably allow the gate potential to be transferred up to a potential in which the gate potential of the voltage/current conversion transistor T1 set to the first potential V1 becomes smaller in its absolute value.
The device of the present embodiment comprises:
a first transistor in which a gate is connected to the other terminal of a first capacitor C1, where an input terminal Vin inputted with a voltage is connected to the one terminal, and the terminal of the second capacity, and a drain is connected to the output terminal from which a current is outputted,
a second transistor T2 in which a source is connected to the other terminal of the first capacity C1 and the gate of the first transistor T1, and a drain is connected to the output terminal Iout, and a gate is controlled by an independent control signal S2,
a third transistor T3 in which a source or a drain is connected to the drain of the first transistor T1, and the drain or the source is connected to a first potential V1, and a gate is controlled by an independent control signal S3,
a fourth transistor T4 in which a drain is connected to the source of the first transistor T1 and a source is connected to a second potential V2, and a gate is controlled by an independent control signal S4, and
a fifth transistor T5 in which a drain is connected to the source of the first transistor T1, and a source is connected to the other terminal of the second capacitor C2 and a third potential V3, and a gate is controlled by an independent control signal S5.
Here, the first, second and third potentials is preferably set so that a potential difference between the third potential and the second potential becomes equal to or more than the voltage remained in the gate potential after the self-bias of the first transistor.
Further, the third potential is preferably a common potential of the input voltage.
The first to fifth transistors are preferably a thin film transistor constituted by using a non-single crystal semiconductor.
As described above, in the embodiment of
The voltage current conversion device of
The operation of the device of
In the time t1, the control signals S2, S3 and S4 become a high level H, respectively, and the second, third, and fourth transistors T2, T3 and T4 turn on. In this manner, the source potential VS(T1) of the first transistor T1 is set to the second potential V2 trough the fourth transistor T4, and the gate potential VG(T1) is pre-charged by the first potential V1 through the second and third transistors T2 and T3, and becomes the potential V1.
Next, in the time t2, the control signal S3 becomes a low level L, and the third transistor T3, which constitutes a gate potential setting circuit, turns off. Then, the first transistor T1 is applied with the self-bias toward a turn on voltage, and the gate potential VG(T1) of the transistor T1 draws a gentle curve so as to perform a discharging operation. At this time, the source potential VS(T1) of the first transistor T1 is set to the second potential V2 by the source potential setting circuit. Hence, the gate potential VG(T1) of the first transistor T1 advances toward the second potential V2 until it becomes the threshold value Vth of the transistor T1, thereby performing the discharging of the charge in a short period of time comparing to
In the time t3, when S2 and S4 becomes L, the second and fourth transistors T2 and T4 turn off, and the discharge of the first transistor T1 completes. The gate potential at this time is sufficiently low, that is, it becomes a potential Va small in absolute value. Subsequently, in the time t4, when S1 and S5 become H, the input control transistor T0 and the fifth transistor T5 turn on, and the source potential VS(T1) of the first transistor T1 is set to the third potential V3, and at the same time, the gate potential VG(T1) becomes Vb. Here, “Vb=the threshold value Vth of the first transistor T1+the self bias residual voltage Vr−(the third potential V3−the second potential V2)+C1 and C2 capacitor split voltages of the input voltage Vin.” In the time t5, the control signals S1 and S5 become L, and the input control transistor T0 and the first transistor T1 turn off. Subsequent to this time, when, in an appropriate time, the control signal S6 is allowed to become H and the sixth transistor T6 is allowed to turn on, the output current Iout corresponding to the gate potential VG(T1) of the first transistor T1 set in the times t4 to t5 is obtained through the sixth transistor T6 and the first transistor T1.
Consequently, in the above-described voltage current conversion device, in case the input voltage Vin is 0, the gate potential VG(T1) of the first transistor T1 becomes “the threshold value Vth of the first transistor T1+the self bias residual voltage Vr−(the third potential V3−the second potential V2).” Here, since the second potential V2, as described above, is set so that “the third potential V3−the second potential V2≧the self-bias residual voltage Va”, the gate potential VG(T1) becomes lower than the threshold value Vth of the first transistor T1, and the first transistor T1 is sufficiently shut off.
As described above, in the voltage current conversion device of the present embodiment, when the second potential and the third potential are set to a predetermined relation according to the self bias period, the effect of the self-bias residual voltage at the time when the input voltage is zero is eliminated, and the output current can be made zero.
Further, a correction effect by the irregularity of the threshold value of the transistor in case of using a plurality of voltage current conversion devices of the present embodiment in parallel is the same as the voltage conversion device of
The voltage current conversion device of the present invention is preferably used in a display device, and hence, it is also preferably used in the case of a thin film transistor in which the first to fifth transistors are constituted by using a non single crystal semiconductor thin film such as a non crystal silicon.
The above described device can be adapted to the light emitting device comprising a light emitting portion 3 having a plurality of light emitting elements in the light emitting device and a signal source 1 for supplying a current signal to the light emitting portion 3, wherein the signal source 1 includes the voltage current conversion device of
Here, the light emitting portion 3 is preferable to be an active matrix type organic EL light emitting display portion having a light emitting element and a transistor. The pixel circuit of the light emitting portion 3 is as follows.
The transistors M1 and M2 are turned on, and the transistor M3 is turned off, and the current signal Iout is programmed to the pixel circuit 2. Subsequently, the transistors M1 and M2 are turned off, and the transistor M3 is turned on, and the current is let flow to the light emitting element EL from a power source line Vcc, so that the light emitting element EL is emitted. Reference character P1 is a scan control line.
This application claims priority from Japanese Patent Application No. 2004-109102 filed on Apr. 1, 2004, which is hereby incorporated by reference herein.
Number | Date | Country | Kind |
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2004-109102 | Apr 2004 | JP | national |
Number | Name | Date | Kind |
---|---|---|---|
6229506 | Dawson et al. | May 2001 | B1 |
6411162 | Minamizaki et al. | Jun 2002 | B2 |
6577302 | Hunter et al. | Jun 2003 | B2 |
6657394 | Nasman | Dec 2003 | B2 |
6670773 | Nakamura et al. | Dec 2003 | B2 |
6777888 | Kondo | Aug 2004 | B2 |
6812768 | Kawasaki et al. | Nov 2004 | B2 |
6870553 | Kondo et al. | Mar 2005 | B2 |
6992663 | Nakamura et al. | Jan 2006 | B2 |
7126565 | Kawasaki et al. | Oct 2006 | B2 |
20040183752 | Kawasaki et al. | Sep 2004 | A1 |
20060119552 | Yumoto | Jun 2006 | A1 |
Number | Date | Country |
---|---|---|
2-188019 | Jul 1990 | JP |
7-283708 | Oct 1995 | JP |
2002-40074 | Feb 2002 | JP |
2002-514320 | May 2002 | JP |
2003-195808 | Jul 2003 | JP |
2003-529805 | Oct 2003 | JP |
0239420 | May 2002 | WO |
Number | Date | Country | |
---|---|---|---|
20050248372 A1 | Nov 2005 | US |