Patent Grant
12094402
The present invention relates to a display driving device that operates by applying power supply voltages of a plurality of different voltage levels.
Generally, in accordance with miniaturization of an internal circuit, an operating voltage lowers to, for example, 1.2 V, in a semiconductor device, and thus consumed power is reduced. Since the circuit part is configured as a semiconductor device in a display driving device as well, a logic circuit, such as a control circuit, operates at a low voltage. On the other hand, in an output stage including an output circuit that outputs a driving voltage to a display panel, for example, to generate the driving voltage corresponding to a luminance level of each pixel, a high operating voltage like 7 V is required. A pre-stage circuit, such as an input interface unit of a video signal, operates at a medium operating voltage, for example, 1.8 V. Therefore, all components in the display driving device cannot operate at a single low voltage, and thus reduction in electricity consumption did not proceed.
However, the reduction in electricity consumption is especially required for a recent display driving device used for a mobile device, such as a smartphone, for higher definition display and to avoid frequent charging of a battery as the main power supply.
Patent Document 1 discloses a voltage regulator configured to generate any given one or more voltages from a high voltage. The voltage regulator steps down an external power supply voltage by a first regulator circuit to generate a first power supply voltage and includes a second regulator circuit and a third regulator circuit. The second regulator circuit and the third regulator circuit each operate using the first power supply voltage as a power supply, and step down the external power supply voltage using a voltage drop element, generate a second power supply voltage and a third power supply voltage, respectively, using a driver element for voltage control using the stepped-down voltage as an input voltage to ensure outputting them to individual loads.
However, decreasing the power supply voltage and an operating current for lower electricity consumption in the conventional display driving device causes problems that a desired property cannot be obtained, an operating condition needs to be changed, or in some cases, changing a circuit to obtain the desired property increases a manufacturing cost, and thus reducing the consumed power easily was difficult.
Therefore, an object of the present invention is to provide a display driving device that can effectively reduce consumed power comparatively easily.
A display driving device for driving a display panel according to the present invention includes a high voltage operating unit that includes an output circuit to supply a driving voltage to the display panel, the high voltage operating unit being coupled to a first voltage application line to which a high power supply voltage is applied, the high voltage operating unit obtaining an operating current according to the application of the high power supply voltage from the first voltage application line; a low voltage operating unit that operates according to an application of a low power supply voltage lower than the high power supply voltage to control the high voltage operating unit; a recycling circuit that receives the operating current from the high voltage operating unit via a relay coupling line, the recycling circuit applying the low power supply voltage to the low voltage operating unit while supplying the received operating current to a reference potential line via the low voltage operating unit; and a current bypass circuit that flows a part of the operating current flowing through the relay coupling line into the reference potential line without supplying the part of the operating current to the recycling circuit according to a voltage increase in the low power supply voltage applied to the low voltage operating unit.
According to the display driving device of the present invention, the recycling circuit applies the low power supply voltage to the low voltage operating unit while supplying the operating current flowing through the high voltage operating unit to the reference potential line via the low voltage operating unit to effectively use the operating current of the high voltage operating unit, and thus an amount of electricity consumption can be reduced. According to the voltage increase in the low power supply voltage applied to the low voltage operating unit, a part of the operating current flowing through the relay coupling line is flowed into the reference potential line without being supplied to the recycling circuit, and therefore, a variation in the driving voltage can be reduced and an excessive increase in the applied voltage to the low voltage operating unit can be prevented.
The following describes embodiments of the present invention in detail with reference to the drawings.
The driving device includes a driver unit 12 that drives an organic EL display panel 11 and a medium voltage power supply unit 13 and a high voltage power supply unit 14 that supply a power supply voltage to the driver unit 12.
For example, in the organic EL display panel 11, a plurality of organic EL elements are arranged in a matrix as respective pixels to configure a display panel. The medium voltage power supply unit 13 generates a medium voltage MV (a medium power supply voltage) as a power supply voltage, and the high voltage power supply unit 14 generates a high voltage HV (a high power supply voltage), which is a power supply voltage higher than the medium voltage MV.
The driver unit 12 includes a MV circuit 21 to which the medium voltage MV is applied as the power supply voltage, a LV circuit 22 (a low voltage operating unit) to which a low voltage LV (a low power supply voltage), which is a power supply voltage lower than the medium voltage MV, is applied, a HV circuit 23A, a HV circuit 23B, and a HV output circuit 24 as high voltage operating units to which the high voltage HV is applied as the power supply voltage, and a recycling circuit 25 that supplies the low voltage LV to the LV circuit 22. The LV circuit 22, the HV circuit 23A, the HV circuit 23B, and the HV output circuit 24 are disposed by a plurality of channels (a plurality of source lines) as illustrated in
The MV circuit 21 is, for example, a part that generates luminance data of each pixel for each source line in the organic EL display panel 11 according to an input image signal, in response to the input image signal. The LV circuit 22 is a control circuit configured of a logic circuit that handles a stage prior to an output stage in the driver unit 12. In response to the input image signal input from the MV circuit 21, the LV circuit 22 controls the HV circuits 23A and 23B and the HV output circuit 24 based on a synchronization signal.
To the MV circuit 21 and the recycling circuit 25, respective voltage application line 31 and ground line 32 (a reference potential line) are individually coupled. The voltage application line 31 is an application line of the medium voltage MV coupled to an output end of the medium voltage power supply unit 13. The ground line 32 is a grounding line and is a grounding line of the medium voltage power supply unit 13. A current IMV generated by the medium voltage MV supplied via the voltage application line 31 flows into the MV circuit 21 and the recycling circuit 25 as an operating current, and the current IMV flows out to the ground line 32 from the circuits.
The HV circuit 23A is a logic circuit and a level shifter for HV circuit control and is a circuit that requires a voltage range from the ground level to the high voltage HV. To the HV circuit 23A, respective voltage application line 33 (first voltage application line) and ground line 36 (reference potential line) are coupled. The ground line 36 may be coupled to the ground line 32. A current IHVA generated by the high voltage HV supplied via the voltage application line 33 flows into the HV circuit 23A as an operating current, and the current IHVA flows out to the ground line 36 from the HV circuit 23A.
For example, the HV circuit 23B is a bias circuit, and the HV output circuit 24 is, for example, an output amplifier circuit. The HV circuit 23B and the HV output circuit 24 operate at an electric potential on the ground side of the low voltage LV or more, and are circuits to which the application of the electric potential at the high voltage HV is required or desirable.
A voltage application line 33 and a relay coupling line 34 are individually coupled to the HV circuit 23B and the HV output circuit 24. The relay coupling line 34 is coupled to the HV circuit 23B via a relay coupling line 341, and similarly is coupled to the HV output circuit 24 via a relay coupling line 342. The relay coupling line 341 is a line to couple the HV circuits 23B of a plurality of channels in common, and the relay coupling line 342 is a line to couple the HV output circuits 24 of a plurality of channels in common.
A current IHV2 generated by the high voltage HV supplied via the voltage application line 33 flows into the HV circuit 23B as an operating current, a current IHV3 generated by the high voltage HV supplied via the voltage application line 33 flows into the HV output circuit 24 as an operating current, and the currents IHV2 and IHV3 flow out to the relay coupling line 34 via the relay coupling lines 341 and 342 from the HV circuit 23B and the HV output circuit 24 as a resultant current IHVB. Further, a bypass capacitor 26 is coupled between the relay coupling line 34 and the ground line 36.
The relay coupling line 34 is coupled to the recycling circuit 25. A voltage application line 35 (a third voltage application line) is further coupled to the recycling circuit 25. The recycling circuit 25 receives the current IHVB supplied from the relay coupling line 34 to control such that a voltage of the voltage application line 35 becomes the low voltage LV equal to a reference voltage as will be described later. To the LV circuit 22, the voltage application line 35 and the ground line 32 are coupled. A current ILV flows into the LV circuit 22 from the recycling circuit 25 via the relay coupling line 35 as an operating current, and the current ILV flows out from the LV circuit 22 to the ground line 32.
A clamp circuit 27 is coupled between the relay coupling line 342 of the relay coupling line 34 and the ground line 36. The clamp circuit 27 is a current bypass circuit that flows a part of a current IHV3 flowing through the relay coupling line 342 into the ground line 36 without supplying it to the recycling circuit 25 according to the voltage increase of the low voltage LV applied to the LV circuit 22. The clamp circuit 27 is disposed in each channel, and the coupling position of the clamp circuit 27 to the relay coupling line 342 is in a vicinity of an output position of the current IHV3 from the HV output circuit 24.
As illustrated in
All of the high voltage HV, the medium voltage MV, and the low voltage LV (the reference voltage) are positive voltages and have the relationship HV>MV>LV as described above. In this embodiment, HV=7 [V], MV=1.8 [V], and LV=1.2 [V].
A driving voltage VOUT output from the HV output circuit 24 to the organic EL display panel 11 is a what is called a source driver output, and as illustrated in
As illustrated in
As illustrated in
The voltage application line 31 (the second voltage application line) and the ground line 32 are individually coupled to the respective reference voltage generating circuit 41 and operational amplifier 42, and the medium voltage MV is applied as a power supply voltage. The reference voltage generating circuit 41 is a reference voltage generating unit that generates the low voltage LV as the reference voltage based on the medium voltage MV. To obtain the low voltage LV from the medium voltage MV, the reference voltage generating circuit 41 includes, for example, a simple constant voltage circuit using a zener diode and a resistor or a voltage dividing circuit formed of series-coupled two resistors, and a voltage follower. The voltage follower in the reference voltage generating circuit 41 receives the low voltage LV supplied from the above-described constant voltage circuit or voltage dividing circuit as an input voltage, and outputs the low voltage LV at a low impedance.
The operational amplifier 42 is a driving unit that controls gate voltages of the respective field effect transistors 43 and 44. A positive input end of the operational amplifier 42 is coupled to an output end of the reference voltage generating circuit 41, and a negative input terminal is coupled to respective drains of the field effect transistors 43 and 44. An output end of the operational amplifier 42 is coupled to respective gates of the field effect transistors 43 and 44. A source of the field effect transistor 43 is coupled to the voltage application line 31. A source of the field effect transistor 44 is coupled to the relay coupling line 34. The respective drains of the field effect transistors 43 and 44 are coupled to the voltage application line 35.
The start-up circuit 45 is coupled to the voltage application line 35 and the ground line 32 and temporarily applies a start-up voltage SV1, which is approximately equal to the reference voltage of the low voltage LV, to the voltage application line 35 when the power is turned on. Although not illustrated, the start-up circuit 45 is coupled to the voltage application line 31, and, for example, generates the start-up voltage SV1 based on the medium voltage MV. After the power is turned on, the start-up voltage SV1 is generated for a period until the operation of the LV circuit 22 stabilizes.
The start-up circuit 46 is coupled to the relay coupling line 34 and the ground line 32, and temporarily applies a start-up voltage SV2 slightly higher than the medium voltage MV, for example, from 2.0 to 2.5 [V] to the relay coupling line 34 when the power is turned on. Although not illustrated, the start-up circuit 46 is coupled to the voltage application line 33 and, for example, steps down and generates the start-up voltage SV2 based on the high voltage HV. After the power is turned on, the start-up voltage SV2 is generated for a period until the operation of a HV circuit 23 stabilizes.
The clamp circuit 47 is disposed between the relay coupling line 34 and the ground line 32 to prevent the voltage of the relay coupling line 34 from excessively increasing to, for example, 3 [V] or more. The bypass capacitor 48 is a capacitor disposed between the relay coupling line 34 and the ground line 32 to prevent a ripple of the voltage of the relay coupling line 34.
With the driving device according to the embodiment having the configuration, when both of the power supply units 13 and 14 start operating and the power supply voltage is supplied, first, the start-up circuits 45 and 46 immediately operate. Accordingly, the level of the voltage application line 35 increases up to the start-up voltage SV1, or the level of the relay coupling line 34 increases up to the start-up voltage SV2.
The reference voltage generating circuit 41 generates a reference voltage of the low voltage LV. The reference voltage is supplied to the positive input end of the operational amplifier 42, and the operational amplifier 42 compares it with a voltage of a negative input end. The operational amplifier 42 and the field effect transistor 43 operate as a voltage regulator. That is, since the field effect transistor 43 flows a current from the voltage application line 31 to the voltage application line 35 via between the source and the drain of the field effect transistor 43 such that the voltage of the positive input end becomes equal to the voltage of the negative input end. As a result, the voltage of the voltage application line 35 is stabilized to the low voltage LV equal to the reference voltage, and is applied to the LV circuit 22.
When the high voltage HV as the output voltage of the high voltage power supply unit 14 is applied to the HV circuits 23A and 23B and the HV output circuit 24 via the voltage application line 33, the respective HV circuits 23A and 23B and HV output circuit 24 operate. The operating current IHVA of the HV circuit 23A flows out to the ground line 36. On the other hand, the operating currents IHV2 and IHV3 of the HV circuit 23B and the HV output circuit 24 flow through the relay coupling lines 341 and 342, respectively, join together at the relay coupling line 34, and turn into the current IHVB, and the current IHVB flows into the recycling circuit 25. In the recycling circuit 25, the current IHVB flows out to the voltage application line 35 via between the source and the drain of the field effect transistor 44. The voltage of the voltage application line 35 is stabilized to the low voltage LV equal to the reference voltage and applied to the LV circuit 22. Accordingly, the resultant current of a part of the current IMV and the current IHVB flows through the LV circuit 22 as the current ILV. IHVB=IHV−IHVA.
Since the field effect transistor 44 performs the on/off operation according to an output voltage of the operational amplifier 42 together with the field effect transistor 43, the flowing of the operating current IHVB of the HV circuit 23B and the HV output circuit 24 into the voltage application line 35 is controlled between the source and the drain of the field effect transistor 44 such that the voltage of the voltage application line 35 is stabilized to the low voltage LV equal to the reference voltage. Since a voltage Vds between the source and the drain of the field effect transistor 44 is determined by the current flowing through between the source and the drain of the field effect transistor 44 and the gate potential of the field effect transistor 44, the electric potential of the relay coupling line 34 is determined by the voltage.
Depending on a balance between the current IHVB and the current ILV, there is a possibility that the current flows in both directions between the voltage application line 31 and the relay coupling line 34 via the field effect transistors 43 and 44, and therefore a size ratio of the field effect transistors 43 and 44 is set so as to prevent it, and the currents flowing through the respective field effect transistors 43 and 44 are optimized.
A consumed power A of the driving device according to the embodiment illustrated in
Consumed power A=medium voltage MV×(current IMV−current IHVB)+high voltage HV×current IHVA+high voltage HV×current IHVB (1)
For comparison with this consumed power A,
A consumed power B of the driving device illustrated in
Consumed power B=medium voltage MV×current IMV+high voltage HV×current IHV (2)
Assume that the current IMV is 40 [mA] and the current IHV is 35 [mA], as described above, since HV=7 [V], MV=1.8 [V], and LV=1.2 [V], using Formula (2), the consumed power B becomes:
Consumed power B=1.8 [V]×40 [mA]+7 [V]×35 [mA]=317 [mW]
On the other hand, assuming that the current IHVA flowing through the HV circuit 23A is 5 [mA], the resultant current IHVB of the currents IHV2 and IHV3 flowing through the HV circuit 23B and the HV output circuit 24 is 30 [mA], and as described above, HV=7 [V] and MV=1.8 [V], when the other voltage value and current value are equal to the values in the calculation of the above-described consumed power B, the consumed power A calculated using Formula (1) becomes:
Consumed power A=1.8 [V]×(40 [mA]−30 [mA])+7 [V]×5 [mA]+7 [V]×30 [mA]=263 [mW]
It is seen that the consumed power A of the driving device according to the embodiment illustrated in
In a case where the operations of the HV circuit 23B and the HV output circuit 24 change the current IHVB, the voltage of the relay coupling line 34 also varies. The clamp circuit 47 suppresses the voltage variation of the relay coupling line 34. The bypass capacitor 48 reduces a ripple voltage of the relay coupling line 34.
When the output of the HV output circuit 24 significantly varies especially, as equivalently illustrated in
The gate voltage of the field effect transistor 29 and its transistor size are determined by how much the electric potential increase in the relay coupling line 342 is reduced. In the embodiment, for example, a voltage higher than the low voltage LV by a gate threshold voltage Vt of the field effect transistor 29 is set.
Note that the resistor 30 restricts the current flowing through the field effect transistor 29 at the above-described increase in the electric potential of the relay coupling line 342, ESD surge, or the like to prevent the field effect transistor 29 from breaking.
In the respective embodiments described above, the example of the driving device that drives the organic EL display panel as the display panel is described, but the present invention is not limited to this. The present invention is also applicable to a display driving device that drives another display panel and operates then by application of power supply voltages of a plurality of different voltage levels.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2019-066090 | Mar 2019 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2020/014570 | 3/30/2020 | WO |
| Publishing Document | Publishing Date | Country | Kind |
|---|---|---|---|
| WO2020/203974 | 10/8/2020 | WO | A |
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| Number | Date | Country | |
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| 20220172675 A1 | Jun 2022 | US |
