Patent Document

FIELD OF THE INVENTION 
     The present invention relates to a chip having a comparator; and, more particularly, to a chip having a comparator for operating in multi-power conditions with low power consumption through an auto-off function, and a system having the same. 
     DESCRIPTION OF RELATED ART 
     When installing image sensor chips on mobile phones or the like, there may occur a problem in an interface function if a power voltage used for an internal chip of the mobile phone having a function of interfacing with the image sensor chip is different from a power voltage used for an interface of the image sensor chip. Therefore, it is necessary for the power voltage to be controlled such that the same power voltage should be used at the interface of the two chips. 
       FIG. 1  is a block diagram setting forth a conventional system having a chip with a multi-power selective function. 
     Referring to  FIG. 1 , the conventional system includes a base band chip  10 , a chip  11  such as an image sensor chip interfaced with the base band chip  10  for performing a predetermined operation, and a power supplier  12  for supplying the base band chip  10  and the image sensor chip  11  with a multi-power. 
     The image sensor chip  11  includes a reference voltage generator  112  for generating a reference voltage VREF, a comparator  111  and an input/output unit  110 . Herein, the comparator  111  compares the power voltage supplied from the power supplier  12  with the reference voltage VREF, and determines a power voltage which will be used for the interface and the image sensor chip  11  according to the comparison result. The input/output unit  110  performs the function of interfacing with the base band chip  10  using the power voltage determined by the comparison result of the comparator  111 . 
     While the image sensor chip  11  may further include a sensing unit for generating an image signal besides the above constitutions, it is omitted for the sake of conciseness. 
     The conventional system of  FIG. 1  incorporates the image sensor chip  11  with multi input/output functions, in which a chip power down signal PWDN is intactly used for the comparison operation of the comparator  111 . That is, both the comparator  111  and the reference voltage generator  112  operate in response to the chip power down signal PWDN. 
     Therefore, the comparator  111  is always turned on while the chip is operating, which causes the unnecessary power consumption to occur in the conventional system. Meanwhile, since the current consumption in the comparator  111  is about 50 μA, the current as much as about 50 μA is unnecessarily and inevitably consumed on and on in the comparator  111  while the chip is operating. 
     However, after the comparison operation, the comparator  111  may be turned off. Thus, it is required for developing a new system for automatically turning off the comparator  111  after the comparison operation has been completed, in order to reduce unnecessary power consumption. 
     SUMMARY OF THE INVENTION 
     It is, therefore, an object of the present invention to provide a chip for operating in multi-power conditions capable of reducing power consumption by designing a comparator and a reference voltage generator with an auto-off function, and a system having the chip. 
     In accordance with an aspect of the present invention, there is provided an apparatus for controlling an I/O interface of a chip operated in multi-power conditions, including: an enable signal generator for generating an enable signal based on a chip power down signal; a reference voltage generator for generating a predetermined reference voltage in response to the enable signal; a comparator for determining a voltage required for operating the chip by comparing an external power voltage with the reference voltage in response to the enable signal; and an input/output means for performing an I/O interface function based on the voltage determined according to the comparison result of the comparator. 
     In accordance with another aspect of the present invention, there is provided a system including: a power supplier for supplying a multi-power; a first chip for operating using the power supplied from the power supplier; and a second chip for comparing an internal reference voltage with the power supplied from the power supplier to determine a voltage for the first and the second chips, the second chip operating to interface with the first chip by using the determined voltage, wherein the second chip includes: an enable signal generator for generating an enable signal using a chip power down signal; a reference voltage generator for generating a predetermined reference voltage in response to the enable signal; a comparator for storing the enable signal for a predetermined time and determining a voltage required for operating the chip by comparing the reference voltage with an external power voltage in response to the enable signal during the predetermined time, the comparator being automatically turned off after a lapse of the predetermined time; and an input/output means for performing an interface function using the voltage determined according to the comparison result of the comparator. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other objects and features of the present invention will become better understood with respect to the following description of the preferred embodiments given in conjunction with the accompanying drawings, in which: 
         FIG. 1  is a block diagram setting forth a conventional system having a chip with a multi-power selective function; 
         FIG. 2  is a block diagram of a chip with a multi-power selective function in accordance with an embodiment of the present invention; 
         FIGS. 3A to 3C  are circuit diagrams and a timing diagram setting forth an enable signal generator and its operation; 
         FIG. 4  is a circuit diagram of a comparator in accordance with an embodiment of the present invention; 
         FIG. 5  is a circuit diagram of a reference voltage generator in accordance with an embodiment of the present invention; 
         FIG. 6  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; 
         FIG. 7  is a graph of power consumption comparing the system of the present invention with the conventional system; 
         FIG. 8  is a timing diagram representing a simulation result of the system when the input is 1.8 V in accordance with the present invention; and 
         FIG. 9  is a timing diagram showing a simulation result of the system when the input is 2.8 V in accordance with the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     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. 
       FIG. 2  is a block diagram of a chip with a multi-power selective function in accordance with an embodiment of the present invention. 
     Referring to  FIG. 2 , 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  FIG. 1 , 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. 
       FIGS. 3A to 3C  are circuit diagrams and a timing diagram setting forth the enable signal generator  20  and its operation. 
     Referring to  FIG. 3A , 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  FIG. 3C , 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  FIG. 3B , 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. 
       FIG. 4  is a circuit diagram of a comparator in accordance with an embodiment of the present invention. 
     Referring to  FIG. 4 , 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. 
       FIG. 7  is a graph of power consumption comparing the system of the present invention with the conventional system. 
     Referring to  FIG. 7 , 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. 
       FIG. 5  is a circuit diagram of the reference voltage generator  21  in accordance with an embodiment of the present invention. 
     Referring to  FIG. 5 , 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 . 
       FIG. 6  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  FIG. 6 , 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  FIG. 2  in which only reference numerals are denoted differently, and its detail constitutions are also similar to those described in  FIGS. 3 to 5 , further detail illustrations for the constitution and the operation will be omitted, herein. 
     If the system constitution of  FIG. 6  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. 
       FIG. 8  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  FIG. 8 , 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. 
       FIG. 9  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  FIG. 8 , two lines E and F denote the power inputted to the comparator and the digital data outputted from the comparator, respectively. In  FIG. 9 , 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.

Technology Category: 5