DE102023111616A1 - Time-of-flight camera system and method for operating a time-of-flight camera system - Google Patents

Abstract

The invention relates to a time-of-flight camera system with a sensor circuit, the sensor circuit comprising a light emitting unit (12), a photodetector (102) based on the time-of-flight method, a modulator (30) for providing a modulation signal (M ₀ ), a control circuit (110), and a driver circuit (104), wherein
- the driver circuit (104) is electrically connected to the light emitting unit (12),
- an output of the control circuit (110) is electrically connected to an input of the photodetector (102), and
- a modulator output of the modulator (30) is electrically connected to a detector input of the photodetector (102) and a driver input (104E) of the driver circuit (104).
The sensor circuit (10) further comprises a detection circuit (112) for detecting a propagation delay (PD) of the modulation signal, wherein the detection circuit (112) is electrically connected on the input side to the driver circuit (104) and on the output side to the control circuit (110).

Description

The invention relates to a time-of-flight camera system with a sensor circuit for determining a propagation delay of a modulation signal, as well as to methods for operating the time-of-flight camera system.

The time-of-flight camera system relates in particular to time-of-flight camera systems or TOF (time-of-flight) camera systems, which obtain time-of-flight information from the phase shift of radiation emitted by a light emitting unit and received by a photodetector. PMD time-of-flight cameras with photomixing detectors (PMD) are particularly suitable as time-of-flight or TOF cameras, as described in the applications EP 1 777 747 B1 , US 6 587 186 B2 and also DE 197 04 496 C2 The PMD camera allows in particular a flexible arrangement of the light emitting unit and the photodetector, which can be arranged either in one housing or separately.
To determine a distance from the time of flight information via the phase shift, the phase position of a modulation signal and the phase position of the radiation detected by the photodetector are usually compared. However, inaccuracies in the distance measurement can easily occur due to time delays of the modulation signal when passing through different components of the time of flight camera. In particular, temperature drift, aging processes and scattering in the manufacturing process of the components can lead to variable time of flight delays, which cannot be satisfactorily compensated by calibration during the manufacture of the time of flight camera or experimentally determined parameters. The time of flight camera system can comprise a photodetector with at least one time of flight pixel, a pixel row, or a pixel array.

The object of the invention is to provide a time-of-flight camera system which enables a high accuracy in distance measurement and which has only a comparatively small measurement error due to propagation delays of the modulation signal.

The object is advantageously achieved by a time-of-flight camera system according to the invention. Embodiments of the invention are specified in the subclaims. In a further aspect, the invention relates to a method for operating a time-of-flight camera system according to the invention.

A time-of-flight camera system with a sensor circuit is specified, the sensor circuit comprising a light emitting unit, a photodetector based on the time-of-flight method, a modulator for providing a modulation signal, a control circuit, and a driver circuit. The driver circuit is electrically connected to the light emitting unit, an output of the control circuit is electrically connected to an input of the photodetector, and a modulator output of the modulator is electrically connected to an input of the photodetector and a driver input of the driver circuit. The sensor circuit further comprises a detection circuit for detecting a propagation delay of the modulation signal, the detection circuit being electrically connected on the input side to the driver circuit and on the output side to the control circuit.

Advantageously, the actual propagation delay of the modulation signal can be measured by the driver circuit and taken into account in the distance measurement by the control circuit. In particular, differences in the propagation delay due to temperature changes, component variation during production, or aging processes can be compensated. The propagation delay can be measured continuously or at intervals, for example.

The light emitting unit can in particular comprise at least one LED (light-emitting diode), a surface emitter (VCSEL, vertical-cavity surface-emitting laser), a laser or a laser diode. Without being restricted to this, the control circuit can be designed as a microcontroller (µC) or as an application-specific integrated circuit (AISIC). The control circuit can be set up to calculate a distance, taking the propagation delay into account. For example, a corresponding firmware can be stored on a non-volatile memory of the control circuit and executed by the control circuit.
It is preferably provided that the detection circuit comprises at least a first detector input and a second detector input, wherein the first detector input is electrically connected to the driver input and the second detector input is electrically connected to the driver output. As a result, the modulation signal can be tapped before and after passing through the driver and the propagation delay can be determined by a simple comparison of the two signals.

The photodetector preferably comprises a photomixer. A photomixer advantageously enables a simple measurement of distances by comparing the detected optical signal and the electrical reference signal of the modulator.

The modulator preferably comprises an adjustable or digitally controllable oscillator. In some embodiments of the time-of-flight camera system, the detection circuit comprises at least one logic gate or at least one bistable flip-flop. At least one JK flip-flop can be provided as a bistable flip-flop. The input signals can be detected to determine the propagation delay using a logic gate or a connection of several gates. In some developments, the logic gate can comprise at least one XOR gate. In some embodiments, the XOR gate can be formed by a connection of several logic gates, for example by a connection of NAND gates. Other embodiments for forming an XOR gate can also be provided, for example a suitable connection and control of field-effect transistors (FETs), such as metal-oxide-semiconductor field-effect transistors (MOSFETs). When using an XOR gate, the detectable propagation delay is limited to half the period of the modulation signal. If a measurement range longer than this time period is required, a JK flip-flop can preferably be used. A JK flip-flop is edge-triggered, so that only one output pulse is generated per period of the modulation signal, which extends the detection range to a full period T of the modulation signal.

The detection circuit can further comprise a filter circuit or be coupled thereto, wherein the detection circuit is connected to the control circuit via an output of the filter circuit. The filter circuit can in particular comprise a low-pass filter, for example a first-order low-pass filter, a second-order low-pass filter, a second-order LC filter, or an active high-order low-pass filter.

The filter circuit preferably comprises an analog-digital converter arranged on the output side, wherein a reference voltage of the analog-digital converter corresponds to an operating voltage of the driver. Because the analog-digital converter and the driver are operated with the same or the same voltages, the propagation delay PD can then be detected independently of the operating voltage of the driver.

• - Detektieren der Laufzeitverzögerung des Modulationssignals beim Durchlaufen des Treibers durch die Detektionsschaltung,
• - Generieren und Ausgeben eines Laufzeitverzögerungssignals als Maß für die Laufzeitverzögerung durch die Detektionsschaltung,
• - Empfangen des Laufzeitverzögerungssignals von der Detektionsschaltung durch die Steuerschaltung,
• - Empfangen eines Phasendifferenzsignals von dem Photosensor durch die Steuerschaltung, und
• - Ermitteln einer Entfernung aus dem Phasendifferenzsignal und der Laufzeitverzögerung durch die Steuerschaltung.

Furthermore, a method for operating a time-of-flight camera system according to the invention is specified, wherein the photodetector is preferably designed to detect a phase difference between the light received by the photodetector and the modulation signal and wherein the detection circuit is designed to detect a propagation delay of the modulation signal when passing through the driver. The method comprises:

• - Detecting the propagation delay of the modulation signal as it passes through the driver through the detection circuit,
• - generating and outputting a propagation delay signal as a measure of the propagation delay through the detection circuit,
• - Receiving the propagation delay signal from the detection circuit by the control circuit,
• - receiving a phase difference signal from the photosensor by the control circuit, and
• - Determining a distance from the phase difference signal and the propagation delay by the control circuit.

The propagation delay of the modulation signal can thus be detected directly by the driver. A specific propagation delay can therefore be detected for each time-of-flight camera system. In particular, the effects of temperature drift, component scattering and/or aging effects on the propagation delay can be compensated. The method therefore provides a simple way of achieving high accuracy in distance measurement. The propagation delay can advantageously be detected using a voltage level of the modulation signal or using a voltage level change of the modulation signal, for example by means of edge detection.

• - das Detektieren eines ersten Spannungspegels oder einer ersten Spannungspegeländerung des Modulationssignals am Eingang des Treibers durch die Detektionsschaltung,
• - das Detektieren eines zweiten Spannungspegels oder einer zweiten Spannungspegeländerung des Modulationssignals am Ausgang des Treibers durch die Detektionsschaltung,
• - das Generieren des Laufzeitverzögerungssignals aus dem ersten Spannungspegel und dem zweiten Spannungspegel oder aus der ersten Spannungspegeländerung und der zweiten Spannungspegeländerung.

In some training courses, the procedure therefore includes:

• - detecting a first voltage level or a first voltage level change of the modulation signal at the input of the driver by the detection circuit,
• - detecting a second voltage level or a second voltage level change of the modulation signal at the output of the driver by the detection circuit,
• - generating the propagation delay signal from the first voltage level and the second voltage level or from the first voltage level change and the second voltage level change.

The propagation delay signal can then be provided at the output of the detection circuit and received by the control circuit. Thus, by comparing the two voltage levels or by detecting the edges of the voltage signals, a simple embodiment of the method can be provided, which can be carried out without great computational effort in the signal processing.

• - Detektieren eines ersten Logikwertes in Abhängigkeit des ersten Spannungspegels,
• - Detektieren eines zweiten Logikwertes in Abhängigkeit des zweiten Spannungspegels,
• - Vergleichen des ersten und des zweiten Logikwertes,
• - Ausgeben des Laufzeitverzögerungssignals in Abhängigkeit des Vergleichs.

The first and the second voltage level can be detected in particular as a logic value with a high level or a low level. In some developments, it is therefore provided that the determination of the propagation delay signal comprises the following method steps:

• - Detecting a first logic value depending on the first voltage level,
• - Detecting a second logic value depending on the second voltage level,
• - Comparing the first and second logic values,
• - Output of the propagation delay signal depending on the comparison.

This allows a particularly simple evaluation of the detected signals in the form of logic values.

In particular, the detection circuit for determining the propagation delay can comprise at least one exclusive-OR gate (XOR gate), wherein the first voltage level and the second voltage level are fed to the XOR gate for generating the propagation delay signal. The method can then be used to implement a corresponding logic combination of the two input signals of the detection circuit.

Furthermore, a duty cycle η and/or an average value of the propagation delay signal can be processed or analyzed. The method can then include determining a temporal average value of the propagation delay signal, wherein the propagation delay is determined taking into account the temporal average value of the propagation delay signal. The averaging can be carried out, for example, with the aid of a filter circuit. In particular, it can be provided that the detection circuit comprises a filter circuit, for example a low-pass filter, or that the propagation delay signal of the detection circuit is present at a filter input of the filter circuit.

The averaging can include converting an analog value into a digital value. In particular, the method can provide for the averaged propagation delay signal to be converted into a digital value using the analog-digital converter mentioned above. It is particularly advantageous if the analog-digital converter is operated with a reference voltage that is equal to the operating voltage of the driver 104. The propagation delay can thus be detected in the method independently of the operating voltage of the driver.

For example, the phase delay of the modulation signal can be determined by detecting the phase delay using an XOR gate and then averaging the delay signal of the XOR gate. Typical drivers invert the modulation signal. If the modulation signal is now tapped before the driver and fed to the first detector input of the XOR gate, while the modulation signal is fed to the second detector input of the XOR gate after passing through the driver, the delay PD for the XOR gate/an inverting driver can be determined as follows: $$\text{PD}=\left(1-\frac{{\text{SY}}_{\text{avg}}}{{\text{SY}}_{\text{max}}}\right)\cdot \frac{\text{<figure-callout id="2" label="T" filenames="DE102023111616A1\_0010.png,DE102023111616A1\_0011.png" state="{{state}}">T</figure-callout>}}{2}$$

Here, SY _max denotes a maximum value and SY _avg denotes an average value of a propagation delay signal SY, which is provided as an output signal at the output of the detector circuit. T denotes the period of the modulation signal. In such embodiments, the maximum detectable propagation delay PD is therefore limited by half the period T/2 of the modulation signal. In principle, the invention can be used with any driver. For example, the driver can also comprise an AND gate, a NAND gate, a NOR gate, or an amplifier. It is advantageous if the output signal of the driver is a square wave signal.

The magnitude of typical propagation delays in time-of-flight camera systems can be estimated as follows:

For a modulation frequency of, for example, 25 MHz and a typical propagation delay of 6 ns at a temperature of Temp = 25°C, the error of a calculated light path length is s25 = c · 6 ns = 1799 mm. For a temperature of Temp = 85°C, the propagation delay can be, for example, 6.6 ns, which corresponds to a light path length s85= 1979 mm. With linear temperature dependence and taking into account a factor of “2” for the double path length of the light path, compared to the simple target tabstand, a typical temperature drift ds/dTemp can be estimated as follows: $$\frac{\text{ds}}{\text{dTemp}}=\frac{180\cdot {10}^{-3}\text{m}}{60\text{K}\cdot \text{2}}=\frac{1.5\cdot {10}^{-3}\text{m}}{\text{K}}$$

For example, the measurement error can be 1.5 mm per degree Kelvin K of temperature drift. Furthermore, with a modulation frequency of 25 MHz, the period T = 40 ns, so that in this case a propagation delay of a maximum of 20 ns can be detected using an XOR gate.

Preferably, the modulation signal applied to the driver input and the driver output each has a duty cycle η in the range 25% ≤ η ≤ 75%, preferably in the range 40% ≤ η ≤ 60%. Ideally, η = 50%. This advantageously makes it possible to provide a large detection range so that typical propagation delays are within the detection range. In the above example, the maximum measuring range of 20 ns can only be provided for the case η = 50%. If, however, η is in the range 25% to 75%, the measuring range in the example is reduced to a maximum of 10 ns propagation delay.

The invention is explained in more detail below using embodiments with reference to the drawings.

• - 1 schematisch das grundlegende Prinzip der Photomischdetektion;
• - 2 einen Querschnitt eines Lichtlaufzeitpixels;
• - 3 eine modulierte Integration der erzeugten Ladungsträger;
• - 4 schematisch eine beispielhafte Ausgestaltung einer Sensorschaltung für ein erfindungsgemäßes Lichtlaufzeitkamerasystem;
• - 5a beispielhafte Signalverläufe an einem ersten Detektoreingang A und einem zweiten Detektoreingang B der Detektionsschaltung;
• - 5b einen beispielhaften Signalverlauf an einem Detektorausgang Y einer als XOR-Gatter ausgebildeten Detektionsschaltung für die in der 5a dargestellten Eingangssignale;
• - 6a beispielhafte Signalverläufe an den zwei Detektoreingängen der Detektionsschaltung im Falle eines invertierenden Treibers;
• - 6b einen beispielhaften Signalverlauf am Detektorausgang Y einer als XOR-Gatter ausgebildeten Detektionsschaltung für die in der 6a dargestellten Eingangssignale;
• - 7a eine schematische Darstellung der Filterverstärkung eines XOR-Gatters, welches zur Verwendung in einer beispielhaften Detektionsschaltung eines Lichtlaufzeitkamerasystems gemäß der Erfindung geeignet ist; und
• - 7b eine schematische Darstellung der Filterverstärkung des XOR-Gatters aus 7a, wobei eine das XOR-Gatter übersteuert ist.

They show:

• - 1 schematically the basic principle of photonic detection;
• - 2 a cross-section of a time-of-flight pixel;
• - 3 a modulated integration of the generated charge carriers;
• - 4 schematically shows an exemplary embodiment of a sensor circuit for a time-of-flight camera system according to the invention;
• - 5a exemplary signal curves at a first detector input A and a second detector input B of the detection circuit;
• - 5b an exemplary signal curve at a detector output Y of a detection circuit designed as an XOR gate for the 5a displayed input signals;
• - 6a exemplary signal curves at the two detector inputs of the detection circuit in the case of an inverting driver;
• - 6b an exemplary signal curve at the detector output Y of a detection circuit designed as an XOR gate for the 6a displayed input signals;
• - 7a a schematic representation of the filter gain of an XOR gate suitable for use in an exemplary detection circuit of a time-of-flight camera system according to the invention; and
• - 7b a schematic representation of the filter gain of the XOR gate from 7a , where one of the XOR gates is overdriven.

In the following description of the embodiments, the same reference symbols designate the same or comparable components.

1 shows a measurement situation for an optical distance measurement with a time-of-flight camera, as it is shown for example in the DE 197 04 496 C2 is known.

The time-of-flight camera system 1 comprises a light transmitting unit 12, or an illumination module 10 with illumination and associated beam-forming optics 15, as well as a photodetector, or a time-of-flight camera 20, with receiving optics 25 and a time-of-flight sensor 22. The time-of-flight sensor 22 has at least one time-of-flight pixel, or a pixel row, preferably a pixel array, and is designed in particular as a PMD sensor. The receiving optics 25 typically consist of several optical elements to improve the imaging properties. The beam-forming optics 15 of the transmitting unit 10 can be designed, for example, as a reflector or lens optics. In a very simple embodiment, optical elements, both on the receiving and transmitting side, can also be dispensed with if necessary.

The measuring principle of this arrangement is essentially based on the fact that the transit time, and thus the distance traveled by the received light, can be determined based on the phase shift of the emitted and received light. For this purpose, a light transmission unit 12 and the light transit time sensor 22 are supplied with a specific modulation signal M _o with a base phase position φ ₀ via a modulator 30. In the example shown, a phase shifter 35 is also provided between the modulator 30 and the light transmission unit 12, with which the base phase φ ₀ of the modulation signal M ₀ of the light transmission unit 12 can be shifted by defined phase positions φ _var . For typical phase measurements, phase positions of φ _var = 0°, 90°, 180°, 270° are preferably used.

According to the set modulation signal, the light emitting unit 12 emits an intensity-modulated signal S _p1 with the first phase position p1 or p1 = φ ₀ + φ _var . This signal S _p1 , or the electromagnetic radiation, is In the case shown, it is reflected by an object 40 (target) and, due to the distance traveled, hits the light transit time sensor 22 as a received signal S _p2 with a corresponding phase shift Δφ(t _L ) and a second phase position p2 = φ ₀ + φ _var + Δφ(t _L ). In the light transit time sensor 22, the modulation signal M ₀ is mixed with the received signal S _p2 , whereby the phase shift or the object distance d is determined from the resulting signal.

Furthermore, a modulation control device 38 is provided, with which the form and in particular the pulse and pause ratios of the modulation signal are specified. The phase shifter 35 can also be controlled via the modulation control device 38 depending on the measurement task to be carried out.

Infrared light-emitting diodes are preferably suitable as the illumination source or light-emitting unit 12. Of course, other radiation sources in other frequency ranges are also conceivable, in particular light-emitting units in the visible frequency range are also possible.

2 shows a cross-section through a time-of-flight pixel of a photonic mixer detector, as used for example in the DE 197 04 496 C2 is known. The modulation photogates Gam, G0, Gbm form the light-sensitive area of a PMD pixel. Depending on the voltage applied to the modulation gates Gam, G0, Gbm, the photonically generated charges q are directed either to one or the other accumulation gate or integration node Ga, Gb.

Alternatively, such a time-of-flight pixel can also be designed without modulation gates, as is the case, for example, in the EP 1 332 594 A1 shown and described.

2b shows a potential curve in which the charges q flow towards the first integration point Ga, while the potential according to 2c which allows the charge q to flow in the direction of the second integration node Gb. The potentials are specified according to the applied modulation signals. Depending on the application, the modulation frequencies are preferably in a range of 1 to 100 MHz. For a modulation frequency of 1 MHz, for example, this results in a period of one microsecond, so that the modulation potential changes every 500 nanoseconds.

In 2a a readout unit 100 is also shown, which may already be part of a PMD light transit time sensor designed as a CMOS. The integration nodes Ga, Gb designed as capacitors or diodes integrate the photonically generated charges over a large number of modulation periods. In a known manner, the voltage then applied to the gates Ga, Gb can be tapped off with high impedance, for example via the readout unit 100. The integration times should preferably be selected so that the light transit time sensor or the integration nodes and/or the light-sensitive areas do not become saturated for the expected amount of light.

The basic principle of phase measurement is shown schematically in 3 The upper curve shows the temporal progression of the modulation signal M ₀ with which the lighting 12 and the light transit time sensor 22 are controlled. The light reflected from the object 40 hits the light transit time sensor 22 as a received signal S _p2 in accordance with its light transit time t _L with a phase shift Δφ(t _L ).

The light travel time sensor 22 typically has a first and second accumulation gate Ga, Gb in which the photonically generated charges q are alternately collected over several modulation periods depending on the potential profile in the light-sensitive area. The charges q generated in the unshifted phase position are collected in the first accumulation gate Ga and those in the phase position M ₀ + 180° shifted by 180° are collected in the second accumulation gate Gb. The phase shift Δφ(t _L ) and thus a distance d of the object can be determined from the ratio of the charges qa, qb collected in the first and second gates Ga, Gb.

In a time-of-flight camera system, which, for example, is based on the 1 to 3 However, even if the system works as described above, there are also delays in the modulation signal as it passes through the electronic components, which distorts the distance measurement of the time-of-flight camera system.

The 4 shows schematically an exemplary embodiment of a sensor circuit 80 for a time-of-flight camera system according to the invention. With the aid of the sensor circuit 80, the error in distance measurements, which arises due to the time delay of the modulation signal through the electronic components, can be significantly reduced. The sensor circuit 80 comprises the light emitting unit 12, the emitted light of which is reflected by a target and can be detected by a photodetector 102. The photodetector 102 is designed, for example, as a PMD sensor. The light emitting unit 12 is designed, for example, as a laser diode and is controlled on the cathode side via a resistor 106 by a driver 104 for power amplification/control. The The anode of the laser diode is connected to a voltage source 108. Alternatively, an anode-side control of the light emitting unit 12 by the driver 104 can also be provided, for example in combination with a circuit for automatic power control. The sensor circuit 80 also comprises a modulator 30. The modulation signal output by the modulator 30 is applied to the photodetector 102. The photodetector 102 is designed in particular to compare the phase position of the modulation signal with the detected optical signal, i.e. with the radiation emitted by the laser diode after it has been reflected by a target. The result of the comparison is converted by a control circuit 112 into a distance, the target distance. The control circuit 112 can also be designed and set up to control the photodetector 102, for example to control the modulation gates of the aforementioned PMD sensor.

The modulation signal is also applied in parallel to a driver input 104E of the driver 104, for example an inverter logic gate. A driver output 104A of the driver 104 is, as mentioned above, converted from voltage to current via the resistor 106, so that a corresponding light modulation is generated in the laser diode.

This means that in addition to the light propagation time, there are also propagation delays of the driver 104, the resistor 106, the laser diode and the lines. This propagation delay of the driver 104 can now be measured by a detection circuit 112. For this purpose, the modulation signal is tapped at the input 104E of the driver 104 and, after passing through the driver 104, at the output 104A of the driver 104. The driver input 104E is connected to a detector input A of the detection circuit 112 and the driver output 104A is connected to a detector input B of the detection circuit 112. The detection circuit 112 can now compare the phase positions of the signal SA at the input A and the signal SB at the detector input B and thus detect the propagation delay PD. A corresponding propagation delay signal SY is output at an output Y of the detection circuit 112. The detection circuit 112 is designed, for example, as an XOR gate. An optional filter circuit 114 is also shown, which receives the signal SY output at the output Y of the detection circuit. The filter circuit can be designed in particular to form an average value of the propagation delay signal S _y . For example, the filter circuit 114 can comprise a low-pass filter. In addition, an analog-digital converter stage (ADC) can be provided for outputting a digital signal at the output of the filter circuit 114.

The detection circuit 112 is connected to the control circuit 112 via the filter circuit 114. The filter circuit 112 can also be integrated in the detection circuit 112 or in the control circuit 110. The control circuit 112 is set up to calculate a distance DIst based on the measurement data received from the photodetector 102 and the propagation delay signal SY received from the detection circuit 112 or from the filter circuit 114. The calculation of the distance Dist can, for example, include calculating a first distance Dist1 based on the light propagation time measurement of the photodetector 102 and calculating a second distance Dist2, which is defined by the product of the propagation delay PD and the speed of light c. The distance Dist can then be determined by forming the difference Dist = Dist2 - Dist1. Of course, the difference between the light propagation time detected by the photodetector 102 and the measured propagation delay PD can also be calculated first and then the distance Dist can be calculated using the speed of light c. The detection circuit 112 and the filter circuit 114 can each be designed as a digital circuit, as an analog circuit, or as a combined circuit. The control circuit 110 can in particular be designed as a µC or AISIC and have a non-volatile data memory on which a computer program for carrying out the method steps is stored and can be executed by the control circuit 110.

The 4 The components shown are purely schematic and can be integrated in any way, provided it is technically feasible. For example, two or more components can be combined into a single component.

In the 5a and 5b Examples of signals are SA and SB ( 4a) , as well as the propagation delay signal SY of the detection circuit 112 at the output Y ( 4b) for the case where the driver 104 is not inverting and an XOR gate is used as detection circuit 112. The x-axis shows the time t in the unit nanoseconds, while the y-axis indicates the voltage U in the unit volts. In the 4a It is now clearly visible that the propagation delay signal SB at the detector input B of the detection circuit 112 has a delay of 7 ns compared to the signal SA at the detector input A. At the rising and falling edges, a pulse is generated in the output signal, the propagation delay signal SY, the width of which corresponds to the propagation delay PD The propagation delay PD is then calculated as: $$\text{PD}=\frac{{\text{SY}}_{\text{avg}}}{{\text{SY}}_{\text{max}}}\cdot \frac{\text{<figure-callout id="2" label="T" filenames="DE102023111616A1\_0010.png,DE102023111616A1\_0011.png" state="{{state}}">T</figure-callout>}}{2}$$

The 6a and 6b show the analog case with an inverting driver 104. The signal at the detector input B is now inverted, so that the signal output at the detector output Y also changes accordingly. As already stated above, the propagation delay PD can then be determined according to the following relation: $$\text{PD}=\left(1-\frac{{\text{SY}}_{\text{avg}}}{{\text{SY}}_{\text{max}}}\right)\cdot \frac{\text{<figure-callout id="2" label="T" filenames="DE102023111616A1\_0010.png,DE102023111616A1\_0011.png" state="{{state}}">T</figure-callout>}}{2}$$

berechnet werden, wobei ADC(SY_avg) den vom ADC gewandelten, digitalen Integer-Wert bei dem analogen Eingangssignal SY_avg und FS (von englisch: Full Scale) den maximalen digitalen Integer-Wert des ADC-Ausgangssignals angibt. Solch eine Ausgestaltung ist besonders vorteilhaft, da sich die Laufzeitverzögerung PD unabhängig von der Betriebsspannung des Treibers 104 berechnen lässt.The propagation delay signal SY can be fed to a simple RC filter for averaging, for example, and then converted into a digital signal using an ADC. Assuming that the reference voltage of the ADC corresponds to an operating voltage of the driver 104, SY _avg /SY _max can now be calculated from $$\frac{{\text{SY}}_{avG}}{{\text{SY}}_{max}}=\frac{\text{ADC}\left({\text{SY}}_{avG}\right)}{\text{FS}}$$

where ADC(SY _avg ) indicates the digital integer value converted by the ADC for the analog input signal SY _avg and FS (full scale) indicates the maximum digital integer value of the ADC output signal. Such an embodiment is particularly advantageous because the propagation delay PD can be calculated independently of the operating voltage of the driver 104.

In the 7a and 7b The behavior of an XOR gate as a phase detector is shown as an example. 7a shows the case where the duty cycle η of the two input signals is 50%. The mean value SY _avg of the propagation delay signal SY is shown in units K _d · π/2 as a function of the phase difference, here referred to as the phase error φ _e with φ _e = φ _B - φ _A. φ _A and φ _B denote the phases of the signals SA and SB at the detector inputs A and B and K _d the detector gain. The unambiguity of the measured values is limited to a phase error φ _e in the range -90° to +90°, so that a linear measuring range of 180° phase difference can be provided. The mean value of the detector output signal SY _avg for small phase errors is then SY _avg = K _d φ _e . With a voltage supply with voltage potentials V _cc and 0 V this results in K _d = V _cc / π.

7b illustrates the situation when asymmetrical input signals are present at the inputs A and B of the XOR gate, i.e. when the duty cycle η of at least one of the input signals SA, SB is not equal to 50%. In this case, the XOR gate reaches a saturation range (clipping) at values |φ _e | < 90°, which reduces the measuring range. In the example, saturation is reached at |φ _e | = 70°.

Therefore, in some embodiments of the invention, it is preferred if the duty cycle η of the modulation signal is in the range of 25% ≤ η ≤ 75%, in particular in the range 40% ≤ 60%, so that a large measuring range is available. It is particularly advantageous to select η to be η = 50%. This ultimately allows the propagation delay PD to be detected in a comparatively large range.

list of reference symbols

10

lighting module

12

light emitting unit

22

time-of-flight sensor

27

evaluation unit

30

modulator

35

phase shifter, lighting phase shifter

38

modulation control unit

50

differential circuit

60

inverter

100

reading unit

102

photodetector

104

driver

104A

driver output

104E

driver input

106

Resistance

108

voltage source

110

control circuit

112

detection circuit

114

filter circuit

Δφ(tL)

runtime-related phase shift

φvar

phase position

φ0

base phase

M0

modulation signal

p1

first phase

p2

second phase

Sp1

transmission signal with first phase

Sp2

received signal with second phase

Ga, Gb

accumulation gates

Ua, Ub

Voltages at the modulation gate

φe

phase difference

φA

Phase of the modulation signal at the driver input/detector input A

φB

Phase of the modulation signal at the driver output/detector input B

AWAY

detector inputs

Y

detector output

SA, SB

input signals of the detector

SY

propagation delay signal (output signal of the detector)

Kd

detector gain

QUOTES INCLUDED IN THE DESCRIPTION

This list of documents listed by the applicant was generated automatically and is included solely for the better information of the reader. 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

• EP 1 777 747 B1 [0002]
• US 6 587 186 B2 [0002]
• DE 197 04 496 C2 [0002, 0030, 0036]
• EP 1 332 594 A1 [0037]

Claims (14)

Light-time-of-flight camera system with a sensor circuit, the sensor circuit comprising a light-emitting unit (12), a photodetector (102) based on the light-time-of-flight method, a modulator (30) for providing a modulation signal (M ₀ ), a control circuit (110), and a driver circuit (104), wherein - the driver circuit (104) is electrically connected to the light-emitting unit (12), - the control circuit (110) is electrically connected to the photodetector (102), and - a modulator output of the modulator (30) is electrically connected to an input of the photodetector (102) and to a driver input (104E) of the driver circuit (104), the sensor circuit (10) further comprising a detection circuit (112) for detecting a propagation delay (PD) of the modulation signal (M ₀ ), wherein the detection circuit (112) is connected on the input side to the driver circuit (104) and on the output side to the control circuit (110) is electrically connected. Time-of-flight camera system according to claim 1 , wherein the detection circuit (112) comprises at least a first detector input (A) and a second detector input (B), and wherein the first detector input (A) is electrically connected to the driver input (104E) and the second detector input (B) is electrically connected to the driver output (104B) of the driver circuit (104). Time-of-flight camera system according to claim 1 or 2 , wherein the photodetector (102) comprises a photomixer and/or wherein the modulator (30) comprises an adjustable or digitally controllable oscillator. Time-of-flight camera system according to one of the preceding claims, wherein the detection circuit (112) comprises at least one logic gate or at least one bistable flip-flop. Time-of-flight camera system according to claim 4 , wherein the logic gate comprises at least one XOR gate, or wherein the bistable flip-flop comprises at least one JK flip-flop. A time-of-flight camera system according to any one of the preceding claims, wherein the detection circuit (112) further comprises a filter circuit (114), and wherein the detection circuit (112) is connected to the control circuit (110) via an output of the filter circuit (114). Time-of-flight camera system according to claim 6 , wherein the filter circuit (114) comprises or is connected to an analog-digital converter arranged on the output side, and wherein a reference voltage of the analog-digital converter corresponds to an operating voltage of the driver (104). Time-of-flight camera according to one of the preceding claims, wherein the modulation signal present at the driver input and that at the driver output each has a duty cycle η in the range 25% ≤ η ≤ 75%, preferably in the range 40% ≤ η ≤ 60%. Method for operating a time-of-flight camera system according to one of the preceding claims, wherein the photodetector (102) is designed to detect a phase difference between the light received by the photodetector (102) and the modulation signal (30), and wherein the detection circuit (110) is designed to detect a propagation delay (PD) of the modulation signal (30) as it passes through the driver (104), the method comprising: - detecting the propagation delay (PD) of the modulation signal (M ₀ ) as it passes through the driver (104) by the detection circuit (112), - outputting a propagation delay signal (SY) as a measure of the propagation delay (PD) by the detection circuit (112), - receiving the propagation delay signal (SY) from the detection circuit (112) by the control circuit (110), - receiving a phase difference signal from the photodetector (102) by the control circuit (110), and - determining a distance from the phase difference signal and the propagation delay signal (SY) by the control circuit (110). procedure according to claim 9 , the method comprising: - detecting a first voltage level or a first voltage level change of the modulation signal at the driver input (104E) of the driver (104) by the detection circuit (112), - detecting a second voltage level or a second voltage level change of the modulation signal at the driver output (104A) of the driver (104) by the detection circuit (112), - generating the propagation delay signal (SY) from the first voltage level and the second voltage level or from the first voltage level change and the second voltage level change. procedure according to claim 10 , wherein the determination of the propagation delay signal (SY) comprises the following method steps: - detecting a first logic value depending on the first voltage level, - detecting a second logic value depending ity of the second voltage level, - comparing the first and the second logic value, - generating the propagation delay signal (SY) depending on the comparison. Method according to one of the Claims 10 or 11 , wherein the detection circuit (112) for determining the propagation delay (PD) comprises an XOR gate, wherein the first voltage level and the second voltage level are supplied to the XOR gate for generating the propagation delay signal (SY). Method according to one of the Claims 9 until 12 , the method comprising determining a temporal average value (SY _avg ) of the propagation delay signal (SY), wherein the propagation delay (PD) is determined taking into account the temporal average value (SY _avg ) of the propagation delay signal (SY). Method according to one of the Claims 9 until 13 , wherein the propagation delay is detected independently of the operating voltage of the driver (104).

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