MicroLED array with adaptive PWM phase shift
An approach for controlling pixel turn on and turn off within an LED array is described. Turn-on delays for pixels within the LED array is based on the duty cycles of the pixels. The pixels are grouped based on corresponding duty cycles. The turn-on delay for each pixel is based on the group that includes the pixel, as well as position of the pixel within the group. The LED array is driven by circuitry in a CMOS backplane.
1. A complementary metal oxide semiconductor (CMOS) die for controlling pixels of a light-emitting diode (LED) array, the CMOS die comprising:
a digital interface to provide control signals to the LED array; and
logic coupled to the digital interface, the logic configured to:
determine duty cycles for each pixel of the pixels based on image data to display an image using the pixels;
segment the pixels into at least first pixels of a first group and second pixels of a second group based on duty cycles of the pixels, the duty cycles of the first pixels being different from the duty cycles of the second pixels; and
determine first turn-on delays for the first pixels based on a first number of the first pixels and second turn-on delays for the second pixels based on a second number of the second pixels for activation of the first pixels and the second pixels in accordance with the first and second turn-on delays, respectively, using the control signals to display the image, wherein LEDs of the LED array are independently-controllable and have lateral dimensions of less than about 100 μm.
2. The CMOS die of claim 1 , wherein:
the duty cycles of the first pixels are within a first range of duty cycles,
the duty cycles of the second pixels are within a second range of duty cycles, and
the first range of duty cycles is separate from the second range of duty cycles.
3. The CMOS die of claim 1 , wherein:
each of the first pixels has a unique first order number,
each of the second pixels has a unique second order number, and
the logic is further configured to:
divide a period of a cycle by the first number to produce a first delay increment and multiply the first delay increment by the unique first order number for each of the first pixels to produce the first turn-on delay for each of the first pixels; and
divide the period of the cycle by the second number to produce a second delay increment and multiply the second delay increment by the unique second order number for each of the second pixels to produce at least a portion of the second turn-on delays.
4. The CMOS die of claim 3 , wherein the logic is further configured to:
determine each first order number based on a position of the associated first pixel within the LED array; and
determine each second order number based on a position of the associated second pixel within the LED array.
5. The CMOS die of claim 3 , wherein the logic is further configured to:
determine a shift for the second group, the shift for the second group being equal to a smaller of the first and second delay increment; and
add the shift to the turn-on delays produced by the multiplication to produce the second turn-on delays.
6. A light-emitting diode (LED) structure comprising:
a complementary metal oxide semiconductor (CMOS) die configured to provide control signals based on image data of an image; and
a LED array comprising pixels, the pixels segmented into at least first pixels of a first group and second pixels of a second group based on duty cycles of the pixels, first turn-on delays of the first pixels based on a first number of the first pixels, second turn-on delays of the second pixels based on a second number of the second pixels, the first pixels and the second pixels configured to be activated in accordance with the first and second turn-on delays, respectively, using the control signals to display the image, wherein each pixel of the plurality of pixels has a lateral dimension of less than 100 μm.
7. The LED structure of claim 6 , wherein:
each of the pixels within the first group of pixels has a unique first order number,
each of the pixels within the second group of pixels has a unique second order number,
the turn-on delays for the pixels within the first group of pixels is a period of a cycle divided by a number of the pixels within the first group of pixels to produce a first delay increment and the first delay increment multiplied by the unique first order number to produce, for each pixel within the first group of pixels, the turn-on delay for the pixel, and
the turn-on delays for the pixels within the second group of pixels is the period of the cycle divided by a number of the pixels within the second group of pixels to produce a second delay increment and the second delay increment multiplied by the unique second order number to produce, for each pixel within the second group of pixels, at least a portion of the turn-on delay for the pixel.
8. The LED structure of claim 7 , wherein:
the unique first order number for each of the pixels within the first group of pixels is determined based on a position of the pixel within the LED array relative to other pixels within the first group of pixels; and
the unique second order number for each of the pixels within the second group of pixels is determined based on a position of the pixel within the LED array relative to other pixels within the second group of pixels.
9. The LED structure of claim 7 , wherein a first pixel within the first group of pixels and a first pixel within the second group of pixels are configured to be simultaneously activated.
10. The LED structure of claim 7 , wherein:
a shift is applied to the turn-on delays for the pixels within the second group of pixels to determine the turn-on delays for the pixels within the second group of pixels, and
the shift for the second group is equal to a smaller of the first and second delay increment.
11. The LED structure of claim 6 , further comprising a pulse width modulation (PWM) generator to generate a PWM signal in accordance with the turn-on delays and the duty cycles of the plurality of pixels, the PWM signal causing PWM switches corresponding to plurality of pixels to activate and deactivate.
12. The LED structure of claim 6 , further comprising an LED die that includes the LED array.
13. The LED structure of claim 6 , wherein LEDs of the LED array are independently-controllable.