Abstract:
This disclosure concerns a semiconductor device that includes a booster portion including first switches and first capacitors; and a voltage converter comprising boosting stages each of which includes a second capacitor whose one end is connected to a first voltage source via a second switch and whose other end is connected to a reference voltage via a third switch, the second capacitor being charged on the basis of a voltage difference between the first voltage source and the reference voltage, and comprising fourth switches each of which is provided between two of the boosting stages to control the number of the second capacitors connected in series between a second power source and the other ends of the first capacitors according to the voltages of the first and second voltage sources, the voltage converter outputting clock signals with phases opposed to each other to adjacent ones of the first capacitors.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
   This application is based upon and claims the benefit of priority from the prior Japanese Patent Applications No. 2003-429150, filed on Dec. 25, 2003, the entire contents of which are incorporated herein by reference. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a semiconductor device provided with a booster circuit. 
   2. Background Art 
     FIG. 15  is a circuit diagram of a booster circuit  10  housed in a conventional semiconductor device (JP2002-51538A, hereinafter, referred to as Patent literature 1). 
   The booster circuit  10  is provided with transistors QNA 1  to QNA m  connected in series between an input IN and an output OUT and capacitors CA 1  to CA m  whose one ends are respectively connected to the respective transistors QNA 1  to QNA m . The other ends of the capacitors CA 1  to CA m  are connected to a clock supplying source via a voltage converting portion  12 , 
   The voltage converting portion  12  has voltage converting circuits VB 1  to VB m  connected to respective other ends of the respective capacitors CA 1  to CA m . The voltage converting circuits VB 1  to VB m  receive clock signals Φ and Φbar having phases opposed to each other alternately and they boosts voltages of these clock signals to supply them to the capacitors CA 1  to CA m . Timing charts of the clock signal Φ and Φbar are illustrated in  FIG. 17 . Thereby, the booster portion  11  boosts the input voltage Vin to output an output voltage Vout higher than the input voltage Vin. 
     FIG. 16  is a circuit diagram illustrating a constitution of one (hereinafter, called “voltage converting circuit VB) of the voltage converting circuits VB 1  to VB m . The voltage converting circuit VB has a plurality of boosting stages including capacitors CB 1  to CB k  whose one ends are connected to a voltage source Vin via n-type transistors QNB 1  to QNB k  and whose other ends are grounded via n-type transistors QNC 1  to QNC k . The voltage converting circuit VB further has p-type transistors QPA 1  to QPA k . The transistors QPA 1  to QPA k  can connect all the capacitors CB 1  to CB k  in series between input and output. 
   Since the transistors QNB 1  to QNB k  and QNC 1  to QNC k , and the transistors QPA 1  to QPA k  are different in conductive type, they are alternately switched by the clock signal Φ or Φbar. When the clock signal Φ or Φbar is High, the respective capacitors CB 1  to CB k  are connected in parallel between the input voltage Vin and the ground, and when the clock signal Φ or Φbar is Low, the capacitors CB 1  to CB k  are connected in series between the input voltage Vin and the output CLKOUT. As illustrated in  FIG. 17 , according to repetition of the clock signal Φ or Φbar between High and Low, the voltage converting circuit VB boosts the input voltage Vin to output the same from the output CLKOUT to either of the other ends of the capacitor CA 1  to CA m . 
   Now, it is preferable that a power source voltage supplied externally of the semiconductor device (hereinafter, also simply called “power source voltage”) is low for reducing power consumption. Conventionally, the power source voltage is lowered stepwise such as 5V and 3.3V (or 2.5V). In recent years, the power source voltage is further lowered from 3.3V to 1.8V. In such a transient term where the power source voltage is being lowered in this manner, a semiconductor device is required to accommodate a plurality of power source voltages with voltages different from one another. 
   Further, even in a semiconductor device corresponding to a single power source voltage in an ordinary operation, there occurs a case that a power source voltage higher than a power source voltage in the ordinary operation is used in a test step before shipping. For example, in order to make a judgement about an initial defective, a high voltage is used as a power source for accelerating failure in a burn-in step where a device is made defective by accelerating the defective condition. Thereby, it is preferable that the semiconductor device corresponds to a plurality of power source voltages with different voltages. 
   In general, in case that an operation of a semiconductor device is ensured when a power source voltage applied externally is in a range of Vccmin to Vccmax, such a design is made that the booster circuit outputs a desired output voltage when the power source voltage is Vccmin. An internal supply voltage (hereinafter, simply called “supply voltage”) Vin is an external power source voltage itself or a voltage obtained by voltage-reducing this voltage, and it increases/decreases depending on the power source voltage. Thereby, assuming that the supply voltage Vin is in a range of Vinmin to Vinmax, the booster circuit is designed such that the supply voltage Vin outputs a desired output voltage, when the supply voltage Vin is Vinmin. For example, when voltages with two different ranges of 1.8V and 3V are used as the power source voltage Vcc, such a setting can be made that Vin=1.5V in case of Vcc=1.8V range (Vcc=1.5V to 2V) and Vin=2.5V in case of Vcc=3V range (Vcc=2.5V to 3.6V). In this case, the booster circuit  10  is generally designed so as to output a desired output voltage in case of Vcc=1.5V, namely, Vin=1.5V. 
   In this case, however, when the power source voltage Vcc is on the side of the Vccmax, or when the power source voltage Vcc in the burn-in step is higher than Vccmax, if the supply voltage Vin is set to be High according to the power source voltage Vcc, the booster circuit  10  results in possession of an excessive boosting capacity. For example, in case that the booster circuit  10  is designed so as to output a desired output voltage in case of Vcc=1.5V and Vin=1.5V, the booster circuit  10  has an excessive capacity with setting of Vcc=3V and Vin=2.5V (&gt;1.5V). 
   Further, when the supply voltage Vin is set to be higher according to a relatively high power source voltage Vcc, all the boosting stages in the voltage converting circuit VB are boosted on the basis of the supply voltage Vin, so that excessive voltages are applied to transistors in the voltage converting circuit VB. Therefore, some or all of the transistors QNB 1  to QNB k  must comprise high breakdown voltage transistors. Since the high breakdown voltage transistor has a lower conductance than that of a low breakdown voltage transistor, it is necessary to increase the size (the channel width) of the former transistor in order to maintain a conductance approximately equal to that of the low breakdown voltage transistor. As a result, since a parasitic capacitance increases, there occur a problem that an operation efficiency of the voltage converting circuit VB lowers and a problem that a circuit area of the booster circuit  10  becomes large. 
   In order to solves the above problem, for example, Vin can be set to 1.5V even in case of Vcc=3V. However, a voltage drop of Vcc=3V down to 1.5V causes waste of power, which is undesirable. That is, considering the power consumption in the range of Vcc=3V, a consumed current of a product corresponding to both Vcc=1.8V range and Vcc=3V range becomes larger than that of a product corresponding to only Vcc=3V range. 
   SUMMARY OF THE INVENTION 
   A semiconductor device comprises a booster circuit portion including a plurality of first switching elements connected in series from an output portion and a plurality of first capacitors whose one ends are connected between respective adjacent ones of the first switching elements, the booster circuit portion being inputted with clock signals from the other ends of the first capacitors to output a boosted voltage from the output portion; and 
   a voltage converting circuit portion comprising a plurality of boosting stages each of which includes a second capacitor whose one end is connected to a first voltage source via a second switching element and whose other end is connected to a reference voltage via a third switching element, said second capacitor being charged according to a voltage difference between the first voltage source and the reference voltage, and comprising a plurality of fourth switching elements each of which is provided at least between adjacent ones of the boosting stages to control the number of the second capacitors connected in series between a second power source and the other ends of the first capacitors on the basis of the voltages of the first and second voltage sources, said voltage converting circuit portion outputting clock signals with phases opposed to each other to adjacent ones of the first capacitors. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a circuit diagram of a booster circuit  100  which is housed in a semiconductor device according to a first embodiment of the present invention; 
       FIG. 2  is a circuit diagram illustrating a constitution of any one of voltage converting circuits VA 1  to VA m  (hereinafter, referred to as “a voltage converting circuit VA); 
       FIG. 3  is a timing chart of a clock signal CS IN , a clock signal CLK 1  and a clock signal CLK 2  in Mode  1 ; 
       FIG. 4  is a timing chart of the clock signal CS IN , the clock signal CLK 1  and the clock signal CLK 2  in mode  2 ; 
       FIG. 5  is a circuit diagram of a booster circuit  200  which is housed in a semiconductor device according to a second embodiment of the present invention; 
       FIG. 6  is a circuit diagram illustrating a constitution of a voltage converting circuit VC; 
       FIG. 7  is an equivalent circuit diagram illustrating an action in Mode  1  of the voltage converting circuit VC; 
       FIG. 8  is an equivalent circuit diagram illustrating an action in Mode  2  of the voltage converting circuit VC; 
       FIG. 9  is an equivalent circuit diagram illustrating an action in Mode  3  of the voltage converting circuit VC; 
       FIG. 10  is one embodiment of a switching element SW 1 ; 
       FIG. 11  is one embodiment of a switching element SW 2 ; 
       FIG. 12  is one embodiment of a switching element SW 3 ; 
       FIG. 13  is a circuit diagram of a voltage converting circuit VD inside a booster circuit according to a third embodiment of the present invention; 
       FIG. 14  is a circuit diagram of a voltage converting circuit VE inside the booster circuit according to a fourth embodiment of the present invention; 
       FIG. 15  is a circuit diagram of a booster circuit  10  housed in a conventional semiconductor device; 
       FIG. 16  is a circuit diagram illustrating a constitution of a voltage converting circuit VB; and 
       FIG. 17  is a timing chart of clock signals Φ and Φbar. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Embodiments of the present invention will be explained below with reference to the drawings. The present invention is not limited to the following embodiments. Same constitutional elements or parts in respective embodiments are attached with same reference numerals. Further, in the following embodiments, even if p-type transistors are used instead of the n-type transistors and n-type transistors are used instead of the p-type transistors, advantages or merits obtained by these embodiments are not lost. 
   A semiconductor device according each of the following embodiments is provided between a clock supplying portion and a booster portion with a voltage converting circuit which can increase/decrease the number of boosting stages according to a power source voltage. Therefore, a booster circuit in the semiconductor device can supply a stable output voltage in a wide range of a power source voltage. These embodiments can be each used in a semiconductor device requiring a voltage higher than that of a power source voltage for a NAND type non-volatile memory or the like. 
   FIRST EMBODIMENT 
     FIG. 1  is a circuit diagram of a booster circuit  100  embedded in a semiconductor device according to a first embodiment of the present invention. A semiconductor device is further provided with, for example, a non-volatile memory (not shown), and the booster circuit  100  outputs a boosted voltage to the non-volatile memory. 
   The booster circuit  100  is provided with a booster portion  110  and a voltage converting circuit portion  120 . The booster portion  110  includes n-type transistors QNA 1  to QNA m , and capacitors CA 1  to CA m-1 . Incidentally, m is an integer which is 2 or more. The transistors QNA 1  to QNA m  are connected in series from an output portion OUT. Each of the capacitors CA 1  to CA m-1  is connected at its one terminal to a connection point between adjacent transistors of the transistors QNA 1  to QNA m . The other terminals of the capacitors CA 1  to CA m-1  are connected to the voltage converting circuit portion  120 . Each of the transistors QNA 1  to QNA m  is a MOSFET (Metal-Oxide Semiconductor Field Effect Transistor), for example. Each of the capacitors CA 1  to CA m-1  is a MOS capacitor comprising a gate electrode, a gate insulating film, a semiconductor substrate or a well diffusion layer and a diffusion layer coming in electrical contact with the semiconductor substrate or the well diffusion layer, which constitute the transistors QNA 1  to QNA m . The gate electrode comprises, for example, a doped silicon, the gate insulating film comprises, for example, a silicon oxide film, and the well diffusion layer comprises, for example, an N-type well diffusion layer formed on the semiconductor substrate. 
   A large voltage can be applied to insulating films between both electrodes of the capacitors CA 1  to CA m-1  at a time of boosting operation. Therefore, in order to avoid breakdown of the capacitors CA 1  to CA m-1 , a gate insulating film of a high breakdown voltage transistor is used for an insulating film of each of the capacitors CA 1  to CA m-1 . 
   The voltage converting circuit portion  120  includes voltage converting circuits VA 1  to VA m . Each of the voltage converting circuits VA 1  to VA m  is provided with a clock input portion CLKIN, a clock output portion CLKOUT and a mode input portion MODE. The clock input portion CLKIN of a voltage converting circuit VA 2k-1  is inputted with a clock signal Φ, and the clock input portion CLKIN of a voltage converting circuit VA 2k  is inputted with a clock signal Φbar (Φbar is a reversed signal of Φ). Incidentally, k is a natural number of m/2 or less. The clock output portion CLKOUT is connected to the other electrode of the capacitors CA 1  to CA m-1  or the transistor QNA 1 . Each of the voltage converting circuits VA 1  to VA m  has boosting stages (refer to  FIG. 2 ) therein, and it boosts the clock signal Φ or the clock signal Φbar to output the boosted signals from the clock output portion CLKOUT. 
   A mode signal inputted into the mode input portion MODE is used for changing the number of boosting stages inside the voltage converting circuits VA 1  to VA m  according to magnitudes of the supply voltages Vin 1  to Vin 5  (refer to  FIG. 2 ). In this embodiment, the mode signal takes two values of High and Low, and switching between the values is conducted according to High or Low of the supply voltage. 
   An operation of the booster circuit  100  will be explained. The clock signals Φ and Φbar have opposite phases to each other, and they repeat High and Low, as illustrated in  FIG. 17 . The voltage converting circuits VA 1  to VA m  boost the clock signal Φ or Φbar by the boosting stages of the number based upon the mode signal and output the boosted signal to the capacitors CA 1  to CA m-1  as the clock signal CS out . The clock signal CS out  boosted by the voltage converting circuit VA 1  charges the electrode of the capacitor CA 1  via the transistor QNA 1 , which electrode is connected to the transistor QNA 2 . 
   Next, the capacitor CA 1  receives a clock signal CS out  bar with an opposite phase to the clock signal CS OUT  at an electrode connected to the voltage converting circuit VA 2 , and it further boosts a voltage at an electrode connected to the transistor QNA 2 . Thereby, the transistor QNA 2  is made conductive, and the capacitor CA 1  charges an adjacent capacitor CA 2  via the transistor QNA 2 . 
   Thereafter, the capacitor CA 2  receives a clock signal CS out  via the voltage converting circuit VA 3  and it further boosts a voltage at an electrode connected to the transistor QNA 3 . Thereby, the transistor QNA 3  is made conductive and the capacitor CA 2  charges an adjacent capacitor CA 3  via the transistor QNA 3 . By repeating such an operation, the capacitor CA m-1  outputs the boosted voltage from the output portion OUT via the transistor QNA m  as an output voltage Vout. 
     FIG. 2  is a circuit diagram illustrating a constitution of any one of the voltage converting circuits VA 1  to VA m  (hereinafter, referred to as “a voltage converting circuit VA”). The voltage converting circuit VA is provided with boosting stages BS 1  to BS 4 , p-type transistors QPB 1  to QPB 5  and an OR gate G 1 . 
   The boosting stage BS 1  includes an n-type transistor QND 1 , an n-type transistor QNE 1  and a capacitor CD 1 . The boosting stage BS 2  includes an n-type transistor QND 2 , an n-type transistor QNE 2  and a capacitor CD 2 . The boosting stage BS 3  includes an n-type transistor QND 3 , an n-type transistor QNE 3  and a capacitor CD 3 . Further, the boosting stage BS 4  includes an n-type transistor QND 4 , an n-type transistor QNE 4  and a capacitor CD 4 . The transistor QND 1 , the capacitor CD 1  and the transistor QNE 1  are connected in series between the supply voltage Vin 1  and the ground. The transistor QND 2 , the capacitor CD 2  and the transistor QNE 2  are connected in series between the supply voltage Vin 2  and the ground. The transistor QND 3 , the capacitor CD 3  and the transistor QNE 3  are connected in series between the supply voltage Vin 3  and the ground. Further, the transistor QND 4 , the capacitor CD 4  and the transistor QNE 4  are connected in series between the supply voltage Vin 4  and the ground. Each of the gates of the transistors QND 1 , QND 2 , QNE 1  and QNE 2  is inputted with a clock signal CLK 2 . Each of the gates of the transistors QND 3 , QND 4 , QNE 3  and QNE 4  is inputted with a clock signal CLK 1 . 
   Each of the transistors QPB  2  to QPB 4  is provided between adjacent boosting stages of the boosting stages BS 1  to BS 4 . The transistor QPB 2  is connected between an electrode on the side of a supply voltage Vin 1  of the capacitor CD 1  and an electrode on the side of a ground of the capacitor CD 2 . Similarly, the transistor QPB 3  is connected between an electrode of the capacitor CD 2  on the side of the supply voltage Vin 2  and an electrode of the capacitor CD 3  on the ground side thereof. The transistor QPB 4  is connected between an electrode on the side of a supply voltage Vin 3  of the capacitor CD 3  and an electrode on the side of a ground of the capacitor CD 4 . 
   The transistor QPB 1  is connected between a supply voltage Vin 5  and an electrode on the side of a ground of the capacitor CD 1 , and the transistor QPB 5  is connected between an electrode on the side of the supply voltage Vin 4  of the capacitor CD 4  and the clock output portion CLKOUT. Each of the gates of the transistors QPB 1  and QPB 2  is inputted with a clock signal CLK 2 . Each of the gates of the transistors QPB 3  to QPB 5  is inputted with a clock signal CLK 1 . 
   The clock signals CLK 1  and CLK 2  are generated by a clock signal CSIN (Φ or Φbar) from the clock input portion CLKIN. The clock signal CLK 1  is the same signal as the clock signal CSIN. The OR gate G 1  outputs a logical OR of the clock signal CSIN and a mode signal from the mode input terminal MODE as the clock signal CLK 2 . 
   In this embodiment, the transistors QND 1  to QND 4 , QNE 1  to QNE 4  and QPB 1  to QPB 5  may be MOSFETs. The capacitors CD 1  to CD 4  are, for example, MOS capacitors comprising a gate electrode, a gate insulating film, a semiconductor substrate or a well diffusion layer, and a diffuser layer coming in electrical contact with the semiconductor substrate or the well diffusion layer, which constitute the transistors QND 1  to QND 4 , QNE 1  to QNE 4  and QPB 1  to QPB 5 . The gate electrode comprises, for example, doped silicon, the gate insulating layer comprises, for example, a silicon oxide film, and the well diffusion layer comprises, for example, an N-type well diffusion layer formed on the semiconductor substrate. Further, it is preferable that the n-type transistors QND 1 , QND 2 , QND 3  and QND 4  are depression type transistors or enhancement type transistors whose threshold voltage is very low. Thereby, the capacitors CD 1 , CD 2 , CD 3  and CD 4  can be charged to voltages which have not been dropped from the supply voltages Vin 1 , Vin 2 , Vin 3  and Vin 4 . 
   The transistors QND 1  to QND 4 , QNE 1  to QNE 4  and QPB 1  to QPB 5  all may be low breakdown voltage transistors. The low breakdown voltage transistor is a transistor having a gate insulating film thickness of about 10 nm or less in an Equivalent Oxide Thickness (EOT). An insulating film between electrodes of each of the capacitors CD 1  to CD 4  may have a low breakdown voltage film thickness, namely, a film thickness of 10 nm or less. Since the transistors QND 1  to QND 4 , QNE 1  to QNE 4  and QPB 1  to QPB 5  are the low breakdown voltage transistors, a parasitic capacitance degrading a capacity of the booster circuit becomes small, and a circuit area also becomes small. Since the capacitors CD 1  to CD 4  are ones for the low breakdown voltage, they can have larger capacitances with smaller areas. Thereby, the entire booster circuit  100  can be reduced in area. It is preferable for facilitating manufacture that an insulating film thickness between the electrodes of each of the capacitors CD 1  to CD 4  is equal to any one of the gate insulating films of the transistors QND 1  to QND 4 , QNE 1  to QNE 4  and QPB 1  to QPB 5 . 
     FIG. 3  and  FIG. 4  are timing charts of clock signals CSIN, clock signals CLK 1  and CLK 2  in Mode  1  and Mode  2 , respectively. In the Mode  1  illustrated in  FIG. 3 , the mode signal is Low (non-active state). The Mode  1  is a mode used when the supply voltages Vin 1  to Vin 5  are relatively low. The case that the supply voltages are Low means a case that, for example, a security range of the power source voltage from the outside of the semiconductor device is a wide range or a dual range and the supply voltages Vin 1  to Vin 5  are the minimum voltage Vccmin or so in the security range. 
   In Mode  2  illustrated in  FIG. 4 , the mode signal is High (an active state). The Mode  2  is a mode used when the supply voltages Vin 1  to Vin 5  are relatively high. The case that the supply voltages are High means a case that, for example, the security range of the power source voltage from the outside of the semiconductor device is a wide range or a dual range and the supply voltages Vin 1  to Vin 5  are close to the maximum voltage Vccmax in an security range or the supply voltages Vin 1  to Vin 5  are set to the voltage Vccmax or more in a burn-in step on trial. An operation of the voltage converting circuit VA will be explained below for each Mode. 
   (Mode  1 ) 
   In Mode  1 , the clock signals CLK 1  and CLK 2  have the same phase and High and Low are repeated. Thereby, all the boosting stages BS 1  to BS 4  operate. 
   First, when the clock signals CLK 1  and CLK 2  are High (Vin 6 ), the transistors QND 1  to QND 4  and QNE 1  to QNE 4  are turned on and the transistors QPB 1  to QPB 5  are turned off. Thereby, the capacitors CD 1  to CD 4  are respectively charged between the supply voltages Vin 1  to Vin 4  and the ground. For example, assuming that drop of charging voltage due to respective thresholds of the transistors QND 1  to QND 4  does not occur, voltages of the supply voltages Vin 1 , Vin 2 , Vin 3  and Vin 4  are charged between respective electrodes of each of the capacitors CD 1  to CD 4 . 
   Next, when the clock signals CLK 1  and CLK 2  are Low (a ground potential), the transistors QPB 1  to QPB 5  are turned on and the transistors QND 1  to QND 4  and QNE 1  to QNE 4  are turned off. Thereby, the capacitors CD 1  to CD 4  are connected in series via the transistors QPB 1  to QPB 5  between the supply voltage Vin  5  and the clock output portion CLKOUT. As a result, clock signal CSOUT boosted from the supply voltages Vin 1  to Vin 5  is supplied from the clock output portion CLKOUT to any one of the capacitors CA 1  to CA m  illustrated in  FIG. 1 . The clock signal CSOUT is boosted up to Vin 1 +Vin 2 +Vin 3 +Vin 4 +Vin 5  or so. A voltage of the clock signal CSOUT at this time is defined as VCLK 1 . 
   (Mode  2 ) 
   In Mode  2 , the clock signal CLK 2  is kept High and the clock signal CLK 1  repeats High and Low. Thereby, the boosting stages BS 1  and BS 2  do not operate but only the boosting stages BS 3  and BS 4  operate. 
   First, when the clock signal CLK 1  is High, the transistors QND 3 , QND 4 , QNE 3  and QNE 4  are turned on and the transistors QPB 3  to QPB 5  are turned off. Thereby, each of the capacitors CD 3  and CD 4  is charged between each of the supply voltages Vin 3 , Vin 4  and the ground. Each of the voltages of the supply voltages Vin 3  and Vin 4  is charged between the electrodes of each of the capacitors CD 3  and CD 4 . 
   Next, when the clock signal CLK 1  is Low, the transistors QPB 3  to QPB 5  are turned on and the transistors QND 3 , QND 4 , QNE 3  and QNE 4  are turned off. Further, since the clock signal CLK 2  is always High, the transistors QND 1 , QND 2 , QNE 1  and QNE 2  are ON and the transistors QPB 1  to QPB 2  are OFF. Thereby, capacitors CD 3  to CD 4  are connected in series via the transistors QND 2  and QPB 3  to QPB 5  between the supply voltage Vin 2  and the clock output portion CLKOUT. As a result, the clock signal CSOUT boosted from the supply voltages Vin 2  to Vin 4  is supplied from the clock output portion CLKOUT to any one of the capacitors CA 1  to CA m  illustrated in  FIG. 1 . The clock signal CSOUT is boosted up to Vin 2 +Vin 3 +Vin 4  or so. The voltage of the clock signal CS OUT  at this time is defined as VCLK 2 . 
   It is apparent that the voltage VCLK 2  is smaller than the voltage VCLK 1 . For example, assuming that the supply voltages Vin 1  to Vin 5  are Vin, VCLK 1 =5*Vin and VCLK 2 =3*Vin. 
   Therefore, the voltage converting circuit VA in this embodiment boosts a clock signal relatively largely according to Mode  1 , when the supply voltages Vin 1  to Vin 5  are relatively low (for example, about 1.5V), and the voltage converting circuit VA boosts the clock signal relatively small according to Mode  2 , when the supply voltages Vin 1  to Vin 6  are relatively high (for example, about 2.5V or more). 
   As a result, the voltage converting circuit VA can supply a clock signal CSOUT with a stable voltage to the capacitors CA 1  to CA m  without depending on the supply voltages Vin 1  to Vin 5 . That is, the booster circuit  100  illustrated in  FIG. 1  can have a stable boosting capacity even if supply voltages from the outside have various voltage values different from each other. 
   Further, according to this embodiment, when the supply voltages are relatively high, the capacitors CD 1  and CD 2  in the first and second boosting stages BS 1  and BS 2  are not charged/discharged. Thereby, even if the supply voltages become large, increase in consumed power in the voltage converting circuit VA is suppressed. 
   In this embodiment, the voltage converting circuits VA 1  to VA m  have been provided so as to correspond to the transistors QNA 1  to QNA m , respectively. However, the voltage converting circuit may be provided for each plurality of transistors of the transistors QNA 1  to QNA m . As illustrated in  FIG. 5 , for example, two voltage converting circuits VA may be provided so as to correspond to the clock signals Φ and Φbar. 
   All the supply voltages Vin 1  to Vin 5  may be equal in order to facilitate voltage control on the clock output portion CLKOUT. On the other hand, some of the supply voltages Vin 1  to Vin 5  may be set to different values and the others may be set to equal values. For example, only the value of the supply voltage Vin 5  is larger than those of the other supply voltages. 
   In this embodiment, all the transistors QPB 1  to QPB 5 , QND 1  to QND 4  and QNE 1  to QNE 4  have been the low breakdown voltage transistors, but some of these transistors may be high breakdown voltage transistors due to that some of the supply voltages are set to high voltages. The high breakdown voltage transistor is a transistor having a gate insulating film with a film-thickness of about 10 nm or more in an oxide film conversion film thickness. For example, when only the supply voltage Vin 2  is made larger than those of the other supply voltages, the transistors QPB 2 , QND 2  and QNE 2  may be high breakdown voltage transistors. In this case, the size and parasitic capacitance of the transistors QPB 2 , QND 2  and QNE 2  become large, but such an advantage that a boosting capacity is stabilized can be obtained. 
   In this embodiment, the number of boosting stages is four of the stages BS 1  to BS 4 . However, the number of boosting stages may be three or less, or five or more. Incidentally, it is preferable that the number of boosting stages is four stages or less so as not to increase the parasitic capacitance and not to increase the voltage loss. 
   Further, in this embodiment, the transistors QPB 1  to QPB 5  and the transistors QNE 1  to QNE 4  are driven in a synchronism with each other by the clock signals CLK 1  and CLK 2 . However, in order to prevent the voltage loss from increasing, the transistors QPB 1  to QPB 5  may be driven with a delay to the transistors QNE 1  to QNE 4 . Further, in this embodiment, such a constitution is employed that the clock signal CLK 2  whose amplitude is Vin 6  is inputted in all the transistors QND 1  and QND 2 , QNE 1  and QNE 2 , and QPB 1  and QPB 2 , but such a constitution may be employed that some of the these transistors are inputted with a clock signal with the same phase as and an amplitude different from the clock signal CLK 2 . Further, such a constitution is employed that the clock signal CLK 1  whose amplitude is Vin 6  is inputted in all the transistors QND 3  and QND 4 , QNE 3  and QNE 4 , and QPB 3  to QPB 5 , but such a constitution may be employed that some of these transistors are inputted with a clock signal with the same phase as and an amplitude different from the clock signal CLK 1 . 
   SECOND EMBODIMENT 
     FIG. 5  is a circuit diagram of a booster circuit  200  housed in a semiconductor device according to a second embodiment of the present invention. The booster circuit  200  is provided with a booster portion  210  and a voltage converting circuit portion  220 . The booster portion  210  includes n-type transistors QNA 0  to QNA m , and capacitors CA 1  to CA m . The transistors QNA 0  to QNA m  are connected in series between a supply voltage Vin and an output portion OUT. Each of the capacitors CA 1  to CA m  is connected at its one electrode to a node between adjacent transistors of the transistors QNA 0  to QNA m . The other electrodes of the capacitors CA 1  to CA m  are connected to the voltage converting circuit portion  220 . 
   The transistors QNA 0  to QNA m  may be MOSFETs similar to the transistors QNA 1  to QNA m  in the first embodiment. The capacitors CA 1  to CA m  may be MOS capacitors similar to the capacitors CA 1  to CA m-1  in the first embodiment. 
   The voltage converting circuit portion  220  has voltage converting circuits VC 1  and VC 2 . Each of the voltage converting circuits VC 1  and VC 2  comprise a clock input portion CLKIN, a clock output portion CLKOUT, and a mode input portion MODE. The clock input portion CLKIN of the voltage converting circuit VC 1  is inputted with a clock signal Φ, and the clock input portion CLKIN of the voltage converting circuit VC 2  is inputted with a clock signal Φbar. The clock output portion CLKOUT of the voltage converting circuit VC 1  is connected to the other electrode of the capacitor CA 2k-1 , and the clock output portion CLKOUT of the voltage converting circuit VC 2  is connected to the other electrode of the capacitor CA 2k . The voltage converting circuit VC 1  or VC 2  has boosting stages (refer to  FIG. 6 ) therein, and it boosts a clock signal Φ or Φbar illustrated in  FIG. 17  to output the same from the clock output portion CLKOUT. 
   A mode signal inputted into the mode input portion MODE is used for changing the number of boosting stages or capacitance of the boosting stage inside the voltage converting circuit VC 1  or VC 2  according to the magnitude of the supply voltages Vin 1  to Vin 3  (refer to  FIG. 6 ). In this embodiment, the mode signal includes three kinds of MODE 1  to MODE 3 . The details of the MODE 1  to MODE 3  will be explained with reference to  FIG. 7  to  FIG. 9 . 
     FIG. 6  is a circuit diagram illustrating a constitution of the voltage converting circuit VC 1  or VC 2  (hereinafter, called “a voltage converting circuit VC”). The voltage converting circuit VC comprises boosting stages BS 1  and BS 2 , p-type transistors QPB 1  to QPB 3 , and switching elements SW 1  to SW 3 . The boosting stages BS 1  and BS 2 , and the transistors QPB 1  to QPB 3  may have constitutions similar to the boosting stages BS 1  and BS 2 , and the transistors QPB 1  to QPB 3  in the first embodiment, respectively. 
   In this embodiment, the switching elements SW 1  to SW 3  are provided between the boosting stage BS 1  and the boosting stage BS 2 . The switching element SW 1  is connected between an electrode of the capacitor CD 1  on the supply voltage Vin 1  side thereof and an electrode of the capacitor CD 2  on the ground side thereof and is also connected to the transistor QPB 2  in series. The switching element SW 2  is connected between electrodes of the capacitor CD 1  and the capacitor CD 2  on the ground sides thereof. The switching element SW 3  is connected between electrodes of the capacitor CD 1  and CD 2  on the respective supply voltages Vin 1  sides. 
     FIG. 7  to  FIG. 9  are equivalent circuit diagrams illustrating operations in respective modes of the voltage converting circuit VC illustrated in  FIG. 6 . Mode  1  to Mode  3  will be explained with reference to  FIG. 7  to  FIG. 9 . 
   (Mode  1 ) 
   In Mode  1 , as illustrated in  FIG. 7 , the switching element SW 1  is ON, and switching elements SW 2  and SW 3  are OFF. Therefore, since both the boosting stages BS 1  and BS 2  boost the clock signal CSIN, the Mode  1  is an operation mode corresponding to a case that the supply voltages Vin 1  to Vin 3  are relatively low. 
   First, when the clock signal CSIN is High, the transistors QND 1 , QND 2 , QNE 1  and QNE 2  are turned on, and the transistors QPB 1  to QPB 3  are turned off. Thereby, the capacitors CD 1  and CD 2  are respectively charged between the supply voltages Vin 1 , Vin 2  and the ground. For example, assuming that charging voltage drop does not occur due to respective threshold values of the transistors QND 1  and QND 2 , voltages of Vin 1  and Vin 2  are charged between respective electrodes of the capacitors CD 1  and CD 2 . 
   Next, when the clock signal CSIN is Low, the transistors QPB 1  to QPB 3  are turned on and the transistors QND 1 , QND 2 , QNE 1  and QNE 2  is turned off. Thereby, the capacitors CD 1  and CD 2  are connected in series between the supply voltage Vin 3  and the clock output portion CLKOUT via the transistors QPB 1  to QPB 3 . As a result, the clock signal CSOUT boosted from the supply voltages Vin 1  to Vin 3  is supplied from the clock output portion CLKOUT to any one of the capacitors CA 1  to CA m  illustrated in  FIG. 5 . The clock signal CSOUT is boosted up to Vin 1 +Vin 2 +Vin 3  or so. The clock signal CS OUT  at this time is defined as VCLK 3 . 
   (Mode  2 ) 
   In Mode  2 , as illustrated in  FIG. 8 , the switching element SW 2  is ON and the switching elements SW 1  and SW 3  are OFF. Thereby, since the boosting stage BS 1  does not boost the clock signal CSIN and only the boosting stage BS 2  boosts the clock signal CSIN, Mode  2  is an operation mode corresponding to a case that the supply voltages Vin 1  to Vin 3  are relatively high. 
   First, when the clock signal CSIN is High, the transistors QND 2 , QNE 1  and QNE 2  are turned on and the transistors QPB 1  and QPB 3  are turned off. Thereby, the capacitor CD 2  is charged between the supply voltage Vin 2  and the ground. The capacitor CD 2  is charged to Vin 2 . 
   Next, when the clock signal CSIN is Low, the transistors QPB 1  and QPB 3  are turned on and the transistors QND 2 , QNE 1  and QNE 2  are turned off. Thereby, the capacitor CD 2  is serially connected between supply voltage Vin 3  and the clock output portion CLKOUT via the transistors QPB 1  and QPB 3 . As a result, the clock signal CSOUT boosted from the supply voltages Vin 2  and Vin 3  is supplied from the clock output portion CLKOUT to any one of the capacitors CA 1  to CA m  illustrated in  FIG. 5 . The clock signal CSOUT is boosted up to Vin 2 +Vin 3  or so. The voltage of the clock signal CSOUT at this time is defined as VCLK 4 . 
   It is apparent that the degree of boosting of the voltage VCLK 4  is smaller than that of the voltage VCLK 3 . For example, assuming that the supply voltages Vin 1  to Vin 5  are Vin, VCLK 3 =3*Vin and VCLK 4 =2*Vin are obtained. 
   Therefore, the voltage converting circuit VC in this embodiment boosts the clock signal relatively large according to Mode  1 , when the supply voltage Vin 1  to Vin 3  are relatively low (for example, about 1.5V), and it boosts the clock signal relatively small according to Mode  2 , when the supply voltages Vin 1  to Vin 3  are relatively high (for example, about 2.2V or more). 
   (Mode  3 ) 
   In Mode  3 , as illustrated in  FIG. 9 , the switching elements SW 2  and SW 3  are ON and the switching element SW 1  is OFF. Therefore, the capacitors CD 1  and CD 2  are connected in parallel. Thereby, the boosting stages BS 1  and BS 2  is equivalent to one boosting stage provided with a capacitor (defined as CD 12 ) having a large capacitance corresponding to the capacitance of the capacitor CD 1  plus the capacitance of the capacitor CD 2 . The Mode  3  is an operation mode corresponding to a case that the booster circuit  200  is operated at a power source voltage and a temperature higher than those in the operation security range, particularly in a burn-in step. Incidentally, in Mode  3 , the supply voltages Vin 1  and Vin 2  are Vin 12 . 
   First, when the clock signal CSIN is High, the transistors QND 1 , QND 2 , QNE 1  and QNE 2  are turned on and the transistors QPB 1  and QPB 3  are turned off. Thereby, the capacitor CD 12  is charged between the supply voltage Vin 12  and the ground. For example, the capacitor CD 12  is charged to Vin 12 . 
   Next, when the clock signal CSIN is Low, the transistors QPB 1  and QPB 3  are turned on and transistors QND 1 , QND 2 , QNE 1  and QNE 2  are turned off. Thereby, the capacitor CD 2  is connected between the supply voltage Vin 3  and the clock output portion CLKOUT via the transistors QPB 1  and QPB 3 . As a result, the clock signal CS OUT  boosted from the supply voltages Vin 12  and Vin 3  is supplied from the clock output portion CLOUT to any one of the capacitors CA 1  to CA m  illustrated in  FIG. 5 . For example, the clock signal CS OUT  is boosted up to Vin 12 +Vin 3 . The voltage of the clock signal CSOUT at this time is defined as VCLK 5 . Assuming that Vin 3  and Vin 12  are Vin, the voltage VCLK 5  becomes 2*Vin and it is equal to the voltage VCLK 4  in Mode  2 . Therefore, when supply voltages Vin 1  to Vin 3  are relatively high (for example, about 2.2V or more), the clock signal can be boosted relatively small even according to Mode  3 . 
   Further, since the capacitance of the capacitor CD 12  is larger than that of the capacitor CD 2  in Mode  2 , an output current thereof is larger than that in Mode  2 . Therefore, Mode  3  is suitable for the burn-in step where a load current on the booster circuit increases due to a leak current and due to an operation at a high temperature. Here, the leak current means a junction leak between the diffusion layers, a sub-threshold leak of a transistor or the like. Since the boosting capacity is high, a consumption current in Mode  3  is larger than that in Mode  2 , but increase in consumption current does not cause a problem in the burn-in step. 
   According to this embodiment, even when voltages supplied externally have different values, respectively, the booster circuit  200  can have a stable boosting capacity. Even in the burn-in step, a stable output voltage can be outputted by using Mode  3  while increasing an output current. Further, in Mode  2 , even if the supply voltages are large, increase in consumption power in the voltage converting circuit VC can be suppressed. 
   The gate oxide films of the low breakdown voltage transistors are used for the insulating films of the capacitors CD 1  and CD 2 . Thereby, the area of the whole booster circuit  200  is reduced. 
   The capacitance values of the capacitors CD 1  and CD 2  may be equal to each other. However, the capacitance of the capacitor CD 1  may be made larger than that of the capacitor CD 2 . Thereby, in Mode  1  where the capacitors CD 1  and CD 2  are connected in series, the amplitude of the clock signal CSOUT can be prevented from lowering from an ideal value due to parasitic capacitances of the transistors QND 1 , QND 2 , QNE 2 , QPB 2  and QPB 3 , the capacitors CD 1  and CD 2  and wires connecting these members. 
   In this embodiment, the voltage converting circuits VC 1  and VC 2  are provided as two sets to correspond to the clock signals Φ and Φbar. As illustrated in  FIG. 15 , however, the voltage converting circuits VC may be provided so as to correspond to the transistors QNA 1  to QNA m , respectively. 
   The supply voltages Vin 1  to Vin 3  all may be equal to one another in order to facilitate voltage control of the clock output portion CLKOUT. On the other hand, the supply voltages Vin 1  to Vin 3  may be set to include a different voltage while having the remaining voltages to be equal to each other. For example, only the supply voltage Vin 3  may be larger than the remaining supply voltages. 
   In this embodiment, all the transistors QPB 1  to QPB 3 , QND 1 , QND 2 , QNE 1  and QNE 2  have been the low breakdown voltage transistors. However, some of these transistors may be constituted of high breakdown voltage transistors according to high voltage setting in some of the supply voltages. For example, when only the supply voltage Vin 2  is made larger than the other supply voltages, the transistors QPB 2 , QND 2  and QNE 2  may be high breakdown voltage transistors. In this case, though the sizes and parasitic capacitances of the transistors QPB 2 , QND 2  and QNE 2  become large, such an advantage as a boosting capacity stabilization can be obtained. 
   In this embodiment, the number of boosting stages is two of the stages BS 1  and BS 2 . However, the number of boosting stages may be three or more. Incidentally, in fact, in order to prevent increase in parasitic capacitance and increase in voltage loss, it is preferable that the number of boosting stages is 4 or less. 
   In this embodiment, also, the transistors QPB 1  to QPB 3  and the transistors QNE 1  and QNE 2  are driven in synchronism with each other by the clock signal CSIN. However, in order to prevent voltage loss from increasing, the transistors QPB 1  to QPB 3  may be driven with a delay to the transistors QNE 1  and QNE 2 . In the embodiment, further, such a constitution has been employed that all the transistors QND 1  and QND 2 , QNE 1  and QNE 2 , and QPB 1  to QPB 3  are inputted with the same clock signal CLKIN, but such a constitution may be adopted that some of the transistors may be inputted with a clock signal with the same phase as that of the remaining transistors and an amplitude different from that thereof. 
   Next, specific examples of the switching elements SW 1  to SW 3  according to the second embodiment will be shown. 
     FIG. 10  is a circuit diagram illustrating one embodiment of the switching element SW 1 . Terminals TM 1  and TM 2  are respectively connected to the transistor QPB 2  and the boosting stage BS 2 . Conductive state or non-conductive state between the terminal TM 1  and the terminal TM 2  is set by the mode signal MODE 1 . 
   The switching element SW 1  is provided with a PMOS transistor QP 3 , a NMOS transistor QN 8 , a capacitor C 3 , a NMOS transistor QN 6 , a NMOS transistor QN 7 , a NOR gate NOR 1  and an inverter INV 1 . The transistor QP 3  may has the same constitution as any one of the transistors QPB 1  to QPB 3 . The transistors QN 6 , QN 7  and QN 8  may have the same constitution as the transistor QND 1 , QND 2 , QNE 1  or QNE 2 . The capacitor C 3  may have the same constitution as the capacitor CD 1  or CD 2 . 
   The transistor QP 3  is connected between the terminal TM 1  and the terminal TM 2 . A back gate of the transistor QP 3  is connected to the terminal TM 1 . The transistor QN 7 , the capacitor C 3  and the transistor QN 6  are connected in series between the supply voltage Vin and the ground. The transistor QN 8  is connected to a gate of the transistor QP 3  and is further connected between a connection node of the transistor QN 7  and the capacitor C 3 , and the ground. 
   The NOR gate NOR 1  is inputted with a signal of the mode signal MODE 1  inverted by the inverter INV 1  and inputted with a clock signal CSIN, and outputs a NOR of these signals to the gate of the transistor QN 8 . The gates of the transistors QN 7  and QN 6  are inputted with a clock signal CSIN. Incidentally, Vin may be any one of Vin 1  to Vin 3 . 
   When the clock signal CSIN is High (Vin), the transistors QN 6  and QN 7  are turned on and the transistor QN 8  is turned off. Thereby, the terminal TM 1  becomes a ground potential and the gate potential of the transistor QP 3  becomes Vin, so that the transistor QP 3  is turned off. Incidentally, it has been assumed that a voltage drop does not occur due to a threshold value of the transistor QN 7 . At this time, the other electrode of the capacitor C 3  is charged to the voltage of the Vin 1 . The terminal TM 2  is grounded via the boosting stage BS 2 , when the clock signal CSIN is High. Thereby, a forward bias is not applied between the drain and the N well (channel portion) of the transistor QP 3 . As a result, the terminal TM 1  and the terminal TM 2  are made in a non-conductive state to each other. 
   When the clock signal CSIN is Low (a ground potential), the transistors QN 6  and QN 7  are turned off. At this time, when the mode signal MODE 1  is High (in an active state), the transistor QN 8  is turned on. Thereby, the gate potential of the transistor QP 3  becomes the ground potential, so that the transistor QP 3  is turned on. That is, the terminal TM 1  and the terminal TM 2  are put in a conductive state to each other. 
   On the other hand, when the mode signal MODE 1  is Low (in a non-active state), the transistor QN 8  is turned off. Thereby, since the voltage Vin 1  is held between the gate and the source of transistor QP 3  by the capacitor C 3 , the transistor QP 3  is turned off. That is, the terminal TM 1  and the terminal TM 2  are put in a non-conductive state. 
   The switching element SW 1  is made conductive or non-conductive between the terminal TM 1  and TM 2  depending on the clock signal CSIN, when the mode signal MODE 1  is High. However, the switching element SW 1  may maintain a conductive state between the terminals TM 1  and TM 2  regardless of the state of the clock signal CSIN, when the mode signal MODE 1  is High. 
     FIG. 11  is a circuit diagram illustrating one embodiment of the switching element SW 2 . Terminals TM 3  and TM 4  are respectively connected to electrodes of the capacitors CD 1  and CD 2  on the ground sides. The terminal TM 3  and the terminal TM 4  are made conductive or non-conductive according to the mode signal MODE 2  and MODE 3 . 
   The switching element SW 2  is provided with a PMOS transistor QP 4 , a NMOS transistor QN 9 , a capacitor C 4 , a NAND gate NAND 1 , a NOR gate NOR 2  and an inverter INV 2 . The transistor QP 4  may have the same constitution as any one of the transistors QPB 1  to QPB 3 . The transistor QN 9  may have the same constitution as the transistor QND 1 , QND 2 , QNE 1  or QNE 2 . The capacitor C 4  may have the same constitution as the capacitor CD 1  or CD 2 . 
   The transistor QP 4  is connected between the terminal TM 3  and the terminal TM 4 . The back gate of the transistor QP 4  is connected to the terminal TM 3 . The capacitor C 4  is connected between the gate of the transistor QP 4  and the terminal TM 3 . The transistor QN 9  is connected between the gate of the transistor QP 4  and the ground. 
   The NOR gate NOR 2  is inputted with the mode signal MODE 2  and the mode signal MODE 3  to output NOR of these signals. The NAND gate NAND 1  is inputted with a signal of the clock signal CSIN inverted by the inverter INV 2  and an output signal from the NOR gate NOR 2  to output NAND of these signals to the gate of the transistor QN 9 . 
   When the mode signal MODE 2  or the mode signal MODE  3  is High (in an active state), the transistor QN 9  is turned on. Thereby, since the transistor QP 4  is turned on, the terminal TM 3  and the terminal TM 4  are make conductive to each other. 
   When the mode signal MODE 2  and the mode signal MODE  3  are Low (in a non-active state) and the clock signal CSIN is High (Vin), the transistor QN 9  is turned on, so that the gate potential of the transistor QP 4  becomes the ground potential (0V). However, since the terminal TM 3  and the terminal TM 4  have been grounded via the boosting stages BS 1  and BS 2 , the transistor QP 4  is not turned on. At this time, the potential difference between both the electrodes of the capacitor C 4  becomes almost 0V. 
   When the mode signal MODE 2  and the mode signal MODE 3  are Low (in a non-active state) and the clock signal CSIN is Low (0V), the transistor QN 9  is turned off. At this time, since the potential difference 0V is held between the gate and the source of the transistor QP 4  by the capacitor C 4 , the transistor QP 4  is turned off. That is, the terminal TM 3  and the terminal TM 4  are put in a non-conductive state. 
     FIG. 12  is a circuit diagram illustrating one embodiment of the switching element SW 3 . Terminals TM 5  and TM 6  are respectively connected to electrodes of the capacitors CD 1  and CD 2  on their supply voltage sides. The terminal TM 5  and the terminal TM 6  are made conductive or non-conductive to each other by the mode signal MODE 3 . 
   The switching element SW 3  is provided with a PMOS transistor QP 5 , NMOS transistors QN 10  and QN 11 , a capacitor C 5 , a NOR gate NOR 3  and an inverter INV 3 . The transistor QP 5  may have the same constitution as any one of the transistors QPB 1  to QPB 3 . The transistors QN 10  and QN 11  may have the same constitution as the transistor QND 1 , QND 2 , QNE 1  or QNE 2 . The capacitor C 5  may have the same constitution as the capacitor CD 1  or CD 2 . 
   The transistor QP 5  is connected between the terminal TM 5  and the terminal TM 6 . The back gate of the transistor QP 5  is connected to the terminal TM 5 . The capacitor C 5  is connected between the gate of the transistor QP 5  and the terminal TM 5 . The transistor QN 10  is connected between the gate of the transistor QP 5  and the ground. The transistor QN 11  is connected between the gate of the transistor QP 5  and the supply voltage Vin. The NOR gate NOR 3  is inputted with a signal of the clock signal CSIN inverted by the inverter INV 3  and the mode signal MODE 3  to output NOR of these signals to the gate of the transistor QN 11 . Further, the mode signal MODE 3  is inputted to the gate of the transistor QN 10 . 
   When the mode signal MODE  3  is High (in an active state), the transistor QN 10  is turned on so that the gate potential of the transistor QP 5  becomes the ground potential (0V). Furthermore, when the clock signal CSIN is High, the terminal TM 5  and the terminal TM 6  are respectively connected to the supply voltage Vin via the boosting stages BS 1  and BS 2 . Moreover, when the clock signal CSIN is Low, the terminal TM 5  and the terminal TM 6  are boosted up to the supply voltage Vin or more. Thereby, by turning on the transistor QP 5 , the terminal TM 5  and the terminal TM 6  are made conductive to each other. 
   Next, when the mode signal MODE 3  is Low (in a non-active state), the transistor QN 10  is turned off. Further, when the clock signal CSIN is High (Vin), the transistor QN 11  is turned on, and the gate potential of the transistor QP 5  becomes Vin. Incidentally, it has been assumed that a voltage drop due to the threshold value of the transistor QN 11  does not occur. At this time, the terminal TM 5  and the terminal TM 6  are respectively connected to the supply voltage Vin via the boosting stages BS 1  and BS 2 . Incidentally, setting is made to be Vin  1 =Vin 2 =Vin. Thereby, the transistor QP 5  is turned off. At this time, the potential difference between the both electrodes of the capacitor C 5  becomes 0V. 
   When the mode signal MODE 3  is Low (in a non-active state) and the clock signal CSIN is Low (0V), the transistor QN 11  is turned off, but the potential difference 0V is held between the gate and the source of the transistor QP 5  by the capacitor C 5 . Thereby, the transistor QP 5  is turned off. That is, the terminal TM 5  and the terminal TM 6  are put in a non-conductive state to each other. 
   In this connection, the aspects of the switching elements SW 1  to SW 3  illustrated in  FIG. 10  to  FIG. 12  are merely examples and any switch circuit having a function similar to these switching elements can be used. 
   THIRD EMBODIMENT 
     FIG. 13  is a circuit diagram of a voltage converting circuit VD in a booster circuit according to the third embodiment of the present invention. As a booster portion may be similar to the booster circuit  110  or  210  in the first or second embodiment, explanation thereof will be omitted. Further, as arrangement of the voltage converting circuits VD in the voltage converting circuit portion may also be similar to that in the voltage converting circuit portion  120  or  220  in the first or second embodiment, explanation thereof will be omitted. 
   The voltage converting circuit VD has a constitution where the voltage converting circuit VC in the second embodiment has been added with boosting stages BS 30  and BS 40 , p-type high breakdown voltage transistors QPB 30  to QPB 50 , and switching elements SW 1  to SW 3  for a high breakdown voltage. 
   The boosting BS 30  includes an n-type high breakdown voltage transistor QND 30 , a capacitor CD 3  and an n-type high breakdown voltage transistor QNE 30 . The transistor QND 30 , the capacitor CD 3  and the transistor QNE 30  are connected in series between the supply voltage Vin 3  and the ground. The boosting BS 40  includes an n-type high breakdown voltage transistor QND 40 , a capacitor CD 4  and an n-type high breakdown voltage transistor QNE 40 . The transistor QND 40 , the capacitor CD 4  and the transistor QNE 40  are connected in series between the supply voltage Vin 4  and the ground. 
   The transistor QPB 30  is connected between an electrode of the capacitor CD 2  on the supply voltage side thereof and an electrode of the capacitor CD 3  on the ground side thereof. The transistor QPB 40  and the switching element SW 1  are connected in series between an electrode of the capacitor CD 3  on the supply voltage side thereof and an electrode of the capacitor CD 4  on the ground side thereof. The transistor QPB 50  is connected between an electrode of the capacitor CD 4  on the supply voltage side thereof and the clock output portion CLKOUT. 
   The switching element SW 2  is connected between electrodes of the capacitor CD 3  and the capacitor CD 4  on their respective ground sides. The switching element SW 3  is connected between electrodes of the capacitor CD 3  and CD 4  on their respective supply voltage sides. 
   The voltage converting circuit VD has four boosting stages whose number is more than the number boosting stages included in the voltage converting circuit VC in the second embodiment. Thereby, since a high voltage is generated at the downstream boosting stages BS 30  and BS 40  generating a high voltage, high breakdown voltage transistors are used as transistors disposed inside the boosting stages BS 30  and BS 40 . On the other hand, since only a potential difference between the supply voltage Vin 3  or Vin 4  and the ground is applied to the capacitors CD 3  and CD 4 , gate insulating films for a low breakdown voltage may be used in these capacitors. Thereby, a circuit area can be made relatively small. 
   Like the second embodiment, when the mode signal MODE 1  is High (in an active state), the switching element SW 1  is ON and the switching elements SW 2  and SW 3  are OFF. When the mode signal MODE 2  is High, the switching element SW 2  is ON and the switching elements SW 1  and SW 3  are OFF. When the mode signal MODE 3  is High, the switching elements SW 2  and SW 3  are ON and the switching element SW 1  is OFF. Respective modes will be explained below. 
   (Mode  1 ) 
   The switching element SW 1  is on and the switching elements SW 2  and SW 3  are OFF. At this time, since all the boosting stages BS 1  to BS 40  boost the clock signal CSIN, Mode  1  is an operation mode conducted when the supply voltages Vin 1  to Vin 3  are relatively low. 
   First, when the clock signal CSIN is High, the capacitors CD 1  to CD 4  are respectively charged between the supply voltages Vin 1  to Vin 4  and the ground. For example, assuming that a charging voltage drop due to the threshold values of the transistors QND 1  to QND 40  does not occur, the voltages of the supply voltages Vin 1 , Vin 2 , Vin 3  and Vin 4  are charged between respective electrodes of the capacitors CD 1  to CD 4 . 
   Next, when the clock signal CSIN is Low, the capacitors CD 1  to CD 4  are connected in series between the supply voltage Vin 5  and the clock output portion CLKOUT via the transistors QPB 1  to QPB 50 . As a result, the clock signal CSOUT boosted from the supply voltages Vin 1  to Vin 5  is outputted. The clock signal CSOUT is boosted up to Vin 1 +Vin 2 +Vin 3 +Vin 4 +Vin 5  or so. The voltage of the clock signal CSOUT at this time is defined as VCLK 7 . Assuming that the supply voltages Vin 1  to Vin 5  are Vin, the voltage VCLK 5  becomes 5*Vin or so. 
   (Mode  2 ) 
   The switching element SW 2  is ON and the switching elements SW 1  and SW 3  are OFF. Thereby, since the boosting stages BS 1  and BS 30  do not operate and only the boosting stages BS 2  and BS 40  operate, Mode  2  is an operation mode where the supply voltages Vin 1  to Vin 3  are relatively high. 
   First, when the clock signal CSIN is High, the capacitors CD 2  and CD 40  are respectively charged between the supply voltages Vin 2  and Vin 4 , and the ground. For example, the capacitors CD 2  and CD 40  are respectively charged to Vin 2  and Vin 4 . 
   Next, when the clock signal CSIN is Low, the capacitors CD 2  and CD 40  are connected in series between the supply voltage Vin 5  and the clock output portion CLKOUT via the transistors QPB 1 , QPB 30  and QPB 50 . As a result, a clock signal CSOUT boosted from the supply voltages Vin 2 , Vin 4  and Vin 5  is outputted. For example, the clock signal CSOUT is boosted up to Vin 2 +Vin 4 +Vin 5  or so. The voltage of the clock signal CSOUT at this time is defined as VCLK 8 . For example, assuming that the supply voltages Vin 2 , Vin 4  and Vin 5  are Vin, the voltage VCLK 8  becomes 3*Vin or so. 
   It is apparent that the degree of boosting of the voltage VCLK 8  is smaller than that of the voltage VCLK 7 . Therefore, the voltage converting circuit VD boosts the clock signal relatively large according to Mode  1 , when the supply voltages Vin 1  to Vin 5  are relatively low (for example, about 1.5V), and it boosts the clock signal relatively small according to Mode  2 , when the supply voltages Vin 1  to Vin 5  are relatively high (for example, about 2.5V or more). 
   (Mode  3 ) 
   In Mode  3 , the switching elements SW 2  and SW 3  are ON and the switching element SW 1  is OFF. Therefore, the capacitors CD 1  and CD 2  are connected in parallel, and the capacitors CD 30  and CD 40  are connected in parallel. Thereby, the boosting stages BS 1  and BS 2  is equivalent to one boosting stage provided with a capacitor (referred to as “CD 12 ”) having a large capacitance corresponding to the capacitance of the capacitor CD 1  plus the capacitance of the capacitor CD 2 . Similarly, the boosting stages BS 3  and BS 4  is equivalent to one boosting stage provided with a capacitor (referred to as “CD 34 ”) having a large capacitance corresponding to the capacitance of the capacitor CD 30  plus the capacitance of the capacitor CD 40 . Mode  3  is an operation mode where the booster circuit is operated at power source voltage and a temperature equal to or more than those in an operation security range, particularly in a burn-in step. Incidentally, it is assumed that the supply voltages Vin 1  and Vin 2  are Vin 12 , and the supply voltages Vin 3  and Vin 4  are Vin 34 . 
   First, when the clock signal CSIN is High, the capacitors CD 12  and CD 34  are respectively charged between the supply voltages Vin 12  and Vin 13  and the ground. For example, the capacitors CD 12  and CD 34  are respectively charged to Vin 12  and Vin 34 . 
   Next, when the clock signal CSIN is Low, the capacitors CD 12  and CD 34  are connected in series between the supply voltage Vin 5  and the clock output portion CLKOUT via the transistors QPB 1 , QPB 30  and QPB 50 . As a result, the boosted clock signal CSOUT is outputted from the supply voltages Vin 12 , Vin 34  and Vin 5 . For example, the clock signal CSOUT is boosted up to Vin 12 +Vin 34 +Vin 5  or so. The voltage of the clock signal CSOUT at this time is defined as VCLK 9 . 
   For example, assuming that Vin 1  to Vin 5 , Vin 12  and Vin 34  are Vin, both the voltage VCLK 8  and the voltage VCLK 9  become 3*Vin or so. Thereby, when the supply voltages Vin 1  to vin 5  are relatively high (for example, about 2.5V or more), the clock signal can be boosted relatively small even in Mode  3 . 
   Further, since the capacitances of the capacitors CD 12  and CD 34  are larger than those of the capacitors CD 2  and CD 4  in Mode  2 , an output current is larger than that in Mode  2 . Therefore, this Mode  3  is suitable for a burn-in step where a load current on the booster circuit increases due to a leak current and an operation at a high temperature. Here, the leak current means a junction leak of the diffusion layer, a sub-threshold leak of a transistor or the like. Since the boosting capacity is high, a consumption current in Mode  3  is larger than that in Mode  2 , but increase in consumption current does not cause a problem in a burn-in step. 
   Thereby, this embodiment has an advantage or merit similar to that in the second embodiment. The boosting stages BS 30  and BS 40  of a downstream stage are constituted of high breakdown voltage transistors. Thereby, each voltage converting circuit VD can boost the clock signal CSIN largely. 
   All the supply voltages Vin 1  to Vin 5  may be equal in order to facilitate voltage control of the clock output portion CLKOUT. On the other hand, some of the supply voltages Vin 1  to Vin 5  may be different in voltage from the remaining supply voltages while having the remaining voltages to be equal to each other. 
   In this embodiment, the number of boosting stages has been four stages of BS 1  to BS 4 , but it may be three or less, or it may be five or more. Incidentally, in order to prevent increase in parasitic capacitance and in order to increase in voltage loss, it is preferable that the number of boosting stages is four or less. 
   Further, In this embodiment, the transistors QPB 1  to QPB 50  and the transistors QNE 1  to QNE 40  are driven in synchronism with each other by the clock signal CSIN. However, in order to prevent voltage loss from increasing, the transistors QPB 1  to QPB 50  may be driven with a delay from the transistors QNE 1  and QNE 40 . In the embodiment, further, such a constitution has been employed that all the transistors QND 1  and QND 40 , QNE 1  and QNE 40 , and QPB 1  to QPB 50  are inputted with the same clock signal CLKIN, but such a constitution may be adopted that some of the transistors may be inputted with a clock signal with the same phase as that of the remaining transistors and an amplitude different from that thereof. 
   FOUR EMBODIMENT 
     FIG. 14  is a circuit diagram of a voltage converting circuit VE inside a booster circuit according to a fourth embodiment of the present invention. Since a booster portion may be similar to the booster circuit  110  or  210  in the first or second embodiment, explanation thereof will be omitted. Further, since an arrangement of the voltage converting circuits VE inside the voltage converting circuit portion may also be similar to the voltage converting circuit portion  120  or  220  in the first or second embodiment, explanation thereof will be omitted. 
   The voltage converting circuit VE comprises boosting stages BS 1  and BS 2 , and switching elements SW 4  and SW 5 . The switching element SW 4  is connected between an electrode of the capacitor CD 1  on the supply voltage side thereof and an electrode of the capacitor CD 2  on the ground side thereof. Thereby, the switching element SW 4  operates in the same manner as the switching element SW 1  and the transistor QPB 4  illustrated in  FIG. 7 . The switching element SW 5  is connected between electrodes of the capacitors CD 1  and CD 2  on their supply voltage sides thereof. Thereby, the switching element SW 5  operates in the same manner as the switching element SW 3  illustrated in  FIG. 7 . 
   The switching element SW 4  is provided with a PMOS transistor QP 6 , a capacitor C 6 , an NMOS transistors QN 12  and QN 13 , a NOR gate NOR 4 , and an inverter INV 4 . The source and the drain of the transistor QP 6  are connected between an electrode of the capacitor CD 1  on the supply voltage side thereof and an electrode of the capacitor CD 2  on the ground side thereof. The transistors QN 12  and QN 13  are connected in series between the supply voltage Vin and the ground. A gate of the transistor QP 6  is connected to a connection node between the transistors QN 12  and QN 13 , and it is further connected an electrode of the capacitor CD 1  on the supply voltage side thereof via a capacitor C 6 . A back gate of the transistor QP 6  is connected to a source of the transistor QP 6  and an electrode of the capacitor CD 1  on the supply voltage side thereof. 
   The NOR gate NOR 4  is inputted with a mode signal MODE 1  through the inverter INV 4  and with a clock signal CSIN to output NOR of these signals to the gate of the transistor QN 13 . The gate of the transistor QN 12  is connected to the clock input portion CLKIN. 
   Next, an operation of the switching element SW 4  will be explained. When the mode signal MODE 1  is High (in an active state) and the clock signal CSIN is Low, the transistors QN 12  and QN 13  are turned off and on, respectively. Thereby, since the gate of the transistor QP 6  becomes a ground potential, the transistor QP 6  is turned on. 
   When the mode signal MODE 1  is High (in an active state) and the clock signal CSIN is High, the transistors QN 12  and QN 13  are turned on and off, respectively. Thereby, a gate potential of the transistor QP 6  is charged to Vin 1 . Incidentally, it has been assumed that a voltage drop due to a threshold of the transistor QN 12  does not occur. At this time, since the source of the transistor QP 6  has also been charged to Vin 1 , the transistor QP 6  are turned off. Incidentally, it has been assumed that a voltage drop due to a threshold of the transistor QND 1  does not occur. Therefore, when clock signal CSIN is Low, the switching element SW 1  makes the boosting stages BS 1  and BS 2  conductive to each other, and when the clock signal CSIN is High, the switching element SW 1  makes the boosting stages BS 1  and BS 2  non-conductive to each other. 
   When the mode signal MODE 1  is Low (in a non-active stage), the transistor QN 13  is always off. The transistor Q 12  is turned on, when the clock signal CSIN is High. Therefore, the gate potential of the transistor QP 6  is charged to Vin 1 . At this time, the source of the transistor QP 6  has been charged to Vin 1  by the transistor QND 1 . That is, the source and the gate of the transistor QP 6  becomes equal. When the clock signal CSIN is Low, the potential of the source of the transistor QP 6  becomes high, but the potential of the gate of the transistor QP 6  is kept in a potential approximately equal to that of the source thereof by the capacitor C 6 , so that the transistor QP 6  remains in an off state. 
   The switching element SW 5  is provided with a PMOS transistor QP 7 , a capacitor C 7 , an NMOS transistors QN 14  and QN 15 , an inverter INV 5 , and a NOR gate NOR 5 . The source and the drain of the transistor QP 7  are respectively connected to electrodes of the capacitors CD 1  and CD 2  on their supply voltage sides. The transistors QN 14  and QN 15  are connected in series between the supply voltage Vin and the ground. The gate of the transistor QP 7  is connected to a connection point between the transistors QN 14  and QN 15  and it is further connected to an electrode of the capacitor CD 1  on the supply voltage side via the capacitor C 7 . The back gate of the transistor QP 7  is connected to the source of the transistor QP 7  and an electrode of the capacitor CD 1  on the supply voltage side thereof. 
   The NOR gate NOR 5  is inputted with a clock signal CSIN via the inverter INV 4  and with a mode signal MODE 2  to output a NOR of these signals to the gate of the transistor QN 14 . The gate of the transistor QN 15  is inputted with the mode signal MODE 2 . 
   Next, an operation of the switching element SW 5  will be explained. When the mode signal MODE 2  is High (in an active state), the transistor QN 14  is always OFF and the transistor QN 15  is always ON Therefore, the potential of the gate of the transistor QP 7  becomes a ground potential and the switching element SW 5  is put in a conductive state. 
   When the mode signal MODE 2  is Low (in a non-active state), the transistor QN 15  is always OFF. When the clock signal CSIN is High, the transistor QN 14  is turned on. Therefore, the gate potential of the transistor QP 7  is charged to Vin 1 . Incidentally, it is assumed that a voltage drop due to the threshold of the transistor QN 14  does not occur. At this time, since the source of the transistor QP 7  has also been charged to Vin 1  by the transistor QND 1 , the source and the gate of the transistor QP 7  become the same in potential. When the clock signal CSIN is Low, the potential of the source of the transistor QP 7  becomes High, but the potential of the gate of the transistor QP 7  is kept in a potential approximately equal to that of the source thereof, so that the transistor QP 7  remains in an OFF state. 
   According to this embodiment, when the mode signal MODE 1  is High, the amplitude of the clock signal CSOUT becomes about Vin 1 +Vin 2 +Vin 3 , since the boosting stages BS 1  and BS 2  are connected in series. When the mode signal MODE 2  is High, since the boosting stage BS 2  does not operate for boosting, the amplitude of the clock signal CSOUT becomes Vin 1 +Vin 3 . 
   Thus, this embodiment can reduce the number of boosting stages inside the voltage converting circuit VE according to change of the modes. Accordingly, the present embodiment can achieve the same advantage or merit as the first embodiment. 
   All the supply voltages Vin 1  to Vin 3  may be the same for facilitating voltage control on the clock output portion CLKOUT. On the other hand, any of the supply voltages Vin 1  to Vin 3  may be different from the remaining supply voltages while having the remaining voltages to be equal to each other. 
   In this embodiment, gate insulating layers of low breakdown voltage transistors may be used for the insulating layers of the capacitors constituting the boosting stages BS 1  and BS 2 . Therefore, the areas of these capacitors can be reduced so that a circuit area is reduced. 
   In this embodiment, the number of boosting stages BS 1  to BS 2  has been two. However, the number of boosting stages may be three or more. In this connection, in fact, in order to prevent parasitic capacitance from increasing and prevent voltage loss from increasing, it is preferable that the number of boosting stages is four or less. 
   The capacitance values of the capacitors CD 1  and CD 2  may be the same. However, the capacitance of the capacitor CD 1  may be larger than that of the capacitor CD 2 . Thereby, in Mode  1  where the capacitors CD 1  and CD 2  are connected in series, the amplitude of the clock signal CSOUT can be prevented from lowering from an ideal value due to parasitic capacitances of the transistors QND 1 , QND 2 , QNE 2 , QP 6 , QP 7 , QN 12  to QN 15 , the capacitors CD 1 , CD 2 , C 6 , C 7 , and wires connecting these members.