Patent Description:
Image sensors of the time of flight type are known. Among these sensors, indirect time of flight sensors are configurated to determine a dephasing between periodic light emitted by the sensor towards a scene to capture, and light received by pixels of the sensor, the received light corresponding to the light reflected by the scene when illuminated by the sensor. Based on the dephasing determined for each pixel of the sensor, a distance between this pixel and a conjugated point of the scene may be calculated, and a depth map of the scene may be generated. Examples of time of flight sensors are discussed in <CIT> and <CIT>.

There is a need to overcome all or some of the drawbacks of known indirect time of flight sensors.

One embodiment addresses all or some of the drawbacks of known indirect time of flight sensors.

One embodiment provides an indirect time of flight sensor comprising:.

According to one embodiment, the illumination device comprises an array of laser sources and an optical device configurated to direct light emitted by the array of laser sources towards the scene, and wherein:.

According to one embodiment, the first circuit is configured to control, by means of the second signals, a reading of all the pixels after each illumination of a first area, before an illumination of a next first area.

According to one embodiment, the second circuit is configured, before each reading of all the pixels controlled by the first circuit, to control several successive illumination cycles each comprising a unique illumination of each first area, and to control an absence of light emission by the illumination device during said reading.

According to one embodiment, the first circuit is configured to control, after each illumination of a first area, a reading of only the pixels of the second area corresponding to said first area.

According to one embodiment, the second circuit is configured to control an absence of light emission by the illumination device when the first circuit control the reading of the pixels of a second area.

According to one embodiment, for each voltage level intended to be provided to at least one pixel of the first half of the matrix, and, simultaneously, to at least one pixel of the second half of the matrix, the sensor comprises a generator of said voltage level for the first half and a generator of said voltage level for the second half, the generators being electrically decoupled from each other.

According to one embodiment, the sensor comprises a first reading circuit coupled the second lines of the first half of the matrix, and a second reading circuit coupled to the second lines of the second half of the matrix, a reference voltage of the first reading circuit being electrically decoupled from a reference voltage of the second reading circuit.

According to one embodiment, the first reading circuit is disposed along a first edge of the matrix, on the side of the first half, and the second reading circuit is disposed along a second edge of the matrix, on the side of the second half, the first and second edges being parallel.

According to one embodiment, the sensor comprises a control circuit for controlling the commutators such that the output of each commutator is coupled to the first input of said commutator during a reading of pixels of the first half of the matrix, and to the second input of said commutator during a reading of pixels of the second half of the matrix.

For the sake of clarity, only the operations and elements that are useful for an understanding of the embodiments described herein have been illustrated and described in detail. In particular, usual electronic systems and applications in which an indirect time of flight sensor may be provided are not described in detail, the described embodiments being compatible with these usual systems and applications.

Unless specified otherwise, the expressions "around", "approximately", "substantially" and "in the order of" signify within <NUM> %, and preferably within <NUM> %.

<FIG> illustrates an example of a circuit of a pixel <NUM> of an indirect time of flight sensor.

Pixel <NUM> comprises a photoconversion region, or photosensitive region, PD, for example a photodiode, preferably a pinned photodiode. The photoconversion region PD has an electrode, for example its anode, which is connected to a node <NUM> configured to receive a reference voltage, for example the ground GND. The photoconversion region PD is configured such that charges are generated therein when light is received by the region PD.

Pixel <NUM> further comprises two identical sets E1 and E2, delimited by dashed lines in <FIG>. Each set E1, E2 is coupled to the region PD, and more particularly to the electrode <NUM> of the region PD which is not connected to the node <NUM>.

Each set E1, E2 of the pixel <NUM> comprises a charges storage region mem1, mem2 and a controllable charge transfer device TGmem1, TGmem2.

Device TGmem1, respectively TGmem2, is connected between the region PD and the region mem1, respectively mem2. Device TGmem1, respectively TGmem2, is configured to transfer charges from the region PD to the region mem1, respectively mem2. More precisely, device TGmem1, respectively TGmem2, is configured to transfer charges from the region PD to the region mem1, respectively mem2, when its control signal TG1, respectively TG2, is active, for example at a high level, and to avoid any charge transfer between the region PD and the region mem1, respectively mem2, when this control signal is inactive, for example at a low level. Each device TGmem1, TGmem2 is, for example, a transfer gate.

Region mem1, respectively mem2, is configured to store charges which are transferred therein by the transfer device TGmem1, respectively TGmem2, until these charges are transferred elsewhere in the pixel <NUM> during a reading phase. Each region mem1, mem2 is, for example, a pinned diode. Each pinned diode mem1, mem2 has an electrode, for example its anode, connected to the node <NUM>, and another electrode <NUM>, for example its cathode, coupled to the electrode <NUM> of the region PD by the corresponding transfer device TGmem1, TGmem2.

Pixel <NUM> has an output <NUM>. During a reading phase of the pixel <NUM>, outputs signals of the pixel <NUM> are available on the output <NUM>.

Pixel <NUM> comprises a selection device <NUM>, for example a MOS ("Metal Oxide Semiconductor") transistor. The device <NUM> is connected between the output <NUM> and a reading conductive line Vx. The selection device <NUM> is configured to selectively couple the output <NUM> of the pixel <NUM> to the line Vx. More precisely, during a reading phase of the pixel <NUM>, for example when a control signal RD of the device <NUM> is active, for example at a high level, the device <NUM> couples the output <NUM> to line Vx, and outside of a reading phase of the pixel <NUM>, for example when signal RD is inactive, for example at a low level, the device <NUM> isolates output <NUM> from line Vx.

For example, in known time of flight sensors comprising a matrix of pixels <NUM> arranged in rows and columns, a line Vx is shared by all the pixels <NUM> which belong to the same column. To read a given pixel of the matrix, all the pixels of the row to which belongs this pixel are selected by activating signal RD for this row of pixels.

Pixel <NUM> comprises a controllable output circuit <NUM>, delimited in dashed lines in <FIG>. The circuit <NUM> is configured to selectively generate, on the output <NUM>, an output signal indicative of the number of charges stored in the charge storage region mem1 of the pixel or an output signal indicative of the number of charges stored in the charge storage region mem2 of the pixel.

For example, during a reading phase of the pixel, when a first signal RD1 is active, for example at a high level, the circuit <NUM> provides a signal, for example a voltage referenced to node <NUM>, indicative of the number of charges stored in region mem1, and, when a second signal RD2 is active, for example at a high level, the circuit <NUM> provides a signal, for example a voltage referenced to node <NUM>, indicative of the number of charges stored in region mem2.

In the particular example of <FIG>, the circuit <NUM> comprises, for each set E1, E2, a controllable coupling device TGRD1, TGRD2, for example a transfer gate. Device TGRD1, respectively TGRD2, is connected to the set E1, respectively E2, and, more precisely, to region mem1, respectively mem2, for example to the electrode <NUM> of the region mem1, respectively mem2. The device TGRD1, respectively TGRD2, is configured to couple the region mem1, respectively mem2, to a node <NUM> when the signal RD1, respectively RD2, is active, and to insulate the region mem1, respectively mem2, from node <NUM> when the signal RD1, respectively RD2, is inactive. Circuit <NUM> further comprises a source follower MOS transistor <NUM> having its gate connected to node <NUM>, its source connected to output <NUM> and its drain connected to a node <NUM> configurated to receive a supply voltage Vdd.

The pixel <NUM>, for example, further comprises a transistor AB connected between the electrode <NUM> of the region PD and a node <NUM> configured to receive a bias voltage VAB. The transistor AB is controlled by a signal TGAB. The transistor AB is configured, when off, to operate as an antiblooming device for the region PD, and, when on, to reset the region PD, that is to say to evacuate all the photo-generated charges accumulated in the region PD towards the node <NUM>.

In a usual indirect time of flight sensor comprising a matrix of pixels <NUM> arranged in rows and columns, during an integration phase, all the transfer devices TGmem1 and TGmem2 of all the pixels <NUM> of the matrix are driven simultaneously to transfer charges photo-generated in the region PD of each pixel towards regions alternatively mem1 and mem2 of this pixel. Further, during the integration phase, the scene to capture is illuminated by the sensor in a flash manner, that is to say that each time the sensor emits light, the whole scene is illuminated. During the integration phase, the light is, for example, emitted under the form of a burst of successive periodic pulses of light. After an integration phase, all the pixels <NUM> of the matrix are read. More particularly, during the reading of all the pixels <NUM> of the matrix, the rows of pixels are selected the one after the other with the signals RD, and all the pixels <NUM> of a selected row are read simultaneously.

Although in the example of <FIG> the pixel comprises only two identical sets E1 and E2, in other examples not illustrated, the pixel may comprise more than two identical sets, for example four identical sets.

Further, although in the example of <FIG> the pixel <NUM> has only one output <NUM>, in other examples not illustrated, the pixel may comprise more than one output <NUM>. For example, the pixel may comprise one output <NUM> for each set E1, E2, the circuit <NUM> being then connected between the sets E1, E2 and the outputs <NUM>. The selection device <NUM> is then configured to selectively couple the outputs <NUM> to at least one corresponding line Vx. For example, the output <NUM> associated to the set E1 is selectively coupled to a first line Vx by the device <NUM>, and the output <NUM> associated to the set E2 is selectively coupled to a second line Vx by the device <NUM>.

More generally, many different pixels known by those skilled in the art may be used in a matrix of pixels of an indirect time of flight sensor, and the pixel <NUM> of <FIG> is only one example of these known pixels. Further, usual controls of these different pixels during an integration phase and during a reading phase are well known by those skilled in the art.

In the following description, unless indicated otherwise, when reference is made to a pixel of an indirect time of flight sensor, this means a reference to the pixel <NUM> of <FIG>. However, those skilled in the art will be capable of adapting the following description to other pixels, for example to pixels comprising more than two identical sets and/or more than one output <NUM>.

It is here proposed to capture a scene with an indirect time of flight sensor by illuminate successively different areas of the scene, only one area of the scene being illuminated at a time. Said otherwise, the scene is divided in a plurality of area, and the scene is fully illuminated by successively illuminating each area of scene, each of these areas being illuminated at least once.

<FIG> illustrates an indirect time of flight sensor <NUM> according to one embodiment.

The sensor <NUM> comprises a matrix <NUM> of pixels <NUM>, only one pixel <NUM> being referenced on <FIG> to avoid surcharging the drawing. Pixels <NUM> are arranged in rows (horizontally on <FIG>) and columns (vertically on <FIG>). In the example of <FIG>, the matrix <NUM> comprises <NUM> rows and <NUM> columns, although, in practice, the matrix <NUM> may comprise hundreds of rows and hundreds of columns.

The sensor <NUM> comprises a reading circuit READOUT. Circuit READOUT is configured to received output signals of the pixels of the matrix <NUM> which are coupled to the Vx lines when these pixels are selected. In other words, circuit READOUT is configured to received output signals of the pixels having their outputs <NUM> coupled to corresponding lines Vx thank to their selection devices <NUM> (<FIG>). As it is usual in indirect time of flight sensors, in the sensor <NUM>, the Vx lines are arranged parallel to the columns of the matrix <NUM>, or, said in other words, the Vx lines are vertical on <FIG>. Each Vx line is coupled, preferably connected, to the circuit READOUT. In order to avoid surcharging the <FIG>, only one Vx line is fully represented, in dashed lines, in this Figure. As it can be seen on <FIG>, each Vx line is shared by several pixels, and, more particularly, by all the pixels of a corresponding column in the embodiment of <FIG>. The reading circuit READOUT for example comprises a plurality of analog-to-digital converters (ADC), preferably one ADC for each Vx line.

The sensor <NUM> comprises a control circuit CTRL1. The circuit CTRL1 is configured to control reading phases and integration phases for the pixels of the matrix <NUM>.

To provide control signals TG1 and TG2 to the transfer devices TGmem1 and TGmem2 of each pixel <NUM> (<FIG>), the sensor <NUM> comprises parallel conductive lines <NUM>. Lines <NUM> are connected to circuit CTRL1. The circuit CTRL1 is configured to provide the control signals TG1 and TG2 (<FIG>) to the lines <NUM>.

In the embodiment of <FIG>, the lines <NUM> are parallel to the lines Vx. Each line <NUM> is for example shared by all the pixels of a corresponding column of the matrix. In <FIG>, only one line <NUM> is fully represented, in dashed lines, in order to avoid surcharging the Figure. Further, in order to avoid surcharging the Figure, only one line <NUM> by column is represented in <FIG>. However, in practice, each pixel receives control signals TG1 and TG2 (<FIG>) via two corresponding lines <NUM>, and each column is thus associated to a line <NUM> for transmitting signal TG1 to all the pixels of the column, and to another line <NUM> for transmitting signal TG2 to all these pixels.

To provide control signal RD to the selection device <NUM> of each pixel <NUM> (<FIG>), the sensor <NUM> further comprises parallel conductive lines <NUM>. Lines <NUM> are connected to circuit CTRL1. The circuit CTRL1 is configured to provide the control signals RD to the lines <NUM>.

In this embodiment, the lines <NUM> are perpendicular to the lines Vx. Each line <NUM> is for example shared by all the pixels of a corresponding row of the matrix. In <FIG>, only one line <NUM> is fully represented in dashed lines in order to avoid surcharging the Figure.

Although not shown in <FIG>, the other control signals provided to the pixels of the matrix <NUM> are preferably provided by the circuit CTRL1. As usual in indirect time of flight sensors, the sensor <NUM> comprises other conductive lines (not shown) to provide other control signals and voltages to the pixels of the matrix <NUM>. For example, in the embodiment of <FIG>, the sensor <NUM> comprises:.

The sensor <NUM> comprises an illumination device <NUM>. The illumination device <NUM> is configured to illuminate a scene to capture. The sensor <NUM> further comprises a control circuit CTRL2 configured to control the device <NUM>. For example, the circuit CTRL2 provides a control signal cmd to the device <NUM>. The signal cmd is, for example, a digital signal comprising several bits.

As indicated above, the scene to capture is divided in a plurality of areas, and it is here proposed to successively illuminate each area of the scene, by illuminating only one area at a time, being understood that, in practice, parts of the scene which are adjacent to the illuminated area may also receive some light. Said in other words, the device <NUM> and its control circuit CTRL2 are configured to successively illuminate each area of the scene. For example, the device <NUM> is configured to illuminate different areas of the scene to capture, the area which is illuminated by the device <NUM> being determined by the signal cmd.

Control circuits CTRL1 and CTRL2 are synchronized, for example by means of a synchronization circuit SYNC which couples circuits CTRL1 and CTRL2. Said in other words, circuit SYNC receives and/or sends synchronization signals to and/or from circuits CTRL1 and CTRL2.

In a similar manner to the scene, the matrix <NUM> is divided in a plurality of areas, the total number of areas of the matrix being, preferably, equal to the total number of areas of the scene. In the example of <FIG>, the matrix <NUM> is divided in four areas M1, M2, M3 and M4.

Each area M1, M2, M3, M4 comprises adjacent lines of pixels <NUM>, these lines of pixels being parallel to the conductive lines <NUM>. In the embodiment of <FIG>, each area M1, M2, M3, M4 comprises two adjacent lines of pixels <NUM> which are parallel to the lines <NUM>, or, said in other words, each area M1, M2, M3, M4 comprises two adjacent columns of pixels <NUM>.

The matrix <NUM> and the device <NUM> are disposed relative to each other such that each area M1, M2, M3, M4 of the matrix <NUM> corresponds to an area of the scene, taken among the areas the scene is divided in and which are successively illuminated. Said in other words, the matrix <NUM> and the device <NUM> are disposed relative to each other such that, each time an area of the scene, taken among the plurality of areas the scene is divided in, is illuminated by the device <NUM>, the light reflected by this area of the scene is received by the pixels <NUM> of the corresponding area M1, M2, M3 or M4 of the matrix <NUM>, being understood that, in practice, some other pixels of the matrix, which are disposed near this corresponding area M1, M2, M3 of M4, may also receive part of the light reflected by the scene. The implementation of this disposition of the matrix <NUM> and the device <NUM> relative to each other is in the abilities of those skilled in the art.

The sensor <NUM> allows a scanned illumination of the scene to capture. For a given power supply provided to device <NUM> during an illumination of an area of the scene, all the light generated by the device <NUM> is directed towards this area of the scene. This differs from usual indirect time of flight sensors in which this given power supply is used to provide a flash illumination of the whole scene to capture. As a result, the signal-to-noise ratio of the light received by the sensor <NUM> is increased compared to that of the light received by these usual sensors. Indeed, for a given power supply, with a flash illumination, the light received by each area of scene carries less optical power than the light received by the only area of the scene which is illuminated by the sensor <NUM> during a scanned illumination.

The circuit CTRL1 is further configured to provide different control signals TG1 and TG2 to the different areas M1, M2, M3 and M4 of the matrix <NUM>. Said in other words, the circuit CTRL1 is configured to control the charge transfers independently in each area M1, M2, M3, M4 of the matrix <NUM>, or, said differently, independently between the areas M1, M2, M3 and M4. For example, circuit CTRL1 comprises a different sub-circuit (not shown on <FIG>) for each area M1, M2, M3, M4 of the matrix, each sub-circuit being configured to provide control signals for charge transfer in the pixels of the area M1, M2, M3 or M4 this sub-circuit is associated with.

For example, the circuit CTRL1 is configured to control an integration phase for the pixels of any one of the areas M1, M2, M3 and M4, while the circuit CTRL1 controls no integration phase for the pixels of the other areas. More particularly, when an area of the scene is illuminated by the device <NUM>, and the light reflected by this area of the scene is received by the corresponding area M1, M2, M3 or M4 of the matrix <NUM>, control signals TG1, TG2 are maintained, by circuit CTRL1, at the inactive state for the other areas of the matrix <NUM>. The control signals TG1, TG2 are repeatedly commuted between active and inactive states only for the pixels <NUM> of the area M1, M2, M3 or M4 which is receiving light. Said in other words, control signals TG1, TG2 are repeatedly commuted between active and inactive states only for the pixels <NUM> of the area of the matrix <NUM> corresponding to the area of the scene which is illuminated, such that in each pixel of said area of the matrix <NUM>, charges are alternatively transferred, from the region PD, to each storage regions mem1, mem2 of the pixel.

In practice, each commutation of the signal TG1, respectively TG2, corresponds to a charge or a discharge of a capacitance, typically the gate capacitance of the charge transfer device TGmem1, respectively TGmem2. Thus, by reducing the number of pixels for which signals TG1 and TG2 simultaneously commute, a power consumption of the sensor <NUM> is reduced compared to that of a usual indirect time of flight sensor, in which signals TG1, respectively TG2, commute simultaneously in all the pixels of the sensor.

<FIG> illustrates, in a very schematic manner, the illumination device <NUM> according to one embodiment.

The illumination device <NUM> comprises an array <NUM> of laser sources <NUM>, only one laser source being referenced in <FIG> in order to avoid surcharging the Figure. Each laser source <NUM> is, preferably, a VCSEL ("Vertical-Cavity Surface-Emitting Laser"). In the example of <FIG>, the array <NUM> comprises 8X2 laser sources <NUM>, although the number of light sources <NUM> of the array can be different in other examples.

Device <NUM> further comprises an optical device <NUM>, represented in the form of a block in <FIG>. Optical device <NUM> is configurated to direct, or orientate, the light emitted by the array <NUM> of laser sources <NUM> towards the scene to capture.

In this embodiment, the array <NUM> is divided in a plurality of sets of laser sources. In the example of <FIG>, the array <NUM> is divided into four sets A1, A2, A3 and A4 of laser sources <NUM>. Preferably, the number of sets of the array <NUM> is equal to the number of areas of the scene, and to the number of areas M1, M2, M3, M4 of the matrix <NUM> (<FIG>).

Each set A1, A2, A3, A4 is configured to illuminate a corresponding area of the scene to capture. Indeed, the laser sources <NUM> of the array can be each controlled independently from the other laser sources <NUM>. For example, the array <NUM> is controlled such that, when laser sources <NUM> of a given sets A1, A2, A3 or A4 of the array <NUM> is emitting light, the laser sources <NUM> of the other sets are emitting no light. For example, the laser sources <NUM> which are emitting light and those which are emitting no light are determined by the signal cmd.

The circuit CTRL2 (<FIG>) is configured to control, with the signal cmd, an emission of light by sets A1, A2, A3 and A4 the one after the other. More precisely, the set A1, A2, A3 or A4 which emits light depends on the value of the signal cmd.

For each set A1, A2, A3, A4, when the laser sources <NUM> of the set are emitting light, the emitted light is directed towards a corresponding area of the scene to capture by the device <NUM>, the illuminated area of the scene being different for each set A1, A2, A3, A4 of the array <NUM> of laser sources <NUM>.

For example, in <FIG>, the optical device <NUM>, for example a lens or an objective, is configured to direct the light emitted by the laser sources <NUM> of the respective set A1, A2, A3 or A4 in a respective direction O1, O2, O3 or O4. Thus, when set A1 (respectively A2, A3 or A4) emits light, a first (respectively a second, a third or a fourth) area of the scene is illuminated and reflected light is received by the area M1 (respectively M2, M3 or M4) of the matrix <NUM> (<FIG>).

For example, the device <NUM> comprises a control circuit CTRL3 configured to control the emission of light by each light source <NUM> of the array <NUM> based on signal cmd.

In the device <NUM> of <FIG>, a given power supply provided to the array <NUM> is shared, or split, between those of the light sources <NUM> which are emitting light. Thus, for a given power supply provided to the array <NUM>, the optical power of the light received by an area of the scene is greater when only the light sources of the set A1, A2, A3 or A4 corresponding to this area are emitting light (scanned illumination), than when all the light sources <NUM> are emitting light simultaneously (flash illumination).

<FIG> illustrates the illumination device <NUM> according to one alternative embodiment.

The device <NUM> of <FIG> comprises, as the one of <FIG>, the array <NUM> of laser sources <NUM>, and the optical device <NUM>.

However, in the embodiment of <FIG>, the array <NUM> is not divided in a plurality of sets of light independently controllable. For example, depending on the signal cmd, all the light sources <NUM> emit light, or do not emit any light. For example, the device <NUM> comprises the control circuit CTRL3 configured to control the emission of light by all light sources <NUM> of the array <NUM> based on signal cmd.

Further, in the embodiment of <FIG>, the optical device <NUM> is controllable. More precisely, the direction in which the light emitted by the array <NUM> is directed by the device <NUM> is controllable. Said in other words, the device <NUM> is configured to direct the emitted light differently depending on signal cmd. The control circuit CTRL2 (<FIG>), which provides the control signal cmd to the device <NUM>, is configured to provide, at each illumination of an area of the scene to capture, the control signal cmd which corresponds to a directing of the light, by the device <NUM>, towards this area of the scene.

For example, in <FIG>, the optical device <NUM> is configured to direct the light emitted by the array of laser sources <NUM> in four different directions O1, O2, O3 or O4, each corresponding to a different area of the scene. Thus, when signal cmd is at a first (respectively a second, a third or a fourth) value, a first (respectively a second, a third or a fourth) area of the scene is illuminated and reflected light is received by the area M1 (respectively M2, M3 or M4) of the matrix <NUM> (<FIG>).

The device <NUM> for example comprises mirror(s) and/or one or several lens, the orientation of which being controllable by the signal cmd. Preferably, the optical device <NUM> comprises at least one controllable movable micro-mirror, or, in other words, a MEMs (Microelectromechanical systems) controllable movable micro-mirror. The implementation of the optical device <NUM> is in the abilities of those skilled in the art.

In the device <NUM> of <FIG>, a given power supply which is provided to the array <NUM> during an illumination phase is shared between all the light sources <NUM>. However, all the light emitted by the array <NUM> is concentrated towards a given area of the scene by the optical device <NUM>. This differs from a flash illumination for which the light emitted by the array <NUM> is directed, or spread, towards the whole scene to capture. Thus, for a given power supply provided to the array <NUM>, a scanned illumination of the scene allows to improve the optical power of the light successively received by each area of the scene, compared to that of the light received simultaneously by all the areas of the scene during a flash illumination.

The embodiments of <FIG> may be combined. Further, the described embodiments of indirect time of flight sensors are not limited to the embodiments of the device <NUM> described in relation with <FIG>. Those skilled in the art are capable of using other illumination devices which are controllable, such that the emitted light is directed only towards an area of the scene to capture, selected in a controllable manner among a plurality of areas of the scene.

<FIG> shows chronograms illustrating operation of the sensor of <FIG> according to one embodiment. More specifically, in this example the scene to capture is divided in four area S1, S2, S3 and S4, and the <FIG> shows, depending on time t, the light ("light") emitted by the illumination device <NUM> (<FIG>), which area S1, S2, S3 or S4 receives the light ("illuminated area of the scene"), which corresponding area M1, M2, M3 or M4 of the matrix <NUM> (<FIG>) receives the reflected light and has its pixels in an integration phase ("integrated area"), and which pixels of the matrix are read ("read"). In this example, the device <NUM> emits light under the form of a burst of periodic pulses of light.

Between an instant t0 and an instant t1 posterior to instant t0, device <NUM> emits light with the direction O1, towards the area S1 of the scene. The light reflected by this area S1 is received by the corresponding area M1 of the matrix. An integration phase of the received light is done in the pixels of the area M1 only, by commutating the control signals TG1, TG2 of the charge transfer devices TGmem1, TGmem2 of these pixels between their active and inactive states, at a frequency upper than that of the emitted light.

Between the instant t1 and an instant t2 posterior to instant t1, no light is emitted by the device <NUM> and the pixels of the area M1 are read. Because the lines <NUM> are parallel to the lines Vx (<FIG>), the reading of the pixels of the area M1 implies that all the pixels of the matrix are read ("all matrix"). Thus, between instants t1 and t3, the circuit CTRL1 is configured to control, by means of signals RD, a reading of all the pixels of the matrix <NUM>, by reading the rows of the matrix ones after the other.

Between the instant t2 and an instant t3 posterior to instant t2, device <NUM> emits light with the direction O2, towards the area S2 of the scene. The light reflected by the area S2 is received by the corresponding area M2 of the matrix, and an integration phase is performed in the pixels of the area M2 only.

Between the instant t3 and an instant t4 posterior to instant t3, no light is emitted by the device <NUM> and the pixels of the area M2 are read, by reading all the pixels of the matrix ("all matrix"), similarly to what has been done between instants t1 and t2.

Between the instant t4 and an instant t5 posterior to instant t4, device <NUM> emits light with the direction O3, towards the area S3 of the scene. The light reflected by the area S3 is received by the corresponding area M3 of the matrix, and an integration phase is performed in the area M3 only.

Between the instant t5 and an instant t6 posterior to instant t5, no light is emitted by the device <NUM> and the pixels of the area M3 are read, by reading all the pixels of the matrix ("all matrix").

Between the instant t6 and an instant t7 posterior to instant t6, device <NUM> emits light with the direction O4, towards the area S4 of the scene. The light reflected by the area S4 is received by the corresponding area A4 of the matrix, and an integration phase is performed in the area M4 only.

At the instant t7, all the areas S1, S2, S3, S4 of the scene has been illuminated once during the scanned illumination of the scene.

Between the instant t7 and an instant t8 posterior to instant t7, no light is emitted by the device <NUM> and the pixels of the area M4 are read, by reading all the pixels of the matrix ("all matrix").

At the instant t8, the outputs signals of the pixels of the area M1 read after the illumination of the area M1 (between instants t1 and t2), the outputs signals of the pixels of the area M2 read after the illumination of the area M2 (between instants t3 and t4), the outputs signals of the pixels of the area M3 read after the illumination of the area M3 (between instants t5 and t6), and the outputs signals of the pixels of the area M4 read after the illumination of the area M4 (between instants t7 and t8) may be used to generate, or compute, an image, or depth map, of scene.

At the instant t8, a new scanned illumination of the scene begins, by illuminating, with the device <NUM>, the area M1 of the scene.

In the operating mode described in relation with <FIG>, after each illumination of an area S1, S2, S3 or S4 of the matrix <NUM>, all the pixels of the matrix are read to get the output signals of the pixels of the area M1, M2, M3 or M4 of the matrix <NUM> corresponding to the illuminated area. More precisely, after each illumination of an area S1, S2, S3 or S4, all the pixels of the matrix are read before the next area S1, S2, S3 or S4 is illuminated.

Preferably, when capturing a scene, during the successive illuminations of the areas of the scene, the device <NUM> is supplied with an average power supply having a given peak power, which is equal to an average power, having the same peak power, provided to an illumination device of a usual sensor during a flash illumination of the scene. In this case, the duration T of the illumination phase of each area of the scene during a scanned illumination is preferably equal to the duration of the flash illumination divided by the number of areas of the scene. This allows to further increase, the signal-to-noise ratio in the sensor <NUM> compared to a usual sensor, without modifying the power supply used to illuminate the scene to capture.

<FIG> shows chronograms illustrating operation of the sensor of <FIG> according to one alternative embodiment. In this example the scene to capture is divided in four area S1, S2, S3 and S4, and the <FIG> shows, depending on time t, the light ("light") emitted by the illumination device <NUM>, which area S1, S2, S3 or S4 receives the light ("illuminated area of the scene"), which corresponding area M1, M2, M3 or M4 of the matrix <NUM> receives the reflected light and has its pixels in an integration phase ("integrated area"), and which pixels of the matrix are read. In this example, the device <NUM> emits light under the form of a burst of periodic pulses of light.

Between an instant t10 and an instant t11 posterior to instant t10, device <NUM> emits light with the direction O1, towards the area S1 of the scene. The light reflected by this area S1 is received by the corresponding area M1 of the matrix. An integration phase of the received light is done in the pixels of the area M1 only, by commutating the control signals TG1, TG2 of the charge transfer devices TGmem1, TGmem2 of these pixels between their active and inactive states, at a frequency upper than that of the emitted light.

Between the instant t11 and an instant t12 posterior to instant t11, device <NUM> emits light with the direction O2, towards the area S2 of the scene. The light reflected by the area S2 is received by the corresponding area M2 of the matrix, and an integration phase is performed in the pixels of the area M2 only.

Between the instant t12 and an instant t13 posterior to instant t12, device <NUM> emits light with the direction O3, towards the area S3 of the scene. The light reflected by the area S3 is received by the corresponding area M3 of the matrix, and an integration phase is performed in the pixels of the area M3 only.

Between the instant t13 and an instant t14 posterior to instant t13, device <NUM> emits light with the direction O4, towards the area S4 of the scene. The light reflected by the area S4 is received by the corresponding area M3 of the matrix, and an integration phase is performed in the pixels of the area M4 only.

As illustrated in <FIG>, a cycle of successive illuminations of the areas S1, S2, S3 and S4, in which each area S1, S2, S3, S4 is illuminated once, may be then repeated several times before a reading of all the pixels of the matrix ("all matrix"). In the example of <FIG>, before the reading, the cycle of successive illuminations of the area S1, S2, S3 and S4 is performed four times, once between the instants t10 and t14, once between the instant t14 and an instant t15 posterior to instant t14, once between the instant t15 and an instant t16 posterior to instant t15, and once between the instant t16 and an instant t17 posterior to instant t16.

At the instant t17, the circuit CTRL1 (<FIG>) controls, by means of signals RD, a reading of all the pixels of the matrix ("all matrix"), by reading the rows of the matrix ones after the other. No light is emitted during this reading phase. At the end of the reading phase, a depth map of the scene can be generated, or computed, based on the outputs signals of the pixels read during the reading phase.

In the operation described in relation with <FIG>, before each reading of all the pixels, the reading being controlled by the circuit CTRL1, the circuit CTRL2 is configured to control several successive illumination cycles, each comprising a unique illumination of each area S1, S2, S3 and S4. The circuit CTRL1 is further configured to control an absence of emission of light by the illumination device <NUM> during the reading.

Compared to the operation described in relation with <FIG> to capture a full scene, only one reading of all the pixels of the matrix is performed in the operation described in relation <FIG>, which results in a decrease of the time needed to capture the scene.

Preferably, in <FIG>, the duration T1 of each illumination phase of each area S1, S2, S3 and S4 is equal to the duration T of the illumination phase of each area S1, S2, S3 and S4 described in relation with <FIG>, divided by the number of times the illumination cycle of the areas S1, S2, S3 and S4 is repeated before a full reading of the matrix. Said in other words, in this example, the illumination duration T1 is equal to a quarter of the illumination duration T (<FIG>). As a result, the power supply provided to device <NUM> for capturing the scene is the same in the operation mode of <FIG> and in the operation mode of <FIG>. Further, in case the device <NUM> is implemented as described in relation with <FIG>, the operation described in relation with <FIG> allows to mitigate the temperature elevation in the array <NUM> of the device <NUM>, compared to the operation described in relation with <FIG>.

In the embodiments described in relation with <FIG>, the lines <NUM> for providing the control signals TG1, TG2 to the transfer devices TGmem1, TGmem2 of the pixels are parallel to the lines Vx. Other embodiments will be described below, in which lines <NUM> are perpendicular to the lines Vx.

<FIG> illustrates an indirect time of flight sensor <NUM>' according to a further embodiment, in which lines <NUM> are perpendicular to lines Vx.

The sensor <NUM>' comprises, as the sensor <NUM> (<FIG>), the matrix <NUM> of pixels <NUM>, the circuit READOUT, the lines Vx coupled to the circuit READOUT, the lines <NUM>, and the illumination device <NUM> and its control circuit CTRL2, which will not be described again.

Instead of the circuit CTRL1, the sensor <NUM>' comprises a control circuit CTRL1'. The circuit CTRL1' is configured to control reading phases and integration phases for the pixels of the matrix <NUM>. The circuit CTRL1' is configured to provide the control signals TG1 and TG2 (<FIG>) to the lines <NUM>. The circuit CTRL1' is further configured to provide the control signals RD to the lines <NUM>.

In the embodiment of <FIG>, the lines <NUM>, which are each connected to circuit CTRL1', are perpendicular to the lines Vx. Each line <NUM> is shared by all the pixels of a corresponding row of the matrix. In <FIG>, only one line <NUM> is fully represented in dashed lines, in order to avoid surcharging the Figure. Further, in order to avoid surcharging the Figure, only one line <NUM> by row is represented in <FIG>. However, in practice, each pixel receives control signals TG1 and TG2 (<FIG>) via two corresponding lines <NUM>, and each row is thus associated to a line <NUM> for transmitting signal TG1 to all the pixels of the row, and to another line <NUM> for transmitting signal TG2 to all these pixels.

Although not shown on <FIG>, the other control signal provided to the pixels of the matrix <NUM> are preferably provided by the circuit CTRL1'. Further, similarly to what has been described for the sensor <NUM> of <FIG>, the sensor <NUM>' comprises other conductive lines (not shown) to provide other control signals and voltages to the pixels of the matrix <NUM>. For example, in the embodiment of <FIG>, the sensor <NUM>' comprises:.

Control circuits CTRL1' and CTRL2 are synchronized, for example by means of a synchronization circuit SYNC which couples circuits CTRL1' and CTRL2. Said in other words, circuit SYNC receives and/or sends synchronization signals to and/or from circuits CTRL1' and CTRL2.

As for sensor <NUM>, the matrix <NUM> of sensor <NUM>' is divided in a plurality of areas, the total number of areas of the matrix being, preferably, equal to the total number of areas of the scene. In the example of <FIG>, the matrix <NUM> is divided in four areas M1, M2, M3 and M4.

Each area M1, M2, M3, M4 comprises adjacent lines of pixels <NUM>, these lines of pixels being parallel to the conductive lines <NUM>. In the embodiment of <FIG>, each area M1, M2, M3, M4 comprises two adjacent lines of pixels <NUM> which are parallel to the lines <NUM>, or, said in other words, each area M1, M2, M3, M4 comprises two adjacent rows of pixels <NUM>.

As already described for the sensor <NUM>, in the sensor <NUM>' the matrix <NUM> and the device <NUM> are disposed relative to each other such that each area M1, M2, M3, M4 of the matrix <NUM> corresponds to an area of the scene.

The sensor <NUM>' allows, as the sensor <NUM> of <FIG>, a scanned illumination of the scene to capture. As a result, the signal-to-noise ratio of the light received by the sensor <NUM>' is increased compared to that of the light received by the usual sensors.

The circuit CTRL1' is configured to provide different control signals TG1 and TG2 to the different areas M1, M2, M3 and M4 of the matrix <NUM>. Said in other words, the circuit CTRL1' is configured to control the charge transfers independently in each area M1, M2, M3, M4 of the matrix <NUM>. For example, circuit CTRL1' comprises a different sub-circuit (not shown on <FIG>) for each area M1, M2, M3, M4 of the matrix, each sub-circuit being configured to provide control signals for charge transfer in the pixels of the area M1, M2, M3 or M4 this sub-circuit is associated with.

For example, the circuit CTRL1' is configured to control an integration phase for the pixels of any one of the areas M1, M2, M3 and M4, while the circuit CTRL1' controls no integration phase for the pixels of the other areas. More particularly, when an area of the scene is illuminated by the device <NUM>, and the light reflected by this area of the scene is received by the corresponding area M1, M2, M3 or M4 of the matrix <NUM>, control signals TG1, TG2 are maintained, by circuit CTRL1', at the inactive state for the other areas of the matrix <NUM>. The control signals TG1, TG2 are repeatedly commuted between active and inactive states only for the pixels <NUM> of the area M1, M2, M3 or M4 which is receiving light. Said in other words, control signals TG1, TG2 are repeatedly commuted between active and inactive states only for the pixels <NUM> of the area of the matrix <NUM> corresponding to the area of the scene which is illuminated, such that in each pixel of said area of the matrix <NUM>, charges are alternatively transferred, from the region PD, to each storage regions mem1, mem2 of the pixel. As a result, a power consumption of the sensor <NUM>' is reduced compared to that of a usual indirect time of flight sensor.

An advantage of the sensor <NUM>' compared to the sensor <NUM> is that the pixels of a given area M1, M2, M3 or M4 of the matrix <NUM> of sensor <NUM>' may be read without performed a full reading of the matrix <NUM>, by reading ones after the other only the rows of this area.

<FIG> shows chronograms illustrating operation of the sensor <NUM>' of <FIG> according to one embodiment. More specifically, in this example the scene to capture is divided in four area S1, S2, S3 and S4, and the <FIG> shows, depending on time t, the light ("light") emitted by the illumination device <NUM> (<FIG>), which area S1, S2, S3 or S4 receives the light ("illuminated area of the scene"), which corresponding area M1, M2, M3 or M4 of the matrix <NUM> (<FIG>) receives the reflected light and has its pixels in an integration phase ("integrated area"), and which pixels of the matrix are read ("read"). In this example, the device <NUM> emits light under the form of a burst of periodic pulses of light.

The chronograms of <FIG> are identical to those of <FIG>, except for the reading phase. Indeed, in the operation of <FIG>, each illumination of an area S1, S2, S3 or S4 of the scene is followed by a reading of the pixels of only the area M1, M2, M3 or M4 of the matrix which corresponds to this area of the scene. Said in other words the circuit CTRL1' is configured to control, after each illumination of an area S1, S2, S3 or S4, a reading of only the pixels of the area M1, M2, M3 or M4 corresponding to this area S1, S2, S3 or S4, before an illumination of a next area of the scene. During the reading of the pixels of a given area M1, M2, M3 or M4 of the matrix, the circuit CTRL2 is configured to control an absence of light emission by the device <NUM>.

In the sensor <NUM>', the duration of the reading of the pixels of a given area of the matrix is reduced compared to that of the sensor <NUM>, because it is not anymore needed to read the all the pixels of the matrix to read the pixels of a given area of the matrix.

In an alternative embodiment, the sensor <NUM>' operates as described in relation with <FIG>. In such alternative embodiment, the circuit CTRL2 is configured, before each reading of all the pixels, which is controlled by the circuit CTRL1', to control several successive illumination cycles each comprising a unique illumination of each area S1, S2, S3 and S4 of the scene. The circuit CTRL2 is further configured to control an absence of light emission by the illumination device <NUM> during the reading of the matrix.

To take profit of the fact that lines <NUM> are perpendicular to lines Vx, it is here proposed to read the pixels of an area M1, M2, M3 or M4 of the matrix <NUM> whereas another area of the matrix <NUM> is receiving light. However, when pixels of a given area M1, M2, M3 or M4 receiving light are in an integration phase and when pixels of another area are simultaneously in a reading phase, it has been shown that the high frequency commutations of the signals transmitted using lines <NUM> to the pixels of in the integration phase generate noise in the outputs signals of the pixels in the reading phase, the outputs signals being available on the Vx lines. This noise is for example transmitted via the reference voltage GND which is provided to the different circuits and to all the pixels of the sensor, and/or by the cross coupling between lines Vx and lines <NUM>.

To suppress this noise, it is here proposed a split ground and bias strategy to minimise unwanted coupling. More specifically, the pixels matrix is split into two insulated halves. Further, separated, or electrically decoupled, supply voltage, reference voltage, bias voltages and control signals are provided to each matrix half. It is then possible to read pixels of one half of the matrix while pixels of the other half are integrating, without generating noise. Different embodiments of indirect time of flight sensors implementing this strategy will be now described.

<FIG> illustrates an indirect time of flight sensor <NUM>'' according to a further embodiment. The sensor <NUM>'' is similar to the sensor <NUM>' of <FIG>, and only the difference between these two sensors will be described in detail. In <FIG>, the illumination device <NUM> and its control circuit CTRL2 are not shown.

In sensor <NUM>'', the matrix <NUM> is split into two halves P1 and P2. More specifically, a limit between parts P1 and P2 of the matrix <NUM> is parallel to the lines <NUM>.

The parts P1 and P2 of the matrix <NUM> are adjacent, the part P1 being disposed along the part P2. More specifically, each column comprises a first portion, or half, belonging to part P1, and a second portion, or half, belonging to part P2 and being aligned with the first portion of the column. For example, the parts P1 and P2 have a common edge, which corresponds to the limit between parts P1 and P2.

Further, the lines Vx, which are parallel to the column of the matrix and perpendicular to lines <NUM>, are interrupted at the limit between parts P1 and P2 of the matrix <NUM>. Said in other words, the lines Vx of the part P1 of the matrix <NUM> and the lines Vx of the part P2 of the matrix end at the limit between parts P1 and P2 of the matrix <NUM>. Said differently, the lines Vx of part P1 of the matrix are insulated from the lines Vx of part P2 of the matrix, and the lines Vx of part P1, respectively P2, do not extend above or below the part P2, respectively P1. In <FIG>, in order to not surcharging the Figure, only one line Vx of the part P1 is represented in dashed line, and only one corresponding line Vx of the part P2 is represented in dashed line.

A line Vx of the part P2 corresponds to a line Vx of the part P1 when these two lines Vx belong to the same column of the matrix <NUM>. For example, in each column of the matrix <NUM>, a line Vx of the part P2 corresponds to a line Vx of the part P1 when the line Vx of the part P1 is selectively coupled to given outputs of the pixels of the part P1 disposed in this column, and the line Vx is selectively coupled to the corresponding outputs of the pixels of the part P2 disposed in this column.

The part P1 of the matrix <NUM> is electrically decoupled from the part P2 of the matrix <NUM>. More specifically, a semiconductor substrate to which the pixels <NUM> of the matrix <NUM> belong has a first part which comprises the part P1 of the matrix <NUM> and a second part which comprises the part P2 of the matrix <NUM>. Said in other words, the first part of the substrate comprises the half P1 of the matrix and a second part of the substrate comprises the half P2 of the matrix.

The first and second parts of the substrate are insulated from each other using insulation structures passing through the substrate, the insulation structures being preferably insulation structures provided between pixels to insulate the pixels from each other.

<FIG> shows a very schematic top view of two adjacent pixels <NUM> of the sensor of <FIG>, according to an example. <FIG> shows a very schematic cross section view along plan AA of <FIG>. In this example, the two adjacent pixels <NUM> belong to the same column of the matrix, but to two different adjacent rows. The pixels <NUM> are disposed in and on a semiconductor substrate <NUM>.

In the example of <FIG> and <FIG>, the two adjacent pixels are laterally delimited, or surrounded, by an insulation structure <NUM>, which is schematically represented by a simple line in <FIG>. The insulation structure <NUM> passes through the substrate <NUM>. As it can be seen in more detail in <FIG>, the insulation structure <NUM> is preferably a capacitive deep trench insulation (CDTI), that is to say a trench filled with a conductive material <NUM>, insulated from the semiconductor substrate <NUM> by an insulative layer <NUM>. Preferably, the conductive material is a metal, for example tungsten or aluminium, or a metal alloy. Indeed, the use of a metal or metal alloy allows to reduce the optical cross-talk.

In this example, the region PD of each pixel <NUM> is laterally delimited by a capacitive deep trench insulation <NUM>, for example a U-shaped insulation structure <NUM> in the view of <FIG>. The storage region mem1 and mem2 of each pixel <NUM> are defined, or delimited, by a portion of the structure <NUM> and a portion of the structure <NUM> which is opposite and parallel to this portion of the structure <NUM>. Said in other words, each storage region mem1, mem2 is laterally delimited, in a direction perpendicular to its length, by two parallel portions of the respective structures <NUM> and <NUM>.

In this example, each pixel <NUM> further comprises transfer devices TGmem1 and TGmem2, the coupling devices TGRD1 and TGRD2, the transistor <NUM> and the selection device <NUM>, the transistors <NUM> and <NUM> being shared by the two adjacent pixels.

The example shown in <FIG> and <FIG> is not limitative. For example, the pixels of the matrix <NUM> can be arranged by groups of four pixels, the pixels of each group sharing the same transistors <NUM> and <NUM>. In another example, each pixel of matrix <NUM> has its own transistors <NUM> and <NUM>. Further, the storage region mem1 and mem2 of each pixel may be delimited by CDTI which are not portion of the insulation structure <NUM> which laterally delimitate the pixel.

Further, although in the example of <FIG> and <FIG>, the insulation structure <NUM> is of the CDTI type, in other example, this insulation structure may be a deep trench insulation (DTI), that is to say a trench filled with an insulating material, the DTI passing through the substrate.

Referring back to the <FIG>, for example, the set of all the pixels <NUM> of the part P1 of the matrix are surrounded by an insulation structure <NUM>, which delimits the first part of the substrate, and the set of all the pixels of the part P2 of the matrix are surrounded by another insulation structure <NUM>, which delimits the second part of the substrate.

The reference voltage GND which is provided to the first part of the substrate and the reference voltage GND which is provided to the second part of the substrate are electrically decoupled from each other. For example, the reference voltage GND provided to the first part of the substrate, or, in other words, to each pixel of the part P1 of the matrix, is provided by a first bonding pad <NUM> of the sensor <NUM>'', and the other reference voltage GND provided to the second part of the substrate, or, in other words, to each pixel of the part P2 of the matrix, is provided by a second bonding pad <NUM> of the sensor <NUM>''. Each bonding pad <NUM>, <NUM> receives an off-chip reference voltage GND. Each bonding pad <NUM>, <NUM> acts as a low-pass filter, as it is schematically represented in <FIG> by a resistance R and an inductance L series-connected in each bonding pad.

Preferably, the insulation structures <NUM> are CDTI. In this case, it is preferable to provide a bias voltage to structure <NUM> delimiting the part P1 of the matrix <NUM>, which is electrically decoupled from a bias voltage provided to structure <NUM> delimiting the part P2 of the matrix <NUM>. For example, in <FIG>, the bias voltage of the CDTI <NUM> of the part P1 of the matrix <NUM> is provided by a voltage generator <NUM>, and the bias voltage of the CDTI <NUM> of the part P2 of the matrix <NUM> is provided by a voltage generator <NUM>, which is electrically decoupled form the generator <NUM>.

Instead of the circuit CTRL1', the sensor <NUM>" comprises a control circuit CTRL1''. The circuit CTRL1'' is configured to control reading phases and integration phases for the pixels of the matrix <NUM>. The circuit CTRL1'' is configured to provide the control signals TG1 and TG2 (<FIG>) to the lines <NUM>. The circuit CTRL1'' is further configured to provide the control signals RD to the lines <NUM>.

In the embodiment of <FIG>, the lines <NUM>, which are each connected to circuit CTRL1'', are parallel to the lines Vx. Each line <NUM> is shared by all the pixels of a corresponding row of the matrix. In <FIG>, only one line <NUM> for each part P1, P2 of the matrix is fully represented in dashed lines, in order to avoid surcharging the Figure. Further, in order to avoid surcharging the Figure, only one line <NUM> by row is represented in <FIG>. However, in practice, each pixel receives control signals TG1 and TG2 (<FIG>) via two corresponding lines <NUM>, and each row is thus associated to a line <NUM> for transmitting signal TG1 to all the pixels of the row, and to another line <NUM> for transmitting signal TG2 to all these pixels.

Although not shown on <FIG>, the other control signal provided to the pixels of the matrix <NUM> are preferably provided by the circuit CTRL1''. Further, similarly to what has been described for the sensor <NUM>' of <FIG>, the sensor <NUM>" comprises other conductive lines (not shown) to provide other control signals and voltages to the pixels of the matrix <NUM>. For example, in the embodiment of <FIG>, the sensor <NUM>'' comprises:.

Control circuits CTRL1'' and CTRL2 (not shown in <FIG>) are synchronized, for example by means of a synchronization circuit SYNC (not shown in <FIG>), which couples circuits CTRL1'' and CTRL2.

As for sensor <NUM>', the matrix <NUM> of sensor <NUM>" is divided in a plurality of areas, the total number of areas of the matrix being, preferably, equal to the total number of areas of the scene. In the example of <FIG>, the matrix <NUM> is divided in four areas M1, M2, M3 and M4. Each area M1, M2, M3, M4 comprises adjacent lines of pixels <NUM>, parallel to the conductive lines <NUM>. In the embodiment of <FIG>, each area M1, M2, M3, M4 comprises two adjacent lines of pixels <NUM> which are parallel to the lines <NUM>, or, said in other words, each area M1, M2, M3, M4 comprises two adjacent rows of pixels <NUM>. As already described for the sensors <NUM> and <NUM>', in the sensor <NUM>" the matrix <NUM> and the device <NUM> (not shown in <FIG>) are disposed relative to each other such that each area of the scene corresponds to an area M1, M2, M3, M4 of the matrix <NUM>. In the example of <FIG>, areas M1 and M2 belong to part P1 of the matrix <NUM>, areas M3 and M4 belonging to part P2 of the matrix <NUM>.

The circuit CTRL1" is configured to provide different control signals TG1 and TG2 to the different areas M1, M2, M3 and M4 of the matrix <NUM>, in a way similar to that described for the circuit CTRL1' (<FIG>). Compared to the circuit CTRL1' of the sensor <NUM>' of <FIG>, the circuit CTRL1'' is further configured to simultaneously control charge transfers in the pixels of an area of one of the halves P1 and P2 of the matrix <NUM>, and a reading of the pixels of an area of the other one of the halves P1 and P2. For example, when the pixels of the area M1 or M2 of the part P1 are in a reading phase (respectively in an integration phase) controlled by the circuit CTRL1'', the pixels of the area M3 or M4 of the part P1 are in an integration phase (respectively in a reading phase) controlled by the circuit CTRL1".

Preferably, for each voltage level which is provided to at least one pixel <NUM> of the part P1 of the matrix <NUM>, and simultaneously to at least one pixel <NUM> of the other part P2 of the matrix, the sensor <NUM>'' comprises a voltage generator configured to provides this voltage level to the part P1 of the matrix, and a voltage generator configured to provides this voltage level to the other part P2 of matrix. These two generators are electrically decoupled form each other.

In <FIG>, this is for example illustrated for the signals TG1 and TG2 provided to lines <NUM> by the circuit CTRL1". More specifically, when a pixel <NUM> of the matrix is in a reading phase, there is no charge transfer between the region PD (<FIG>) and the regions mem1 and mem2 (<FIG>) of this pixel. Thus, the control signals TG1 and TG2 provided to the transfers devices TGmem1 and TGmem2 (<FIG>) of this pixel, via corresponding lines <NUM>, are maintained at an inactive state, which corresponds to a low voltage level TGmemL in this example. The same occurs when the pixel <NUM> is neither in a reading phase, nor in an integration phase. However, when a pixel <NUM> of the matrix is in an integration phase, charge transfers between the region PD (<FIG>) and the regions mem1 and mem2 (<FIG>) are performed. Thus, the control signals TG1 and TG2 provided to the transfers devices TGmem1 and TGmem2 (<FIG>) of this pixel, via corresponding lines <NUM>, are repeatedly commuted between their inactive state (the low voltage level TGmemL in this example) and their active state, which corresponds to a high voltage level TGmemH in this example. As a result, in the sensor <NUM>'', the voltage level TGmemH of the signals TG1 and TG2 is never provided simultaneously to a pixel of the part P1 and to a pixel of the part P2, whereas the low voltage level TGmemL is provided simultaneously to a pixel of the part P1 and to a pixel of the part P2. Thus, the sensor <NUM>" comprises a voltage generator <NUM> configured to provide the voltage level TGmemL to part P1 of the matrix <NUM>, and a voltage generator <NUM> configured to provide the voltage level TGmemL to the part P2 of the matrix <NUM>. Further, as illustrated by <FIG>, the sensor <NUM>'' may comprise only one voltage generator <NUM> configured to provide the voltage level TGmemH, which is for example alternatively to the part P1 and to the part P2 of the matrix by the circuit CTRL1''.

Although the prevision of two generators which are electrically decoupled from each other and configured to provide simultaneously the same voltage level to both parts P1 and P2 of the matrix <NUM> is here illustrated only for the voltage level TGmemL, those skilled in the art are capable to implement other pairs of electrically decoupled voltage generator for generating any voltage level which is provided simultaneously to both parts P1 and P2 of the matrix.

According to one embodiment, which is illustrated by <FIG>, the sensor <NUM>" comprises a first reading circuit READOUT1 coupled the lines Vx of the half P1 of the matrix <NUM>, and a second reading circuit READOUT2 coupled to the lines Vx of the half P2 of the matrix <NUM>.

Circuit READOUT1, respectively READOUT2, is configured to received output signals of the pixels of the part P1, respectively P2, of matrix <NUM> which are coupled to the Vx lines of part P1, respectively P2, when these pixels are selected. Each reading circuit READOUT1 and READOUT2 for example comprises a plurality of analog-to-digital converters (ADC), preferably one ADC for each Vx line coupled to this reading circuit.

The circuit READOUT1 receives a reference voltage, in this example the ground GND, and the circuit READOUT2 receives a reference voltage, in this example the ground GND. The reference voltage GND of the circuit READOUT1 is electrically decoupled from that of the circuit READOUT2. For example, the reference voltage GND applied to the circuit READOUT1 is provided by a third bonding pad <NUM> of the sensor <NUM>'', and the other reference voltage GND applied to the circuit READOUT2 is provided by a fourth bonding pad <NUM> of the sensor <NUM>". Each bonding pad <NUM>, <NUM> receives the off-chip reference voltage GND. Each bonding pad <NUM>, <NUM> acts as a low-pass filter as schematically represented in <FIG> by a resistance R and an inductance L series-connected in each bonding pad.

<FIG> shows chronograms illustrating operation of the sensor of <FIG> according to one embodiment. More specifically, in this example the scene to capture is divided in four area S1, S2, S3 and S4, and the <FIG> shows, depending on time t, the light ("light") emitted by the illumination device <NUM> of the sensor <NUM>'', which area S1, S2, S3 or S4 receives the light ("illuminated area of the scene"), which corresponding area M1, M2 of part P1 or M3, M4 of part P2 receives the reflected light and has its pixels integrating light ("integrated area of P1" and "integrated area of P2"), and which area M1, M2 of part P1 or M3, M4 of part P2 is read ("read area of P1" and "read area of P2"). In this example, the device <NUM> emits light under the form of a burst of periodic pulses of light.

Between an instant t20 and an instant t21 posterior to instant t20, device <NUM> emits light with the direction O1, towards the area S1 of the scene. The light reflected by this area S1 is received by the corresponding area M1 of part P1 of the matrix. An integration phase of the received light is done in the pixels of the area M1 only, thus only in part P1 of the matrix.

Between the instant t21 and an instant t22 posterior to instant t21, device <NUM> emits light with the direction O3, towards the area S3 of the scene. The light reflected by this area S3 is received by the corresponding area M3 of part P2 of the matrix. An integration phase of the received light is done in the pixels of the area M3 only, thus only in part P2 of the matrix. In the same time, the area M1 of the part P1 of the matrix is read. More specifically, the reading of the pixels of the area M1 is controlled by circuit CTRL1'', and is done by reading the rows of pixels of the area M1 ones after the other.

Between the instant t22 and an instant t23 posterior to instant t22, device <NUM> emits light with the direction O2, towards the area S2 of the scene. The light reflected by the area S2 is received by the corresponding area M2 of the matrix, and an integration phase is performed in the pixels of the area M2 only, thus only in part P1 of the matrix. In the same time, the area M3 of the part P2 of the matrix <NUM> is read, similarly to the manner the area M1 was read between instants t21 and t22.

Between the instant t23 and an instant t24 posterior to instant t23, device <NUM> emits light with the direction O4, towards the area S4 of the scene. The light reflected by the area S4 is received by the corresponding area M4 of the matrix, and an integration phase is performed in the pixels of the area M4 only, thus only in part P2 of the matrix. In the same time, the area M2 of the part P1 of the matrix <NUM> is read, similarly to the manner the area M1 was read between instants t21 and t22.

Between the instant t24 and an instant t25 posterior to instant t24, the area M4 of part P2 of the matrix <NUM> is read, similarly to the manner the area M1 was read between instants t21 and t22. At the instant t25, a depth map of the scene may be computed. More specifically, the depth map is generated based on the output signals of the pixels of the area M1 read between the instants t21 and t22, of the area M2 read between the instants t22 and t23, of the area M3 read between the instants t23 and t24, and of the area M4 read between the instants t24 and t25.

As it is represented in <FIG>, between the instants t24 and t24, device <NUM> may emits light with the direction O1, towards the area S1 of the scene, such that the reflected light is integrated by the area M1 only. This allows to start a new acquisition of the scene to capture, similar to that described between the instants t20 and t25. In another example, a blanking time is provided after the instant t25, and before a new acquisition of the scene implemented as described between instants t20 and t25.

<FIG> illustrates, in a very schematic manner, an implementation of the sensor of <FIG>, according to one embodiment. <FIG> is a top view of the disposition of the circuit READOUT1 and READOUT2 relative to the matrix <NUM>.

In this embodiment, circuit READOUT1 is disposed along a first edge of the matrix <NUM>, on the side of the half P1 of the matrix, circuit READOUT2 being disposed along a second edge of the matrix, on the side of the half P2. The first and second edges are parallel. More specifically, the first and second edges are perpendicular to the lines Vx (not shown on <FIG>).

This disposition of the circuits READOUT1 and READOUT2 relative to the matrix <NUM> is for example used when the circuits READOUT1 and READOUT2 belongs to the same semiconductor substrate than the matrix <NUM>.

<FIG> illustrates, in a very schematic manner, an implementation of the sensor of <FIG>, according to one alternative embodiment. <FIG> is a perspective view of the disposition of the circuit READOUT1 and READOUT2 relative to the matrix <NUM>.

In the embodiment of <FIG>, the matrix belongs to a first semiconductor substrate, and the circuits READOUT1 and READOUT2 belongs to a second semiconductor substrate. The first substrate is stacked over the second substrate.

The lines Vx of the part P1 of the matrix <NUM> are coupled to the circuit READOUT1, for example thank to an interconnexion structure (not shown) which is sandwiched between the first and second substrates. Similarly, the lines Vx of the part P2 of the matrix <NUM> are coupled to the circuit READOUT2, for example thank to same interconnexion structure. In <FIG>, only one line Vx is represented in dashed line, in each part P1, P2 of the matrix <NUM>.

Preferably, as shown in <FIG>, the circuit READOUT1 is disposed below the part P1 of the matrix <NUM>, the circuit READOUT2 being disposed below the part P2 of the matrix.

The embodiment of <FIG> allows to get a more compact sensor <NUM>''.

Preferably, the second substrate further comprises digital circuits, for example in CMOS technology, for example a circuit for processing signals provided by the circuits READOUT1 and READOUT2 in order to generate a depth map of a scene.

<FIG> illustrates an alternative embodiment of the indirect time of flight sensor <NUM>'' of the <FIG>. Only the differences between the sensor <NUM>" of <FIG> and the sensor <NUM>" of <FIG> are detailed. In <FIG>, the two parts P1 and P2 of the matrix <NUM> are spaced from each other to simplify the illustration of the sensor <NUM>'', although, in practice, these two parts P1 and P2 are adjacent to each other, the part P1 being disposed along the part P2, similarly to what has been described in relation with <FIG>.

In this alternative embodiment, a first semiconductor substrate comprises the matrix <NUM>, and lies on a second semiconductor substrate. In other words, the two substrates are stacked one over the other.

The sensor <NUM>'' further comprises commutators <NUM>, only one of the commutators <NUM> being referenced in <FIG> in order to avoid surcharging the Figure. The commutators <NUM> belong to the second substrate. Preferably, the commutators <NUM> are disposed below the limit between the two parts P1 and P2 of the matrix <NUM>. The sensor <NUM>'' comprises as much commutators <NUM> as the half P1 of the matrix <NUM> comprises lines Vx.

Each commutator <NUM> comprises a first input <NUM>, a second input <NUM>, an output <NUM> and is controlled by a signal Sel. Each commutator <NUM> is configured to electrically couple its input <NUM> to its output <NUM> when signal Sel is in a first state, and to couple its input <NUM> to its output <NUM> when signal Sel is in a second state.

In the alternative embodiment illustrated by <FIG>, each commutator <NUM> has its input <NUM> connected to a line Vx of the part P1 of the matrix <NUM>, and its input <NUM> connected to a corresponding line Vx of the part P2 of the matrix <NUM>. A line Vx of the part P2 corresponds to a line Vx of the part P1 when these two lines belong to the same column of the matrix <NUM>. In each column of the matrix <NUM>, a line Vx of the part P2 of the matrix <NUM> corresponds to a line Vx of the part P1 of the matrix <NUM>, for example, when the line Vx of the part P1 is selectively coupled to given outputs of the pixels of the part P1 disposed in this column, and the line Vx of part P2 is selectively coupled to corresponding outputs of the pixels of the part P2 disposed in said column.

In this alternative embodiment, instead of the two circuits READOUT1 and READOUT2, the sensor <NUM>" comprises only one reading circuit READOUT3. Preferably, the circuit READOUT3 belongs to the same substrate as the commutators <NUM>. Although in <FIG>, the lines Vx of the part P1 seems to pass through the circuit READOUT3, as represented by portions of the lines Vx in dashed lines, in practice this is not the case. Preferably, a reference voltage GND applied to the circuit READOUT3 is provided by a bonding pad <NUM> of the sensor <NUM>'', which receives the off-chip reference voltage GND and acts as a low-pass filter as schematically represented in <FIG> by a resistance R and an inductance L series-connected in the bonding pad <NUM>.

Each commutator <NUM> has its outputs <NUM> coupled, preferably connected, to the circuit READOUT3. The circuit READOUT3 for example comprises an ADC for each commutator <NUM>.

A control circuit, for example the circuit CTRL1'', is configured to control the commutators <NUM> such that the output <NUM> of each commutator is coupled to the input <NUM> of this commutator during a reading of pixels of the half P1 of the matrix, and to the input <NUM> of this commutator during a reading of pixels of the half P2 of the matrix. Said in other words, the circuit for controlling the commutators, in this example the circuit CTRL1'', is configured to provide the signal Sel at its first state during a reading of pixels of the half P1 of the matrix, and at its second state during a reading of pixels of the half P2 of the matrix.

In sensor <NUM>'' of the <FIG>, when reading pixels of the part P1, respectively P2, of the matrix <NUM>, each line Vx of part P1, respectively P2, is coupled by a corresponding commutator <NUM> to the circuit READOUT3 which then receives output signals of theses pixels. Further, when reading pixels of the part P1, respectively P2, of the matrix <NUM>, the circuit READOUT3 is insulated from the lines Vx of part P2, respectively P1, by the commutators <NUM>.

Compared to the sensor <NUM>" described in relation with <FIG>, the sensor <NUM>'' of <FIG> is more compact as it comprises only one reading circuit.

<FIG> illustrates, in a very schematic manner, an implementation of the sensor <NUM>'' of <FIG> according to one embodiment. <FIG> is perspective view of the disposition of the circuit READOUT3 and the commutators <NUM> relative to the matrix <NUM>.

As already indicated in relation with <FIG>, the matrix <NUM> belongs to a first semiconductor substrate (not represented in <FIG>), and the commutators <NUM> belong to a second semiconductor substrate (not represented in <FIG>), the first substrate being stacked over the second substrate.

The lines Vx of the parts P1 and P2 of the matrix <NUM> are, for example, conductive lines of an interconnexion structure which is sandwiched between the first and second substrates, only one line Vx of the part P1 and one corresponding line Vx of the part P2 being represented in <FIG> in order to avoid surcharging the Figure.

The commutators <NUM> are disposed below the limit between the parts P1 and P2 of matrix <NUM>, or, said in other words, below the common edge of the parts P1 and P2 of the matrix <NUM>.

In this particular embodiment, the circuit READOUT3 belongs to the same substrate as the commutators <NUM>. The circuit READOUT3 is preferably disposed below the matrix <NUM>, for example below the part P2 of the matrix as represented in <FIG>.

Preferably, the second substrate further comprises digital circuits, for example in CMOS technology, for example a circuit for processing signals provided by the circuit READOUT3 in order to generate a depth map of a scene.

The embodiments described in relation with <FIG> and <FIG> for example correspond to a case where the pitch of the inputs of the circuit READOUT3, which are each connected to an output <NUM> of a corresponding commutator <NUM>, is equal to or narrower than the pitch of the pixels <NUM> of the matrix <NUM> between two adjacent column of the matrix <NUM>.

<FIG> illustrates another alternative embodiment of the sensor <NUM>'' of the <FIG>. Only the differences between the sensor <NUM>'' of <FIG> and the sensor <NUM>" of <FIG> are here detailed.

In this alternative embodiment, the sensor <NUM>'' comprises two reading circuits READOUT4 and READOUT5 instead of the reading circuit READOUT3. Preferably, the circuits READOUT4 and READOUT5 belong to the same substrate as the commutators <NUM>. Although in <FIG>, the lines Vx of the part P1, respectively P2, seems to pass through the circuit READOUT4, respectively READOUT5, as represented by portions of the lines Vx in dashed lines, in practice this is not the case. Preferably, a reference voltage GND applied to the circuit READOUT4 is provided by a bonding pad <NUM> of the sensor <NUM>'', and a reference voltage GND applied to the circuit READOUT5 is provided by a bonding pad <NUM> of the sensor <NUM>''. Each bonding pad <NUM> and <NUM> receives the off-chip reference voltage GND and acts as a low-pass filter, as schematically represented in <FIG> by a resistance R and an inductance L series-connected in each bonding pad.

As in <FIG>, each commutator <NUM> has its input <NUM> connected to a line Vx of the part P1 of the matrix and its input <NUM> connected to a corresponding line Vx of the part P2 of the matrix.

However, in the embodiment of <FIG>, each commutator <NUM> connected to lines Vx of an odd column of the matrix <NUM> has its output <NUM> connected to the circuit READOUT4, whereas each commutator <NUM> connected to lines Vx of an even column of the matrix <NUM> has its output <NUM> connected to the circuit READOUT5. Each circuit READOUT4, REDAOUT5 for example comprises an ADC for each commutator <NUM> coupled, preferably connected, to this circuit.

As already indicated in relation with <FIG>, a control circuit, for example the circuit CTRL1'', is configured to control the commutators <NUM> such that the output <NUM> of each commutator is coupled to the first input <NUM> of this commutator during a reading of pixels of the half P1 of the matrix, and to the second input <NUM> of this commutator during a reading of pixels of the half P2 of the matrix.

In the sensor <NUM>'' of <FIG>, when reading pixels of the part P1, respectively P2, of the matrix <NUM>, each line Vx of part P1, respectively P2, is coupled by a corresponding commutator <NUM> to the circuit READOUT4 when this line Vx belongs to an odd column of the matrix <NUM> and to the circuit READOUT5 when this line Vx belongs to an even column of the matrix <NUM>, such that each output signal of each of these pixels is received either by the circuit READOUT4 or the circuit READOUT <NUM>. Further, during a reading of pixels of part P1, respectively P2, circuits READOUT4 and READOUT5 are insulated from the lines Vx of part P2, respectively P1, by the commutators <NUM>.

Preferably, the commutators <NUM> are disposed below the limit between the parts P1 and P2 of the matrix <NUM>. Preferably, the circuit READOUT4 is disposed below one of the parts P1 and P2 of the matrix <NUM>, the circuit READOUT5 being disposed below the other one of the parts P1 and P2.

<FIG> illustrates, in a very schematic manner, an implementation of the sensor <NUM>'' of <FIG> according to one embodiment. <FIG> is perspective view of the disposition of the circuits READOUT4 and READOUT5 and of the commutators <NUM> relative to the matrix <NUM>.

The lines Vx of the parts P1 and P2 of the matrix <NUM> are for example conductive lines of an interconnexion structure which is sandwiched between the first and second substrates, only one line Vx of the part P1 and one corresponding line Vx of the part P2 being represented in <FIG> in order to avoid surcharging the Figure.

The commutator <NUM> are disposed below the limit between the parts P1 and P2 of matrix <NUM>, or, said in other words, below the common edge of the parts P1 and P2 of the matrix <NUM>.

In this particular embodiment, circuits READOUT4 and REDAOUT5 belong to the same substrate as the commutators <NUM>. The circuit READOUT4 is disposed below one of the parts P1 and P2 of the matrix <NUM>, the circuit READOUT5 being disposed below the other one of the parts P1 and P2. In the example of <FIG>, the circuit READOUT4 is disposed below the part P1 of the matrix, the circuit READOUT5 being disposed below the part P2 of the matrix.

Preferably, the second substrate further comprises digital circuits, for example in CMOS technology, for example a circuit for processing signals provided by the circuits READOUT4 and READOUT5 in order to generate a depth map of a scene.

The embodiments described in relation with <FIG> and <FIG> for example correspond to a case where the pitch of the inputs of the circuits READOUT4 and READOUT5, which are each connected to an output <NUM> of a corresponding commutator <NUM>, is larger than the pitch of the pixels <NUM> of the matrix <NUM> between two adjacent column of the matrix <NUM>.

Various embodiments and variants have been described. Those skilled in the art will understand that certain features of these embodiments can be combined and other variants will readily occur to those skilled in the art. In particular, although in the above described embodiments, the scene to capture divided in only four areas S1, S2, S3 and S4, the illumination device <NUM> is configured to direct the light towards each of the areas S1, S2, S3, S4 of the scene by illuminating only one area at a time, and the matrix <NUM> is divided in four corresponding areas M1, M2, M3 and M4, those skilled in the art are capable to implement embodiment wherein the scene is divided into more (or less) than four areas, the device <NUM> is configured to independently illuminate each of these areas of the scene, and the matrix <NUM> is divided in areas such that each area of the matrix corresponds to an area of the scene. Further, those skilled in the art are capable of implementing embodiments in which the pixels of the matrix <NUM> are different from pixel <NUM> described in relation with <FIG>, and in more for a specific example in relation with <FIG> and <FIG>.

Claim 1:
An indirect time of flight sensor (<NUM>; <NUM>'; <NUM>'') comprising:
a matrix (<NUM>) of pixels (<NUM>) each comprising a photoconversion region (PD) and at least two sets (E1; E2) each comprising a charge storage region (mem1; mem2) and
a controllable transfer device (TGmem1; TGmem2) for transferring charges from the photoconversion region (PD) towards said storage region (mem1; mem2) when its control signal (TG1, TG2) is active;
first conductive lines (<NUM>) parallel to each other, configured to transmit first control signals (TG1; TG2) to the transfer devices (TGmem1; TGmem2);
a first circuit (CTRL1; CTRL1'; CTRL1") configured to provide the first control signals (TG1; TG2) to the first conductive lines (<NUM>);
an illumination device (<NUM>) for illuminating a scene to capture; and
a second circuit (CTRL2) configured to control the illumination device (<NUM>),
wherein:
the scene is divided into first areas (S1, S2, S3, S4);
the illumination device (<NUM>) and the second circuit (CTRL2) are configured to illuminate successively each first area (S1, S2, S3, S4);
the matrix (<NUM>) is divided into second areas (M1, M2, M3,
M4) each comprising adjacent lines of pixels (<NUM>), parallel to the first conductive lines (<NUM>);
a disposition of the matrix (<NUM>) and of the illumination device (<NUM>) is configured such that each first area (S1, S2, S3, S4) corresponds to one of the second areas (M1, M2, M3, M4); characterised in that the first circuit (CTRL1) is configured to provide different first control signals (TG1, TG2) to the different second areas (M1, M2, M3, M4) such that the first control signals (TG1, TG2) are repeatedly commuted between active and inactive states only for the pixels (<NUM>) of the second area (M1, M2, M3, M4) of the matrix (<NUM>) corresponding to the first area (S1, S2, S3, S4) of the scene which is illuminated.