Time-of-flight sensor and method for calibrating errors therein

Abstract

A method for calibrating errors in a time-of-flight (ToF) sensor includes: illuminating a test object with emitted light modulated based on a modulation signal; generating a plurality of demodulated signals having different local delay phases using a cache chain circuit; providing a plurality of measured phase differences by providing the plurality of demodulated signals to a plurality of pixel groups included in the ToF sensor to sample received light reflected from the test object based on the plurality of demodulated signals; determining a swing error based on the plurality of measured phase differences, the swing error depending on the phase difference between the emitted light and the received light; and calibrating a measured distance from the ToF sensor to the target object based on the swing error.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority from Korean Patent Application No. 10-2019-0113980 filed on September 17, 2019, with the Korean Intellectual Property Office (KIPO), the disclosure of which is incorporated herein by reference in its entirety. Technical Field

[0003] At least some example embodiments of the inventive concepts relate generally to semiconductor integrated circuits, and more particularly, to a time-of-flight (ToF) sensor and a method of calibrating errors in the ToF sensor. Background Art

[0004] Recently, there has been an increasing interest in sensing to obtain three-dimensional information of an object, and various three-dimensional cameras have been developed. Among three-dimensional cameras, ToF sensors have the advantages of a simple circuit structure and high distance resolution. A ToF sensor uses a light source to illuminate an object with emitted light, and calculates the distance to the object by measuring the phase difference of the received light reflected from the object. The received light can be modeled as a sine wave for distance calculation, and periodic errors may be caused by modeling errors (called swing errors). Swing errors are a direct factor in the decline of the ranging accuracy of ToF sensors. Summary of the Invention

[0005] Some example embodiments may provide a method of calibrating an error in a time-of-flight (ToF) sensor, which method can effectively compensate for a swing error induced in the ToF sensor.

[0006] Some example embodiments may provide a ToF sensor and a test system capable of effectively correcting a swing error.

[0007] According to at least some example embodiments of the present inventive concepts, a method of calibrating errors in a time-of-flight (ToF) sensor includes: illuminating a test object with emitted light modulated based on a modulation signal; generating a plurality of demodulated signals having different local delay phases using a cache chain circuit; providing a plurality of measured phase differences by providing the plurality of demodulated signals to a plurality of pixel groups included in a ToF sensor to sample received light reflected from the test object based on the plurality of demodulated signals; determining a swing error based on the plurality of measured phase differences, the swing error depending on a phase difference between the emitted light and the received light; and calibrating a measured distance from the ToF sensor to a target object based on the swing error.

[0008] According to at least some example embodiments of the present inventive concepts, a test system includes a time-of-flight (ToF) sensor and a test device configured to measure a swing error of the ToF sensor. The ToF sensor includes a light source configured to illuminate a test object with emitted light modulated based on a modulation signal; a cache chain circuit configured to generate a plurality of demodulated signals having different local delay phases; and a pixel array including a plurality of pixels configured to sample received light reflected from the test object based on the plurality of demodulated signals, the plurality of pixels being grouped into a plurality of pixel groups, each of which receives a plurality of demodulated signals having a corresponding local delay phase.

[0009] According to at least some example embodiments of the present inventive concepts, a time-of-flight (ToF) sensor includes: a light source configured to illuminate a test object with emitted light modulated based on a modulation signal; a cache chain circuit configured to generate a plurality of demodulation signals having different local delay phases; and a pixel array including a plurality of pixels configured to sample received light reflected from the test object based on the plurality of demodulation signals, the plurality of pixels being grouped into a plurality of pixel groups that respectively receive the plurality of demodulation signals having corresponding local delay phases.

[0010] A ToF sensor and a method of calibrating an error in a ToF sensor according to at least some example embodiments of the inventive concepts may improve efficiency and accuracy of error calibration of a ToF sensor by artificially generating a local delay phase using a cache chain circuit.

[0011] A ToF sensor and a method of calibrating an error in a ToF sensor according to at least some example embodiments of the present inventive concepts can obtain a swing error using a small number of measurement cycles because samples of various distances or phase differences can be obtained through a single chart image using multiple local delay phases and a variable global delay phase.

[0012] The ToF sensor and the method for calibrating errors in the ToF sensor according to at least some example embodiments of the present invention can have no restrictions on the distance to the test object such as a plane, the tilt and form of the test object, the timing parameters of the delay, etc. This is because the method is based on the following assumption: when the control code is changed for the global delay phase, the change in the phase difference is linear.

[0013] A ToF sensor and a method of calibrating an error in a ToF sensor according to at least some example embodiments of the inventive concepts may have an effect of being robust to spatial filtering of noise because data of many pixels are used in obtaining a swing error for each measured phase difference. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] The above and other features and advantages of the exemplary embodiments of the present invention will become more apparent by describing in detail exemplary embodiments of the present invention with reference to the accompanying drawings. The accompanying drawings are intended to illustrate exemplary embodiments of the present invention and should not be interpreted as limiting the intended scope of the claims. Unless explicitly stated, the accompanying drawings should not be considered to be drawn to scale.

[0015] Figure 1 is a flowchart illustrating a method of calibrating an error in a ToF sensor according to at least some example embodiments of the inventive concepts.

[0016] Figure 2 is a block diagram illustrating a test system according to at least some example embodiments of the inventive concepts.

[0017] Figure 3 and Figure 4 is a diagram illustrating a ToF sensor according to at least some example embodiments of the inventive concepts.

[0018] Figure 5 is a diagram for describing an example method of calculating a distance to an object.

[0019] Figure 6 is a diagram illustrating an example pixel structure of a ToF sensor according to at least some example embodiments of the inventive concepts.

[0020] Figure 7 is shown with Figure 6 A top view of the layout corresponding to the pixel structure.

[0021] Figure 8 is a timing diagram for describing the operation of a ToF sensor.

[0022] Figure 9A and Figure 9B is a diagram for describing a method of measuring a swing error.

[0023] Figure 10 is a diagram illustrating example embodiments of a cache chain circuit included in a ToF sensor according to at least some example embodiments of the inventive concepts.

[0024] Figure 11 is a diagram for describing a local delay phase of a ToF sensor according to at least some example embodiments of the inventive concepts.

[0025] Figure 12 is a diagram illustrating example embodiments of a variable delay circuit included in a ToF sensor according to at least some example embodiments of the inventive concepts.

[0026] Figure 13 and Figure 14is used to describe Figure 12 A diagram of the operation of the variable delay circuit.

[0027] Figure 15 is a flowchart illustrating an example embodiment of determining a swing error of a method for calibrating an error in a ToF sensor according to at least some example embodiments of the inventive concepts.

[0028] Figure 16 and Figure 17 is used to describe Figure 15 Graph of the determination of the wobble error.

[0029] Figure 18 is a diagram for describing a local delay phase of a ToF sensor according to at least some example embodiments of the inventive concepts.

[0030] Figures 19A to 21 is a diagram for describing the effects of a method of calibrating an error in a ToF sensor according to at least some example embodiments of the inventive concepts.

[0031] Figure 22 is a block diagram illustrating a camera system according to at least some example embodiments of the inventive concepts.

[0032] Figure 23 is a block diagram illustrating error calibration by a camera system according to at least some example embodiments of the inventive concepts.

[0033] Figure 24 is a block diagram illustrating a computing system including a ToF sensor according to at least some example embodiments of the inventive concepts.

[0034] Figure 25 It shows Figure 24 A block diagram of an example of an interface used in a computing system. DETAILED DESCRIPTION

[0035] As common in the field of the present invention, embodiment is described and shown in the accompanying drawings in terms of functional blocks, units and / or modules. It will be appreciated by those skilled in the art that these blocks, units and / or modules are physically realized by electronic (or optical) circuits such as logic circuits, discrete components, microprocessors, hard-wired circuits, memory elements, wiring connections, and the like, and the electronic (or optical) circuits can be formed using semiconductor-based manufacturing techniques or other manufacturing techniques. When blocks, units and / or modules are realized by microprocessors etc., they can be programmed using software (for example, microcode) to perform the various functions discussed herein, and can be optionally driven by firmware and / or software. Alternatively, each block, unit and / or module can be realized by dedicated hardware or be implemented as a combination of dedicated hardware that performs some functions and a processor (for example, one or more programmed microprocessors and associated circuits) that performs other functions. In addition, without departing from the scope of the present invention, each block, unit and / or module of the embodiment can be physically divided into two or more interactive and discrete blocks, units and / or modules. Furthermore, without departing from the scope of the inventive concept, the blocks, units and / or modules of the embodiments may be physically combined into more complex blocks, units and / or modules.

[0036] Figure 1 is a flowchart illustrating a method of calibrating an error in a ToF sensor according to at least some example embodiments of the inventive concepts.

[0037] Figure 1 An error calibration method is shown with respect to a ToF sensor configured to measure a distance to an object by illuminating the object with transmitted light using a light source and measuring a phase difference between the transmitted light and received light.

[0038] Reference Figure 1 The test object is illuminated using emission light modulated based on a modulation signal (S100). For example, the light source may be turned on and off by toggling at a frequency of approximately 10 MHz to 200 MHz in response to the modulation signal.

[0039] A cache chain circuit is used to generate a plurality of demodulated signals with different local delay phases (S200). The cache chain circuit can be integrated into the ToF sensor. Figure 10 Example embodiments of cache chain circuits are described.

[0040] A plurality of measured phase differences are provided by providing a plurality of demodulation signals to a plurality of pixel groups included in the ToF sensor to sample received light reflected from the test object based on the plurality of demodulation signals (S300). In some example embodiments, each of the plurality of pixel groups may include a pixel column including pixels arranged in a column. In at least some other example embodiments of the present inventive concepts, each of the plurality of pixel groups may include a pixel row including pixels arranged in a row.

[0041] A swing error is determined based on a plurality of measured phase differences, wherein the swing error depends on a phase difference between the emitted light and the received light (S400). In some example embodiments, as will be described below with reference to Figure 17 As described, the swing error may be provided as a mapping table, which represents a mapping relationship between the plurality of measured phase differences and a plurality of representative offset values.

[0042] A measured distance from the ToF sensor to the target object is calibrated based on the swing error ( S500 ).

[0043] As such, a ToF sensor and a method of calibrating errors in a ToF sensor according to at least some example embodiments of the inventive concepts may improve the efficiency and accuracy of error calibration of a ToF sensor by artificially generating a local delay phase using a cache chain circuit.

[0044] In some example embodiments, the modulated signal may have different global delay phases in multiple measurement cycles. In this case, the swing error can be obtained with a small number of measurement cycles because samples of various distances or phase differences can be obtained using a single chart image using multiple local delay phases and a variable global delay phase.

[0045] Figure 2 is a block diagram illustrating a test system according to at least some example embodiments of the inventive concepts.

[0046] Reference Figure 2 , the test system 10 may include a test device 20 and a ToF sensor 30 corresponding to the device under test.

[0047] The ToF sensor 30 may include a light source LS and a sensing unit SEN. The sensing unit SEN may include a pixel array (not shown) and a cache chain circuit DBC. Figures 3 to 8 To describe the configuration and operation of the ToF sensor.

[0048] The light source LS can illuminate the test object using emitted light modulated based on the modulation signal MOD. The buffer chain circuit DBC can generate a plurality of demodulation signals with different local delay phases. The pixel array can include a plurality of pixels configured to sample received light reflected from the test object based on the plurality of demodulation signals. The plurality of pixels can be grouped into a plurality of pixel groups, and the plurality of pixel groups can respectively receive a plurality of demodulation signals with corresponding local delay phases. Figure 10 and Figure 11 Example embodiments of a cache chain circuit DBC and pixel groups are described below.

[0049] The test device 20 may include a controller CTRL, a memory MEM, and a variable delay circuit GDL.

[0050] The controller CTRL may control the overall operation of the test device 20 , and the memory MEM may store data, control program codes, and the like used for the operation of the test device 20 .

[0051] The variable delay circuit GDL may generate a modulation signal MOD having different global delay phases in a plurality of measurement cycles. The modulation signal MOD having a variable phase may be provided from the test device 20 to the ToF sensor 30. In some example embodiments, the variable delay circuit GDL may be included in the ToF sensor 30.

[0052] In some example embodiments, as will be referred to Figure 12 As described below, the variable delay circuit GDL can generate a modulation signal MOD based on a control code, such that the modulation signal MOD has a variable delay corresponding to the control code. In this case, the test device 20 can sequentially change the control code during multiple measurement cycles, so that the modulation signal MOD has different global delay phases in each of the multiple measurement cycles.

[0053] The controller CTRL may include a phase difference generator PDG and an error generator WGG.

[0054] According to at least some example embodiments of the present inventive concepts, the phase difference generator PDG may be or include a circuit or electronic circuit configured to provide a plurality of measured phase differences based on the sample data SDATA provided from the ToF sensor 30. In this specification, the phase difference generator PDG may also be referred to as a phase difference generator circuit PDG. The ToF sensor 30 may sample the received light reflected from the test object based on a plurality of demodulated signals. According to at least some example embodiments of the present inventive concepts, the phase difference generator PDG may be provided in the ToF sensor. In this case, the test device 20 may receive a plurality of measured phase differences from the ToF sensor 30 instead of the sample data SDATA.

[0055] The error generator WGG may be or include a circuit or electronic circuit configured to determine a swing error based on a plurality of measured phase differences. In this specification, the error generator WGG may also be referred to as an error generator circuit WGG. The swing error depends on the phase difference between the transmitted light and the received light.

[0056] Now we will refer to Figure 3 TOF sensor 100 and Figure 4 Example implementations of the TOF sensor 30 are discussed with reference to the TOF sensor 101 shown in FIG.

[0057] Figure 3 and Figure 4 is a diagram illustrating a ToF sensor according to at least some example embodiments of the inventive concepts.

[0058] Reference Figure 3 , the ToF sensor 100 includes a pixel array 110, a buffer chain circuit DBC, an analog-to-digital conversion (ADC) unit 120, a row scanning circuit 130, a column scanning circuit 140, a control unit 150, and a light source module 200. According to at least some example embodiments of the present inventive concept, the ADC unit 120 and the control unit 150 may be implemented by an electric circuit or an electronic circuit. According to at least some example embodiments of the present inventive concept, the operations discussed below and the operations in the Figure 1 Steps S100 to S500 are shown.

[0059] The pixel array 110 may include depth pixels that receive light RX reflected from an object OBJ after the light source module 200 emits light TX to the object OBJ. The depth pixels may convert the received light RX into an electrical signal. The depth pixels may provide information about the distance between the object OBJ and the ToF sensor 100 and / or black and white image information.

[0060] The pixel array 110 may further include color pixels for providing color image information. In this case, the ToF sensor 100 may be a three-dimensional color image sensor that provides color image information and depth information. According to at least some example embodiments of the present inventive concepts, an infrared filter and / or a near-infrared filter may be formed on the depth pixels, and a color filter (e.g., a red filter, a green filter, and a blue filter) may be formed on the color pixels. According to at least some example embodiments of the present inventive concepts, the ratio of the number of depth pixels to the number of color pixels may vary as needed.

[0061] The ADC unit 120 may convert an analog signal output from the pixel array 110 into a digital signal. According to at least some example embodiments of the inventive concepts, the ADC unit 120 may perform column analog-to-digital conversion, which converts analog signals in parallel using a plurality of analog-to-digital converters respectively coupled to a plurality of column lines. According to at least some example embodiments of the inventive concepts, the ADC unit 120 may perform single analog-to-digital conversion, which sequentially converts analog signals using a single analog-to-digital converter.

[0062] According to at least some example embodiments of the present inventive concepts, the ADC unit 120 may further include a correlated double sampling (CDS) unit for extracting a valid signal component. According to at least some example embodiments of the present inventive concepts, the CDS unit may perform analog double sampling, which extracts a valid signal component based on a difference between an analog reset signal including a reset component and an analog data signal including a signal component. According to at least some example embodiments of the present inventive concepts, the CDS unit may perform digital double sampling, which converts an analog reset signal and an analog data signal into two digital signals and extracts a valid signal component based on a difference between the two digital signals. According to at least some example embodiments of the present inventive concepts, the CDS unit may perform dual correlated double sampling, which performs both analog double sampling and digital double sampling.

[0063] The row scanning circuit 130 may receive a control signal from the control unit 150 and may control a row address and row scanning of the pixel array 110. In order to select a row line among a plurality of row lines, the row scanning circuit 130 may apply a signal for activating the selected row line to the pixel array 110. According to at least some example embodiments of the inventive concepts, the row scanning circuit 130 may include a row decoder that selects a row line of the pixel array 110 and a row driver that applies a signal for activating the selected row line.

[0064] The column scanning circuit 140 may receive a control signal from the control unit 150 and may control the column address and column scanning of the pixel array 110. The column scanning circuit 140 may output the digital output signal from the ADC unit 120 to a digital signal processing circuit (not shown) and / or to an external host (not shown). For example, the column scanning circuit 140 may provide a horizontal scanning control signal to the ADC unit 120 to sequentially select a plurality of analog-to-digital converters included in the ADC unit 120. According to at least some example embodiments of the present inventive concepts, the column scanning circuit 140 may include a column decoder that selects one of the plurality of analog-to-digital converters and a column driver that applies the output of the selected analog-to-digital converter to a horizontal transmission line. The horizontal transmission line may have a bit width corresponding to the bit width of the digital output signal.

[0065] The control unit 150 may control the ADC unit 120, the row scan circuit 130, the column scan circuit 140, the buffer chain circuit DBC, and the light source module 200. The control unit 150 may provide control signals, such as clock signals, timing control signals, etc., to the ADC unit 120, the row scan circuit 130, the column scan circuit 140, the buffer chain circuit DBC, and the light source module 200. According to at least some example embodiments of the present inventive concepts, the control unit 150 may include a control logic circuit, a phase-locked loop circuit, a timing control circuit, a communication interface circuit, etc.

[0066] The light source module 200 can emit light of a desired (or alternatively, predetermined) wavelength. For example, the light source module 200 can emit infrared light and / or near-infrared light. The light source module 200 may include a light source 210 and a lens 220. The light source 210 may be controlled by the control unit 150 to emit light TX having a desired intensity and / or characteristics (e.g., periodicity). For example, the intensity and / or characteristics of the light TX may be controlled so that the light TX has a waveform such as a pulse wave, a sine wave, a cosine wave, etc. The light source 210 may be implemented by a light emitting diode (LED), a laser diode, etc.

[0067] Hereinafter, a normal operation of the ToF sensor 100 according to at least some example embodiments of the inventive concepts will be described below.

[0068] The control unit 150 can control the light source module 200 to emit light TX having a periodic intensity. The light TX emitted by the light source module 200 can be reflected from the object OBJ and returned to the ToF sensor 100 as received light RX. The received light RX can be incident on the depth pixels, and the depth pixels can be activated by the row scanning circuit 130 to output analog signals corresponding to the received light RX. The ADC unit 120 can convert the analog signals output from the depth pixels into sample data SDATA. The sample data SDATA can be provided to the control unit 150 by the column scanning circuit 140 and / or the ADC 120.

[0069] The control unit 150 can calculate the distance between the object OBJ and the ToF sensor 100, the horizontal position of the object OBJ, the vertical position of the object OBJ, and / or the size of the object OBJ based on the sample data SDATA. The control unit 150 can control the emission angle or projection (or incident) area of ​​the light TX based on the distance, horizontal position, vertical position, and / or size of the object OBJ. For example, the control unit 150 can control the spacing between the light source 210 and the lens 220, the relative position (or arrangement) of the light source 210 and the lens 220 relative to each other, the refractive index of the lens 220, the curvature of the lens 220, etc. As a result, the light TX emitted by the light source module 200 can be focused on the area where the object OBJ of interest is located, thereby improving the accuracy of the depth information provided by the depth pixels. In addition, the control unit 150 can adjust the amplitude of the light TX (or the maximum intensity of the light TX during each cycle) according to the reduction or increase of the emission angle of the light TX or the size of the area where the light TX is projected (or incident). For example, the control unit 150 can reduce the amplitude of the light TX as the emission angle of the light TX decreases. As a result, in the ToF sensor 100 according to at least some example embodiments of the inventive concepts, power consumption may be reduced.

[0070] The sample data SDATA and / or depth information may be provided to a digital signal processing circuit and / or an external host. According to at least some example embodiments of the inventive concepts, the pixel array 110 may include color pixels, and color image information and depth information may be provided to a digital signal processing circuit and / or an external host.

[0071] Hereinafter, a calibration operation of the ToF sensor 100 according to at least some example embodiments of the inventive concepts will be described below.

[0072] In the calibration operation, the selector MUX may provide the modulation signal MOD provided from the variable delay circuit GDL to the light source module 200 in response to the test mode signal TST instead of the signal from the control unit 150. As described above, the variable delay circuit GDL may generate the modulation signal MOD having different global delay phases in a plurality of measurement cycles.

[0073] The buffer chain circuit DBC can generate a plurality of demodulated signals with different local delay phases.

[0074] The pixel array 110 may include a plurality of pixels configured to sample received light reflected from a test object based on a plurality of demodulation signals. The plurality of pixels may be grouped into a plurality of pixel groups, and the plurality of pixel groups may respectively receive a plurality of demodulation signals having corresponding local delay phases.

[0075] Figure 2 The test device 20 in FIG. 2 may determine a swing error based on a plurality of measured phase differences, wherein the swing error depends on a phase difference between the transmitted light and the received light.

[0076] Will refer to below Figures 15 to 17 Example embodiments for determining swing error are described.

[0077] In addition to the variable delay circuit GDL, Figure 4 ToF sensor 101 and Figure 3 The ToF sensors 100 are substantially the same, and repeated descriptions are omitted.

[0078] In some example embodiments, Figure 3 As shown, the variable delay circuit GDL may be provided outside the ToF sensor 100. For example, the variable delay circuit GDL may be included in Figure 2 In this case, the test device 20 may provide the ToF sensor 100 with the modulation signal MOD having different global delay phases in a plurality of measurement cycles.

[0079] In at least some other example embodiments of the present inventive concepts, Figure 4 As shown, the variable delay circuit GDL may be included in the ToF sensor 101. In this case, the test device 20 may provide a control signal to the ToF sensor 101, so that the ToF sensor can generate a modulation signal MOD having different global delay phases in multiple measurement cycles. For example, the control signal may be a control code having multiple bits that is sequentially changed in multiple measurement cycles.

[0080] Figure 5is a diagram for describing an example method of calculating a distance to an object.

[0081] Reference Figures 3 to 5 The light TX emitted by the light source module 200 may have periodic intensity and / or characteristics. For example, the intensity of the light TX (ie, the number of photons per unit area) may have a sinusoidal waveform.

[0082] The light TX emitted by the light source module 200 may be reflected from the object OBJ and then may be incident on the pixel array 110 as the received light RX. The pixel array 110 may periodically sample the received light RX. According to at least some example embodiments of the present inventive concepts, during each cycle of the received light RX (e.g., corresponding to the cycle of the emitted light TX), the pixel array 110 may perform sampling on the received light RX by, for example, the following operations: sampling at two sampling points with a phase difference of approximately 180 degrees, at four sampling points with a phase difference of approximately 90 degrees, or at more than four sampling points. For example, the pixel array 110 may extract four samples A0, A1, A2, and A3 of the received light RX at phases of approximately 90 degrees, approximately 180 degrees, approximately 270 degrees, and approximately 360 degrees, respectively, for each cycle.

[0083] The offset B of the received light RX may be different from the offset of the light TX emitted by the light source module 200 due to background light, noise, etc. The offset B of the received light RX may be calculated by Formula 1.

[0084] [Formula 1]

[0085]

[0086] Here, A0 represents the intensity of the received light RX sampled at a phase of approximately 90 degrees of the transmitted light TX, A1 represents the intensity of the received light RX sampled at a phase of approximately 180 degrees of the transmitted light TX, A2 represents the intensity of the received light RX sampled at a phase of approximately 270 degrees of the transmitted light TX, and A3 represents the intensity of the received light RX sampled at a phase of approximately 360 degrees of the transmitted light TX.

[0087] Due to loss (eg, light loss), the amplitude A of the received light RX may be lower than the amplitude of the light TX emitted by the light source module 200. The amplitude A of the received light RX may be calculated by Equation 2.

[0088] [Formula 2]

[0089]

[0090] Black and white image information about the object OBJ may be provided by each depth pixel included in the pixel array 110 based on the amplitude A of the received light RX.

[0091] The received light RX may be delayed relative to the transmitted light TX by a phase difference Φ corresponding to, for example, twice the distance between the object OBJ and the ToF sensor 100. The phase difference Φ between the transmitted light Tx and the received light RX may be calculated using Equation 3.

[0092] [Formula 3]

[0093]

[0094] The phase difference Φ between the transmitted light TX and the received light RX can correspond to, for example, the time of flight (TOF). The distance between the object OBJ and the ToF sensor 100 can be calculated using the formula "R = c*TOF / 2," where R represents the distance between the object OBJ and the ToF sensor 100, and c represents the speed of light. Furthermore, the phase difference Φ between the transmitted light TX and the received light RX can be used to calculate the distance between the object OBJ and the ToF sensor 100 using Formula 4.

[0095] [Formula 4]

[0096]

[0097] Here, f represents a modulation frequency, which is the frequency of the intensity of the transmitted light TX (or the frequency of the intensity of the received light RX).

[0098] As described above, the ToF sensor 100 according to at least some example embodiments of the inventive concepts may obtain depth information about the object OBJ using the light TX emitted by the light source module 200. Figure 5 Although the light TX having a sinusoidal waveform is shown, according to at least some example embodiments of the present inventive concepts, the ToF sensor 100 may use light TX having various waveforms. In addition, the ToF sensor 100 may extract depth information based on the waveform of the intensity of the light TX, the structure of the depth pixel, etc.

[0099] Figure 6 is a diagram illustrating an example pixel structure of a ToF sensor according to at least some example embodiments of the inventive concepts, Figure 7 is shown with Figure 6 The top view of the layout corresponding to the pixel structure, and Figure 8 is a timing diagram for describing the operation of a ToF sensor.

[0100] Reference Figure 6 and Figure 7, the pixel set GR may include a floating diffusion node FD, a first pixel 210, a second pixel 220, a third pixel 230, a fourth pixel 240, and a read circuit 300. The first pixel 210, the second pixel 220, the third pixel 230, and the fourth pixel 240 may be connected to the floating diffusion node FD in common. Figure 6 and Figure 7 As shown, the pixel set GR can be Figure 3 The pixels are repeatedly arranged in the row direction and the column direction in the pixel array 110 .

[0101] The control signals TX1 , TX2 , TX3 , TX4 , and RX may be provided from the row driver 30 through the wires MW extending in the row direction X.

[0102] The first pixel 210 may include a first photodiode PD1 and a first transfer transistor MT1. The second pixel 220 may include a second photodiode PD2 and a second transfer transistor MT2. The third pixel 230 may include a third photodiode PD3 and a third transfer transistor MT3. The fourth pixel 240 may include a fourth photodiode PD4 and a fourth transfer transistor MT4. Each of the first to fourth photodiodes PD1 to PD4 may collect photocharge corresponding to the phase of the corresponding photogate control signal from the first to fourth photogate control signals PG1 to PG4. Control signals TX1, TX2, TX3, and TX4 may be applied to transfer gates TG1 to TG4, i.e., the gates of transfer transistors MT1 to MT4, respectively.

[0103] The read circuit 300 may include a reset transistor MR, a source follower transistor or a drive transistor MD, and a select transistor MS. Figure 6 A non-limiting example is shown in which each pixel includes one transistor and the read circuit includes three transistors, but methods according to at least some example embodiments of the inventive concepts may be applied to operate in addition to Figure 6 Image sensors of various configurations other than the configuration.

[0104] Figure 8 Shows about Figure 6 and Figure 7 The pixel structure of FIG. 1 has a modulation timing represented by the emission light TX and a demodulation timing represented by the photogate control signals PG1 to PG4.

[0105] Reference Figure 8, the emission light TX from the light source can be output synchronously with the modulation signal MOD. The first photogate control signal PG1 to the fourth photogate control signal PG4 are generated synchronously with the demodulation signal DEM. The first photogate control signal PG1 to the fourth photogate control signal PG4 have a phase difference of 0 degrees, 90 degrees, 180 degrees and 270 degrees. As mentioned above Figure 5 As described above, the four samples A0 , A1 , A2 , and A3 of the received light RX may be sampled at phases of approximately 90 degrees, approximately 180 degrees, approximately 270 degrees, and approximately 360 degrees, respectively, for each cycle.

[0106] Figure 8 An example is shown in which the phase of the first photogate control signal PG1 is consistent with the phase of the modulation signal MOD (i.e., the phase of the emitted light TX), which means that the global delay phase is zero. According to at least some example embodiments of the present inventive concepts, the modulation signal MOD may have different global delay phases in multiple measurement cycles, thereby causing an artificial distance difference so that the test object does not move during the compensation operation.

[0107] Figure 9A and Figure 9B is a diagram for describing a method of measuring a swing error.

[0108] The swing error is a systematic error determined by the characteristics of the ToF sensor. The swing error can be eliminated by measuring the error corresponding to one cycle period (i.e., 2π or 360 degrees) of the modulated signal and the demodulated signal during calibration, and the measured swing error can be reflected or compensated during normal operation. In order to determine the swing error, as Figure 9A and Figure 9B As shown, various phase differences need to be measured within one cycle.

[0109] Reference Figure 9A , a test object such as a plan view PLC can be moved during multiple measurement cycles to change the distance d1 between the ToF sensor and the plan view PLC and measure various phase differences. The varying distance d1 can be measured, for example, using a laser distance measurement device LDM.

[0110] However, such methods require many measurement cycles to obtain the full range of the swing error because the number of samples obtained from a single chart image is limited. Furthermore, obtaining the exact distance between the planar PLC and the ToF sensor is difficult, and these methods are severely affected by noise in the sample data.

[0111] Reference Figure 9BAccording to at least some example embodiments of the present inventive concepts, a test object, such as a planar image, can be fixed at the same position during multiple measurement cycles. As described above, a cache chain circuit can be used to generate multiple demodulation signals with different local delay phases during each measurement cycle, and the multiple demodulation signals with different local delay phases can be provided to each pixel group. Therefore, various phase differences can be achieved for each pixel group.

[0112] Alternatively, as described above, a variable delay circuit can be used to generate the modulation signal to have a different global delay phase for each measurement cycle. In this case, even if the plan view PLC is fixed, a change in the global delay phase has the same effect, i.e., the plan view PLC is moving.

[0113] In this way, a ToF sensor and a method of calibrating an error in a ToF sensor according to at least some example embodiments of the present inventive concepts can obtain a swing error using a small number of measurement cycles because samples of various distances or phase differences can be obtained through a single chart image by using multiple local delay phases and a variable global delay phase.

[0114] Figure 10 is a diagram illustrating an example embodiment of a cache chain circuit included in a ToF sensor according to at least some example embodiments of the inventive concepts, and Figure 11 is a diagram for describing a local delay phase of a ToF sensor according to at least some example embodiments of the inventive concepts.

[0115] Reference Figure 10 The buffer chain circuit DBC may include a plurality of delay buffer units DU1 to DUm connected in series to generate a plurality of demodulation signals DEM1 to DEMm. The plurality of delay buffer units DU1 to DUm may sequentially delay a single DEM to generate a plurality of demodulation signals DEM1 to DEMm with different local delay phases. Based on each of the demodulation signals DEM1 to DEMm, for Figure 6 and Figure 7 The pixel set has fixed relative phase differences of 0, 90, 180 and 270 degrees. Figure 8 The first to fourth photogate control signals PG1 to PG4 may have different local delay phases for each pixel group. According to at least some example embodiments of the inventive concepts, the delay amounts of the delay buffer units DU1 to DUm may be the same or different.

[0116] like Figure 10As shown, the pixel array 110 may be grouped into a plurality of pixel groups CG1-CGm. For example, each pixel group may include one or more pixel columns PC1-PCk. In some example embodiments, each pixel group in the plurality of pixel groups may include a pixel column including pixels arranged in a column, such as Figure 10 In at least some other example embodiments of the present inventive concepts, each of the plurality of pixel groups may include a pixel row including pixels arranged in a row.

[0117] The pixel groups CG1 to CGm respectively receive the demodulated signals DEM1 to DEMm to sample the received light reflected from the test object, so that various phase differences can be measured through each chart image.

[0118] exist Figure 11 The left part of FIG shows the phase delay of the pixel array 110 when the cache chain circuit DBC is not used, and Figure 11 The right part of shows the phase delay of the pixel array 110 when the buffer chain circuit DBC is used. Figure 10 By forming pixel groups based on columns in this manner, the phase delay can be increased in the right direction, and a maximum phase difference MXPD can be achieved between the leftmost pixel group and the rightmost pixel group.

[0119] Thus, by applying a different phase delay to each pixel group, various phase differences can be measured using one chart image.

[0120] Figure 12 is a diagram illustrating example embodiments of a variable delay circuit included in a ToF sensor according to at least some example embodiments of the inventive concepts.

[0121] Reference Figure 12 , the variable delay circuit GDL may include a plurality of delay units 71 to 74 connected in series. Each of the plurality of delay units 71 to 74 may include one of the delay circuits 51 to 54 and one of the selectors 61 to 64. Each delay circuit may delay the output signal of the previous delay unit to output a delayed signal. In response to each bit Bx of the control code [B1 to Bn], each selector may select and output one of the output signal of the previous delay unit and the delayed signal. For example, the delay unit 72 may include: a delay circuit 52, configured to: delay the output signal of the previous delay unit 71 to output a delayed signal; and a selector 62, configured to: select and output one of the output signal of the previous delay unit 71 and the delayed signal of the delay unit 71 in response to each bit B2 of the control code [B1 to Bn].

[0122] Figure 13 and Figure 14 is used to describe Figure 12 A diagram of the operation of the variable delay circuit.

[0123] Figure 13 The figure shows the phase delay when the control code values ​​are C1, C2, and C3 in three consecutive measurement cycles. In this way, the control code can be sequentially changed over multiple measurement cycles, resulting in the modulated signal having different global delay phases in each measurement cycle. As described above, the pixel array has different local delay phases for each pixel group and also different global delay phases for each measurement cycle. By implementing different global delay phases based on the measurement cycle and different local delay phases based on the pixel position, various phase differences can be effectively measured.

[0124] When the image reference Figure 9B When capturing a fixed plane PLC as described above, the input phase difference can be Modeled as Equation 5.

[0125] [Formula 5]

[0126]

[0127] Here, x indicates the pixel position of the ToF sensor, Indicates the basic delay phase difference, Indicates the rate of change of the phase difference, c indicates the value of the control code, Indicates swing error, indicates other phase differences including a local delay phase and the like, and N indicates a phase difference due to noise.

[0128] According to Formula 5, when the test object is captured during multiple measurement cycles by changing the control code, the input phase difference is changed The factor is and operands is a constant, so Increases linearly according to the control code. Figure 14 The results of measuring the phase difference MPD, which is measured with respect to the center pixel of the pixel array while increasing the value of the control code, are shown.

[0129] like Figure 14 As shown, the actual measured phase difference MPD can increase linearly according to the value of the control code. Here, the slight curvature in the graph indicates the influence of the swing error. Figures 15 to 17 As described, first, the change in phase difference is obtained for each pixel, and the change rate can be fitted to a linear function and an offset value can be obtained as a result of the fitting. The offset value can be used to determine the swing error.

[0130] Figure 15 is a flowchart illustrating an example embodiment of determining a swing error of a method for calibrating an error in a ToF sensor according to at least some example embodiments of the inventive concepts, and Figure 16 and Figure 17 is used to describe Figure 15 According to at least some example embodiments of the present inventive concept, the method of determining the swing error may be Figure 2 The test device 20 (eg, error generator WGG) shown hereunder is used to perform the test described below for Figures 15 to 17 Furthermore, according to at least some example embodiments of the present inventive concept, the operation of Figure 3 and Figure 4 The controller 150 shown performs or alternatively controls the following instructions for Figures 15 to 17 The operations discussed are steps S10 to S40.

[0131] Reference Figure 15 , for each of a plurality of pixels included in the ToF sensor, a measured phase difference corresponding to each pixel and measured during a plurality of measurement cycles may be fitted to a linear function ( S10 ).

[0132] A plurality of offset values ​​may be obtained such that each offset value corresponds to a difference between each measured phase difference and a corresponding value of the linear function (S20).

[0133] A plurality of representative offset values ​​may be obtained, each representative offset value being obtained based on an offset value corresponding to one measured phase difference (S30).

[0134] A mapping function representing the wobble error may be obtained based on the plurality of representative offset values ​​and the plurality of measured phase differences ( S40 ).

[0135] Figure 16 The measured phase differences MPD corresponding to the values ​​C1 to C8 of the control code corresponding to the same pixel, represented by dots, and a linear function as a fitting result are shown.

[0136] like Figure 16 As shown, each offset value OFS corresponding to the difference between a measured phase difference Vm and a corresponding value Vt of the linear function can be obtained. In this way, a large number of offset values ​​corresponding to various measured phase differences can be obtained for each of the plurality of pixels included in the ToF sensor.

[0137] exist Figure 17 The left portion of φ shows a plurality of offset values ​​OFS obtained as described above. The offset values ​​are arranged to correspond to values ​​V1 to V6 of the measured phase difference MPD.

[0138] For all values ​​of the measured phase difference V1 to V6, each representative offset value ROFS may be based on an offset value corresponding to a measured phase difference value MPD. For example, the average value of the offset values ​​corresponding to the same measured phase difference may be determined as the representative offset value of the same measured phase difference, such as Figure 17 Based on the representative offset value, a mapping function representing the swing error can be determined, as will be described below with reference to Figure 21 In some example embodiments, the mapping function may be provided as a mapping table TAB, such as Figure 17 As shown in the right part of , the mapping table TAB represents a mapping relationship between a plurality of measured phase differences and a plurality of representative offset values, and the mapping relationship includes a mapping relationship between a representative offset value and a measured phase difference.

[0139] Figure 18 is a diagram for describing a local delay phase of a ToF sensor according to at least some example embodiments of the inventive concepts.

[0140] exist Figure 18 , the first sensor SEN1 and the second sensor SEN2 correspond to ToF sensors according to at least some example embodiments of the inventive concepts, and the third sensor SEN3 and the fourth sensor SEN4 correspond to conventional ToF sensors. Figure 18 An operating frequency in MHz for modulation and demodulation and a ratio (MXPD / 2π) of a maximum phase difference MXPD to one cycle period 2π for each of the sensors SEN1 to SEN4 are shown.

[0141] Even though the conventional sensors SEN3 and SEN4 have local delay phases, their values ​​are very small. When a 100 MHz light source is used in the first sensor SEN1, 54.5% of the distance information of one cycle can be measured and sampled from one frame of data of the test object.

[0142] Considering an ideal situation, at 20 MHz, the third sensor SEN3 requires at least 108 measurement cycles, and the fourth sensor SEN4 requires at least 17 measurement cycles. However, the first sensor SEN1 according to at least some example embodiments of the inventive concepts can determine the swing error for all ranges through at least three measurement cycles at 80 MHz.

[0143] In addition, by using a variable delay circuit GDL that can be provided inside or outside the ToF sensor, a change in the global delay phase has the same effect even if the test object such as a planar graph PLC is fixed, ie, the test object is moving.

[0144] In this way, by implementing different global delay phases according to the measurement period and different local delay phases according to the pixel position, various phase differences can be effectively measured.

[0145] Figures 19A to 21 is a diagram for describing an effect of using a method of calibrating an error in a ToF sensor according to at least some example embodiments of the inventive concepts.

[0146] Figures 19A to 21 The results of the wobble calibration of the ToF sensor at an operating frequency of 100 MHz are shown. The horizontal axis indicates the normalized phase 0 to 1 of one cycle period 0 to π, and the vertical axis indicates the representative offset value of the determined wobble error.

[0147] 19A to 20B Shown by Figure 9A The lookup function or lookup table for the swing calibration is generated by the moving plane map PLC. A white plate with a reflectivity of 94% has been used as the plane map PLC and has been aligned to be parallel to the optical axis of the ToF sensor. The white plate has been sequentially moved 20 times according to the desired (or alternatively, predetermined) unit distance to cover a range of 1500mm corresponding to one cycle of the 100MHz signal. Only the values ​​of 3*3 pixels in the central part of the white plate are sampled, and the average value is determined as a representative offset value of the phase difference for the corresponding distance. Figure 19A The measurement results of 21 measurement cycles are shown in Figure 19B The fitting results are shown in . For comparison purposes, the range of 1500 mm can be divided by 10, i.e., 11 measurement cycles can be performed. Figure 20A The measurement results of 11 measurement cycles are shown in Figure 20B The fitting results are shown in .

[0148] like Figure 19A and Figure 19B As shown in Figure 1, even with 21 measurement cycles, it is difficult to obtain sufficient data. Since the wobble calibration is performed for each ToF sensor one by one, this traditional moving chart method takes a lot of testing time.

[0149] In contrast, according to at least some example embodiments of the inventive concepts, the whiteboard has been fixed at a position 500 mm away from the ToF sensor and captured during 21 measurement cycles and 11 measurement cycles as in the conventional case.

[0150] As reference Figures 15 to 17 As described, the swing error can be determined based on the measured phase differences of all pixels and multiple measurement cycles. Figure 21In the figure, the measurement results of 21 measurement cycles and the measurement results of 11 measurement cycles are superimposed.

[0151] In the case of conventional moving planar PLC, the whiteboard must be moved minutely, thus taking approximately 5-6 minutes for 21 measurement cycles. In contrast, the capture and calculation of the required mapping table can be completed in seconds.

[0152] If the temperature changes during the swing calibration, an error may be caused in measuring the phase difference. According to at least some example embodiments of the present inventive concepts, the swing calibration can be completed in about three seconds, and thus the method according to at least some example embodiments of the present inventive concepts is robust to temperature changes.

[0153] like Figure 21 As shown in , a concise and smooth mapping table can be obtained according to at least some example embodiments of the present inventive concept without the need for additional nonlinear fitting. Figure 21 It is shown that the results of 11 measurement cycles are substantially the same as the results of 21 measurement cycles, which means that the wobble error can be obtained with a smaller number of measurement cycles.

[0154] Figure 22 is a block diagram illustrating a camera system according to at least some example embodiments of the inventive concepts, and Figure 23 is a diagram illustrating error calibration by a camera system according to at least some example embodiments of the inventive concepts.

[0155] Reference Figure 22 , the camera system 500 may include a ToF sensor 530 coupled to and in communication with a processor CPU or a host 520. The camera system 500 may further include a memory module 510 coupled to the processor 520 to store information content, such as, but not limited to, data received from the ToF sensor 530. In addition, the memory module 510 may store a mapping table TAB of swing errors determined by methods according to at least some example embodiments of the inventive concepts.

[0156] According to at least some example embodiments of the inventive concepts, the entire camera system 500 may be packaged in a single integrated circuit (IC) or chip. Alternatively, one or more of the modules 510, 520, and 530 may be implemented in separate chips.

[0157] The processor 520 may include a phase difference generator PDG and an error calibration unit CALB. According to at least some example embodiments of the inventive concepts, the phase difference generator PDG and the error calibration unit CALB may each be implemented by a circuit or an electronic circuit.

[0158] The phase difference generator PDG may provide a measured phase difference based on sample data provided by sampling the received light. According to at least some example embodiments of the present inventive concepts, the phase difference generator PDG may be provided in the ToF sensor 530, and in this case, the processor 520 may provide a measured phase difference instead of the sample data.

[0159] The error calibration unit CALB may calibrate a measured distance from the ToF sensor to a target object based on the swing error or the mapping table TAB. Figure 23 The first case CS1 in indicates the deviation before the swing calibration, and Figure 23 The second case CS2 in indicates the deviation after the wobble calibration.

[0160] The camera system 500 may be non-portable or portable. Some examples of non-portable versions of the camera system 500 may include, but are not limited to, vehicles such as cars or trucks, aircraft, airborne platforms, ships, rail vehicles, driver-side cameras in vehicles (e.g., to monitor driver sobriety), gaming machines in video arcades, interactive video terminals, machine vision systems, industrial robots, VR devices, and the like.

[0161] Some examples of portable versions of the camera system 500 may include, but are not limited to, popular consumer electronics such as mobile devices, cell phones, smartphones, user equipment (UE), tablet computers, digital cameras, laptop or desktop computers, electronic smart watches, machine-to-machine (M2M) communication units, virtual reality (VR) devices or modules, robots, and the like.

[0162] In some example embodiments, the processor 520 may be a CPU, which may be a microprocessor that processes program code. A processor that executes program code is a programmed processor and is therefore a special-purpose computer. In the discussion herein, for ease of discussion, the terms "processor" and "CPU" may be used interchangeably. However, it should be understood that, instead of or in addition to a CPU, the processor 119 may include any other type of processor, such as, but not limited to, a microcontroller, a digital signal processor (DSP), a graphics processing unit (GPU), an application-specific integrated circuit (ASIC) processor, and the like.

[0163] Figure 24 is a block diagram illustrating a computing system including a ToF sensor according to at least some example embodiments of the inventive concepts.

[0164] Reference Figure 24 , the computing system 1000 may include a processor 1010, a memory device 1020, a storage device 1030, an input / output device 1040, a power supply 1050 and / or a ToF sensor 100. Figure 24 Although not shown, the computing system 1000 may also include ports for communicating with electronic devices such as video cards, sound cards, memory cards, USB devices, and the like.

[0165] The processor 1010 may perform specific calculations and / or tasks. For example, the processor 1010 may be a microprocessor, a central processing unit (CPU), a digital signal processor, etc. The processor 1010 may communicate with the memory device 1020, the storage device 1030, and the input / output device 1040 via an address bus, a control bus, and / or a data bus.

[0166] The processor 1010 may be coupled to an expansion bus such as a Peripheral Component Interconnect (PCI) bus. The memory device 1020 may store data used to operate the computing system 1020.

[0167] For example, the memory device 1020 may be implemented by dynamic random access memory (DRAM), mobile DRAM, static random access memory (SRAM), phase change random access memory (PRAM), resistive random access memory (RRAM), nanometer floating gate memory (NFGM), polymer random access memory (PoRAM), magnetic random access memory (MRAM), ferroelectric random access memory (FRAM), etc. The storage device 1030 may include a solid-state drive, a hard disk drive, a CD-ROM, etc. The input / output device 1040 may include input devices such as a keyboard, a mouse, and a keypad, and output devices such as a printer and a display device. The power supply 1050 may supply power to the computing device 1000.

[0168] The ToF sensor 100 can be coupled to the processor 1010 via a bus or other desired communication link. As described above, the ToF sensor 100 can effectively measure various phase differences by implementing different global delay phases according to the measurement period and different local delay phases according to the pixel position. The ToF sensor 100 can be integrated into the same chip as the processor 1010, or they can be integrated into separate chips.

[0169] Figure 25 It shows Figure 24 A block diagram of an example of an interface used in a computing system.

[0170] Reference Figure 25, the computing system 1100 may adopt or support the MIPI interface and may include an application processor 1110, a ToF sensor 1140, and a display device 1050. A camera serial interface (CSI) host 1112 of the application processor 1110 may use the CSI to perform serial communication with a CSI device 1141 of the three-dimensional image sensor 1140. In an example embodiment, the CSI host 1112 may include a deserializer DES, and the CSI device 1141 may include a serializer SER. A display serial interface (DSI) host 1111 of the application processor 1110 may use the DSI to perform serial communication with a DSI device 1151 of the display device 1150. In an example embodiment, the DSI host 1111 may include a serializer SER, and the DSI device 1151 may include a deserializer DES.

[0171] The computing system 1100 may further include a radio frequency (RF) chip 1160, which includes a physical layer PHY 1161 and a DigRF slave device 1162. The physical layer PHY 1113 of the application processor 1110 may use MIPI DigRF to perform data transmission with the physical layer PHY 1161 of the RF chip 1160. The PHY 1113 of the application processor 1110 may interface (or alternatively communicate) with a DigRF master device 1114 to control data transmission with the PHY 1161 of the RF chip 1160.

[0172] The computing system 1100 may further include a global positioning system (GPS) 1120, a storage device 1170, a microphone 1180, a DRAM 1185, and / or a speaker 1190. The computing system 1100 may communicate with external devices using ultra-wideband (UWB) communication 1210, wireless local area network (WLAN) communication 1220, world-wide microwave interoperability (WIMAX) communication 1230, and the like. However, example embodiments are not limited to Figure 24 and Figure 25 The configuration or interface of computing system 1000 and computing system 1100 is shown.

[0173] The processors discussed in this specification (e.g., processor 520, processor 1010, and processor 1110) can be processing electronic circuits, such as hardware including logic circuits; hardware / software combinations that execute software; or combinations thereof. For example, the processing electronic circuits can more specifically include, but are not limited to, a central processing unit (CPU), an arithmetic logic unit (ALU), a digital signal processor, a microcomputer, a field programmable gate array (FPGA) and a programmable logic unit, a microprocessor, an application-specific integrated circuit (ASIC), and the like.

[0174] As described above, a ToF sensor and a method of calibrating an error in a ToF sensor according to at least some example embodiments of the present inventive concepts can obtain a swing error with a small number of measurement cycles because samples of various distances or phase differences can be obtained through a single chart image by using multiple local delay phases and a variable global delay phase.

[0175] At least some example embodiments of the present inventive concept can be applied to any device and system including a ToF sensor. For example, at least one example embodiment of the present inventive concept can be applied to systems such as mobile phones, smart phones, personal digital assistants (PDAs), portable multimedia players (PMPs), digital cameras, video cameras, personal computers (PCs), server computers, workstations, laptop computers, digital televisions, set-top boxes, portable game consoles, and navigation systems.

[0176] Having thus described the exemplary embodiments of the present invention, it will be apparent that they may be modified in many ways. These variations should not be regarded as departing from the intended spirit and scope of the exemplary embodiments of the present invention, and it will be apparent to those skilled in the art that all such modifications are intended to be included within the scope of the appended claims.

Claims

1. A method for calibrating errors in a time-of-flight (ToF) sensor, the method comprising: Generate a modulation signal so that the modulation signal has different global delay phases in multiple measurement cycles, wherein generating the modulation signal includes: generating the modulated signal using a variable delay circuit such that the modulated signal has a variable delay depending on a control code; and sequentially changing the control code in the multiple measurement cycles so that the modulated signal has different global delay phases in the multiple measurement cycles; illuminating a test object with emission light modulated based on the modulation signal; generating a plurality of demodulated signals having different ones of a plurality of local delay phases using a buffer chain circuit; providing a plurality of measured phase differences by providing the plurality of demodulated signals to a plurality of pixel groups included in the ToF sensor to sample received light reflected from the test object based on the plurality of demodulated signals; determining a swing error based on the plurality of measured phase differences, the swing error being dependent on a phase difference between the emitted light and the received light; and A measured distance from the ToF sensor to a target object is calibrated based on the swing error.

2. The method according to claim 1, wherein During the plurality of measurement cycles, the test object is fixed at the same position.

3. The method according to claim 1, wherein During the plurality of measurement cycles, the plurality of local delay phases are fixed.

4. The method according to claim 1, in, The swing error is determined based on the plurality of measured phase differences measured for all pixels included in the ToF sensor, and The plurality of measured phase differences are provided during each of the plurality of measurement cycles.

5. The method according to claim 1, wherein The variable delay circuit is provided outside the ToF sensor.

6. The method according to claim 1, in, Determining the swing error includes: fitting, for each of a plurality of pixels included in the ToF sensor, a measured phase difference corresponding to each pixel and measured during the plurality of measurement cycles, to a linear function; obtaining a plurality of offset values, each offset value corresponding to a difference between a measured phase difference corresponding to each pixel and a corresponding value of the linear function; obtaining, for each of the plurality of measured phase differences, a representative offset value based on an offset value corresponding to each measured phase difference; and A mapping function representing the wobble error is obtained based on the obtained representative offset values ​​respectively corresponding to the measured phase differences having different values.

7. The method according to claim 6, wherein: Obtaining the mapping function includes generating a mapping table that maps the measured phase differences having the different values ​​to the representative offset values.

8. The method according to claim 1, wherein The cache chain circuit is integrated into the ToF sensor.

9. A testing system comprising: Time-of-flight (ToF) sensors; as well as a test device configured to measure a wobble error of the ToF sensor, The ToF sensor includes: a light source configured to illuminate a test object with emitted light modulated based on a modulation signal; a buffer chain circuit configured to generate a plurality of demodulated signals having different local delay phases; and a pixel array comprising a plurality of pixels configured to sample received light reflected from the test object based on the plurality of demodulation signals, the plurality of pixels being grouped into a plurality of pixel groups, the plurality of pixel groups respectively receiving the plurality of demodulation signals having corresponding local delay phases, The modulation signal has different global delay phases in multiple measurement cycles. The ToF sensor includes a variable delay circuit having a variable delay, wherein the variable delay circuit is configured to: generate the modulation signal based on a control code so that the modulation signal has a variable delay corresponding to the control code, and The test device sequentially changes the control code in the multiple measurement cycles, so that the modulated signal has different global delay phases in the multiple measurement cycles.

10. The test system according to claim 9, wherein: The test device includes a variable delay circuit having a variable delay, the variable delay circuit being configured to generate the modulation signal based on a control code so that the modulation signal has a variable delay corresponding to the control code, and The test device sequentially changes the control code in the multiple measurement cycles, so that the modulated signal has different global delay phases in the multiple measurement cycles.

11. The test system according to claim 9, wherein: The variable delay circuit includes a plurality of delay units connected in series, and each of the plurality of delay units includes: a delay circuit configured to delay an output signal of a previous delay unit to output a delayed signal; and The selector is configured to select and output one of the output signal of the previous delay unit and the delayed signal in response to each bit of the control code.

12. The test system according to claim 9, wherein: The test equipment is configured to: fitting, for each of a plurality of pixels included in the ToF sensor, a measured phase difference corresponding to each pixel and measured during the plurality of measurement cycles, to a linear function; obtaining a plurality of offset values, each offset value corresponding to a difference between a measured phase difference and a corresponding value of the linear function; obtaining a plurality of representative offset values, each representative offset value being obtained based on an offset value corresponding to a measured phase difference value; as well as A mapping function representing the wobble error is obtained based on the plurality of representative offset values ​​and the plurality of measured phase differences.

13. The test system according to claim 12, wherein: The test device provides the mapping function as a mapping table, wherein the mapping table represents a mapping relationship between the plurality of measured phase differences and the plurality of representative offset values, and The ToF sensor calibrates a measured distance from the ToF sensor to a target object based on the mapping table.

14. A time-of-flight (ToF) sensor, comprising: a light source configured to illuminate a test object with emitted light modulated based on a modulation signal; a buffer chain circuit configured to generate a plurality of demodulated signals having different local delay phases; a pixel array comprising a plurality of pixels configured to sample received light reflected from the test object based on the plurality of demodulation signals, the plurality of pixels being grouped into a plurality of pixel groups, the plurality of pixel groups respectively receiving the plurality of demodulation signals having corresponding local delay phases; as well as a variable delay circuit configured to generate the modulation signal based on a control code so that the modulation signal has a variable delay depending on the control code, and The ToF sensor receives the control code from an external test device, and the test device sequentially changes the control code in a plurality of measurement cycles, so that the modulated signal has different global delay phases in the plurality of measurement cycles.

15. The ToF sensor according to claim 14, wherein: The variable delay circuit includes a plurality of delay cells connected in series and configured to generate the plurality of demodulated signals.

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