Abstract:
In a semiconductor device, a voltage generating section is operatively connected with a first voltage line portion and a second voltage line portion. A first voltage detecting section detects a voltage of the first voltage line portion, and a second voltage detecting section which detects a voltage of the second voltage line portion. A control unit controls the voltage generating section based on the detecting results of the first and second voltage detecting sections such that the first voltage line portion and the second voltage line portion are respectively set to a first voltage and a second voltage. A switch section is provided between the first voltage line portion and the second voltage line portion. The switch section selectively disconnects the second voltage line portion from the first voltage line portion based on the detection result of the second voltage detecting section.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a semiconductor device, and more particularly a semiconductor device including a power supply voltage generating unit. 
     2. Description of the Related Art 
     A power supply voltage generating unit is conventionally known in “A Precise On-Chip Voltage Generator for a Giga-Scale DRAM with a Negative Word-line Scheme” (1998 Symposium on VLSI Circuits Digest of Technical Papers, pp. 94 to 95) by Hitoshi Tanaka et al. 
     In Japanese Laid Open Patent application (JP-A-Heisei 10-255469) is disclosed a circuit for generating a voltage higher than a power supply voltage externally supplied and a circuit for generating a negative voltage lower than a ground voltage. In this reference, the circuit is composed of a charge pump, two level detectors and two ring oscillators. The charge pump generates an internal power supply voltage higher than the external power supply voltage. The two level detectors detects the internal power supply voltage outputted from the charge pump. The two ring oscillators are respectively connected to the two level detectors and has different oscillation frequencies. A multiple ring oscillator selectively outputs to the charge pump, the signal generated by one of the ring oscillators in accordance with the internal power supply voltage which is outputted from the charge pump. 
     Also, the following matters are disclosed in the above reference. A MOS-type semiconductor integrated circuit at present includes a boosting circuit, which generates the internal power supply voltage higher than the power supply voltage externally supplied. The internal power supply voltage is supplied to the inside of the semiconductor integrated circuit such that a high level signal can be propagated without decrease, even if N-type MOSFETs are used. Also, a junction capacitance of a drain node is decreased so as to accomplish a high-speed operation and small power consumption. Also, the change of a threshold voltage due to the substrate effect is reduced to extend an operation margin. For these purposes, a power supply circuit system is provided to generate the internal voltage which is lower than the ground voltage externally supplied and to supply the inside of the semiconductor integrated circuit. At this time, the above power supply circuit system is requested to detect the change of the internal voltage due to operation current and leak current, and to hold the internal voltage such that the semiconductor integrated circuit is held in the normal operation. 
     It should be noted that various types of current flow such as the leak current equal to or less than 100 nA which is caused through the deviation in a manufacturing process and the semiconductor physics in a stand-by state, and the operation current of order of 10 μA which is caused by the circuit structure for bias current. Considering the various types of current which extend over 5 digits, the internal voltage changes. 
     A conventional power supply voltage generating unit will be described with reference to FIGS. 1 and 2. 
     FIG. 1 shows the circuit structure of the power supply voltage generating unit for generating a negative voltage. The power supply voltage generating unit  10  is composed of a charge pump circuit CP, an oscillator OSC, a charge pump regulator Ha, an N-channel output transistor NH 1 , and a regulator H. The charge pump circuit CP is connected with a V BB  voltage. The oscillator OSC is connected with the charge pump circuit CP. The charge pump regulator Ha has a voltage detecting circuit (level detector) Ld. The N-channel output transistor NH 1  has the drain and source connected with the V BB  voltage and a V NN  voltage, respectively. The regulator H compares the V NN  voltage with a reference value V REFN  and outputs the comparing result to the gate of the output transistor NH 1 . The V BB  voltage is a negative voltage of a substrate (Sub) voltage. The V NN  voltage is a negative voltage which is connected with a circuit group (not shown) and is used in the operation of the circuit group. The V BB  voltage and the V NN  voltage are in the relation of V BB &lt;V NN . 
     When the circuit group connected with the side of V NN  voltage operates, noise is generated so that the V NN  voltage sometimes changes. For example, the noise contained on the side of V NN  voltage has the amplitude of hundreds of mV. A load capacitance of thousands of pF is added to the side of V NN  voltage and a load capacitance of hundreds of thousands of pF is added to the side of V BB  voltage. 
     The operation of power supply voltage generating unit  10  will be described with reference to FIG.  2 . 
     First, as shown in waveform A, the V NN  voltage increases when the circuit group operates to introduce the noise. When a determination time t DET1  passes after the V NN  voltage to start to increase, the regulator H operates as shown in waveform A as “regulator act” to output a high level signal of Vcc as an output signal H 3  as shown in FIG.  42 C. 
     When the H 3  signal of the high level is supplied to the gate of the output transistor NH 1 , the output transistor NH 1  is set to a conductive state. As a result, current flows from the side of V NN  voltage to the side of V BB  voltage to increase the V BB  voltage as shown in waveform B. The noise on the side of V BB  voltage, i.e., the V BB  voltage noise shown in waveform B has the amplitude of tens of mV. While the output transistor NH 1  is turned on, the current flows from the side of V NN  voltage to the side of V BB  voltage. Therefore, the noise contained on the side of V NN  voltage decreases, and finally, the V NN  voltage decreases and returns to the original level, as shown in waveform A. 
     The H 3  signal goes to a low level of the V BB  voltage to turn off the output transistor NH 1 , when the noise contained on the side of V NN  voltage decreases so that the V NN  voltage decreases lower than a predetermined voltage, as shown in waveform C. At this time, the V NN  voltage is in a stable state as shown in waveform A. In this case, the side of V BB  voltage is in the state in which the V BB  voltage noise is contained. After a time t DET2  passes after the output transistor NH 1  is turned on and the noise flows to the side of V BB  voltage, as shown in waveform C, the output signal Hi of the level detector Ld becomes high level, as shown in waveform D. When the signal H 1  becomes high level, the operation of the oscillator OSC is started, as shown in waveform E. 
     The charge pump circuit CP operates in response to the output signal H 2  from the oscillator OSC (charge pump act shown in waveform E), the charge pump circuit CP removes the V BB  voltage noise to decrease the V BB  voltage, as shown in waveform B. When the V BB  voltage falls lower than a preset voltage, the output signal H 1  of the level detector Ld becomes the low level, as shown in waveform B. As a result, the operation of the oscillator OSC and the operation of the charge pump circuit CP are stopped as shown in waveform E. 
     By the way, when noise is contained on the side of V BB  voltage and the V BB  voltage as a substrate voltage changes from a predetermined value, the threshold voltage Vt of the transistor formed on the substrate changes so that the margin sometimes reduces. Therefore, it is desirable that a quantity of the V BB  voltage noise transferred when the output transistor NH 1  is set to the conductive state is small. Also, it is desirable that an attenuation time td is short from when the noise moves from the side of V NN  voltage to the side of V BB  voltage to when the V BB  voltage noise is eliminated, as shown in waveform B. 
     In above-mentioned structure, the V BB  voltage noise starts to be removed after the noise is contained on the side of V NN  voltage and then the determination time t DET1  and the detection time t DET2  of the level detector Ld have elapsed. Here, the determination time t DET1  is 10 nsec, and the detection time t DET2  is 1 μsec, for example. 
     Also, when the V BB  voltage level is near the V NN  voltage, the level change on the side of V BB  voltage becomes late so that the noise produced on the side of V NN  voltage does not attenuate immediately. This is because the operation of the charge pump circuit CP is started after the change of the voltage level on the side of V BB  voltage, when the noise is generated on the side of V NN  voltage. 
     FIG. 3 shows the circuit structure of the power supply voltage generating unit for generating a boosted voltage. In the power supply voltage generating unit  10 A, a charge pump circuit CP is connected with a V pp  voltage. The V pp  voltage is a positive boosted voltage. A V CH  voltage is the boosted voltage connected with a circuit group (not shown) and used for the operation of the circuit group. The V pp  voltage and the V CH  voltage are in the relation of V PP &gt;V CH . 
     The power supply voltage generating unit  10 A is the same in structure as the power supply voltage generating unit  10  shown in FIG. 1, and different from that in polarity. As shown in FIG. 4, the operation of the power supply voltage generating unit  10 A is substantially the same as that of the power supply voltage generating unit  10 . The charge pump circuit CP operates to recover the V PP  voltage to the original boosted voltage, when the noise generated on the side of V CH  decreases V PP  voltage to a predetermined value or below through a P-channel output transistor PG 1 . 
     SUMMARY OF THE INVENTION 
     Therefore, an object of the present invention is to provide a semiconductor device with a short decay or attenuation time of noise. 
     Another object of the present invention is to provide a semiconductor device in which noise is small. 
     Still another object of the present invention is to provide a semiconductor device in which noise generated on the first voltage side is not almost propagated to the second voltage. 
     Yet still another object of the present invention provides a semiconductor device in which a power supply voltage can be recovered to an original level at a short time, even if the first voltage level is near the second voltage level. 
     In order to achieve an aspect of the present invention, a semiconductor device includes a voltage generating section operatively connected with a first voltage line portion and a second voltage line portion; a first voltage detecting section which detects a voltage of the first voltage line portion; a second voltage detecting section which detects a voltage of the second voltage line portion; and a control unit which controls the voltage generating section based on the detecting results of the first and second voltage detecting sections such that the first voltage line portion and the second voltage line portion are respectively set to a first voltage and a second voltage. 
     Here, the semiconductor device may further include a switch section provided between the first voltage line portion and the second voltage line portion, wherein the switch section selectively disconnects the second voltage line portion from the first voltage line portion based on the detection result of the second voltage detecting section. 
     In this case, the switch section operates to prevent the second voltage line portion voltage from changing from a second voltage due to the voltage generating section when the second voltage line portion voltage is set to the second voltage. 
     Also, the voltage generating section may generate the negative first voltage, and the second voltage is higher than the first voltage. Alternately, the voltage generating section may generate a boosted voltage, and the second voltage is lower than the first voltage. 
     Also, the semiconductor device may further include a connecting section provided between the output terminal the voltage generating section and the switch section to connect the first voltage line portion and the second voltage line portion. 
     Also, the semiconductor device may further include an auxiliary switch section provided between the voltage generating section and the first voltage line portion, to selectively disconnect the output terminal from the first voltage line portion based on the detection result of the first voltage detecting section. In this case, the auxiliary switch section operates to prevent the voltage of the first voltage line portion from changing due to the voltage of the second voltage line portion when the voltage of the second voltage line portion is different from the second voltage. 
     Also, the control unit controls the voltage generating section to operate when at least one of the first voltage line portion and the second voltage line portion is different from a corresponding one of the first voltage and the second voltage. 
     In order to achieve another aspect of the present invention, a semiconductor device includes a voltage generating section connected at an output terminal with first and second voltage line portions; and a control unit which controls the voltage generating section such that the first voltage line portion and the second voltage line portion are respectively set to a first voltage and a second voltage. When one of the first voltage line portion and the second voltage line portion is different from a corresponding one of the first voltage and the second voltage, the control unit controls the voltage generating section to generate a voltage directly to the one of the first voltage line portion and the second voltage line portion without passing through the other of the first voltage line portion and the second voltage line portion. 
     Also, the control unit controls the voltage generating section to operate when at least one of the first voltage line portion and the second voltage line portion is different from a corresponding one of the first voltage and the second voltage. 
     In order to achieve still another aspect of the present invention, a semiconductor device includes a voltage generating section connected at an output terminal with a first voltage line portion and a second voltage line portion and outputting a voltage from the output terminal in response to a control signal; a first voltage detecting section which outputs a first detection signal when the voltage of the first voltage line portion is different from the first voltage; a second voltage detecting section which outputs a second detection signal the voltage of the second voltage line portion is different from the second voltage; a control signal outputting section which outputs the control signal to the voltage generating section in response to at least one of the first detection signal and the second detection signal. 
     Also, the semiconductor device may further includes a wiring line which connects the first voltage line portion and the second voltage line portion; a MOS transistor provided between a node connected to the wiring line and the second voltage line portion, to connect the node and the second voltage line portion in response to an operation signal; and an operation signal generating section which generates the operation signal based on the second detection signal. 
     Also, the semiconductor device may further include a first MOS transistor provided to connect the output terminal of the voltage generating section to the first voltage line portion in response to a first operation signal; a second MOS transistor provided to connect the output terminal of the voltage generating section and the second voltage line portion in response to a second operation signal; a first operation signal generating section which generates the first operation signal based on the first detection signal; and a second operation signal generating section which generates the second operation signal based on the second detection signal. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a circuit block diagram showing the structure of a first conventional power supply voltage generating unit which generates a negative voltage; 
     FIG. 2 is a timing chart showing the operation of the first conventional power supply voltage generating unit of FIG. 1; 
     FIG. 3 is a circuit block diagram showing the structure of a second conventional power supply voltage generating unit which generates a boosted voltage; 
     FIG. 4 is a timing chart showing the operation of the second conventional power supply voltage generating unit shown in FIG. 3; 
     FIG. 5 is a circuit block diagram showing the structure of a power supply voltage generating unit for generating a negative voltage according to a first embodiment of the present invention; 
     FIG. 6 is a timing chart showing the operation of the power supply voltage generating unit in the first embodiment; 
     FIG. 7 is a circuit block diagram showing the internal structure of a charge pump circuit of the power supply voltage generating unit in the first embodiment; 
     FIGS. 8A to  8 I are timing charts showing signal waveforms at nodes of the charge pump circuit of FIG. 7; 
     FIG. 9 is a circuit block diagram showing an OR circuit of the power supply voltage generating unit in the first embodiment; 
     FIG. 10 is a circuit block diagram showing the structure of an oscillator of the power supply voltage generating unit in the first embodiment; 
     FIG. 11 is a circuit block diagram showing a first level detector of the power supply voltage generating unit in the first embodiment; 
     FIG. 12 is a circuit block diagram showing a second level detector of the power supply voltage generating unit in the first embodiment; 
     FIG. 13 is a circuit block diagram showing a level converter of the power supply voltage generating unit in the first embodiment; 
     FIGS. 14A and 14B are timing charts showing the signal waveforms of an input signal and an output signal in the level converter of FIG. 13; 
     FIG. 15 is a circuit block diagram showing the structure of the power supply voltage generating unit for generating a boosted voltage according to a second embodiment of the present invention; 
     FIG. 16 is a timing chart showing the operation of the power supply voltage generating unit in the second embodiment; 
     FIG. 17 is a circuit block diagram showing the internal structure of a charge pump circuit of the power supply voltage generating unit in the second embodiment; 
     FIGS. 18A to  18 I are timing charts showing signal waveforms at nodes of the charge pump circuit of FIG. 17; 
     FIG. 19 is a circuit block diagram showing an OR circuit of the power supply voltage generating unit in the second embodiment; 
     FIG. 20 is a circuit block diagram showing the structure of an oscillator of the power supply voltage generating unit in the second embodiment; 
     FIG. 21 is a circuit block diagram showing a first level detector of the power supply voltage generating unit in the second embodiment; 
     FIG. 22 is a circuit block diagram showing a second level detector of the power supply voltage generating unit in the second embodiment; 
     FIG. 23 is a circuit block diagram showing a level converter of the power supply voltage generating unit in the second embodiment; 
     FIGS. 24A and 24B are timing charts showing the signal waveforms of an input signal and an output signal in the level converter of FIG. 23; 
     FIG. 25 is a circuit block diagram showing the structure of the power supply voltage generating unit for generating a negative voltage according to a third embodiment of the present invention; 
     FIG. 26 is a circuit block diagram showing the structure of a level converter of the power supply voltage generating unit in the third embodiment; 
     FIGS. 27A to  27 D are timing charts showing signal waveforms at nodes of the level converter of FIG. 26; 
     FIG. 28 is a circuit block diagram showing the structure of the power supply voltage generating unit for generating a boosted voltage according to a fourth embodiment of the present invention; 
     FIG. 29 is a circuit block diagram showing the structure of a level converter of the power supply voltage generating unit in the fourth embodiment; 
     FIGS. 30A to  30 D are timing charts showing signal waveforms at nodes of the level converter of FIG. 29; 
     FIG. 31 is a circuit block diagram showing the structure of the power supply voltage generating unit for generating a negative voltage according to a fifth embodiment of the present invention; 
     FIG. 32 is a timing chart showing the operation of the power supply voltage generating unit in the fifth embodiment; 
     FIG. 33 is a circuit block diagram showing the structure of a first level converter of the power supply voltage generating unit in the fifth embodiment; 
     FIGS. 34A to  34 D are timing charts showing signal waveforms at nodes of the first level converter of FIG. 33; 
     FIG. 35 is a circuit block diagram showing the structure of a second level converter of the power supply voltage generating unit in the fifth embodiment; 
     FIGS. 36A to  36 D are timing charts showing signal waveforms at nodes of the second level converter of FIG. 35; 
     FIG. 37 is the circuit block diagram showing the structure of the power supply voltage generating unit for generating a boosted voltage according to a sixth embodiment of the present invention; 
     FIG. 38 is a timing charts showing the operation of the power supply voltage generating unit in the sixth embodiment; 
     FIG. 39 is a circuit block diagram showing the structure of a first level converter of the power supply voltage generating unit in the sixth embodiment; 
     FIGS. 40A to  40 D are timing charts showing signal waveforms at nodes of the first level converter of FIG. 39; 
     FIG. 41 is a circuit block diagram showing the structure of a second level converter of the power supply voltage generating unit in the sixth embodiment; 
     FIGS. 42A to  42 D are timing charts showing signal waveforms at nodes of the second level converter of FIG. 41; 
     FIG. 43 is a circuit block diagram showing the structure of a modification example of the power supply voltage generating unit according to the fifth or sixth embodiment of the present invention; and 
     FIG. 44 is a circuit block diagram showing the structure of a separating section of the power supply voltage generating unit according to the first to fourth embodiments of the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Hereinafter, a semiconductor device of the present invention will be described with reference to the attached drawings. 
     FIG. 5 shows the circuit structure of the power supply voltage generating unit  20  according to the first embodiment of the present invention. The power supply voltage generating unit  20  generates a negative voltage. 
     Referring to FIG. 5, the power supply voltage generating unit  20  is composed of a charge pump circuit CP, an oscillator OSC, an OR circuit Co, two level detectors Ld 1  and Ld 2 , a level converter Lc 2 , and an N-channel output transistor NB 1 . A V BB  voltage is a negative voltage (a substrate voltage) which is used as a substrate bias for memory cell transistors. A V NN  voltage is a word line voltage for the memory cell transistor and is a negative voltage. The V BB  voltage and the V NN  voltage are in the relation of V BB &lt;V NN . 
     The charge pump circuit CP is directly connected with the V BB  voltage and is connected with the V NN  voltage through a wiring line L 1 . The charge pump circuit CP operates in response to an output signal B 5  from the oscillator OSC. The charge pump circuit CP functions to absorb current from the side of V BB  voltage and/or the side of V NN  voltage and to decrease the V BB  voltage and/or the V NN  voltage. 
     The N-channel output transistor NB 1  is connected with the side of V NN  voltage to disconnect the V NN  voltage from the V BB  voltage. The output transistor NB 1  has the source connected with the V NN  voltage and the drain connected with the V BB  voltage at the node La on the wiring line L 1  on the side of V NN  voltage. 
     The level detector Ld 1  detects the V BB  voltage. When the V BB  voltage is higher than a predetermined value, the level detector Ld 1  outputs the signal of the high level as an output signal B 2 . The level detector Ld 2  detects the V NN  voltage. When the V NN  voltage is higher than the predetermined value, the level detector Ld 1  outputs the signal of a high level as an output signal B 3 . 
     The OR circuit Co outputs a signal of the high level as an output signal B 1  when at least one of the output signals B 2  and B 3  is in the high level. The oscillator OSC outputs an output signal B 5  to the charge pump circuit CP in response to the output signal B 1  of the high level. 
     The level converter Lc 2  receives the output signal B 3  from the level detector Ld 2  and converts the output signal B 3  in level into an output signal B 4  to output to the gate of the output transistor NB 1 . 
     Next, the operation of power supply voltage generating unit  20  will be described with reference to FIG.  6 . Hereinafter, three cases, i.e., case (1) where noise is generated on the side of V NN  voltage, case (2) where noise is generated on the side of V BB  voltage, and case (3) where noise is generated in both of the side of V NN  voltage and the side of V BB  voltage, will be described. It should be noted that a V NNst  voltage shows a voltage set for the V NN  voltage in the stable state in which noise is not contained in the V NN  voltage in waveform A. Also, in waveform B, a V BBst  voltage shows a voltage set for the V BB  voltage in the stable state in which noise is not contained to the V BB  voltage. 
     First, the case (1) where the noise is generated on the side of V NN  voltage will be described. 
     When the noise from a circuit group is contained on the side of V NN  voltage, the V NN  voltage increases, as shown in waveform A. At this time, the level detector Ld 2  outputs the high signal as the output signal B 3  after a predetermined time t DET1 , as shown in waveform C. The output signal B 4  is generated from the output signal B 3  of the high level by the level converter Lc 2  and is supplied to the gate of the output transistor NB 1 , so that the output transistor NB 1  is set to the conductive state. Then, the noise contained on the side of V NN  voltage is transferred to the side of V BB  voltage through the output transistor NB 1  and the wiring line L 1 , as shown by an arrow Y 1  in FIG.  5  and by V BBnoise  in FIG. 6, waveform B. 
     On the other hand, as mentioned above, when the output signal B 3  of the high level is outputted from the level detector Ld 2 , the output signal B 1  from the OR circuit Co becomes the high level as shown in waveform C. As a result, the oscillator OSC starts the operation, as shown in waveform D. Thus, the charge pump circuit CP operates and the noise contained on the side of V NN  voltage is removed, as shown by an arrow Y 2  in FIG.  5  and by V BBnoise  in FIG. 6, waveform B. 
     As mentioned above, the noise is transferred from the side of V NN  voltage to the side of V BB  voltage as shown by the arrow Y 1  once when the output transistor NB 1  is set to the conductive state. In this case, the charge pump circuit CP absorbs the V BB  voltage noise V BBnoise  transferred as shown by the arrow Y 1 , in addition to the noise contained on the side of V NN  voltage, as shown in the arrow Y 2 . The V BB  voltage noise is the noise moved from the side of V NN  voltage to the side of V BB  voltage for a short time from the time of the setting to the conductive state of the output transistor NB 1  to the operation start of the charge pump circuit CP. Therefore, a quantity of the V BB  voltage noise generated on the side of V BB  voltage when the output transistor NB 1  is set to the conductive state is suppressed to a small level, unlike the conventional example. 
     As mentioned above, in the power supply voltage generating unit  20 , the noise contained on the side of V NN  voltage is reduced in the directions shown by both of the arrows Y 1  and Y 2 . Therefore, the noise can be quickly removed from the side of V NN  voltage. 
     Also, in the conventional example, the noise generated on the side of V NN  voltage is removed as the V BB  voltage noise after the times t DET1  and t DET2  from the generation of the noise. On the other hand, both of the removal of the noise contained on the side of V NN  voltage and the removal of the V BB  voltage noise are started immediately after the time t DET1  in the power supply voltage generating unit  20 . In addition, in this case, as mentioned above, there is little quantity of the V BB  voltage noise. Therefore, the decay time td of the V BB  voltage noise is shorter, compared with the conventional example. 
     Next, the case (2) where the noise is generated on the side of V BB  voltage will be described. 
     In this case, the output signal B 1  from the OR circuit Co and the output signal B 2  from the level detector Ld 1  are set to the high level. Thus, the operation of the oscillator OSC is started. The charge pump circuit CP operates in response to the operation of the oscillator OSC to remove the noise which generated on the side of V BB  voltage. In this case, the output signal B 3  from the level detector Ld 2  is in the low level so that the output transistor NB 1  is not set to the conductive state. Therefore, the charge pump circuit CP never absorbs current from the side of V NN  voltage with a higher voltage than the V BB  voltage and the noise removal on the side of V BB  voltage is carried out as it is. 
     Next, the case (3) where the noise is generated in both on the side of V NN  voltage and the side of V BB  voltage will be described. In this case, the output signals B 2  and B 3  from the level detectors Ld 1  and Ld 2  become high level so that the output signal B 1  from the OR circuit Co becomes the high level. As a result, the charge pump circuit CP is operated by the oscillator OSC. The charge pump circuit CP removes the noise on the side of V BB  voltage and the noise on the side of V NN  voltage through the wiring line L 1 . 
     The following effects can be attained according to the power supply voltage generating unit  20 . 
     The noise to the V BB  voltage becomes small when the V NN  voltage increases. Also, even when the level of the V BB  voltage is near the level of the V NN  voltage, the time necessary to recover the changed power supply voltage to the original level can be made short. The above effects are attained because it is possible to reduce the influence of the power supply noise by operating the charge pump circuit CP when the V BB  voltage or the V NN  voltage increases. 
     FIGS. 7 to  13  and  14 A and  14 B show the circuit structures and operations of each of the components of the power supply voltage generating unit  20 . 
     The internal structure of the charge pump circuit CP is shown in FIG.  7 . FIGS. 8A to  8 I are timing charts showing signal waveforms at the nodes G 0 , H 0 , G′, H′, E 0 , F 0 , E′, F′ of FIG.  7 . As shown in FIG. 7, the charge pump circuit CP receives the output signal B 5  (FIG. 5) from the oscillator OSC as the V osc  signal. The V osc  signal is propagated from the left to the right in FIG. 7 in the circuit group composed of an inverter, a NAND circuit, a NOR circuit, capacitors CPB 1 , CPB 2 , CPB 3 , and CPB 4 , MOS transistors PC 1 , PC 2 , PC 3 , PD 1 , PD 2 , and PD 3 . As shown in FIGS. 8A to  8 I, the voltage of each node takes either of VCC, GND and −VCC. In this way, the charge pump circuit CP operates to the V NN  voltage and/or the V BB  voltage as mentioned above. 
     FIG. 9 shows the OR circuit Co and the input signals B 2  and B 3  and the output signal B 1  in FIG. 5 correspond to signals V det1 , V det2  and V det , respectively. 
     As shown in FIG. 10, the oscillator OSC is a ring oscillator and a NAND circuit and a plurality of inverters connected in series. The V det  signal in FIG. 9 is received by one of the input terminals of the NAND circuit, and the signal outputted from one of the inverters is fed back to the other input terminal of the NAND circuit. The V osc  signal outputted from the oscillator OSC is received by the charge pump circuit CP, as shown in FIG.  7 . 
     The circuit structure of the level detector Ld 1  is shown in FIG.  11 . The circuit structure of the level detector Ld 2  is shown in FIG.  12 . As shown in FIG. 11, one of the gates of two MOS transistors of an input stage is connected with ground (GND) and the other is connected with the V BB  voltage, as shown in FIG.  11 . As shown in FIG. 12, the level detector Ld 2  has the same structure as the level detector Ld 1 . One of the gates of two MOS transistors of an input stage is connected with ground (GND) and the other is connected with the V NN  voltage, as shown in FIG.  12 . The reference voltages V REFN1  and V REFN2  are different from each other and used to detect the V BB  voltage and the V NN  voltage by the level detectors Ld 1  and Ld 2 , as shown in FIG.  11  and FIG.  12 . 
     The circuit structure of the level converter Lc 2  is shown in FIG.  13 . FIGS. 14A and 14B are timing charts showing the input signal V DET2  and the output signals OUT of the level converter Lc 2 . The input signal V DET2  of the level converter Lc 2  corresponds to the B 3  signal of FIG.  5  and FIGS. 14A, and the output signal OUT in FIG. 13 and 14B corresponds to the B 4  signal in FIG.  5 . When the input signal V DET2  is in the low level of the ground (GND) level, the level converter Lc 2  outputs the signal of the V BB  voltage as the output signal OUT, as shown in FIG.  13  and FIG.  14 B. When the input signal Vdet 2  is in the high level of the Vcc voltage level, the level converter Lc 2  outputs the signal of the Vcc voltage just as it is, as output signal OUT. 
     In the first embodiment, the power supply voltage generating unit is described to generate a negative voltage. When a boosted voltage should be generated in place of the negative voltage, only the polarity is changed and the structure and operation are substantially the same as in the first embodiment. FIGS. 15 to FIG. 24 show the power supply voltage generating unit to generate the boosted voltage according to the second embodiment of the present invention. 
     FIG. 5 showing the negative voltage generating unit  20  corresponds to FIG. 15 showing a boosted voltage generating unit  20 A. FIG. 6 corresponds to FIG.  16 . FIG. 7 corresponds to FIG.  17 . Hereinafter, in the same way, FIGS. 8A to  8 I correspond to FIGS. 18A to  181 , FIG. 9 corresponds to FIG.  19  and FIG. 10 corresponds to FIG.  20 . FIG. 11 corresponds to FIG. 21, FIG. 12 corresponds to FIG. 22, FIG. 13 corresponds to FIG.  23  and FIGS. 14A and 14B correspond to FIGS. 24A and 24B, respectively. Because the boosted voltage generating unit  20 A shown in FIGS. 15 to  24 B is attained by only inverting in polarity the negative voltage generating unit  20  shown from FIG. 5 to FIG. 14B, the detailed description is omitted. 
     Next, the power supply voltage generating unit  30  according to the third embodiment of the present invention will be described with reference to FIG.  25 . 
     The power supply voltage generating unit  30  generate a negative voltage. The power supply voltage generating unit  30  of FIG. 25 is basically the same as the power supply voltage generating unit  20  of FIG. 5 in the first embodiment. The power supply voltage generating unit  30  of FIG. 25 is different from the power supply voltage generating unit  20  of FIG. 5 in the first embodiment in the following points. That is, the output transistor NB 1  of FIG. 5 is the N-channel transistor while an output transistor PD 1  of FIG. 25 is a P channel transistor. Also, the internal structure of a level converter Lc 4  is different. In FIG. 25, the same components as those of FIG. 5 are allocated with the same reference numerals or symbols, and has the same structures and operate in the same manner. 
     The operation of the power supply voltage generating unit  30  is as shown in FIG.  6  and is substantially the same as that of the power supply voltage generating unit  20  of FIG.  5 . 
     The internal structure of the level converter Lc 4  is shown in FIG.  26 . FIGS. 27A to  27 D are timing charts showing the signal waveforms of nodes A 4  and B 4  in the level converter Lc 4 . As shown in FIG.  26  and FIGS. 27A to  27 D, it is supposed that the signal V det2  as the signal D 3  (FIG. 25) supplied from the level detector Ld 2  is in the high level. In this case, the level converter Lc 4  supplies the signal of low level (−Vcc) to the gate of the output transistor PD 1  as the signal OUT of the output signal D 4  to set the output transistor PD 1  to the conductive state. 
     In the third embodiment, the power supply voltage generating unit  30  is described. When a boosted voltage should be generated in place of the negative voltage, only the polarity is changed and the structure and operation are substantially the same as in the third embodiment. FIGS. 28 to FIG. 30 show the power supply voltage generating unit to generate the boosted voltage according to the fourth embodiment of the present invention. 
     FIG. 25 showing the negative voltage generating unit  30  corresponds to FIG. 28 showing a boosted voltage generating unit  30 A. FIG. 26 correspond to FIG. 29, and FIGS. 27A to  27 D correspond to FIGS. 30A to  30 D. The boosted voltage generating unit  30 A shown in FIGS. 28 to  30  can be attained by only inverting in polarity the negative voltage generating unit  30  shown FIGS. 25 to  27 D. Therefore, the detailed description is omitted. 
     Next, the power supply voltage generating unit  40  according to the fifth embodiment of the present invention will be described with reference to FIG.  31 . 
     The power supply voltage generating unit  40  generate a negative voltage. The power supply voltage generating unit  40  of FIG. 31 is basically the same as the power supply voltage generating unit  30  of FIG. 25 in the third embodiment. The power supply voltage generating unit  40  of FIG. 31 is different from the power supply voltage generating unit  30  of FIG. 25 in the third embodiment in the following points. That is, a P-channel transistor PF 2  is added on the side of V BB  voltage to separate the V BB  voltage and the V NN  voltage and a level converter Lc 4 B is added to operate the P-channel transistor PF 2 . In addition, the internal structure of the level converter Lc 4 A is different. 
     In FIG. 31, the same components as those of FIG. 5 or  25  are allocated with the same reference numerals or symbols, and have the same structures and operate in the same manner. 
     The operation of the power supply voltage generating unit  40  is as shown in FIG.  32  and is different from that of the power supply voltage generating unit in the first or third embodiment. 
     When the power supply voltage generating unit  40  is applied, the substrate (Sub) voltage of the transistors PF 1  and PF 2  is set to the V NN  voltage, ground (GND) voltage or the VINT voltage, as shown in FIG.  31 . 
     In the power supply voltage generating unit  40 , the output transistor PF 2  is provided on the side of V BB  voltage to separate the V BB  voltage level and the V NN  voltage level. The output transistor PF 2  has the source connected with the output terminal of the charge pump circuit CP and the drain connected with the side of the V BB  voltage (the side of a noise generating source on the side of V BB  voltage). The gate of the output transistor PF 2  is connected with the output terminal of the level converter Lc 4 B. The level converter Lc 4 B receives the output signal F 2  from the level detector Ld 1  and outputs an output signal F 3 . 
     The level detector Ld 1  is connected with the node Nb on the side of V BB  voltage. The node Nb is located on the side near the noise generating source, i.e., on the right-hand side in the figure from the output transistor PF 2 . The level detector Ld 1  is not connected with the side of V NN  voltage. 
     The level detector Ld 2  is connected on the side of V NN  voltage with the node Nn near the noise generating source, i.e., the right-hand side in the figure from the output transistor PF 1 . The input terminal of the level detector Ld 1  is not connected with the side of V BB  voltage. The source of the output transistor PF 1  is not connected with the level detector Ld 1  and is connected with the node Nc on the side near the charge pump circuit CP than the position of the output transistor PF 2 . 
     The output transistor PF 2  prevents current flow from the side of V NN  voltage to the side of V BB  voltage when noise is generated on the side of V NN  voltage and the output transistor PF 1  on the side of V NN  voltage is set to the conductive state. Accordingly, there is not a problem that the large noise is generated on the side of V BB  voltage when the noise is generated on the side of V NN  voltage and the output transistor PF 1  is set to the conductive state, as shown in FIG. 32, waveform B. When the noise is not generated on the side of V BB  voltage, the side of V BB  voltage never receives influence of noise from the side of V NN  voltage. As mentioned above, the noise which generated on the side of V NN  voltage does not run away to the V BB  voltage, because the output transistor PF 2  is provided. Therefore, the decay time of the noise necessary to recover the V NN  voltage shown in FIG. 32, waveform A to the original voltage becomes late, compared with FIG. 6, waveform A. 
     In this case, when noise is generated on the side of V BB  voltage, the output signal F 2  from the level detector Ld 1  becomes high level. As a result, the signal F 3  is generated from the output signal F 2  by the level converter Lc 4 B and is used to set the output transistor PF 2  to the conductive state. By this, the noise on the side of V BB  voltage is absorbed by the charge pump circuit CP. 
     The internal structure of the level converter Lc 4 A is shown in FIG.  33 . FIGS. 34A to  34 D are timing charts showing the signal waveforms of nodes A 4  and B 4  of the level converter Lc 4 A. As shown in FIG.  33  and FIGS. 34A to  34 D, it is supposed that the signal V det2  as the signal F 4  (FIG. 31) supplied from the level detector Ld 2  is in the high level. In this case, the level converter Lc 4 A supplies the signal of low level (−Vcc) to the gate of the output transistor PF 1  as the signal OUT of the output signal F 5  to set the output transistor PF 1  to the conductive state. 
     The internal structure of the level converter Lc 4 B is shown in FIG.  35 . FIGS. 36A to  36 D are timing charts showing the signal waveforms of nodes A 4  and B 4  of the level converter Lc 4 B. As shown in FIG.  35  and FIGS. 36A to  36 D, when the signal V det2  as the signal F 4  (FIG. 31) supplied from the level detector Ld 2  is in the high level, the level converter Lc 4 A supplies the signal of low level (−VCC) to the gate of the output transistor PF 1  as the signal OUT of the output signal F 5  to set the output transistor PF 1  to the conductive state. 
     In the fifth embodiment, the power supply voltage generating unit  40  is described. When a boosted voltage should be generated in place of the negative voltage, only the polarity is changed and the structure and operation are substantially the same as in the fifth embodiment. FIGS. 37 to FIG. 42 show the power supply voltage generating unit to generate the boosted voltage according to the sixth embodiment of the present invention. 
     FIG. 31 showing the negative voltage generating unit  40  corresponds to FIG. 37 showing the boosted voltage generating unit  40 A. FIG. 32 corresponds to FIG. 38, and FIGS. 33A to  33 D correspond to FIGS. 34A to  34 D. Because the boosted voltage generating unit  40 A shown in FIGS. 37 to  42  is only opposed in polarity from the negative voltage generating unit  30  shown FIGS. 31 to  36 , the detailed description is omitted. 
     It should be noted that in the first to sixth embodiments, two different voltages, the V BB  voltage and the V NN  voltage, are handled, as shown in FIGS. 5,  25  and  31 . In place of the two different voltages, three or more voltages (hereinafter, to be referred to as object voltages) may be handled. By adopting the following structure, the power supply voltage generating unit which can handle three or more w object voltages can be realized. FIG. 43 shows the structure of the power supply voltage generating unit  40 B which can handle three object voltages using the power supply voltage generating unit  40  in the fifth embodiment. 
     A charge pump set CPS composed of a single charge pump circuit CP and a single oscillator OSC is provided. The charge pump circuit CP is connected with each of three or more object voltages, the voltage V BB  voltage, the V NN  voltage, the voltage V INT , . . . and is operable to them. The level detectors Ld corresponding to the number of object voltages (three in the example in FIG. 43) are necessary. The output signal of each of these level detectors Ld is supplied to a single OR circuit Co such that the oscillator OSC is operated in response to the output signal from the OR circuit Co. 
     When the charge pump circuit CP is connected with each of the object voltages, separating units for separating the object voltages of V BB  voltage, V NN  voltage, V INT , . . . from each other are necessary. The separating units composed of MOS transistors PJ which are connected with the object voltages of V BB  voltage, V NN  voltage, V INT , . . . , respectively. 
     Each of these output transistors PJ operates in response to a signal generated based on the corresponding object voltage level (a level converted signal obtained through conversion of the output signal from the level detector Ld) to connect the charge pump circuit CP to the corresponding object voltage. It should be noted that in FIG. 43, the separating unit is provided for each of the object voltage of V BB  voltage, the V NN  voltage, V INT  . . . . In place of this structure, the separating units may be provided for the object voltages such as V NN  voltage and so on other than one object voltage V BB  voltage it which excludes the V BB  voltage, like the first to fourth embodiments (FIG.  5  and FIG.  25 ). 
     In this case, the following point is important. Here, the case of the power supply voltage generating unit  20  of FIG. 5 will be described as an example. 
     In the power supply voltage generating unit  20  of FIG. 5, the output transistor NB 1  and the level converter Lc 2  are provided on the side of V NN  voltage. The level converter Lc 2  operates the output transistor NB 1  based on the voltage detection signal B 3  of the V NN  voltage. In place of this structure, as shown in FIG. 44, it is supposed that the output transistor NB 7  and a level converter Lc 7  are provided on the side of V BB  voltage such that the output transistor NB 7  is operated based on t the voltage detection signal B 7  of the V BB  voltage. 
     When noise is generated on the side of V BB  voltage, the output transistor NB 7  is set to the conductive state in response to the V BB  voltage detection signal B 7  and the charge pump circuit CP absorbs the noise contained on the side of V BB  voltage. In this case, the V BB  voltage and the V NN  voltage are in the relation of V BB  voltage&lt;V NN  voltage as mentioned above. Therefore, when the charge pump circuit CP absorbs the noise on the side of V BB  voltage, the V NN  voltage is decreased (see an arrow Y 3 ). As a result, when the noise contained in the V BB  voltage is removed and recovers to the original voltage, the V NN  voltage is decreased to the same level as the V BB  voltage. 
     For this reason, the separating units (output transistors) should be provided on the side of the object voltages to avoid the influence of the charge pump circuit CP in the normal state, or when noise is not generated. The separating units should be provided on the side of the higher object voltages, e.g., the V NN  voltage in the negative voltage generating unit  20  or  30  shown in FIG. 5 or FIG.  25 . In the boosted voltage generating unit  20 A or  30 A shown in FIG. 15 or  28 , the separating units are provided on the side of the lower object voltages, e.g., the V CH  voltage. In this way, the charge pump circuit CP never changes the object voltage in which the noise is generated. 
     Also, when the power supply voltage generating unit  20  of FIG. 5 is described using as an example, the output transistor NB 1  should be provided on the side of V NN  voltage in the power supply voltage generating unit  20  from the following viewpoint different from the above, as shown in FIG.  5 . 
     As mentioned above, a circuit group is connected with the side of V NN  voltage. Therefore, the side of V NN  voltage is easy for noise to be contained, compared with the side of V BB  voltage as the substrate voltage. When noise is contained on the side of V NN  voltage, the output transistor NB 1  is set to the conductive state immediately before operation of the charge pump circuit CP, and the noise on the side of V NN  voltage moves to the side of V BB  voltage lower than the V NN  voltage through the output transistor NB 1  without the operation of the charge pump circuit CP. Thus, the noise on the side of V NN  voltage is more quickly removed. 
     According to the semiconductor device of the present invention, the decay time of the noise can be made short. Also, according to the semiconductor device of the present invention, the movement of the noise generated on the side of a first voltage such as the V NN  voltage and the V CH  voltage to a second voltage such as the V BB  voltage and the V pp  voltage can be restrained.