2022PF00563 1 RECEIVER AND LIDAR SYSTEM LIDAR ("Light Detection And Ranging") systems, in particular, FMCW LIDAR systems ("Frequency Modulated Continuous Wave") are increasingly used in e.g. vehicles, for example for autonomously driving. For example, they are used for detecting distances or objects. Generally, attempts are being made to provide LIDAR systems requiring a reduced space. It is an object of the present invention to provide an improved receiver for a LIDAR system as well as an improved LIDAR system. According to embodiments, the above object is achieved by the claimed matter according to the independent claims. Further developments are defined in the dependent claims. SUMMARY According to embodiments, a receiver, suitable for a LIDAR system, is configured to receive an input signal. The input signal is based on a detection of a superposition of a transmit signal emitted towards an object and a reflected signal reflected by the object, the input signal being a periodically varying signal having a period T. The receiver comprises a first filter configured to delay the input signal by a first retardation time to generate a first delayed signal. The receiver further comprises a second filter configured to delay the first delayed signal by T/2 to generate a second delayed signal. The receiver additionally comprises a frequency detector that is configured to determine a frequency of an evaluation signal which is based on a difference of the first delayed signal and the second delayed signal. For example, the term “evaluation signal which is based on a difference of the first delayed signal and the second delayed signal” may refer to a signal that may correspond to the difference signal of the first delayed signal and the second delayed signal, wherein the difference signal may have been further processed. By
2022PF00563 2 way of example, the difference signal may have been further amplified. According to further examples, the receiver may comprise an analog digital converter. In this case, the evaluation signal may be the digitally converted and optionally amplified difference signal. For example, the receiver may be configured to determine a distance and a speed of the object based on the frequency determined by the frequency detector. The receiver may further comprise an amplifier which determines the difference of the first delayed signal and the second delayed signal. For example, the amplifier may be an offset-compensated amplifier. By way of example, the receiver may further comprise a duty cycle detector which is configured to receive the evaluation signal, to analyze a duty cycle in dependence from time of the evaluation signal and to generate a duty cycle detector signal. For example, the duty cycle detector may determine whether the duty cycle is substantially constant over time. According to embodiments, the receiver may further comprise a control device configured to receive the duty cycle detector signal and to determine a control signal for controlling the first filter. According to further embodiments, the control device may further determine a second control signal for controlling the second filter. The frequency detector may further be configured to determine the frequency of the evaluation signal in dependence from time and to generate a frequency detector signal. The control device may be further configured to receive the frequency detector signal and to determine the control signal further based on the frequency detector signal. For example, the control device may determine an operating point of the first filter based on the duty cycle detector signal and/or the
2022PF00563 3 frequency detector signal. For example, the operating point may be set when a substantially constant duty cycle and/or a substantially frequency have been detected. The control device may be further configured to output a driver control signal to a driving system that modulates the transmit signal. According to embodiments, a LIDAR system comprises a laser device configured to emit a transmit signal towards an object, wherein a wavelength of the transmit signal is variable by varying a current injected in the laser device. The LIDAR system further comprises a laser driving system for driving the laser device and a receiver configured to receive an input signal. The input signal may be based on a superposition of the transmit signal and a reflected signal reflected by the object, the input signal being a periodically varying signal having a period T. The receiver may comprise a first filter configured to delay the input signal by a first retardation time to generate a first delayed signal, a second filter configured to delay the first delayed signal by T/2 to generate a second delayed signal, and a frequency detector configured to determine a frequency of an evaluation signal which is based on a difference of the first delayed signal and the second delayed signal. For example, the receiver may be implemented in the manner as has been explained above. For example, the laser device may be a component of a measurement configuration. According to embodiments, the measurement configuration may further comprise a photodetector for detecting an intensity of the superposed signals. The LIDAR system may be configured to determine a distance and a speed of the object based on the frequency determined by the frequency detector.
2022PF00563 4 The LIDAR system may further comprise an offset compensated amplifier which determines the difference of the first delayed signal and the second delayed signal. According to embodiments, the LIDAR system may further comprise a duty cycle detector configured to receive the evaluation signal, to analyze a duty cycle in dependence from time of the evaluation signal and to generate a duty cycle detector signal. The LIDAR system may further comprise a control device configured to receive the duty cycle detector signal and to determine a control signal for controlling the first filter. The frequency detector may further be configured to determine the frequency of the evaluation signal in dependence from time and to generate a frequency detector signal. The control device may further be configured to receive the frequency detector signal and to determine the control signal further based on the frequency detector signal. The control device may further be configured to output a driver control signal to the laser driving system. The laser driving system may be configured to generate a triangularly modulated current signal and a slope of the triangularly modulated current signal may be controlled by the driver control signal. According to further embodiments, an electronic device comprises the LIDAR system as defined above. For example, the electronic device may be selected from a smartphone, a digital camera an autonomously driving unit, and wearables. BRIEF DESCRIPTION OF THE DRAWINGS The accompanying drawings are included to provide a further understanding of embodiments of the invention and are incorporated in and constitute a part of this specification. The drawings illustrate the embodiments of the present invention and together
2022PF00563 5 with the description serve to explain the principles. Other embodiments of the invention and many of the intended advantages will be readily appreciated, as they become better understood by reference to the following detailed description. The elements of the drawings are not necessarily to scale relative to each other. Like reference numbers designate corresponding similar parts. Figs. 1A to 1C are schematic drawings for illustrating a method for determining a distance and a velocity using a LIDAR system. Figs. 2A to 2D illustrate a method for processing a received signal using a receiver according to embodiments. Fig. 3 shows a schematic diagram of a receiver according to embodiments. Figs. 4A to 4C show different implementations of measurement configurations. Fig. 5 shows a LIDAR system according to embodiments. Fig. 6 shows a LIDAR system according to further embodiments. Fig. 7 shows an electronic device according to embodiments. DETAILED DESCRIPTION In the following detailed description reference is made to the accompanying drawings, which form a part hereof and in which are illustrated by way of illustration specific embodiments in which the invention may be practiced. In this regard, directional terminology such as "top", "bottom", "front", "back", "over", "on", "above", "leading", "trailing" etc. is used with reference to the orientation of the Figures being described. Since components of embodiments of the invention can be positioned in a number of different orientations, the directional terminology is used for purposes of illustration and is in no way limiting. It is to be understood that
2022PF00563 6 other embodiments may be utilized and structural or logical changes may be made without departing from the scope defined by the claims. As employed in this specification, the terms “coupled” and/or “electrically coupled” are not meant to mean that the elements must be directly coupled together - intervening elements may be provided between the “coupled” or “electrically coupled” elements. The term “electrically connected” intends to describe a low-ohmic electric connection between the elements electrically connected together. The term “connected” may refer to components that may be connected by wire or wirelessly. As used herein, the terms “having”, “containing”, “including”, “comprising” and the like are open ended terms that indicate the presence of stated elements or features, but do not preclude additional elements or features. The articles “a”, “an” and “the” are intended to include the plural as well as the singular, unless the context clearly indicates otherwise. A frequency-modulated continuous-wave LIDAR system is a measurement system according to which a transmit signal is irradiated on an object and a reflected signal reflected by the object is received. Using the Doppler effect, the object can be detected by determining the frequency difference between the transmit signal and the reflected signal. In order to simultaneously detect speed and distance of the object, the frequency of the transmit signal is modulated, e.g. according to a sawtooth or triangular shape as illustrated in Fig. 1A. As is seen, the frequency of the reflected signal Rx is delayed and offset with respect to the transmit signal Tx. Fig. 1A shows the variation of the frequency of the transmit signal and the reflected signal with time. Fig. 1B illustrates the frequency difference between the two signals with time. Fig. 1C shows an example of a measurement signal, e.g. a voltage signal that may be detected using a photodetector. As is seen, the detection signal is periodic having a frequency corresponding to the
2022PF00563 7 frequency difference between the transmit signal and the reflected signal as e.g. illustrated in Fig. 1A. Generally, the beat frequencies shown in Fig. 1B may be determined as F = F - F , F
wherein F corresponds to the Doppler frequency, i.e. F =2Vf/c, wherein V corresponds to the speed of the object to be detected. The distance R may be determined as )
The speed v may be determined as )
According to concepts, laser devices may be employed for LIDAR measurements, wherein a frequency of the emitted laser beam, i.e. the transmit signal may be modulated using a modulation of the injected current. For example, VCSELs ("Vertical Cavity Surface Emitting Laser") are increasingly employed. When the frequency of the emitted laser beam is modulated using modulation of the injected current, for example, the detection signal illustrated in Fig. 2A may be detected by a corresponding photodetector. Fig. 2A shows an example of an output signal of a photodetector. As can be seen, the detected signal 81 that may be also referred to as an SMI signal ("Self-Mixing Interference" signal) comprises a triangularly modulated portion 80 which is due to the modulation of the current source of the laser device. The detected signal further
2022PF00563 8 comprises a comparatively fast changing portion. To be more specific, the frequency of the comparatively fast changing portion may be more than ten times the frequency of the modulated current signal corresponding to the triangularly modulated portion 80. For example, the triangularly modulated signal may add a compensation signal (nonlinearity) to compensate for temperature behavior. As a result, the accuracy of the distance and speed measurement may be improved. The amplitude of the fast changing portion is much smaller than the amplitude of the triangularly modulated portion. For example, the amplitude of the periodically changing portion may be less than 1/10 or less than 1/100 of the amplitude of the triangularly modulated portion. The periodically changing portion may also be referred to as fringes. Referring to Fig. 2B to 2D the basic principle for preprocessing the detected SMI signal 81 will be explained. The preprocessing uses a suitable combination of the SMI signal with the SMI signal shifted so as to remove the triangularly modulated portion 80. Accordingly, preprocessing is performed by using the detected signal itself as a reference in an analog preconditioning stage. Fig. 2B shows a schematic view of the SMI signal 81 including the triangularly modulated portion 80. A shifted signal 82 is generated by introducing a time delay and an offset. Fig. 2C shows a combination of both signals. ^t denotes a time delay between the two signals. Thereafter, as is illustrated in Fig. 2D, the two signals are subtracted. In more detail, the shifted signal 82 is subtracted from the SMI signal 81. As a result, the signal 84 as shown in Fig. 2D is obtained. The signal 84 is a SMI signal without the triangularly modulated portion. By evaluating the signal 84, the frequency change may be detected and the distance and speed of the object may be calculated.
2022PF00563 9 Fig. 3 shows an implementation of a receiver 10 according to embodiments. The receiver 10 is configured to receive an input signal (SMI signal) 81 from a measurement configuration 30. Examples of a measurement configuration 30 will be given with reference to Figs. 4A to 4C. The input signal 81 is based on a detection of a superposition of a transmit signal emitted towards an object and a reflected signal that has been reflected by the object 31. For example, the transmit signal may be a laser beam emitted by a laser device (not shown in Fig. 3). The laser device may be driven by a laser driving system 25. The laser driving system 25 may generate a current signal that is modulated as has been explained above with reference to Figs. 1 and 2. For example, the current signal may have a triangularly periodically changing shape, as has been discussed with reference to Fig. 2A. According to embodiments, the laser driving system 25 does not form a component of the receiver 10. The laser driving system 25 may be connected to the receiver 10. According to further embodiments, the laser driving system 25 may form a component of the LIDAR system. For example, the input signal 11 may be based on a voltage drop in a laser diode. According to further examples, depending on the implementation of the measurement configuration, the input signal 11 may be based on a current of a photodiode. The input signal 11 may be fed to a buffer 12, followed by a first filter 13 that is configured to delay the input signal 11 by a first retardation time to generate a first delayed signal. The receiver further comprises a second filter 14 which is configured to delay the first delay signal by T/2 to generate a second delayed signal. T refers to the period of the periodically changing portion of the input signal, i.e. the fringe signal. In more detail, as has been explained above with reference to Fig. 2A, the input signal comprises a comparatively fast changing portion. T refers to the period of the comparatively fast changing portion. The first delayed signal and the second delayed signal are fed to a differential amplifier 15. The differential amplifier 15 determines the difference between the
2022PF00563 10 first and the second delayed signals. In particular, the differential amplifier 15 may subtract the second delayed signal from the first delayed signal. As a consequence, due to this processing, the amplitude of the comparatively fast changing portion is doubled, and the gain may be 2. The pass frequency of the first and the second filters 13, 14 may be set to find a certain fringe signal. For example, a dedicated relationship between both filter characteristics may ensure a steep filter characteristic. The first filter 13 may cut off high frequency components. The second filter 14 works as a phase shifter. For example, the delay of the first filter 13 may correspond to a quarter of the period T. According to further embodiments, the delay of the first filter 13 may be different from T/4. Generally, as will be explained below, during operation the first and the second filters 13, 14 are adapted. For example, a fixed relationship in the frequency response may be set between the first and second filter. The delay of the second filter 14 corresponds to half the period T. When using a narrow band filter, distance and speed may be measured more precisely. The amplified analog signal 87 that is output by the differential amplifier 15 is schematically illustrated in the upper portion of Fig. 3. The signal output from the amplifier 15 may be further set to an offset compensation module 16. The offset compensation module 16 may compensate for the offset of the amplifier. The signal output by the differential amplifier 15 is fed to an ADC ("Analog-Digital Converter") 17. An example of a digital signal 88 generated by the ADC 17 is illustrated in the upper portion of Fig. 3. The digital signal then is fed to a frequency detector 18 which may detect the frequency, e.g. using a counter. A signal indicating the frequency is fed to the calculation module 27 which may determine frequency and speed of the object 31. The determined values may be output via an output module 28, e.g. to a user interface (not illustrated).
2022PF00563 11 Since the frequency of the SMI signal 81 is unknown a-priori, the receiver 10 may further comprise a duty cycle detector 19. The actual duty cycle may be analyzed together with a frequency to generate a performance indicator for the actual working point. This performance indicator may be used to match the transfer function of the first filter 13 to the potential available SMI signal. In more detail, the duty cycle detector 19 may analyze the digital signal and determine a duty cycle signal in dependence from time. To be more specific, the duty cycle detector 19 may analyze the variation of the duty cycle period. Moreover, the frequency detector 18 may analyze the variation of the detected frequency over time. Signals from the duty cycle detector 19 and the frequency detector 18 may be fed to an error detection module 26. The error detection module 26 may determine errors in determining the frequency and may correct the distance and speed determined by the calculation module 27. For example, a control device 22 may be arranged to receive an output of the duty cycle detector 19 and the frequency detector 18. The control device 22 may determine a suitable working point in which the duty cycle and the frequency are constant over time. According to implementations, the operating point may be determined during a searching sequence. During the searching sequence the filter coefficients may be swept in order to find a potential fringe signal in the detected signal, e.g. on top of the voltage drop of the laser diode. As has been discussed above, this fringe signal is very tine and may be below the noise level. The control device 22 may control the first filter 13 in order to adjust the time delay of the first filter 13. Further, the control device 22 may also control the second filter 14. For example, a fixed relationship between the first and the second filter may be set during the searching sequence.
2022PF00563 12 The transfer function and the time delay of the first filter 13 may be set so that the available input signal 11 (SMI signal 81) is transmitted by the combination of the first filter 13 and the second filter 14. Moreover, the control device 22 may perform slope control and may output a slope control signal 24 to adjust the slope of the triangularly modulated portion 80. The slope control signal 24 may be applied to the laser driving system 25. For example, the control device 22 may determine a suitable working point corresponding to a slope of the frequency generated by the laser driving system 25. The laser driving system 25 may change a current signal applied to the laser device in accordance with the slope control signal 25. As a consequence the change rate of the current signal supplied to the laser device is increased or decreased. The signal received from the measurement configuration while applying the slope may be analyzed to determine optimum filter coefficients of the first filter 13. For example, the time delay of the first filter 13 and the slope of the current ramp generated by the laser driving system 25 may be adjusted via a control loop until the SMI frequency and the filter setting match. The SMI frequency is then detected and used for calculation of speed and distance according to the formulas given above. Due to the specific arrangement discussed with reference to Fig. 3, the frequency of the SMI signal 81 may be determined in a precise manner while using a simple system using a reduced amount of hardware resources, silicon floor space and power consumption. The receiver works and reacts very fast so that a lower latency time may be achieved. Figs. 4A to 4C show examples of a measurement configuration 30 that may be employed to generate the input signal 11. A laser device 32 receives a driving current signal 36 that may be generated by a laser driving system 25 (not shown in Fig. 4A). The laser device 32 emits a transmit signal 33 having a varying frequency, e.g. as
2022PF00563 13 illustrated in Fig. 1A. A portion of the transmit signal 33 may be shaped by an optical element 39 and is reflected by the object 31 to generate the reflected signal 34. Another portion of the transmit signal 33 may be divided using e.g. a beam splitter. The reflected signal 34 is superposed on the divided portion of the transmit signal 33. Detector 35 that may be implemented as a photodiode detects the interfered signal and outputs a detected current signal 37. According to the implementation illustrated in Fig. 4A, the detected current signal 37 may be the input signal 11 received by the receiver 10 as e.g. illustrated in Fig. 3. Fig. 4B shows a further implementation of the measurement configuration 30. The laser device 32 emits a transmit signal 33 that may be shaped by an optical element 39 and reflected by the object 31 to generate a reflected signal 38. The transmit signal 33 and the reflected signal 38 are superposed and impinge on the laser device 32 that also acts as a detector. As a result, a detected voltage signal 38 is output by the laser device 32. According to the implementation of Fig. 4C, a photodetector 35 is additionally provided to the laser device 32. The photodetector 35 detects the superposed signal of the transmit signal 33 and the reflected signal 38. The detector 35 outputs a current signal 37 to the receiver 10 as e.g. illustrated in Fig. 3. Fig. 5 shows an example of a LIDAR system 1 according to embodiments. The LIDAR system shown in Fig. 5 comprises a measurement configuration 30. The measurement configuration 30 may comprise a laser device (not illustrated in Fig. 5) that is configured to emit a transmit signal towards an object, wherein an emission wavelength of the laser beam is variable by varying a current injected in the laser device. The LIDAR system further comprises a laser driving system 25 for driving the laser device. The laser driving system 25 is configured to change a driving current signal 36 injected in the laser device.
2022PF00563 14 The LIDAR system further comprises a receiver 10 configured to receive a detected current or voltage signal 37, 38 as an input signal. The input signal is based on a superposition of the transmit signal emitted towards the object and a reflected signal reflected by the object. The receiver 10 may be implemented in the manner as described above. For example, the receiver 10 may comprise a first filter and a second filter (not illustrated in Fig. 5). The first filter may be configured to delay the input signal by a first retardation time to generate a first delayed signal. Moreover, the second filter may be configured to delay the first delayed signal by T/2 to generate second delayed signal. T corresponds to a period of the input signal, e.g., the comparatively fast changing portion of the input signal. The first filter and the second filter may be components of a signal preconditioning system 41. The signals that are output by the different components of the LIDAR system are illustrated in the lower portion of Fig. 5. The signal output by the signal preconditioning system 41 is input to the frequency detector 18 which determines the frequency of the signal. These values are given to a digital signal processor 43. A user interface 42 may be coupled to the digital signal processor 43. The digital signal processor 43 may determine speed and distance of an object. A feedback signal from the digital signal processor 43 may be input to a digital analog converter (DAC) 44. There may be a feedback loop 54 that inputs further control signals to the signal preconditioning system 41 e.g. for adjusting the filter characteristics as has been discussed above. Moreover, a signal output from the DAC 44 may be input to the laser driving system 25 e.g. for adjusting a slope of the triangularly modulated current that is applied to the laser device.
2022PF00563 15 Fig. 6 illustrates a further example of a LIDAR system. Fig. 6 shows components of the LIDAR system without illustrating the specifics of the measurement configuration. Waveforms that are received or processed by the single components are illustrated in the lower portion of Fig. 6. The LIDAR system of Fig. 6 is similar to the LIDAR system of Fig. 5. However, differing from the implementation of Fig. 5, the LIDAR system of Fig. 6 does not comprise a signal preconditioning system 41. Instead, a detected current signal 37 or a detected voltage signal 38 received from the measurement configuration 30 may be input to an analog to digital converter (ADC) 17. The digital signal output by the ADC 17 is input to a Fourier transformation module 46, e.g. a Fast Fourier transformation module. The input signal 11 that is input to the ADC 17 is the same as has been discussed above. The Fourier transformation module 46 may generate the digital signal 89 that is shown in the lower portion of Fig. 6. The frequency detector 18 receives the digital input signal 89 and determines the frequency of the respective signals. The calculation module 27 determines speed and velocity of the detected object using the determined frequency. These values are input to the digital signal processor 43 that may be coupled to a user interface. The digital signal processor 43 may be connected to a digital analog converter 44 which may be coupled to the laser driving system 25. For example, a slope of the modulated current may be adjusted depending on measurement values determined by the calculation module 27. Fig. 7 shows an example of an electronic device 5. The electronic device may comprise the LIDAR system 1 that has been explained above. For example, the electronic device may be selected from a smartphone, a digital camera, an autonomously driving unit and wearables. Since, as has been explained above, the receiver may be implemented so as to have a reduced space and a reduced power consumption, the LIDAR system may be incorporated in any electronic device with restricted area and power supply.
2022PF00563 16 Further, the receiver 10 may be used in arrays of so-called SMI pixels comprising a plurality of measurement configurations which have been explained e.g. with respect to Figs. 4A to 4C. For example, an array of receivers 10 may be combined with an SMI pixel. According to further implementations, one receiver, which is driven in a time-multiplexed mode, may be used in combination with an SMI pixel. In this case, for example, the delay setting may be taken as a starting point for the next pixel. While embodiments of the invention have been described above, it is obvious that further embodiments may be implemented. For example, further embodiments may comprise any subcombination of features recited in the claims or any subcombination of elements described in the examples given above. Accordingly, this spirit and scope of the appended claims should not be limited to the description of the embodiments contained herein.
2022PF00563 17 LIST OF REFERENCES 1 LIDAR system 5 electronic device 10 receiver 11 input signal 12 buffer 13 first filter 14 second filter 15 differential amplifier 16 offset compensation 17 analog-digital converter 18 frequency detector 19 duty cycle detector 22 control device 23 filter control 24 slope control signal 25 laser driving system 26 error detection module 27 calculation module 28 output module 30 measurement configuration 31 object 32 laser device 33 transmit signal 34 reflected reflected 35 detector 36 driving current signal 37 detected current signal 38 detected voltage signal 39 optical element 41 signal preconditioning system 42 user interface 43 digital signal processor 44 digital analog converter 45 feedback 46 Fourier transformation module
2022PF00563 18 80 triangularly modulated portion 81 SMI signal 82 shifted signal 84 SMI signal without triangularly modulated portion 85 first delayed signal 86 second delayed signal 87 analog signal 88 digital signal 89 transformed signal
The speed v may be determined as )