CN100590704C - Current matching circuit and method - Google Patents

Abstract

The invention provides a current matching circuit and a method, and the method comprises the following steps: providing a plurality of current paths; dividing the plurality of current paths into W groups, each group comprising Q current paths; and matching currents on paths of the same group with each other, wherein W and Q are integers greater than or equal to 2. The invention relates to a current matching circuit, which comprises an X-layer tree-shaped hierarchical structure, wherein each layer comprises a plurality of matching elements, one matching element of the front layer corresponds to a plurality of matching elements of the secondary layer, and a certain number of matching elements form a group; each matching element in each group of the last layer controls the current on one path, and the currents on the paths of the same group are matched with each other, wherein X is an integer greater than or equal to 2. The invention controls whether the currents of the organic light emitting diodes are matched or not so as to achieve the optimal panel display effect.

Description

Current matching circuit and method

technical field

The present invention relates to a current matching circuit and method, in particular to a circuit and method for matching currents on a very large number of paths. The circuit and method are especially suitable for application in organic light-emitting panel circuits.

Background technique

Please refer to FIG. 1 , which is an example of a conventional passive organic light emitting panel control circuit. As shown in the figure, the circuit 10 includes n organic light emitting diodes OLED1-OLEDn, which are respectively located on the paths 11-1n. The conduction of each path 11-1n is controlled by the corresponding column signal RS1-RSn; in a passive organic light emitting panel, the column signal RS1-RSn usually makes each path conduct in turn, forming a plane image through visual persistence . The brightness of each organic light emitting diode OLED1-OLEDn corresponds to the amount of current on each path 11-1n, which are respectively controlled by the digital-to-analog conversion circuits DAC1-DACn. (For the sake of simplification, each digital-to-analog conversion circuit is connected to only one organic light-emitting diode in the shown figure, but in the actual panel, each digital-to-analog conversion circuit is usually connected to more than one organic light-emitting diode.) Each digital-to-analog conversion circuit DAC1-DACn can be a relatively simple type as shown in FIG. 2, or a cascoded type as shown in FIG. 3.

In detail, the brightness control method of the OLEDs OLED1-OLEDn is as follows. The current amount of the current source CS is proportionally mirrored into each digital-to-analog conversion circuit DAC1-DACn through the current mirror formed by the transistor Q and each transistor in each digital-to-analog conversion circuit DAC1-DACn. Using the digital switch control signal SW (also called the row signal column signal, or the area signal segment signal), it can determine which transistors in the digital-to-analog conversion circuit are turned on, and for example, the turn-on voltage of each transistor shown in Figure 2 can be turned on. The flow rates are designed to be 1x, 2x, 4x, and 8x respectively, so that 16-bit brightness changes can be generated according to the digital switch control signal SW.

As the size of the OLED panel gradually increases, the number of OLEDs used in it also increases accordingly; the number of OLED paths on the OLED panel may exceed hundreds or even thousands. The problem we are facing is that the amount of current on each path is not easy to completely match, resulting in uneven luminance of the panel, and in severe cases, there may even be differences visible to the naked eye. Therefore, it is necessary to provide a circuit and a method that can match the amount of current on a very large number of paths. However, if a matching control circuit is provided for each path separately, and the matching check and correction are performed on each path in a sample-and-hold manner, it will obviously make the circuit very large, and the checking procedure will take too long, which is not ideal .

Contents of the invention

In view of this, the present invention aims at the shortcomings of the above-mentioned prior art, and proposes a circuit that can match the currents on a large number of paths to solve the aforementioned problems without greatly increasing the size and complexity of the circuit.

The second object of the present invention is to provide a control circuit for an organic light emitting panel.

A third object of the present invention is to provide a method that can match the amounts of currents on a very large number of paths with each other.

To achieve the above purpose, in one embodiment of the present invention, a current matching circuit is provided, which includes a tree-like hierarchical structure of X layers, each layer includes a plurality of matching elements, and a matching element in the front layer corresponds to A plurality of matching elements in the second layer, the plurality of matching elements form a group; each matching element in each group of the last layer controls the current on one path, and the currents on the paths in the same group match each other, where X is An integer greater than or equal to 2.

In addition, according to another embodiment of the present invention, an organic light emitting panel control circuit is also provided, including: a first plurality of digital-to-analog conversion circuits, each controlling the current on a corresponding path, and each path has a corresponding organic light emitting diode, Wherein the first plurality of digital-to-analog conversion circuits are divided into W groups, Q in each group; W current sources, the current amount of which is controlled by the corresponding reference voltage input; and W current mirror circuits, the corresponding W The current amount of the current source is proportionally mirrored to the same group of Q digital-to-analog conversion circuits; wherein, the W current sources are divided into M groups, each group is N (W=M*N), and the same group of M The reference voltages of the current sources in the group are controlled so that the currents on the N*Q paths match each other; where M, N, Q, and W are integers, and N, Q, and W are all greater than or equal to 2.

In addition, according to another embodiment of the present invention, a current matching method is also provided, including the following steps: providing multiple current paths; dividing the multiple current paths into M groups, each group is N groups, and each group is Q lines; providing Matching components to each of the N groups; and matching the matching components of each group in the same group, wherein M, N and Q are integers greater than or equal to 2.

In the above-mentioned embodiments, the sampling and holding method can be used to sequentially control the currents on the paths of the same group in parallel in each group of the last layer.

In addition, in the above-mentioned embodiments, if current sources are used to control the current, the current sources can be grouped and each current source in the same group receives the same reference voltage, or each current source individually receives the corresponding reference voltage, and according to Calibration results to individually adjust the reference voltage of each current source.

In the following, specific embodiments will be described in detail, and it will be easier to understand the purpose, technical content, characteristics and effects of the present invention.

Description of drawings

FIG. 1 is a schematic circuit diagram of a conventional passive organic light emitting panel control circuit.

FIG. 2 is a schematic circuit diagram of a simpler type of digital-to-analog conversion circuit.

FIG. 3 is a schematic circuit diagram of a series-type digital-to-analog conversion circuit.

FIG. 4 is used to illustrate the tree-like hierarchical structure of the present invention.

FIG. 5 is a schematic circuit diagram showing one embodiment of the current matching circuit according to the present invention.

Fig. 6 is a schematic circuit diagram showing another embodiment of the current matching circuit according to the present invention.

Figure 7 shows a current source circuit using transistors in series.

FIG. 8 and FIG. 9 respectively illustrate the application of JFET.

Figure 10 shows that the variance among the amplifiers does not have a substantial impact on the component matching of the overall circuit.

Fig. 11 shows an example of a sample-and-hold circuit.

Figure 12 shows an example of the calibration circuit.

FIG. 13 shows an example of a sampling measurement circuit.

14 and 15 illustrate active OLED devices.

Explanation of symbols in the figure

10 Organic light-emitting panel control circuit (prior art)

11-1n path

20 Current matching circuit

41, 42 sample and hold circuit

50 Calibration circuit

51-5n multiplex circuit

60 Sampling measurement circuit

62 Analog to Digital Converter

70 sample and hold circuit

C01, C02 capacitor

CS, CS1-CSn current source

DAC1-DACn Digital to Analog Conversion Circuit

EA11-EA1n error amplifier

N-JFET, P-JFET N-junction transistor, P-junction transistor

OLED1-OLEDn organic light emitting diode

OP1, OP61 operational amplifier

Q, Qc, Q1-Qp, Q01, Q02 Transistors

R, R01-R0m, R11-R1n resistors

Rs1-Rsn serial signal

Detailed ways

First, the concept of the present invention will be explained. As mentioned in the "Background" paragraph, the number of OLED paths on a large OLED panel may exceed hundreds or even thousands, and it is difficult to perform matching correction one by one. Therefore, according to the present invention, a "tree-like hierarchical structure" is adopted to solve the above problems. Please refer to the example in FIG. 4 , assuming that the current matching circuit 20 uses a four-level tree structure, the first layer uses m elements, and the m elements are matched with each other; the second layer uses m groups of n elements each, and makes The n elements in each group are matched with each other; in the third layer, each element in the second layer is made to correspond to p elements respectively, and the p elements in the same group are matched with each other; in the fourth layer, Similarly, each element in the third layer corresponds to q elements, and the q elements in the same group are matched with each other, so that m*n*p*q current paths can be controlled finally, and m, None of n, p, and q need to be too large a number. Of course, FIG. 4 is only an example, and the number of layers and the number of components in each layer can be determined according to design requirements.

The specific embodiment of the concept shown in FIG. 4 is described as follows with two examples. Please refer to FIG. 5 and FIG. 6 , wherein FIG. 5 shows a three-level tree structure, and FIG. 6 shows a four-level tree structure. Please refer to FIG. 5 first. In this embodiment, the matching elements of the first layer are resistors R01-R0m, the matching elements of the second layer are resistors R11-R1n, and the third layer is the output stage. As shown in the figure, taking the first group of circuits of the second layer circuit as an example, the operational amplifier OP1 compares the voltage of the node A1 with the reference voltage VR0, and the generated output voltage VR1 is supplied to all the error amplifiers EA11-EA1n. Error amplifiers EA11-EA1n are part of corresponding current sources CS1-CSn. Each current source CS1-CSn respectively controls a group of output stage circuits, and each group of output stage circuits controls q current paths in the group according to the current amount of the corresponding current source. According to the above structure, the q current paths in each group of output stage circuits are controlled by the same current source to match each other, and because the number q is not very large, it is less likely to be too large due to the relationship between the circuit area and the winding. big difference. And control the current sources CS1-CSn of each group of output stage circuits, in the second layer circuit, through the matching between the resistors R11-R1n, and the output control of the operational amplifier OP1, all the current sources CS1-CSn are controlled to match each other . As for the voltages of the nodes A1-Am in the circuits of the second layer, they are matched through the resistors R01-R0m in the circuits of the first layer.

Please refer to FIG. 6 again, which is an example of a four-level tree structure. Compared with the previous embodiment, a third layer structure is added in this embodiment, and the original third layer output stage corresponds to the current fourth layer. As shown in the figure, in the third layer structure of this embodiment, taking the first group of circuits as an example, the same current source CS1 includes multiple groups of control transistors Q1-Qp, and cooperates with the error amplifier EA11 to generate p groups of the same current I1-Ip are supplied to p groups of output stage circuits.

In the embodiments of FIG. 5 and FIG. 6 , a cascoded transistor Qc can be added in the current source to further improve the accuracy of the current source, as shown in FIG. 7 .

The advantages of the above-mentioned embodiments over the prior art are explained as follows. In the above-mentioned embodiments of the present invention, except for the output stage, the matching elements of other layers can use elements with better matching performance, instead of using MOSFETs, such as the resistors used in the above-mentioned embodiments. Compared with MOSFETs, resistors have better matching, because the mismatching only comes from the variation in size, while the differences of MOSFETs are still related to surface effects such as threshold voltage and mobility. In today's semiconductor manufacturing process, the device size can be controlled within a fairly precise range, so the matching of resistors is much better than that of MOSFETs.

In addition, as shown in FIG. 8 and FIG. 9, according to the other two embodiments of the present invention, when using a series transistor structure (such as FIG. 3 or FIG. 7), it can be made by using a junction field effect transistor (JunctionFET, JFET) . The difference of JFET also only comes from the variation in size, so it also has better matching than MOSFET. The circuits shown in FIG. 8 and FIG. 9 can be applied to each layer of the circuit of the present invention, including the output stage.

Also, although the operational amplifier and error amplifier used in the embodiments of Fig. 5 and Fig. 6 have the problem of internal input bias voltage (input offset voltage), as shown in Fig. 10, the voltage at point A is much greater than the internal voltage of the amplifier. Input bias voltage Vofs, so the difference among the amplifiers will not have a substantial impact on the matching of the components of the overall circuit.

The above embodiments of the present invention are better than the prior art; and if it is necessary to further ensure that the currents of the paths in the output stage match each other, a sample-and-hold circuit can be provided in the circuit. For an example of a sample-and-hold circuit, please refer to the circuits 41 and 42 in Fig. 11. As shown in the figure, the currents on the transistors Q01, Q02, ... can be made the same by switching the switches SW1, SW2... The gate or source voltage across the gate or source is stored in the capacitors C01, C02, . . . , so that the transistors can be matched more precisely. Since the sample-and-hold circuit needs to switch the switches in turn in a similar scanning procedure, this method is time-consuming. Therefore, in the prior art, it is obviously impractical to sequentially scan hundreds or thousands of current paths. However, in the present invention, the current paths in each group can be scanned synchronously and in parallel, and the number of paths is small (may be only a single digit), so it can be completed within a limited time. The scan procedure of the sample-and-hold circuit can be performed at power-up, and/or periodically during circuit operation.

In addition to the above, according to the present invention, the input reference voltages of the error amplifiers can be used as a tool for further fine-tuning the matching conditions. In detail, please refer to FIG. 12 and compare FIG. 5 or FIG. 6. In the embodiments of FIG. 5 and FIG. 6, the operational amplifier OP1 has only one output level, and the reference voltage inputs of all error amplifiers EA11-EA1n are the same . However, in the embodiment in Fig. 12, a calibration circuit 50 is provided, which includes n multiplexing circuits MUX 51-5n. The operational amplifier OP1 has multiple output levels V1-Vx, and the multiplexing circuit 51-5n can determine which output level of the operational amplifier OP1 to select according to its selection signal input S. In this embodiment, the input S can be a multi-digit digital correction signal. By selecting the output level of the operational amplifier OP1, the matching of each group of circuits can be adjusted. The digital correction signal can be sampled and measured in the calibration procedure, for example. The current of a certain path in each group of circuits is generated. There are many methods for sampling and measuring the circuit. For example, as shown in the circuit 60 in Figure 13, the current signal is converted into a voltage signal, compared with the reference voltage Vc, and the difference is amplified by the operational amplifier OP61, and then used An analog-to-digital converter ADC 62 converts it into a digital signal. The circuit for sampling and measuring can be built in the current matching circuit, or set in other circuits matched with the current matching circuit (such as OLED panel circuit), or set in a tool specially used for calibration. The calibration procedure may be performed at power-up, and/or periodically during circuit operation.

In the above-mentioned embodiments, the organic light emitting diode control circuit in the passive organic light emitting panel is taken as an example, but the present invention can also be applied in the active organic light emitting panel. The organic light emitting diodes in the active organic light emitting panel are controlled in an active manner, as shown in FIG. 14 and FIG. 15 . In these two figures, whether the organic light emitting diodes light up and their brightness are controlled according to the current signal Idata. According to the present invention, it is also possible to control whether the currents of the organic light emitting diodes match to achieve the best panel display effect.

The present invention has been described above for preferred embodiments, and it can be seen from the above description that the matching accuracy and circuit simplification of the present invention are far better than those of the prior art. The above description is only to make those skilled in the art understand the contents of the present invention easily, and is not intended to limit the scope of rights of the present invention. As mentioned above, those skilled in the art should immediately conceive of various equivalent changes within the spirit of the invention. For example, in all the embodiments where two elements are directly connected, a circuit that does not affect the meaning of the signal can be inserted between them, such as a delay circuit, a switch circuit, and the like. As another example, arranging the OLED control circuit in a tree structure to control the matching of each current path is only one application of the present invention; the concept of the present invention can also be applied to other occasions that require current matching. Therefore, all equivalent changes or modifications made according to the concept and spirit of the present invention shall be included in the patent application scope of the present invention.

Claims (25)

1. current matching circuit comprises the tree-shaped hierarchical structure of X layer, and its each layer comprises a plurality of matched elements, and a matched element of anterior layer is corresponding to a plurality of matched elements of sublevel, and these a plurality of matched elements constitute one group; Each matched element is controlled electric current on the paths in each group of its last one deck, and the electric current on the path on the same group matches each other, and wherein X is the integer more than or equal to 2.

2. current matching circuit as claimed in claim 1, wherein each group of last one deck is controlled by a current source respectively.

3. current matching circuit as claimed in claim 2 comprises a plurality of transistors in the wherein same current source, cooperates same error amplifier, produces the identical electric current of many groups.

4. current matching circuit as claimed in claim 2, wherein this current matching circuit comprises every group of a plurality of current source of many groups therein in one deck, Nei current source is shared identical reference voltage on the same group, reference voltage on the same group produces according to a node voltage, the node that this node couples for this group one deck preceding with it.

5. current matching circuit as claimed in claim 4 is wherein imported this node voltage one operational amplification circuit and is compared with a given voltage, and with the output of this operational amplification circuit as above-mentioned reference voltage.

6. current matching circuit as claimed in claim 2, wherein this current matching circuit comprises every group of a plurality of current source of many groups therein in one deck, and each current source can be accepted to calibrate and adjust its magnitude of current.

7. current matching circuit as claimed in claim 6, wherein each current source is accepted corresponding reference voltage respectively, and the reference voltage of each current source can be according to selecting signal to adjust individually on the same group.

8. current matching circuit as claimed in claim 6, wherein each current source is accepted corresponding reference voltage respectively, and on the same group the reference voltage of each current source respectively be subjected to an operational amplification circuit one of output control, this operational amplification circuit has a plurality of outputs, can be according to selecting signal to select the corresponding relation of each current source and output.

9. current matching circuit as claimed in claim 1 more includes sample-and-hold circuit, to control the electric current on each paths.

10. current matching circuit as claimed in claim 9, wherein this sample-and-hold circuit is controlled the electric current on each paths abreast in regular turn in each group.

11. current matching circuit as claimed in claim 9, the every group of a plurality of transistor that wherein comprises many groups in the matched element of this last one deck, and this sample-and-hold circuit sampling maintenance in regular turn each transistorized grid or source voltage in a plurality of transistors on the same group abreast.

12. current matching circuit as claimed in claim 1, wherein said matched element comprise one of following or many persons: resistance, junction field effect transistor, metal-oxide half field effect transistor, error amplifier.

13. an organic luminous panel control circuit comprises:

More than first D/A conversion circuit, each controls the electric current on the respective path, has corresponding organic light emitting diode on each path, and wherein this more than first D/A conversion circuit is divided into the W group, every group Q;

W current source, its magnitude of current are controlled by the input of corresponding reference voltage respectively; And

W current mirroring circuit, with the magnitude of current of W current source of correspondence pro rata mirror to Q D/A conversion circuit on the same group;

Wherein, this W current source is divided into the M group, and every group N (W=M*N), the reference voltage of the interior current source on the same group of this M group is controlled, and the magnitude of current on the N*Q paths is matched each other;

M wherein, N, Q, W are integer, and N, Q, W are all more than or equal to 2.

14. organic luminous panel control circuit as claimed in claim 13, wherein, this M group current source is controlled by a corresponding matched element for every group, and this altogether M matched element match each other.

15. organic luminous panel control circuit as claimed in claim 13, wherein, each current source in this W current source respectively comprises P transistor, cooperates same error amplifier, produce the identical electric current of P group, in the P group wherein one group be supplied to an aforementioned W current mirroring circuit; And described organic luminous panel control circuit also comprises:

More than second D/A conversion circuit, each controls the electric current on the respective path, has corresponding organic light emitting diode on each path, and wherein this more than second D/A conversion circuit is divided into (P-1) group, every group Q; And

(P-1) * W current mirroring circuit, with (P-1) * W of W the correspondence that current source produced group magnitude of current pro rata mirror to Q D/A conversion circuit on the same group;

Thus, with the electric current on the control M*N*P*Q paths.

16. organic luminous panel control circuit as claimed in claim 13 also includes sample-and-hold circuit, to control the electric current on the Q paths abreast in regular turn in each W group.

17. organic luminous panel control circuit as claimed in claim 13, wherein the reference voltage of each current source can be according to selecting signal to adjust individually on the same group.

18. organic luminous panel control circuit as claimed in claim 17, wherein this selection signal is taken a sample from each path and is measured the electric current in one part path and produce.

19. a currents match method comprises following steps:

Many current paths are provided;

Should be divided into M group by many current paths, every group of N groups, every group of Q bar;

Matched element each group to the N group is provided; And

Matched element with each group in the group is matched each other,

Wherein M, N and Q are the integer more than or equal to 2.

20. currents match method as claimed in claim 19, wherein said matched element comprise one of following or many persons: resistance, junction field effect transistor, metal-oxide half field effect transistor, error amplifier.

21. currents match method as claimed in claim 19 more comprises: each path in each group, scanning on the same group in regular turn abreast, and sampling keeps the electric current on each path.

22. currents match method as claimed in claim 19, the step that the electric current on the path is on the same group matched each other comprises: for this group provides a current source, and with the magnitude of current of this current source pro rata mirror to path on the same group.

23. currents match method as claimed in claim 22 more comprises: for each group provides a current source, and current source is divided into M group, every group N, wherein M and N are the integer more than or equal to 2; Accept identical reference voltage with each current source of group.

24. currents match method as claimed in claim 22 more comprises: each group of organizing for N provides a current source, and each current source is accepted corresponding reference voltage individually, and can be according to selecting signal adjust individually with the reference voltage of each current source of group.

25. current matching circuit as claimed in claim 24, wherein this selection signal is taken a sample from each path and is measured the electric current in one part path and produce.

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