Optical detection method and optical detection device

Abstract

In an optical detection method, a carrier signal having a carrier signal period is generated and a code sequence is generated over an exposure time period. Each code (406) in the sequence includes a plurality of symbols (408, 410, 412, 414, 416) having a timing delay (418, 420, 422, 424) between the symbols. The carrier signal is phase shifted in response to the code sequence (406) according to the values of the symbols (408, 410, 412, 414, 416). The modulated carrier signal is applied to a light source, thereby modulating the emitted light. An electrical sensor signal is generated in response to received reflected light. A plurality of predetermined phase offset values are applied to the modulated carrier signal and a plurality of electrical output signals are generated and stored by applying the resulting signals to the electrical sensor signal over the exposure time period according to an indirect time-of-flight measurement technique. Each symbol (408, 410, 412, 414, 416) has a duration that is greater than the carrier signal period.

Description

Technical Field

[0001] This invention relates to an optical inspection method, of which, for example, employs an indirect time-of-flight measurement technique. The invention also relates to an optical inspection apparatus, of which, for example, employs an indirect time-of-flight measurement technique. Background Technology

[0002] In so-called time-of-flight sensing systems and other systems (such as night vision systems), it is known to employ a light source to illuminate the surrounding environment (sometimes referred to as the "scene") within the field of view of that light source, and to process the light reflected by features of that scene. Such so-called LiDAR (Light Detection and Ranging) systems use a light source to illuminate the scene with light, and use detection devices (such as photodiode arrays, some optical elements, and a processing unit) to detect the light reflected from objects in the scene. The light reflected from objects in the scene is received by the detection device and converted into an electrical signal, which is then processed by the processing unit by applying time-of-flight (ToF) calculations to determine the distance of the object from the detection device. Although different types of LiDAR systems are known to be based on different operating principles, these systems essentially all illuminate the scene and detect reflected light.

[0003] In this regard, so-called "flash LiDAR" technology (a direct Time-of-Flight ranging technology) employs a light source that emits light pulses, which are then reflected by features of the scene and detected by a detector device. In this type of technology, the distance to the reflecting feature is directly calculated using the measured round-trip time of the light pulse to the reflecting feature and back to the detector device. The light pulses incident on the detector device are sampled at a very high sampling rate in the time domain. Therefore, the signal path in the processing circuitry used to implement this technology requires high signal bandwidth and a large silicon wafer space ("real estate"), meaning that such implementations require a relatively large area on a silicon wafer, which in turn limits the number of channels that can be supported on the integrated circuit. Therefore, the actual number of spatial channels that such flash LiDAR sensors can support is typically less than 100. To overcome this limitation, mechanical scanning systems requiring moving parts are implemented.

[0004] Another known LiDAR system employs a technique called "indirect time-of-flight" (iTOF). An iTOF system emits a continuous-wave light signal, and the reflections of this signal are received and analyzed by a detector device. Multiple samples (e.g., four samples) of light reflected from features of the scene are obtained, each sample with a phase step of, for example, 90°. Using this illumination and sampling method, the phase angle between illumination and reflection can be determined, and the determined phase angle can be used to determine the distance to the reflective features of the scene.

[0005] However, the presence of more than one modulated light source in the field of view of an iToF LiDAR system causes interference relative to the iToF LiDAR system, and the distance calculated from the measured phase angle is prone to error. Susceptibility to interference is a common problem, particularly, and not exclusively, concerning the interior of a vehicle's cockpit (i.e., the interior of a car).

[0006] Several different solutions exist to attempt to mitigate the effects of modulated light interference sources on iToF LiDAR modules. One technique to counteract the interference between multiple iToF LiDAR systems in a shared environment (such as inside a vehicle cockpit) is to use different wavelengths of light for different iToF LiDAR modules. However, using multiple wavelengths of light in a coordinated manner depends on the multiple iToF LiDAR modules supporting such an approach, which typically requires these modules to share a common manufacturer. Moreover, this approach requires the shared environment to be well-controlled; for example, the presence of all light sources in the environment needs to be known and configured to avoid interference with each other.

[0007] Similarly, it is known to provide iToF modules with different modulation frequencies in such environments as described above. However, the common environment must also be well controlled, and these iToF modules with different frequencies typically need to be manufactured by the same manufacturer.

[0008] In another technique, when the iToF LiDAR modules are not from the same manufacturer, the modulation frequency of one iToF module "jumps" (i.e., changes continuously) during the operation of that iToF module, thereby mitigating interference from other iToF LiDAR modules in the same common environment. However, this statistical interference mitigation method offers limited benefit in terms of interference suppression.

[0009] It is also known to employ so-called on / off codes for the modulation and demodulation signals of iToF LiDAR modules. While such methods are effective in reducing interference, they also have the adverse effect of significantly reducing the signal-to-noise ratio (SNR) of iToF LiDAR modules employing these methods.

[0010] U.S. Patent No. 2019 / 285749 discloses modulation of LiDAR pulses to detect and suppress interference. The processor uses a known modulation signal to distinguish between desired and unwanted received pulses.

[0011] In U.S. Patent No. 9,977,128, the iToF LiDAR system mitigates interference caused by secondary light sources by employing detection technology to detect secondary interference sources of light. Detection of the secondary light source allows light received by the iToF LiDAR module from that secondary source to be discarded.

[0012] U.S. Patent No. 2019 / 179017 discloses an iToF LiDAR system employing two different modulation frequencies, one of which can be randomly phase-modulated. This technique mitigates interference, but requires dedicated common-mode cancellation circuitry to achieve this mitigation. Summary of the Invention

[0013] According to a first aspect of the invention, an optical detection method is provided, the method comprising: emitting continuous wave light; generating a carrier signal having an associated carrier signal period; generating a code sequence during an exposure time period, each code in the code sequence comprising a plurality of symbols; applying a phase shift to the carrier signal in response to the code sequence to generate a phase-modulated carrier signal; applying the phase-modulated carrier signal to a light source to modulate the continuous wave light according to the phase-modulated carrier signal; emitting the modulated continuous wave light according to an indirect time-of-flight measurement technique; receiving reflected modulated continuous wave light; generating an electrical sensor signal in response to the reflected modulated continuous wave light; generating a mixed signal by applying a plurality of predetermined phase offset values ​​to the phase-modulated carrier signal; generating and storing a plurality of electrical output signals by applying the mixed signal to the electrical sensor signal according to an indirect time-of-flight measurement technique and for the exposure time period; wherein each symbol has a duration greater than the carrier signal period; the phase modulation of the carrier signal includes shifting the phase of the carrier signal according to the values ​​of the symbols among the plurality of symbols; and providing a timing delay between each symbol among the plurality of symbols.

[0014] The timing delay provided between each symbol in the plurality of symbols can be a guard delay, which is configured to minimize the reduction in the signal-to-noise ratio of the plurality of electrical output signals caused by the transition at the boundary between the symbols in the plurality of symbols.

[0015] Each symbol may include a first binary value or a second binary value; the first binary value may correspond to a first predetermined phase shift value, and the second binary value may correspond to a second phase shift value.

[0016] The difference between the first phase shift value and the second phase shift value can be 180 degrees. The first phase shift value can be 180 degrees and the second phase shift value can be 0 degrees, or vice versa.

[0017] The code sequence may include the repetition of the occurrence of multiple symbols. The repetition of the occurrence of multiple symbols may simply include the repetition of the multiple symbols and the timing delay.

[0018] The method may further include selecting the duration of a timing delay for subsequent insertion between each symbol in a plurality of symbols.

[0019] The method may further include using a simulated time source to generate a timing delay.

[0020] The timing delay can be generated using the system time source of an optical ranging device.

[0021] The method may further include a timing ratio between the duration of the timing delay and the duration of each symbol; this timing ratio may be between 1:2 and 1:50. Alternatively, the timing ratio may be between approximately 1:5 and approximately 1:20.

[0022] Each code in the code sequence may include multiple code elements as a pseudo-random binary sequence.

[0023] The method may further include optimizing the timing ratio by modifying the carrier signal period, thereby modifying the duration of each symbol.

[0024] The method may further include optimizing the timing ratio by modifying the duration of each symbol by changing the number of symbols per code in each code sequence.

[0025] The method may further include optimizing the timing ratio by modifying the duration of each symbol by changing the duration of the exposure time period.

[0026] The method may further include: selecting the signal-to-noise ratio and / or interference suppression with respect to the plurality of electrical output signals; and selecting the duration of each symbol as a multiple of the carrier frequency period to achieve the selected signal-to-noise ratio and / or interference suppression; and / or selecting the duration of a timing delay to achieve the selected signal-to-noise ratio and / or interference suppression.

[0027] The method may further include: processing multiple electrical output signals according to an indirect time-of-flight measurement technique to calculate a measurement vector and calculate the measured phase angle from the measurement vector.

[0028] According to a second aspect of the present invention, a method for determining the distance to a feature of a scene is provided, the method comprising: an optical detection method as described above with respect to the first aspect of the present invention; and calculating the distance using a measured phase angle.

[0029] According to a third aspect of the invention, an optical detection apparatus is provided, comprising: a light source configured to emit continuous-wave light; a modulation signal generator configured to generate a carrier signal having an associated carrier signal period; a code generator configured to generate a code sequence during an exposure time period, each code in the code sequence comprising a plurality of symbols; a phase shifter configured to apply a phase shift to the carrier signal in response to the code sequence to generate a phase-modulated carrier signal; a light source driver configured to apply the phase-modulated carrier signal to the light source to modulate the continuous-wave light according to the phase-modulated carrier signal; the light source being configured to emit the modulated continuous-wave light according to an indirect time-of-flight measurement technique; and a detector. The detector is configured to receive reflected modulated continuous-wave light and to generate an electrical sensor signal in response to the reflected modulated continuous-wave light; a phase signal generator is configured to generate a mixed signal by applying a plurality of predetermined phase offset values ​​to a phase-modulated carrier signal; a photonic mixer unit is operatively coupled to the detector and configured to generate and store a plurality of electrical output signals by applying the mixed signal to the electrical sensor signal according to the indirect time-of-flight measurement technique and for an exposure time period; wherein each symbol has a duration greater than the period of the carrier signal; a phase shifter is configured to shift the phase of the carrier signal according to the value of a symbol among the plurality of symbols; and a code generator is configured to provide a timing delay between each symbol among the plurality of symbols.

[0030] According to a fourth aspect of the present invention, an optical detection method is provided, the method comprising: a light source emitting continuous wave light; a modulation signal generator generating a carrier signal having an associated carrier signal period; a code generator generating a code sequence during an exposure time period, each code in the code sequence comprising a plurality of symbols; a phase shifter applying a phase shift to the carrier signal in response to the code sequence to generate a phase-modulated carrier signal; a light source driver receiving and applying the phase-modulated carrier signal to modulate the continuous wave light according to the phase-modulated carrier signal; and the light source emitting the modulated continuous wave light according to an indirect time-of-flight measurement technique. The detector receives reflected modulated continuous wave light and generates an electrical sensor signal in response to the reflected modulated continuous wave light; the phase signal generator generates a mixed signal by applying multiple predetermined phase offset values ​​to the phase-modulated carrier signal; the photonic mixer unit generates and stores multiple electrical output signals by applying the mixed signal to the electrical sensor signal according to the indirect time-of-flight measurement technique and for the exposure time period; wherein each symbol has a duration greater than the period of the carrier signal; the phase shifter shifts the phase of the carrier signal according to the value of the symbol in the multiple symbols; and the code generator provides a timing delay between each symbol in the multiple symbols.

[0031] Therefore, it is possible to provide a detection method and apparatus that improves immunity to interference originating from other emitters (e.g., LiDAR modules). This method and apparatus do not sacrifice signal-to-noise ratio performance to improve interference performance. Attached Figure Description

[0032] Now, referring to the accompanying drawings, at least one embodiment of the invention will now be described by way of example only, in which:

[0033] Figure 1 This is a schematic diagram of an indirect time-of-flight ranging device constituting an embodiment of the present invention;

[0034] Figure 2 It is by Figure 1 A flowchart of a method for illuminating a scene using the apparatus and constituting another embodiment of the present invention;

[0035] Figure 3 It is by Figure 1 The device and Figure 2 and Figure 6 A flowchart illustrating a method for generating a code sequence that constitutes yet another embodiment of the present invention;

[0036] Figure 4 Is with Figure 2 and Figure 3 A schematic diagram of the structure of the code sequence related to the method;

[0037] Figure 5 It is based on Figure 2 and Figure 3 The method generated Figure 4 A schematic diagram of the distribution of code elements in the sequence over time; and

[0038] Figure 6 It is by Figure 1 The flowchart illustrates a method for demodulating a received optical signal using the apparatus, which constitutes a further embodiment of the present invention. Detailed Implementation

[0039] Throughout the following description, the same reference numerals will be used to identify the same parts.

[0040] refer to Figure 1 The indirect time-of-flight ranging device 100, constituting an optical detection device, includes a transmitting module 102 and a detection and ranging module 104. The transmitting module 102 includes a carrier signal generator 106 and a code generator 108. Both the carrier signal generator 106 and the code generator 108 are coupled to a first input terminal and a second input terminal of a phase shifter 110. The output terminal of the phase shifter 110 is coupled to an input terminal of a driver circuit 112. The output terminal of the driver circuit 112 is operatively coupled to an electromagnetic radiation source 114, such as a laser diode (LD) or a light-emitting diode (LED), which constitutes a light source. In this example, the electromagnetic radiation source 114 emits infrared light, which constitutes a continuous-wave optical signal. In this example, the continuous-wave optical signal is continuous-wave light.

[0041] The detection and ranging module 104 of device 100 includes an optical receiver photonics mixer pixel device 116, which includes a photodiode 108 having an anode operatively coupled to ground potential and a cathode coupled to a first input terminal of a photonics mixer 120, the output terminal of which is coupled to the input terminal of an integrator 122. In this example, for the sake of brevity and clarity, a single photonics mixer pixel device 116 is described. However, those skilled in the art will appreciate that the detection and ranging module 104 typically includes a larger number of pixels, such as an array of photonics mixer pixel devices of the type described above.

[0042] The control output terminal 124 of the timing control unit 126 is operatively coupled to the control signal input terminal 128 of the phase signal generator 130, and the output terminal of the phase signal generator 130 is coupled to the second input terminal of the photon mixer 120. The output terminal of the phase shifter 110 is also operatively coupled to the modulation signal input terminal 132 of the phase signal generator 130. The synchronization output terminal 134 of the timing control unit 126 is operatively coupled to the timing input terminal 136 of the digital Fourier transform (DFT) unit 138.

[0043] As will be described in further detail later herein, the phase signal generator 130 is configured to manipulate the continuous wave electrical signal provided by the phase shifter 110. In this regard, the phase shift applicable to the continuous wave electrical signal can be selected via control signal input 128, and the phase of the continuous wave electrical signal can be selected from the following set of phase shifts: [θ0, θ1, ..., θ...]. m-1 ].

[0044] The output of integrator 122 is also coupled to the input of DFT unit 138. In this respect, phase angle measurements are transmitted serially to DFT unit 138, thereby reducing the memory requirements of detection and ranging module 104. DFT unit 138 includes an internal buffer (not shown) to support the serial transmission of measurements from integrator 122.

[0045] DFT unit 138 has multiple digital in-phase (I) / quadrature (Q) outputs 140. In this example, DFT unit 138 includes b pairs of digital I / Q outputs corresponding to different harmonics of the measured signal. Since the output of integrator 122 is accumulated charge, and therefore in this example, the output of integrator 122 needs to be converted to the digital domain in the analog domain. This can be achieved, for example, by employing a photon counter as integrator 122 or by providing an analog-to-digital converter (not shown) before DFT unit 136.

[0046] The first pair of I / Q outputs among the multiple digital I / O outputs 140, which are related to the first harmonic of the received reflected optical signal, are coupled to a phase angle calculation unit, such as an arctangent unit 142. In this example, the DFT unit 138 and the arctangent unit 142 constitute a signal processing circuit.

[0047] In operation ( Figure 2 In this process, the transmitting module 102 transmits a continuous-wave optical signal to illuminate the scene using iToF measurement technology, and the detection and ranging module 104 detects light reflected from features (e.g., objects) in the scene using iToF measurement technology. Using the principles of iToF measurement technology, the detection and ranging module 104 also processes the electrical signal generated from the reflected light to generate data indicating the distance to the features in the scene responsible for reflecting the incident light to obtain the detected reflected light.

[0048] First, the operation of the transmitting module 102 is initiated, and the modulation signal generator 106 generates (step 200) a carrier signal, which is, for example, a continuous wave electrical signal with a square wave waveform. In this regard, although the carrier signal is generally referred to as the modulation signal in the field of optical ranging, the naming convention of carrier signal will be followed herein. Essentially simultaneously, the code generator 108 generates (step 202) a code sequence for each exposure period. In this regard, the exposure period is the time required to measure the reflected light according to indirect time-of-flight measurement techniques for ranging purposes.

[0049] In general, each codeword in a code sequence comprises multiple symbolic elements representing the code. In this example, the code does not change between codeword instances in the code sequence; that is, the code sequence comprises repeating single codes. However, in other examples, it should be understood that the code sequence may include code that changes between consecutive code instances. In some examples, the code in the code sequence may be repeated after a predetermined number of changes. In other examples, the content of each code may constitute randomly generated code or pseudo-randomly generated code.

[0050] refer to Figure 3 The code sequence is generated relative to the exposure period of a given scene. First, a pre-stored codeword length can be retrieved to enable the generation of codewords that form the basis of the repeating codewords in the code sequence. In this regard, as indicated above, codeword generation may include pseudo-randomly generating binary symbols to produce codewords that conform to the codeword length mentioned above. However, in this example, instead of the codeword length, the codeword is predetermined and therefore pre-stored and retrieved (step 300). The retrieved codeword is then analyzed, and the code generator 108 generates (step 302) a first symbol of the codeword, which is output to the phase shifter 110. The code generator 108 then generates (step 304) a delay, such as a timing delay, which is inserted between the symbols to form a guard delay.

[0051] In this respect, the provision of a protection delay is used to mitigate the signal-to-noise ratio (SNR) reduction caused by transitions at the boundaries between symbols in multiple symbols. The duration of the timing delay is selectable, thereby allowing tuning of the SNR and sensitivity to interference from external light sources (e.g., from other LiDAR systems) (interference suppression). The system clock (not shown) of device 100 can be used as the time base for generating the timing delay. However, in other examples, analog circuitry can be used to generate the time delay.

[0052] Technicians will understand that the timing ratio exists between the duration of the timing delay and the duration of each symbol. In this respect, the timing ratio can be between approximately 1:2 and approximately 1:50, for example, between approximately 1:5 and approximately 1:20.

[0053] After providing a time delay after the symbol, code generator 108 then determines (step 306) whether the end of the codeword has been reached. If not, code generator 108 selects the next symbol in the codeword and generates and outputs the next symbol along with the guard delay (steps 302 and 304). This process (steps 302 to 306) is repeated until code generator 108 has determined that the end of the codeword has been reached and the last symbol of the codeword has been generated and output to phase shifter 110. Thereafter, code generator 110 determines whether further repetition of the codeword should be generated (step 308) or whether further codewords are not required, for example, whether the operation of device 100 should be placed in standby mode.

[0054] If more codewords need to be generated, the code generator 108 continues to generate codewords repeatedly (steps 302 to 308), with a guard delay between consecutive codewords.

[0055] Turn Figure 4 The technique described above enables the generation of codeword sequences comprising multiple codewords, such as a first codeword 400, a second codeword 402, and an Mth codeword 404. Each of the multiple codewords 400, 402, and 404, having M codewords, comprises multiple symbolic elements 406. In this example, the multiple symbolic elements 406 are defined by pre-stored codewords. Furthermore, in this and other examples, each of the multiple symbolic elements 406 has an associated duration that is n times greater than the period of the carrier signal.

[0056] refer to Figure 5The multiple code elements 406 include a first code element 408, a second code element 410, a third code element 412, a fourth code element 414, and a fifth code element 416. This is purely illustrative, and the multiple code elements constituting a repeating codeword may include more or fewer code elements. In any case, the first code element 408, the second code element 410, the third code element 412, the fourth code element 414, and the fifth code element 416 have a duration of n carrier signal cycles. The first guard delay 418, the second guard delay 420, the third guard delay 422, and the fourth guard delay 424 are respectively positioned between the first code element 408 and the second code element 410, between the second code element 410 and the third code element 412, between the third code element 412 and the fourth code element 414, and between the fourth code element 414 and the fifth code element 416. The duration of the carrier signal period can be adjusted to optimize the number of carrier signal periods elapsed per symbol (e.g., first symbol 408, second symbol 410, third symbol 412, fourth symbol 414, and fifth symbol 416). This optimization helps modify the ratio between the guard time and the duration of each symbol. In this respect, the dominance of the sum of guard times within a codeword helps to change the total number of codewords in the codeword sequence within the exposure time. Thus, the number of codewords constituting the codeword sequence affects the signal-to-noise ratio (SNR) of the signal received by the DFT unit 138 (described later herein) and thereby affects its output, and the interference suppression of the device 100 (e.g., optimized to increase the number of codewords in the codeword sequence) improves interference suppression but reduces the SNR. Conversely, optimization to reduce the number of codewords in the codeword sequence helps to reduce interference suppression but increases the SNR. Another optimization of the ratio between the guard time and the duration of each symbol involves modifying the number of symbols included in the codeword. Yet another optimization of this ratio involves modifying the duration of the exposure period. Regarding the above optimizations, device 100 can be pre-configured to set the signal-to-noise ratio (SNR) performance parameters and interference suppression parameters to account for the degradation of one performance parameter due to a modification of the other. Once set, one or more of the above optimizations can be employed to achieve the desired performance parameter settings, based on the number of carrier signal cycles and / or the symbol duration of each guard delay. In other embodiments, the SNR performance parameters and interference suppression performance parameters can be dynamically set in response to environmental factors encountered during operation, and these parameters can be adjusted on-the-fly by device 100 (e.g., by the signal processing circuitry of device 100).

[0057] Return to reference Figure 2The carrier signal and code sequence are received by phase shifter 110 and thus applied (step 204). In this respect, phase shifter 110 modifies the phase of the carrier signal in response to the state or value of each symbol of the codeword in the code sequence (step 206). For example, a logic 1 or binary 1 in the codeword represents a phase shift of 0° for the carrier signal, while a logic 0 or binary 0 in the codeword represents a phase shift of 180° for the carrier signal. Of course, in other examples, the logic 0 and logic 1 states represented by the symbols of the codeword can represent the opposite application of those phase shift values ​​described above. Thus, it can be seen that the symbol can represent a first value or a second value, the first value corresponding to a first phase shift value, and the second value corresponding to a second phase shift value. In this example, the difference between the first predetermined phase shift value and the second predetermined phase shift value is 180°.

[0058] Subsequently, a phase-modulated carrier signal is provided to the phase signal generator 130 and the driver circuit 112. The application of the phase-modulated carrier signal by the phase signal generator 130 will be described later in this document in conjunction with the operation of the detection and ranging module 104. However, regarding the driver circuit 112, the driver circuit 112 modulates and amplifies the received phase-modulated carrier signal and drives the light source 114 to emit a continuous-wave optical signal according to the phase-modulated carrier signal, thereby generating phase-modulated continuous-wave light.

[0059] After emission, for example, the optical signal emitted is reflected by a feature of the scene. The detection and ranging module 104 is responsible for detecting this reflected light and generating data indicating the distance from the detection and ranging module 104 to the feature. In this regard, some of the modulated continuous wave light is reflected by the feature and received by a photodetector 118, which generates an electrical sensor signal in response.

[0060] In this regard, and referring to Figure 6 Phase signal generator 130 receives (step 500) the phase-modulated carrier signal generated by phase shifter 110. The phase-modulated carrier signal is a continuous wave electrical signal. Timing control unit 126 controls the cyclic traversal of the phase offset set and the application of the phase offset set to the phase-modulated carrier signal relative to the phase-modulated continuous wave optical signal (step 502). In this regard, after the phase shift from the phase offset set mentioned above is applied to the phase-modulated carrier signal, phase signal generator 130 outputs the phase-modulated carrier signal. A synchronization signal is also applied to DFT unit 138 by synchronization output 134 to ensure proper timing processing of the output of integrator 122.

[0061] The electrical signal generated by phase signal generator 130, together with the electrical sensor signal from photodetector 118, is applied to photonic mixer 116. According to iToF measurement technology, the phase shift of the electrical signal (phase-modulated carrier signal) is cyclically iterated through the aforementioned set of phase shifts. Integrator 122 stores the accumulated charge generated by photonic mixer 116 for each cycle in which each phase shift is applied, constituting a measurement subframe. In this respect, integrator 122 is reset for each measurement subframe, corresponding to the application of different phase shift values. For each phase shift in the set of phase shifts, a digital representation of the charge stored in integrator 122 is measured (step 504), which constitutes an electrical output signal and is serially received by DFT unit 138 and converted into a pair of I / Q outputs constituting an I / Q vector V, which represents a complex value of analog electrical measurement with respect to the fundamental frequency. In this regard, integrator 122 provides a plurality of phase-separated amplitude measurement outputs serially, which represent the respective accumulated charge levels with respect to the applied phase offset values ​​of photonic mixer pixel device 116. DFT unit 138 calculates intermediate I and Q values ​​for each serially received phase-separated amplitude measurement for each subframe, which are accumulated in a frame cycle to generate final I and Q value results. Operation of this arrangement includes iteratively calculating a vector using DFT unit 138 for each incoming phase angle measurement.

[0062] DFT unit 138 can also generate additional I / Q vectors for the harmonics of the charge measured by integrator 122. After the electrical measurement signal is converted to the frequency domain, the fundamental I and Q values ​​are provided at the output of DFT unit 138. In this example, a synchronization signal ensures that the fundamental I / Q output of the current measurement frame of DFT unit 138 is received synchronously by arctangent unit 142. Arctangent unit 142 then calculates (step 506) the angle of vector V according to indirect time-of-flight measurement techniques, which constitutes the calculated phase angle extracted from the fundamental I and Q values ​​in the complex plane (measured). The calculated phase angle can then be used to calculate the distance to the source of the emitted light.

[0063] Repeat (step 508) the above steps (steps 500 to 506) until it is no longer necessary to calculate the measured angle.

[0064] Those skilled in the art should understand that the implementations described above are merely examples of various implementations conceivable within the scope of the appended claims. Indeed, it should be understood that techniques employing 0° and 180° phase shifts, as described above, are merely exemplary, and other phase shift values ​​(e.g., 90° and 270°, respectively) can be attributed to the logic levels of the codeword's symbols. However, the examples above employ 0° and 180° phase shifts because these values ​​result in a narrower autocorrelation of the codeword compared to using other phase shift values.

[0065] It should be understood that, unless otherwise explicitly stated, references to “light” herein are intended to refer to an optical range relating to the electromagnetic spectrum, such as between about 350 nm and about 2000 nm, such as between about 550 nm and about 1400 nm, or between about 600 nm and about 1000 nm.

Claims

1. An optical detection method, the method comprising: Emitting continuous wave light; Generate a carrier signal, the carrier signal having a carrier signal period associated with the carrier signal; A code sequence is generated during the exposure period, wherein each code in the code sequence includes multiple code elements; A phase shift is applied to the carrier signal in response to the code sequence in order to generate a phase-modulated carrier signal; The phase-modulated carrier signal is applied to the light source so as to modulate the continuous wave light according to the phase-modulated carrier signal; Modulated continuous wave light is emitted based on indirect time-of-flight measurement technology; Receive the reflected, modulated continuous wave light; An electrical sensor signal is generated in response to the reflected modulated continuous wave light; A mixed signal is generated by applying multiple predetermined phase offset values ​​to the phase-modulated carrier signal; By applying the mixed signal to the electrical sensor signal according to the indirect time-of-flight measurement technique and for the exposure time period, a plurality of electrical output signals are generated and stored. in Each symbol has a duration greater than the period of the carrier signal; Phase modulation of the carrier signal includes shifting the phase of the carrier signal according to the value of a symbol among the plurality of symbols; and A timing delay is provided between each of the plurality of symbols; The method further includes optimizing the timing ratio between the duration of the timing delay and the duration of each symbol by modifying the carrier signal period thereby modifying the duration of each symbol.

2. The method as described in claim 1, wherein, The timing delay provided between each of the plurality of symbols is a guard delay, which is configured to minimize the reduction in the signal-to-noise ratio of the plurality of electrical output signals caused by the transition at the boundary between the symbols of the plurality of symbols.

3. The method as described in any one of claims 1 or 2, wherein, Each symbol includes a first binary value or a second binary value, the first binary value corresponding to a first predetermined phase shift value, and the second binary value corresponding to a second phase shift value.

4. The method of claim 1, wherein, The code sequence includes the repetition of the occurrence of the plurality of code elements.

5. The method of claim 1, further comprising: The duration of the timing delay is selected for subsequent insertion between each of the plurality of symbols.

6. The method of claim 1, further comprising: The timing delay is generated using a simulated time source.

7. The method of claim 1, wherein, The timing ratio is between 1:2 and 1:

50.

8. The method of claim 1, further comprising: The timing ratio is optimized by modifying the duration of each symbol by changing the number of symbols in each code in the code sequence.

9. The method of claim 1, further comprising: The timing ratio is optimized by modifying the duration of each symbol by changing the duration of the exposure time period.

10. The method of claim 1, further comprising: Select the signal-to-noise ratio and / or interference suppression of the plurality of electrical output signals; as well as The duration of each symbol is selected relative to a multiple of the carrier signal period to achieve the selected signal-to-noise ratio and / or interference suppression; and / or Select the duration of the timing delay to achieve the selected signal-to-noise ratio and / or interference suppression.

11. The method of claim 1, further comprising: The plurality of electrical output signals are processed according to the indirect time-of-flight measurement technique in order to calculate a measurement vector and calculate the measured phase angle from the measurement vector.

12. A method for determining the distance to a feature of a scene, the method comprising: The optical detection method as described in claim 11; as well as The distance is calculated using the measured phase angle.

13. An optical detection device, comprising: A light source configured to emit continuous wave light; A modulation signal generator configured to generate a carrier signal having a carrier signal period associated with the carrier signal; A code generator configured to generate a code sequence during an exposure time period, each code in the code sequence comprising multiple code elements; A phase shifter configured to apply a phase shift to the carrier signal in response to the code sequence in order to generate a phase-modulated carrier signal; A light source driver configured to apply the phase-modulated carrier signal to the light source in order to modulate the continuous wave light according to the phase-modulated carrier signal; The light source is configured to emit modulated continuous wave light according to indirect time-of-flight measurement techniques; A detector configured to receive reflected modulated continuous wave light and to generate an electrical sensor signal in response to the reflected modulated continuous wave light; A phase signal generator configured to generate a mixed signal by applying a plurality of predetermined phase offset values ​​to the phase-modulated carrier signal; A photonic mixer unit, operatively coupled to the detector, and configured to generate and store a plurality of electrical output signals by applying the mixed signal to the electrical sensor signal according to the indirect time-of-flight measurement technique and for the exposure time period; in Each symbol has a duration greater than the period of the carrier signal; The phase shifter is configured to shift the phase of the carrier signal according to the value of a symbol among the plurality of symbols; The code generator is configured to provide a timing delay between each of the plurality of symbols; and The modulation signal generator is configured to optimize the timing ratio between the duration of the timing delay and the duration of each symbol by modifying the carrier signal period, thereby modifying the duration of each symbol.

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