Abstract:
An internal voltage generator generates an internal voltage that is obtained by up-converting or down-converting an external power supply voltage. A resistor-voltage divider, having a plurality of resistors, outputs a first divided voltage that is obtained by dividing the internal voltage according to a resistance ratio of the resistors. A capacitor-voltage divider, having a plurality of capacitors connected in series between an output terminal of the internal voltage generator and a ground level, outputs a second divided voltage from the capacitors. A comparator compares a reference voltage and the first divided voltage for controlling the internal voltage generator according to a result of comparison. The comparator judges whether to halt operation of the internal voltage generator or not based on the result of comparison between the reference voltage and the first divided voltage while the internal voltage generator is operating. On the other hand, the comparator operates the internal voltage generator based on the result of comparison between the reference voltage and the second divided voltage while the internal voltage generator is not operating. The comparator further controls the resistor-voltage divider so that a current flows therethrough only when the internal voltage generator is operating.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a semiconductor device for generating voltages that are used as internal power supply voltages for semiconductor devices, such as, DRAMS, by using an external power supply voltage fed by a peripheral circuitry. 
     Semiconductor devices, such as, DRAMS, operating at several levels of power supply voltages in the internal circuitry are provided with an up- or a down-converter for up-converting or down-converting an external power supply voltage fed by a peripheral circuitry. 
     Shown in FIG. 12 is a circuit diagram of a typical up-converter. 
     The up-converter is provided with an operational amplifier  1 , a resistor-voltage divider  5  connected to the positive input terminal of the operational amplifier  1 , and an inverter IV 1  connected to the output terminal of the operational amplifier  1 , a ring oscillator  2  driven by the output of the inverter IV 1 , a charge pump  3  driven by the output of the ring oscillator  2 , and a capacitor Cpp connected to the output terminal of the charge pump  3 . 
     The resistor-voltage divider  5  divides an up-converted voltage Vpp that has been up-converted by the charge pump  3 . 
     The operational amplifier  1  compares a divided voltage TAP of the resistor-voltage divider  5  with a reference voltage VBGR, to output a positive signal if the former voltage level is higher than the latter, whereas a negative signal if the latter is higher than the former. 
     This results in an output OSCE of the inverter IV 1  being brought into a low level state if TAP&gt;VBGR, whereas a high level if TAP&lt;VBGR. 
     The reference voltage VBGR is set at, for example, 1. 25V, that is generated by a band-gap reference circuit (not shown) exhibiting no thermal behavior. 
     Illustrated in FIG. 13 are voltage waveforms of the up-converted voltage Vpp, the divided voltage TAP, and the output OSCE of the inverter IV 1 . 
     The operation of the up-converter shown in FIG. 12 will be explained with reference to the voltage waveforms illustrated in FIG.  13 . 
     Transition of the up-converted voltage Vpp from its stable condition (a desired voltage level) to a lower level with the divided voltage TAP lower than the reference voltage VBGR triggers the transition of the inverter output voltage OSCE from a low to a high level. 
     This voltage transition initiates the ring oscillator  2  for oscillation and also the charge pump  3  for up-conversion. 
     The up-converted voltage Vpp at a high level gradually raises the divided voltage TAP higher than the reference voltage VBGR, thus the inverter output voltage OSCE being brought into a low level state. 
     This voltage transition halts the oscillation of the ring oscillator  2  and also the up-conversion of the charge pump  3 . 
     Repetition of the operation described above obtains the up-converted voltage Vpp expressed as follows: 
     
       
         Vpp={1+(R2/R1)}X VBGR . . .   (1) 
       
     
     Shown in FIG. 14 is the equivalent circuit of the operational amplifier  1  of FIG.  12 . 
     The operational amplifier  1  shown in FIG. 14 is provided with PMOS transistors Q 1  and Q 2  that constitute a current mirror, NMOS transistors Q 3  and Q 4  that turns on or off according to the logic of an input signal, an NMOS transistor Q 5  that enables or disables the operational amplifier  1 , and an NMOS transistor Q 6  that validates or invalidates the output of the operational amplifier  1 . 
     In FIG. 14, the transistor Q 3  turns on when its gate voltage is higher than a gate voltage of the transistor Q 4 , thus the transistors Q 1  and Q 2  turn on to generate an output voltage VOUT almost equal to the positive power supply voltage Vdd. 
     On the other hand, the transistor Q 4  turns on when its gate voltage is lower than a gate voltage of the transistor Q 3 , thus an output voltage VOUT becoming almost equal to the ground level. 
     Present DRAMs and FRAMs, etc., turn on its up-converter in operation when the memories are on (an operating mode), whereas turns it off when the memories are off (a waiting mode) for power saving. Up-converted power supply voltages are, however, used at many sections of the memories, thus resulting in a heavy load. Such an up-converter control takes a considerably long time for up-converting power supply voltages at desired levels. 
     An up-converter shown in FIG. 15 has been proposed for solving such a problem. 
     The up-converter shown in FIG. 15 is provided with a voltage controller  21   a  for the operating mode and a voltage controller  21   b  for the waiting mode. Both controllers have almost the same circuitry. An operational amplifier Is of the voltage controller  21   b  is a low power consumption-type. Resistors R 1 H and R 2 H in the voltage controller  21   b  have resistance higher than those of resistors R 1 L and R 2 L in the voltage controller  21   a.    
     The operational amplifier  1 a operates when a signal “active” indicating the operating mode is high, whereas and the operational amplifier  1 b operates when a signal “standby” indicating the waiting mode is high. 
     The up-converter shown in FIG. 15, however, has the following drawbacks: 
     The driving performance of the up-converter is preferably restricted in the waiting mode because almost no circuitry in the semiconductor device operates in this mode. The waiting mode requires a small current consumed by the operational amplifier  1   s , while larger resistance for the resistors R 1 H and R 2 H that constitute the resistor-voltage divider  5  (FIG. 12) for a small pass-current. 
     Decrease in current consumed by the operational amplifier  1   s  can be achieved by a well known technique, such as, provision of a current-limiting transistor. 
     However, the larger the resistance of the resistors R 1 H and R 2 H, the larger the area of resistor-wiring, and the larger the stray capacitance of the resistor-wiring. This results in signal delay due to resistor and capacitor, which causes a low voltage-feedback control. 
     Not only the up-converter, but also the down-converter has the same disadvantages as discussed below. 
     Shown in FIG. 16 is a circuit diagram of a typical down-converter. 
     The down-converter is provided with an operational amplifier  1 , a PMOS transistor Q 8 , and resistors R 1  and R 2  that constitute a resistor-voltage divider. 
     Decrease in down-converted voltage Vout lower than a desired voltage causes decrease in a divided voltage TAP of the resistor-voltage divider lower than a reference voltage VBGR, which brings the output of the operational amplifier  1  into a lower level, to turn on the transistor Q 8  for raising the voltage Vout. 
     Shown in FIG. 17 is a circuit diagram of another typical down-converter, provided with voltage controllers for the operating and waiting modes. 
     Like the up-converter shown in FIG. 12, the down-converter (FIG. 17) inevitably has a large chip size, a large delay through wiring, and a high production cost for power saving in the waiting mode due to the existence of resistor-voltage divider. 
     SUMMARY OF THE INVENTION 
     A purpose of the present invention is to provide a semiconductor device having a small chip size for power saving. 
     The present invention provides a semiconductor device including: an internal voltage generator for generating an internal voltage that is obtained up-converting or down-converting an external power supply voltage; a resistor-voltage divider, having a plurality of resistors, to output a first divided voltage that is obtained by dividing the internal voltage according to a resistance ratio of the first resistors; a capacitor-voltage divider, having a plurality of capacitors connected in series between an output terminal of the internal voltage generator and a ground level, to output a second divided voltage from the capacitors; and a comparator to compare a reference voltage and the first divided voltage for controlling the internal voltage generator according to a result of comparison, the comparator judging whether to halt operation of the internal voltage generator or not based on the result of comparison between the reference voltage and the first divided voltage while the internal voltage generator is operating, on the other hand, the comparator operating the internal voltage generator based on the result of comparison between the reference voltage and the second divided voltage while the internal voltage generator is not operating, the comparator further controlling the resistor-voltage divider so that a current flows therethrough only when the internal voltage generator is operating. 
     Moreover, the present invention provides a semiconductor device including: an internal voltage generator for generating an internal voltage that is obtained up-converting or down-converting an external power supply voltage; a resistor-voltage divider, having a plurality of resistors, to output a first divided voltage that is obtained by dividing the internal voltage according to a resistance ratio of the resistors; a capacitor-voltage divider, having a plurality of capacitors connected in series between an output terminal of the internal voltage generator and a ground level, to output a second divided voltage from the capacitors; and a comparator to compare a reference voltage and the first divided voltage for controlling the internal voltage generator according to a result of comparison, the comparator controlling the first resistor-voltage divider so that no current flows therethrough when the internal voltage generator is out of operation, to operate the internal voltage generator based on the result of comparison between the reference voltage and the second divided voltage. 
     Furthermore, the present invention provides a method of controlling an internal voltage of a semiconductor device, including the steps of: generating an internal voltage that is obtained up-converting or down-converting an external power supply voltage; outputting a first divided voltage that is obtained by dividing the internal voltage according to a resistance ratio of a plurality of resistors; connecting the internal voltage and a ground level via capacitance, to output a second divided voltage by the capacitance-connection; judging whether or not to halt the internal voltage generation according to a result of comparison between a reference voltage and the first divided voltage while the internal voltage generation is proceeding, on the other hand, starting the internal voltage generation according to the result of comparison between the reference voltage and the second divided voltage while the internal voltage generation is not proceeding; and outputting the first divided voltage only when the voltage obtained up-converting or down-converting the external power supply voltage is being generated. 
     Moreover, the present invention provides a method of controlling an internal voltage of a semiconductor device, including the steps of: generating an internal voltage that is obtained up-converting or down-converting an external power supply voltage; outputting a first divided voltage that is obtained by dividing the internal voltage according to a resistance ratio of a plurality of resistors; connecting the internal voltage and a ground level via capacitance, to output a second divided voltage by the capacitance-connection; placing the first divide-voltage as a ground level when the internal voltage obtained up-converting or down-converting the external power supply voltage is not generated; starting the internal voltage generation according to the result of comparison between a reference voltage and the second divided voltage. 
    
    
     BRIEF DESCRIPTION OF DRAWINGS 
     FIG. 1 shows a circuit diagram of an up-converter as the first preferred embodiment according to the present invention; 
     FIG. 2 shows a circuit diagram of an up-converter as the second preferred embodiment according to the present invention; 
     FIG. 3 shows a circuit diagram of an operational amplifier  61  shown in FIG. 2; 
     FIG. 4 illustrates waveforms of an up-converted voltage Vpp, a voltage at a positive input terminal TAPC of an operational amplifier  1 , an output voltage SOSCE of a power controller  6 , and an output voltage OSCE of an inverter IV 1  shown in FIG. 2; 
     FIG. 5 shows a circuit diagram of an up-converter as the third preferred embodiment according to the present invention; 
     FIG. 6 shows a circuit diagram of a capacitor-voltage divider and its periphery; 
     FIG. 7 illustrates a sectional view of a capacitor C 1 ′shown in FIG. 6; 
     FIG. 8 shows an exemplary circuit diagram where transistor switches SW 1  and SW 2  in FIG. 6 are replaced with a CMOS-type; 
     FIG. 9 shows a circuit diagram of a down-converter where a resistor-voltage divider and a capacitor-voltage divider are connected in parallel, like shown in FIG. 1; 
     FIG. 10 shows a circuit diagram of a down-converter provided with a power controller that controls a power supply to an operational amplifier, like shown in FIG. 2; 
     FIG. 11 shows a circuit diagram of a down-converter provided with another resistor-voltage divider; 
     FIG. 12 shows a circuit diagram of a typical up-converter; 
     FIG. 13 illustrates waveforms of an up-converted voltage Vpp, a divided voltage TAP, and an output voltage OSCE of an inverter IV 1  shown in FIG. 12; 
     FIG. 14 shows the equivalent circuit of the operational amplifier shown in FIG. 12; 
     FIG. 15 shows a circuit diagram of a typical up-converter provided with a voltage controller for an operating mode and a voltage controller for a waiting mode; 
     FIG. 16 shows is a circuit diagram of a typical down-converter; and 
     FIG. 17 shows a circuit diagram of another typical down-converter provided with voltage controllers for the operating and waiting modes. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Preferred embodiments according to the present invention will be disclosed with reference to the attached drawings. 
     Disclosed below, as examples of a semiconductor device, are an up-converter that up-converts a power supply voltage fed by the external circuitry and a down-converter that down-converts the externally-fed power supply voltage. 
     In the following disclosure, an up-converted voltage is an internal voltage obtained by up-converting a power supply voltage fed by the external circuitry and a down-converted voltage is an internal voltage obtained by down-converting the externally-fed power supply voltage. 
     [The First Preferred Embodiment] 
     The feature of the first embodiment of the up-converter lies in low power consumption in the waiting mode. 
     Shown in FIG. 1 is first embodiment of the up-converter. Elements in this embodiment that are the same as or analogous to elements in FIG. 12 are referenced by the same reference numbers. 
     Like shown in FIG. 12, the up-converter (FIG. 1) is provided with an operational amplifier  1  (the first operational amplifier), an inverter IV 1 , a ring oscillator  2 , and a charge pump  3 . 
     In addition to these elements, the up-converter (FIG. 1) is provided with a capacitor-voltage divider  4  constituted by capacitors C 1  and C 2  series-connected between an up-converted Vpp and the ground level, a first resistor-voltage divider  5  constituted by resistors R 1  and R 2  series-connected between the up-converted Vpp and the ground level, an NMOS transistor switch SW 1  (the first switch) connected between the resistors R 1  and R 2 , and an NMOS transistor switch SW 2  (the second switch) connected between the divided-voltage output terminals of the capacitor-voltage divider  4  and the first resistor-voltage divider  5 . 
     The output OSCE of the inverter IV 1  is fed to both gates of the transistor switches SW 1  and SW 2 . The operational amplifier  1  is constructed as shown in FIG.  14 . The ring oscillator  2  and charge pump  3  constitute an internal voltage generator. 
     The operation of the up-converter shown in FIG. 1 is disclosed. 
     A steady state provides the same voltage to the positive input terminal TAPC and the negative input terminal VBGR of the operational amplifier  1 . 
     Increase in up-converted voltage Vpp over a desired voltage triggers the operational amplifier  1  to output a positive output voltage, that brings the output OSCE of the inverter INV 1  into a low level state. This voltage transition halts the oscillation of the ring oscillator  2 ; hence the charge pump  3  stops an up-conversion operation. 
     As time lapses under no up-conversion operation, the up-converted voltage Vpp gradually decreases due to leakage at PN-junction capacitance of transistors of a load circuitry (not shown) to which the up-converted voltage Vpp is supplied. 
     Decrease in up-converted voltage Vpp lower than the desired voltage causes decrease in a voltage at the positive input terminal TAPC of the operational amplifier  1  lower than the reference voltage VBGR. The output of the operational amplifier  1  thus lowers to bring the output of the inverter INV 1  into a high level. This transition initiates the oscillation of the ring oscillator  2 ; hence the charge pump  3  starts an up-conversion operation. 
     The high level-output of the inverter INV 1  turns on the transistor switches SW 1  and SW 2 , which provides the same voltage level to the positive input terminal TAPC of the operational amplifier  1  and the node TAPR of the resistors R 1  and R 2 . 
     As disclosed, the up-converted Vpp is controlled by means of the resistors R 1  and R 2  during the up-conversion operation of the charge pump  3 . 
     On the other hand, increase in up-converted voltage Vpp higher than the desired voltage causes increase in a voltage at the positive input terminal TAPC of the operational amplifier  1  higher than the reference voltage VBGR, to bring the output of the inverter INV 1  into a low level. This transition halts the oscillation of the ring oscillator  2 ; hence the charge pump  3  stops the up-conversion operation. 
     The non-up-conversion state turns off the transistor switches SW 1  and SW 2 , thus no current flowing through the resistors R 1  and R 2 . The up-converted voltage Vpp is then detected only by the capacitors C 1  and C 2 . 
     As disclosed, while the charge pump  3  executes no up-conversion operation, or during decrease in up-converted voltage Vpp, the up-converted voltage Vpp is detected only by the capacitors C 1  and C 2 . Decrease in up-converted voltage Vpp lower the desired voltage again brings the output of the inverter INV 1  into a high level state to initiate the up-conversion operation of the charge pump  3 . 
     As disclosed above,the first embodiment is provided with the transistor SW 1  between the resistors R 1  and R 2  constituting the first resistor-voltage divider  5  and the capacitor-voltage divider  4  connected to the positive input terminal of the operational amplifier  1 . The up-converted voltage Vpp in the waiting mode (no up-conversion operation by the charge pump  3 ) is detected only by the capacitor-voltage divider  4  while no current is flowing through the first resistor-voltage divider  5 . The first embodiment thus achieves power saving in the waiting mode. 
     [The Second Preferred Embodiment] 
     The feature of the second embodiment of the up-converter lies also in low power consumption in the waiting mode, lower than the first embodiment. 
     Shown in FIG. 2 is the second embodiment of the up-converter. Elements in this embodiment that are the same as or analogous to elements in FIG. 1 are referenced by the same reference numbers. 
     The second embodiment is unique in a power controller  6  that controls a power supply voltage fed to the power supply terminal of the operational amplifier  1 . 
     The power controller  6  is provided with an operational amplifier  61  (the second operational amplifier) and an inverter IV 2  connected to the output terminal of the operational amplifier  61 . 
     The operational amplifier  61  operates at an operating speed slower than the operational amplifier  1 , however, is a low power consumption-type with a small operating current. 
     Like the operational amplifier  1 , the operational amplifier  61  compares a divided voltage TAPC of the capacitor-voltage divider  4  and the reference voltage VBGR. The power supply voltage Vcc is always supplied to the power supply terminal of the operational amplifier  61 , different from the operational amplifier  1 . 
     Shown in FIG. 3 is the circuitry of the operational amplifier  61 . The circuit components in FIG. 3 that are the same as or analogous to elements in FIG. 14 are referenced by the same reference numbers. 
     As shown in FIG. 3, the operational amplifier  61  is provided with a transistor Q 7  between the transistors Q 3  and Q 4 , and the transistor Q 5 . 
     Control of a gate voltage BIAS of the transistor Q 7  limits a current flowing from the transistors Q 1  to Q 4  for decrease in current consumption. 
     Illustrated in FIG. 4 are voltage waveforms of the up-converted voltage Vpp, the voltage at the positive input terminal TAPC of the operational amplifier  1 , the output voltage SOSCE of the power controller  6 , and the output OSCE of the inverter IV 1 . 
     The operation of the up-converter shown in FIG. 2 will be explained with reference to the voltage waveforms illustrated in FIG.  4 . 
     A steady state provides the same voltage to the positive input terminal TAPC and the negative input terminal VBGR of the operational amplifier  1 . 
     Increase in up-converted voltage Vpp over a desired voltage raises the output voltage of the operational amplifier  1  to bring the output OSCE of the inverter INV 1  into a low level state. This voltage transition halts the oscillation of the ring oscillator  2 ; hence the charge pump  3  stops an up-conversion operation. 
     The transistors SW 1  and SW 2  are turned off during no up-conversion operation; hence the up-converted voltage Vpp is detected only by the capacitor-voltage divider  4 . 
     Increase in up-converted voltage Vpp over the desired voltage also raises the output voltage of the operational amplifier  61  to bring the output voltage of the inverter INV 2  into a low level state, thus no power supply voltage being fed to the power supply terminal of the operational amplifier  1 . 
     As disclosed, no up-conversion operation by the charge pump  3  provides no current to the first resistor-voltage divider  5  and also the operational amplifier  1 , for achieving further power saving. 
     On the other hand, decrease in up-converted voltage Vpp below the desired voltage lowers the output voltage of the operational amplifier  61  to bring the output voltage of the inverter INV 2  into a high level state. The power supply voltage is thus fed to the power supply terminal of the operational amplifier  1  to operate again. The decrease in up-converted voltage Vpp brings the output of the operational amplifier  1  into a low level for initiating the oscillation of the ring oscillator  2 , hence the charge pump  3  re-starting the up-conversion operation. 
     The high-level output voltage of the inverter INV 2  turns on the transistor switches SW 1  and SW 2  to provide almost the same voltage to the positive input terminal TAPC of the operational amplifier  1  and the divided voltage TAPR of the first resistor-voltage divider  5 . 
     As disclosed, the up-conversion operation by the charge pump  3  provides a current to the first resistor-voltage divider  5  and the power supply voltage to the operational amplifier  1 . The operational amplifier  1  thus controls the up-converted voltage Vpp with the first resistor-voltage divider  5 . 
     As disclosed above, the second embodiment provides no power supply voltage to the operational amplifier  1  so as not to control the up-converted voltage Vpp during no up-conversion operation of the charge pump  3 , thus achieving further power saving compared to the first embodiment. 
     [The Third Preferred Embodiment] 
     The third embodiment is a modification of the first and second embodiments, for achieving a stable positive input voltage to the operational amplifier. 
     Shown in FIG. 5 is third embodiment of the up-converter. Elements in this embodiment that are the same as or analogous to elements in FIG. 2 are referenced by the same reference numbers. 
     The third embodiment is unique in a second resistor-voltage divider  7  in addition to the elements of the second embodiment. The second resistor-voltage divider  7  is constituted by resistors R 1 ′ and R 2 ′ connected between the up-converted voltage Vpp and the ground level. 
     In the second embodiment shown in FIG. 2, no up-conversion operation of the charge pump  3  turns off the transistor switches SW 1  and SW 2 , so that the positive input terminal of the operational amplifier  1  is connected only to the node TAPC of the capacitors C 1  and C 2 . The positive input terminal of the operational amplifier  1  is brought into a complete floating state. Ideally, a voltage corresponding to a capacitance-ratio of the capacitors C 1  and C 2  is fed to the positive input terminal of the operational amplifier  1 . However, in reality, the voltage at the positive input terminal of the operational amplifier  1  gradually lowers due to leakage at the PN-junction of the drain of the transistor switch SW 2  connected to the node TAPC, thus increasing the number of operations of the charge pump  3 . This results in large power consumption in the waiting mode. 
     Contrary to this, the resistors R 1 ′ and R 2 ′ connected to the capacitors C 1  and C 2  in parallel, as shown in FIG. 5, do not bring the positive input terminal of the operational amplifier  1  into a floating state even in the waiting mode. 
     The resistance ratio of the resistors R 1 ′ and R 2 ′ is preferably the same as that of the resistors R 1  and R 2 , however, this is not a must. The resistances of the resistors R 1 ′ and R 2 ′ are preferably larger than those of the resistors R 1  and R 2 . The former resistance, for example, hundred times the latter limits the current flowing through the resistors R 1 ′ and R 2 ′ in the waiting mode to 1/100 of the current flowing through the resistors R 1  and R 2  in the operating mode. 
     As disclosed above, the third embodiment provided with the second resistor-voltage divider  7  connected in parallel to the capacitor-voltage divider  4  prevents the positive input terminal of the operational amplifier  1  from being brought into a floating state while the charge pump  3  is out of operation. The third embodiment offers a stable voltage level at the positive input terminal of the operational amplifier  1 , thus achieving power saving. 
     Like the second embodiment, the third embodiment is provided with the capacitor-voltage divider  4  for quick suppression of voltage variation in response to a sudden change in up-converted voltage Vpp, thus achieving suppression of voltage variation in up-converted voltage Vpp. 
     The second resistor-voltage divider  7  may be added to the up-converter shown in FIG. 1, which also prevents the positive input terminal of the operational amplifier  1  from being brought into a floating state while the charge pump  3  is out of operation, thus achieving power saving. 
     [The Fourth Preferred Embodiment] 
     The feature of the fourth embodiment lies in depression-type capacitors for avoiding leakage at a transistor PN-junction even in the floating state at the node of the capacitors. 
     Shown in FIG. 6 is a circuit diagram of a capacitor-voltage divider  4  and its periphery. The capacitor-voltage divider  4  is provided with depression-type capacitors C 1 ′and C 2 ′connected in series between the up-converted voltage Vpp and the ground level. 
     Illustrated in FIG. 7 is a sectional view of the capacitor C 1 ′. The drain D and the source S of a MOS transistor at the ground level do not cause leakage at the PN-junction between the drain terminal and the substrate. On the other hand, the capacitor C 2 ′ is constructed such that the drain and the source of a MOS transistor are placed at the power supply voltage level so as not cause leakage at the PN-junction. 
     Shown in FIG. 8 is a circuit diagram provided with CMOS-type transistor switches SW 1  and SW 2 . The CMOS-type transistor is not affected by a threshold level of a MOS transistor for accurate voltage transfer to the operational amplifier  1  according to the resistance ratio of the first resistor-voltage divider  5  and the capacitance ratio of the capacitor-voltage divider  4 . 
     [The Other Preferred Embodiments] 
     The preferred embodiments described so far relate to an up-converter for power saving. However, not only the up-converter, but also the present invention is applicable to a down-converter. 
     Shown in FIG. 9 is a circuit diagram of a down-converter provided with a resistor-voltage divider and a capacitor-voltage divider, like shown in FIG.  1 . 
     Elements in this embodiment that are the same as or analogous to elements in FIG. 1 are referenced by the same reference numbers. 
     The down-converter (FIG. 9) is provided with an operational amplifier  1 , a PMOS transistor Q 8 , a capacitor-voltage divider  4  constituted by capacitors C 1  and C 2  connected in series between a down-converted voltage Vout and the ground level, a first resistor-voltage divider  5  constituted by resistors R 1  and R 2  connected in series between the down-converted voltage Vout and the ground level, a PMOS transistor switch SW 10  (the first switch) connected between the resistors R 1  and R 2 , and a PMOS transistor switch SW 20  (the second switch) connected between the capacitor-voltage divider  4  and the first resistor-voltage divider  5 . 
     The output OSCE of the operational amplifier  1  is fed to both the gates of the transistor switches SW 1 O and SW 20 . 
     Increase in down-converted voltage Vout higher than a desired voltage brings a divided voltage TAPR of the resistor-voltage divider  5  into a level higher than a reference voltage VBGR. The transition gradually raises the output voltage of the operational amplifier  1 , to turn off the transistor Q 8  for lowering the down-converted voltage Vout. 
     The high level-output of the operational amplifier  1  turns off the transistor switches SW 10  and SW 20 , which provides no current flowing therethrough. The down-converted voltage Vout is thus detected only by the capacitors C 1  and C 2  for power saving. 
     This embodiment is provided with the capacitor-voltage divider  4  for quick suppression of voltage variation in response to a sudden change in down-converted voltage Vout. 
     On the other hand, decrease in down-converted voltage Vout lower than the desired voltage brings a divided voltage TAPR of the resistor-voltage divider  5  into a level lower than the reference voltage VBGR. The transition gradually lowers the output voltage of the operational amplifier  1 , to turn on the transistor Q 8  for raising the down-converted voltage Vout. 
     The down-converter shown in FIG. 10 is unique in a power controller  6  that controls a power supply voltage fed to the power supply terminal of the operational amplifier  1 . 
     Elements in this embodiment that are the same as or analogous to elements in FIG. 9 are referenced by the same reference numbers. 
     The power controller  6  is provided with an operational amplifier  61  (the second operational amplifier) and an inverter IV 2  connected to the output terminal of the operational amplifier  61 . 
     The operational amplifier  61  operates at an operating speed slower than the operational amplifier  1 , however, is a low power consumption-type with a small operating current, like shown in FIG.  3 . 
     Like the operational amplifier  1 , the operational amplifier  61  compares a divided voltage TAPC of the capacitor-voltage divider  4  and the reference voltage VBGR. The power supply voltage Vcc is always supplied to the power supply terminal of the operational amplifier  61 , different from the operational amplifier  1 . 
     In FIG. 10, a steady state provides the same voltage to the positive input terminal TAPC and the negative input terminal VBGR of the operational amplifier  1 . 
     Increase in down-converted voltage Vout over a desired voltage raises the output voltage of the operational amplifier  1  to turn off the transistor Q 8  for down-conversion operation. The transistors SW 10  and SW 20  are turned off during down-version operation; hence the down-converted voltage Vout is detected only by the capacitor-voltage divider  4 . 
     Increase in down-converted voltage Vout over the desired voltage also raises the output voltage of the operational amplifier  61  to bring the output voltage of the inverter INV 2  into a low level state, thus no power supply voltage being fed to the power supply terminal of the operational amplifier  1 . 
     As disclosed, down-conversion operation provides no current to the operational amplifier  1 , for achieving power saving. 
     On the other hand, decrease in down-converted voltage Vout below the desired voltage lowers the output voltage of the operational amplifier  61  to bring the output voltage of the inverter INV 2  into a high level state. The power supply voltage is thus fed to the power supply terminal of the operational amplifier  1  to operate again. The decrease in down-converted voltage Vpp brings the output of the operational amplifier  1  in to a low level to turn on the transistor Q 8  for raising the down-converted voltage Vout. 
     As disclosed above, this embodiment provides no power supply voltage to the operational amplifier  1  during down conversion operation, thus achieving further power saving compared to the embodiment shown in FIG.  9 . 
     The embodiment shown in FIG. 11 is unique in a second resistor-voltage divider  7  in addition to the elements shown in FIG.  10 . The second resistor-voltage divider  7  is constituted by resistors R 1 ′ and R 2 ′ connected between the down-converted voltage Vout and the ground level. 
     In the embodiment shown in FIG. 10, increase in down-converted voltage Vout turns off the transistor switches SW 10  and SW 20 , so that the positive input terminal of the operational amplifier  1  is connected only to the node TAPC of the capacitors C 1  and C 2 . The positive input terminal of the operational amplifier  1  is brought into a complete floating state. Ideally, a voltage corresponding to a capacitance-ratio of the capacitors C 1  and C 2  is fed to the positive input terminal of the operational amplifier  1 . However, in reality, the voltage at the positive input terminal of the operational amplifier  1  gradually lowers due to leakage at the PN-junction of the drain of the transistor switch SW 20  connected to the node TAPC, to turn on the transistor Q 8 , thus increasing the number of operations of raising the down-converted voltage Vout. This results in large power consumption in the waiting mode. 
     Contrary to this, the resistors R 1 ′ and R 2 ′ connected to the capacitors C 1  and C 2  in parallel, as shown in FIG. 11, do not bring the positive input terminal of the operational amplifier  1  into a floating state. 
     The resistance ratio of the resistors R 1 ′ and R 2 ′ is preferably the same as that of the resistors R 1  and R 2 , however, this is not a must. The resistances of the resistors R 1 ′ and R 2 ′ are preferably larger than those of the resistors R 1  and R 2 . The former resistance, for example, hundred times the latter limits the current flowing through the resistors R 1 ′ and R 2 ′ in the waiting mode to 1/100 of the current flowing through the resistors R 1  and R 2  in the operating mode. 
     As disclosed above, the embodiment shown in FIG. 11 provided with the second resistor-voltage divider  7  connected in parallel to the capacitor-voltage divider  4  prevents the positive input terminal of the operational amplifier  1  from being brought into a floating state while lowering the down-converted voltage Vout. This embodiment offers a stable voltage level at the positive input terminal of the operational amplifier  1 , thus achieving power saving. 
     Like the embodiment shown in FIG. 9, this embodiment is provided with the capacitor-voltage divider  4  for quick suppression of voltage variation in response to a sudden change in down-converted voltage Vout, thus achieving suppression of voltage variation in down-converted voltage Vout. 
     The down-converters shown in FIGS. 9 to  11  are constructed almost same as the up-converters, such as, shown in FIG. 1, except the transistor Q 9  instead of the ring oscillator  2  and the charge pump  3  and the PMOS transistor switches TW 10  and TW 20  instead of the NMOS transistor switches TW 1  and TW 2 . Therefore, the present invention achieves power saving with a small chip size also in the down-converter. 
     As disclosed above, according to the present invention, the internal voltage, such as, the up-converted voltage and the down-converted voltage, is detected by the capacitor-voltage divider while no current is flowing through the resistor-voltage divider in the waiting mode where the internal voltage generator is out of operation. The present invention therefore achieves power saving in the waiting mode. 
     Moreover, since the capacitor-voltage divider quickly follows internal voltage variation, the present invention achieves a feedback control to regain a desired internal voltage even if it varies suddenly.