Differential sensing system and method

Abstract

To provide a system and method for sensing a drive current in a pixel.SOLUTION: In some embodiments, the system includes a first pixel, a second pixel, a differential sensing circuit, a reference current source, and a control circuit. The differential sensing circuit may have a first input, a second input and an output, the first input being connected to a node at which a reference current generated by the reference current source is subtracted from a first pixel current, the first pixel current including a current generated by the first pixel. The second input may be configured to receive a second pixel current, the second pixel current including a current generated by the second pixel. The output may be configured to produce an output signal on the basis of a difference between a current received at the first input and a current received at the second input.SELECTED DRAWING: Figure 2a

Description

[Technical field]

[0001] This application claims priority to and the benefit of U.S. Provisional Patent Application No. 62 / 887,395, entitled “FULLY DIFFERENTIAL FRONT-END WITH SENSING OF ADJACENT SUB-PIXELS,” filed on August 15, 2019, the entire contents of which are incorporated herein by reference.

[0002] One or more aspects of the embodiments according to the present invention relate to displays, and more particularly to measuring pixel characteristics. [Background technology]

[0003] A video display, such as that used in a computer or mobile device, may have a number of pixels and, within each pixel, a number of transistors, including a drive transistor configured to control a drive current through a display element, such as a light emitting diode (LED) (e.g., an organic light emitting diode (OLED)). Variations in the characteristics of the display's drive transistors, or changes in the characteristics of any one of the drive transistors over time, may degrade the quality of the image or video displayed by the display if they are not compensated for. To compensate for such variations or changes, it is useful to measure the characteristics of the drive transistors.

[0004] Therefore, there is a need for a system and method for measuring the characteristics of drive transistors in a display. Summary of the Invention

[0005] According to one embodiment of the present invention, there is provided a system including a first pixel, a second pixel, a differential sensing circuit, a reference current source, and a control circuit, the differential sensing circuit having a first input, a second input, and an output, the first input is connected to a node at which a reference current generated by the reference current source is subtracted from the first pixel current, the first pixel current comprising a current generated by the first pixel, the second input configured to receive a second pixel current, the second pixel current comprising a current generated by the second pixel, the output configured to generate an output signal based on a difference between the current received at the first input and the current received at the second input, and the control circuit configured to control the first pixel to turn on and the second pixel to turn off and to control the reference current source to generate the reference current.

[0006] In some embodiments, a display panel may include a first pixel and a second pixel, where the first pixel is located in a first column of the display panel and the second pixel is located in a second column of the display panel, and the first pixel and the second pixel may be adjacently located in the same row of the display panel.

[0007] In some embodiments, the first pixel current may further include leakage current from a plurality of pixels in the first column other than the first pixel, and the second pixel current may include leakage current from a plurality of pixels in the second column other than the second pixel.

[0008] In some embodiments, the differential sensing circuit may include a low pass current filter.

[0009] In some embodiments, the low pass current filter may include a fully differential amplifier.

[0010] In some embodiments, the low pass current filter may further include a common mode feedback circuit having at least a 1 MHz bandwidth.

[0011] In some embodiments, the differential sensing circuit may further include an integrator connected to the output of the low pass current filter.

[0012] In some embodiments, the display panel further includes a drive circuit, a first conductor of the display panel connected to the first pixel, the first conductor configured to carry a first pixel current in a first state of the system and to carry a current from the drive circuit to the first pixel in a second state of the system.

[0013] In some embodiments, the control circuit is configured, in the second state, to control the low pass current filter to operate in a reset state and to control the drive circuit to drive the first conductor as a reference voltage.

[0014] According to one embodiment of the present invention, there is provided a method of sensing a current in a display, the display including a first pixel, a second pixel, a differential sensing circuit, and a differential sensing circuit having a reference current source, a first input, a second input, and an output. The method includes providing a difference between a first pixel current and a reference current generated by a reference current source to the first input, the first pixel current comprising a current generated by the first pixel, providing a second pixel current to the second input, the second pixel current comprising a current generated by the second pixel, generating an output signal at an output based on the difference between the current received at the first input and the current received at the second input, turning on the first pixel, turning off the second pixel, and generating the reference current.

[0015] In some embodiments, the display includes a display panel including a first pixel and a second pixel, the first pixel being located in a first column of the display panel and the second pixel being located in a second column of the display panel, the first pixel and the second pixel being adjacently located in the same row of the display panel.

[0016] In some embodiments, the first pixel current further includes leakage current from a plurality of pixels in a first column other than the first pixel, and the second pixel current includes leakage current from a plurality of pixels in a second column other than the second pixel.

[0017] In some embodiments, the differential sensing circuit includes a low pass current filter.

[0018] In some embodiments, the low pass current filter includes a fully differential amplifier.

[0019] In some embodiments, the low pass current filter further includes a common mode feedback circuit having a bandwidth of at least 1 MHz.

[0020] In some embodiments, the differential sensing circuit further includes an integrator connected to the output of the low pass current filter.

[0021] In some embodiments, the display further includes a drive circuit, wherein a first conductor of the display panel is connected to the first pixel, and the first conductor is configured to carry a first pixel current in a first state of the system and to carry a current from the drive circuit to the first pixel in a second state of the system.

[0022] In some embodiments, the method further includes, in the second state, the low pass current filter operating in a reset state, and the drive circuit driving the first conductor as a reference voltage.

[0023] According to one embodiment of the present invention, there is provided a system comprising a first pixel, a second pixel, a differential sensing circuit, a reference current source, and a control means for controlling the differential sensing circuit having a first input, a second input, and an output, the first input being connected to a node at which a reference current generated by the reference current source is subtracted from the first pixel current, the first pixel current comprising a current generated by the first pixel, the second input configured to receive a second pixel current, the second pixel current comprising a current generated by the second pixel, the output configured to generate an output signal based on a difference between the current received at the first input and the current received at the second input, the control means configured to control the first pixel to turn on and the second pixel to turn off and to control the reference current source to generate the reference current.

[0024] In some embodiments, the system includes a display panel including a first pixel and a second pixel, where the first pixel is located in a first column of the display panel and the second pixel is located in a second column of the display panel, and the first pixel and the second pixel are adjacently located in the same row of the display panel. [Brief description of the drawings]

[0025] These and other features and advantages of the present invention will be appreciated and understood with reference to the specification, claims, and accompanying drawings. [Figure 1] 1 is a context diagram according to one embodiment of the present invention. [Figure 2a] 1 is a schematic diagram of a display panel and driving and sensing integrated circuits according to one embodiment of the present invention; [Figure 2b] 1 is a schematic diagram of a display panel and driving and sensing integrated circuits according to one embodiment of the present invention; [Figure 2c] 1 is a schematic diagram of a display panel and driving and sensing integrated circuits according to one embodiment of the present invention; [Figure 3a]FIG. 2 is a schematic diagram of a front end according to one embodiment of the present invention. [Figure 3b] FIG. 2 is a schematic diagram of a front end according to one embodiment of the present invention. [Figure 3c] FIG. 2 is a schematic diagram of a front end according to one embodiment of the present invention. [Figure 4] FIG. 1 is a schematic diagram according to one embodiment of the present invention. [Figure 5a] FIG. 1 is a schematic diagram according to one embodiment of the present invention. [Figure 5b] FIG. 1 is a schematic diagram according to one embodiment of the present invention. [Figure 5c] FIG. 1 is a schematic diagram according to one embodiment of the present invention. [Figure 5d] FIG. 1 is a schematic diagram according to one embodiment of the present invention. [Figure 5e] FIG. 1 is a schematic diagram according to one embodiment of the present invention. [Figure 5f] 4 is a graph of a transition function according to one embodiment of the present invention. [Figure 6] 2 is a flow chart according to an embodiment of the present invention. [Figure 7] FIG. 2 is a timing diagram according to one embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0026] The detailed description set forth below in conjunction with the accompanying drawings is intended as a description of exemplary embodiments of the systems and methods for sensing drive current in a pixel provided by the present invention, and is not intended as the only manner in which the present invention may be constructed or utilized. The description describes features of the present invention in conjunction with the illustrated embodiments. However, it should be understood that the same or equivalent functions and structures may be accomplished by different embodiments that are also intended to be within the scope of the present invention. As shown elsewhere in this application, like element reference numbers are intended to indicate like elements or features.

[0027] Referring to FIG. 1, in some embodiments, a display (e.g., a mobile device display) 105 may include a number of pixels arranged in rows and columns. Each pixel may be configured to generate light of one color (e.g., red, green, or blue) and may be part of a composite pixel that may include, for example, three such pixels and may be configured to generate any of a wide range of colors (in some descriptions, what is referred to herein as a "pixel" may instead be referred to as a "subpixel" and what is referred to herein as a "composite pixel" may instead be referred to as a "pixel"). Each pixel may include a drive circuit, for example a 7-transistor, 1-capacitor (7T1C) drive circuit as shown on the left side of FIG. 1 or a 4-transistor, 1-capacitor (4T1C) drive circuit as shown at the bottom of FIG. 1. In a 4T1C drive circuit, a drive transistor 110 (with gate-source voltage controlled by a capacitor 115) controls the current through a light emitting diode 120 when the pixel is to emit light. The upper pass-gate transistor 125 may be used to selectively connect the gate of the drive transistor 110 (and one end of the capacitor 115) to a power supply voltage, and the lower pass-gate transistor 130 can be used to selectively connect the drive sense conductor 135 to a source node 140 (a node connected to the source of the drive transistor 110, the anode of the light-emitting diode 120, and the other end of the capacitor 115).

[0028] A pixel drive and sense circuit 145 (described in more detail below) may be coupled to the drive sense conductor 135. The pixel drive and sense circuit 145 may include drive amplifiers and sense circuits configured to be selectively coupled to the drive sense conductors 135, one at a time. When current flows through the drive transistor 110 and the lower pass-gate transistor 130 is turned off, the drive sense conductor 135 may be disconnected from the source node 140 and current may flow through the light emitting diode 120, causing the light emitting diode 120 to emit light. When the lower pass-gate transistor 130 is turned on and the drive sense conductor 135 is driven at a lower voltage than the cathode of the light emitting diode 120, the light emitting diode 120 is reverse biased and any current flowing in the drive sense conductor 135 may flow to the pixel drive and sense circuit 145 where it is sensed. This sensed current may be compared to a desired current (e.g., the current that an ideal or nominal transistor would drive with the same gate-source voltage) and the extent to which the sensed current differs from the ideal current, and steps are taken to compensate for the discrepancy (e.g., the gate-source voltage is adjusted).

[0029] Referring to FIG. 2a, in some embodiments, the current of any pixel may be sensed in a differential manner for improved accuracy. For example, if the current driven by the drive transistor 110 of the pixel on the left side of FIG. 2a (sometimes referred to as the "odd pixel") is sensed, the odd pixel may be turned on (charging the odd pixel's capacitor and turning on the odd pixel's drive transistor 110), and the drive transistor 110 of the pixel on the right side of FIG. 2a (sometimes referred to as the "even pixel") may be turned off (discharging the even pixel's capacitor and turning off the even pixel's drive transistor 110), and the difference between the two corresponding currents flowing from each of the two conductors, which may be referred to as "column conductors" 205, may be measured. Each column conductor 205 may be connected to all pixels in a column of the display. As a result, even if all pixels except the identified odd pixel are turned off, the total leakage current at the other pixels may be significant. As long as the leakage currents of adjacent columns (including even pixels) are identical, the contribution of the leakage current to the current flowing in the column conductor connected to the odd pixel can be cancelled out when the difference between the currents in the two column conductors 205 is sensed.

[0030] The SCAN1, SCAN2, and EMIT control lines are provided for each row and may have different timing between rows. As previously mentioned, differential sensing is used so that half of the pixels in a row are sensed per operation. There is no distinction between odd and even pixels as the same set of gate control signals are applied to odd and even pixels. Each digital-to-analog converter and associated drive amplifier 220 may be used to drive the column conductor 205 to charge the pixel's capacitor, and to generate a reference current when the current driven by the drive transistor 110 is being sensed. This may be accomplished using a multiplexer as shown in the drawing. The embodiment of FIG. 1 does not include this feature, but instead includes two separate digital-to-analog converters.

[0031] Referring to FIG. 2b, in some embodiments, when the circuit (also referred to as the control circuit) is in drive mode, the voltage at the gate of each pixel's drive transistor 110 is ELVSS and the source of each pixel's drive transistor 110 is driven with a voltage of ELVSS-VDRIVE, such that VGS=ELVSS-(ELVSS-VDRIVE)=VDRIVE.

[0032] The light emitting transistor of each pixel may be maintained in a turned off state.

[0033] In this process, the respective VDRIVE may be stored in the pixel capacitor of each pixel. When sensing odd pixels, the source of the drive transistor 110 of the even pixels may be driven by ELVSS, so that the even pixels are turned off as described above.

[0034] 2c, in some embodiments, when the circuit is in the sense mode, the upper pass-gate transistor 125 (FIG. 1) is turned off and the gate of the drive transistor 110 is floated to keep the charge on each pixel's capacitor constant. The source of each pixel's drive transistor 110 is driven (e.g., at VREF slightly less than ELVSS) and each light-emitting diode 120 is reverse biased and no current flows through the light-emitting diode 120. Because each pixel's emitter transistor is turned on and the light-emitting diode 120 is reverse biased, all current driven by the pixel's drive transistor 110 flows through the respective column conductor 205 to the sense circuit. In this mode, the digital-to-analog converter and the drive amplifier 220 (also referred to as a reference current source) connected thereto may generate a reference current IREF. In some embodiments, the reference current is generated by controlling the digital-to-analog converter and drive amplifier 220 to generate a voltage ramp that is applied to the capacitor to provide a current according to the following Equation 1:

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[0035] When sensing pixel current, various sources of error may be involved. For example, referring to FIG. 3a, when the current is sensed with a single-ended front-end, the ground noise (V g ) may be connected to the output signal of the amplifier.

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[0036] For display systems, C P is C i As a result, ground noise (V g ) may be very large.

[0037] Referring to FIG. 3b, pseudo-differential sensing (sensing the difference between on and off pixels using a pseudo-differential front-end as described above) involves detecting the column capacitance (C P ) are effective, but even a mismatch between 1% and 5% may be ineffective. Also, noise induced common mode currents may be excessive and the dynamic range requirements of the front end may increase.

[0038] Referring to FIG. 3c, when the current is sensed with a single-ended front end, the thermal noise (V r ) may be connected to the output signal of the amplifier.

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[0039] The resistance of the column conductor 205 (resistance R P The effect of this wideband thermal noise generated by the (DC) signal being sensed (I pixel) or may be attenuated using a front end that includes a low pass filter. An example of such a low pass filter (integrator) is shown in Figure 3c.

[0040] In operation, the front-end integrator may be reset before a sensing operation. Before each sensing operation, a drive operation may occur in which the drive amplifier 220 (FIGS. 2a-c) drives the column conductor 205 to a set voltage. Before a sensing operation begins, the voltage on the column conductor 205 may be restored to VREF. Another problem associated with the circuit of FIG. 3c is that because the column conductor 205 has a large capacitance to ground, it may take a long time for the sense amplifier (reset mode) to drive the voltage on the column conductor 205 to VREF.

[0041] FIG. 4 shows a differential sensing circuit 400 having two inputs for sensing the difference between the currents (each current minus a respective reference current) from a first pixel (e.g., an odd pixel in FIGS. 2a-2c) and a second pixel (e.g., an even pixel in FIGS. 2a-2c). The differential sensing circuit has a two-stage structure with a low-pass current filter 405 (e.g., a first integrator as shown in the figures) as a first stage and an integrator 410 (e.g., a second integrator as shown in the figures) as a second stage. The integrator 410 may be connected to the low-pass current filter 405 by two mirroring capacitors 425. The low-pass current filter 405 and the integrator 410 may each include a fully differential operational amplifier with a capacitor (or "feedback capacitor") in a respective feedback path. As mentioned above, the circuit may be used to perform differential sensing between two adjacent pixels (e.g., a red pixel and a green pixel of a composite pixel including three pixels, a red pixel, a green pixel, and a blue pixel, or a green pixel and a blue pixel of a composite pixel). A wideband common-mode feedback amplifier 415 (which may have an open loop bandwidth of 10 MHz to 100 MHz) is fed back around the low pass current filter 405 .

[0042] For ease of explanation, the circuit of Figure 4 shows both the drive amplifier 220 and the differential sensing circuit 400 connected simultaneously to the pixel 420 through the respective resistor-capacitor networks used to model the column conductors 205. However, in some embodiments, there is only one column conductor 205 per pixel, and either the drive amplifier 220 or the differential sensing circuit 400 is connected to the column conductor 205 at any given time (as shown in Figures 2A-2C, a multiplexer is used to select whether the drive amplifier 220 or the differential sensing circuit is connected to the column conductor 205 at any given time).

[0043] In some embodiments, the lowpass current filter 405 and the integrator 410 may be fully differential. As used herein, a fully differential circuit is a circuit that does not compare a signal to ground (unlike a single-ended or pseudo-differential amplifier). Instead, for example, each differential gain stage of a fully differential amplifier directly compares the two signals being processed to each other.

[0044] The wideband common-mode feedback amplifier 415 may calculate a common-mode output signal at the output of the lowpass current filter 405 (e.g., a resistor network can be used to calculate the average of the voltages at the two output conductors) and feed back to the common-mode input of the lowpass current filter 405. The common-mode input may be, for example, (i) the gate of a current source (or “tail current source”) connected to the two sources of the differential pair of the lowpass current filter 405, or (ii) a node connected to two corresponding transistors of the load network of the differential pair of the lowpass current filter 405.

[0045] In some embodiments, the performance of the circuit of Figure 4 is superior to that of a pseudo-differential circuit (eg, as shown in Figure 3b). This can be shown as follows.

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[0046] FIG. 5c shows the circuit used to analyze the low pass current filter 405 of FIG. 4. In this circuit,

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[0047] Referring to FIG. 5d, the differential impedance is:

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[0048] Referring to FIG. 5e, the following may be approximate component values.

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[0049] TIFF0007658722000014.tif9164

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[0050] For even higher frequencies, the following results are obtained:

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[0051] The resulting transfer function is shown in Figure 5f. At low frequencies,

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[0052] f 3dB For frequencies below 100 MHz, the differential impedance looking into the input terminals may be the impedance of a large capacitor Ci*A (opamps use a relatively small capacitor C i appears much larger, i.e., C i *A). It may be advantageous for this apparent size to be much larger than the capacitance of the channel itself, i.e., the impedance looking into the low pass current filter is significantly smaller than the impedance of the channel itself. In this situation, most of the current driven by the drive transistor 110 flows into the low pass current filter. 3dB and f ug For frequencies between 0 and 1, the differential impedance probing the input terminals can have the characteristics of a resistor.

[0053] 6 shows a flow chart of a method for sensing using the circuitry described herein. First, in step 605, odd pixels are sensed using the desired V gs and even pixels are driven with V, which corresponds to black (no light emission from the light emitting diode 120). gsThen, in step 610, the upper pass-gate transistor 125 of each pixel is turned off, and both pixels are driven with V gs 410) to reset the column conductors 205 (this drive phase does not affect the charge on the pixel's capacitors because the upper pass-gate transistor 125 of each pixel is turned off). Then, in step 615, the circuit enters the sense mode. During this phase, the front-end is in reset mode; that is, the switches (e.g., transistor switches) connected across the low-pass current filter 405 and the feedback capacitors of the integrator 410 are closed (e.g., the transistors are turned on) and these capacitors are discharged during reset and remain discharged. The circuit may remain in reset mode until the sense front-end voltage and the voltage on the column conductors 205 are identical. The effect of this state may be to sample the front-end offset. During the reset mode, the pixel current may be on or off (i.e., the control signal EMIT_ENB may be high or low). Then, in step 620, the front-end is released from reset mode (e.g., the transistors connected to the feedback capacitors are turned off) and integration (of the sensed current) begins. Finally, in step 625, the output of the integrator 410 is sampled.

[0054] FIG. 7 is a timing diagram illustrating the control signals for cycling through the states shown in FIG. 6. The reference numbers of FIG. 6 are repeated to show the correspondence between the steps of FIG. 6 and the periods of FIG. 7. Other features not shown in FIG. 7 may be present in some embodiments. For example, a wait state 705 (in which the low pass current filter 405 is placed out of reset while the integrator 410 is in the reset state) may precede the integrate state 620 (which may begin correspondingly thereafter). As another example, in some embodiments, the integrate state is partitioned into two parts, one in which both the even and odd pixels are turned off (by turning off the lower pass-gate transistor 130 using the SCAN2_EN control signal) and the other in which both the even and odd pixels are turned on (by turning on the lower pass-gate transistor 130 using the SCAN2_EN control signal). During the transition between the two parts, the polarity of the connection between the low pass current filter 405 and the integrator 410 is reversed, and the output of the integrator at the end of the second part is the difference between the current when the pixel is on and the current when the pixel is off (of which the latter may include contributions of no interest (e.g., leakage currents from other pixels whose effects are magnified are not the same for even and odd pixels)). Thus, operation in this state may reduce errors due to currents that are not the sensed currents (the currents driven by the drive transistors 110 of odd pixels). A hold state 710 may also be present while the low pass current filter 405 is disconnected from the integrator 410, reducing errors that may be caused as a result of imperfect timing when the pixel current and the reference current turn on. The SENSE_RESETB and SENSE_INTEG_EN signals are used to control the reset state of the low pass current filter and the integrator, respectively. The SENSE_INTEG_EN signal may remain low until the end of the wait state 705, if a wait state is used.

[0055] As used herein, an "input" of a circuit may include one or more conductors and may include additional inputs. For example, a differential input may include a first conductor identified as a non-inverting input and a second conductor identified as an inverting input. Similarly, an "output" of a circuit as used herein may include one or more conductors and may include additional outputs. For example, a differential output may include a first conductor identified as a non-inverting output and a second conductor identified as an inverting output. As used herein, when a first component is described as being "selectively connected" to a second component, the first component may be connected to the second component by a switch (e.g., a transistor switch) and depending on the state of the switch, the first component may be connected to or disconnected from the second component.

[0056] Although the present invention provides an example of a fully differential circuit in an application used for sensing pixel circuits, the invention is not limited to such applications and the systems and methods disclosed herein can be used in other applications, such as, for example, biomedical applications.

[0057] In some embodiments, control of circuits such as the various control signals and digital-to-analog converters is performed by a processing circuit. The term "processing circuit" is used herein to mean any combination of hardware, firmware, and software used to process data or digital signals. Processing circuit hardware may include, for example, application specific integrated circuits (ASICs), general-purpose or special-purpose central processing units (CPUs), digital signal processors (DSPs), graphics processing units (GPUs), and programmable logic devices such as field programmable gate arrays (FPGAs). In a processing circuit as used herein, each function is performed by general-purpose hardware such as a CPU configured to execute instructions stored in a non-transitory storage medium, i.e., hard-wired hardware configured to perform that function. A processing circuit may be fabricated on a single printed circuit board (PCB) or distributed across several interconnected PCBs. A processing circuit may include other processing circuits. For example, a processing circuit may include two processing circuits, an FPGA, and a CPU, interconnected on a PCB.

[0058] It will be understood that although terms such as "first," "second," and "third" are used herein to describe various elements, components, regions, layers, and / or sections, these elements, components, regions, layers, and / or sections should not be limited by these terms. These terms are used only to distinguish one element, component, region, layer, or section from another element, component, region, layer, or section. Thus, a first element, component, region, layer, or section described herein can be referred to as a second element, component, region, layer, or section without departing from the spirit and scope of the inventive concept.

[0059] Spatially relative terms such as "below," "beneath," "lower," "down," "above," and the like are used herein for ease of description to describe the relationship of one element or feature to other elements or features as shown in the figures. It will be understood that such spatially relative terms are intended to include different orientations of the device in use or operation in addition to the orientation shown in the figures. For example, if the device in the figures is turned over, an element described as "beneath" or "beneath" or "below" the other element or feature would be oriented "above" the other element or feature. Thus, the exemplary terms "beneath" and "beneath" can include both an orientation of above and below. The device can be otherwise oriented (e.g., rotated 90 degrees or at other orientations) and the spatially relative descriptions used herein should be interpreted accordingly. It is also understood that when a layer is referred to as being "between" two layers, this may be the only layer between the two layers or there may be one or more intervening layers.

[0060] The terms used herein are intended to describe specific embodiments and are not intended to limit the concept of the invention. The terms "substantially," "about," and similar terms are used herein as terms of approximation, not as terms of degree, to account for inherent deviations in measurements or calculations that one of ordinary skill in the art can appreciate. The term "majority" as used herein means at least half of an item when applied to a plurality of items.

[0061] As used herein, the singular forms "a" and "an" are intended to include the plural unless the context indicates otherwise. It will be further understood that the terms "comprise" and / or "comprising" as used herein indicate the presence, but do not exclude the presence, of the stated features, integers, stages, operations, components and / or elements. Or may include the addition of one or more other features, integers, stages, operations, elements, components and / or groups. As used herein, the term "and / or" includes any and all combinations of one or more of the associated listed items. A phrase such as "at least one" when preceding a list of elements modifies the entire list of elements and does not modify the individual elements of the list. Additionally, the use of "may" when describing an embodiment of the inventive concept means "one or more embodiments of the invention." Additionally, the term "exemplary" is intended to refer to an example or illustration. As used herein, the terms "use," "using," and "used" may be considered synonymous with the terms "utilize," "utilizing," and "utilized," respectively.

[0062] When an element or layer is referred to as "on," "connected," "coupled," or "adjacent to" another element or layer, it is understood that it may be directly on, connected, coupled, or adjacent to the other element or layer, or there may be one or more intervening elements or layers. In contrast, when an element or layer is referred to as "directly on," "directly connected," "directly coupled," or "immediately adjacent to" another element or layer, there are no intervening elements or layers present.

[0063] Any numerical range recited herein is intended to include all subranges of the same numerical precision contained within the recited range. For example, a range "1.0 to 10.0" includes all subranges between (and including) the recited minimum of 1.0 and the recited maximum of 10.0, i.e., having a minimum of 1.0 or greater and a maximum of 10.0 or less, such as, for example, 2.4 to 7.6. Any maximum numerical limitation recited herein is intended to include all lower numerical limitations contained therein, and any minimum numerical limitation recited herein is intended to include all higher numerical limitations contained therein.

[0064] While exemplary embodiments of the system and method for sensing drive current in a pixel have been specifically described and illustrated herein, many variations and modifications will be apparent to those skilled in the art. It should therefore be understood that the system and method for sensing drive current in a pixel constructed according to the principles of the present invention may be embodied other than as specifically described herein. The present invention is also defined in the following claims and equivalents thereof.

Claims

1. A first pixel; A second pixel; and A differential sensing circuit; A reference current source; A control circuit, The differential sensing circuit comprises: First input, a second input, and an output; the first input is connected to a node at which a reference current generated by the reference current source is subtracted from a first pixel current; the first pixel current comprises a current generated by the first pixel; the second input configured to receive a second pixel current; the second pixel current comprises a current generated by the second pixel; the output is configured to generate an output signal based on a difference between a current received at the first input and a current received at the second input; The control circuit includes: Controlling the first pixel to be turned on; Controlling the second pixel to be turned off; configured to control the reference current source to generate the reference current; The differential sensing circuit comprises: A low pass current filter; a common mode feedback amplifier for calculating a common mode output signal at an output of the low pass current filter and feeding the common mode output signal back to an input corresponding to a differential pair of the low pass current filter; system.

2. a display panel including the first pixel and the second pixel; a first pixel located in a first row of the display panel; a second pixel located in a second row of the display panel; The system of claim 1 , wherein the first pixel and the second pixel are adjacently located in the same row of the display panel.

3. the first pixel current further includes leakage current from a plurality of pixels in the first column other than the first pixel; 3. The system of claim 2, wherein the second pixel current comprises leakage current from pixels in the second column other than the second pixel.

4. The system of claim 3 , wherein the low pass current filter comprises a fully differential amplifier.

5. The system of claim 4 , wherein the common mode feedback amplifier has a bandwidth of at least 1 MHz.

6. The system of claim 5 , wherein the differential sensing circuit further comprises an integrator connected to the output of the low pass current filter.

7. 1. A method of sensing current in a display, comprising: The display comprises: A first pixel; A second pixel; and A differential sensing circuit; A reference current source; a differential sensing circuit having a first input, a second input, and an output; The method comprises: providing a difference between a first pixel current and a reference current generated by the reference current source to the first input; providing a second pixel current to the second input; generating an output signal at the output based on a difference between a current received at the first input and a current received at the second input; turning on the first pixel; turning off the second pixel; generating the reference current; the first pixel current comprises a current generated by the first pixel; the second pixel current comprises a current generated by the second pixel; The differential sensing circuit comprises: A low pass current filter; a common mode feedback amplifier that calculates a common mode output signal at an output of the low pass current filter and feeds it back to an input corresponding to a differential pair of the low pass current filter.

8. the display includes a display panel including the first pixel and the second pixel; the first pixel is located in a first row of the display panel; the second pixel is located in a second row of the display panel; The method of claim 7 , wherein the first pixel and the second pixel are adjacently located in the same row of the display panel.

9. the first pixel current further includes leakage current from a plurality of pixels in the first column other than the first pixel; 9. The method of claim 8, wherein the second pixel current comprises leakage current from pixels in the second column other than the second pixel.

10. The method of claim 9 , wherein the low pass current filter comprises a fully differential amplifier.

11. The method of claim 10 , wherein the common mode feedback amplifier has a bandwidth of at least 1 MHz.

12. The method of claim 11 , wherein the differential sensing circuit further comprises an integrator connected to the output of the low pass current filter.

13. A first pixel; A second pixel; and A differential sensing circuit; A reference current source; control means for controlling a differential sensing circuit having a first input, a second input, and an output; the first input is connected to a node at which a reference current generated by the reference current source is subtracted from a first pixel current; the first pixel current comprises a current generated by the first pixel; the second input configured to receive a second pixel current; the second pixel current comprises a current generated by the second pixel; the output is configured to generate an output signal based on a difference between a current received at the first input and a current received at the second input; The control means Controlling the first pixel to be turned on; Controlling the second pixel to be turned off; configured to control the reference current source to generate the reference current; The differential sensing circuit comprises: A low pass current filter; a common mode feedback amplifier for calculating a common mode output signal at an output of the low pass current filter and feeding the common mode output signal back to an input corresponding to a differential pair of the low pass current filter; system.

14. The system includes a display panel including the first pixel and the second pixel; a first pixel located in a first row of the display panel; a second pixel located in a second row of the display panel; 14. The system of claim 13, wherein the first pixel and the second pixel are adjacently located in the same row of the display panel.

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