Distance measuring system
By using a common shift register to drive sensor columns and pixel combinations in time-of-flight optical sensors, the design of triangulation systems is simplified, the problems of complex wiring and incompatible pixel sizes are solved, and the signal-to-noise ratio and measurement accuracy are improved.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- IFM ELECTRONIC GMBH
- Filing Date
- 2021-12-09
- Publication Date
- 2026-07-03
AI Technical Summary
Existing time-of-flight optical sensor triangulation systems are complex to design, require a large amount of wiring, and have pixel sizes that are not adapted to changes in light spot size over different distances, which affects performance.
A common shift register is used to drive the sensor column. A switching matrix is used to switch time-of-flight pixels to column lines or drop nodes. In combination with pixel combination and differential amplifier, the pixel layout is optimized to adapt to the light spot changes in different distance ranges.
The structure of the time-of-flight optical sensor was simplified, the wiring workload was reduced, the signal-to-noise ratio was improved, the effects of parasitic capacitance and leakage current were reduced, and the accuracy and efficiency of distance measurement were optimized.
Smart Images
Figure CN116670535B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to a distance measurement system according to the type of independent claims. Background Technology
[0002] Distance measurement systems involve time-of-flight camera systems, which obtain time-of-flight information or distance based on the phase shifts of emitted and received radiation. For example, a PMD camera with a photonic mixing detector (PMD), as described in DE19704496A1, is particularly suitable as a time-of-flight or 3D-TOF camera.
[0003] A device for distance measurement using time-of-flight pixels is known from DE102004037137A1, wherein, among other things, an arrangement based on the principle of triangulation is proposed. The time-of-flight pixels are arranged side-by-side in at least one row. The distance to the object can be determined by triangulation calculations based on the radiation detected by the time-of-flight pixels and reflected from the object. Furthermore, the distance can also be determined via the time of flight or phase shift of the emitted and received light.
[0004] A time-of-flight sensor for triangulation is known from DE102015223675A1, wherein time-of-flight pixels that receive useful light are switched to a common integrator, while time-of-flight pixels that do not receive useful signals are switched to discard nodes. Summary of the Invention
[0005] The purpose of this invention is to simplify the structure of a time-of-flight optical sensor designed for a triangulation system. Attached Figure Description
[0006] The invention will now be explained in more detail with reference to the accompanying drawings and exemplary embodiments.
[0007] The attached diagram schematically illustrates:
[0008] Figure 1 Time-of-flight camera system;
[0009] Figure 2 Time-of-flight pixels based on the PMD principle;
[0010] Figure 3 : Triangulation for near and far ranges;
[0011] Figure 4 :according to Figure 3 A top view of the layout;
[0012] Figure 5 Interconnected sensor arrays according to the present invention;
[0013] Figure 6 Multiple amplifiers arranged downstream of the switching matrix;
[0014] Figure 7 Details of the pixel matrix;
[0015] Figure 8 : Pixel binning of time-of-flight pixels according to the present invention;
[0016] Figure 9 Examples of switch matrices; and
[0017] Figure 10 : This schematically illustrates another variation, in which columns are hardwired according to their distance range. Detailed Implementation
[0018] In the following description of preferred embodiments, the same reference numerals denote the same or equivalent parts.
[0019] Figure 1 The measurement is shown using an optical distance measurement with a time-of-flight camera, as known for example from DE19704496.
[0020] The time-of-flight camera system 1 includes a transmitting unit or illumination module 10 and a receiving unit or time-of-flight camera 20. The transmitting unit or illumination module 10 has an illumination device 12 and an associated beamforming optics 15, and the receiving unit or time-of-flight camera 20 includes a receiving optics 25 and a time-of-flight sensor 22.
[0021] The time-of-flight sensor 22 includes at least one time-of-flight pixel 21, preferably a pixel array, and is specifically designed as a PMD sensor. The receiving optics 25 typically consists of multiple optical elements for improving imaging characteristics. The beamforming optics 15 of the transmitting unit 10 can be configured, for example, as a reflector or lens optics. In a very simplified embodiment, optical elements on both the receiving and transmitting sides may be omitted.
[0022] The measurement principle of this arrangement is largely based on the fact that the flight time of the received light can be determined from the phase shift of the emitted and received light, and thus the distance traveled by the received light. For this purpose, the light source 12 and the time-of-flight sensor 22 are jointly provided with a base phase position via the modulator 30. The specific modulation signal M0 is 0. In the example shown, a phase shifter 35 is also provided between the modulator 30 and the light source 12, by means of which the base phase of the modulation signal M0 of the light source 12 is... 0 can be based on a defined phase position var Shift. For typical phase measurements, phase position is preferably used. var =0°, 90°, 180°, 270°.
[0023] According to the set modulation signal, the light source 12 emits light with a first phase position p1 or p1=( 0+ var The intensity modulation signal S p1 In the case shown, the signal S p1 Or the electromagnetic radiation is reflected by object 40, and changes phase by a corresponding phase shift Δ due to the distance traveled. (t L With the second phase position p2= 0+ var +Δ (t L Impact time-of-flight sensor 22, as the received signal S p2 .
[0024] The modulation signal M0 and the signal S received in the time-of-flight sensor 22 p2 The mixture is used to determine the phase shift or object distance d based on the obtained signal.
[0025] Preferably, the illumination source or light source 12 is implemented by an infrared light-emitting diode. Of course, other radiation sources in other wavelength ranges are also conceivable.
[0026] Figure 2 A cross-section of a time-of-flight pixel of an optical mixer detector, known for example, according to DE19704496C2, is shown. Modulation photogate G am G0, G bm The photosensitive area of the PMD pixel is formed. This is determined by the application of the modulation gate G. am G0, G bm The voltage directs the photogenerated charge q to one or another accumulating gate or integrating / diode node G. a G b .
[0027] In the design of the modulation gate, the center modulation gate G0 can be omitted if necessary. Alternatively, this time-of-flight pixel can also be designed without a modulation gate, as shown and described in EP1332594A1, for example.
[0028] Figure 2 b shows the potential curve, where the charge q is at the first integration node G. a Flowing in the direction of, and according to Figure 2 The potential of c allows charge q to be applied at the second integration node G. bThe voltage flows in the direction specified by the provided modulation signal. Depending on the application, the modulation frequency is preferably in the range of 1 MHz to 500 MHz or even higher. For example, a modulation frequency of 1 MHz produces a time period of one microsecond, causing the modulation potential to change accordingly every 500 nanoseconds.
[0029] Figure 2 a also shows a readout unit 400, which may already be a component of a PMD time-of-flight sensor in the form of a CMOS or receiving element 22. An integrating node G is formed as a capacitor or diode. a G b The photogenerated charge is integrated over multiple modulation cycles. Then, in a known manner, it is applied to the gate G. a G b The voltage provided at this point can be tapped with high impedance, for example, via the readout unit 400. Here, the first integration node G a Second integration node G b The interconnection and evaluation form what are called the A-channel and B-channel.
[0030] Figure 3 A triangulation arrangement is shown, in which the time-of-flight sensor 22 is composed of rows of time-of-flight pixels 21. The illumination device 10 emits a single modulated beam, preferably with a diameter of a few μm. When reflected from an object, the beam strikes the corresponding time-of-flight pixel 21 according to the distance to the object. If the focal length of the lens 15 is fixed and the focal point is at infinity, the beam reflected from a distant object is clearly imaged as a dot (solid line), while the beam reflected from a nearby object is blurred (dashed line).
[0031] The distance to an object can be determined by using the detected position or time-of-flight pixel, as known from triangulation. In addition to the geometric calculation of the position, the corresponding time-of-flight pixel 21 also provides the time of flight, and thus provides a second distance value.
[0032] Figure 4 The plan shows the following based on Figure 3 The arrangement of the light spots. The area of the light spots increases according to the distance from distant objects to nearby objects.
[0033] Especially in security applications, these diverse and redundantly obtained distance values can be processed individually, with the distance value only being output as a valid value if the deviation is within a predetermined tolerance limit. In particular, the distance values can also be evaluated independently via separate evaluation units, providing additional redundancy in the evaluation path.
[0034] Pixel combining is a technique known for use in 2D and 3D image sensors to improve the signal-to-noise ratio at the expense of resolution. In this process, uniformly spaced pixels are combined into a single pixel, and their signal values are either summed together in the analog domain or averaged after conversion to the digital domain.
[0035] like Figure 3 and Figure 4 As shown, in one-dimensional distance measurement, the triangulation effect causes the light spot to shift above the sensor. This is true for any system where the emission of the light signal does not occur vertically above the sensor but at a distance between the transmitting and receiving channels. Moreover, by using an optical system with a fixed focal length, the size of the light spot varies according to the object distance.
[0036] Time-of-flight applications are susceptible to interference from background light and noise from the pixels. Reducing the readout pixel area to the size of the incident light spot significantly reduces the proportion of foreign light in the pixel current, thus improving the signal-to-noise ratio. For sensors with current readout, i.e., active integrators outside the pixel array, illuminated pixels in the current / charge domain can be similarly interconnected, while pixels with little or no active light can be discarded. Furthermore, the configurability of the pixel combination is advantageous, for example, to compensate for manufacturing tolerances in the placement of the transmitter and receiver.
[0037] Sensor lines with small pixels, suitable for long-range applications but too small for short-range applications, must be grouped into large switch matrices or within the sensor lines themselves. In this case, the large number of switches required negatively impacts performance due to parasitic capacitance and leakage current. However, having pixels with optimized sizes for each distance range results in irregular and therefore unfavorable layouts.
[0038] The concept according to the present invention significantly reduces the amount of wiring work.
[0039] like Figure 5 As schematically illustrated, according to the present invention, it is envisioned that pixels 21 of at least two sensor columns are driven via a common shift register. Based on the register value, the diode node G of the time-of-flight pixel 21... a G b Switch to the column line leading to switch matrix 80 or discard / reset potential ( Figure 5 (Not shown in the image). The switch matrix 80 is configured such that several columns can be routed together to the differential amplifier 100.
[0040] like Figure 6As shown, for example, suppression of background illumination (SBI) can also be integrated upstream of amplifier 100. According to the invention, it is now contemplated that one or more columns or column lines be switched in groups to the common amplifier 100 via switch matrix 80. During the exposure / integration time, diode node G... a G b The column lines cola and colb are used as integrating capacitors to accumulate photoelectric charge at the connected pixels. The voltage provided at the input of the differential amplifier 100 is amplified and can be branched into a differential signal at the output of the amplifier 100.
[0041] After completing the integration, the column lines and diode node G a G b It is set to the reset potential.
[0042] Figure 7 An example of possible wiring for a pixel array according to the present invention is shown. Time-of-flight pixel 21 in... Figure 7 In this example, the sensor column is represented by BPIX. In the example shown, each sensor column includes two column lines cola and colb, which transport the pixel charge to the switch matrix 80 according to the register value, and then to the differential amplifier 100.
[0043] In addition, the modulation gate G am G bm The signal lines for G0 and, if necessary, the signal line for the split gate sep are guided column by column. The shift register's register FF is connected to the clock line clk and the select line pixel-sel_n. The pixel is driven according to the register entries via the select line pixel-sel_n.
[0044] In addition, lines with a reset potential vreset are guided row by row.
[0045] As already described, diode node G a G b Switch to the reset potential vreset or column lines cola and colb based on the register value.
[0046] To further reduce wiring workload, such as Figure 8 As shown, a group of at least four pixels is further provided within a sensor array. This hardwired pixel combination within the array provides a further reduction in the number of switches required. Therefore, combined with shift registers, the number of wires that need to be routed into the array is significantly reduced.
[0047] The shift register or register FF allocated to the pixel group is transmitted via signal line px_sel_n <r>Control switches S1 and S2. In the example shown, when a signal is applied to sel_n, switch S2 closes and switch S1 opens via a NAND gate. If no signal is present, S1 closes and S2 opens. Therefore, S1 and S2 are configured as toggle switches.
[0048] All diode nodes (diodes a and b) of the combined pixels PMD1-4 can be switched together via switch group S1 to readout lines cola and colb, and together via switch group S2 to the reset potential vreset.
[0049] Here, one switch group is always open, while the other switch group is always closed. This prevents negative effects caused by saturated pixels, which are not read out on adjacent pixels used for measurement. In the example shown, diode nodes a and b of time-of-flight pixels PMD1 to PMD4 are switched to column lines cola and colb via the first switch S1. Switch S2, which connects diode nodes a and b to the reset line vreset, is open.
[0050] Because of the fixed focal length of the receiving optics, the light spot becomes larger as it moves from far to near across the sensor row. This effect is utilized by writing the same data word to several adjacent shift registers within a nearby range. The number of registers written in the same manner decreases from the near range to the far range. This process also saves on logic and wiring outside the pixel row.
[0051] The pixel current connected to the readout lines within the column is routed to the switch matrix 80 outside the pixel array, such as... Figure 9 As shown. Here, each column preferably has its own matrix 80.1. Using this matrix, the currents of column lines cola and colb are routed to a common line, which is distributed to exactly one differential amplifier 100. That is, readouta <1> / readoutb <1> Assigned to the first amplifier 100.1, and readouta <n> / readoutb <n>Assigned to the nth amplifier 100.n.
[0052] Therefore, several columns can be combined in the x-direction. For the far range, due to the small spot size, it may be expected that only one column will be allocated to the amplifier. Unused columns can be switched to discard nodes or discarded within the switching matrix. This effectively prevents negative impacts on pixels in adjacent columns.
[0053] Figure 10 Another variation is schematically shown, in which columns are hardwired according to their distance range. For example, four pixels are wired in the left region of the far range and wired to the left, thus reducing the number of columns from three, two, to one for the near range. Illuminated pixels are connected to differential amplifier 100, while unilluminated pixels are turned off, i.e., their diode nodes are switched to the reset potential.
[0054] The exemplary embodiments shown can be applied individually and in combination. In particular, it is conceivable to hardwire one part of the sensor while connecting another part of the sensor to the amplifier 100 via the switch matrix 80.
[0055] For distance measurements, it is advantageous to perform several measurements, for example, by first determining the position of the incident light spot in the original measurement. After the position is determined, columns without incident light can be switched to a reset potential. Thus, the x-position of the light spot is essentially determined.
[0056] Furthermore, the register entries can be adjusted so that only the illuminated pixels are evaluated in the y-direction.
[0057] List of reference numerals
[0058] 1 PMD Distance Measurement System
[0059] 10 Lighting Modules
[0060] 15-beamforming optics
[0061] 20 Time-of-Flight Cameras
[0062] 21 Time-of-Flight Pixels
[0063] 22 Time-of-Flight Sensor
[0064] 25 Receiving optical components
[0065] 30 Modulator
[0066] 35 Phase shifter
[0067] 40 objects
[0068] 80-Switch Matrix
[0069] 90 SBI
[0070] 100 amplifier
[0071] 400 readout units
[0072] G a Integration node, diode node channel A
[0073] G b Integration node, diode node channel B
[0074] G am Modulation gate
[0075] G bm Modulation gate
[0076] G0 Modulation Gate
[0077] FF register, shift register< / n> < / n> < / r>
Claims
1. A PMD time-of-flight sensor (22) for an optical distance measurement system, comprising: PMD time-of-flight pixel (21) array, wherein the time-of-flight pixel comprises a diode node (G a , G b ) for A and B channels (A, B) and is connectable to an associated column line (cola, colb) via a first switch (S1) and to a reset potential (vreset) via a second switch (S2); Multiple shift registers are constructed and connected to the pixel such that, starting from each register (FF) in the register entry, the two switches (S1, S2) can be alternately switched, allowing the diode node (G) to... a G b The register value is used to switch to the reset potential (vreset) or to the column line (cola, colb). In this process, multiple columns or rows are at least partially allocated to the shift register; It also includes a switching matrix (80) configured such that the column lines (cola, colb) can be switched to one of the plurality of amplifiers (100), and the plurality of column lines (cola, colb) can be switched to a common amplifier (100). The time-of-flight sensor (22) is configured such that during the integration time, the charge generated at the time-of-flight pixel accumulates at the diode nodes (diode a, diode b) and the connected column lines (cola, colb). In this process, pixels from at least two sensor columns are driven via a common shift register (21); and Among them, the diode node (G) a G b The column lines (cola, colb) and the column lines are used as integrating capacitors to allow photogenerated charges to accumulate at the connected pixels (21).
2. The time-of-flight sensor (22) according to claim 1, wherein, The time-of-flight pixels (21, PMD) in the column are combined into groups of at least two pixels, and the group of pixels includes a common channel-wise single first switch (S1) and a single second switch (S2).
3. A distance measuring device (1), comprising a time-of-flight sensor (22) according to any one of the preceding claims, wherein, The time-of-flight sensor is configured to determine distance based on the time-of-flight phase measurement principle and the triangulation principle.