Light emitting diode (LED) driver for backlight improving accuracy of output current and increasing uniformity of brightness between LED channels

Patent metadata

Field	Value
Publication number	US-11900865-B2
Application number	US-202218056406-A
Country	US
Kind code	B2
Filing date	Nov 17, 2022
Priority date	Nov 18, 2021
Publication date	Feb 13, 2024
Grant date	Feb 13, 2024

Abstract

A light-emitting diode (LED) driving circuit for driving an LED channel including a plurality of LED elements includes a switch-capacitor amplifier circuit configured to sample received input current and amplify an input voltage corresponding to the input current, a replica circuit configured to connect to the switch-capacitor amplifier circuit in a first period to define a first feedback loop, and an output circuit configured to connect to the switch-capacitor amplifier in a second period to define a second feedback loop. The second period is after the first period, and the output circuit is configured to generate output current according to an output voltage of the switch-capacitor amplifier circuit and provide the output current to the LED.

First claim

What is claimed is:

1. A light-emitting diode (LED) driving circuit for driving an LED channel comprising a plurality of LED elements, the LED driving circuit comprising:
a switch-capacitor amplifier circuit configured to sample received input current and amplify an input voltage corresponding to the input current;
a replica circuit configured to connect to the switch-capacitor amplifier circuit in a first period to define a first feedback loop, the replica circuit including a first transistor and a first resistor connected to the first transitor, and the first transistor configured to generate a current based on an output voltage of the switch-capacitor amplifier circuit in the first period; and
an output circuit configured to connect to the switch-capacitor amplifier circuit in a second period to define a second feedback loop, the second period being after the first period, the output circuit including a second transistor and a second resistor connected to the second transistor, and the output circuit configured to generate output current according to the output voltage of the switch-capacitor amplifier circuit in the second period and provide the output current to the LED channel.

2. The LED driving circuit of claim 1 , wherein the switch-capacitor amplifier circuit comprises:
an amplifier comprising a first input end and a second input end;
a first capacitor having an end connected to the first input end of the amplifier, the first capacitor configured to store the input voltage; and
a second capacitor having a first end connected to the second input end of the amplifier.

3. The LED driving circuit of claim 2 , wherein a capacitance of the first capacitor and a capacitance of the second capacitor are identical.

4. The LED driving circuit of claim 3 , wherein
the switch-capacitor amplifier circuit and the replica circuit are configured to connect to each other in the first period, and
the second capacitor is configured to store an offset voltage according to an offset of the amplifier.

5. The LED driving circuit of claim 2 , wherein the switch-capacitor amplifier circuit further comprises:
a third resistor configured to conduct the input current in the first period;
a first switch configured to connect an end of the third resistor to the end of the first capacitor in the first period;
a second switch configured to connect the end of the third resistor to a second end of the second capacitor in the first period;
a third switch configured to connect the first end of the second capacitor to the replica circuit in the first period; and
a fourth switch configured to connect the second end of the second capacitor to the output circuit in the second period.

6. The LED driving circuit of claim 5 , wherein
the first switch, the second switch, and the third switch are configured to turn off in the second period, and
a voltage change amount of the first input end due to leakage current of the first switch is same as a voltage change amount of the second input end due to leakage current of the second switch.

7. The LED driving circuit of claim 1 , wherein,
in the first period, the output circuit is configured to be in an off state, and
in the second period, the replica circuit is configured to be in an off state, and the output circuit is configured to generate the output current in response to a dimming control signal.

8. The LED driving circuit of claim 1 , further comprising a digital-to-analog converter configured to generate a reference current, provide the reference current as the input current to the switch-capacitor amplifier circuit, and vary the reference current according to input data.

9. A light-emitting diode (LED) driving circuit for driving a backlight unit comprising a plurality of LED channels, the LED driving circuit comprising:
a current source configured to generate a reference current; and
a plurality of channel driving circuits configured to sequentially sample the reference current received from the current source, and generate output current,
wherein each of the plurality of channel driving circuits comprises
a switch-capacitor amplifier circuit configured to sample the reference current and amplify an input voltage corresponding to an input current, the switch-capacitor amplifier circuit including,
an amplifier including a first input end and a second input end,
a first capacitor having an end connected to the first input end of the amplifier, the first capacitor configured to store the input voltage, and
a second capacitor having a first end connected to the second input end of the amplifier,

an output circuit configured to generate output current according to an output voltage of the switch-capacitor amplifier circuit in response to a dimming control signal, and provide the output current to LED elements, and
a replica circuit connected to the switch-capacitor amplifier circuit to define a feedback loop when the output circuit is in an off state.

10. The LED driving circuit of claim 9 , wherein
the current source comprises a digital-to-analog converter configured to generate the reference current based on input data corresponding to each of the plurality of channel driving circuits, and
the reference current has a current value corresponding to each of the plurality of channel driving circuits.

11. The LED driving circuit of claim 9 , wherein,
in a first period, the replica circuit is configured to connect to the switch-capacitor amplifier circuit to sample the input current, and the output circuit is configured to turn off; and
in a second period consecutive to the first period, the output circuit is configured to connect to the switch-capacitor amplifier circuit to generate output current based on the output voltage, and the replica circuit is configured to turn off.

12. The LED driving circuit of claim 9 , wherein a period in which a first one of the plurality of channel driving circuits generates the output current, and a period in which a second one of the plurality of channel driving circuits samples the reference current, overlap each other.

13. The LED driving circuit of claim 9 , wherein the switch-capacitor amplifier circuit comprises:
an input resistor having an end configured to receive the reference current;
a first switch configured to turn on to connect the end of the input resistor to the end of the first capacitor; and
a second switch configured to turn on to connect the end of the input resistor to a second end of the second capacitor.

14. A backlight device comprising:
a backlight unit (BLU) comprising a plurality of dimming groups;
a plurality of pixel circuits each configured to drive a corresponding one of the plurality of dimming groups, each of the plurality of pixel circuits comprising a plurality of channel driving circuits configured to provide a plurality of output currents to a plurality of light-emitting diode (LED) channels included in the corresponding one of the plurality of dimming groups; and
a pixel driving circuit configured to provide a reference current to the plurality of pixel circuits,
wherein each of the plurality of channel driving circuits comprises
a switch-capacitor amplifier circuit configured to sample the reference current in a first period,
a replica circuit configured to define a feedback loop with the switch-capacitor amplifier circuit in the first period, the replica circuit including a transistor and a resistor connected to the transistor, the transistor configured to operate based on an output of the switch-capacitor amplifier circuit in the first period, and
an output circuit including a driving transistor

Assignees

• Samsung Electronics Co Ltd

Inventors

• Kwak Yongsik
• Kim Sunkwon
• Kwon Yongil
• Song Uijong
• Jeong Moonsuk
• Choi Youngkil

Classifications

• G09G3/32 Primary

  semiconductive, e.g. using light-emitting diodes [LED] · CPC title

• G09G3/2007

  Display of intermediate tones · CPC title

• G09G2300/0828

  forming a digital to analog [D/A] conversion circuit · CPC title

• G09G2300/0852

  being a dynamic memory with more than one capacitor · CPC title

• G09G2310/0291

  Details of output amplifiers or buffers arranged for use in a driving circuit · CPC title