Abstract:
A current mirror for driving an OLED panel is provided. The current mirror of the present invention adopts low voltage MOS transistors as the primary part of the current mirror so as to provide currents with high uniformity. The present invention also utilizes high voltage devices to bias the current mirror, such that the high voltage used for the OLED panel could serve for the claimed current mirror. The performance of the OLED panel is improved due to the uniformity of currents provided by the current mirror of the present invention.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to an OLED panel and the related current mirrors for driving the same, and more particularly, to an OLED panel and the related current mirrors capable of providing stable driving currents for driving the OLED panel.  
         [0003]     2. Description of the Prior Art  
         [0004]     With rapid development of technology, light and portable electronic devices with low power consumption are widely used in everyday life. Among these electronic devices such as cellular phones, personal digital assistants (PDAs) or notebook computers, displays are required as interaction interfaces between users and machines. Recently, flat panel display (FPD) devices have been developed for providing high-resolution images, large screen size and reduced costs. Among various FPD devices, organic light-emitting diode (OLED) panels have gradually gained more and more attention in mid/small-sized applications due to advantages such as self-emitting light sources, wide viewing angles, fast response time, low power consumption, high contrast, high brightness, full color, simple structure, and a large range of operational temperatures. With manufacturing problems such as low yield, improper mask applications or unstable cap sealing processes being solved in recent years, OLED panels have become the future trends.  
         [0005]     An OLED panel is a current-driven device whose luminance is determined by its passing current. Therefore the stability of the driven current is very important. For a panel using high-resolution passive matrix OLEDs (PMOLEDs) or current-mode active matrix OLEDs (AMOLEDs), the uniformity between current provided to different pixels of the OLED panel is crucial for providing quality images.  
         [0006]     A PMOLED panel can be driven by means of pulse width modulation (PWM) in which the duty cycles of pulse voltages are changed for controlling the luminance of the PMOLED. Conventionally, a current mirror is used for driving an OLED panel. Since high voltage sources are required, the current mirror includes high voltage metal oxide semiconductor (HV MOS) transistors. Reference is made to  FIG. 1  showing a prior art current mirror  100  for driving an OLED panel by means of PWM. The current mirror  100  includes n+1 high voltage p-type metal oxide semiconductor (HV PMOS) transistors P 0 -Pn (only P 0 , P 1 , P 2  and Pn are depicted in  FIG. 1 ). The current mirror  100  receives a high voltage Vcc_HV. As shown in  FIG. 1 , the source and base terminals of each HV PMOS transistor are coupled to the high voltage source Vcc_HV. The current mirror  100  outputs currents I 1 -In to an OLED panel at the drain terminals of the HV PMOS transistors P 0 -Pn. However, the threshold voltages of the HV PMOS transistors P 0 -Pn can deviate from the nominal value differently, resulting in large variations between the currents I 1 -In. Therefore, the prior art current mirror  100  cannot provide the OLED panel with stable driving currents required for achieving high-resolution images.  
         [0007]     Reference is made to  FIG. 2  showing another prior art current mirror  200  for driving an OLED panel by means of PWM. Compared to the prior art current mirror  100 , the prior art current mirror  200  has a cascode structure and further includes n+1 HV PMOS transistors PC 0 -PCn (only PC 0 , PC 1 , PC 2  and PCn are depicted in  FIG. 2 ) coupled in series with the corresponding HV PMOS transistors P 0 -Pn. Since the transistors P 0 -Pn are HV PMOS transistors, voltages established at the drain terminals (nodes A 0 -An in  FIG. 2 ) can be very high. For safety reasons, all devices used in the prior art current mirror  200  have to be HV PMOS transistors. Therefore, the threshold voltages of the HV PMOS transistors P 0 -Pn and PC 0 -PCn can still deviate from the nominal value differently, resulting in large variations between the currents I 1 -In. Therefore, the prior art current mirror  200  cannot provide the OLED panel with stable driving currents required for achieving high-resolution images.  
         [0008]     A PMOLED panel can also be driven by means of pulse amplitude modulation (PAM). Reference is made to  FIG. 3  showing an M-bit PAM module  30 . The PAM module  30  includes switches SW 1 -SWm and NMOS transistors N 1 -Nm. I DC1 -I DCm  represent currents passing through the NMOS transistors N 1 -Nm, respectively. The PAM module  30  controls passages of the current I DC1 -I DCm  using the switches SW 1 -SWn, thereby controlling the amount of the total current I DC .  
         [0009]     Reference is made to  FIG. 4  showing a prior art current mirror  400  for driving an OLED panel by means of PAM. The current mirror  400  includes a current source I DC , an n-type metal oxide semiconductor (NMOS) transistor N 0 , 2n HV PMOS transistors P 1 -Pn and P 1 ′-Pn′, and PAM modules PAM 1 -PAMn. The current mirror  300  receives a high voltage Vcc_HV. As shown in  FIG. 3 , the source and base terminals of each HV PMOS transistor is coupled to the high voltage Vcc_HV, and the drain terminals the HV PMOS transistors P 1 ′-Pn′ are coupled to the PAM modules PAM 1 -PAMn, respectively. The PAM modules PAM 1 -PAMn can each include the M-bit PAM module  30  shown in  FIG. 3 . The drain currents I 1 ′-In′ of the HV PMOS transistors P 1 ′-Pn′ are outputted to an OLED panel. The PAM modules PAM 1 -PAMn control the amount of the drain currents I 1 -In passing through the HV PMOS transistors P 1 -Pn, thereby controlling the amount of the drain currents I 1 ′-In′ passing through the HV PMOS transistors P 1 ′-Pn′. The threshold voltages of the HV PMOS transistors P 1 -Pn and P 1 ′-Pn′ can deviate from the nominal value differently, resulting in large variations between the currents I 1 ′-In′. Therefore, the current mirror  400  cannot provide the OLED panel with stable driving currents required for achieving high-resolution images.  
         [0010]     Reference is made to  FIG. 5  showing another prior art current mirror  500  for driving an OLED panel by means of PAM. Compared to the prior art current mirror  400 , the prior art current mirror  500  has a cascode structure and further includes 2n HV PMOS transistors PC 1 -PCn and PC 1 ′-PCn′ coupled in series with the corresponding HV PMOS transistors P 1 -Pn and P 1 ′-Pn′, respectively. Since transistors P 1 -Pn and P 1 ′-Pn′ are HV PMOS transistors, voltages established at the drain terminals (nodes A 1 -An in  FIG. 5 ) can be very high. For safety reasons, all devices used in the prior art current mirror  500  have to be HV PMOS transistors. Therefore, the threshold voltages of the HV PMOS transistors P 1 -Pn and P 1 ′-Pn′ can still deviate from the nominal value differently, resulting in large variations between the currents I 1 ′-In′ outputted to the OLED panel. Therefore, the current mirror  500  cannot provide the OLED panel with stable driving currents required for achieving high-resolution images.  
         [0011]     Reference is made to  FIG. 6  showing another prior art current mirror  600  for driving an OLED panel by means of PAM. Compared to the prior art current mirror  500 , the prior art current mirror  600  also has a cascode structure, but the drain terminals of the HV PMOS transistors PC 1 -PCn are respectively coupled to the gate terminals of the HV PMOS transistors P 1 -Pn, and the base terminals of the HV PMOS transistors PC 1 -PCn and PC 1 ′-PCn′ are coupled to a reference voltage. In the current mirror  600 , the threshold voltages of the HV PMOS transistors P 1 -Pn and P 1 ′-Pn′ can deviate from the nominal value differently, resulting in large variations between the currents I 1 ′-In′ outputted to the OLED panel. Therefore, the current mirror  600  cannot provide the OLED panel with stable driving currents required for achieving high-resolution images.  
         [0012]     In an AMOLED panel, each OLED pixel is controlled by a thin film transistor (TFT) switch. The data driver for driving the AMOLED panel includes a digital-to-analog converter (DAC) capable of generating driving currents corresponding to image data. Depending on current directions, data drivers can be categorized into two types: sink-mode data drivers and source-mode data drivers. Reference is made to  FIG. 7  showing a prior art sink-mode current mirror  700  for driving an AMOLED panel. The current mirror  700  includes a current source I DC , n HV NMOS transistors N 0 -Nn, and switches SW 1 -SWn. The drain terminal of the HV NMOS transistor N 0  is coupled to current source I DC , and the drain terminals of the HV NMOS transistors N 1 -Nn are coupled to the AMOLED panel via the switches SW 1 -SWn, respectively. Therefore, the current mirror  700  controls the amount of the driving current I by turning on/off the switches SW 1 -SWn. However, the threshold voltages of the HV NMOS transistors N 1 -Nn can still deviate from the nominal value differently, resulting in large variations between the currents passing through each HV NMOS transistor. Therefore, the current mirror  700  cannot provide the AMOLED panel with stable driving currents required for achieving high-resolution images.  
         [0013]     Reference is made to  FIG. 8  showing a prior art source-mode current mirror  800  for driving an AMOLED panel. The current mirror  800  includes a current source I DC , n HV PMOS transistors P 0 -Pn, and switches SW 1 -SWn. The drain terminal of the HV PMOS transistor P 0  is coupled to current source I DC , and the drain terminals of the HV PMOS transistors P 1 -Pn are coupled to the AMOLED panel via the switches SW 1 -SWn, respectively. Therefore, the current mirror  800  controls the amount of the driving current I by turning on/off the switches SW 1 -SWn. However, the threshold voltages of the HV PMOS transistors P 0 -Pn can still deviate from the nominal value differently, resulting in large variations between the currents passing through each HV PMOS transistor. Therefore, the current mirror  800  cannot provide the AMOLED panel with stable driving currents required for achieving high-resolution images.  
       SUMMARY OF THE INVENTION  
       [0014]     The present invention provides a current mirror for driving an organic light-emitting diode panel comprising: a first low voltage P-type metal oxide semiconductor (LV PMOS) transistor comprising a source terminal coupled to a first reference voltage, a drain terminal, and a gate terminal coupled to the drain terminal of the first LV PMOS transistor; a second LV PMOS transistor comprising a source terminal coupled to the first reference voltage; a drain terminal, and a gate terminal coupled to the gate terminal of the first LV PMOS transistor; a first high voltage (HV) device coupled between the drain terminal of the first LV PMOS transistor and a first current source for biasing the first LV PMOS transistors to operate at a predetermined low voltage; and a second HV device coupled to the drain of the second LV PMOS transistor and an OLED panel for biasing the second LV PMOS transistors to operate at the predetermined low voltage.  
         [0015]     The present invention further provides an OLED display comprising an OLED panel and a current mirror for driving the OLED panel. The current mirror includes a first LV PMOS transistor comprising a source terminal coupled to a first reference voltage, a drain terminal, and a gate terminal coupled to the drain terminal of the first LV PMOS transistor; a second LV PMOS transistor comprising a source terminal coupled to the first reference voltage, a drain terminal, and a gate terminal coupled to the gate terminal of the first LV PMOS transistor; a first HV device coupled between the drain terminal of the first LV PMOS transistor and a first current source for biasing the first LV PMOS transistor to operate at a predetermined low voltage; and a second HV device coupled between the drain terminal of the second LV PMOS transistor and the OLED panel for biasing the second LV PMOS transistor to operate at the predetermined low voltage.  
         [0016]     The present invention further provides a current mirror for driving a PMOLED panel comprising a current source; a first LV PMOS transistor comprising a source terminal coupled to a first reference voltage, a drain terminal, and a gate terminal coupled to the drain terminal of the first LV PMOS transistor; a second LV PMOS transistor comprising a source terminal coupled to the first reference voltage, a drain terminal, and a gate terminal coupled to the drain terminal of the first LV PMOS transistor; a first HV device coupled to the drain terminal of the first LV PMOS transistor for biasing the first LV PMOS transistor to operate at a predetermined low voltage; a second HV device coupled to the drain terminal of the second LV PMOS transistor and the PMOLED panel for biasing the second LV PMOS transistor to operate at the predetermined low voltage; a pulse amplitude modulation module coupled to the first HV device for controlling the current passing through the first LV PMOS transistor; and an N-type metal oxide semiconductor transistor comprising a source terminal coupled to the current source, a drain terminal, and a gate coupled to the PAM module for enabling the PAM module.  
         [0017]     The present invention further provides a PMOLED display comprising a PMOLED panel and a current source for driving the PMOLED panel. The current source includes a first LV PMOS transistor comprising a source terminal coupled to a first reference voltage, a drain terminal, and a gate terminal coupled to the drain terminal of the first LV PMOS transistor; a second LV PMOS transistor comprising a source terminal coupled to the first reference voltage, a drain terminal, and a gate terminal coupled to the drain terminal of the first LV PMOS transistor; a first HV device coupled to the drain terminal of the first LV PMOS transistor for biasing the first LV PMOS transistor to operate at a predetermined low voltage; a second HV device coupled to the drain terminal of the second LV PMOS transistor and the PMOLED panel for biasing the second LV PMOS transistor to operate at the predetermined low voltage; a PAM module coupled to the first HV device for controlling the current passing through the first LV PMOS transistor; and an NMOS transistor comprising a source terminal coupled to the current source, a drain terminal, and a gate terminal coupled to the PAM module for enabling the PAM module.  
         [0018]     The present invention further provides a current mirror for driving an AMOLED panel comprising a current source; a first LVNMOS transistor comprising a source terminal, a drain terminal, and a gate terminal coupled to the drain terminal of the first LVNMOS transistor; a second LVNMOS transistor comprising a source terminal coupled to the source terminal of the first LVNMOS transistor, a drain terminal, and a gate terminal coupled to the gate terminal of the first LVNMOS transistor; a first HV device coupled between the drain terminal of the first LVNMOS transistor and the current source for biasing the first LVNMOS transistor to operate at a predetermined low voltage; a second HV device coupled to the drain terminal of the second LVNMOS transistor for biasing the second LV NMOS transistor to operate at the predetermined low voltage; and a switch coupled between the second HV device and the AMOLED panel.  
         [0019]     The present invention further provides an AMOLED display device comprising an AMOLED panel and a current source for driving the AMOLED panel. The current source includes a first LVNMOS transistor comprising a source terminal, a drain terminal, and a gate terminal coupled to the drain terminal of the first LVNMOS transistor; a second LVNMOS transistor comprising a source terminal coupled to the source terminal of the first LVNMOS transistor, a drain terminal, and a gate terminal coupled to the gate terminal of the first LVNMOS transistor; a first HV device coupled between the drain terminal of the first LVNMOS transistor and the current source for biasing the first LVNMOS transistor to operate at a predetermined low voltage; a second HV device coupled to the drain terminal of the second LVNMOS transistor for biasing the second LVNMOS transistor to operate at the predetermined low voltage; and a switch coupled between the second HV device and the AMOLED panel.  
         [0020]     The present invention further provides a current mirror for driving an AMOLED panel comprising a current source; a first LV PMOS transistor comprising a source terminal, a drain terminal, and a gate terminal coupled to the drain terminal of the first LV PMOS transistor; a second LV PMOS transistor comprising a source terminal coupled to the source terminal of the first LV PMOS transistor, a drain terminal, and a gate terminal coupled to the gate terminal of the first LV PMOS transistor; a first HV device coupled between the drain terminal of the first LVNMOS transistor and the current source for biasing the first LV PMOS transistor to operate at a predetermined low voltage; a second HV device coupled to the drain of the second LVNMOS transistor for biasing the second LV PMOS transistor to operate at the predetermined low voltage; and a switch coupled between the second HV device and the AMOLED panel.  
         [0021]     The present invention further provides an AMOLED display device comprising an AMOLED panel and a current source for driving the AMOLED panel. The current mirror includes a first LV PMOS transistor comprising a source terminal, a drain terminal, and a gate terminal coupled to the drain terminal of the first LV PMOS transistor; a second LV PMOS transistor comprising a source terminal coupled to the source terminal of the first LV PMOS transistor, a drain terminal, and a gate terminal coupled to the gate terminal of the first LV PMOS transistor; a first HV device coupled between the drain terminal of the first LV PMOS transistor and the current source for biasing the first LV PMOS transistor to operate at a predetermined low voltage; a second HV device coupled to the drain terminal of the second LV PMOS transistor for biasing the second LV PMOS transistor to operate at the predetermined low voltage; and a switch coupled between the second HV device and the AMOLED panel.  
         [0022]     These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0023]      FIG. 1  shows a prior art current mirror for driving an OLED panel by means of PWM.  
         [0024]      FIG. 2  shows another prior art current mirror for driving an OLED panel by means of PWM.  
         [0025]      FIG. 3  shows an M-bit PAM module.  
         [0026]      FIG. 4  shows a prior art current mirror for driving an OLED panel by means of PAM.  
         [0027]      FIG. 5  shows another prior art current mirror for driving an OLED panel by means of PAM.  
         [0028]      FIG. 6  shows another prior art current mirror for driving an OLED panel by means of PAM.  
         [0029]      FIG. 7  shows a prior art sink-mode current mirror for driving an AMOLED panel.  
         [0030]      FIG. 8  shows a prior art source-mode current mirror for driving an AMOLED panel.  
         [0031]      FIG. 9  shows a current mirror for driving a PMOLED panel by means of PWM according to the present invention.  
         [0032]      FIG. 10  shows a current mirror for driving a PMOLED panel according to a first embodiment of the present invention.  
         [0033]      FIG. 11  shows a current mirror for driving a PMOLED panel according to a second embodiment of the present invention.  
         [0034]      FIG. 12  shows a current mirror for driving a PMOLED panel according to a third embodiment of the present invention.  
         [0035]      FIG. 13  shows a current mirror for driving a PMOLED panel according to a fourth embodiment of the present invention.  
         [0036]      FIG. 14  shows a current mirror for driving a PMOLED panel by means of PAM according to the present invention.  
         [0037]      FIG. 15  shows a current mirror for driving a PMOLED panel according to a fifth embodiment of the present invention.  
         [0038]      FIG. 16  shows a current mirror for driving a PMOLED panel according to a sixth embodiment of the present invention.  
         [0039]      FIG. 17  shows a current mirror for driving a PMOLED panel according to a seventh embodiment of the present invention.  
         [0040]      FIG. 18  shows a current mirror for driving a PMOLED panel according to an eighth embodiment of the present invention.  
         [0041]      FIG. 19  shows a sink-mode current mirror for driving an AMOLED panel according to the present invention.  
         [0042]      FIG. 20  shows a source-mode current mirror for driving an AMOLED panel according to the present invention.  
         [0043]      FIG. 21  shows a sink-mode current mirror for driving an AMOLED panel according to a ninth embodiment of the present invention.  
         [0044]      FIG. 22  shows a sink-mode current mirror for driving an AMOLED panel according to a tenth embodiment of the present invention.  
         [0045]      FIG. 23  shows a sink-mode current mirror for driving an AMOLED panel according to an eleventh embodiment of the present invention.  
         [0046]      FIG. 24  shows a sink-mode current mirror for driving an AMOLED panel according to a twelfth embodiment of the present invention.  
         [0047]      FIG. 25  shows a source-mode current mirror for driving an AMOLED panel according to a thirteenth embodiment of the present invention.  
         [0048]      FIG. 26  shows a source-mode current mirror for driving an AMOLED panel according to a fourteenth embodiment of the present invention.  
         [0049]      FIG. 27  shows a source-mode current mirror for driving an AMOLED panel according to a fifteenth embodiment of the present invention.  
         [0050]      FIG. 28  shows a source-mode current mirror for driving an AMOLED panel according to a sixteenth embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION  
       [0051]     Reference is made to  FIG. 9  showing a current mirror  900  for driving a PMOLED panel by means of PWM according to the present invention. Unlike the prior art current mirrors, the current mirror  900  includes n+1 low voltage p-type metal oxide semiconductor (LV PMOS) transistors PL 0 -PLn (only PL 0 , PL 1 , PL 2  and PLn are depicted in  FIG. 9 ) and HV devices  90 - 9   n  respectively coupled in series with the LV PMOS transistors PL 0 -PLn. The HV devices  90 - 9   n  provide bias voltages for the LV PMOS transistors PL 0 -PLn. As shown in  FIG. 9 , the current mirror  900  also receives a high voltage Vcc_HV. In other words, the source and base terminals of each LV PMOS transistor are coupled to the high voltage Vcc_HV. Since the threshold voltage of an LV PMOS transistor is more stable than that of a HV PMOS transistor, the current mirror  900  can provide stable driving currents Ih 1 -Ihn to the PMOLED panel for achieving high-resolution images. The sizes (W/L ratios) of the LV PMOS transistors PL 0 -PLn can be determined based on their operating voltage limits, and appropriate bias voltages can be provided at the drain terminals of the LV PMOS transistors PL 0 -PLn using the HV devices  90 - 9   n . Therefore, although the current mirror  900  receives the high voltage Vcc_HV, it can still provide stable driving currents Ih 1 -Ihn to the PMOLED panel for achieving high-resolution images.  
         [0052]     Reference is made to  FIG. 10  showing a current mirror  1000  for driving a PMOLED panel according to a first embodiment of the present invention based on the structure of the current mirror  900 . As shown in  FIG. 10 , the current mirror  1000  has a cascode structure and includes n+1 HV PMOS transistors PH 0 -PHn (only PH 0 , PH 1 , PH 2  and PHn are depicted in  FIG. 10 ) for respectively biasing the LV PMOS transistors PL 0 -PLn. The gate terminals of the HV PMOS transistors PH 0 -PHn are coupled to a reference voltage Vref, and the source terminals of the HV PMOS transistors PH 0 -PHn are respectively coupled to the drain terminals of the LV PMOS transistors PL 0 -PLn.  
         [0053]     References are made to  FIGS. 11-13  showing current mirrors  1100 - 1300  according to a second, third and fourth embodiments of the present invention based on the structure of the current mirror  900 . Similar to the current mirror  1000 , the HV PMOS transistors PH 0 -PHn are used for the HV devices  90 - 9   n  in the current mirrors  1100 - 1300 . However, the gate terminals of the HV PMOS transistors PH 0 -PHn are coupled differently in the current mirrors  1100 - 1300 . In the current mirror  1100  shown in  FIG. 11 , the gate terminals of the HV PMOS transistors PH 0 -PHn are coupled to the drain terminal of the HV PMOS transistor PH 0 . In the current mirror  1200  shown in  FIG. 12 , the gate terminal of the HV PMOS transistor PH 0  is coupled to a first reference voltage Vref 1 , and the gate terminals of the HV PMOS transistors PH 1 -PHn are coupled to a second reference voltage Vref 2 . In the current mirror  1300  shown in  FIG. 13 , the gate terminal and the drain terminal of the HV PMOS transistor PH 0  are coupled together, and the gate terminals of the HV PMOS transistors PH 1 -PHn are coupled to a reference voltage Vref. Various circuits commonly known to those skilled in the art can be used for generating the reference voltages Vref, Vref 1 , and Vref 2 .  
         [0054]     Reference is made to  FIG. 14  showing a current mirror  1400  for driving a PMOLED panel by means of PAM according to the present invention. Unlike the prior art current mirror  400 , the current mirror  1400  includes 2n LV PMOS transistors PL 0 -PLn and PL 0 ′-PLn′, together with HV devices  140 - 14   n  respectively coupled in series with the LV PMOS transistors PL 0 -PLn and PL 0 ′-PLn′. The HV devices  140 - 14   n  provide bias voltages for the LV PMOS transistors PL 0 -PLn and PL 0 ′-PLn′. As shown in  FIG. 14 , the current mirror  1400  also receives a high voltage Vcc_HV. In other words, the source and base terminals of each LV PMOS transistor are coupled to the high voltage Vcc_HV, and the drain terminals of the LV PMOS transistor PL 1 -PLn are coupled to PAM modules PAM 1 -PAMn via the HV devices  140 - 14   n , respectively. The PAM modules PAM 1 -PAMn can each include the M-bit PAM module  30  shown in  FIG. 3 . The HV devices  140 - 14   n  coupled to the LV PMOS transistors PL 0 -PLn output currents Ih 1 -Ihn, while the HV devices  140 - 14   n  coupled to the LV PMOS transistors PL 0 ′-PLn′ output currents Ih 1 ′-Ihn′ to the PMOLED panel. The PAM modules PAM 1 -PAMn control the amount of the drain currents Ih 1 -Ihn passing through the LV PMOS transistors PL 1 -PLn, thereby controlling the amount of the drain currents Ih 1 ′-Ihn′ passing through the LV PMOS transistors PL 1 ′-LPn′. Since the threshold voltage of an LV PMOS transistor is more stable than that of a HV PMOS transistor, the current mirror  1400  can provide stable driving currents Ih 1 ′-Ihn′ to the PMOLED panel for achieving high-resolution images. The size (W/L ratio) of each LV PMOS transistor can be determined based on its operating voltage limit, and appropriate bias voltages can be provided at the drain terminals of the LV PMOS transistors PL 0 -PLn and PL 0 ′-PLn′ using the HV devices  140 - 14   n . Therefore, although the current mirror  1400  receives the high voltage Vcc_HV, it can still provide stable driving currents Ih 1 ′-Ihn′ to the PMOLED panel for achieving high-resolution images.  
         [0055]     Reference is made to  FIG. 15  showing a current mirror  1500  for driving a PMOLED panel according to a fifth embodiment of the present invention based on the structure of the current mirror  1400 . As shown in  FIG. 15 , the current mirror  1500  includes 2n HV PMOS transistors PCH 1 -PCHn and PCH 1 ′-PCHn′ for respectively biasing the LV PMOS transistors PL 0 -PLn and PL 1 ′-PLn′. The gate terminals of the HV PMOS transistors PCH 1 -PCHn and PCH 1 ′-PCHn′ are coupled to a reference voltage Vref, and the source terminals of the HV PMOS transistors PCH 1 -PCHn and PCH 1 ′-PCHn′ are respectively coupled to the drain terminals of the LV PMOS transistors PL 0 -PLn and PL 0 ′-PLn′. Since the threshold voltage of an LV PMOS transistor is more stable than that of a HV PMOS transistor, the current mirror  1500  can provide stable driving currents Ih 1 ′-Ihn′ to the PMOLED panel for achieving high-resolution images.  
         [0056]     References are made to  FIGS. 16-18  showing current mirrors  1600 - 1800  according to a sixth, seventh and eighth embodiments of the present invention based on the structure of the current mirror  1500 . Similar to the current mirror  1500 , the HV PMOS transistors PCH 1 -PCHn and PCH 1 ′-PCHn′ are used for the HV devices in the current mirrors  1600 - 1800 . However, the gate terminals of the HV PMOS transistors PCH 1 -PCHn and PCH 1 ′-PCHn′ are coupled differently in the current mirrors  1600 - 1800 . In the current mirror  1600  shown in  FIG. 16 , the gate terminals and drain terminals of the HV PMOS transistors PCH 1 -PCHn are coupled together, and the gate terminals of the HV PMOS transistors PCH 1 ′-PCHn′ are coupled to a reference voltage Vref. In the current mirror  1700  shown in  FIG. 17 , the gate terminals of the HV PMOS transistor PCH 1 -PCHn are coupled to a first reference voltage Vref 1 , and the gate terminals of the HV PMOS transistors PCH 1 ′-PCHn′ are coupled to a second reference voltage Vref 2 . In the current mirror  1800  shown in  FIG. 18 , the gate terminals and the drain terminals of the HV PMOS transistor PCH 1 -PCHn are coupled together. Various circuits commonly known to those skilled in the art can be used for generating the reference voltages Vref, Vref 1 , and Vref 2 .  
         [0057]     Reference is made to  FIG. 19  showing a sink-mode current mirror  1900  for driving an AMOLED panel according to the present invention. The current mirror  1900  includes a current source I DC , n+1 LV NMOS transistors NL 0 -NLn (only NL 0 , NL 1 , NL 2  and NLn are depicted in  FIG. 19 ), HV devices  190 - 19   n  (only  190 ,  191 ,  192  and  19   n  are depicted in  FIG. 19 ), and switches SW 1 -SWn (only SW 1 , SW 2  and SWn are depicted in  FIG. 19 ). Unlike the prior art current mirror  700 , the current mirror  1900  of the present invention includes the LV NMOS transistors NL 0 -NLn and the HV devices  190 - 19   n  for respectively biasing the LV NMOS transistors NL 0 -NLn. The HV devices  190 - 19   n  can include HV NMOS transistors. The drain terminal of the LV NMOS transistor NL 0  is coupled to the current source I DC  via the HV device  190 , and the drain terminals of the LV NMOS transistor NL 1 -NLn are coupled to the AMOLED panel via the HV device  191 - 19   n  and the switches SW 1 -SWn, respectively. The current mirror  1900  controls the amount of the driving current using the switches SW 1 -SWn. Since the threshold voltage of an LV NMOS transistor is more stable than that of a HV NMOS transistor, the currents passing through the LV NMOS transistors NL 1 -NLn do not have large variations. Therefore, the current mirror  1900  can provide stable driving currents to the AMOLED panel for achieving high-resolution images.  
         [0058]     Reference is made to  FIG. 20  showing a source-mode current mirror  2000  for driving an AMOLED panel according to the present invention. The current mirror  2000  includes a current source I DC , n+1 LV PMOS transistors PL 0 -PLn (only PL 0 , PL 1 , PL 2  and PLn are depicted in  FIG. 20 ), HV devices  200 - 20   n  (only  200 ,  201 ,  202  and  20   n  are depicted in  FIG. 20 ), and switches SW 1 -SWn (only SW 1 , SW 2  and SWn are depicted in  FIG. 20 ). Unlike the prior art current mirror  800 , the current mirror  2000  of the present invention includes the LV PMOS transistors PL 0 -PLn and the HV devices  200 - 20   n  for respectively biasing the LV PMOS transistors PL 0 -PLn. The HV devices  200 - 20   n  can include HV PMOS transistors. The drain terminal of the LV PMOS transistor PL 0  is coupled to the current source I DC  via the HV device  200 , and the drain terminals of the LV PMOS transistor PL 1 -PLn are coupled to the AMOLED panel via the HV device  201 - 20   n  and the switches SW 1 -SWn, respectively. The current mirror  2000  controls the amount of the driving current using the switches SW 1 -SWn. Since the threshold voltage of an LV PMOS transistor is more stable than that of a HV PMOS transistor, the currents passing through the LV PMOS transistors PL 1 -PLn do not have large variations. Therefore, the current mirror  2000  can provide stable driving currents to the AMOLED panel for achieving high-resolution images.  
         [0059]     References are made to  FIGS. 21-24  showing current mirrors  2100 - 2400  according to a ninth, tenth, eleventh and twelfth embodiments of the present invention based on the structure of the sink-mode current mirror  1900 . Similar to the sink-mode current mirror  1900 , the HV NMOS transistors NH 0 -NHn are used for the HV devices in the current mirrors  2100 - 2400 . However, the gate terminals of the HV NMOS transistors NH 1 -NHn are coupled differently in the current mirrors  2100 - 2400 . In the current mirror  2100  shown in  FIG. 21 , the gate terminals of the HV NMOS transistors NH 0 -NHn are coupled to a reference voltage Vref. In the current mirror  2200  shown in  FIG. 22 , the gate terminal and the source terminal of the HV NMOS transistor NH 0  are coupled together. In the current mirror  2300  shown in  FIG. 23 , the gate terminal of the HV NMOS transistor NH 0  is coupled to a first reference voltage Vref 1 , and the gate terminals of the HV NMOS transistors NH 1 -NHn are coupled to a second reference voltage Vref 2 . In the current mirror  2400  shown in  FIG. 24 , the gate terminal and the source terminal of the HV NMOS transistor NH 0  are coupled together, and the gate terminals of the HV NMOS transistors NH 1 -NHn are coupled to a reference voltage Vref. Various circuits commonly known to those skilled in the art can be used for generating the reference voltages Vref, Vref 1 , and Vref 2 .  
         [0060]     References are made to  FIGS. 25-28  showing current mirrors  2500 - 2800  according to a thirteenth, fourteenth, fifteenth and sixteenth embodiments of the present invention based on the structure of the source-mode current mirror  2000 . Similar to the source-mode current mirror  2000 , the HV PMOS transistors PH 1 -PHn are used for the HV devices in the current mirrors  2500 - 2800 . However, the gate terminals of the HV PMOS transistors PH 1 -PHn are coupled differently in the current mirrors  2500 - 2800 . In the current mirror  2500  shown in  FIG. 25 , the gate terminals of the HV PMOS transistors PH 0 -PHn are coupled to a reference voltage Vref. In the current mirror  2600  shown in  FIG. 26 , the gate terminal and the source terminal of the HV PMOS transistor PH 0  are coupled together. In the current mirror  2700  shown in  FIG. 27 , the gate terminal of the HV PMOS transistor PH 0  is coupled to a first reference voltage Vref 1 , and the gate terminals of the HV PMOS transistors PH 1 -PHn are coupled to a second reference voltage Vref 2 . In the current mirror  2800  shown in  FIG. 28 , the gate terminal and the source terminal of the HV PMOS transistor PH 0  are coupled together, and the gate terminals of the HV PMOS transistors PH 1 -PHn are coupled to a reference voltage Vref. Various circuits commonly known to those skilled in the art can be used for generating the reference voltages Vref, Vref 1 , and Vref 2 .  
         [0061]     In conclusion, the present invention provides a current mirror using LV transistors in connection to HV devices providing biasing voltages. The current mirrors according to the present invention can receive a high voltage used for an OLED panel, and at the same time provide stable driving currents using LV transistors with stable threshold voltages, so that the OLED panel can provide high-resolution images. Diagrams illustrated in  FIG. 9 - FIG. 28  are merely embodiments of the present invention and do not limit the scope of the present invention.  
         [0062]     Those skilled in the art will readily observe that numerous modifications and alterations of the device and method may be made while retaining the teachings of the invention. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of the appended claims.