# US 10,764,975 B2 · Pulse-width-modulation control of micro light emitting diode

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- Number: US 10,764,975 B2
- Document ID: US10764975B2
- Status: Granted
- Kind: B2
- Application number: 15/942,377
- Filed: 2018-03-30
- Published: 2019-10-03
- Granted: 2020-09-01
- Earliest claimed: 2018-03-30
- Assignees: Facebook Technologies, LLC
- Applicants: Facebook Technologies, LLC
- Inventors: Gareth John Valentine
- Web page: https://patentgrep.com/patent/US10764975B2

## CPC

- H03K 7/08: Duration or width modulation {; Duty cycle modulation}
- G09G 3/2014: {by modulation of the duration of a single pulse during which the logic level remains constant}
- G09G 3/32: semiconductive, e.g. using light-emitting diodes [LED]
- H03M 1/123: {Simultaneous, i.e. using one converter per channel but with common control or reference circuits for multiple converters}
- H03M 1/56: Input signal compared with linear ramp
- H03M 1/822: {using pulse width modulation}
- H05B 45/20: Controlling the colour of the light
- H05B 47/10: Controlling the light source
- G09G 2300/0842: forming a memory circuit, e.g. a dynamic memory with one capacitor
- G09G 2300/0861: with additional control of the display period without amending the charge stored in a pixel memory, e.g. by means of additional select electrodes
- G09G 2310/027: Details of drivers for data electrodes, the drivers handling digital grey scale data, e.g. use of D/A converters
- G09G 2310/0272: Details of drivers for data electrodes, the drivers communicating data to the pixels by means of a current
- G09G 2310/066: Waveforms comprising a gently increasing or decreasing portion, e.g. ramp
- G09G 2320/064: by time modulation of the brightness of the illumination source
- H03K: PULSE TECHNIQUE (measuring pulse characteristics G01R; modulating sinusoidal oscillations with pulses H03C; transmission of digital information H04L; discriminator circuits detecting phase difference between two signals by counting or integrating cycles of oscillation H03D3/04; automatic control, starting, synchronisation or stabilisation of generators of electronic oscillations or pulses where the type of generator is irrelevant or unspecified H03L; coding, decoding or code conversion, in general H03M)
- G09G: ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION (arrangements for transferring data between digital computers and displays G06F3/14; static indicating arrangements comprising an association of a number of separate sources or light control cells G09F9/00; static indicating arrangements comprising integral associations of a number of light sources H01J, H01K, H10H, H05B33/12; scanning, transmission or reproduction of documents or the like, e.g. facsimile transmission, details thereof H04N1/00)
- H03M: CODING; DECODING; CODE CONVERSION IN GENERAL (using fluidic means F15C4/00; optical analogue/digital converters G02F7/00; coding, decoding or code conversion, specially adapted for particular applications, see the relevant subclasses, e.g. G01D, G01R, G06F, G06T, G09G, G10L, G11B, G11C, H04B, H04L, H04M, H04N; ciphering or deciphering for cryptography or other purposes involving the need for secrecy G09C)
- H05B: ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL

## Abstract

Embodiments relate to a light-emitting-diode (LED) cell that includes a LED and a controller. The controller receives a brightness data signal and generates a driving signal corresponding to the brightness data signal. The controller includes a comparator that receives the brightness data signal and a control waveform signal. The controller is coupled to a switched current source that generates a driving current based on the driving signal.

## Claims

### Claim 1

A light-emitting-diode (LED) display device comprising:
a LED disposed within a cell of the LED display device, the LED configured to emit light; and
a controller disposed within the cell of the LED display device, the controller receiving an analog brightness control data signal corresponding to a desired brightness of the LED, and generating a driving signal having a fixed amplitude and a varying duration corresponding to an amplitude of the analog brightness control data signal, the controller comprising:
a sample and hold circuit configured to receive the analog brightness control data signal, and store the analog brightness control data signal as a frame brightness signal in a storing element responsive to receiving a select signal having a predetermined value, wherein the received analog brightness control data signal is not based on a voltage at a terminal of the LED, and
a comparator circuit having an input coupled to an output of the sample and hold circuit, the comparator circuit configured to receive the frame brightness signal and a control waveform signal, and generate the driving signal based on a comparison between a voltage level of the frame brightness signal and a voltage level of the control waveform signal, wherein the control waveform signal is a periodic signal that changes from a first value to a second value within each display frame; and
a switched current source configured to receive the driving signal and generate a driving current based on the driving signal for driving the LED, the driving current having a fixed amplitude and a varying duration corresponding to the amplitude of the analog brightness control data signal.

### Claim 2 (depends on 1)

The LED display device of claim 1, wherein the sample and hold circuit comprises:
a sampling switch receiving the analog brightness control data signal, the sampling switch configured to turn on and off based on the select signal; and
a holding capacitor coupled to an output of the sample switch, the holding capacitor configured to store the analog brightness control data signal as the frame brightness signal responsive to the sample switch being on.

### Claim 3 (depends on 1)

The LED display device of claim 1, wherein the comparator circuit comprises:
a differential pair including a first transistor receiving the frame brightness signal, and a second transistor receiving the control waveform signal.

### Claim 4 (depends on 1)

The μLED display device of claim 1, wherein the control waveform signal includes one of a plurality of linear features and a nonlinear periodic waveform.

### Claim 5 (depends on 1)

The LED display device of claim 1, wherein the controller further comprises:
a digital-to-analog converter (DAC) configured to receive a digital brightness data signal and convert the digital brightness data signal to the analog brightness signal, an output of the DAC coupled to an input of the sample and hold circuit.

### Claim 6 (depends on 1)

The LED display device of claim 1, wherein the switched current source comprises a transistor that is configured to turn on and off based on the output of the controller.

### Claim 7

A light emitting diode (LED) driver circuit comprising:
a controller receiving a brightness data signal corresponding to a desired brightness of the LED, and generating a driving signal corresponding to the brightness data signal, the controller comprising:
a sample and hold circuit configured to receive the brightness data signal, and store the brightness data signal as a frame brightness signal in a storing element responsive to receiving a select signal having a predetermined value, wherein the received brightness data signal is not based on a voltage at a terminal of the LED, and
a comparator circuit having an input coupled to an output of the sample and hold circuit, the comparator circuit configured to receive the frame brightness signal and a control waveform signal, and generate the driving signal based on a comparison between a voltage level of the frame brightness signal and a voltage level of the control waveform signal, wherein the control waveform signal is a periodic signal that changes from a first value to a second value within each display frame; and
a switched current source configured to receive the driving signal and generate a driving current based on the driving signal for driving the LED.

### Claim 8 (depends on 7)

The LED display device of claim 7, wherein the LED is driven with a current density above 1 A/cm2.

### Claim 9 (depends on 7)

The LED display device of claim 7, wherein the sample and hold circuit comprises:
a sampling switch receiving the brightness data signal, the sampling switch configured to turn on and off based on the select signal; and
a holding capacitor, the holding capacitor coupled to an output of the sample switch, the holding capacitor configured to store the brightness data signal as the frame brightness signal responsive to the sample switch being on.

### Claim 10 (depends on 7)

The LED display device of claim 7, wherein the comparator comprises:
a differential pair including a first transistor receiving the frame brightness signal, and a second transistor receiving the control waveform signal.

### Claim 11 (depends on 7)

The LED display device of claim 7, wherein the control waveform signal includes a plurality of sawtooth pulses.

### Claim 12 (depends on 7)

The LED display device of claim 7, wherein the controller further comprises:
a digital-to-analog converter (DAC), configured to receive a digital brightness data signal and generate the brightness data signal provided to the sample and hold circuit by converting the digital brightness data signal to an analog signal, an output of the DAC coupled to an input of the sample and hold circuit.

### Claim 13 (depends on 7)

The LED display device of claim 7, wherein the switched current source comprises a transistor that is configured to turn on and off based on the output of the controller.

### Claim 14

A method for operating a light-emitting-diode (LED) of an LED display device, the LED display device displaying images in display frames, comprising:
receiving a digital brightness data signal corresponding to a desired brightness of the LED in a subsequent display frame;
converting the digital brightness data signal to an analog brightness data signal;
storing the analog brightness data signal as a frame brightness signal responsive to receiving a select signal having a predetermined value, wherein the stored analog brightness data signal is not based on a voltage at a terminal of the LED;
receiving a sawtooth pulse signal;
generating a control signal by comparing the stored frame brightness signal and the sawtooth pulse signal, wherein the sawtooth pulse signal is a periodic signal that changes from a first value to a second value within each display frame;
generating a driving current having a fixed amplitude and a varying duration based on the generated control signal, the duration of the generated driving current corresponding to an amplitude of the analog brightness data signal; and
driving the LED using the generated control signal.

### Claim 15 (depends on 14)

The method of claim 14, wherein the control signal has a preset amplitude.

### Claim 16 (depends on 14)

The method of claim 14, further comprising:
turning a sampling switch based on a sample signal, the sampling switch for providing the analog brightness data signal to a holding capacitor when the sampling switch is on;
storing the analog brightness data signal in the holding capacitor, wherein the received frame brightness signal is a voltage level of the holding capacitor.

### Claim 17 (depends on 14)

The method of claim 14, wherein the LED is driven with a current density above 1 A/cm2.

### Claim 18 (depends on 1)

The LED display device of claim 1, wherein the analog brightness control data signal is a signal external to an individual pixel drive electronics.

### Claim 19 (depends on 1)

The LED display device of claim 1, wherein the analog brightness control data signal is a desired brightness of the LED in a subsequent display frame.

### Claim 20 (depends on 1)

The LED display device of claim 1, the first value is larger than the second value, and wherein the control waveform signal decreases from the first value to the second value within each display frame of the LED display device.