Patent Description:
The present disclosure relates to light emitting diodes (LEDs) and more particularly to systems and methods for reducing the persistence effect of LEDs.

The information provided in this section is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.

A light emitting diode (LED) is a semiconductor based light source. The LED emits light when current flows through the LED. Electrons in the semiconductor recombine with electron holes to release energy in the form of photons. The color of the light emitted by the LED corresponds to the energy of the photons.

LEDs are used in various different industries. For example, some LEDs emit low intensity infrared (IR) light and are used in remote control circuits, such as to control televisions. As another example, LEDs may be used as visual indicators and replace light bulbs. LEDs may also be used as other light sources, such as in residential and commercial lighting. As yet another example, LEDs may be used in seven-segment displays and other types of displays. LEDs have advantages over incandescent light sources (e.g., bulbs), such as lower energy consumption, lower heat generation, longer life, etc.
<CIT> discloses a drive circuit and light emitting device.

The invention is defined by a system according to claim <NUM> and by a method according to claim <NUM>. Further embodiments are set out in the dependent claims.

In a feature, a system is provided according to claim <NUM>.

In further features, when in the second state, the switching circuit is configured to connect the ground reference potential to the anode of the LED.

In further features: the switching circuit includes: a first switch having a first terminal connected to the positive reference potential and a second terminal connected to a first node; a second switch having a first terminal connected to the first node and a second terminal connected to a second node; the anode of the LED is connected to the first node; the cathode of the LED is connected to the second node; and the ground reference potential is connected to the second node.

In further features, the driver module is configured to: close the first switch and open the second switch to operate the switching circuit in the first state; and open the first switch and close the second switch to operate the switching circuit in the second state.

In further features, when in the second state, the switching circuit is configured to connect the negative reference potential to the anode of the LED.

In further features: the switching circuit includes: a first switch having a first terminal connected to the positive reference potential and a second terminal connected to a first node; a second switch having a first terminal connected to the negative reference potential and a second terminal connected to the first node; and a second node connected to the cathode of the LED; and the anode of the LED is connected to the first node.

In further features, the driver module is configured to: operate the switching circuit in the first state by closing the first switch and opening the second switch; and operate the switching circuit in the second state by opening the first switch and closing the second switch.

In further features, the driver module is configured to: maintain the first switch open and the second switch closed for a predetermined persistence period; and open the second switch once the predetermined persistence period has elapsed.

In further features, when in the second state, the switching circuit is configured to connect the cathode of the LED to the positive reference potential and connect the anode of the LED to the ground reference potential, thereby enabling current flow in the second direction through the LED.

In further features, the switching circuit includes: a first switch having a first terminal connected to the positive reference potential and a second terminal connected to a first node; a second switch having a first terminal connected to the positive reference potential and a second terminal connected to a second node; a third switch having a first terminal connected to the first node and a second terminal connected to the ground reference potential; and a fourth switch having a first terminal connected to the second node and a second terminal connected to the ground reference potential; the anode of the LED is connected to the first node; and the cathode of the LED is connected to the second node.

In further features, the driver module is configured to: operate the switching circuit in the first state by closing the first switch and fourth switches and opening the second switch and third switches; and operate the switching circuit in the second state by opening the first and fourth switches and closing the second and third switches.

In further features, the driver module is configured to: maintain the first and fourth switches open and the second and third switches closed for a predetermined persistence period; and open the second and third switches once the predetermined persistence period has elapsed.

In further features, the driver module is further configured to close the fourth switch once the predetermined persistence period has elapsed.

In further features, the LED is configured to emit light having a wavelength of between <NUM> nanometers (nm) and <NUM> millimeter (mm).

In further features: a camera; and an imaging module configured to: actuate the camera and capture a first image using the camera while the switching circuit is in the first state; and actuate the camera and capture a second image using the camera while the switching circuit is in the second state.

In further features, the imaging module is configured to actuate the camera and capture images at a predetermined frequency, where the predetermined frequency is at least <NUM>.

In further features, the driver module is configured to transition the switching circuit from the second state to the first state at the predetermined frequency.

In further features, the imaging module is configured to adjust the first image using the second image.

In further features, the camera is an infrared (IR) camera and is configured to capture images within a passenger cabin of a vehicle.

In a feature a method includes: selectively operating a switching circuit in a first state, thereby: connecting an anode of a light emitting diode (LED) to a positive reference potential; connecting a cathode of the LED to a ground reference potential; and enabling current flow in a first direction through the LED; and selectively operating a switching circuit in a second state, thereby one of: connecting the ground reference potential to the anode of the LED; connecting a negative reference potential to the anode of the LED; and connecting the cathode of the LED to the positive reference potential, connecting the anode of the LED to the ground reference potential, and enabling current flow in a second direction through the LED, where the second direction is opposite the first direction; and selectively transitioning the switching circuit from the first state to the second state and from the second state to the first state.

Further areas of applicability of the present disclosure will become apparent from the detailed description, the claims and the drawings. The detailed description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the disclosure.

Light emitting diodes (LEDs) may be used for illumination, such as illumination within a passenger cabin of a vehicle. An LED may be turned on when a camera is used such that an environment in an image captured using the camera is illuminated by the LED. This sort of image may be referred to as a content image. Background images may also be captured with the LED off. Characteristics of the background images (e.g., background illumination) may be used to adjust characteristics of the content images.

The LED emits light for a period of time after current through the LED is disabled. This phenomenon may be referred to as the persistence of the LED. The persistence of the LED may affect one or more characteristics of the background images. The background images (taken during persistence) may affect the adjustment of the content images.

The present application involves minimizing persistence of the LED. For example, a driver module of an LED may shunt an anode of the LED to ground to minimize the persistence (period) of the LED. As another example, the driver module may apply a negative reference potential to the anode of the LED or apply power to the LED in reverse of normal orientation to minimize the persistence (period) of the LED. This may improve the background images.

<FIG> includes a functional block diagram of an example vehicle <NUM>. While the example of a vehicle is provided, the present application is also applicable to non-vehicle implementations including LEDs (e.g., machine vision, optical inspection, lighting) and other uses of LEDs in vehicles.

The vehicle <NUM> includes a passenger cabin that includes one or more seats, such as seats <NUM>. Vehicle occupants may sit on seats within the passenger cabin while the vehicle moves. The vehicle <NUM> may be an autonomous vehicle (that drives without user input), a semiautonomous vehicle (that drives without user input under some circumstances and based on user input under other circumstances), or a non-autonomous vehicle (that is driven by a user). While the example of two seats is provided, the vehicle <NUM> may include more than two seats or only one seat. A seatbelt is provided with each seat.

A camera <NUM> is configured and arranged to capture images within the passenger cabin. The camera <NUM> may be, for example, an infrared (IR) camera or another suitable type of camera.

An imaging module <NUM> triggers the camera <NUM> to capture images at a predetermined frequency, such as <NUM>-<NUM> Hertz (Hz) or another suitable frequency. As such, the camera <NUM> captures one image every predetermined period, where the predetermined period corresponds to <NUM> divided by the predetermined frequency. The images alternate back and forth between content images and background images. In other words, one image captured by the camera <NUM> is a content image, a next image captured by the camera <NUM> is a background image, a next image captured by the camera <NUM> is a content image, a next image captured by the camera <NUM> is a background image, and so on.

A light emitting diode (LED) <NUM> is on while the camera <NUM> captures content images. The LED <NUM> is off while the camera <NUM> captures background images. While the example of the single LED <NUM> is provided and will be discussed for simplicity, the LED <NUM> may include more than one LEDs connected in series, parallel, or a combination of series and parallel. The LED <NUM> may be, for example, an IR LED (that emits light in the IR range between <NUM> nanometers and <NUM> millimeter) or another suitable type of LED.

A driver module <NUM> controls turning on and turning off of the LED <NUM> by controlling switches of a switching circuit <NUM> to control application of power to the LED <NUM> from one or more power sources, such as power source <NUM>. The power source <NUM> may include a direct current (DC) voltage. The power source <NUM> may include or be generated based on a battery, such as a <NUM> volt vehicle battery or another suitable type of battery. In various implementations, the power source may include a voltage converter that converts voltage from another power source (e.g., a vehicle battery) into a voltage suitable for application to the LED <NUM>. The driver module <NUM> turns the LED <NUM> on for content images and turns the LED <NUM> off for background images. The driver module <NUM> therefore turns the LED <NUM> on and off at a predetermined LED frequency, such as corresponding to <NUM>-<NUM> times per second.

The imaging module <NUM> may perform one or more image processing functions based on the images captured by the camera <NUM>. For example, the imaging module <NUM> may remove background illumination from a content image using the background image taken next after that content image was captured. The imaging module <NUM> may perform one or more functions based on the resulting content image. For example, the imaging module <NUM> may determine whether an occupant is seated on a seat based on the resulting content image.

The LED <NUM>, however, naturally emits light for some amount of time after power is removed from the LED <NUM>. In other words, the LED <NUM> does not turn off (and stop emitting light) immediately when current flow through the LED <NUM> is stopped. This may be referred to as the persistence of the LED <NUM>. If background images are captured while the LED <NUM> is still on (due to its persistence), the LED <NUM> may (artificially) contribute to the background lighting. This may affect the image processing functions performed by the imaging module <NUM>, such as the removal of background illumination from content images.

According to the present application, the driver module <NUM> minimizes or reduces the persistence of the LED <NUM>. For example, the driver module <NUM> may shunt the anode of the LED <NUM> to a ground reference potential after turning off power to the LED <NUM>. Additionally or alternatively, the driver module <NUM> may connect the anode of the LED <NUM> to a negative power source after turning off power to the LED <NUM>. Additionally or alternatively, the driver module <NUM> may reverse power the LED <NUM> (e.g., apply a positive reference potential to the cathode and a negative reference potential or ground to the anode) after turning off power to the LED <NUM>.

<FIG> is a schematic of an example circuit for minimizing persistence of the LED <NUM>. In the example of <FIG>, the switching circuit <NUM> includes a first switch <NUM> (A) and a second switch <NUM> (B), and the driver module <NUM> minimizes persistence by shunting the anode of the LED <NUM> to ground.

A first terminal <NUM> of the first switch <NUM> is connected to a positive (+) reference potential (e.g., + <NUM> volts DC) from the power source <NUM>. A second terminal <NUM> of the first switch <NUM> is connected to a node <NUM>. The first switch <NUM> may be, for example, a metal oxide semiconductor field effect transistor (MOSFET) or another suitable type of switch.

A first terminal <NUM> of the second switch <NUM> is connected to the node <NUM>. A second terminal <NUM> of the second switch <NUM> is connected to a node <NUM>. The second switch <NUM> may be, for example, a MOSFET or another suitable type of switch. The node <NUM> is connected to a ground reference potential, such as a chassis ground of the vehicle. A negative reference potential of the power source <NUM> may also be connected to the ground reference potential.

An anode <NUM> of the LED <NUM> is connected to the node <NUM>. A cathode <NUM> of the LED <NUM> is connected to the node <NUM>.

The driver module <NUM> controls the first and second switches <NUM> and <NUM> to control the LED <NUM>. To turn the LED <NUM> on, the driver module <NUM> closes the first switch <NUM> (e.g., turns the first switch <NUM> on) and concurrently opens the second switch <NUM> (e.g., turns the second switch <NUM> off). To turn the LED <NUM> off and minimize the persistence of the LED <NUM>, the driver module <NUM> closes the second switch <NUM> (e.g., turns the second switch <NUM> on) and concurrently opens the first switch <NUM> (e.g., turns the first switch <NUM> off). Below is an example table illustrative of the states of the first and second switches <NUM> and <NUM> to turn the LED <NUM> on and off.

<FIG> is a schematic of an example circuit for minimizing persistence of the LED <NUM>. In the example of <FIG>, the switching circuit <NUM> includes a first switch <NUM> (A) and a second switch <NUM> (B), and the driver module <NUM> minimizes persistence by applying a negative reference potential to the LED <NUM>.

A first terminal <NUM> of the first switch <NUM> is connected to a positive (+) reference potential (e.g., + <NUM> volts DC) from a power source <NUM>. A second terminal <NUM> of the first switch <NUM> is connected to a node <NUM>. The first switch <NUM> may be, for example, a MOSFET or another suitable type of switch.

A first terminal <NUM> of the second switch <NUM> is connected to the node <NUM>. A second terminal <NUM> of the second switch <NUM> is connected to a negative reference potential of a power source <NUM>. The second switch <NUM> may be, for example, a MOSFET or another suitable type of switch.

A negative reference potential of the power source <NUM> is connected to a node <NUM>. A positive reference potential (e.g., + <NUM> volts DC) of the power source <NUM> is also connected to the node <NUM>. The power source <NUM> includes the power source <NUM> and the power source <NUM> in this example.

The driver module <NUM> controls the first and second switches <NUM> and <NUM> to control the LED <NUM>. To turn the LED <NUM> on, the driver module <NUM> closes the first switch <NUM> (e.g., turns the first switch <NUM> on) and concurrently opens the second switch <NUM> (e.g., turns the second switch <NUM> off). To turn the LED <NUM> off and minimize the persistence of the LED <NUM>, the driver module <NUM> closes the second switch <NUM> (e.g., turns the second switch <NUM> on) and concurrently opens the first switch <NUM> (e.g., turns the first switch <NUM> off). The driver module <NUM> maintains the second switch <NUM> closed and the first switch <NUM> open for a predetermined persistence period. The LED <NUM> is completely off when the predetermined persistence period has passed. Once the predetermined persistence period has passed, the driver module <NUM> transitions the second switch <NUM> to open and maintains the first switch <NUM> open.

Below is an example table illustrative of the states of the first and second switches <NUM> and <NUM> to turn the LED <NUM> on and off.

<FIG> is a schematic of an example circuit for minimizing persistence of the LED <NUM>. In the example of <FIG>, the switching circuit <NUM> includes a first switch <NUM> (A), a second switch <NUM> (B), a third switch <NUM> (C), and a fourth switch <NUM> (D). The driver module <NUM> minimizes persistence by reverse powering the LED <NUM> (by applying a positive reference potential to the cathode and a negative reference potential or ground to the anode).

A positive (+) reference potential (e.g., + <NUM> volts DC) of the power source <NUM> is connected to a node <NUM>. A negative (-) reference potential of the power source <NUM> is connected to a node <NUM>. The node <NUM> is connected to a ground reference potential, such as a chassis ground of the vehicle.

A first terminal <NUM> of the first switch <NUM> is connected to the node <NUM>. A second terminal <NUM> of the first switch <NUM> is connected to a node <NUM>. The first switch <NUM> may be, for example, a MOSFET or another suitable type of switch.

A first terminal <NUM> of the third switch <NUM> is connected to the node <NUM>. A second terminal <NUM> of the third switch <NUM> is connected to the node <NUM>. The third switch <NUM> may be, for example, a MOSFET or another suitable type of switch.

A first terminal <NUM> of the second switch <NUM> is connected to the node <NUM>. A second terminal <NUM> of the second switch <NUM> is connected to a node <NUM>. The second switch <NUM> may be, for example, a MOSFET or another suitable type of switch.

A first terminal <NUM> of the fourth switch <NUM> is connected to the node <NUM>. A second terminal <NUM> of the fourth switch <NUM> is connected to the node <NUM>. The fourth switch <NUM> may be, for example, a MOSFET or another suitable type of switch.

An anode <NUM> of the LED <NUM> is connected to the node <NUM>. A cathode <NUM> of the LED <NUM> is connected to the node <NUM>. In this example, the first, second, third, and fourth switches <NUM>, <NUM>, <NUM>, and <NUM> form a bridge.

The driver module <NUM> controls the first, second, third, and fourth switches <NUM>, <NUM>, <NUM>, and <NUM> to control the LED <NUM>. To turn the LED <NUM> on, the driver module <NUM> closes the first and fourth switches <NUM> and <NUM> (e.g., turns the first and fourth switches <NUM> and <NUM> on) and concurrently opens the second and third switches <NUM> and <NUM> (e.g., turns the second and third switches <NUM> and <NUM> off). To turn the LED <NUM> off and minimize the persistence of the LED <NUM>, the driver module <NUM> closes the second and third switches <NUM> and <NUM> (e.g., turns the second and third switches <NUM> and <NUM> on) and concurrently opens the first and fourth switches <NUM> and <NUM> (e.g., turns the first and fourth switches <NUM> and <NUM> off). The driver module <NUM> maintains the second and third switches <NUM> and <NUM> closed and the first and fourth switches <NUM> and <NUM> open for a predetermined persistence period. The LED <NUM> is completely off when the predetermined persistence period has passed. Once the predetermined persistence period has passed, the driver module <NUM> transitions the second and third switches <NUM> and <NUM> to open and maintains the first switch <NUM> open. The driver module <NUM> may also maintain the fourth switch <NUM> open or transition the fourth switch <NUM> closed after the predetermined persistence period has passed.

Below is an example table illustrative of the states of the first, second, third, and fourth switches <NUM>, <NUM>, <NUM>, and <NUM> to turn the LED <NUM> on and off.

In the table above, for LED OFF (after the predetermined persistence period), the driver module <NUM> may set both the third (C) and fourth (D) switches <NUM> and <NUM> on or off. When both the first (A) and second (B) switches <NUM> and <NUM> are off, the states of the third (C) and fourth (D) switches <NUM> and <NUM> do not matter and the LED <NUM> will be off. Also, if the third (C) and fourth (D) switches <NUM> and <NUM> are off, the driver module <NUM> may control the first (A) and second (B) switches <NUM> and <NUM> to be either on or off. In other words, if top side switches are off, the LED <NUM> will be off regardless of the states of the bottom side switches. Conversely, if bottom side switches are off, the LED <NUM> will be off regardless of the states of the top side switches.

<FIG> is a flowchart depicting an example method of turning the LED <NUM> on and off while minimizing persistence of the LED <NUM>. Control begins with <NUM> where the driver module <NUM> actuates the switching circuit <NUM> such that (positive) current flows through the LED <NUM> and the LED <NUM> is on and emits light. The imaging module <NUM> may prompt the driver module <NUM> to turn the LED <NUM> on for the capturing of a content image.

At <NUM>, the imaging module <NUM> determines whether to capture a content image. For example, the imaging module <NUM> may determine whether a predetermined period has passed since a last (e.g., background) image was captured. If <NUM> is true, control continues with <NUM>. If <NUM> is false, control returns to <NUM> and the driver module <NUM> maintains the LED <NUM> on.

At <NUM>, the imaging module <NUM> actuates the camera <NUM> to capture a content image. At <NUM>, after the content image has been captured, the driver module <NUM> actuates the switching circuit <NUM> to turn the LED <NUM> off and minimize the persistence of the LED <NUM>. The imaging module <NUM> may prompt the driver module <NUM> to turn the LED <NUM> off for the capturing of a background image. The driver module <NUM> may control the switching circuit <NUM> as described above with respect to the examples of <FIG>, <FIG>, or <FIG>.

At <NUM>, the imaging module <NUM> determines whether to capture a background image. For example, the imaging module <NUM> may determine whether a predetermined period has passed since the last (e.g., content) image was captured (e.g., at <NUM>). If <NUM> is true, control continues with <NUM>. If <NUM> is false, control returns to <NUM> and the driver module <NUM> maintains the LED <NUM> off. At <NUM>, the imaging module <NUM> actuates the camera <NUM> to capture a background image. The imaging module <NUM> may perform one or more image processing functions on the content image (e.g., captured at <NUM>) and the background image (e.g., captured at <NUM>). For example, the imaging module <NUM> may remove background illumination in the content image based on background illumination in the background image. Control may return to <NUM>.

The foregoing description is merely illustrative in nature and is in no way intended to limit the disclosure, its application, or uses. The broad teachings of the disclosure can be implemented in a variety of forms. Therefore, while this disclosure includes particular examples, the true scope of the disclosure should not be so limited since other modifications will become apparent upon a study of the drawings, the specification, and the following claims. It should be understood that one or more steps within a method may be executed in different order (or concurrently) without altering the principles of the present disclosure.

Spatial and functional relationships between elements (for example, between modules, circuit elements, semiconductor layers, etc.) are described using various terms, including "connected," "engaged," "coupled," "adjacent," "next to," "on top of," "above," "below," and "disposed. " Unless explicitly described as being "direct," when a relationship between first and second elements is described in the above disclosure, that relationship can be a direct relationship where no other intervening elements are present between the first and second elements, but can also be an indirect relationship where one or more intervening elements are present (either spatially or functionally) between the first and second elements. As used herein, the phrase at least one of A, B, and C should be construed to mean a logical (A OR B OR C), using a non-exclusive logical OR, and should not be construed to mean "at least one of A, at least one of B, and at least one of C.

In the figures, the direction of an arrow, as indicated by the arrowhead, generally demonstrates the flow of information (such as data or instructions) that is of interest to the illustration. For example, when element A and element B exchange a variety of information but information transmitted from element A to element B is relevant to the illustration, the arrow may point from element A to element B. This unidirectional arrow does not imply that no other information is transmitted from element B to element A. Further, for information sent from element A to element B, element B may send requests for, or receipt acknowledgements of, the information to element A.

In this application, including the definitions below, the term "module" or the term "controller" may be replaced with the term "circuit. " The term "module" may refer to, be part of, or include: an Application Specific Integrated Circuit (ASIC); a digital, analog, or mixed analog/digital discrete circuit; a digital, analog, or mixed analog/digital integrated circuit; a combinational logic circuit; a field programmable gate array (FPGA); a processor circuit (shared, dedicated, or group) that executes code; a memory circuit (shared, dedicated, or group) that stores code executed by the processor circuit; other suitable hardware components that provide the described functionality; or a combination of some or all of the above, such as in a system-on-chip.

The term memory circuit is a subset of the term computer-readable medium. The term computer-readable medium, as used herein, does not encompass transitory electrical or electromagnetic signals propagating through a medium (such as on a carrier wave); the term computer-readable medium may therefore be considered tangible and non-transitory. Non-limiting examples of a non-transitory, tangible computer-readable medium are nonvolatile memory circuits (such as a flash memory circuit, an erasable programmable read-only memory circuit, or a mask read-only memory circuit), volatile memory circuits (such as a static random access memory circuit or a dynamic random access memory circuit), magnetic storage media (such as an analog or digital magnetic tape or a hard disk drive), and optical storage media (such as a CD, a DVD, or a Blu-ray Disc).

The apparatuses and methods described in this application may be partially or fully implemented by a special purpose computer created by configuring a general purpose computer to execute one or more particular functions embodied in computer programs. The functional blocks, flowchart components, and other elements described above serve as software specifications, which can be translated into the computer programs by the routine work of a skilled technician or programmer.

The computer programs include processor-executable instructions that are stored on at least one non-transitory, tangible computer-readable medium. The computer programs may also include or rely on stored data. The computer programs may encompass a basic input/output system (BIOS) that interacts with hardware of the special purpose computer, device drivers that interact with particular devices of the special purpose computer, one or more operating systems, user applications, background services, background applications, etc..

Claim 1:
A system, comprising:
a light emitting diode, LED, (<NUM>) having an anode and a cathode;
a switching circuit (<NUM>) configured to:
when in a first state, turn the LED on by connecting the anode (<NUM>, <NUM>, <NUM>) of the LED (<NUM>) to a positive reference potential and connecting the cathode (<NUM>, <NUM>, <NUM>) of the LED (<NUM>) to a ground reference potential, thereby enabling current flow in a first direction through the LED (<NUM>); and
when in a second state, turn the LED off by one of:
i.) shunting the ground reference potential to the anode (<NUM>) of the LED (<NUM>);
ii.) connecting a negative reference potential to the anode (<NUM>) of the LED (<NUM>); and
iii.) connecting the cathode (<NUM>) of the LED to the positive reference potential and connecting the anode (<NUM>) of the LED to the ground reference potential, thereby enabling current flow in a second direction through the LED (<NUM>), wherein the second direction is opposite the first direction; and
a driver module (<NUM>) configured to selectively transition the switching circuit (<NUM>) from the first state to the second state and from the second state to the first state.