Self-mixing interferometric sensor, method for operating a self-mixing interferometric sensor device and electronic device

Abstract

A self-mixing interferometric sensor device comprises a laser diode, a photodiode, a first readout unit for generating a first readout signal from a measurement signal of the photodiode, a second readout unit for generating a second readout signal from a junction voltage of the laser diode, and a switching unit configured to generate an output signal from the first readout signal in a first operating mode and to generate the output signal from a second readout signal in a second operating mode. The sensor device is configured to switch between operation in the first operating mode and operation in the second operating mode.

Description

[0001] The present invention relates to a self-mixing interferometric sensor device, a method for operating a self-mixing interferometric sensor device and an electronic device.

[0002] This patent application claims priority over German patent application 10 2023 128 608.0, the disclosure content of which is hereby incorporated by reference.

[0003] Self-mixing interferometric sensor devices are known from the prior art. Publication US 11,243,686 B2 describes an example of a self-mixing interference-based sensor for identifying user input.

[0004] It is an object of the present invention to provide a self-mixing interferometric sensor device. Furthermore, it is an object of the invention to provide a method for operating a self-mixing interferometric sensor device. A further object of the present invention is to provide an electronic device. These objects are achieved by a self-mixing interferometric sensor device, a method for operating a self-mixing interferometric sensor device, and an electronic device as disclosed in the independent claims. Further variants are specified in the dependent claims.

[0005] A self-mixing interferometric sensor device comprises a laser diode, a photodiode, a first readout unit for generating a first readout signal from a measurement signal of the photodiode, a second readout unit for generating a second readout signal from a junction voltage of the laser diode, and a switching unit configured to generate an output signal from the first readout signal in a first operating mode and an output signal from a second readout signal in a second operating mode. The sensor device is configured to switch between operation in the first operating mode and operation in the second operating mode.

[0006] This sensor device allows the output signal to be generated from either the first readout signal, derived from a measurement signal of the photodiode, or the second readout signal, derived from a junction voltage of the laser diode. Advantageously, this allows the output signal to be generated from the readout signal that provides the better signal quality. In particular, the output signal can be generated from the readout signal that offers the better signal-to-noise ratio. This enables the sensor device to adapt to situations where background light impairs the quality of the signal provided by the photodiode.

[0007] Some versions of the sensor device are designed to detect signal bias in the first readout signal. The sensor device operates in the first operating mode when the first signal bias is below a threshold, and in the second operating mode when the signal bias exceeds the threshold. Advantageously, this allows the sensor device to switch to generating the output signal from the second readout signal, which is derived from the junction voltage of the laser diode, if excessive signal bias impairs the quality of the first readout signal, which is generated from the photodiode's measurement signal. Excessive signal bias can be caused by background light incident on the photodiode.

[0008] Some versions of the sensor device are designed to receive a switching signal for toggling between operation in the first operating mode and operation in the second operating mode. Advantageously, this allows the sensor device to be switched between the first and second operating modes using an external switching signal. This enables the sensor device to be adapted to conditions that it cannot automatically detect.

[0009] Some variants of the sensor device further feature a driver circuit for operating the laser diode with a first driver current in the first operating mode and with a second driver current in the second operating mode. The first driver current is higher than the second driver current. Advantageously, this allows the sensor device to operate at a favorable operating point in both the first and second operating modes. The signal-to-noise ratio of the first readout signal generated from the photodiode's measurement signal can be higher when the laser diode is operated with the first driver current instead of the second. Similarly, the signal-to-noise ratio of the second readout signal generated from the laser diode's junction voltage can be higher when the laser diode is operated with the second driver current instead of the first.Simultaneously, the first readout signal can provide a better signal-to-noise ratio than the second readout signal if the laser diode is operated with the first driver current, at least if there is no excessive background light. The second readout signal can provide a higher signal-to-noise ratio than the first readout signal if the laser diode is operated with the second driver current. Operating the laser diode with the second driver current can provide the additional benefit of reduced energy consumption of the sensor device.

[0010] In some variants of the sensor device, the switching unit is designed to generate the output signal in the first operating mode from both the first and second readout signals. Advantageously, using both the first and second readout signals to generate the output signal can enable even higher signal quality and an even better signal-to-noise ratio.

[0011] In some variants of the sensor device, the laser diode is a VCSEL. Advantageously, such a laser diode is well suited for the application of self-mixing interferometry.

[0012] In some versions of the sensor device, the first readout unit incorporates a transimpedance amplifier. Advantageously, this allows the generation of a voltage signal from a current signal supplied by the photodiode.

[0013] Some variants of the sensor device feature an ASIC chip mounted on a substrate. The ASIC chip can provide the logic required for the operation of the sensor device.

[0014] In some versions of the sensor device, the laser diode and the photodiode are arranged side by side above the substrate. This advantageously allows for a particularly simple arrangement of the sensor device's components.

[0015] In some versions of the sensor device, the photodiode is integrated into the ASIC chip. This advantageously allows the sensor device to be designed with reduced dimensions.

[0016] In some versions of the sensor device, the photodiode and the laser diode are integrated into a single chip.

[0017] This advantageously allows the size of the sensor device to be reduced.

[0018] In some versions of the sensor device, the laser diode is located on the ASIC chip. This advantageously allows for a reduction in the size of the sensor device.

[0019] In some variants, the sensor device is a force sensor, a particle sensor, a proximity sensor, an eye-tracking sensor, a distance measurement sensor, and an autofocus sensor. Advantageously, the self-mixing interferometric sensor device can be adapted for each of these applications.

[0020] A method for operating a self-mixing interferometric sensor device comprising a laser diode and a photodiode includes switching between operation in a first operating mode and operation in a second operating mode. The first operating mode comprises generating a first readout signal from a measurement signal of the photodiode and generating an output signal from the first readout signal. The second operating mode comprises generating a second readout signal from a junction voltage of the laser diode and generating the output signal from the second readout signal.

[0021] This method allows the output signal to be generated from either the first readout signal, derived from a measurement signal of the photodiode, or the second readout signal, derived from a junction voltage of the laser diode. Advantageously, this enables the generation of the output signal from the readout signal that provides the better signal quality. In particular, the output signal can be generated from the readout signal that offers the better signal-to-noise ratio. This allows the method to be adapted to situations where background light impairs the quality of the signal supplied by the photodiode.

[0022] Some variations of the method include the detection of signal bias in the first readout signal, operation in the first operating mode when the signal bias is below a threshold, and operation in the second operating mode when the signal bias exceeds the threshold. Advantageously, this allows switching to the generation of the output signal from the second readout signal, derived from the junction voltage of the laser diode, if excessive signal bias impairs the quality of the first readout signal generated from the photodiode's measurement signal. Excessive signal bias can be caused by background light incident on the photodiode.

[0023] Some variations of the method involve receiving a switching signal and switching between operation in the first operating mode and operation in the second operating mode depending on the switching signal. Advantageously, this allows switching between the first and second operating modes by means of an external switching signal.

[0024] In some variations of the method, the first operating mode involves operating the laser diode with a first driver current, and the second operating mode involves operating the laser diode with a second driver current. The first driver current is higher than the second driver current. Advantageously, this allows the sensor device to operate at a favorable operating point in both the first and second operating modes. Operating the laser diode with the second driver current can offer the additional benefit of reduced energy consumption by the sensor device.

[0025] In some variations of the method, the first operating mode involves generating a second readout signal from a junction voltage of the laser diode and generating the output signal from both the first and second readout signals. Advantageously, this allows for the use of both the first and second readout signals to generate the output signal, resulting in even higher signal quality and an even better signal-to-noise ratio.

[0026] An electronic device includes a sensor device as described above.

[0027] The properties, features, and advantages of this invention described above, as well as the manner in which they are achieved, will become clearer and more readily understandable in connection with the following description of the exemplary embodiments, which are explained in more detail in conjunction with the drawings. These drawings show, in schematic form: Fig. 1 a cross-section through a sensor device of an electronic device; Fig. 2 a schematic circuit diagram of the sensor device; Fig. 3 Signal-to-noise ratios of readout signals generated in the sensor device; Fig. 4 a cross-section of another variant of the sensor device; Fig. 5 a cross-section of another variant of the sensor device; Fig. 6 a cross-section of another variant of the sensor device; and Fig. 7 a cross-section of another variant of the sensor device.

[0028] Fig. Figure 1 shows a schematic sectional view of an electronic device 10 comprising a sensor device 100. The sensor device 100 is a self-mixing interferometric sensor device based on the principle of amplitude-modulated self-mixing interferometry. The sensor device 100 can be, for example, a force sensor, a particle sensor, a proximity sensor, an eye-tracking sensor, a rangefinder, or an autofocus sensor. The electronic device 10 can be, for example, an earbud, an air purifier or other household appliance, a mobile phone, a tablet, a drone, a camera, a robot, or smart glasses.

[0029] The sensor device 100 comprises a laser diode 120, a photodiode 110, and an ASIC chip 130. In the Fig. In the example shown, the laser diode 120, the photodiode 110, and the ASIC chip 130 are arranged side by side on the top surface of a carrier 140. This enables a flat profile for the sensor device 100 and cost-effective manufacturing of the sensor device 100.

[0030] The laser diode 120 can, for example, be a VCSEL. The laser diode 120 is configured to emit light 300 towards and through an optical interface 150 of the sensor device 100. The optical interface 150 can, for example, comprise an optical lens. Part of the emitted light 300 is reflected at the optical interface 150 and reaches the photodiode 110 as reflected light 310. The photodiode 110 is configured to measure the intensity of the reflected light 310 incident on the photodiode 110.

[0031] The sensor device 100 can be exposed to background light 320, which falls onto the photodiode 110 through the optical interface 150. The presence of the background light 320 can distort the measurement of the intensity of the reflected light 310 by the photodiode 110 by generating a signal bias.

[0032] Fig. Figure 2 shows a schematic circuit diagram of the sensor device 100. The sensor device 100 comprises a first readout unit 210, a second readout unit 220, a switching unit 230, a driver circuit 240, and a control unit 260. At least some of these components or parts of these components can be integrated into the ASIC chip 130 of the sensor device 100.

[0033] The first readout unit 210 is configured to generate a first readout signal 211 from a measurement signal 111 of the photodiode 110. The measurement signal 111 can, for example, be an electric current (photocurrent). The first readout unit 210 can, for example, comprise a transimpedance amplifier.

[0034] The second readout unit 220 is designed to generate a second readout signal 221 from a junction voltage 121 of the laser diode 120.

[0035] The driver circuit 240 is designed to operate the laser diode 120 with a driver current 250. The driver circuit 240 can change the value of the driver current 250.

[0036] When the sensor device 100 is operated, both the first readout signal 211 and the second readout signal 221 are modulated depending on a self-mixing interference occurring in the laser diode 120 of the sensor device 100. Both the first readout signal 111 and the second readout signal 121 can be used to detect the amplitude modulation caused by the self-mixing interference.

[0037] Fig. Figure 3 shows a schematic diagram illustrating the signal-to-noise ratio 212 of the first readout signal 211 and the signal-to-noise ratio 222 of the second readout signal 221 as a function of the drive current 250 used to operate the laser diode 120. The signal-to-noise ratio 212 of the first readout signal 211 is higher with a first drive current 251 than with a second drive current 252. The signal-to-noise ratio 222 of the second readout signal 221 is higher with the second drive current 252 than with the first drive current 251. The signal-to-noise ratio 212 of the first readout signal 211 with the first drive current 251 can be higher than the signal-to-noise ratio 222 of the second readout signal 221 with the second drive current 252.

[0038] The first driver current 251 is higher than the second driver current 252. The first driver current 251 can be, for example, 2 mA. The second driver current can be, for example, 0.5 mA.

[0039] Fig. Figure 3 shows that the first readout signal 211 generally provides a better signal-to-noise ratio than the second readout signal 221 when the driver circuit 240 operates the laser diode 120 with the first driver current 251. The second readout signal 221 provides a higher signal-to-noise ratio than the first readout signal 211 when the laser diode 120 is operated with the second driver current 252. A particularly high signal-to-noise ratio can be achieved when the first readout signal 211 is evaluated at the first driver current 251. An even higher signal-to-noise ratio can be achieved by evaluating both the first readout signal 211 and the second readout signal 221 at the first driver current 251.

[0040] In the presence of background light 320, the measurement signal 111 from photodiode 110 is superimposed with a bias. This bias can distort the first readout signal 211 and reduce its signal quality. The distortion can be caused, for example, by a problem in the dynamic range of the transimpedance amplifier 215. Consequently, the first readout signal 211 can become unusable in the presence of background light 320. In this case, it may be better to operate the laser diode 120 with the second driver current 252 and use the second readout signal 221.

[0041] For this purpose, the sensor device 100 is designed to operate in a first operating mode and a second operating mode and to switch between operation in the first operating mode and operation in the second operating mode. As shown in Fig. As shown in Figure 2, the switching unit 230 is configured to generate an output signal 231 of the sensor device 100 from the first readout signal 211 in the first operating mode, and to generate the output signal 231 from the second readout signal 221 in the second operating mode. The first operating mode thus involves generating the first readout signal 211 from the measurement signal 111 of the photodiode 110 and generating the output signal 231 from the first readout signal 211. The second operating mode involves generating the second readout signal 221 from the junction voltage 121 of the laser diode 120 and generating the output signal 231 from the second readout signal 221.

[0042] In the first operating mode, the driver current 240 operates the laser diode 120 with the first driver current 251. In the second operating mode, the driver circuit 240 operates the laser diode 120 with the second driver current 252. Since the second driver current 252 is smaller than the first driver current 251, operation in the second operating mode can reduce the energy consumption of the sensor device 100 compared to operation in the first operating mode.

[0043] The sensor device 100 can be configured to detect a signal bias of the first readout signal 211, which may be caused, for example, by the presence of background light 320 and which may impair the quality of the first readout signal 211. The sensor device 100 can be configured to switch between the first operating mode and the second operating mode depending on the signal bias, such that the sensor device 100 operates in the first operating mode when the signal bias is below a threshold value, and operates in the second operating mode when the signal bias exceeds the threshold value.

[0044] Alternatively or additionally, the sensor device can be configured to receive a switching signal 235 and, depending on the switching signal 235, to switch between operation in the first operating mode and operation in the second operating mode. The switching signal 235 enables the sensor device 100 to switch between operation in the first operating mode and operation in the second operating mode depending on external factors, such as an energy-saving mode, or depending on an input from a user of the electronic device 10. In the exemplary representation of Fig. 2. The switching unit 230 is able to receive the switching signal 235.

[0045] In some variants, the switching unit 230 can be configured to generate the output signal 231 from both the first readout signal 211 and the second readout signal 221 in the first operating mode. In this case, the first operating mode also includes generating the second readout signal 221 from the junction voltage 121 of the laser diode 120. Generating the output signal 231 from both the first readout signal 211 and the second readout signal 221 can, for example, use a differential mode and offer improved signal quality and a better signal-to-noise ratio.

[0046] The Fig. Figures 4 to 7 show schematic cross-sectional views of alternative variants of the sensor device 100. In these variants, the components of the sensor device 100 are arranged differently than in the one shown in Fig. Variant 1 shown. Apart from the differences described below, the above description of sensor device 100 also applies to the variants of Fig. 4 to 7.

[0047] In the Fig. In variant 4, the photodiode 110 is integrated into the ASIC chip 130. This can enable a miniaturization of the sensor device 100.

[0048] In the Fig. In the variant shown in Figure 5, the photodiode 110 is the same as in the variant of Fig. 4 are integrated into the ASIC chip 130. Additionally, the laser diode 120 is arranged next to the photodiode 110 on the ASIC chip 130. This arrangement allows for an even smaller size of the sensor device 100.

[0049] In the version of Fig. In 6, the photodiode 110 is integrated into the ASIC chip 130. The laser diode 120 is arranged on the ASIC chip 130. In contrast to the variant of Fig. In Figure 4, the laser diode 120 is arranged on the photodiode 110. In this configuration, the laser diode 120 emits not only light 300 towards the optical interface 150, but also light 305 backwards towards the photodiode 110. The photodiode 110 detects not the light 310 reflected at the optical interface 150, but the backwards emitted light 305. In the arrangement of Fig. 6 is the sensor device 100 less susceptible to backlight 320.

[0050] In the Fig. In the variant shown in Figure 7, the laser diode 120 and the photodiode 110 are integrated into a common chip 115. The common chip 115 is located on the ASIC chip 130. In this arrangement, the photodiode 110 detects, as in the arrangement of Fig. 6, not the light 310 reflected at the optical interface 150, but directly the light 305 emitted by the laser diode 120. This results in the arrangement of Fig.7 less susceptible to the presence of backlight 320.

[0051] The invention has been explained and described in more detail using exemplary variants. However, the invention is not limited to the disclosed examples. Rather, further variants can be derived from them by a person skilled in the art. REFERENCE MARK LIST 10 electronic devices 10 Sensor device 110 photodiode 111 Measurement signal 115 shared chip 120 laser diode 121 Junction voltage 130 ASIC chips 140 carriers 150 optical interface 210 first readout unit 211 first readout signal 212 Signal-to-noise ratio 215 Transimpedance Amplifiers 220 second display unit 221 second readout signal 222 Signal-to-noise ratio 230 switching unit 231 Output signal 235 Switching signal 240 driver circuit 250 driver current 251 first driver current 252 second driver current 260 Control unit 300 emitted light 305 backward emitted light 310 reflected light 320 backlight QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] DE 10 2023 128 608.0

[0002] US 11,243,686 B2

[0003]

Claims

[1] Comprising a self-mixing interferometric sensor device (100) - a laser diode (120), - a photodiode (110), - a first readout unit (210) for generating a first readout signal (211) from a measurement signal (111) of the photodiode (110), - a second readout unit (220) for generating a second readout signal (221) from a junction voltage (121) of the laser diode (120), - a switching unit (230) configured to generate an output signal (231) from the first readout signal (211) in a first operating mode and to generate the output signal (231) from the second readout signal (221) in a second operating mode, wherein the sensor device (100) is configured to switch between operation in the first operating mode and operation in the second operating mode. [2] Sensor device (100) according to claim 1, wherein the sensor device (100) is configured to detect a signal bias of the first readout signal (211), wherein the sensor device (100) is configured to operate in the first operating mode when the signal bias is below a threshold value, and to operate in the second operating mode when the signal bias exceeds the threshold value. [3] Sensor device (100) according to one of the preceding claims, wherein the sensor device (100) is configured to receive a switching signal (235) for switching between operation in the first operating mode and operation in the second operating mode. [4] Sensor device (100) according to one of the preceding claims, which further comprises a driver circuit (240) for operating the laser diode (120) with a first driver current (251) in the first operating mode and for operating the laser diode (120) with a second driver current (252) in the second operating mode, where the first driver current (251) is higher than the second driver current (252). [5] Sensor device (100) according to one of the preceding claims, wherein the switching unit (230) is configured to generate the output signal (231) in the first operating mode from both the first readout signal (211) and the second readout signal (221). [6] Sensor device (100) according to one of the preceding claims, wherein the laser diode (120) is a VCSEL. [7] Sensor device (100) according to one of the preceding claims, wherein the first readout unit (210) comprises a transimpedance amplifier (215). [8] Sensor device (100) according to one of the preceding claims, wherein the sensor device (100) comprises an ASIC chip (130) arranged on a carrier (140). [9] Sensor device (100) according to claim 8, wherein the laser diode (120) and the photodiode (110) are arranged side by side above the carrier (140). [10] Sensor device (100) according to one of claims 8 and 9, wherein the photodiode (110) is integrated into the ASIC chip (130). [11] Sensor device (100) according to claim 8, wherein the photodiode (110) and the laser diode (120) are integrated into a common chip (115). [12] Sensor device (100) according to one of claims 8 to 11, wherein the laser diode (120) is arranged on the ASIC chip (130). [13] Sensor device (100) according to one of the preceding claims, wherein the sensor device (100) is a force sensor, a particle sensor, a proximity sensor, an eye-tracking sensor, a distance measurement sensor and an autofocus sensor. [14] Method for operating a self-mixing interfero- metric sensor device (100), wherein the sensor device (100) comprises a laser diode (120) and a photodiode (110), wherein the method involves switching between operation in a first operating mode and operation in a second operating mode, the first operating mode has: - Generating a first readout signal (211) from a measurement signal (111) of the photodiode (110); - Generating an output signal (231) from the first readout signal (211); and the second operating mode features: - Generating a second readout signal (221) from a junction voltage (121) of the laser diode (120); - Generating the output signal (231) from the second readout signal (221). [15] The method of claim 14, wherein the method comprises - Capturing a signal bias of the first readout signal (211); - Operates in the first operating mode when the signal bias is below a threshold; - Operates in the second operating mode when the signal bias exceeds the threshold. [16] Method according to one of claims 14 and 15, wherein the method comprises - Receiving a switching signal (235); - Switching between operation in the first operating mode and operation in the second operating mode depending on the switching signal (235). [17] Method according to any one of claims 14 to 16, the first operating mode has: - Operating the laser diode (120) with a first driver current (251); and the second operating mode has: - Operating the laser diode (120) with a second driver current (252); where the first driver current (251) is higher than the second driver current (252). [18] Method according to any one of claims 14 to 17, wherein the first operating mode comprises: - Generating a second readout signal (221) from a junction voltage (121) of the laser diode (120); - Generating the output signal (231) from both the first readout signal (211) and the second readout signal (221). [19] Electronic device (10) with a sensor device (100) according to any one of claims 1 to 13.

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