a chip for operating in multi - power conditions and a system having the same in accordance with exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings . fig2 is a block diagram of a chip with a multi - power selective function in accordance with an embodiment of the present invention . referring to fig2 , the chip for operating in multi - power conditions , includes an enable signal generator 20 , a reference voltage generator 21 , a comparator 22 , and an input / output unit 23 . herein , the enable signal generator 20 generates an enable signal enable using a chip power down signal pwdn . the reference voltage generator 21 generates a reference voltage vref in response to the enable signal enable . the comparator 22 stores the enable signal enabel for a predetermined time , and determines a voltage required for operating the chip by comparing an external power voltage with the reference voltage vref in response to the enable signal enable for the predetermined time . on the contrary , after a lapse of the predetermined time that the enable signal enable is being activated , the comparator 22 is automatically turned off . the input / output unit 23 performs an interface function using the voltage determined by the comparison result of the comparator 22 . while the image sensor chip may further include a sensing unit for generating an image signal besides the above constitutions , it is omitted for the sake of conciseness . in comparison with the conventional image sensor chip of fig1 , the image sensor chip of the present invention further includes the enable signal generator 20 for reducing power consumption that is severe problem in the conventional one . fig3 a to 3c are circuit diagrams and a timing diagram setting forth the enable signal generator 20 and its operation . referring to fig3 a , it is shown that the chip power down signal pwdn is delayed while passing through four inverters inv 1 to inv 4 so that a delayed power down signal pwdn_d is generated . herein , although there are employed the four inverters inv 1 to inv 4 for generating the in - phase delayed power down signal pwdn_d , there may be employed an even number of inverters to generate an in - phase delayed power down signal pwdn - n instead of the four inverters . referring to fig3 c , it is a timing diagram illustrating the enable signal enable . the enable signal enable is generated by performing a predetermined operation on the chip power down signal pwdn and the delayed power down signal pwdn_d . herein , the enable signal enable maintains its logic high level during the delayed time d . that is , since the enable signal enable is deactivated regardless of the chip power down signal pwdn after a predetermined time , i . e ., the delayed time d , it is possible to reduce the unnecessary power consumption by automatically turning off the comparator 22 and the reference voltage generator 21 when using the enable signal enabel as a control signal of the comparator 22 and the reference voltage generator 21 . referring to fig3 b , there is shown a circuit diagram of the enable signal generator 20 in accordance with an embodiment . the enable signal generator 20 is configured with an inverter inv 5 for inverting the delayed power down signal pwdn_d to output the delayed power down bar signal / pwdn_d , and an and gate performing a logic and operation on the chip power down signal pwdn and the delayed power down bar signal / pwdn_d to output the enable signal enable . in order to constitute the comparator 22 with low power consumption , there is employed a latch having a memory function in the present invention . fig4 is a circuit diagram of a comparator in accordance with an embodiment of the present invention . referring to fig4 , the comparator 22 includes a plurality of pmos transistors p 1 , p 2 , p 3 and p 4 , a plurality of nmos transistors n 1 and n 2 , and an inverter inv . herein , although an enable signal enable_d is a signal that an actual enable signal is delayed for a certain delay time , it will be defined as the enable signal enable_d for the sake of illustrative convenience . the pmos transistor p 1 of which a gate is controlled through the enable signal enable_d is connected between a power voltage vdd and a first node node 1 . the pmos transistor p 2 is connected in parallel with the pmos transistor p 1 and a gate is connected to a second node node 2 . the pmos transistor p 4 of which a gate is controlled through the enable signal enable_d is connected between the power voltage vdd and the second node node 2 . the pmos transistor p 3 is connected to the pmos transistor p 4 in parallel and a gate is connected to the first node node 1 . the nmos transistor n 1 receives an external power voltage vin through a gate thereof and it is connected between the first node node 1 and a third node node 3 . the nmos transistor n 2 receives the reference voltage vref through a gate thereof and it is connected between the second node node 2 and the third node node 3 . the nmos transistor n 4 of which a gate is controlled through the enable signal enable_d is connected between the third node node 3 and the ground voltage vss . meanwhile , the inverter inv inverts the signal of the first node node 1 . the inverter inv is configured with a pmos transistor p 5 and an nmos transistor n 3 which are connected to each other in series between the power voltage vdd and the ground voltage vss . both mos transistors p 5 and n 3 receive the signal of the first node node 1 through each gate . the nmos transistor n 4 is used for implementing a low power performance when the comparator 22 operates , while the pmos transistors p 1 and p 2 are used for a power - down during an unnecessary operation . the comparator 22 having the above structure is configured in a latch structure so as to store its output value vout . there is a lot of power consumption at a first comparison operation , but afterwards , the comparator 22 of the present invention shows an advantage that the power consumption is relatively low and further its response speed is high with respect to any reference voltage vref . because the amount of current flowing via the comparator 22 may be controlled by adjusting a width - to - length ratio of the nmos transistor n 4 , it is possible to control the amount of current flowing via the comparator 22 with ease through the above method . in addition to this , the nmos transistor n 4 receives the enable signal enable_d through the gate thereof so that it plays a role in turning off the comparator 22 in whole during the unnecessary operation . the pmos transistors p 1 and p 4 are turned on in coincidence with the power - off of the comparator 22 so that they act as resetting the comparator 22 . that is , since the first and the second nodes node 1 and node 2 maintain almost the power voltage vdd level when the pmos transistors p 1 and p 4 are turned on , the pmos transistors p 2 and p 3 are turned off so that the comparator 22 is turned off after all . as a result , there is no unnecessary power consumption . this case is that the enable signal enable_d is in logic low level , i . e ., deactivated . when the enable signal enable_d is in logic high level , the pmos transistors p 1 and p 4 are turned off and the pmos transistors p 2 and p 3 are turned off . in addition , the nmos transistor n 4 is turned on . if the external power voltage vin is larger than the reference voltage vref , the level of the first node node 1 becomes smaller than that of the second node node 2 because the nmos transistor n 1 is strongly turned on in comparison with the nmos transistor n 2 . as a result , the pmos transistor p 3 is strongly turned on in comparison with the pmos transistor p 2 . therefore , the first node node 1 has a logic level 0 , whereas the output value vout of the comparator 22 has a logic level 1 . on the contrary , if the reference voltage vref is larger than the external power voltage vin , the level of the second node node 2 becomes smaller than that of the first node node 1 because the nmos transistor n 2 is strongly turned on in comparison with the nmos transistor n 1 . accordingly , the pmos transistor p 2 is strongly turned on in comparison with the pmos transistor p 3 . therefore , the first node node 1 has a logic level 1 , whereas the output value has a logic 0 level . the comparator 22 is configured in a latch structure as if two inverters are connected to each other in series so that the comparator 22 is automatically turned off after latching the data for the time being . compared with the prior art , the chip power down signal pwdn is directly applied to three transistors p 1 , p 4 and n 4 in the conventional comparator so that the comparator is continuously turned on after the comparison operation , whereas the enable signal which is only activated for the predetermined time is applied to the transistors p 1 , p 4 and n 4 instead of the power down signal pwdn so that the inventive comparator 22 is only turned on during the comparison operation and automatically is turned off besides the comparison operation . as a result , the present invention is effective for reducing unnecessary power consumption . fig7 is a graph of power consumption comparing the system of the present invention with the conventional system . referring to fig7 , it is understood that the current is unnecessarily consumed as much as about 500 μa after the actual operation of the comparator 22 has been completed in the conventional comparator 22 , which is denoted as a doted line a . on the contrary , while the inventive comparator is similar in current consumption to the conventional one during the activation period of the enable signal ennable_d , the current is rarely consumed when the enable signal enable_d is deactivated , i . e ., the comparison operation of the comparator 22 is completed . fig5 is a circuit diagram of the reference voltage generator 21 in accordance with an embodiment of the present invention . referring to fig5 , the reference voltage generator 21 includes a plurality of pmos transistors p 11 , p 12 and p 13 , and a plurality of nmos transistors n 11 , n 12 , n 13 and n 14 . herein , the pmos transistor p 12 of which a gate is controlled by the enable signal enable_d is connected between a power voltage vdd and a first node n 51 . the pmos transistor p 11 of which a gate is connected to the first node n 51 , is connected between the power voltage vdd and the first node n 51 . the nmos transistor n 11 of which a gate is connected to the first node n 51 , is connected between the first node n 51 and a second node n 52 . the nmos transistor n 12 of which a gate is controlled by the enable signal enable_d , is connected between the second node n 52 and the ground voltage vss . the pmos transistor p 13 of which a gate is connected to the first node n 51 , is connected to the power voltage vdd and a third node n 53 , wherein the reference voltage vref is outputted through the third node n 53 . the nmos transistor n 13 of which a gate is connected to the third node n 53 , is connected between the third node n 53 and a fourth node n 54 . the nmos transistor n 14 of which a gate is connected to the fourth node n 54 , is connected between the fourth node n 54 and the ground voltage vss . in configuring the reference voltage generator 21 with resistors , there is a problem that a size is too large . whereas , in case of configuring the reference voltage generator 21 with diodes , there is a demerit that a predetermined voltage less than a voltage difference vdd - vt between the power voltage vdd and the threshold voltage vt , should be used . in accordance with the present invention , in order to satisfy demands of low power performance and small layout size , the pmos transistors p 11 and p 13 have a structure similar to a current mirror configuration . therefore , by adjusting the width to length ratio of each transistor , it is possible to set a desired voltage level , e . g ., 2 . 3 v . an operation of the reference voltage generator 21 with the above structure will be set forth herebelow . when the reference voltage generator 21 is disabled , the pmos transistor p 12 is turned on . that is , since the enable signal enable_d is in logic low level , the pmos transistor p 12 is turned on . therefore , a level of the first node n 51 becomes almost the level of the power voltage vdd . furthermore , the nmos transistor n 11 is turned on but the nmos transistor n 12 is turned off because the enable signal is in logic low level . as a result , the reference voltage vref is not outputted in this case . meanwhile , when the enable signal enable_d becomes logic high level , the pmos transistor p 12 is turned off . on the contrary , the pmos transistor p 11 and the nmos transistor n 12 are turned on so that a certain current flows from the power voltage vdd into the ground vss via the transistors p 11 , n 11 and n 12 . since the gates of the pmos transistors p 11 and p 13 are commonly connected so that they configure the current mirror , the certain current also flows via the pmos transistor p 13 . at last , the voltage level of the third node n 53 becomes the reference voltage vref corresponding to a voltage drop across the diode connected nmos transistors n 13 and n 14 . fig6 is a block diagram setting forth a system having the chip with the multi - power selective function in accordance with an embodiment of the present invention . referring to fig6 , the system of the present invention includes a power supplier 62 for supplying a multi - power , a first chip such as a base band chip 60 operating using the power supplied from the power supplier 62 , and a second chip such as an image sensor chip 61 . the image sensor chip 61 compares the power voltage supplied from the power supplier with the reference voltage vref to determine the voltage for the base band and the image sensor chips 60 and 61 . thereafter , the image sensor chip 61 operates using the determined voltage while interfacing with the base band chip 60 . since the image sensor chip 61 has the constitution of fig2 in which only reference numerals are denoted differently , and its detail constitutions are also similar to those described in fig3 to 5 , further detail illustrations for the constitution and the operation will be omitted , herein . if the system constitution of fig6 is an internal structure of a mobile phone , the power supplier 62 is contained in a border of the mobile phone , which supplies the multi - voltage . this multi - voltage is provided to both the base band chip 60 and the comparator 611 in the image sensor chip 61 . thus , the multi - voltage inputted to the comparator 611 is compared with the reference voltage vref so that the comparator 611 outputs a predetermined digital data , i . e ., 0 or 1 . then , the outputted digital data is inputted to the input / output unit 610 . for instance , if the outputted digital data is 1 , the digital data is provided to a switch such that the voltage of the input / output unit 610 becomes 2 . 5 v . at this time , a driving current is also determined . adversely , when the outputted digital data is 0 , the digital data is provided to the switch such that the voltage of the input / output unit 610 becomes 1 . 8 v , and thus , a driving current is also determined corresponding to the voltage . fig8 is a timing diagram representing a simulation result of the system when the input is 1 . 8 v in accordance with the present invention . herein , an abscissa axis represents a time in micro - second ( μs ), and an ordinate axis represents a voltage in volt ( v ). in addition , two lines c and d denote the power inputted to the comparator and the digital data outputted from the comparator , respectively . in fig8 , it is understood that the digital data outputted from the comparator is 0 in case that the input is 1 . 8 v . an enabling period indicates the period that the enable signal enable_d is in logic high level , i . e ., activated . fig9 is a timing diagram showing a simulation result of the system when the input is 2 . 8 v in accordance with the present invention . as similar to fig8 , two lines e and f denote the power inputted to the comparator and the digital data outputted from the comparator , respectively . in fig9 , it is understood that the digital data outputted from the comparator is 1 in case of 2 . 8 v input . as described above , in accordance with the present invention , the comparator is configured in a latch structure and uses the enable signal as a control signal instead of the chip power down signal so that the comparator stores the enable signal only for the time being . as a result , since the comparator is automatically turned off after the comparison is completed at the comparator , it is possible to reduce the unnecessary power consumption . therefore , the inventive chip for operating in multi - power conditions and the system having the same are effective for reducing the power consumption . the present application contains subject matter related to the korean patent application no . kr 2005 - 13582 , filed in the korean patent office on feb . 18 , 2005 , the entire contents of which being incorporated herein by reference . while the present invention has been described with respect to certain preferred embodiments , it will be apparent to those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the invention as defined in the following claims .