Optical device and method of operating an optical device

Abstract

An optical device (10) comprises a first number N of light emitting diodes (20, 30, 40) and a power supply circuit (50). The first number N is greater than 1. The power supply circuit (50) is configured to set a first light emitting diode (20) of the first number N of light emitting diodes (20, 30, 40) to a light emitting state or an idle state, and to set a second light emitting diode (30) of the first number N of light emitting diodes (20, 30, 40) to a light sensing state. Furthermore, a method for operating an optical device is disclosed.

Description

[0001] This patent application claims the priority of German patent application 10 2022 124 967.0, the disclosure content of which is incorporated herein by reference.

[0002] An optical device and a method for operating the optical device are provided.

[0003] An optical device comprising two or more light emitting diodes, LEDs for short. The LEDs can be implemented as multicolor LEDs. Different LEDs may degrade differently. Therefore, parameters characterizing the light source, such as brightness, luminous intensity values, illuminance, chromaticity, correlated color temperature or tristimulus values, may drift during the service life of the optical device.

[0004] An object is to provide an optical device, and a method for operating an optical device with emitted light monitoring.

[0005] This object is achieved by the subject matter of the independent claims. Further developments are described in the dependent claims.

[0006] In an embodiment, the optical device includes a first number N of light emitting diodes and a power supply circuit. The first number N is greater than 1. The power supply circuit is configured to set a first light emitting diode of the first number N of light emitting diodes to a light emitting state or an idle state, and to set a second light emitting diode of the first number N of light emitting diodes to a light sensing state.

[0007] Advantageously, the second light emitting diode (referred to as the second LED) is configured to detect light emitted by the first light emitting diode (referred to as the first LED). Thus, the first LED can be monitored by the second LED. Monitoring allows electrical regulation of one of the first and second LEDs, for example, by increasing or decreasing a current, an average current and / or a duty cycle of a pulse width modulated current flowing through one of the first and second LEDs.

[0008] In alternative embodiments of the optical device, the first number is 2 or 3 or 4 or at least 3 or at least 4.

[0009] In an embodiment of the optical device, the first LED is configured to emit light at a first wavelength. The second LED is configured to emit light at a second wavelength. The first wavelength is equal to or shorter than the second wavelength. Thus, the second LED is configured to detect light emitted by the first LED.

[0010] In an embodiment of the optical device, the first LED is configured to emit light in a first emission spectrum. The second LED is configured to detect light in a sensitivity spectrum. The first emission spectrum of the first LED overlaps with the sensitivity spectrum of the second LED. Due to the overlap, the second LED is configured to detect light emitted by the first LED.

[0011] In an example, the first wavelength is, for example, a peak wavelength of a first emission spectrum emitted by a first LED. Similarly, the second wavelength is, for example, a peak wavelength of a second emission spectrum emitted by a second LED.

[0012] In an embodiment of the optical device, the first emission spectrum and the second emission spectrum are identical or nearly identical.Thus, both the first LED and the second LED are realized as a white LED, a red LED, a green LED or a blue LED.

[0013] In an alternative embodiment of the optical device, the first emission spectrum and the second emission spectrum are different. Thus, for example, one of the first LED and the second LED is implemented as a white LED, a red LED, a green LED, or a blue LED, and the other of the first LED and the second LED is implemented as another of a white LED, a red LED, a green LED, or a blue LED. As described above, the selection is performed so that there is an overlap between the first emission spectrum of the first LED and the sensitivity spectrum of the second LED.

[0014] In an embodiment of the optical device, the first number N of LEDs includes a third LED. The first number N is greater than 2. The power supply circuit is configured to set the first LED and the second LED to a light emitting state or an idle state, and to set the third LED to a light sensing state. Advantageously, the third LED is configured to detect light emitted by the second LED or light emitted by the first LED and the second LED. Therefore, according to the sensitivity spectrum of the third LED and the first emission spectrum and the second emission spectrum, the third LED is able to detect light emitted only by the second LED or light emitted by the first LED and the second LED. The first LED and the second LED are set to a light emitting state during different periods (and not at the same time).

[0015] Thus, the second LED is monitored by the third LED, and optionally the first LED is also monitored by the third LED (at a different cycle or another point in time).

[0016] In an embodiment of the optical device, the first LED is a blue LED, the second LED is a green LED, and the third LED is a red LED.

[0017] In an alternative embodiment of the optical device, the first LED is a blue LED, the second LED is a green LED, and the third LED is a yellow LED.

[0018] In an alternative embodiment of the optical device, the first number is 4. For example, the first LED is a blue LED, the second LED is a green LED, the third LED is a yellow LED, and the fourth LED is a red LED.

[0019] In an embodiment of the optical device, the second LED is configured to emit light at a second wavelength. The third LED is configured to emit light at a third wavelength. The second wavelength is equal to or shorter than the third wavelength.

[0020] In an embodiment of the optical device, the second LED is configured to emit light in a second emission spectrum. The third LED is configured to detect light in a further sensitivity spectrum. The second emission spectrum of the second LED overlaps with the further sensitivity spectrum of the third LED. The third LED has a third emission spectrum.

[0021] In an embodiment of the optical device, the third LED is configured to detect light emitted by the second LED, and the second LED is configured to detect light emitted by the first LED.

[0022] In an embodiment of the optical device, the first, second and third emission spectra are identical or nearly identical.Therefore, the first, second and third LEDs are implemented as white LEDs, red LEDs, green LEDs or blue LEDs.

[0023] In an alternative embodiment of the optical device, the first, second and third emission spectra are different. Thus, the first LED is implemented as a white LED, a red LED, a green LED or a blue LED, the second LED is implemented as another of the white LED, the red LED, the green LED or the blue LED, and the third LED is implemented as another of the white LED, the red LED, the green LED or the blue LED.

[0024] The selection is performed so that

[0025] The first emission spectrum of the first LED overlaps with the sensitivity spectrum of the second LED or another sensitivity spectrum of the third LED, and

[0026] The second emission spectrum of the second LED overlaps with the further sensitivity spectrum of the third LED.

[0027] In an embodiment of the optical device, in a first measurement phase, the power supply circuit is configured to set the first LED to a light emitting state, set the second LED to a light sensing state, and measure a first light signal provided or detected by the second LED. The first light signal is generated by the second LED. The power supply circuit measures the first light signal. For example, the power supply circuit digitizes the first light signal and generates a first digitized light signal based on the first light signal.

[0028] In an embodiment of the optical device, during a first background measurement phase, the power supply circuit is configured to set the first LED to an idle state, set the second LED to a light sensing state, and measure a first background light signal detected by the second LED. In an example, the first background measurement phase is before the measurement phase or after the measurement phase. In an alternative example, the first background measurement phase is before the measurement phase, and the second background measurement phase is after the measurement phase. The operations during the first background measurement phase and the second background measurement phase are, for example, the same.

[0029] In an embodiment of the optical device, in a normal phase, the power supply circuit is configured to set the first LED and the second LED to a light emitting state; and adjust operating parameters of the first LED and / or the second LED according to the first light signal. In an example, the normal phase is after the measuring phase.

[0030] In an embodiment of the optical device, the power supply circuit includes a control circuit, a memory and an analog-to-digital converter. The analog-to-digital converter is configured to digitize the first optical signal or a signal depending on the first optical signal into a first digitized optical signal. The control circuit is configured to store the first digitized optical signal or a parameter derived from the first digitized optical signal in the memory. These steps are performed in a measurement phase and a background measurement phase. The control circuit is configured to determine an adjustment parameter based on the first digitized optical signal detected in the measurement phase and the background measurement phase, and control one of the first number of LEDs in a subsequent regular phase based on the adjustment parameter.

[0031] In an embodiment of the optical device, the power supply circuit is configured to operate with pulse width modulation. The first duty cycle of the first LED and / or the second duty cycle of the second LED are adjusted according to the first light signal or the first digitized light signal or the adjustment parameter.

[0032] In an embodiment of the optical device, the power supply circuit comprises a first driver stage coupled to the first LED and to the control circuit. The power supply circuit comprises a drive and measurement stage coupled to the second LED and to the control circuit. For example, according to a first duty cycle, the first driver stage is switched on and off during a normal phase, a measurement phase, and a background measurement phase.

[0033] In an embodiment of the optical device, the drive and measurement stage comprises a second drive stage and a measurement stage. The second drive stage or the measurement stage is alternately coupled to the second LED. For example, according to a second duty cycle, the second drive stage is turned on and off in the normal phase, and is continuously turned off in the measurement phase and the background measurement phase. The measurement stage operates in the measurement phase and the background measurement phase.

[0034] For example, in case the third LED monitors the second LED, the second driver stage is switched on and off during the further measurement phase and the further background measurement phase according to the second duty cycle.

[0035] In an embodiment of the optical device, the drive and measurement stage comprises a switch which is coupled on one side to the second LED and on the other side to the second drive stage (e.g. during a regular phase of operation) and the measurement stage (e.g. during a measurement phase and a background measurement phase).

[0036] In an embodiment of the optical device, the measurement stage comprises a transimpedance amplifier, a first input of which is coupled or connected to the second LED.

[0037] In an embodiment of the optical device, the second LED has a first terminal coupled to the supply terminal, and a second terminal coupled to the first input of the transimpedance amplifier.The second input of the transimpedance amplifier is coupled or connected to the supply terminal.

[0038] In an embodiment, the optical device further comprises a package. The package can also be named as a housing, a shell or an LED package. A first number N of light emitting diodes and a power supply circuit are integrated in the package. Therefore, a first driver stage and a driver and measurement stage having a second driver stage and a measurement stage are integrated in the package. In an example, a distance between the first LED and the second LED is less than a predetermined value. The housing comprises an interface, at which light emitted by the first LED is partially reflected, so that the reflected light is at least partially absorbed by the second LED. The distance from the first LED to the interface is greater than a predetermined height value.

[0039] In an embodiment, a method for operating an optical device comprises

[0040] controlling a first LED of a first number N of LEDs by a power supply circuit so that the first LED emits light, and

[0041] The second LED of the first number N of LEDs is controlled by the power supply circuit so that the second LED senses light.

[0042] The optical device described above is particularly suitable for use in a method of operating an optical device. Thus, features described in conjunction with the optical device can be used in a method of operating an optical device, and vice versa, the method of operating an optical device can be used in conjunction with features described in conjunction with the optical device.

[0043] In an example, an optical device comprises a multicolor LED with built-in degradation compensation. The optical device relates to all multicolor LEDs, wherein several LED chips (minimum 2) are placed in a common cavity. The optical device is implemented for an RGB LED with an integrated driver IC, wherein excellent color stability is advantageous, and the IC is configured to provide a test mode. Stable mixed colors over the entire achievable color gamut are achieved without the need for external measurement equipment for both short-term and long-term. Stability is achieved despite the degradation of individual LEDs. Aging testing of the LEDs is not required at the time of assembly (however, aging testing is possible). In order to serve new advanced ambient lighting and signaling applications, the optical device is implemented as an RGB lighting module that implements the integration of at least three LEDs and a dedicated driver IC into a single optical package with minimal size and height.

[0044] In addition, it is advantageous that the LED manufacturer or the company assembling the LED modules can provide optical calibration data ("0 to h") for each LED via package marking or stored in the power supply circuit to simplify integration work at the customer site. The power supply circuit is implemented in an integrated circuit.

[0045] In examples such as the large number of emitters used in modern cars, the color stability of the LEDs (both in terms of temperature stability and changes over time) becomes very important in order to provide the best color perception for the end consumer. Active compensation of color shifts caused by temperature and degradation is only possible through optical feedback. This usually requires additional photodiodes, increasing the size, cost and complexity of the system.

[0046] In an example, an optical device proposes a way to implement optical feedback for controlling temperature and aging induced color shift in a multicolor LED package without requiring additional components, particularly without requiring external components.

[0047] In an example, the first LED and the second LED have different spectra. The first, second and third LEDs have three different spectra.

[0048] Advantageously, the optical arrangement provides a fully integrated solution. The optical arrangement performs direct online feedback on the actual LED behavior (rather than just nominal). The optical arrangement involves a multicolor LED, possibly with an integrated controller unit (IC), which uses the LED itself as an optical sensor in combination with an age-stable red LED to monitor the light output power of the same LED.

[0049] In an example, the LEDs are placed in a common cavity. Accordingly, one LED is used as a photodetector to record the emission of the other LED or other LEDs. The power supply circuit has a readout circuit compatible with the LED device (usually a common anode). There is a non-volatile memory for saving reference and calibration data.

[0050] Advantageously, the optical device emits a stable mixed color over the entire accessible color gamut without the need for external measurement equipment for both short-term and long-term. No aging test of the LED is required at assembly. Due to the online compensation, the criticality of the inherent stability of the LED is reduced and the aging requirements can be relaxed. The method is applicable to two different chip suppliers. In an example, the optical device implements an RGB LED with a built-in driver IC.

[0051] The following description of the drawings of examples or embodiments can further illustrate and explain aspects of the optical device and the method for operating the optical device. Devices, equipment, circuit blocks, and layers having the same structure and the same effect appear with equivalent reference numerals, respectively. Since the functions of the devices, equipment, circuit blocks, and layers in different drawings correspond to each other, their descriptions are not repeated for each of the following drawings.

[0052] Figure 1 An example of an LED and its characteristics is shown;

[0053] FIG. 2A to FIG. 2D An exemplary embodiment of an optical device is shown;

[0054] FIG. 3A to FIG. 3E A further exemplary embodiment of an optical device is shown; and

[0055] FIG. 4A to FIG. 4D An exemplary embodiment of a method for operating an optical device is shown.

[0056] Figure 1 An example of a light emitting diode such as a first light emitting diode 20 and its characteristics is shown. The internal quantum efficiency IQE relative to the current density CD of the first LED 20 is shown. The LED operation is performed at a medium current density CD, and the LED operation covers all three loss channels: Shockley-Read-Hall (marked A, abbreviated as SRH), radiation (marked B) and Auger (marked C). The non-radiative loss channels SRH and Auger reduce the part of the current that actually contributes to visible light emission. The SRH system is full of defects and is the main cause of LED aging. The first LED 20 has a first terminal 21 and a second terminal 22. The first terminal 21 is, for example, the anode of the first LED 20. The second terminal 22 is, for example, the cathode of the first LED 20.

[0057] For a photodetector or an LED used as a photodetector, defects lead to an increase in dark current but do not reduce the generated current, i.e., the sensitivity. The dark current is proportional to the applied reverse bias. Using a transimpedance amplifier setup (TIA setup for short), such as FIG. 3A to FIG. 3E As shown, the photodetector is held at zero bias, effectively eliminating dark current.

[0058] Figure 2A An exemplary embodiment of an optical device 10 is shown. The optical device 10 includes a first number N of LEDs 20, 30, 40 and a power supply circuit 50. The power supply circuit 50 is configured to set the first LED 20 of the first number N of LEDs 20, 30, 40 to a light-emitting state or an idle state. The power supply circuit 50 is configured to set the second LED 30 of the first number N of LEDs 20, 30, 40 to a light-sensing state, a light-emitting state, or an idle state. At different time points, the first LED 20 is set to a light-emitting state and an idle state. At different time points, the second LED 30 is set to a light-sensing state, a light-emitting state, and an idle state. For example, the power supply circuit 50 is implemented as a single integrated circuit. The power supply circuit 50 can be named a driver integrated circuit, and can also be referred to as a driver IC or a controller. An LED in an idle state does not receive current. An LED in an idle state does not emit light.

[0059] The first number N of LEDs 20, 30, 40 includes a third LED 40. For example, the first number N is greater than 1 or greater than 2 or greater than 3. The power supply circuit 50 is configured to set the third LED 40 to a light sensing state, a light emitting state or an idle state. At different time points, the third LED 40 is set to a light sensing state, a light emitting state and an idle state.

[0060] The optical device 10 comprises a package 70. A first number N of LEDs 20, 30, 40 are integrated in the package 70. The power supply circuit 50 is not a part of the package 70. The package 70 has a cavity 77. The first number N of LEDs 20, 30, 40 are attached within the cavity 77.

[0061] The optical device 10 comprises an LED power supply terminal 74 and a reference potential terminal 55. The LED power supply terminal 74 is coupled to the reference potential terminal 55 via a series circuit. The series circuit comprises or consists of a first number N of LEDs 20, 30, 40 and a power supply circuit 50.

[0062] The LED supply terminal 74 is coupled to the supply circuit 50 via the first number N of LEDs 20, 30, 40. The supply circuit 50 is connected or coupled to a reference potential terminal 55. The supply circuit 50 comprises a first number N of terminals 51 to 53 coupled or connected to the first number N of LEDs 20, 30, 40. Thus, one terminal is connected to one LED. The second terminal 22 of the first number N of LEDs 20, 30, 40 is connected or coupled to the first number N of terminals 51 to 53 of the supply circuit 50. The first terminal 21 of the first number N of LEDs 20, 30, 40 is connected or coupled to the LED supply terminal 74. An LED supply voltage VLED is provided at the LED supply terminal 74. A reference potential or ground potential GND is brought out at the reference potential terminal 55. The LED supply voltage VLED is, for example, positive with respect to the reference potential GND.

[0063] The optical device 10 includes an LED triplet and a driver IC 50 mounted in a package 70. Alternatively, the optical device 10 includes two LEDs or more than three LEDs (e.g., 4 LEDs, 5 LEDs, etc.). The power supply circuit 50 includes a power supply terminal 54 and at least input terminals 57 to 60. The at least input terminals 57 to 60 are digital terminals. For example, at least the input terminals 57 to 60 are implemented as input / output terminals. Optionally, the power supply circuit 50 includes an LED power supply input 56. The LED supply voltage VLED is applied to the LED power supply input 56.

[0064] In an example, another contact (eg cathode) of each LED 20, 30, 40 is directly connected to an LED supply input 56 of the supply circuit 50. The LED supply input 56 is a dedicated pad on the integrated driver IC 50 or can be accessed by an external driver IC.

[0065] Figure 2B An exemplary embodiment of an optical device 10 is shown. Figure 2A A further development of the embodiment shown. A first number N of LEDs 20, 30, 40 and a supply circuit 50 are integrated in a package 70. Thus, a single package 70 comprises the first number N of LEDs 20, 30, 40 and the supply circuit 50. The first number N of LEDs 20, 30, 40 and the supply circuit 50 are not separated in different packages.

[0066] The package 70 has the following terminals: an LED supply terminal 74, a ground terminal 75 (connected to the reference potential terminal 55 of the supply circuit 50), at least one input terminal 61 to 64 (connected to at least one input terminal 57 to 60 of the supply circuit 50) and an optional IC supply terminal 76 (connected to the supply terminal 54 of the supply circuit 50). The package 70 may have a further LED supply terminal 74', which is externally connected to, for example, the LED supply terminal 74.

[0067] Figure 2C An exemplary embodiment of an optical device 10 is shown. Figure 2A and 2B Further development of the embodiment shown. Figure 2C An example of a product embodiment / package embodiment is shown. On the left is shown a three-dimensional view of the optical device 10. A first number N of LEDs 20, 30, 40 are located in a cavity 77 of a package 70. The first number of LEDs 20, 30, 40 are coupled to a power supply circuit 50, for example via bonding wires.

[0068] On the right, a cross section of the optical device 10 is illustrated. The cavity 77 is filled with a transparent material or covered by a transparent sheet. The light emitted by the first LED 20 is reflected by the interface 78 into the environment and is directed to the second LED 30. The light emitted by the second LED 30 is reflected by the interface 78 into the environment and is directed to the third LED 40. The interface 78 is implemented as an interface between the environment and a transparent material or is implemented by a transparent sheet. Most of the light emitted by the first number of LEDs 20, 30, 40 reaches the environment, and only a small part of the light is reflected by the interface 78.

[0069] The distance from the first LED 20 to the second LED 30 is less than the predetermined value DL. The distance from the second LED 30 to the third LED 40 is less than the predetermined value DL. The predetermined value DL is, for example, 100 μm to 200 μm or 120 μm to 180 μm. A typical value of the predetermined value DL is 150 μm. The distance from the first LED 20 to the interface 78 is greater than the predetermined height value DH. The distance from the second LED 30 to the interface 78 is greater than the predetermined height value DH. The distance from the third LED 40 to the interface 78 is greater than the predetermined height value DH. The predetermined height value DH is, for example, 20 μm to 500 μm, or 30 μm to 400 μm, or 40 μm to 300 μm, or 50 μm to 200 μm. Therefore, the light emitted by the first LED 20 is detected by the second LED 30. The light emitted by the second LED 30 is detected by the third LED 40.

[0070] Figure 2D An exemplary embodiment of the spectrum of the optical device 10 is shown, which is Figure 1 and FIG. 2A to FIG. 2CFurther development of the illustrated embodiment. Different spectra of SPE are shown depending on the wavelength λ. The first LED 20 emits light in a first emission spectrum EM1. The first wavelength L1 is the peak wavelength of the first emission spectrum EM1.

[0071] The second LED 30 emits light in a second emission spectrum EM2 and detects light in a sensitivity spectrum SP2. The second wavelength L2 is a peak wavelength of the second emission spectrum EM2. The second emission spectrum EM2 is not equal to the sensitivity spectrum SP2. Compared with the second emission spectrum EM2, the sensitivity spectrum SP2 is shifted to a smaller wavelength λ.

[0072] The third LED 40 emits light in a third emission spectrum EM3 and detects light in an additional sensitivity spectrum SP3. The third wavelength L3 is a peak wavelength of the third emission spectrum EM3. The third emission spectrum EM3 is not equal to the additional sensitivity spectrum SP3. Compared to the third emission spectrum EM3, the additional sensitivity spectrum SP3 is shifted to a smaller wavelength λ.

[0073] The first wavelength L1 is shorter than the second wavelength L2. The first emission spectrum EM1 of the first LED 20 and the sensitivity spectrum SP2 of the second LED 30 have an overlap IB.

[0074] The second wavelength L2 is shorter than the third wavelength L3 The second emission spectrum EM2 of the second LED 30 has an overlap IG with the further sensitivity spectrum SP3 of the third LED 40 .

[0075] Since the LEDs 20, 30, 40 are only sensitive to light with wavelengths less than or equal to their emission spectrum, each LED 30, 40 monitors the light output power of the LED 20, 30 with the next shorter wavelength. For example, the first LED 20 is a blue LED, and the second LED 30 is a green LED. The second LED 30 is used as a detector to monitor the first LED 20. The third LED 40 is, for example, a red LED. The third LED 40 is used as a detector to monitor the second LED 30.

[0076] Readout of the photocurrent provided by one of the LEDs 30, 40 is accomplished by an integrated IC or via external circuitry. This signal is then used to compensate for any ageing induced colour shift of the monitored LED.

[0077] The LED with the longest wavelength (the first LED 20 in FIG. 2 ) cannot be stabilized in this way, but serves only as a reference.

[0078] When used as a photodetector, both the brightness of the LED and the sensitivity of the LED show a significant dependence on temperature, so it is advantageous to make a reference measurement under the same conditions (e.g., at a working interval). Alternatively, the temperature dependence can be reduced by measuring the temperature using a temperature sensor, e.g., providing both degradation and temperature compensation. The power supply circuit 50 includes a temperature sensor (not shown).

[0079] The emitters have a set of different emission wavelengths, for example, red, green and blue, and are mounted on separate pads or a common pad (for example, a common anode pad). Except for the last LED 20, 30, the emission spectrum EM1, EM2, EM3 of each LED 20, 30 overlaps with the sensitivity spectrum SP2, SP3 of at least one other LED 30, 40; the overlapping area is Figure 2D The cells are labeled with IB and IG.

[0080] The optical device 10 achieves at least one of the following advantages, for example: Stable mixed colors are emitted over the entire accessible color gamut without the need for external measurement equipment for both short-term and long-term. Aging testing of the LEDs is not required at assembly (although aging testing is possible). Due to the online compensation, the criticality of the inherent stability of the LEDs 20, 30, 40 is reduced and aging requirements can be relaxed. The method is applicable to LEDs from different chip suppliers.

[0081] Figure 3A An exemplary embodiment of an optical device 10 is shown, which is FIG. 2A to FIG. 2D The power supply circuit 50 comprises a first driver stage 80 (eg, coupled to the first LED 20 and to the control circuit 91). Figure 3E ). The first driver stage 80 comprises a switch 81. The power supply circuit 50 comprises a driver and measurement stage 82 coupled to the second LED 30 and to the control circuit 91. The driver and measurement stage 82 comprises a second driver stage 86 and a measurement stage 87. The second driver stage 86 and the measurement stage 87 are coupled to the second LED 30 alternately (which means in different cycles and not simultaneously).

[0082] The measurement stage 87 comprises a transimpedance amplifier 83 (TIA for short), a first input of the TIA being coupled to the second LED 30. The second LED 30 has a first terminal coupled to the LED supply terminal 74 and a second terminal coupled to the first input of the TIA 83. The second input of the TIA 83 is coupled or connected to the supply terminal 74. The TIA 83 comprises an operational amplifier 84 and a resistor 85, which couples the output of the operational amplifier 84 to the first input of the operational amplifier 84. The first input of the operational amplifier 84 forms the first input of the TIA 83. The second input of the operational amplifier 84 forms the second input of the TIA 83. The output of the operational amplifier 84 forms the output of the TIA 83.

[0083] There are many possible ways to read out the photocurrent from a photodiode or an LED used as a photodiode. Figure 3A A configuration compatible with the typical situation in a multicolor LED package 70 is shown: the LEDs 20 , 30 , 40 are typically directly connected to the positive LED supply voltage VLED , and the supply circuit 50 uses low-side switches 81 , 89 to drive the LEDs 20 , 30 , 40 .

[0084] Using TIA 83 in this manner also allows a 0V bias to be maintained on the second LED 30 acting as a photodiode, effectively eliminating dark current. The output voltage or output signal SOUT of TIA 83 is proportional to the photocurrent from the second LED 30 but generated using photons emitted by the first LED 20.

[0085] Figure 3B An exemplary embodiment of an optical device 10 is shown. Figures 2A to 2D 3A and 3A. The driver and measurement stage 82 comprises a changeover switch 88, which is coupled to the second LED 30 on one side and to the second driver stage 86 and the measurement stage 87 on the other side. The changeover switch 88 is controlled by a control circuit 91. The second driver stage 86 comprises a switch 89.

[0086] Figure 3C An exemplary embodiment of a timing signal of the optical device 10 is shown. Figures 2A to 2D , 3A and 3B are further developments of the embodiments shown. In the example, eight phases P0 to P7 are shown as a function of time t. In the preset phase P0, the optical device 10 is idle. The eight phases P0 to P7 are performed sequentially in the order of their numbers.

[0087] In the first background measurement phase P1 , the power supply circuit 50 sets the first LED 20 and the third LED 40 to an idle state, sets the second LED 30 to a light sensing state, and measures a first background light signal BG1 detected by the second LED 30 (eg, via the TIA 83 ).

[0088] In the first measurement phase P2, the power supply circuit 50 sets the first LED 20 to a light emitting state, sets the third LED 40 to (or maintains) an idle state, sets the second LED 30 to a light sensing state, and measures a first light signal SI1 (e.g., by TIA 83) detected by the second LED 30 according to the light emitted by the first LED 20. Phases P1 to P7 can be referred to as an operation phase.

[0089] In the further first background measurement phase P3 , the power supply circuit 50 sets the first LED 20 and the third LED 40 to the idle state, sets the second LED 30 to the light sensing state, and measures the further first background light signal BG2 detected by the second LED 30 .

[0090] In the second background measurement phase P4 , the power supply circuit 50 sets the first LED 20 and the second LED 30 to an idle state, sets the third LED 40 to a light sensing state, and measures a second background light signal BG3 detected by the third LED 40 (eg, via the TIA 83 ).

[0091] In the second measurement phase P5, the power supply circuit 50 sets the first LED 20 to an idle state, sets the second LED 30 to a light emitting state, sets the third LED 40 to a light sensing state, and measures a second optical signal SI2 detected by the third LED 40 based on the light emitted by the second LED 30 (for example, through TIA83).

[0092] In the further second background measurement phase P6 , the power supply circuit 50 sets the first LED 20 and the second LED 30 to the idle state, sets the third LED 40 to the light sensing state, and measures a further second background light signal BG4 detected by the third LED 40 (eg, via the TIA 83 ).

[0093] After the additional second background measurement phase P6, the normal operation phase P7 begins. In the normal operation phase P7, the power supply circuit 50 sets the first LED 20, the second LED 30 and the third LED 40 to a light-emitting state, for example, continuously or using a pulse width modulation control signal with first, second and third duty cycles D1 to D3. At least one operating parameter of the first LED 20, the second LED 30 and / or the third LED 40 is adjusted according to the first light signal SI1, the second light signal SI2, the first background light signal BG1, the additional first background light signal BG2, the second background light signal BG3 and the additional second background light signal BG4.

[0094] These signals SI1, SI2, BG1, BG2, BG3 and BG4 are, for example, the values ​​of the output signal SOUT of TIA83, or are Figure 3E The analog-to-digital converter 90 is shown providing the value of the digitized output signal SD.

[0095] To measure the current brightness of the blue and green LEDs 20, 30, for example, use Figure 3C and Figure 3D One of the two timing sequences shown (to be explained below) is used as a photodiode to simultaneously measure the background signals BG1, BG3 and the background and emitted first light signal SI1 with the other LED. The process is then repeated for the next LED pair, and so on.

[0096] use Figure 3C Then the brightness IB of the first LED 20 is obtained by:

[0097] IB=SI1-0.5(BG1+BG2)

[0098] Then the brightness IG of the second LED 30 is obtained:

[0099] IG = SI2 - 0.5 (BG3 + BG4).

[0100] Figure 3D An exemplary embodiment of a timing signal of the optical device 10 is shown. FIG. 2A to FIG. 2D and FIG. 3A to FIG. 3C Further development of the illustrated embodiment. In the example, six phases P0 to P2, P4, P5 and P7 are shown as a function of time t. The further first background measurement phase P3 and the further second background measurement phase P6 are omitted.

[0101] Conventional phase P7 starts after measuring phases P1 to P6. The optical device 10 involves a multicolor LED, possibly with an integrated controller unit, which monitors the light output power of similar LEDs 20, 30 using the LEDs 30, 40 themselves as optical sensors, for example in combination with an age-stable red LED 40.

[0102] use Figure 3C and Figure 3D The brightness IB of the first LED 20 is obtained by:

[0103] IB=SI1-BG1

[0104] Get the brightness IG of the second LED 30:

[0105] IG=SI2-BG3.

[0106] Figure 3E An exemplary embodiment of an optical device 10 is shown. FIG. 2A to FIG. 2D and FIG. 3A to FIG. 3C A further development of the illustrated embodiment. The power supply circuit 50 includes an analog-to-digital converter 90 (ADC for short), a control circuit 91 and a memory 92. The ADC 90 digitizes the output signal SOUT of the TIA 83 (e.g., the first optical signal SI1 and the second optical signal SI2 or a signal depending on the first optical signal SI1 and the second optical signal SI2) into a first digitized optical signal SD1 and a second digitized optical signal SD2. The control circuit 91 stores the first digitized optical signal SD1 and the second digitized optical signal SD2 or parameters depending on the first digitized optical signal SD1 and the second digitized optical signal SD2 in the memory 92. For example, using a standard ADC 90, the output voltage SOUT of the TIA 83 is digitized into a digitized output signal SD. For example, the memory 92 is non-volatile or volatile. The memory 92 is coupled to the control circuit 91.

[0107] The power supply circuit 50 operates in a pulse width modulation manner. The first duty cycle D1 of the first LED 20 and / or the second duty cycle D2 of the second LED 30 and / or the third duty cycle D3 of the third LED 40 are adjusted according to the first light signal SI1 and the second light signal SI2 and the first background light signal BG1 and the second background light signal BG3 (and optionally also according to the additional first background light signal BG2 and the additional second background light signal BG4). For example, one of the three duty cycles D1, D2, and D3 is kept constant, and the other two of the three duty cycles D1, D2, and D3 are adjusted according to the first light signal SI1 and the second light signal SI2 and the first background light signal BG1 and the second background light signal BG3 (and optionally also according to the additional first background light signal BG2 and the second background light signal BG4).

[0108] Figure 4A An exemplary embodiment of a method for operating an optical device 10 is shown. FIG. 2A to FIG. 2D and FIG. 3A to FIG. 3E A further development of the embodiment shown. Figure 4A , a method for operating the optical device 10 during calibration is shown.

[0109] exist Figure 4A To the left of the dashed line shown, steps or processes performed by the microcontroller unit are shown, and to the right of the dashed line, steps or processes performed by the first number of LEDs 20, 30, 40 are shown ( FIG. 4B to FIG. 4D The control circuit 91 or the external circuit includes a microcontroller unit. Therefore, the control circuit 91 includes, for example, a microcontroller, a microprocessor, a state machine or a logic gate.

[0110] During calibration, the following steps or processes are performed:

[0111] Process S1: Calibration is initiated by the microcontroller unit.

[0112] Process S2: Determine calibration values, such as chromaticity values ​​Cx, Cy and intensity values ​​Iv, using external measurement equipment 99 (eg, a spectrometer).

[0113] Process S3: Storing calibration values, for example, chromaticity values ​​Cx, Cy and intensity values ​​Iv.

[0114] Process S4: Record the initial brightness value.

[0115] Process S5: As above FIG. 3A to FIG. 3D Perform the monitoring process as described.

[0116] Process S6: Store initial brightness values ​​IG0 and IB0.

[0117] Process S7: End calibration.

[0118] Processes S1 to S3 are standard processes. Processes S4 to S6 are processes using the power supply circuit 50 described above.

[0119] The initial brightness values ​​of the blue and green LEDs 20, 30 are measured at the very beginning and stored in some non-volatile memory provided by / with a microcontroller for controlling the LEDs or by a driver IC integrated in the LEDs. In the first case, the memory can be programmed multiple times. In the second case, the memory is likely to be programmed only once. In the example, the control circuit 91 stores the initial brightness values ​​IG0, IB0 in the memory 92.

[0120] Figure 4B and Figure 4CAn exemplary embodiment of a method for operating an optical device 10 is shown. Figures 2A to 2D , Figures 3A to 3E and 4A show a further development of the embodiment.

[0121] like Figure 4B As shown, during operation, the following steps or processes are performed:

[0122] Process S10: Record the current brightness value.

[0123] Process S11: Execute the monitoring process as described above.

[0124] Process S12: Calculate a new intensity value Iv.

[0125] Process S13: Modify the stored calibration value (eg, intensity value Iv).

[0126] Process S14: Modify the stored brightness IB0, IG0.

[0127] Process S15: End

[0128] like Figure 4C As shown, during operation, the following steps or processes are performed:

[0129] Process S20: Calculate PWM settings from stored calibration data (PWM settings include, for example, first, second and third duty cycles D1, D2, D3).

[0130] Process S21: Set PWM settings.

[0131] Process S22 : Applying PWM settings to the first, second and third LEDs 20 , 30 , 40 .

[0132] Process S23: Continue

[0133] Processes S10 to S15 are performed during operation ( Figure 4B ), and for example implement the above-described optical device 10 and method. Processes S20 to S23 are performed during operation ( Figure 4C ), and is, for example, a standard procedure.

[0134] exist Figure 4B and Figure 4C In the first option of performing degradation compensation during the lifetime, a degradation correction is explained. Degradation correction is performed only during operating intervals, for example, every few months. New brightness readings are stored in the non-volatile memory 92, and the original calibration data (for example, intensity values ​​Iv) are overwritten by the correction values. Daily operation continues, for example, without degradation correction. The PWM values ​​can be calculated based on the stored calibration data.

[0135] This method is compatible with non-volatile memory 92 that supports multiple programming cycles (eg, non-volatile memory implemented as flash memory).

[0136] Optionally, the measurement is performed under the same conditions as the initial calibration, for example at the same ambient temperature. Alternatively, a temperature sensor can be used in conjunction with the different temperature dependencies of the LED and of the LED used as a photodetector to compensate for the difference between the calibration temperature and the temperature during the compensation measurement.

[0137] Calculate the corrected intensity values ​​IvB1, IvG1:

[0138] IvB1=IvB0·IB1 / IB0

[0139] as well as

[0140] IvG1=IvG0·IG1 / IG0

[0141] Wherein, IvB1 is the intensity value of the first LED 20, IvG1 is the intensity value of the second LED 30,

[0142] IB1 is the measured brightness of the first LED 20,

[0143] IB0 is the measured brightness of the first LED 20 obtained during the calibration phase,

[0144] IvB0 is the measured intensity value of the first LED 20 obtained during the calibration phase,

[0145] IG1 is the measured brightness of the second LED 30,

[0146] IG0 is the measured brightness of the second LED 30 obtained during the calibration phase, and

[0147] IvG0 is the measured intensity value of the second LED 30 obtained during the calibration phase.

[0148] The intensity value IvG1 of the second LED 30 and the intensity value IvB1 of the first LED 20 are stored instead of the previous intensity values ​​IvB0 and IvG0, or in addition to the previous intensity values ​​IvB0 and IvG0. The intensity value IvXX refers to the luminous intensity emitted by the LED 20, 30, 40, and the brightness IXX refers to the measurement result of the photodetector (implemented as an LED). The intensity value is related to the brightness, but has different units, etc. Therefore, the previous intensity values ​​IvG0 and IvB0 are overwritten by the new intensity values ​​IvG1 and IvB1.

[0149] Figure 4DAn exemplary embodiment of a method for operating an optical device 10 is shown. FIG. 2A to FIG. 2D , FIG. 3A to FIG. 3E and FIG. 4A to FIG. 4C Further development of the embodiment shown.

[0150] like Figure 4D As shown, during operation, the following steps or processes are performed:

[0151] Process S30: Record the current brightness value.

[0152] Process S31: Execute the monitoring process as described above.

[0153] Process S32: Calculate a new intensity value Iv.

[0154] Process S33: Calculate PWM settings from stored and temporary calibration data (eg, PWM settings including first, second and third duty cycles D1 , D2 , D3 ).

[0155] Process S34: Set PWM settings.

[0156] Process S35 : Applying PWM settings to the first, second and third LEDs 20 , 30 , 40 through the power supply circuit 50 .

[0157] Process S36: Continue.

[0158] Processes S30 to S32 are performed during the power-on process. Processes S30 to S32 are the same as processes S20 to S22, and implement the above-described optical device 10 and method, for example.

[0159] Processes S33 to S36 are performed during normal operation. Processes S33 to S36 are implemented by the optical device 10 described above.

[0160] exist Figure 4D In , a second option for performing degradation compensation during the lifetime is explained. Degradation correction is performed each time the optical device 10 is started. A new brightness reading is recorded once at start-up; the calibration value is calculated and saved in the working memory 92 (i.e., volatile memory) of the control circuit 91. The control circuit 91 can be implemented by a microcontroller unit (MCU for short), or a microprocessor.

[0161] Normal operation is performed using the temporary calibration values ​​to calculate the PWM values. This option is compatible with both multi-time and one-time programmable memory 92. Optionally, the measurement is performed under the same conditions as the initial calibration, for example, at the same ambient temperature. Alternatively, a temperature sensor can be used in conjunction with the different temperature dependencies of the LEDs and the photodetector to compensate for the difference between the calibration temperature and the temperature during the compensation measurement.

[0162] Calculate the modified intensity values ​​IvG1 and IvB1 again:

[0163] IvG1=IvG0·IG1 / IG0 and IvB1=IvB0·IB1 / IB0

[0164] Alternatively, the PWM value can be compensated directly using

[0165] PWM_G1=PWM_G0·IG0 / IG1 and

[0166] PWM_B1=PWM_B0·IB0 / IB1

[0167] In the example, PWM_G1 is the duty cycle D1 of the first LED 20, and PWM_G2 is the duty cycle D2 of the second LED 30. The duty cycle D3 of the third LED 40 remains constant. Note that the compensation in this case may be worse compared to the compensated intensity value lv. The modified intensity values ​​IvG1, IvB1 may also be named new intensity values.

[0168] Alternatively, the duty cycle D1 of the first LED 20 is kept constant and the duty cycles D2, D3 of the second and third LEDs 30, 40 are adjusted using similar formulas. Alternatively, the duty cycle D2 of the second LED 30 is kept constant and the duty cycles D1, D3 of the first and third LEDs 20, 40 are adjusted using similar formulas.

[0169] In an alternative embodiment not shown, the first number N is 2 and the optical device 10 comprises exactly two LEDs 20, 30. In an alternative embodiment not shown, the first number N is 4 or greater than 4 and the optical device 10 comprises at least a fourth LED. The method can also be implemented in the case where the first number is 2, 4 or greater than 4.

[0170] Advantageously, the brightness, luminous intensity value, illuminance, chromaticity value, correlated color temperature, or tristimulus value of the optical device 10 can remain constant or nearly constant during the lifetime of the optical device 10 .

[0171] The invention is not limited to the description of the exemplary embodiments. Rather, the invention comprises every new feature and every combination of features, in particular every combination of features in the claims, even if the feature or feature combination itself is not explicitly stated in the claims or exemplary embodiments.

[0172] Reference numerals

[0173] 10 Optical Devices

[0174] 20 First light emitting diode

[0175] 21, 22 terminals

[0176] 30 Second LED

[0177] 40 The third light emitting diode

[0178] 50 Power supply circuit

[0179] 51 to 53 terminals

[0180] 54 Power supply terminal

[0181] 55 Reference potential terminal

[0182] 56 LED power input

[0183] 57 to 60 Input terminals

[0184] 61 to 64 Input terminals

[0185] 70 Package

[0186] Terminals 71 to 73

[0187] 74 LED power supply terminal

[0188] 75 Ground terminal

[0189] 76 IC power supply terminal

[0190] 77 Cavity

[0191] 78 Interface

[0192] 80 First driver stage

[0193] 81, 89 switch

[0194] 82 Drive and measurement stage

[0195] 83 Transimpedance Amplifier

[0196] 84 Operational Amplifier

[0197] 85 Resistor

[0198] 86 Second driver stage

[0199] 87 Measurement level

[0200] 88 Switch

[0201] 90 Analog-to-digital converter

[0202] 91 Control circuit

[0203] 92 Memory

[0204] 99 External measurement equipment

[0205] A, B, C loss channels

[0206] BG1 to BG4 background light signal

[0207] CD current density

[0208] DH Predetermined height value

[0209] DL Predetermined value

[0210] D1 to D3 duty cycle

[0211] EM1 to EM3 emission spectra

[0212] GND Reference potential

[0213] IQE Internal Quantum Efficiency

[0214] L1 to L3 wavelength

[0215] Phases P1 to P7

[0216] SD digital output signal

[0217] SD1 First digital optical signal

[0218] SD2 Second digital optical signal

[0219] SI1 First optical signal

[0220] SI2 Second optical signal

[0221] SOUT Output voltage

[0222] SPE Spectroscopy

[0223] SP2, SP3 sensitivity spectrum

[0224] S1 to S35 process

[0225] t time

[0226] VDD supply voltage

[0227] VLED LED supply voltage

[0228] λ Wavelength

Claims

1. An optical device (10), comprising: A first number N of light emitting diodes (20, 30, 40), wherein the first number N is greater than 1, a power supply circuit (50) configured to set a first light emitting diode (20) of the first number N of light emitting diodes (20, 30, 40) to a light emitting state or an idle state, and to set a second light emitting diode (30) of the first number N of light emitting diodes (20, 30, 40) to a light sensing state, and Encapsulation (70), The first number N of light-emitting diodes (20, 30, 40) and the power supply circuit (50) are integrated in the package (77). The package (70) has a cavity (77), and a first number N of LEDs (20, 30, 40) are attached in the cavity (77). The cavity (77) is filled with a transparent material or covered with a transparent sheet. wherein light emitted by the first LED (20) is reflected by the interface (78) into the environment and directed to the second LED (30), and The interface (78) is realized as an interface between the environment and the transparent material, or is realized by a transparent sheet.

2. The optical device (10) according to claim 1, in, The first light emitting diode (20) is configured to emit light of a first wavelength (L1), wherein the second light emitting diode (30) is configured to emit light of a second wavelength (L2), and Wherein, the first wavelength (L1) is equal to or shorter than the second wavelength (L2).

3. The optical device (10) according to claim 1 or 2, in, The first light emitting diode (20) is configured to emit light in a first emission spectrum (EM1); wherein the second light emitting diode (30) is configured to detect light in a sensitivity spectrum (SP2); The first emission spectrum (EM1) of the first light-emitting diode (20) and the sensitivity spectrum (SP2) of the second light-emitting diode (30) overlap.

4. The optical device (10) according to any one of claims 1 to 3, in, A first emission spectrum (EM1) of the first light-emitting diode (20) is different from a second emission spectrum (EM2) of the second light-emitting diode (30).

5. The optical device (10) according to any one of claims 1 to 4, in, The first number N of light emitting diodes (20, 30, 40) includes a third light emitting diode (40), Wherein, the first number N is greater than 2, The power supply circuit (50) is configured to set the first light-emitting diode (20) and the second light-emitting diode (30) to a light-emitting state or an idle state, and to set the third light-emitting diode (40) to a light-sensing state.

6. The optical device (10) according to claim 5, in, The second light emitting diode (30) is configured to emit light of a second wavelength (L2), wherein the third light emitting diode (40) is configured to emit light of a third wavelength (L3), and Wherein, the second wavelength (L2) is equal to or shorter than the third wavelength (L3).

7. The optical device (10) according to claim 5 or 6, in, The second light emitting diode (30) is configured to emit light in a second emission spectrum (EM2), wherein the third light emitting diode (40) is configured to detect light in a further sensitivity spectrum (SP3), and The second emission spectrum (EM2) of the second light-emitting diode (30) overlaps with the other sensitivity spectrum (SP3) of the third light-emitting diode (40).

8. The optical device (10) according to any one of claims 5 to 7, in, In a first measurement phase, the power supply circuit (50) is configured to set the first light emitting diode (20) to a light emitting state, set the second light emitting diode (30) to a light sensing state, and measure a first light signal (SI1) detected by the second light emitting diode (30).

9. The optical device (10) according to claim 8, in, In a first background measurement phase, the power supply circuit (50) is configured to set the first light emitting diode (20) to an idle state, set the second light emitting diode (30) to a light sensing state, and measure a first background light signal (BG1) detected by the second light emitting diode (30).

10. The optical device (10) according to claim 8 or 9, in, In a normal stage, the power supply circuit (50) is configured to set the first light emitting diode (20) and the second light emitting diode (30) to a light emitting state, wherein the operating parameters of the first light emitting diode (20) and / or the second light emitting diode (30) are adjusted according to the first optical signal (SI1); and The conventional phase is after the measurement phase.

11. The optical device (10) according to any one of claims 8 to 10, in, The power supply circuit (50) comprises an analog-to-digital converter (90), a control circuit (91) and a memory (92), and The analog-to-digital converter (90) is configured to digitize the first optical signal (SI1) or a signal dependent on the first optical signal (SI1) into a first digitized optical signal (SD1), and The control circuit (91) is configured to store the first digitized optical signal (SD1) or a parameter derived from the first digitized optical signal (SD1) in the memory (92).

12. The optical device (10) according to any one of claims 8 to 11, in, The power supply circuit (50) is configured to operate with pulse width modulation and to adjust a first duty cycle (D1) of the first light emitting diode (20) and / or a second duty cycle (D2) of the second light emitting diode (30) according to the first optical signal (SI1).

13. The optical device (10) according to any one of claims 8 to 12, in, The power supply circuit (50) comprises a first driver stage (80) coupled to the first light emitting diode (20) and to the control circuit (91), and A drive and measurement stage (82) coupled to the second light emitting diode (30) and to the control circuit (91).

14. The optical device (10) according to any one of claims 8 to 13, in, The drive and measurement stage (82) comprises a second drive stage (86) and a measurement stage (87), and The second driving stage (86) or the measuring stage (87) is alternately coupled to the second light emitting diode (30).

15. The optical device (10) according to claim 13 or 14, in, The measurement stage (87) comprises a transimpedance amplifier (83) having a first input coupled to the second light emitting diode (30).

16. The optical device (10) according to claim 15, in, The second light emitting diode (30) has a first terminal coupled to the LED supply terminal (74) and a second terminal coupled to the first input of the transimpedance amplifier (83), and Wherein, the second input of the transimpedance amplifier (83) is coupled to the LED power supply terminal (74).

17. A method for operating an optical device (10), comprising: Controlling a first light emitting diode (20) of a first number N of light emitting diodes (20, 30, 40) through a power supply circuit (50) so that the first light emitting diode (20) emits light or is in an idle state, and The second light-emitting diode (30) of the first number N of light-emitting diodes (20, 30, 40) is controlled by the power supply circuit (50) so that the second light-emitting diode (30) senses light, in, Integrating the first number N of light-emitting diodes (20, 30, 40) and the power supply circuit (50) in a package (70), The package (70) has a cavity (77), and a first number N of LEDs (20, 30, 40) are attached in the cavity (77). The cavity (77) is filled with a transparent material or covered with a transparent sheet. wherein light emitted by the first LED (20) is reflected by the interface (78) into the environment and directed to the second LED (30), and The interface (78) is realized as an interface between the environment and the transparent material, or is realized by a transparent sheet.

Images