Abstract:
A voltage generator includes a supply voltage conversion block suitable for converting a supply voltage into an internal voltage, and a supply voltage control block suitable for supplying the supply voltage to the supply voltage conversion block, wherein the supply voltage has different voltage levels that correspond to generation sections of the internal voltage.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application claims priority of Korean Patent. Application No. 10-2015-0025601, filed on Feb. 24, 2015, which is incorporated herein by reference in its entirety. 
     BACKGROUND 
     1. Field 
     Exemplary embodiments of the present invention relate to a semiconductor design technology and, more particularly, to a voltage generator and an image sensing device including the same. 
     2. Description of the Related Art 
     Semiconductor device operations require the use of various different voltages. However, since all the voltages that are used internally are not supplied from an external device, the semiconductor device has voltage generators for generating different internal voltages. The semiconductor device may include a voltage generator for boosting a power supply voltage VDD that is supplied from an external device to generate a boosted voltage VPP having a voltage that is higher than the power supply voltage VDD. The voltage generator includes a DC/DC converter. 
     One example of semiconductor devices that have a voltage generator are image sensing devices. Image sensing devices use the boosted voltage VPP in lieu of the power supply voltage VDD to improve operational reliability. For example, the image sensing device generates an operation control signal, which is used to transmit a photo-electric charge accumulated in a photodiode to a floating diffusion node, based on the boosted voltage VPP. As the transmission capability is improved when the photo-electric charge is transmitted to the floating diffusion node, the operational reliability of the image sensing device may be also improved. 
     An image sensing device captures images using the photosensitive properties of semiconductors. The image sensing device may be classified into charge coupled device (CCD) image sensors and complementary metal oxide semiconductor (CMOS) image sensors. The CMOS image sensors have come into widespread use. This is because CMOS image sensors allow for analog circuits and digital control circuits to be directly implemented on a single integrated circuit (IC). 
     SUMMARY 
     Exemplary embodiments of the present invention are directed to a voltage generator that may generate an internal voltage having reduced ripples, and an image sensing device including the voltage generator. 
     Also, exemplary embodiments of the present invention are directed to a voltage generator that may generate an internal voltage having reduced ripples and may also reduce the initial section (i.e. the initial timing section) for generating the internal voltage, and an image sensing device including the voltage generator. 
     In accordance with an embodiment of the present invention, a voltage generator may include a supply voltage conversion block suitable for converting a supply voltage into an internal voltage, and a supply voltage control block suitable for supplying the supply voltage has different voltage levels that correspond to generation sections (i.e. sections of time or periods) of the internal voltage to the supply voltage conversion block. 
     The generation sections of the internal voltage may include a start-up section (i.e. a startup period) where the internal voltage is developed to a target level and a normal section (i.e. a normal period) after the internal voltage reaches the target level. 
     The supply voltage may have a first voltage level during the start-up section and have a second voltage level lower than the first voltage level during the normal section. 
     In accordance with another embodiment of the present invention, a voltage generator may include a supply voltage conversion part suitable for generating a boosted voltage by boosting a supply voltage based on first and second clocks, a voltage detection part suitable for detecting a voltage level of the boosted voltage, and a voltage supply part suitable for supplying the supply voltage to the supply voltage conversion part in response to a detection signal outputted from the voltage detection part, wherein the supply voltage may have a first voltage level during a start-up section where the boosted voltage is developed to a target level and have a second voltage level lower than the first voltage level during a normal section after the boosted voltage reaches the target level. 
     The voltage detection part may include a division block suitable for dividing the boosted voltage at a predetermined division ratio and generating a divided voltage, and a first comparison block suitable for comparing the divided voltage with a target voltage and generating the detection signal. 
     The voltage supply part may include a reference voltage generation block suitable for generating one among a power supply voltage and a reduced voltage having a voltage level lower than that of the power supply voltage as a reference voltage in response to the detection signal and a supply voltage generation block suitable for generating the supply voltage based on the reference voltage. 
     The reference voltage generation block may include a reduction unit suitable for reducing the power supply voltage and generating the reduced voltage, and a selection unit suitable for outputting the power supply voltage or the reduced voltage as the reference voltage in response to the detection signal. 
     The supply voltage generation block may include a second comparison unit suitable for comparing the reference voltage with the supply voltage, and a driving unit suitable for driving an output terminal of the supply voltage with the power supply voltage in response to a comparison signal outputted from the second comparison unit. 
     In accordance with another embodiment of the present invention, an image sensing device may include a pixel suitable for generating an image signal in response to a plurality of operation control signals, an operation controller suitable for generating one or more of the operation control signals based on an internal voltage, and a voltage generator suitable for generating the internal voltage based on a supply voltage having different voltage levels that correspond to generation sections of the internal voltage. 
     The pixel may include a transistor suitable for electrically coupling a photodiode to a floating diffusion node in response to a first operation control signal among the operation control signals, wherein the operation controller may generate the first operation control signal based on the internal voltage. 
     The generation sections of the internal voltage may include a start-up section where the internal voltage is developed to a target level and a normal section after the internal voltage reaches the target level. 
     The voltage generator may generate the internal voltage based on the supply voltage having a first voltage level during the start-up section and having a second voltage level lower than the first voltage level during the normal section. 
     The voltage generator may include a supply voltage conversion part suitable for converting the supply voltage into the internal voltage, and a supply voltage control part suitable for supplying the supply voltage to the supply voltage conversion part, wherein the supply voltage may have different voltage levels that correspond to the generation sections of the internal voltage. 
     The supply voltage conversion part may boost the supply voltage based on first and second clocks and generate a boosted voltage as the internal voltage. 
     The supply voltage control part may include a voltage detection block suitable for detecting a voltage level of the boosted voltage, and a voltage supply block suitable for supplying the supply voltage to the supply voltage conversion part in response to a detection signal outputted from the voltage detection block, wherein the supply voltage has a first voltage level during a start-up section where the boosted voltage is developed to a target level and has a second voltage level lower than the first voltage level during a normal section after the boosted voltage reaches the target level. 
     The voltage detection block may include a division unit suitable for dividing the boosted voltage at a predetermined division ratio and generating a divided voltage, and a first comparison unit suitable for comparing the divided voltage with a target voltage and generating the detection signal. 
     The voltage supply block may include a reference voltage generation block suitable for generating a power supply voltage or a reduced voltage having a voltage level lower than that of the power supply voltage as a reference voltage in response to the detection signal, and a supply voltage generation block suitable for generating the supply voltage based on the reference voltage. 
     The reference voltage generation block may include a reduction unit suitable for reducing the power supply voltage and generating the reduced voltage, and a selection unit suitable for outputting the power supply voltage or the reduced voltage as the reference voltage in response to the detection signal. 
     The supply voltage generation block may include a second comparison unit suitable for comparing the reference voltage with the supply voltage, and a driving unit suitable for driving an output terminal of the supply voltage with the power supply voltage in response to a comparison signal output from the second comparison unit. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram illustrating an image sensing device in accordance with an embodiment of the present invention. 
         FIG. 2  is a circuit diagram illustrating a pixel included in a pixel array shown in  FIG. 1 . 
         FIG. 3  is a block diagram illustrating a voltage generator shown in  FIG. 1 . 
         FIG. 4  is a circuit diagram illustrating a supply voltage conversion block shown in  FIG. 3 . 
         FIG. 5  is a block diagram illustrating a supply voltage control block shown in  FIG. 3 . 
         FIG. 6  is a circuit diagram illustrating a voltage detection part shown in  FIG. 5 . 
         FIG. 7  is a block diagram illustrating a voltage supply part shown in  FIG. 5 . 
         FIG. 8  is a block diagram illustrating a reference voltage generation unit shown in  FIG. 7 . 
         FIG. 9  is a circuit diagram illustrating a supply voltage generation unit shown in  FIG. 7 . 
         FIG. 10  is a timing diagram for describing an operation of the voltage generator shown in  FIG. 3 . 
     
    
    
     DETAILED DESCRIPTION 
     Exemplary embodiments of the present invention are described below in more detail with reference to the accompanying drawings. These embodiments are provided so that this disclosure is thorough and complete, and fully conveys the scope of the present invention to those skilled in the art. All “embodiments” referred to in this disclosure refer to embodiments of the inventive concept disclosed herein. The embodiments presented are merely examples and are not intended to limit the inventive concept. 
     It is also noted that in this specification, “connected/coupled” refers to one component not only directly coupling another component but also indirectly coupling another component through an intermediate component. In addition, a singular form may include a plural form as long as it is not specifically mentioned. 
       FIG. 1  is a block diagram illustrating an image sensing device in accordance with an embodiment of the present invention.  FIG. 2  is a circuit diagram illustrating a pixel included in a pixel array  130  shown in  FIG. 1 . 
     Referring to  FIG. 1 , the image sensing device  100  may include a voltage generator  110 , a row controller  120 , a pixel array  130 , and an analog-to-digital converter (ADC)  140 . 
     The voltage generator  110  may generate an internal voltage VIN based on a supply voltage VOUT having different voltage levels that correspond to generation sections of the internal voltage VIN and a source voltage VDD having a fixed voltage level regardless of the generation sections of the internal voltage VIN. For example, the voltage generator  110  may generate the internal voltage VIN having voltage level higher than that of the source voltage VDD. The voltage generator  110  is described below in detail.  120  may generate a plurality of operation control signals CTRLS based on the source voltage VDD and the internal voltage VIN. For example, the operation control signals CTRLS may include a transmission signal TX, a reset signal RX, a selection signal SX, etc. for controlling an operation of the pixel array  130 . Although the operation control signals CTRLS actually include a plurality of transmission signals TX&lt;0:N&gt;, a plurality of reset signals RX&lt;0:N&gt;, and a plurality of selection signals SX&lt;0:N&gt; for controlling the pixel array  130  by rows, it is described herein that a single transmission signal TX, a single reset signal RX and a single selection signal SX are included in the operation control signals CTRLs, for a simplified description. The row controller  120  may generate the reset signal RX and the selection signal SX among the operation control signals CTRLS based on the source voltage VDD and the transmission signal TX among the operation control signals CTRLS based on the internal voltage VIN. 
     The pixel array  130  may include a plurality of pixels (not shown in the drawing) arranged in a row and a column direction. The pixel&#39;s may generate a plurality of pixel signals VPX&lt;0:X&gt; by rows in response to the operation control signals CTRLS. One among the pixel&#39;s is representatively described as follows. For example, referring to  FIG. 2 , the pixel may have a 4-transistor structure. The pixel may include a photodiode PD, a reset transistor RXTR, a transmission transistor TXTR, a driving transistor DXTR, and a selection transistor SXTR. The photodiode PD may generate a photo-electric charge in response to incident light. The reset transistor RXTR may drive a floating diffusion node FD with a predetermined voltage, e.g., VDD, in response to the reset signal RX. The transmission transistor TXTR may transmit the photo-electric charge generated from the photodiode PD to the floating diffusion node FD in response to the transmission signal TX. The driving transistor DXTR may drive a corresponding column line COLK in response to a voltage of the floating diffusion node FD. The selection transistor SXTR may couple the driving transistor DXTR to the corresponding column line COLK. The transmission signal TX may be generated based on the internal voltage VIN having a voltage level higher than that of the source voltage VDD as described above. Therefore, since the transmission transistor TXTR is under the control of the transmission signal TX, the transmission capability of the transmission transistor TXTR may be improved. 
     Referring back to  FIG. 1 , the analog-to-digital converter  140  may convert the pixel signals VPX&lt;0:X&gt; into a plurality of digital signals DOUT&lt;0:X&gt;. 
       FIG. 3  is a block diagramming the voltage generator  110  shown in  FIG. 1 . 
     Referring to  FIG. 3 , the voltage generator  110  may include a supply voltage conversion block  111  and a supply voltage control block  113 . 
     The supply voltage conversion block  111  may convert the supply voltage VOUT into the internal voltage VIN in response to first differential clocks PH 1  and /PH 1  and second differential clocks PH 2  and /PH 2 . For example, the supply voltage conversion block  111  may boost the supply voltage VOUT in response to the first differential clocks PH 1  and /PH 1  and the second differential clocks PH 2  and /PH 2  and generate a boosted voltage VIN) having a voltage level higher than that of the source voltage VDD. The supply voltage control block  113  may supply the supply voltage VOUT having different voltage levels that correspond to generation sections of the internal voltage VIN to the supply voltage conversion block  111 . 
     For example, the generation sections may include a start-up section and a normal section. The start-up section may include an initial generation section where the internal voltage VIN is developed from an initial setting level to a target level. The normal section may include a stabilization section after the internal voltage VIN reaches the target level. The supply voltage VOUT may correspond to the source voltage VDD during the start-up section and then correspond to a reduced voltage VDD-α during the normal section. 
       FIG. 4  is a circuit diagram illustrating the supply voltage conversion block  111  shown in  FIG. 3 . 
     Referring to  FIG. 4 , the supply voltage conversion block  111  may include a DC/DC converter. For example, the supply voltage conversion block  111  may include a boosting unit  111 A and an internal voltage maintaining unit  111 B. 
     The boosting unit  111 A may continuously boost the supply voltage VOUT in response to the first differential clocks PH 1  and /PH 1  and the second differential docks PH 2  and /PH 2 . For example, the boosting unit  111 A may include a first PMOS transistor MP 1 , a first NMOS transistor MN 1 , a first boosting capacitor C 1 , a second PMOS transistor MP 2 , a second NMOS transistor MN 2 , and a second boosting capacitor C 2 . The first PMOS transistor MP 1  has a gate coupled to an input terminal where the first secondary clock /PH 1  among the first differential clocks PH 1  and /PH 1  is inputted, and a source and a drain coupled between a supply voltage VOUT terminal and a first node N 1 . The first NMOS transistor MN 1  has a gate coupled to an input terminal where the second primary clock PH 2  among the second differential clocks PH 2  and /PH 2  is inputted, and a source and a drain coupled between a ground voltage VSS terminal and the first node N 1 . The first boosting capacitor C 1  is coupled between the first node N 1  and a second node N 2 . The second PMOS transistor MP 2  has a gate coupled to an input terminal where the second secondary clock /PH 2  among the second differential clocks PH 2  and /PH 2  is inputted, and a source and a drain coupled between the supply voltage VOUT terminal and a third node N 3 . The second NMOS transistor MN 2  has a gate coupled to an input terminal where the first primary clock PH 1  among the first differential clocks PH 1  and /PH 1  is inputted, a source and a drain coupled between the ground voltage VSS terminal and the third node N 3 . The second boosting capacitor C 2  is coupled between the third node N 3  and a fourth node N 4 . 
     The internal voltage maintaining unit  111 B may include a third PMOS transistor MP 3 , a fourth PMOS transistor MP 4 , a third NMOS transistor MN 3 , a fourth NMOS transistor MN 4 , and a load capacitor C 3 . The third PMOS transistor MP 3  has a gate coupled to the fourth node N 4 , and a source and a drain coupled between the second node N 2  and an internal voltage VIN terminal. The fourth PMOS transistor MP 4  has a gate coupled to the second node N 2 , and a source and a drain coupled between the fourth node N 4  and the internal voltage VIN terminal. The third NMOS transistor MN 3  has a gate coupled to the fourth node N 4 , and a source and a drain coupled between a source voltage VDD terminal and the second node N 2 . The fourth NMOS transistor MN 4  has a gate coupled to the second node N 2 , and a source and a drain coupled between the source voltage VDD terminal and the fourth node N 4 . The load capacitor C 3  is coupled between the internal voltage VIN terminal and the ground voltage VSS terminal. 
     Although not illustrated in the drawing, the supply voltage conversion block  111  may further include a precharge unit for precharging the internal voltage VIN terminal with a predetermined voltage, e.g., VDD, during a section where the voltage generator  110  is disabled. 
       FIG. 5  is a block diagram illustrating the supply voltage control block  113  shown in  FIG. 3 . 
     Referring to  FIG. 5 , the supply voltage control block  113  may include a voltage detection part  113 A and a voltage supply part  113 B. 
     The voltage detection part  113 A may detect a voltage level of the internal voltage VIN. For example, the voltage detection part  113 A may detect the voltage level of the internal voltage VIN based on a preset target voltage VT. 
     The voltage supply part  1135  may supply the supply voltage VOUT which corresponds to the source voltage VDD during the start-up section and then the reduced voltage VDD-α during the normal section, to the supply voltage conversion block  111  in response to a detection signal DET outputted from the voltage detection part  113 A. 
       FIG. 6  is a circuit diagram illustrating the voltage detection part  113 A shown in  FIG. 5 . 
     Referring to  FIG. 6 , the voltage detection part  113 A may include a division unit  113 A_ 1  and a first comparison unit  113 A_ 3 . 
     The division unit  113 A_ 1  may divide the internal voltage VIN at a predetermined division ratio and generate a divided voltage VIN/2. For example, the division unit  113 A_ 1  may include a first resistor R 1  coupled between the internal voltage VIN terminal and a division node DN, and a second resistor R 2  coupled between the division node DN and the ground voltage VSS terminal. The first resistor R 1  and the second resistor R 2  may be designed to have the same resistance value. 
     The first comparison unit  113 A_ 3  may compare the divided voltage VIN/2 with the target voltage VT and generate the detection signal DET corresponding to the comparison result. For example, the first comparison unit  113 A_ 3  may disable the detection signal DET when the divided voltage VIN/2 is lower than the target voltage VT as the comparison result of the divided voltage VIN/2 and the target voltage VT. In contrast, the first comparison unit  113 A_ 3  may enable the detection signal DET when the divided voltage VIN/2 is higher than the target voltage VT as the comparison result of the divided voltage VIN/2 and the target voltage VT. 
       FIG. 7  is a block diagram illustrating the voltage supply part  113 B shown in  FIG. 5 . 
     Referring to  FIG. 7 , the voltage supply part  113 B may include a reference voltage generation unit  113 B_ 1  and a supply voltage generation unit  113 B_ 3 . 
     The reference voltage generation unit  113 B_ 1  may generate a reference voltage VREF corresponding to one among the source voltage VDD and the reduced voltage VDD-α in response to the detection signal DET. For example, the reference voltage generation unit  113 B_ 1  may generate the reference voltage VREF corresponding to the source voltage VDD when the detection signal DET is disabled. In contrast, the reference voltage generation unit  113 B_ 1  may generate the reference voltage VREF corresponding to the reduced voltage VDD-α when the detection signal DET is enabled. 
     The supply voltage generation unit  113 B_ 3  may generate the supply voltage VOUT based on the reference voltage VREF. For example, the supply voltage generation unit  113 B_ 3  may generate the supply voltage VOUT based on the reference voltage VREF corresponding to the source voltage VDD during the start-up section. The supply voltage generation unit  113 B_ 3  may generate the supply voltage VOUT based on the reference voltage VREF corresponding to the reduced voltage VDD-α during the normal section. 
       FIG. 8  is a block diagram illustrating the reference voltage generation unit  113 B_ 1  shown in  FIG. 7 . 
     Referring to  FIG. 8 , the reference voltage generation unit  113 B_ 1  may include a reduction unit  113 B_ 11  and a selection unit  113 B_ 13 . 
     The reduction unit  113 B_ 11  may reduce the source voltage VDD and generate the reduced voltage VDD-α. For example, the reduction unit  113 B_ 11  may include a voltage divider. 
     The selection unit  113 B_ 13  may select one among the source voltage VDD and the reduced voltage VDD-α in response to the detection signal DET and supply the selected voltage to the supply voltage generation unit  113 B_ 3  as the reference voltage VREF. For example, the selection unit  113 B_ 13  may include a multiplexer. 
       FIG. 9  is a circuit diagram illustrating the supply voltage generation unit  113 B_ 3  shown in  FIG. 7 . 
     Referring to  FIG. 9 , the supply voltage generation unit  113 B_ 3  may include a second comparison unit  113 B_ 31  and a driving unit  113 B_ 33 . 
     The second comparison unit  113 B_ 31  may compare the supply voltage VOUT with the reference voltage VREF and generate a comparison signal COMP corresponding to the comparison result. For example, the second comparison unit  113 B_ 31  may disable the comparison signal COMP when the supply voltage VOUT is lower than the reference voltage VREF as the comparison result of the supply voltage VOUT and the reference voltage VREF. In contrast, the second comparison unit  113 B_ 31  may enable the comparison signal COMP when the supply voltage VOUT is higher than the reference voltage VREF as the comparison result of the supply voltage VOUT and the reference voltage VREF. 
     The driving unit  113 B_ 33  may drive the supply voltage VOUT terminal with the source voltage VDD in response to the comparison signal COMP. For example, the driving unit  113 B_ 33  may drive the supply voltage VOUT terminal to generate the supply voltage VOUT corresponding to the source voltage VDD during the start-up section and corresponding to the reduced voltage VDD-α during the normal section, based on the reference voltage VREF. 
     Hereinafter, an operation of the image sensing device  100  having the aforementioned structure in accordance with the embodiment of the present invention is described. 
     First, an operation of the voltage generator  110  is described below with reference to  FIG. 10 . 
       FIG. 10  is a timing diagram for describing the operation of the voltage generator  110  shown in  FIG. 3 . 
     Referring to  FIG. 10 , the voltage generator  110  is disabled and does not generate the internal voltage VIN in a waiting section DCDC_OFF and is enabled and generates the internal voltage VIN in a generation section DCDC_ON. 
     An operation of the voltage generator  110  in the waiting section DCDC_OFF is described below. 
     The supply voltage conversion block  111  may be disabled in response to the first differential clocks PH 1  and /PH 1  and the second differential clocks PH 2  and /PH 2  having fixed voltage levels during the waiting section DCDC_OFF. For example, the supply voltage conversion block  111  may wait without performing a boosting operation for generating the internal voltage VIN in response to the first primary clock PH 1  having a fixed logic low voltage level, the first secondary clock /PH 1  having a fixed logic high voltage level, the second primary clock PH 2  having a fixed logic low voltage level and the second secondary clock /PH 2  having a fixed logic high voltage level during the waiting section DCDC_OFF. 
     The precharge unit (not shown in the drawing) may precharge the internal voltage VIN terminal with the source voltage VOD. 
     Next, an operation of the voltage generator  110  in the generation section DCDC_ON is described below. 
     The generation section DCDC_ON may include a start-up section S_UP and a normal section NORM. The start-up section S_UP may include an initial generation section where the internal voltage VIN is developed from an initial setting level, e.g., VDD to a target level, e.g., VPP. The normal section NORM may include a stabilization section after the internal voltage VIN reaches the target level. 
     The first differential clocks PH 1  and /PH 1  and the second differential clocks PH 2  and /PH 2  may toggle opposite to each other and be enabled at a predetermined time interval D during the generation section DCDC_ON. For example, the first primary clock PH 1  and the second primary clock PH 2  may be alternately enabled, and the time interval D may exist between the active sections of the first and second primary clocks PH 1  and PH 2  to a logic high level. The first secondary clock /PH 1  and the second secondary clock /PH 2  may be alternately enabled, and the time interval D may exist between the active sections of the first and second secondary clocks /PH 1  and /PH 2  to a logic low level. This is for reducing leakage current occurring in the supply voltage conversion block  111 . For example, when the first secondary clock /PH 1  and the second primary clock PH 2  are simultaneously enabled, a direct current path may be formed through the first PMOS transistor MP 1  and the first NMOS transistor MN 1 , and consequently leakage of current may occur from the supply voltage VOUT terminal to the ground voltage VSS terminal. When the second secondary clock /PH 2  and the first primary clock. PH 1  are simultaneously enabled, a direct current path may be formed through the second PMOS transistor MP 2  and the second NMOS transistor MN 2  and consequently current leakage may occur from the supply voltage VOUT terminal to the ground voltage VSS terminal. Therefore, when the first differential clocks PH 1  and /PH 1  and the second differential clocks PH 2  and /PH 2  are generated at the time interval D, current leakage does not occur. 
     The voltage generator  110  may be enabled and perform the boosting operation during the generation section DCDC_ON in response to the first differential clocks PH 1  and /PH 1  and second differential clocks PH 2  and /PH 2  toggling. 
     For example, the supply voltage control block  113  may generate the supply voltage VOUT corresponding to the source voltage VDD during the start-up section S_UP, because the internal voltage VIN does not reach the target level VPP as a result of detecting a voltage level of the internal voltage VIN. The supply voltage conversion block  111  may generate the internal voltage VIN during the start-up section S_UP in response to the first differential clocks PH 1 , and /PH 1  and the second differential clocks PH 2  and /PH 2 . The supply voltage conversion block  111  may generate the internal voltage VIN based on the supply voltage VOUT corresponding to the source voltage VDD. To be specific when the first PMOS transistor MP 1  and the second PMOS transistor MP 2  are alternately turned on in response to the first secondary clock /PH 1  and the second secondary clock /PH 2 , the charge corresponding to the source voltage VDD may be alternately accumulated in the first boosting capacitor C 1  and the second boosting capacitor C 2 . The accumulated charge may be alternately transmitted to the internal voltage VIN terminal. A ripple may occur in the internal voltage VIN due to the accumulated charge. To sum up, since the supply voltage conversion block  111  uses the supply voltage VOUT corresponding to the source voltage VDD during the start-up section S_UP, severely large ripple may occur in the internal voltage VIN but the internal voltage VIN may quickly reach the target level VPP. 
     The supply voltage control block  113  may generate the supply voltage VOUT corresponding to the reduced voltage VDD-α during the normal section NORM since the internal voltage VIN reaches the target level VPP as a result of detecting a voltage level of the internal voltage VIN. The supply voltage conversion block  111  may maintain the internal voltage VIN at the target level VPP during the normal section NORM in response to the first differential clocks PH 1  and /PH 1  and the second differential clocks PH 2  and /PH 2 . The supply voltage conversion block  111  may use the supply voltage VOUT corresponding to the reduced voltage VDD-α. To be specific, when the first PMOS transistor MP 1  and the second PMOS transistor MP 2  are alternately turned on in response to the first secondary clock /PH 1  and the second secondary clock /PH 2 , the charge corresponding to the reduced voltage VDD-α may be alternately accumulated in the first boosting capacitor C 1  and the second boosting capacitor C 2 . The accumulated charge may be alternately transmitted to the internal voltage VIN terminal. A ripple may occur in the internal voltage VIN due to the accumulated charge. To sum up, since the supply voltage conversion block  111  uses the supply voltage VOUT corresponding to the reduced voltage VDD-α during the normal section NORM, the ripple occurring in the internal voltage VIN may decrease. 
     As described above, while the internal voltage VIN stabilizes at the target level VPP, the row controller  120  may generate the operation control signals CTRLS based on the internal voltage VIN and the source voltage VDD. For example, the row controller  120  may generate the transmission signal TX based on the internal voltage VIN, and it may generate the reset signal RX and the selection signal SX based on the source voltage VDD. 
     The pixel array  130  may generate the pixel signals VPX&lt;0:X&gt; in response to the operation control signals CTRLS, and the analog-to-digital converter  140  may generate the digital signals DOUT&lt;0:X&gt; corresponding to the pixel signals VPX&lt;0:X&gt;. 
     In accordance with the embodiments of the present invention, a start-up section for generating an internal voltage may be reduced as a source voltage is used for a supply voltage, and a ripple occurring in the internal voltage may be also reduced as a reduced voltage is used for the supply voltage during a normal section following the start-up section. Furthermore, the operational reliability of an image sensing device may be improved as an internal voltage is produced with a reduced amount of rippling. 
     In accordance with the embodiments of the present invention, time until an internal voltage reaches a target level may be shortened as an initial generation section decreases when the internal voltage is generated. Also, when the internal voltage reaches the target level, the internal voltage may be stably generated as rippling in the internal voltage decreases. 
     While the present invention has been described with respect to specific embodiments, the embodiments are not intended to be restrictive, but rather descriptive. Further, it is noted that the present invention may be achieved in various ways through substitution, change, and modification, by those skilled in the art without departing from the scope of the present invention as defined by the following claims. 
     For example, although it is described in the embodiments of the present invention that a voltage generator is applied to an image sensing device, all devices or circuits using an internal voltage are applicable.