Lighting equipment for FM transmission

Abstract

The present disclosure relates to a lighting device (20) for frequency modulated emission. The object is to provide a lighting device (20) comprising a light emitting diode (LED), which allows a higher operating frequency and in particular has an improved emission light signal quality, wherein the lighting device (20) comprises: an LED (26); a resonant driver circuit (22) having a tuning circuit (24); wherein the resonant driver circuit (22) is configured to drive the tuning circuit (24) at the operating frequency, and wherein the tuning circuit (24) comprises the LED (26). The present disclosure also relates to a method of operating the lighting device (20) and a use of the lighting device (20).

Description

Technical Field

[0001] The present disclosure relates to a lighting device for frequency modulated transmission comprising a light emitting diode (LED), in particular for time-of-flight applications. Background Art

[0002] In time-of-flight applications, for example in distance measurement and 3D imaging, frequency modulated light emission of the lighting device can be used. Here, in particular, lighting devices that provide frequency modulated light with an operating frequency in the MHz range can be used. Laser light sources can be used for time-of-flight applications, such as lidar.

[0003] Furthermore, LEDs are also suitable for generating frequency modulated light. Typically, a drive circuit for an LED includes a switching device, such as a field effect transistor, to obtain an operating frequency in the MHz range. The field effect transistor receives an input signal at its gate, which is provided by an external source. The input signal has, for example, a square wave form having the desired operating frequency and periodically switches the field effect transistor on and off. The field effect transistor can then provide an oscillating current in the drive circuit to cause frequency modulated light emission of the LED.

[0004] However, this configuration of a driver circuit for an LED has disadvantages. The maximum operating frequency is limited by the switching speed of the field effect transistor and the characteristics of the driver circuit, i.e. the combined inductance and capacitance of the electronic components in the driver circuit. Therefore, the operating frequency of an LED with such a driver circuit is usually limited to frequencies significantly below 40 MHz.

[0005] Furthermore, due to the layout of the drive circuit, the waveform of the oscillating current may be affected by the inductance and capacitance of the electronic components in the drive circuit. This may cause the waveform of the drive current to deviate significantly from a sinusoidal shape. As a result, the light emitted by an LED driven by such a current may have a non-sinusoidal frequency modulation of the emission intensity, leading to difficulties in detecting and analyzing the reflected light pulses in time-of-flight applications. Summary of the invention

[0006] An object of the invention is to provide a lighting device for frequency modulated emission comprising LEDs, which allows higher operating frequencies and in particular has an improved quality of the emitted light signal. The invention also relates to a method of operating a lighting device and a use of the lighting device based on the above object.

[0007] According to a first aspect of the present invention, there is provided a lighting device for frequency modulated transmission, the lighting device comprising: an LED; a resonant driver circuit having a tuning circuit; wherein the resonant driver circuit is configured to drive the tuning circuit at an operating frequency, and wherein the tuning circuit comprises the LED.

[0008] According to a second aspect of the invention, there is provided a method for operating a lighting device, in particular a lighting device according to the first aspect, the method comprising: operating a resonant driver circuit having a tuning circuit, wherein the tuning circuit is driven by the resonant driver circuit at an operating frequency, wherein the tuning circuit comprises an LED.

[0009] According to a third aspect of the present invention, there is provided use of the lighting device according to the first aspect in a time-of-flight application.

[0010] Exemplary embodiments of the first, second and third aspects of the present invention may have one or more of the characteristics described below.

[0011] An LED for a lighting device may include at least one semiconductor element, such as a pn junction, a diode and / or a transistor. For example, the LED may be provided in the form of an LED die and / or an LED package. The LED may be arranged on a substrate, such as a heat sink, an interposer and in particular a (printed) circuit board, wherein at least part of the tuning circuit and the resonant driver circuit is provided by the (printed) circuit board. The LED may, for example, be integrated into an LED lead frame.

[0012] LEDs are used in lighting devices for frequency modulated transmission. That is, when the lighting device is in operation, the LED is subjected to a (periodically) oscillating drive current, causing the LED to emit light having an amplitude modulated by the oscillation of the drive current. According to the present invention, a resonant driver circuit having a tuning circuit is used to provide the drive current to the LED. The resonant driver circuit is configured to drive the tuning circuit at an operating frequency. The resonant driver circuit can in principle be configured as any type of electronic oscillator circuit, and in particular an LC oscillator circuit. The tuning circuit corresponds to the part that causes current oscillations in the resonant driver circuit. The tuning circuit can also be referred to as a bandpass filter of the resonant driver circuit. For example, when the resonant driver circuit is implemented as an LC oscillator circuit, the tuning circuit can refer to an LC resonant element.

[0013] In the present case, the tuning circuit comprises an LED. For example, in the layout of an LC oscillator circuit, the bandpass filter / LC resonant element is replaced by an LED. That is, the oscillating drive current of the LED is provided by the resonant driver circuit. In contrast to the aforementioned drive circuits which rely on the switching of field effect transistors by means of external input signals, in which the maximum operating frequency is limited by the switching speed of the field effect transistors and the characteristics of the drive circuit, with the present invention, the characteristics of the tuning circuit can essentially correspond to the characteristics of the LED itself, or can be closely adapted to the characteristics of the LED. That is, the tuning circuit can have a particularly simple layout, with very low inductance and capacitance, so that significantly higher operating frequencies can potentially be achieved.

[0014] LEDs can form a tuned circuit for a resonant driver circuit, since LEDs have parasitic inductance and capacitance, so that the LEDs themselves can represent an LC element. Furthermore, LEDs can allow a reverse recovery current, since they can allow a reverse current for a limited time when the drive current is reversed. At higher frequencies, in particular at frequencies in the MHz range, LEDs can therefore represent LC resonant elements. Thus, LEDs can be driven (directly) with the aid of a resonant driver circuit. Furthermore, when the LED is used as an LC resonant element, it has been found that the waveform of the drive current is essentially sinusoidal, resulting in a favorable waveform for the intensity of the frequency modulated emission.

[0015] In another exemplary embodiment according to the invention, the resonant driver circuit comprises an amplifying device and a feedback loop for the amplifying device. Thus, energy losses in the resonant driver circuit, in particular energy losses caused by light emission of the LED, can be supplemented by means of the amplifying device. The feedback loop can ensure that the amplifying device delivers energy to the resonant driver circuit at an operating frequency with a corresponding phase. Thus, the resonant driver circuit and the lighting device can be operated continuously using the amplifying device and the feedback loop.

[0016] The amplifying means may for example comprise at least one bipolar junction transistor, an operational amplifier and / or a vacuum tube. In an exemplary embodiment according to the invention, the amplifying means comprises at least one field effect transistor. Field effect transistors, in particular metal oxide semiconductor field effect transistors, are particularly suitable for providing amplification for resonant driver circuits in the MHz range.

[0017] As mentioned above, the lighting device can provide a higher frequency for the frequency modulation of the emission. In an exemplary embodiment according to the present invention, the operating frequency is greater than 40 MHz, in particular greater than 70 MHz. The corresponding operating frequency can, for example, improve the accuracy of the time of flight measurement based on the lighting device of the present invention. In some embodiments, an operating frequency greater than 75 MHz can be used.

[0018] In another exemplary embodiment according to the present invention, the operating frequency substantially corresponds to the resonant frequency of the LED itself. When the LC resonant element of the LC oscillator circuit is replaced by an LED, the resonant frequency of the tuned circuit can be substantially equal to the resonant frequency of the LED itself, which is determined by the parasitic inductance and parasitic capacitance of the LED. Therefore, the operating frequency of the lighting device is substantially limited only by the characteristics of the LED itself.

[0019] In an exemplary embodiment according to the invention, the tuning circuit consists of an LED and a series connection device for the LED. That is, apart from the LED and the series connection device, no further components are present in the tuning circuit. The series connection device is in particular a direct (and possibly very short) conductive track to connect the terminals of the LED to the resonant driver circuit. That is, the series connection device can have an inductance and a capacitance that are respectively lower than the parasitic inductance and parasitic capacitance of the LED. The resonant frequency of the tuning circuit is then substantially determined by the LED itself, so that the operating frequency can be particularly high (and can be selected to be substantially equal to the resonant frequency of the LED itself).

[0020] In an alternative exemplary embodiment according to the present invention, the tuning circuit consists of an LED, a series device for the LED, and a tuning inductor and / or a tuning capacitor. In contrast to the aforementioned embodiment having only an LED and a series connection device forming a tuning circuit, a tuning inductor and / or a tuning capacitor can be added to the tuning circuit to modify the resonant frequency of the tuning circuit. For example, in the case where the desired operating frequency is lower than the resonant frequency of the LED itself, the resonant frequency of the tuning circuit can be lowered by adding at least one tuning inductor and / or a tuning capacitor.

[0021] The tuning inductor and / or the tuning capacitor may have a fixed inductance and / or capacitance, respectively. In other embodiments, the tuning inductor and / or the tuning capacitor may be tunable in the sense that the inductance and / or the capacitance may vary, so that the same lighting device may operate effectively at different operating frequencies. In one embodiment, the tuning inductor and / or the tuning capacitor are connected in series and / or in parallel to the LED.

[0022] As mentioned above, different electronic oscillator circuit topologies, and in particular LC oscillator circuit topologies, can be used for the configuration of the resonant driver circuit. In an exemplary embodiment according to the invention, the resonant driver circuit is configured as a Colpitts oscillator circuit. The Colpitts oscillator comprises a capacitive voltage divider to provide a feedback loop. A portion of the capacitive voltage divider can, for example, be formed by the parasitic capacitance of the LED. The principle of a Colpitts oscillator allows for a simple layout of the resonant driver circuit, while the Colpitts oscillator is also particularly useful for providing a substantially sinusoidal drive current with an operating frequency in the (high) MHz range.

[0023] In an exemplary embodiment according to the invention, the lighting device further comprises a synchronization circuit for synchronizing the phase and / or operating frequency of the tuning circuit with a reference oscillating signal. Thus, the synchronization circuit may in particular provide a phase-locked loop. At least one sensor may be provided to sense the current, voltage and / or emission intensity of the LED. The signal of at least one sensor may be used to align the phase and / or operating frequency of the tuning circuit with the reference oscillating signal. For example, the reference oscillating signal is used as a reference for analysis of reflected light pulses in time-of-flight applications.

[0024] In another exemplary embodiment according to the invention, the LED is configured to emit light in the infrared (IR) range. The LED may be characterized by a peak wavelength, i.e. a wavelength at which the emission intensity is greatest. The LED may have a peak wavelength in the IR range, e.g. above 780 nm. In particular, the peak wavelength of the IR LED may be in the near IR range, e.g. from 780 nm to 3000 nm, in particular from 800 nm to 1100 nm. Frequency modulated light in the IR range may be used for time-of-flight applications.

[0025] In an exemplary embodiment according to the invention, the resonant driver circuit comprises an end switch. The end switch can be configured to activate and deactivate the resonant driver circuit so that pulses of frequency modulated light can be provided by the lighting device. In particular, an end switch comprising at least one gate switch, such as at least one dual gate switch, is used.

[0026] In a preferred embodiment of the invention, the lighting device is configured for time-of-flight applications. For example, distance measurements can be provided based on frequency modulated light emitted by the lighting device of the invention. The lighting device can be integrated, for example, into a motorized autonomous car, a drone sensor (such as an obstacle avoidance system), a motor vehicle driver monitoring system and / or a motor vehicle gesture control system. Further applications are mobile 3D sensors and games, such as virtual reality and / or augmented reality games.

[0027] The features and exemplary embodiments of the invention described above may also belong to different aspects according to the invention. In particular, by disclosing features related to the lighting device according to the first aspect, corresponding features related to the method according to the second aspect and the use according to the third aspect are also disclosed.

[0028] It should be understood that the embodiments of the present invention presented in this area are exemplary only and not limiting.

[0029] Other features of the present invention will become apparent from the following detailed description considered in conjunction with the accompanying drawings. It should be understood, however, that the drawings are designed for illustrative purposes only and are not intended as a definition of the limits of the present invention, for which reference should be made to the appended claims. It should also be understood that the drawings are not drawn to scale and that they are merely intended to conceptually illustrate the structures and processes described herein. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Examples of the present invention will now be described in detail with reference to the accompanying drawings, in which:

[0031] Figure 1 A schematic diagram of a lighting device with a driving circuit according to the prior art is shown;

[0032] Figure 2 A schematic diagram showing a first embodiment of a lighting device according to the present invention;

[0033] Figure 3 A schematic diagram showing a synchronization circuit of a lighting device according to the present invention is shown;

[0034] Figure 4a shows a schematic diagram of a Colpitts oscillator circuit;

[0035] Figure 4b A schematic diagram showing a second embodiment of a lighting device according to the present invention;

[0036] Figure 5 A schematic diagram showing a third embodiment of a lighting device according to the present invention; and

[0037] Figure 6 A schematic diagram showing driving current and light output obtained by using the lighting device according to the present invention is shown. DETAILED DESCRIPTION

[0038] Figure 1 A schematic diagram of a lighting device 2 with a drive circuit 4 according to the prior art is shown. The drive circuit 4 for an LED 6 comprises a field effect transistor 8 as a switching device. The field effect transistor 8 receives an input signal 10 at the gate, periodically switching the field effect transistor 8 on and off, resulting in an oscillating drive current in the drive circuit 4. The LED 6 emits light in a frequency modulated manner at the operating frequency.

[0039] However, the maximum operating frequency is limited by the switching speed of the field effect transistor 8 and the inductance L1 and capacitance C1 of the driver circuit 4. Therefore, the maximum operating frequency depends on the topology of substantially the entire driver circuit 4 and is often limited to frequencies significantly below 40 MHz.

[0040] Furthermore, the input signal 10 may have a block waveform, such as Figure 1The frequency of the input signal 10 corresponds to the desired operating frequency. However, in many cases, the waveform of the drive current 12 deviates strongly from a sinusoidal waveform due to the contribution of the drive circuit 4, and in particular the contribution of the inductor L1 and the capacitor C1.

[0041] Figure 2 FIG. 2 is a schematic diagram showing a first embodiment of an illumination device 20 according to the present invention. Figure 1 In contrast to the drive circuit 4 having a field effect transistor 8 controlled by an input signal, the lighting device 20 includes a resonant driver circuit 22 having a tuning circuit 24. The resonant driver circuit 22 is configured to drive the tuning circuit 24 at an operating frequency. The tuning circuit 24 includes an LED 26 because the tuning circuit 24 consists only of the LED 26 and the series connection device. Figure 2 , the parasitic inductance Lpar and the parasitic capacitance Cpar of the LED 26 itself are schematically shown.

[0042] Figure 2 The resonant driver circuit 22 shown corresponds to an LC electronic oscillator circuit, in which the LC resonant element is replaced by the LED 26 (i.e., with the parasitic inductance Lpar and parasitic capacitance Cpar of the LED 26). Therefore, the lighting device 20 can be operated at an operating frequency that substantially corresponds to the resonant frequency of the LED 26 itself. Therefore, the maximum operating frequency is significantly higher than, for example Figure 1 Lighting equipment shown.

[0043] The resonant drive circuit 22 comprises a field effect transistor 25 with a current source V1 as an amplifying means and a feedback loop 27 to compensate for energy losses in the resonant driver circuit 22 , in particular energy losses due to light emission of the LED 26 .

[0044] The lighting device 20 further comprises a synchronization circuit 28 for synchronizing the phase and / or the operating frequency of the tuning circuit 24 with a reference oscillating signal connected to the feedback loop 27 as “sync”. Figure 3 A schematic diagram of a synchronization circuit 28 comprising a phase locked loop (PLL) 30 is shown. The PLL 30 may be based on a sensor output of a sensor arrangement 32 that detects light emitted by the lighting device 20.

[0045] Figure 4a A schematic diagram of a Colpitts oscillator circuit 34 is shown. The Colpitts oscillator circuit 34 includes a tuning circuit 36 ​​configured as an LC resonant element having L1 and C2. The Colpitts oscillator circuit 34 may drive the tuning circuit 36 ​​with a resonant frequency of the tuning circuit 36.

[0046] Figure 4b Shown based on Figure 4aSchematic diagram of a second embodiment of the lighting device 20 according to the present invention of the Colpitts oscillator circuit 34. Here, Figure 4a The tuned circuit 36 ​​with L1 and C2 has been replaced by the LED 26 with corresponding parasitic inductance and parasitic capacitance forming a tuned circuit.

[0047] Figure 5 FIG. 2 is a schematic diagram showing a third embodiment of a lighting device 20 according to the present invention. Figure 5 , the characteristics of the electronic components of the resonant driver circuit 22 are described in more detail. However, the characteristics of the electronic components may vary depending on the intended use and according to the general knowledge of a person skilled in the art, for example incorporating other types of LEDs 26 and / or changing the operating frequency.

[0048] exist Figure 5 In the embodiment of the invention, the LED 26 is configured to emit light in the infrared range. An end switch including a dual gate switch FAN3227 is provided for activation and deactivation of the resonant driver circuit 22 so that pulses of frequency modulated light can be provided by the lighting device 20.

[0049] Figure 6 A schematic diagram showing the time variations of a driving current 40 and a light output 42 obtained by using the lighting device according to the present invention is shown. Figure 6 Based on Figure 5 Experimental results obtained with the lighting device 20 of the illustrated embodiment. The drive current 40 and the light output 42 (the latter in the form of the sensor current) are Figure 6 In the figure, the time is shown.

[0050] It can be seen that the waveforms of both the drive current 40 and the light output 42 are substantially sinusoidal, thereby simplifying the detection and analysis of the light output 42 in time-of-flight applications.

[0051] In this embodiment, there is a delay of about 5 ns between the drive current 40 and the light output 42. A period p is indicated for the light output 42, which corresponds to an operating frequency of 78 MHz. In the tuning circuit 24 in the lighting device according to the present invention, by means of a resonant driver circuit 22 with an LED 26, a relatively high operating frequency may be achieved.

Claims

1. A lighting device comprising: a light emitting diode (LED), operable at an operating frequency; a synchronization circuit configured to synchronize an operating frequency with a reference oscillation signal, wherein the operating frequency is based on a parasitic inductance and a parasitic capacitance of the LED; as well as A resonant driver circuit comprising: a field effect transistor having a current source and a feedback loop configured to replenish energy losses in the resonant driver circuit based on a sensor output representative of light emission from the LED during operation, and A tuned LC circuit includes an LED and a series connector electrically coupled directly between terminals of the LED and the field effect transistor.

2. The lighting device of claim 1, wherein the series connector comprises direct conductive traces connecting terminals of the LED to the resonant driver circuit. 3 . The lighting device of claim 1 , wherein the series connector has an inductance and a capacitance that are lower than parasitic inductance and parasitic capacitance of the LED. 4 . The lighting device of claim 1 , wherein the resonant driver circuit further comprises an amplifier and a feedback loop electrically coupled to the amplifier.

5. The lighting device of claim 4, wherein the amplifier comprises at least one field effect transistor. The lighting device according to claim 1 , wherein the operating frequency is greater than 40 MHz.

7. The lighting device of claim 1, wherein the operating frequency is greater than 70 MHz.

8. The lighting device according to claim 1, wherein: The resonant driver circuit is a Colpitts oscillator circuit.

9. The lighting device of claim 1, further comprising a synchronization circuit that synchronizes at least one of a phase or an operating frequency of the tuned LC circuit with a reference oscillating signal.

10. The lighting device of claim 9, wherein the synchronization circuit provides a phase locked loop.

11. The lighting device of claim 1, wherein the LED is configured to emit light in the infrared range.

12. The lighting device of claim 1, wherein the resonant driver circuit comprises an end switch.

13. The lighting device of claim 12, wherein the end switch comprises at least one gate switch.

14. A time-of-flight system comprising: Time-of-flight sensors; a light emitting diode (LED), operable at an operating frequency; a synchronization circuit configured to synchronize an operating frequency with a reference oscillation signal, wherein the operating frequency is based on a parasitic inductance and a parasitic capacitance of the LED; as well as A resonant driver circuit comprising: a field effect transistor having a current source and a feedback loop configured to replenish energy losses in the resonant driver circuit based on a sensor output representative of light emission from the LED during operation, and A tuned LC circuit includes an LED and a series connector electrically coupled directly between terminals of the LED and the field effect transistor.

15. The system of claim 14, wherein the series connector comprises direct conductive traces connecting terminals of the LED to the resonant driver circuit.

16. The system of claim 14, wherein the series connector has an inductance and a capacitance that are lower than parasitic inductance and parasitic capacitance of the LED.

17. The system of claim 14, wherein the operating frequency is greater than 40 MHz.

18. The system of claim 14, wherein the operating frequency is greater than 70 MHz.

19. The system of claim 14, further comprising a synchronization circuit that synchronizes at least one of a phase or an operating frequency of the tuned LC circuit with a reference oscillating signal.

20. The system of claim 19, wherein the synchronization circuit provides a phase locked loop.

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