Video driver architecture for AMOLED displays
View Patent ↗An AMOLED display system, including an AMOLED display panel receiving a video signal, includes a video driver receiving the video signal and generating a video drive signal indicative of the video signal and referenced to a positive power supply voltage of the display panel, and a current driver coupled to an OLED pixel element receiving the video drive signal and the positive power supply voltage and providing a drive current to the OLED pixel element. The drive current is proportional to a current drive voltage which is indicative of the video signal and independent of the positive power supply voltage. In one embodiment, the video drive signal is indicative of the sum of or the difference between the positive power supply voltage and the video signal and the current drive voltage is indicative of the difference between the positive power supply voltage and the video drive signal.
1. An active matrix organic light emitting diode (AMOLED) display system comprising an AMOLED display panel receiving a video signal to be displayed on the AMOLED display panel, the AMOLED display panel comprising a plurality of organic light emitting diode (OLED) pixel elements, the AMOLED display system comprising:
a video driver receiving the video signal and generating a video drive signal indicative of the video signal and referenced to a positive power supply voltage of the AMOLED display panel; and
a current driver coupled to at least one OLED pixel element, the current driver receiving the video drive signal and the positive power supply voltage and providing a drive current to the at least one OLED pixel element, the drive current being proportional to a current drive voltage being indicative of the video signal and independent of the positive power supply voltage.
2. The AMOLED display system of claim 1 , wherein the video drive signal is indicative of the sum of or the difference between the positive power supply voltage and the video signal and the current drive voltage is indicative of the difference between the positive power supply voltage and the video drive signal.
3. The AMOLED display system of claim 2 , wherein the video driver comprises a differential instrumentation amplifier circuit for providing the video drive signal being the difference between the positive power supply voltage and the video signal.
4. The AMOLED display system of claim 3 , wherein the video driver comprises:
an operational amplifier having a positive input terminal coupled to a first resistor, a negative input terminal coupled to a second resistor and an output terminal providing the video drive signal;
the first resistor being coupled between the positive input terminal of the operational amplifier and a ground voltage or a negative power supply voltage;
the second resistor being coupled between the video signal and the negative input terminal of the operational amplifier;
a third resistor being coupled between the positive input terminal of the operational amplifier and the positive power supply voltage; and
a fourth resistor being coupled between the negative input terminal and the output terminal of the operational amplifier.
5. The AMOLED display system of claim 2 , wherein the video driver comprises a current mode isolator circuit for providing the video drive signal being the difference between the positive power supply voltage and the video signal.
6. The AMOLED display system of claim 5 , wherein the video driver comprises:
an operational amplifier having a positive input terminal coupled to receive the video signal, a negative input terminal and an output terminal;
a transistor having a first current handling terminal providing the video drive signal, a second current handling terminal coupled to the negative input terminal of the operational amplifier, and a gate terminal coupled to the output terminal of the operational amplifier;
a first resistor being coupled to the negative input terminal of the operational amplifier and a ground voltage or a negative power supply voltage; and
a second resistor being coupled to the first current handling terminal of the transistor and the positive power supply voltage.
7. The AMOLED display system of claim 2 , wherein the video driver comprises a video clamp circuit for providing the video drive signal being the sum of the positive power supply voltage and the video signal.
8. The AMOLED display system of claim 7 , wherein the video driver comprises:
a first inverter having an input terminal coupled to receive a video blanking signal and an output terminal;
a first transistor having a first current handling terminal coupled to the positive power supply voltage, a second current handling terminal coupled to a first node providing the video drive signal, and a gate terminal coupled to the output terminal of the first inverter, the first transistor being turned on when the video blanking signal is asserted and turned off when the video blanking signal is deasserted;
an amplifier having an input terminal coupled to receive the video signal and an output terminal; and
a capacitor coupled between the output terminal of the amplifier and the first node,
wherein the capacitor is charged to the positive power supply when the video blanking signal is asserted and is charged to a sum of the video signal and the positive power supply voltage when the video blanking signal is deasserted.