Micro-LED amplitude control system
A control system for an LED array relies on defining a first and a second group of separately addressed LED pixels, with the first group including pixels with an average current no less than the current at a Q point and a second group including pixels with an average current less than the current at a Q point. An amplitude signal provided to the first group of separately addressed LED pixels is selectively modulated, while providing a DC mode 100% duty cycle. An amplitude signal provided to the second group of separately addressed LED pixels is fixed, and a modulated duty cycle is provided.
1. A method of illumination, the method comprising:
causing lighting elements of an illumination device to produce light by:
defining a first group of lighting elements and a second group of lighting elements, with the first group of lighting elements including first lighting elements that draw an average current of a current at a Q point or greater and the second group of lighting elements including second lighting elements that draw an average current less than the current at the Q point, wherein the Q point is at a maximum external quantum efficiency (EQE) of an EQE versus current density curve for the lighting elements, and the average current is defined by an image to be provided by the lighting elements;
selectively modulating, by a digital to analog converter (DAC), an amplitude of a first signal provided to the first group of lighting elements, the first signal including a fixed duty cycle; and
fixing, by a pulse width modulator (PWM), an amplitude of a second signal provided to the second group of lighting elements, the second signal including a modulated duty cycle.
2. The method of claim 1 , wherein the first signal is a direct current (DC) mode 100% duty cycle signal.
3. The method of claim 1 , wherein the amplitude of the first signal is set at Iampi*D i , where Iampi is a current amplitude defined by the image and D i is the fixed duty cycle.
4. The method of claim 1 , wherein the amplitude of the second signal is set at the Q point for the second lighting elements and the modulated duty cycle is set at D i *Iampi/IQ, where Iampi is a current amplitude defined by the image, D i is a pixel duty cycle, and IQ is the current at the Q point of the EQE versus current density curve.
5. The method of claim 1 , wherein additional groups of lighting elements are determined, each group of lighting elements having a defined range of pixel intensities.
6. The method of claim 1 , wherein the lighting elements present the image provided by an image processing unit.
7. An illumination system comprising:
lighting elements;
control circuitry configured to control first and second distinct groups of the lighting elements, the first group of lighting elements including first lighting elements with an average current of a current at a Q point of the lighting elements or greater and the second group of lighting elements including second lighting elements with an average current less than the current at a Q point of the lighting elements, wherein the Q point is a maximum external quantum efficiency (EQE) of an EQE versus current curve for the lighting elements, and the average current is defined by an image to be provided by the lighting elements;
a digital to analog controller (DAC) configured to, under control of the control circuitry, selectively adjust amplitude of signals to the lighting elements; and
a pulse width modulator (PWM) coupled to the DAC, the PWM configured to, under control of the control circuitry and with the DAC:
supply the first group of lighting elements with a first signal including a fixed duty cycle and a modulated amplitude, and
supply the second group of lighting elements with a second signal with a fixed amplitude and a modulated duty cycle.
8. The illumination system of claim 7 , wherein the first signal is a direct current (DC) mode 100% duty cycle signal.
9. The illumination system of claim 7 , wherein the DAC further comprises multiple DAC units.
10. The illumination system of claim 7 , further comprising an image processing unit configured to provide PWM and duty cycle data to the control circuitry, the PWM and duty cycle data, when implemented by the control circuitry, cause the lighting elements to present an image.
11. The illumination system of claim 7 , further comprising more than two groups of lighting elements; wherein the DAC is able to, under control of the control circuitry, selectively adjust an amplitude of a respective signal provided to each of the more than two groups of lighting elements.
12. The illumination system of claim 7 , wherein the amplitude of the second signal is less than the amplitude of the first signal.
13. The illumination system of claim 7 , wherein the second signal has amplitude fixed to approach peak external quantum efficiency (EQE) and lower overall system power usage.
14. An illumination method comprising:
providing lighting elements that produce light;
providing a control circuit configured to control first and second distinct groups of the lighting elements, the first group of lighting elements including first lighting elements with an average current no less than a current at a Q point and the second group of lighting elements including second lighting elements with an average current less than the current at the Q point, wherein the Q point is at a maximum external quantum efficiency (EQE) of an EQE versus current density curve for the lighting elements, and the average current is defined by an image to be provided by the lighting elements;
supplying, by a pulse width modulator (PWM) and a digital to analog converter (DAC) and under control of the control circuit, the first group of lighting elements with a first signal that includes a fixed duty cycle and a modulated amplitude; and
supplying, by the DAC and the PWM and under control of the control circuit, the second group of lighting elements with a second signal that includes a modulated duty cycle and a fixed amplitude.
15. The illumination method for an LED array of claim 14 , wherein the first signal is a direct current (DC) mode 100% duty cycle signal.
16. The illumination method for an LED array of claim 14 , wherein the image is provided by an image processing unit.
17. The illumination method for an LED array of claim 14 , wherein the second signal has amplitude decreased and duty cycle increased with respect to the first signal.
18. The illumination method for an LED array of claim 14 , wherein the second signal has amplitude decreased and duty cycle increased with respect to the first signal.
19. The illumination method for an LED array of claim 14 , wherein additional groups of lighting elements are determined, each group of lighting elements having a defined, different signal amplitude from each other group of lighting elements.