Depth pixel of three-dimensional image sensor and three-dimensional image sensor including the same

A depth pixel includes a photo detection unit, an ambient light removal current source, a driving transistor and a select transistor. The photo detection unit is configured to generate a light current based on a received light reflected from a subject, the received light including an ambient light component. The ambient light removal current source configured to generate a compensation current indicating the ambient light component in response to a power supply and at least one compensation control signal. The driving transistor is configured to amplify an effective voltage corresponding to the light current and the compensation current. The select transistor configured to output the amplified effective voltage in response to a selection signal, the amplified effective voltage indicating a depth of the subject.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority under 35 USC §119 to Korean Patent Application No. 2012-0154733, filed on Dec. 27, 2012, in the Korean Intellectual Property Office (KIPO), the contents of which are herein incorporated by reference in their entirety.

BACKGROUND

1. Technical Field

Example embodiments relate to a depth pixel of a three-dimensional image sensor and the three-dimensional image sensor including the same.

2. Description of the Related Art

An image sensor is a semiconductor device configured to convert an optical signal, received incident to the image sensor from the outside, into an electrical signal, and provides image information corresponding to the optical signal. Recently, research on a three-dimensional image sensor for providing distance information as well as image information based on the optical signal has been actively performed. In general, the three-dimensional image sensor may measure distances between depth pixels and a subject by measuring a Time Of Flight (TOF), which is a travel time of a laser pulse taken until the laser pulse reflected back to its origination after irradiation onto the subject.

SUMMARY

Some example embodiments provide a depth pixel of a three-dimensional image sensor, capable of exactly measuring a distance to a subject even when an ambient light is relatively strong.

Some example embodiments provide a three-dimensional image sensor capable of exactly measuring a distance to a subject even when an ambient light is relatively strong.

According to example embodiments, a depth pixel includes a photo detection unit, an ambient light removal current source, a driving transistor and a select transistor. The photo detection unit generates a light current based on a received light reflected from a subject. The ambient light removal current source generates an ambient light component included in the received light in response to a power supply and at least one compensation control signal. The driving transistor amplifies an effective voltage corresponding to the light current and the compensation current. The select transistor outputs the amplified effective voltage as depth information in response to a selection signal.

The ambient light removal current source may include a first transistor connected between the power supply and the photo detection unit and including a gate terminal to which a first compensation control signal is applied. The driving transistor and the select transistor may include a first type transistor and the first transistor may include a second type transistor different from the first type transistor.

The first compensation control signal may be activated in a preset period, and a magnitude of the compensation current may be inversely proportional to a period of the first compensation control signal and proportional to a length of an activation period of the first compensation control signal.

The period and an activation level of the first compensation control signal may be changed depending on an ambient light.

The ambient light removal current source may include a second transistor and a third transistor. The second transistor may be connected between the power supply and the first transistor and may include a gate terminal to which a second compensation control signal is applied. The third transistor may be connected between the first transistor and the photo detection unit and may include a gate terminal to which a third compensation control signal is applied. The second transistor and the third transistor may include the second type transistor, respectively.

The first compensation control signal may maintain an activation state, and the second compensation control signal and the third compensation control signal may be sequentially activated.

The depth pixel may further include a transfer transistor and a reset transistor. The transfer transistor may be connected between the photo detection unit and a floating diffusion node and may include a gate terminal to which a transfer control signal is applied. The reset transistor may be connected between the power supply and the floating diffusion node and may include a gate terminal to which a reset signal is applied. A gate terminal of the driving transistor may be connected to the floating diffusion node, and the ambient light removal current source may be connected between a first node, to which the photo detection unit and the transfer transistor are connected, and the power supply.

The depth pixel may further include a photo transistor formed on the photo detection unit to control the generation of the light current in response to a photo control signal.

The depth pixel may further include a transfer control transistor connected between the gate terminal of the transfer transistor and the transfer control signal and including a gate terminal to which the selection signal is applied.

The depth pixel may further include a transfer transistor connected between the photo detection unit and a floating diffusion node and including a gate terminal to which a transfer control signal is applied. A gate terminal of the driving transistor may be connected to the floating diffusion node, and the ambient light removal current source may be connected between the power supply and the floating diffusion node.

The depth pixel may further include a refresh transistor connected between a first node, to which the photo detection unit and the transfer transistor are connected, and the power supply, and including a gate terminal to which a refresh control signal is applied.

According to example embodiments, a three-dimensional image sensor includes a light source unit and a pixel array. The light source unit irradiates a modulated transmission light to a subject. The pixel array includes a plurality of depth pixels to generate distance information between the three-dimensional image sensor and the subject based on a received light reflected from the subject. Each of the depth pixels includes a photo detection unit, an ambient light removal current source, a driving transistor and a select transistor. The photo detection unit generates a light current based on a received light. The ambient light removal current source generates an ambient light component included in the received light in response to a power supply and at least one compensation control signal. The driving transistor amplifies an effective voltage corresponding to the light current and the compensation current. The select transistor outputs the amplified effective voltage as the distance information in response to a selection signal.

The ambient light removal current source may include a first transistor connected between the power supply and the photo detection unit and including a gate terminal to which a first compensation control signal is applied.

The three-dimensional image sensor may initialize a period and an activation level of the first compensation control signal, may acquire an offset of the receive light based on the first compensation control signal having the initialized period and the initialized activation level, and may compare the acquired offset with a reference offset to determine an optimized period and an optimized activation level of the first compensation control signal.

When the acquired offset is greater than the reference offset, the three-dimensional image sensor may reduce a current period and a current activation level of the first compensation control signal, and may repeat an operation of acquiring the offset of the received light and an operation of comparing the acquired offset with the reference offset based on the first compensation control signal having the reduced period and the reduced activation level, and when the acquired offset is less than the reference offset, the three-dimensional image sensor may select a current period and a current activation level of the first compensation control signal as the optimized period and the optimized activation level of the first compensation control signal.

In the depth pixel of the three-dimensional image sensor according to example embodiments as described above, a compensation current for removing an ambient light component included in a received light is generated in response to a compensation control signal, and the compensation current is generated based on a compensation charge having a polarity opposite to a polarity of a photo charge collected by a photo detection unit. Accordingly, the depth pixel and the three-dimensional image sensor including the same can exactly measure a distance between the three-dimensional image sensor and the subject without saturating the photo detection unit.

At least one example embodiment relates to a depth pixel.

In one embodiment, the depth pixel includes a photo detector configured to generate a current based on an amount of incident light reflected onto the photo detector from a subject, the incident light including an ambient light component; and a current source configured to adjust the generated current to compensate for the ambient light component such that an output voltage indicates a distance between the depth pixel and the subject.

In one embodiment, the current source is configured to adjust the generated current by generating a compensation current in response to a compensation control signal, the compensation control signal being a pulse having a magnitude and a period, the period including an on-time during which the current source is activated, and during a light collection period, the depth pixel is configured to vary one or more of the period of the compensation signal, the on-time of the compensation signal and the magnitude of the compensation signal according to an intensity of the ambient light component.

In one embodiment, the current source is configured to generate the compensation current such that a magnitude of the compensation current varies inversely with the period of the compensation control signal and the magnitude of the compensation current varies directly with a length of the on-time of the compensation control signal.

In one embodiment, the photo detector is configured to detect the incident light in response to a photo control signal, and wherein the photo control signal and a light transmitted onto the subject both have a first phase, and the incident light reflected onto the photo detector has a second phase that is different from the first phase, and a phase difference between the first phase and the second phase indicates a time of flight for a signal to travel between the depth pixel and the subject.

In one embodiment, during a read period after the light collection period, the depth pixel is configured to, sample voltages at a floating diffusion node after transferring the adjusted current to the floating diffusion node, the floating diffusion node connected to the photo detector and the current source; determine the phase difference based on the sampled voltages; and determine the distance between the depth pixel and the subject based on the determined phase difference and a frequency of the incident light.

DETAILED DESCRIPTION OF THE EMBODIMENTS

FIG. 1is a diagram illustrating a depth pixel of a three-dimensional image sensor according to example embodiments.

Referring toFIG. 1, a depth pixel100included in a three-dimensional image sensor includes a photo detection unit110, an ambient light removal current source120, a driving transistor TD, and a select transistor TS.

The photo detection unit110generates a light current Iph based on a received light RX. The received light RX may correspond to a light, which is emitted from a light source unit included in the three-dimensional image sensor and reflected from the subject to the three-dimensional image sensor.

The ambient light removal current source120generates a compensation current Ialc in response to a power supply VDD and at least one compensation control signal CCS. The compensation current Ialc is used to remove an ambient light component included in the received light RX. The ambient light removal current source120may be implemented with at least one transistor, and may be directly or indirectly connected with the photo detection unit110.

The driving transistor TD amplifies an effective voltage Ve corresponding to a sum of a light current Iph and a compensation current Ialc. The select transistor TS outputs the amplified effective voltage Ve as depth information in response to a selection signal SEL. The driving transistor TD includes a gate terminal to which the effective voltage Ve is applied, and the gate terminal may be directly or indirectly connected to the ambient light removal current source120. The select transistor TS may include a gate terminal to which the selection signal SEL is applied. The amplified effective voltage Ve is provided to an output line OL, and the output line OL may correspond to a column line of a pixel array of the three-dimensional image sensor.

FIG. 2illustrating an example of a circuit diagram of the depth pixel of the three-dimensional image sensor shown inFIG. 1.

Referring toFIG. 2, the depth pixel100aincludes a photo detection unit110, an ambient light removal current source120a, a driving transistor TD, and a select transistor TS, and may further include a photo transistor TP, a transfer transistor TT, and a reset transistor TR.

The photo detection unit110may generate photo charges based on light RX received from outside the depth pixel100a. The light current Iph may be generated based on the photo charges. For example, the photo detection unit110may include a photo diode, a pinned photo diode, and may be formed by doping a semiconductor substrate with an impurity having conductivity opposite to that of the semiconductor substrate through an ion implantation process.

The photo transistor TP (or photo gate) is formed on the photo detection unit110, and may control the generation of the light current Iph in response to a photo control signal PGC. When the photo transistor TP is turned-on, the photo detection unit110may detect an incident light to generate the photo charges. In contrast, when the photo transistor TP is turned-off, the photo detection unit110may not detect the incident light.

The ambient light removal current source120amay include a first transistor T1. The first transistor T1 is connected between the power supply VDD and the photo detection unit100(that is, first node N0), and may include a gate terminal to which a first compensation control signal CCS1is applied. The first transistor T1 may control generation of the compensation current Ialc.

In the example embodiments, the first transistor T1 may be implemented by a type different from types of other transistors TP, TT, TR, TD, and TS. That is, the transistors TP, TT, TR, TD, and TS may include a first type transistor, and the first transistor T1 may include a second type transistor different from the first type transistor. For example, when an N type impurity is doped into a P type semiconductor substrate to form the photo detection unit110, that is, when the photo detection unit110collects electrons based on the received light RX, the transistors TP, TT, TR, TD may be an NMOS transistor and the first transistor T1 may be a PMOS transistor.

According to the example embodiments, the first transistor T1 may be the NMOS transistor and the transistors TP, TT, TR, and TD may be the PMOS transistor.

The transfer transistor TT is connected between the photo detection unit110(that is, first node NO) and a floating diffusion node FDN, and may include a gate terminal to which a transfer control signal TGC is applied. The transfer transistor TT may transmit photo charges, which remain from among the photo charges generated by the photo detection unit110without being extinguished by charges introduced from the first transistor T1, to the floating diffusion node FDN in response to the transfer control signal TGC.

The reset transistor TR is connected between the power supply VDD and the floating diffusion node FDN, and may include a gate terminal to which a reset signal RST is applied. The reset transistor TR may discharge charges stored in the floating diffusion node FDN in response to a reset signal RST.

The driving transistor TD and the select transistor TS may be serially connected between the power supply VDD and an output line OL. The gate terminal of the driving transistor TD may be connected to the floating diffusion node FDN. The select transistor TS may provide a voltage VFD of the floating diffusion node FDN amplified by the driving transistor TD to the output line OL.

FIG. 3is a timing chart illustrating an operation of the depth pixel shown inFIG. 2according to an example embodiment.

Referring toFIGS. 2 and 3, a modulated transmission light TX irradiated onto the subject is reflected from the subject and reaches the depth pixel100aas the received light RX during a light collection period TINT. The received light RX is delayed by a Time of Flight (TOF) as compared with the transmission light TX. The photo detection unit110generates photo charges according to the received light RX so that the light current Iph is generated.

The photo control signal PGC having a periodically variable intensity during the light collection period TINT has the same phase as that of the transmission light TX. The TOF may be determined by acquiring an amount of a photo charge Q corresponding to an activation period of the photo control signal PGC from among the photo charges generated by the photo detection unit110according to the received light RX. In this case, the first compensation control signal CCS1is activated in a preset period Trf during the light collection period TINT. The first transistor T1 generates compensation charges (that is, holes) having a polarity opposite to polarities of the photo charges (that is, electrons) and the compensation charges are applied to the photo detection unit110so that the compensation current Ialc is generated during an activation period tbc of the first compensation control signal CCS1(that is, while the first transistor T1 is turned-on). Some of collected electrons combined with the holes are extinguished, so that an ambient light component included in the received light RX is removed. For example, photo charges corresponding to an amount of the compensation charge Q′ corresponding to the activation period tbc of the first compensation control signal CCS1are extinguished from among the photo charges generated from the photo detection unit110according to the received light RX. According to the example embodiments, the photo charge Q and the compensation charge Q′ may be stored in a temporary storage area (not shown) such as a bridge diffusion node.

A magnitude of the compensation current Ialc generated in response to the first compensation control signal CCS1may satisfy a following Equation 1.

In the Equation 1, W, L, Cox, and Vthp represent a channel width, a length of the first transistor T1, capacitance and a threshold voltage level of an oxide, respectively, μp represents mobility of a hole, and the tbc, Trf, VDD, and Vbc represent a length of an activation period, a period, an inactivation level, and an activation level of the first compensation control signal CCS1, respectively. The activation level and the inactivation level represent voltage levels of the first compensation control signal CCS1when the first transistor T1 is turned-on and turned-off.

As illustrated in the equation 1, the magnitude of the compensation current Ialc may be inversely proportional to the preset period Trf of the first compensation control signal CCS1and proportional to the length of the activation period tbc of the first compensation control signal CCS1. According to the example embodiments, the preset period Trf, the activation period tbc and the magnitude Vbc of the first compensation control signal CCS1may be changed according to an intensity of the ambient light, which will be described with reference toFIGS. 15 and 16.

If a read period TRD for measuring an amount of the collected photo charge starts, the reset signal RST is firstly activated so that the floating diffusion node FDN is reset. Next, if a first sampling control signal SMPB is activated, a voltage of the floating diffusion node FDN is detected as a noise voltage VB. After the noise voltage VB is detected, the transfer control signal TGC is activated so that remaining photo charges, which are not extinguished due to the compensation charge Q′, are transmitted to the floating diffusion node FDN. After that, if a second sampling control signal SMPD is activated, a voltage VFD of the floating diffusion node FDN is detected as a demodulation voltage VD. A difference between the demodulation voltage VD and the noise voltage VB may correspond to actual distance information.

FIG. 4is a circuit diagram illustrating another example of the depth pixel of the three-dimensional image sensor shown inFIG. 1according to an example embodiment.

Referring toFIG. 4, a depth pixel200amay include a first half pixel and a second half pixel symmetrical to each other.

The first and second half pixels have substantially the same structure as that of the depth pixel100ashown inFIG. 2. The first half pixel may include a first photo detection unit210a, a first ambient light removal current source220a, a first photo transistor TP1, a first transfer transistor TT1, a first reset transistor TR1, a first driving transistor TD1, and a first select transistor TS1. The second half pixel may include a second photo detection unit210b, a second ambient light removal current source220b, a second photo transistor TP2, a second transfer transistor TT2, a second reset transistor TR2, a second driving transistor TD2, and a second select transistor TS2.

The depth pixel200aofFIG. 4may precisely calculate the TOF by using a plurality of photo control signals PGC1and PGC2, at least one of which having a phase different from that of the transmission light TX. For example, the depth pixel200amay acquire distance information using the first photo control signal PGC1having the same phase as that of the transmission light TX and the second photo control signal PGC2having a phase (that is, a phase difference of 180°) opposite to that of the transmission light TX. Accordingly, the respective half pixels may periodically repeat a charge collecting operation during a light collection period.

FIG. 5is a circuit diagram illustrating an example of the depth pixel of the three-dimensional image sensor shown inFIG. 1according to an example embodiment.

The depth pixel100bofFIG. 5may have a same structure as the depth pixel100aofFIG. 2except that a structure of the ambient light removal current source120bis changed. The ambient light removal current source120bmay include a first transistor T2, a second transistor T3, and a third transistor T4. The first transistor T2, the second transistor T3, and the third transistor T4 may be serially connected to each other between the power supply VDD and a photo detection unit110. For example, the first transistor T2 may be disposed at a central part of the ambient light removal current source120b, the second transistor T3 may be connected between the power supply VDD and the first transistor T2, and the third transistor T4 may be connected between the second transistor T3 and the photo detection unit110(that is, first node N0). The first to third transistors T2, T3, and T4 may include gate terminals to which a first compensation control signal CCS2, a second compensation control signal CCS3, and a third compensation control signal CCS4are applied, respectively.

In the example embodiments, the first to third transistors T2, T3, and T4 may be implemented with a type different from types of other transistors TP, TT, TR, TD, and TS. For example, the transistors TP, TT, TR, TD, and TS may be an NMOS transistor, and the transistors T2, T3, and T4 may be a PMOS transistor.

FIG. 6is a timing chart illustrating an operation of the depth pixel shown inFIG. 5according to an example embodiment.

Referring toFIGS. 5 and 6, a first compensation control signal CCS2maintains an activation state during the light collection period TINT. Second and third compensation control signals CCS3and CCS4may be activated in a preset period Trf and be sequentially activated. For example, the second compensation control signal CCS3may be firstly activated and then the third compensation control signal CCS5may be activated. Each period of the second and third compensation control signals CCS3and CCS4may be substantially the same as a length of the activation period tbc. Compensation charges having a polarity opposite to those of photo charges are generated during the activation period tbc of the second compensation control signal CCS3. The compensation charges are applied to the photo detection unit110so that the compensation current Ialc is generated during the activation period tbc of the third compensation control signal CCS4. In this case, the magnitude of the compensation current Ialc is inversely proportional to the period of the second and third compensation control signals CCS3and CCS4and proportional to the length of the activation period tbc of the second and third compensation control signals CCS3and CCS4, and the period Trf and the activation level Vbc of the second and third compensation control signals CCS3and CCS4may be changed according to an intensity of the ambient light. Photo charges corresponding to an amount of the compensation charge Q′ corresponding to the activation period tbc of the second and third compensation control signal CCS3and CCS4are extinguished from among the photo charges so that the ambient light component included in the received light RX is removed.

The depth pixel100aofFIG. 2turns-on/off the transistor T1 serving as a current source based on a control signal CCS1. In contrast, in the depth pixel100bofFIG. 5, the second transistor T2 serving as the current source is always in a turning-on state, and two transistors T3 and T4 which are sequentially turned-on are disposed at both sides of the current source, so the compensation current Ialc may be efficiently generated.

FIGS. 7 and 8are circuit diagrams illustrating other examples of the depth pixel of the three-dimensional image sensor shown inFIG. 1according to an example embodiment.

The depth pixel100cofFIG. 7may have a same structure as the depth pixel100aofFIG. 2except that the photo transistor is omitted. In this case, the transfer control signal TGC has a periodically variable intensity during the light collection period TINT like the photo control signal PGC ofFIG. 3, and the transfer transistor TT may control generation of the light current Iph in response to the transfer control signal TGC.

The depth pixel100dofFIG. 8may be equal to the depth pixel100aofFIG. 2except that the transfer control transistor TTC is further included therein. The transfer control transistor TTC is connected between a gate terminal of the transfer transistor TT and the transfer control signal TGC, and may include a gate terminal to which a selection signal SEL is applied. The transfer control transistor TTC may selectively apply the transfer control signal TGC to the transfer transistor TT in response to a selection signal SEL.

According to the example embodiments, the ambient light removal current source120ashown inFIGS. 7 and 8may be replaced with the ambient light removal current source120bshown inFIG. 5.

FIG. 9is a circuit diagram illustrating another example of the depth pixel of the three-dimensional image sensor shown inFIG. 1according to an example embodiment.

Referring toFIG. 9, the depth pixel100eincludes a photo detection unit110, an ambient light removal current source120c, a driving transistor TD, and a select transistor TS, and may further include a transfer transistor TT.

In an example embodiment ofFIG. 9, the ambient light removal current source120cmay remove an ambient light component and resets a floating diffusion node FDN. The ambient light removal current source120cis connected between the power supply VDD and the floating diffusion node FDN, and may include a first transistor T2, a second transistor T3, and a third transistor T4. The transistors T2, T3, and T4 may be serially connected to each other between the power supply VDD and the floating diffusion node FDN. For example, the first transistor T2 may be disposed at a central part of the ambient light removal current source120c, the second transistor T3 may be connected between the power supply VDD and the first transistor T2, and the third transistor T4 may be connected between the second transistor T3 and the floating diffusion node FDN. The first to third transistors T2, T3, and T4 may include gate terminals to which a first compensation control signal CCS2, a second compensation control signal CCS3, and a third compensation control signal CCS4are applied, respectively. The transistors T2, T3, and T4 may be implemented by a type different from types of transistors TT, TD, and TS.

FIG. 10is a timing chart illustrating an operation of the depth pixel shown inFIG. 9according to an example embodiment.

Referring toFIGS. 9 and 10, the compensation control signals CCS2, CCS3, and CCS4are all activated before the light collection period TINT so that the floating diffusion node FDN is reset. A transmission light TX irradiated to the subject is reflected from the subject during the light collection period TINT and reaches the depth pixel100eas a received light RX. Photo charges are generated from the photo detection unit110based on the received light RX. A photo charge Q1 corresponding to an activation period of the transfer control signal TGC is stored in the floating diffusion node FDN in response to the transfer control signal TGC which periodically varies during the light collection period TINT and has the same phase as that of the transmission light TX. A first compensation control signal CCS2maintains an activation state during the light collection period TINT. Second and third compensation control signals CCS3and CCS4may be sequentially activated in a preset period Trf. Compensation charges having polarity opposite to that of photo charges are generated during the activation period tbc of the second compensation control signal CCS3. The compensation charges are applied to the floating diffusion node FDN so that the compensation current Ialc is generated during an activation period tbc of the third compensation control signal CCS4. Accordingly, the ambient light component included in the received light RX is removed.

FIGS. 11 and 12are circuit diagrams illustrating other examples of the depth pixel of the three-dimensional image sensor shown inFIG. 1according to an example embodiment.

The depth pixel100fofFIG. 11may be equal to the depth pixel100aofFIG. 2except that a refresh transistor TRF is further included therein. The refresh transistor TRF is connected between the power supply VDD and the photo detection unit110, that is, between the power supply VDD and a first node NO, and may include a gate terminal to which a refresh control signal RFC is applied. The refresh transistor TRF may discharge a photo charge generated from the photo detection unit110to the power supply VDD from the first node NO in response to the refresh control signal RFC. For example, when an ambient light is relatively strong, the refresh transistor TRF is selectively turned-on so that some of photo charges generated from the photo detection unit110may be discharged to the power supply VDD at least once. When the ambient light is relatively weak, the refresh transistor TRF is continuously turned-off so that the discharge of the photo charges to the power supply VDD may be blocked.

The depth pixel100gofFIG. 12may have a same structure as the depth pixel100aofFIG. 2except that the transfer control transistor TTC is further included therein.

According to the example embodiments, the ambient light removal current source120cshown inFIGS. 9,11, and12may be replaced with the ambient light removal current source120ahaving the same configuration as that shown inFIG. 2. Meanwhile, a depth pixel according to the example embodiments may be implemented with a first half pixel and a second half pixel symmetrical to each other as illustrated inFIG. 4. In this case, one half pixel may correspond to depth pixels shown inFIGS. 5,7,8,9,11, and12.

As described above, the ambient light removal current source included in the depth pixel according to the example embodiments may be directly connected to the photo detection unit110as shown inFIGS. 2,5,7, and8or indirectly connected to the photo detection unit110(that is, the floating diffusion node FDN). The gate terminal of the driving transistor TD may be directly (FIGS. 2,5,7, and8) or indirectly (FIGS. 9,11, and12) connected to the ambient light removal current source according to a construction of the ambient light removal current source.

FIG. 13is a block diagram illustrating a three-dimensional image sensor according to example embodiments.

Referring toFIG. 13, a three-dimensional image sensor300may include a pixel array310and a light source unit340, and may further include a row driver (RD)320, an analog-to-digital converter (ADC)330, a digital signal processor (DSP)350, and a control unit360.

The light source unit340may output a modulated transmission light TX (e.g., infrared light or near infrared light) having a predetermined wavelength, and irradiate the modulated transmission light TX to a subject380. The light source unit340may include a light source341and a lens343. For example, the light source341may output the modulated transmission light TX such as a sine wave where intensity periodically varies. The lens343may concentrate the transmission light TX onto the subject380.

The pixel array310may include a plurality of depth pixels311. The pixel array310may generate distance information between the three-dimensional image sensor and the subject380based on the received light RX reflected from the subject380. For example, the received light RX may be generated based on an infrared light or a near infrared light TX and/or an infrared light, a near infrared light, and a visible light.

Each of the depth pixels311may be the depth pixel100ofFIG. 1, and may be implemented by one of the depth pixels100a,200a,100b,100c,100d,100e,100f, and100gshown inFIGS. 2,4,5,7,8,9,11, and12. That is, each of the depth pixels311includes an ambient light removal current source for generating a compensation current Ialc to remove an ambient light component included in the received light RX in response to at least one compensation control signal CCS, to accurately measure a distance to the subject when an ambient light is relatively strong.

According to the example embodiments, the pixel array310may further include a plurality of color pixels (not shown) for providing color image information. In this case, the three-dimensional image sensor300may include a three-dimensional for simultaneously provide the color image information and the depth information.

The row driver320is connected to each row of the pixel array310, and may generate a driving signal for driving each row. The ADC330is connected to each column of the pixel array310, and may convert an analog signal output from the pixel array310into a digital signal. According to the example embodiments, the ADC330may include a correlation dual sampling (CDS) unit (not shown) for extracting an effective signal component. The CDS unit may perform an analog double sampling, a digital double sampling, or a dual correlation double sampling including analog and digital double samplings.

The DSP350may receive a digital signal output from the ADC330to process image data with respect to the digital signal. The control unit360may supply control signals for controlling the row driver320, the ADC330, the light source unit340, and the DSP350, and provide at least one compensation control signal CCS.

In the example embodiments, the control unit360may include a storage unit362. As described later with reference toFIGS. 15 and 16, the three-dimensional image sensor300may vary and optimize a period Trf and an activation level Vbc of at least one compensation control signal CCS. The storage unit362may store a period, an activation level, and a reference value (e.g., reference offset, a reference period, and a reference level) associated with the at least one compensation control signal CCS. For example, the storage unit362may include a volatile memory device such as dynamic random access memory (DRAM) and static random access memory (SRAM) and/or a non-volatile memory device such as a flash memory device, parameter random access memory (PRAM), ferroelectric random access memory (FRAM), resistive random access memory (RRAM), and magneto-resistive random access memory (MRAM). According to the example embodiments, the storage unit362may be disposed outside the control unit360or outside the three-dimensional image sensor300.

FIG. 14is a diagram illustrating an operation of calculating a distance between the three-dimensional image sensor shown inFIG. 13and a subject by the three-dimensional image sensor according to an example embodiment.

Referring toFIGS. 13 and 14, the transmission light TX emitted from the light source unit340may have a periodically variable intensity. For example, the intensity of the transmission light TX (that is, the number of photons per unit area) may have a form of a sine wave.

The transmission light TX is reflected from the subject380and is incident into the pixel array310as the received light RX. The pixel array310may periodically sample the received light RX. For example, the pixel array310may sample the received light RX at phases of 90°, 180°, 270°, and 360° of the transmission light TX in every period of the transmission light TX to extract sampling values A0, A1, A2, and A3.

The receiving light RX may have an offset B different from an offset of the transmission light TX according to additional ambient light and noise. The offset B of the received light RX may be calculated by a following Equation 2.

The received light RX may have amplitude A smaller than amplitude of the transmission light TX according to light loss. The amplitude of the received light RX may be calculated by a following Equation 3.

Depth information, that is, a three-dimensional image with respect to the subject380may be provided based on the amplitude of the received light RX with respect to the depth pixels311included in the pixel array310.

The received light RX is delayed with respect to the transmission light TX by a phase difference φ corresponding to twice of a distance between the three-dimensional image sensor300and the subject380. The phase difference φ of the received light RX with respect to the transmission light TX may be calculated by a following Equation 4.

The phase difference φ of the received light RX with respect to the transmission light TX corresponds to a TOF of light. The distance between the three-dimensional image sensor300and the subject380may be calculated by an Equation “R=c*TOF/2” (where, R represents a distance between the three-dimensional image sensor300and the subject380, and c represents speed of light). Further, the distance between the three-dimensional image sensor300and the subject380may be calculated by a following Equation 5 using the phase φ of the received light RX.

In the Equation 5, f represents a modulation frequency, that is, a frequency of the transmission light TX (or a frequency of the received light RX).

As described above, the three-dimensional image sensor300according to the example embodiments may acquire distance information with respect to the subject380using the transmission light TX emitted from the light source unit340.

FIGS. 15 and 16are flowcharts illustrating an operation of determining a period and an activation level of a compensation control signal in the three-dimensional image sensor shown inFIG. 13according to an example embodiment.

Referring toFIGS. 13 and 15, the three-dimensional image sensor may initialize a period Trf and an activation level Vbc of a compensation control signal CCS to determine the period Trf and the activation level Vbc of the compensation control signal CCS (S110). For example, the period Trf of the compensation control signal CCS may be initialized as a first period Trf1 corresponding to a maximum period and the activation level Vbc of the compensation control signal CCS may be initialized as a first level Vbc1 corresponding to a maximum activation level.

The three-dimensional image sensor may acquire an offset B of the received light RX based on the compensation control signal CCS having the initialized period (that is, first period Trf1) and the initialized activation level (that is, first level Vbc1) (step S120). For example, an offset B of the received light RX may be acquired based on the sampling operation with reference toFIGS. 3,6, and10and the foregoing Equation 2 with reference toFIG. 14.

The acquired offset B may be compared with a reference offset Vref to determine the optimized period and the optimized activation level of the compensation control signal CCS. For example, the reference offset Vref may be defined as “x*Vsat” (where, x represents a real number of 0 to 1, and Vsat represents a pixel saturation voltage).

In detail, when the acquired offset B is greater than the reference offset Vref (Yes of S130), the period Trf or the activation level Vbc of the compensation control signal CCS may be changed. When the activation level Vbc of the compensation control signal CCS is greater than a second level Vbc2 (Yes of step S140), the activation level Vbc of the compensation control signal CCS may be reduced from a current activation level by ΔV. When the activation level Vbc of the compensation control signal CCS is less than or equal to the second level Vbc2 (No of step S140), the period Trf of the compensation control signal CCS may be reduced from a current period by ΔT (step S160). When the activation level Vbc of the compensation control signal CCS is greater than the second level Vbc2 (Yes of step S140), the activation level Vbc may be reduced by ΔV (step S150).

In the example embodiment ofFIG. 15, a priority with respect to the change may be assigned to the activation level Vbc as compared with the period Trf. A step of acquiring the offset (step S120) and a step of comparing the acquired offset B with the reference offset Vref (step S130) may repeat based on the compensation control signal CCS having the changed (that is, reduced) period and the changed (that is, reduced) activation level.

When the acquired offset B is less than or equal to the reference offset Vref (No of step S130), a current period and a current activation level of the compensation control signal CCS may be selected as the optimized period and the optimized activation level of the compensation control signal CCS, respectively (step S170).

As illustrated inFIG. 16, when the period Trf of the compensation control signal CCS is greater than the second period Trf2 (Yes of step S140), the period Trf of the compensation control signal CCS may be reduced from a current period by ΔT (step S160). When the period Trf of the compensation control signal CCS is less than or equal to the second period Trf2 (No of step S140), the activation level Vbc of the compensation control signal CCS may be reduced from a current period by ΔT (step S150). In the example embodiment ofFIG. 16, a priority with respect to the change may be assigned to the period Trf as compared with the activation level Vbc.

The period Trf and the activation level Vbc of the compensation control signal CCS may be simultaneously changed.

FIG. 17is a block diagram illustrating an example of a camera including a three-dimensional image sensor according to example embodiments.

Referring toFIG. 17, the camera500includes a photo-receiving lens510, a three-dimensional image sensor520, a motor unit530, and an engine unit540. The three-dimensional image sensor520may be the three-dimensional image sensor ofFIG. 13, and may include a three-dimensional image sensor chip521and a light source module523.

The photo-receiving lens510may focus incident light on a photo-receiving region (e.g., depth pixels) of the three-dimensional image sensor chip521. The three-dimensional image sensor chip521may generate data DATA1 including depth information based on the incident visible light or infrared light passing through the photo-receiving lens510. The three-dimensional image sensor chip521may provide the data DATA1 to the engine unit540based on a clock signal CLK.

The motor unit530may adjust focus of the photo-receiving lens510or perform shuttering in response to a control signal CTRL. The engine unit540controls the three-dimensional image sensor520and the motor unit530, and provides data DATA2 to the host/application850based on a master clock MCLK.

FIG. 18is a block diagram illustrating an example of a computing system including the three-dimensional image sensor according to example embodiments.

Referring toFIG. 18, a computing system700may include a processor710, a memory device720, a storage device740, an input/output device750, and a power supply760.

The processor710may perform various calculations or tasks. According to example embodiments, the processor710may be a microprocessor or a CPU.

The memory device720may store data for operating the computing system700. For example, the memory device720may include a volatile memory device such as DRAM and SRAM and a non-volatile memory device such as a flash memory device, PRAM, FRAM, RRAM, and MRAM.

The storage device740may include a solid state drive (SSD), a hard disk drive (HDD), a CD-ROM, etc. The input/output device750may include an input device (e.g., a keyboard, a keypad, a mouse, etc.) and an output device (e.g., a printer, a display device, etc.). The power supply760supplies operation voltages for the computing system700.

The three-dimensional image sensor730may be connected to the processor to communicate with the processor710. The three-dimensional image sensor730may be a three-dimensional image sensor ofFIG. 13.

FIG. 19is a block diagram illustrating an example of an interface employable in the computing system shown inFIG. 18according to example embodiments.

Referring toFIG. 19, a computing system1000may be implemented by a data processing device that uses or supports a mobile industry processor interface (MIPI) interface. The computing system1000may include an application processor1110, a three-dimensional image sensor1140, a light source1145, a display device1150, etc.

A CSI host1112of the application processor1110may perform a serial communication with a CSI device1141of the three-dimensional image sensor1140via a camera serial interface (CSI). A DSI host1111of the application processor1110may perform a serial communication with a DSI device1151of the display device1150via a display serial interface (DSI).

The light source1145may communicate with the three-dimensional image sensor1140and the application processor1110. The light source1145may output a modulated transmission light. The three-dimensional image sensor1140provides distance information based on the received light reflected from the subject and includes the depth pixel shown inFIG. 1,2,4,5,7,8,9,11, or12, thereby exactly measuring the distance to the subject without saturating the photo detection unit even when the ambient light is relatively strong. The application processor1110may extract distance information and may correct the distance information through an image interpolation.

The computing system1000may further include a radio frequency (RF) chip1160performing a communication with the application processor1110. A physical layer (PHY)1113of the computing system1100and a physical layer (PHY)1161of the RF chip1160may perform data communications based on a MIPI DigRF. The application processor1110may further include a DigRF MASTER1114that controls the data communications of the PHY1161.

The computing system1000may further include a global positioning system (GPS)1120, a storage1170, a MIC1180, a DRAM device1185, and a speaker1190. In addition, the computing system1100may perform communications using an ultra-wideband (UWB)1120, a wireless local area network (WLAN)1220, a worldwide interoperability for microwave access (WIMAX)1230, etc.

Example embodiments may be applied to a three-dimensional image sensor and an electronic device including the same. For example, example embodiments may be applied to various terminals such as a mobile phone, a smart phone, a tablet PC, a notebook computer, a personal digital assistant (PDA), a portable media player (PMP), a digital camera, a music player, a game console, a navigation system, etc.