Driving for multi-junction polychromic display devices
A lighting system and method of driving an array within the lighting system are disclosed. The array includes vertically-stacked multi-color micro light-emitting diode (microLED) devices that emit light of different colors. Driving circuits and a ground switching circuit are controlled by processing circuitry to sequentially emit the colors of each microLED by independently driving pn junctions of the microLED. Each driving circuit includes multiplexers to receive a sink/source current and selectably provide the sink/source current to a channel based on control signals from the processing circuitry. Dimming of a particular color is effected using a pulse width modulated (PWM) signal to adjust a duty cycle over which the sink/source current is applied to the channel. The ground switching circuit selects another channel using multiplexers, and grounds the channel such that current is limited to flowing through one of the pn junctions at a time.
1 . A light system comprising:
an array of polychromic micro light-emitting diode (microLED) devices, each microLED device having vertically-stacked pn junctions on a substrate in which each junction is configured to emit light of a different color than at least one other pn junction;
a plurality of drivers configured to independently drive each color of each microLED device; and
processing circuitry configured to control the plurality of drivers, for each microLED device, to drive the microLED device to sequentially emit the colors,
wherein each driver comprises an m-channel cascaded analog multiplexer and a plurality of n-channel analog demultiplexers, the m-channel cascaded analog multiplexer being configured to receive a sink/source current at a first input and ground at a second input and selectably provide one of the sink/source current and ground to one of the n-channel analog demultiplexers based on a control signal from the processing circuitry, the n-channel analog demultiplexers configured to select a channel to route the one of the sink/source current and ground based on other control signals from the processing circuitry.
2 . The light system of claim 1 , wherein the processing circuitry is configured to control the plurality of drivers to avoid, for each microLED device, driving of the microLED device to simultaneously emit the colors.
3 . The light system of claim 1 , wherein each microLED device includes:
a first terminal coupled to a first end of a first pn junction, the first pn junction configured to emit first color light,
a second terminal coupled to a first end of a second pn junction, the first end of the second pn junction coupled to a second end of the first pn junction, the second pn junction configured to emit second color light different from the first color light,
a third terminal coupled to a first end of a third pn junction, the first end of the third pn junction coupled to a second end of the second pn junction, the third pn junction configured to emit third color light different from the first color light and the second color light, and
a fourth terminal coupled to a second end of the third pn junction.
4 . The light system of claim 3 , wherein the processing circuitry is configured to control the plurality of drivers to sequentially drive the first pn junction, the second pn junction, and third pn junction by operations comprising:
routing a first constant current to the first terminal via a first driver and grounding the second terminal during a first period of a cycle to limit driving during the first period to the first pn junction,
routing a second constant current to the second terminal via a second driver and grounding the third terminal during a second period of the cycle to limit driving during the second period to the second pn junction, and
routing a third constant current to the third terminal via a third driver and grounding the fourth terminal during a third period of the cycle to limit driving during the third period to the third pn junction.
5 . The light system of claim 4 , wherein the first constant current, the second constant current, and the third constant current are independent of each other and are substantially identical.
6 . The light system of claim 4 , wherein the first constant current, the second constant current, and the third constant current are independent of each other and are different from each other.
7 . The light system of claim 4 , wherein an on-duration of the first constant current, the second constant current, and the third constant current in the cycle are independent of each other and are substantially identical.
8 . The light system of claim 4 , wherein an on-duration of the first constant current, the second constant current, and the third constant current in the cycle are independent of each other and are different from each other.
9 . The light system of claim 3 , wherein the array of microLED devices comprises an array of bus lines coupled to the plurality of drivers in which:
a first bus line is coupled to the first terminal, a third bus line is coupled to the third terminal, and the first bus line is parallel to the third bus line, and
a second bus line is coupled to the second terminal, a fourth bus line is coupled to the fourth terminal, and the second bus line is parallel to the fourth bus line.
10 . The light system of claim 1 , wherein each driving circuit is configured to receive a bias current from a current driver and control signals from the processing circuitry.
11 . The light system of claim 1 , wherein:
the m-channel cascaded analog multiplexer comprises a cascaded multiplexer and a cascaded demultiplexer,
the cascaded demultiplexer is configured to receive the control signal from the processing circuitry and provide the one of the sink/source current and ground to the one of the n-channel analog demultiplexers, and
the cascaded multiplexer is further configured to receive a pulse width modulated (PWM) signal from the processing circuitry to set a duty cycle over which the sink/source current is applied to the channel and dim illumination provided by pn junctions coupled to the channel.
12 . The light system of claim 1 , further comprising a ground switching circuit configured to route ground to one of a plurality of terminals of each pn junction, the ground switching circuit comprising an m-channel analog demultiplexer and a plurality of n-channel analog demultiplexers, the m-channel analog demultiplexer having a grounded input and selectably to provide the ground to one of the n-channel analog demultiplexers based on a control signal from the processing circuitry, the n-channel analog demultiplexers configured to select a channel to route the ground based on other control signals from the processing circuitry.
13 . The light system of claim 1 , wherein the microLED device is configured to emit red, green, and blue light.
14 . A controller comprising:
a plurality of drivers configured to independently drive a plurality of bus lines of an array of polychromic micro light-emitting diode (microLED) devices, each microLED device having vertically-stacked pn junctions on a substrate in which each pn junction is configured to emit light of a different color than at least one other pn junction, each microLED device having terminals each coupled to a different bus line to emit one of the different colors;
a ground switching circuit configured to route ground to one of the bus lines; and
processing circuitry configured to control the plurality of drivers and ground switching circuit to sequentially drive, for each microLED device, the colors of the microLED device by providing a constant current to one of the bus lines and route the ground to another of the bus lines,
wherein each driver comprises an m-channel cascaded analog multiplexer and a plurality of n-channel analog demultiplexers, the m-channel cascaded analog multiplexer being configured to receive a sink/source current at a first input and ground at a second input and selectably provide one of the sink/source current and ground to one of the n-channel analog demultiplexers based on a control signal from the processing circuitry, the n-channel analog demultiplexers configured to select a channel to route the one of the sink/source current and ground based on other control signals from the processing circuitry.
15 . The controller of claim 14 , wherein the processing circuitry is configured to control the plurality of drivers and the ground switching circuit to driving each microLED device to avoid simultaneous emission of the colors.
16 . The controller of claim 14 , wherein the bus lines are arranged such that:
a first bus line is coupled to first terminals of the pn junctions, a third bus line is coupled to third terminals of the pn junctions, and the first bus line is parallel to the third bus line, and
a second bus line is coupled to second terminals of the pn junctions, a fourth bus line is coupled to fourth terminals of the pn junctions, and the second bus line is parallel to the fourth bus line.
17 . The controller of claim 14 , wherein:
the cascaded multiplexer is further configured to receive a pulse width modulated (PWM) signal from the processing circuitry to set a duty cycle over which the sink/source current is applied to the channel and dim illumination provided by pn junctions coupled to the channel.
18 . The controller of claim 14 , wherein the ground switching circuit comprises an m-channel analog demultiplexer and a plurality of n-channel analog demultiplexers, the m-channel analog demultiplexer having a grounded input and selectably route the ground to one of the n-channel analog demultiplexers based on a control signal from the processing circuitry, the n-channel analog demultiplexers configured to select a channel to route the ground based on other control signals from the processing circuitry.
19 . A method of providing light from an array of polychromic micro light-emitting diode (microLED) devices, the method comprising:
independently driving each color of each microLED device in the array, each microLED device having vertically-stacked pn junctions on a substrate in which each junction is configured to emit light of a different color than at least one other pn junction; and
controlling the driving of each microLED device to drive the microLED device to sequentially emit the colors using drivers, wherein each driver comprises an m-channel cascaded analog multiplexer and a plurality of n-channel analog demultiplexers, the m-channel cascaded analog multiplexer being configured to receive a sink/source current at a first input and ground at a second input and selectably provide one of the sink/source current and ground to one of the n-channel analog demultiplexers based on a control signal, the n-channel analog demultiplexers configured to select a channel to route the one of the sink/source current and ground based on other control signals.
20 . The method of claim 19 , wherein:
the m-channel cascaded analog multiplexer comprises a cascaded multiplexer and a cascaded demultiplexer,
the cascaded demultiplexer is configured to receive the control signal from the processing circuitry and provide the one of the sink/source current and ground to the one of the n-channel analog demultiplexers, and
the cascaded multiplexer is further configured to receive a pulse width modulated (PWM) signal from the processing circuitry to set a duty cycle over which the sink/source current is applied to the channel and dim illumination provided by pn junctions coupled to the channel.