CN113129816A - 电流积分器及其信号处理系统 - Google Patents

电流积分器及其信号处理系统 Download PDF

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CN113129816A
CN113129816A CN202011045036.3A CN202011045036A CN113129816A CN 113129816 A CN113129816 A CN 113129816A CN 202011045036 A CN202011045036 A CN 202011045036A CN 113129816 A CN113129816 A CN 113129816A
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operational amplifier
input stage
current integrator
current
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CN113129816B (zh
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林介安
郭彦儒
程智修
黄如琳
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Novatek Microelectronics Corp
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Abstract

本发明公开了一种电流积分器及其信号处理系统，所述电流积分器包括一运算放大器、一积分电容及一偏移消除电容。该运算放大器包括一第一输入级及一第二输入级，该第一输入级耦接于该电流积分器的一输入端，该积分电容耦接于该运算放大器的该第一输入级与该电流积分器的一输出端之间，该偏移消除电容耦接于该运算放大器的该第二输入级。

Description

电流积分器及其信号处理系统
技术领域
本发明涉及一种电流积分器(current integrator)及其信号处理系统，尤其涉及一种可对有机发光二极管(Organic Light-Emitting Diode，OLED)面板进行补偿的电流积分器及其相关的信号处理系统。
背景技术
有机发光二极管(Organic Light-Emitting Diode，OLED)为发光二极管(Light-Emitting Diode，LED)的一种，其电致发光层是由有机化合物所构成，该有机化合物可因接收到电流而发光。有机发光二极管广泛应用于电子装置的显示屏，例如电视屏幕、计算机显示器、各类便携设备例如移动电话、手持式游戏主机及个人数字助理(Personal DigitalAssistant，PDA)等。其中，主动矩阵式有机发光二极管(Active Matrix OLED，AMOLED)为目前有机发光二极管显示器的主流，主动矩阵式有机发光二极管可由薄膜晶体管(Thin-FilmTransistor，TFT)来进行驱动，并包括存储电容用来维持像素的状态，以应用于大尺寸及高分辨率的显示器。
当有机发光二极管面板经过一段长时间的运作之后，在面板上不同像素之间，其部分参数(如薄膜晶体管的临界电压(threshold voltage))可能面临不同程度的衰减或变异。为了改善有机发光二极管面板的画面一致性，需针对以上参数的变化进行补偿，因此需要感测该些参数的特性以判断每一像素单元所需的补偿程度。一般来说，在感测过程中，有机发光二极管像素的衰减或变异信息可作为一电流信号被读出，其可通过电流积分器(current integrator)进行接收。电流信号所对应的电荷可持续累积并存储在电流积分器中的存储电容，随后以模拟数字转换器(Analog-to-Digital Converter，ADC)可识别的信号(如电压信号或电流信号)加以输出。然而，电流积分器通常具有一运算放大器，其往往伴随着输入偏移，导致电流积分器的积分结果产生误差。
以上问题通常借由一偏移消除技术来解决。详细来说，可将一偏移消除电容耦接于运算放大器的差分输入端之间来达到消除偏移的目的，从而消除积分过程中的偏移。然而，由于工艺和电路组件的不理想特性，使得电容存储的电荷易受到各种因素的影响，如电荷注入(charge injection)、时钟馈通(clock feedthrough)、及漏电流等，这些噪声会受到运算放大器的放大之后耦合到电流积分器的输出端。此外，偏移消除电容应能够存储积分期间的偏移信息，因而需具备足够的存储容量，因此，电容的尺寸无法过小，否则无法在积分期间内完成关于偏移的电荷释放。用于存储偏移信息的大尺寸电容是考量成本降低的需求下一项重要的问题。
发明内容
因此，本发明的主要目的即在于提供一种新式电流积分器(current integrator)及其相关的信号处理系统，以解决上述问题。
本发明的一实施例公开了一种电流积分器，其包括一运算放大器、一积分电容及一偏移消除电容。该运算放大器包括一第一输入级及一第二输入级，该第一输入级耦接于该电流积分器的一输入端，该积分电容耦接于该运算放大器的该第一输入级与该电流积分器的一输出端之间，该偏移消除电容耦接于该运算放大器的该第二输入级。
本发明的另一实施例公开了一种信号处理系统，其包括一模拟数字转换器(Analog-to-Digital Converter，ADC)及多个电流积分器。该多个电流积分器中的每一电流积分器都耦接于该模拟数字转换器，且包括一运算放大器、一积分电容及一偏移消除电容。该运算放大器包括一第一输入级及一第二输入级，该第一输入级耦接于该电流积分器的一输入端，该积分电容耦接于该运算放大器的该第一输入级与该电流积分器的一输出端之间，该偏移消除电容耦接于该运算放大器的该第二输入级。
附图说明
图1为本发明实施例一信号处理系统的示意图。
图2为一般电流积分器的示意图。
图3为本发明实施例一电流积分器的示意图。
图4A示出了操作在偏移消除阶段的电流积分器。
图4B示出了操作在积分阶段的电流积分器。
图5A及5B为运算放大器的一示例性电路结构的示意图。
其中，附图标记说明如下：
10 信号处理系统
100 模拟数字转换器
CI_1～CI_N、20、30 电流积分器
IIN_1～IIN_N、IIN 输入电流信号
DOUT 数字输出数据
200、300 运算放大器
Cint 积分电容
CAZ 偏移消除电容
SW1～SW5 开关器
VOS、VOS1、VOS2 输入偏移电压
VREF 参考电压
SW_R1～SW_R3 重置开关器
SW_IN 输入开关器
I1、I2 输入级
VOUT 输出电压
VCAZ 偏移消除电容的跨压
具体实施方式
请参考图1，图1为本发明实施例一信号处理系统10的示意图。信号处理系统10可用来接收并处理来自于有机发光二极管(Organic Light-Emitting Diode，OLED)面板的输入电流信号，用来进行有机发光二极管面板上各种参数的补偿，例如有机发光二极管的亮度和薄膜晶体管(Thin-Film Transistor，TFT)的临界电压(threshold voltage)等。如图1所示，信号处理系统10包括多个信道，分别用来接收来自于有机发光二极管面板上不同像素的输入电流信号IIN_1～IIN_N。其中，每一信道都包括一电流积分器(currentintegrator)CI_1～CI_N，用来对输入电流进行一段特定时间的积分，并输出积分结果。信号处理系统10可包括一模拟数字转换器(Analog-to-Digital Converter，ADC)100，用来将所接收的积分电流信号转换为数字输出数据DOUT，数字输出数据DOUT可作为后续图像数据的补偿信息。
如图1所示，模拟数字转换器100耦接于每一电流积分器CI_1～CI_N，可依序从电流积分器CI_1～CI_N接收输出信号。在一实施例中，每一信道还可包括一开关器(为求简化而未示于图1)，开关器耦接于电流积分器CI_1～CI_N的输出端，使得模拟数字转换器可通过开关器的控制依序接收积分结果。
请参考图2，图2为一般电流积分器20的示意图。如图2所示，电流积分器20包括一运算放大器200、一积分电容Cint、一偏移消除电容CAZ及开关器SW1～SW5。开关器SW1～SW2、积分电容Cint和运算放大器200可共同运作以实现电流信号的积分。通过开关器SW1～SW2的切换电容操作，运算放大器200可在一阶段内进行重置，并且在另一阶段接收输入电流信号IIN，其中，输入电流信号IIN被接收之后存储在积分电容Cint。需注意的是，运算放大器200通常具有一输入偏移电压VOS，其在图2中以一电压源来表示，输入偏移电压VOS造成积分结果偏移其正常值。另外，每一信道上的电流积分器20的运算放大器200可能存在不同的偏移值大小，使得积分结果受到不同程度的偏移影响，导致有机发光二极管像素的感测结果不佳。因此，开关器SW3～SW5和偏移消除电容CAZ可共同运作以消除输入偏移电压VOS。举例来说，通过切换电容操作，可在一阶段内将偏移信息存储在偏移消除电容CAZ中，接着在另一阶段耦合到电流积分器20的输出端以消除偏移。在此例中，运算放大器200包括一差分输入级，其负输入端接收输入电流信号IIN而正输入端接收一参考电压VREF。
由于偏移消除电容CAZ耦接至运算放大器200的输入端，使得偏移消除电容CAZ上的噪声会受到运算放大器200的放大而影响电流积分器20的输出信号。此外，偏移消除电容CAZ的切换电容电路所产生的电荷注入(charge injection)效应也通过运算放大器200的放大并耦合到电流积分器20的输出端，从而影响输出结果。再者，偏移消除电容CAZ须在一积分期间内用来存储偏移信息，因此，电容的尺寸不能过小，否则可能造成相关于偏移信息的电荷在积分期间内漏失，在此情况下，偏移消除电容CAZ应具有足够的大小。由于信号处理系统的每一信道都具有一电流积分器，因此，较大尺寸的偏移消除电容CAZ导致成本难以降低。
在一实施例中，为避免或减少偏移消除电容CAZ中的噪声及/或偏移造成的影响，可将偏移消除电容CAZ从电流积分器的信号路径上移除。请参考图3，图3为本发明实施例一电流积分器30的示意图。如图3所示，电流积分器30包括一运算放大器300、一积分电容Cint、一偏移消除电容CAZ、重置开关器SW_R1～SW_R3及一输入开关器SW_IN。不同于电流积分器20中的运算放大器200仅具有一输入级，电流积分器30中的运算放大器300包括两个输入级I1及I2，其中每一输入级I1及I2各自具有一差分输入对，分别耦接至两个输入端。输入级I1耦接于电流积分器30的输入端，用来从输入端接收输入电流信号IIN。积分电容Cint的运作方式类似于图2中的积分电容Cint，因此以相同符号表示。如图3所示，积分电容Cint耦接于运算放大器300的输入级I1与电流积分器30的输出端之间，用来存储输入电流信号IIN的积分信息。偏移消除电容CAZ的运作方式类似于图2中的偏移消除电容CAZ，因此以相同符号表示。如图3所示，偏移消除电容CAZ耦接于运算放大器300的输入级I2，用来存储运算放大器300的输入偏移信息。更明确来说，偏移消除电容CAZ耦接于输入级I2的负输入端与一接地端之间。在此例中，运算放大器300具有两个输入级I1及I2，因此具有两个输入偏移电压VOS1及VOS2，其在图3中以电压源来表示。
除此之外，电流积分器30还设置有重置开关器SW_R1～SW_R3和输入开关器SW_IN以实现切换电容操作。输入开关器SW_IN耦接于输入级I1与电流积分器30的输入端之间，其运作方式类似于图2中的开关器SW2。重置开关器SW_R1耦接于输入级I1与电流积分器30的输出端之间，其运作方式类似于图2中的开关器SW1。由于运算放大器300具有两个输入级I1及I2，因而设置另一重置开关器SW_R2耦接于输入级I2与运算放大器300的输出端之间。另外一重置开关器SW_R3则耦接于输入级I1的两输入端之间。
在此例中，运算放大器300的输入级I1用来从电流积分器30的输入端接收输入电流信号IIN，同时，偏移消除电容CAZ耦接于运算放大器300的输入级I2且和电流积分器30传送输入电流信号IIN的信号路径隔离。对于输入级I1来说，其负输入端耦接于电流积分器30的输入端，用来接收输入电流信号IIN，而正输入端耦接于一参考端，用来接收一参考电压VREF。对于输入级I2来说，其负输入端耦接于偏移消除电容CAZ，而正输入端耦接于同一参考端以接收参考电压VREF。
电流积分器30的操作可包括两阶段：一偏移消除阶段及一积分阶段。图4A示出了操作在偏移消除阶段的电流积分器30。如图4A所示，在偏移消除阶段中，重置开关器SW_R1、SW_R2及SW_R3都开启，而输入开关器SW_IN关闭。重置开关器SW_R1～SW_R3的开启可对运算放大器300进行重置，使得输入偏移电压VOS1及VOS2的相关信息存入偏移消除电容CAZ。在偏移消除阶段中，电流积分器30的转移函数可由下列方程式表示：
VOUT＝VOS1·Gm1·Ro+(VOUT+VOS2-VREF)·Gm2·Ro；
Figure BDA0002707716320000071
其中，VOUT为运算放大器300的输出电压(也可视为电流积分器30的输出电压)，Gm1为输入级I1的跨导，Gm2为输入级I2的跨导，Ro为运算放大器300的输出阻抗，而VCAZ为偏移消除电容CAZ的跨压。
图4B示出了操作在积分阶段的电流积分器30。如图4B所示，在积分阶段中，输入开关器SW_IN开启，而重置开关器SW_R1、SW_R2及SW_R3关闭。输入开关器SW_IN的开启使得输入电流信号IIN可被接收并存入积分电容Cint。先前存储在偏移消除电容CAZ的偏移信息可耦合至后端以消除输入偏移电压VOS1及VOS2。在积分阶段中，电流积分器30的转移函数可由下列方程式表示：
VOUT＝(VCAZ+VOS2-VREF)·Gm2·Ro+(VOUT+VOS1-VREF)·Gm1·Ro；
Figure BDA0002707716320000072
Figure BDA0002707716320000073
由此可知，输出电压VOUT及参考电压VREF的差值被除以Gm1·Ro-1，其大约等于运算放大器300的开环增益(open loop gain)且通常具有相当大的数值，其意义在于，偏移消除电容CAZ上的噪声、电荷注入及/或漏电流对电流积分器30输出结果产生的影响大幅下降。相较之下，在一般电流积分器20中，运算放大器200仅包括一输入级，使得偏移消除电容CAZ上的噪声会受到运算放大器200的放大而影响输出结果。两者的主要差异在于，电流积分器20的偏移消除电容CAZ位于信号路径上，而电流积分器30的偏移消除电容CAZ不位于接收输入电流信号IIN的信号路径上。
在本发明中，运算放大器300可通过任何类型的运算放大器来实现，只要运算放大器300包括两个输入级即可。请参考图5A及5B，图5A及5B为运算放大器300的一示例性电路结构的示意图。如图5A所示，运算放大器300可以是例如具有两个输入级I1及I2的一AB类放大器(class-AB amplifier)，其中，每一输入级I1或I2都具有由两个P型金氧半场效晶体管(P-type Metal Oxide Semiconductor Transistor，PMOS Transistor)所组成的差分输入对。图5B示出了类似的AB类放大器结构，其中，各差分输入对都是由两个N型金氧半场效晶体管(N-type Metal Oxide Semiconductor Transistor，NMOS Transistor)所组成。
值得注意的是，本发明的目的在于提供一种可用于有机发光二极管面板的电流积分器及其信号处理系统。本领域技术人员当可据此进行修饰或变化，而不限于此。举例来说，在上述实施例中，电流积分器及信号处理系统都应用于有机发光二极管面板，用来感测参数以用于有机发光二极管面板上的像素补偿。在另一实施例中，电流积分器及信号处理系统也可用于其它可输出电流信号以累积在电流积分器并加以读出的装置。除此之外，关于运算放大器的实施方式也不限于本说明书所描述的电路结构。
综上所述，本发明提供了一种可用于有机发光二极管面板补偿的电流积分器及信号处理系统。信号处理系统可包括多个信道，其中每一信道具有一电流积分器。每一电流积分器都需要使用一偏移消除方案，以消除运算放大器的输入偏移。为了降低偏移消除电容的各种噪声及偏移，可将偏移消除电容与电流积分器的信号路径隔离。在一实施例中，运算放大器具有两个输入级，其中一输入级用来接收输入电流信号，并将偏移消除电容耦接到另一输入级。如此一来，偏移消除电容上的噪声及/或偏移对电流积分器输出结果产生的影响可大幅下降。
以上所述仅为本发明的优选实施例而已，并不用于限制本发明，对于本领域的技术人员来说，本发明可以有各种更改和变化。凡在本发明的精神和原则之内，所作的任何修改、等同替换、改进等，均应包含在本发明的保护范围之内。

Claims (19)

1.一种电流积分器，包括：
一运算放大器，包括：
一第一输入级，耦接于该电流积分器的一输入端；以及
一第二输入级；
一积分电容，耦接于该运算放大器的该第一输入级与该电流积分器的一输出端之间；以及
一偏移消除电容，耦接于该运算放大器的该第二输入级。
2.如权利要求1所述的电流积分器，其特征在于，该第一输入级及该第二输入级各自包括一差分输入对。
3.如权利要求1所述的电流积分器，其特征在于，还包括：
一第一重置开关器，耦接于该运算放大器的该第一输入级与该运算放大器的该输出端之间；
一第二重置开关器，耦接于该运算放大器的该第二输入级与该运算放大器的该输出端之间；以及
一第三重置开关器，耦接于该第一输入级的一第一输入端与该第一输入级的一第二输入端之间。
4.如权利要求1所述的电流积分器，其特征在于，还包括：
一输入开关器，耦接于该运算放大器的该第一输入级与该电流积分器的该输入端之间。
5.如权利要求1所述的电流积分器，其特征在于，该运算放大器的该第一输入级用来从该电流积分器的该输入端接收一输入电流信号。
6.如权利要求5所述的电流积分器，其特征在于，该积分电容用来存储该输入电流信号的一积分信息。
7.如权利要求1所述的电流积分器，其特征在于，该偏移消除电容用来存储该运算放大器的一偏移信息。
8.如权利要求1所述的电流积分器，其特征在于，该偏移消除电容耦接于该运算放大器的该第二输入级与一接地端之间。
9.如权利要求1所述的电流积分器，其特征在于，该偏移消除电容与该电流积分器的一信号路径隔离。
10.一种信号处理系统，包括：
一模拟数字转换器；以及
多个电流积分器，其中每一电流积分器耦接于该模拟数字转换器，并包括：
一运算放大器，包括：
一第一输入级，耦接于该电流积分器的一输入端；以及
一第二输入级；
一积分电容，耦接于该运算放大器的该第一输入级与该电流积分器的一输出端之间；以及
一偏移消除电容，耦接于该运算放大器的该第二输入级。
11.如权利要求10所述的信号处理系统，其特征在于，该第一输入级及该第二输入级各自包括一差分输入对。
12.如权利要求10所述的信号处理系统，其特征在于，该多个电流积分器中的每一电流积分器还包括：
一第一重置开关器，耦接于该运算放大器的该第一输入级与该运算放大器的该输出端之间；
一第二重置开关器，耦接于该运算放大器的该第二输入级与该运算放大器的该输出端之间；以及
一第三重置开关器，耦接于该第一输入级的一第一输入端与该第一输入级的一第二输入端之间。
13.如权利要求10所述的信号处理系统，其特征在于，该多个电流积分器中的每一电流积分器还包括：
一输入开关器，耦接于该运算放大器的该第一输入级与该电流积分器的该输入端之间。
14.如权利要求10所述的信号处理系统，其特征在于，该运算放大器的该第一输入级用来从该电流积分器的该输入端接收一输入电流信号。
15.如权利要求14所述的信号处理系统，其特征在于，该积分电容用来存储该输入电流信号的一积分信息。
16.如权利要求10所述的信号处理系统，其特征在于，该偏移消除电容用来存储该运算放大器的一偏移信息。
17.如权利要求10所述的信号处理系统，其特征在于，该偏移消除电容耦接于该运算放大器的该第二输入级与一接地端之间。
18.如权利要求10所述的信号处理系统，其特征在于，该偏移消除电容与该电流积分器的一信号路径隔离。
19.如权利要求10所述的信号处理系统，其特征在于，该模拟数字转换器用来依序从该多个电流积分器接收输出信号。
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