Patent Publication Number: US-8981747-B2

Title: Regulator

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2012-064227, filed Mar. 21, 2012; the entire contents of which are incorporated herein by reference. 
     FIELD 
     Embodiments described herein relate generally to a regulator that carries out regulation of a DC voltage without performing a switching operation. 
     BACKGROUND 
     When a voltage difference between an input voltage VIN and an output voltage Vout is large, a switching regulator, which uses an inductor and a switching transistor to transform magnetic energy stored in the inductor to a DC voltage, is usually employed. However, the switching regulator has a complicated circuit design and a significant noise level. 
     When the voltage difference between the input voltage VIN and the output voltage Vout is small, a series regulator having a simple circuit design and low noise level is usually employed. The series regulator does not use magnetic energy, and instead directly transforms the input voltage VIN to the output voltage Vout, resulting in a significant thermal loss. In addition, there is a proportional relationship between conductive loss and the voltage difference between the input voltage VIN and the output voltage Vout. To reduce conductive loss, a low dropout (LDO) regulator, which is a type of series regulator that can work when the potential difference is as small as about 0.1 V, is often used. 
     In recent years, with progress made in forming finer semiconductor integrated circuit devices and lowering the operating voltages thereof, a tolerable power supply voltage range of CPU and other semiconductor devices has become narrower. However, during operation, the load current drawn by such devices may vary significantly corresponding to their operation mode, and so they usually require the variation in the output voltage to be 50 mV or lower even when there is a drastic change in the load current. 
     In order to meet demand, a broader band low dropout regulator is needed. However, for the conventional low dropout regulator, as the band is made wider, the power consumption rises. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a circuit diagram illustrating the internal constitution of an LDO regulator according to a first embodiment. 
         FIG. 2  is a circuit diagram illustrating a specific example of the internal constitution of various elements shown in  FIG. 1 . 
         FIG. 3  is a circuit diagram illustrating the internal constitution of an LDO regulator according to a second embodiment. 
         FIG. 4  is a circuit diagram illustrating the internal constitution of an LDO regulator according to a third embodiment. 
         FIG. 5  is a circuit diagram illustrating the internal constitution of an LDO regulator according to a fourth embodiment. 
         FIG. 6  is a circuit diagram illustrating the internal constitution of an LDO regulator according to a fifth embodiment. 
         FIG. 7  is a circuit diagram illustrating a modified example related to  FIG. 6 . 
         FIG. 8  is a circuit diagram illustrating the internal constitution of an LDO regulator according to a sixth embodiment. 
         FIG. 9  is a circuit diagram illustrating a modified LDO regulator of  FIG. 8 . 
         FIG. 10  is a circuit diagram illustrating the internal constitution of an LDO regulator according to a seventh embodiment. 
         FIG. 11  is a circuit diagram illustrating a modified LDO regulator of  FIG. 10 . 
         FIG. 12  is a circuit diagram illustrating an LDO regulator according to an eight embodiment. 
         FIG. 13  is a circuit diagram illustrating a modified LDO regulator of  FIG. 12 . 
         FIG. 14  is a circuit diagram illustrating an LDO regulator according to a ninth embodiment. 
         FIG. 15  is a circuit diagram illustrating a modified LDO regulator of  FIG. 6 . 
         FIG. 16  is a circuit diagram illustrating a modified LDO regulator of  FIG. 8 . 
         FIG. 17  is a circuit diagram illustrating the case in which the electroconductive type of the broadband transistor of the LDO regulator shown in  FIG. 15  is inverted, so that the connection configuration of the circuit between the input voltage line and the ground line is also inverted. 
         FIG. 18  is a circuit diagram illustrating the case in which the electroconductive type of the broadband transistor of the LDO regulator shown in  FIG. 16  is inverted, so that the connection configuration of the circuit between the input voltage line and the ground line is also inverted. 
     
    
    
     DETAILED DESCRIPTION 
     According to embodiments disclosed herein, a regulator that can realize a broader band without an increase in power consumption is provided. 
     According to one embodiment, there is provided a regulator that has the following parts: a differential circuit that generates a comparison signal corresponding to the voltage difference between the reference voltage and a voltage related to the output voltage, a first current source that supplies current to the differential circuit, a first transistor that adjusts the output voltage based on the input voltage corresponding to the comparison signal, a first current mirror circuit connected with a pair of differential output lines of the differential circuit, a second transistor that amplifies the high frequency signal superposed on the output voltage and feeds it to one line of the pair of differential output lines, a second current source that supplies the current for amplifying the high frequency signal in the second transistor, and a first capacitor, which accumulates charge therein as a result of the high frequency signal and which controls the current flowing to the one line of the pair of differential output lines via the second transistor in accordance with the charge quantity. 
     (Embodiment 1) 
       FIG. 1  is a circuit diagram illustrating the internal structure of the low dropout regulator (hereinafter to be referred to as LDO regulator) according to Embodiment 1. An LDO regulator  1  shown in  FIG. 1  has the following parts: a differential circuit  2 , a first current mirror circuit  3 , a phase compensating circuit  4 , an output-stage transistor  5  (first transistor), a voltage dividing circuit  6 , a broadband control transistor  7  (second transistor), a phase compensating capacitor Ci 1  (first capacitor), a first current source  8 , a second current source  9 , and an output capacitor Cout (second capacitor). 
       FIG. 2  is a circuit diagram illustrating a specific example of the internal constitution of the differential circuit  2 , the first current mirror circuit  3 , the phase compensating circuit  4 , the output-stage transistor  5  and the voltage dividing circuit  6  shown in  FIG. 1 . What is shown in  FIG. 2  is merely an example, and the internal constitution of these circuit components is not limited to that shown in  FIG. 2 . 
     As shown in  FIG. 2 , the voltage dividing circuit  6  has multiple resistors R 1 , R 2  connected in series between the output voltage line Vout, which outputs the output voltage Vout, and a ground line Vss. A divided voltage Vdiv obtained by dividing output voltage Vout is output from between the resistors R 1 , R 2 . The two ends of the resistor R 1  are connected in parallel with a speedup capacitor Cs. 
     The output capacitor Cout is connected between the output voltage line Vout and the ground line Vss. For the LDO regulator  1  in the related art, in order to make phase compensation, as a specific type of the output capacitor Cout, the capacitor (such as a tantalum capacitor or an electrolytic capacitor) with a high loss resistance component of the dielectric and electrode is used, or ESR (Equivalent Series Resistor) as a part separate from the capacitor is connected in series with the capacitor in many cases. However, according to the present embodiment, as to be explained later, there is no need to carry out phase compensation by the output capacitor Cout, so that a ceramic capacitor may be used. It is well known that a ceramic capacitor has a small resistance value for the ESR arranged inside it. According to the present embodiment, there is no need to attach an external ESR to the ceramic capacitor. 
     It is well known that the tantalum capacitor and electrolytic capacitor are dangerous because they are fire hazards. Because a ceramic capacitor, which is not a fire hazard, can be used here, it is possible to improve the reliability of the LDO regulator. 
     A load resistor Rload is connected in parallel with the output capacitor Cout. It is assumed that the resistance value of the load resistor Rload varies according to the operation of the load. For example, when a CPU is connected as a load, depending on the operation mode of the CPU, there may be a significant variation in the load current, so that the load resistor Rload also changes correspondingly. According to the present embodiment, even when the load resistor Rload varies, variation in the output voltage Vout over a broadband can still be suppressed. 
     The differential circuit  2  generates a comparison signal corresponding to the voltage difference between a reference voltage Vref and the divided voltage Vdiv. Here, the differential circuit  2  has a pair of NMOS transistors M 1 , M 2  with their sources having a common connection. The reference voltage Vref is input to the gate of the NMOS transistor M 1 , and the divided voltage Vdiv is input to the gate of the NMOS transistor M 2 . The first current mirror circuit  3  is connected to the drains of the NMOS transistors M 1 , M 2 . As used herein, the signal route that connects the drains of the pair of NMOS transistors and the first current mirror circuit  3  is referred to as a pair of differential output lines  10 . The first current source  8  is connected between the sources of the NMOS transistors M 1 , M 2  and the ground line Vss. 
     The gate of the NMOS transistor M 1  is the inverted input terminal of the differential circuit  2 , and the gate of the NMOS transistor M 2  is the non-inverted input terminal of the differential circuit  2 . In the present embodiment, the divided voltage Vdiv input to the inverted input terminal of the differential circuit  2  is compared with the reference voltage input to the non-inverted input terminal; a comparison signal corresponding to the voltage difference between them is input to the gate of the output-stage transistor  5 , and the output voltage Vout is feedback controlled. 
     The broadband control transistor  7  and the second current source  9  are connected in series between one of the pair of differential output lines  10  and the ground line Vss. More specifically, the drain of the broadband control transistor  7  is connected to one of the differential output lines, and its source is connected to one end of the second current source  9 . Also, the divided voltage Vdiv is input to the gate of the broadband control transistor  7 . As a result, the broadband control transistor  7  amplifies the high frequency signal superposed on the output voltage Vout, and the obtained signal is sent to one of the pair of differential output lines  10 . The second current source  9  is connected between the source of the broadband control transistor  7  and the ground line Vss, and the phase compensating capacitor Ci 1  is connected in parallel with the second current source  9 . 
     The phase compensating capacitor Ci 1  accumulates the charge as a result of the high frequency signal that is superposed on the output voltage Vout, and controls the current flowing in one of the pair of differential output lines  10  via the broadband control transistor  7  in accordance with the accumulated charge quantity. 
     The other line of the pair of differential output lines  10  is connected to the gate of the output-stage transistor  5 . The input voltage VIN is supplied to the source of the output-stage transistor  5 , and its drain is connected to the output voltage line Vout. Also, the phase compensating circuit  4  is connected between the source and gate of the output-stage transistor  5 . It should be recognized that this phase compensating circuit  4  is optional, and may be omitted. This phase compensating circuit  4  has a capacitor Ci 2  and a resistor R 3  connected in series. 
     In the following, the operation of the LDO regulator  1  shown in  FIG. 2  will be explained. First of all, the DC operation of the LDO regulator  1  will be explained. Here, the differential circuit  2  generates a comparison signal corresponding to the voltage difference between the reference voltage Vref and the divided voltage Vdiv of the output voltage Vout. This comparison signal is input to the gate of the output-stage transistor  5 . The input voltage VIN is fed to the source of the output-stage transistor  5 , and the output voltage Vout is output from the drain. Consequently, by means of the comparison signal, it is possible to change the resistance between the drain and source of the output-stage transistor  5 . As a result, it is possible to control the voltage level of the output voltage Vout by means of Input voltage VIN. 
     For example, if the divided voltage Vdiv of the output voltage Vout is higher than the reference voltage Vref, the gate voltage of the output-stage transistor  5  becomes higher, and the resistance between the source and drain of the output-stage transistor  5 , which is a PMOS transistor, becomes higher. As a result, the output voltage Vout and the divided voltage Vdiv of the output voltage Vout becomes lower. 
     In the following, the AC operation of the LDO regulator  1  will be explained. When a high frequency signal is superposed on the output voltage Vout due to variation in the load, charge is accumulated in the phase compensating capacitor Ci 1  via the broadband control transistor  7 . This charge accumulation operation is carried out instantly. Also, the speedup capacitor Cs is connected to the two ends of the resistor R 1  in the voltage dividing circuit  6 , so that the high frequency signal superposed on the output voltage Vout is instantly transferred to the gate of the broadband control transistor  7 . 
     As the charge is accumulated in the phase compensating capacitor Ci 1 , the drain current of the broadband control transistor  7  instantly rises, and the drain current of the NMOS transistor M 2  also rises. Because the first current mirror circuit  3  is connected to the drains (a pair of differential output lines) of the NMOS transistors M 1 , M 2 , an increase in the drain current of the NMOS transistor M 2  leads to an increase in the drain current of the NMOS transistor M 1 . As a result, the gate voltage of the output-stage transistor  5  rises and the current between the source and the drain of the output-stage transistor  5  falls, so that a variation of the output voltage is suppressed. 
     As a result, for the LDO regulator  1  shown in  FIG. 2 , when a high frequency signal is superposed on the output voltage Vout, control is carried out to suppress the high frequency signal. This control can be carried out very quickly, so that a broader band can be realized. 
     In the LDO regulator  1  shown in  FIG. 2 , among the pair of transistors M 1 , M 2  in the differential circuit  2 , only one transistor M 2  on the inverted input side is connected with the broadband control transistor  7 , the second current source  9  and the phase compensating capacitor Ci 1 , so that the differential circuit  2  has an asymmetric circuit configuration. Consequently, when the pair of transistors M 1 , M 2  are formed with the same size, a high offset voltage is generated at the output voltage Vout. 
     Consequently, for offset adjustment, it is preferred that the ratio of the size of transistors M 1 , M 2  be adjusted, or the ratio of the size of the pair of transistors M 3 , M 4  in the first current mirror circuit  3  be adjusted. 
     For the LDO regulator  1  shown in  FIG. 2 , the output capacitor Cout and the phase compensating capacitor Ci 1  each have one end connected to the ground line Vss. However, it is optional to connect the one end to the ground line Vss; one may also adopt a scheme in which the one end is connected to a stable voltage route with a low impedance. 
     In this way, according to Embodiment  1 , because the broadband control transistor  7 , the phase compensating capacitor Ci 1  and the second current source  9  are arranged on the inverted input side of the differential circuit  2  in the LDO regulator  1 , the high frequency signal superposed on the output voltage Vout can be instantly fed back and suppressed to the gate of the output-stage transistor  5 , so that a broader band can be realized for the LDO regulator  1 . 
     According to the present embodiment, by adjusting the various element parameters of the broadband control transistor  7 , the phase compensating capacitor Ci 1 , and the second current source  9 , so that the circuit is free from the risk of oscillation, it is possible to use a ceramic capacitor as the output capacitor Cout without the phase compensating circuit  4 . Although the ceramic capacitor has a problem that ESR with an effect on phase compensation is small, there is no need to perform phase compensation by the output capacitor Cout because the circuit has been set up to be free from the risk of oscillation; also, the ceramic capacitor does not pose a fire hazard that would be present for the tantalum capacitor and electrolytic capacitor, and it has less of a ripple component, so that it has better reliability and improved electrical characteristics. In addition, as mentioned previously, since the phase compensating circuit  4  can be omitted, the circuit constitution becomes simpler and the cost of the parts can be cut as well. 
     (Embodiment 2) 
     In Embodiment 2 to be explained below, as a characteristic feature, the connection destination of the gate of the broadband control transistor  7  is different from that in Embodiment 1. 
       FIG. 3  is a circuit diagram illustrating the internal constitution of the LDO regulator  1  related to Embodiment 2. The same keys as those in the above in  FIG. 2  are adopted in  FIG. 3  and, in the following, only the different features will be explained. 
     The gate of the broadband control transistor  7  in the LDO regulator  1  shown in  FIG. 3  is set at the output voltage Vout. 
     A comparison between  FIG. 2  and  FIG. 3  indicates that for the scheme shown in  FIG. 2 , the voltage between the second current source  9  and the source of broadband control transistor  7 , and the voltage between the first current source  8  and the differential circuit  2 , have a better relative precision. On the other hand, for the scheme shown in  FIG. 3 , there is the effect that the high frequency signal superposed on the output voltage Vout can be directly transferred to the gate of the broadband control transistor  7 . That is, the schemes shown in  FIG. 2  and  FIG. 3  have other respective advantages and disadvantages. 
     Just as shown in  FIG. 2 , in the case of the LDO regulator  1  shown in  FIG. 3 , in order to adjust the offset, it is preferred that the size ratio of the transistors M 1 , M 2  be changed, or the size ratio of the pair of transistors M 3 , M 4  in the first current mirror circuit  3  be changed. 
     In the LDO regulator  1  shown in  FIG. 3 , instead of connecting one end of each of the output capacitor Cout and the phase compensating capacitor Ci 1  to the ground line Vss, they may also be connected to a stable voltage route with a low impedance. In addition, the phase compensating circuit  4  also can be omitted. 
     (Embodiment 3) 
     Embodiment 3 to be explained below has a characteristic feature that the inverted input side and the non-inverted input side of the differential circuit  2  have a symmetric configuration. 
       FIG. 4  is a circuit diagram illustrating the internal constitution of the LDO regulator  1  according to Embodiment 3. The same reference numbers as those in  FIG. 2  above are used in  FIG. 4  when referring to the same features, and only the different features will be explained below. 
     The LDO regulator  1  shown in  FIG. 4  has a third current source  11  connected between the drain of the NMOS transistor M 1  in the differential circuit  2  and the ground line Vss. 
     Because of the symmetric configuration, it is preferred that the third current source  11  have the same electric characteristics as those of the second current source  9 . As a result, it is possible to have the voltage between the third current source  11  and the drain of the NMOS transistor M 1 , the voltage of the route between the second current source  9  and the source of the broadband control transistor  7 , and the voltage of the route between the first current source  8  and the sources of NMOS transistors M 1 , M 2  uniform with respect to each other. As a result, it is possible to have a high relative precision for the first current source  8 , second current source  9  and third current source  11 . In addition, since the symmetry of the differential circuit  2  is improved, it is possible to decrease the offset voltage of the output voltage Vout. 
     In the LDO regulator  1  shown in  FIG. 4 , instead of connecting one end of each of the output capacitor Cout and the phase compensating capacitor Ci 1  to the ground line Vss, one may also adopt a scheme in which they are connected to a stable voltage route with a low impedance. In addition, the phase compensating circuit  4  may be omitted. 
     As shown in  FIG. 4 , the third current source  11  is added to the LDO regulator  1  shown in  FIG. 2 . However, one may also adopt a scheme in which the third current source  11  is added to the LDO regulator  1  shown in  FIG. 3  to form a symmetric configuration. 
     (Embodiment 4) 
     In Embodiment 4 to be explained below, the same transistor as the broadband control transistor  7  is also set on the non-inverted input side of the differential circuit  2 , and the offset voltage of the output voltage Vout is decreased. 
       FIG. 5  is a circuit diagram illustrating the internal constitution of the LDO regulator  1  according to Embodiment 4. For the LDO regulator  1  shown in  FIG. 5 , in addition to the constitution shown in  FIG. 4 , it also has an NMOS transistor  12  connected between the third current source  11  and the drain of the NMOS transistor M 1 . The drain of the NMOS transistor  12  is connected to the drain of the NMOS transistor M 1  and the source of the NMOS transistor  12  is connected to the third current source  11 . The gate of the NMOS transistor  12  is set at the reference voltage Vref, and it is also connected to the gate of the NMOS transistor M 1 . 
     Because the gate voltage of the NMOS transistor  12  is at the reference voltage Vref, the source voltage also becomes a voltage corresponding to the reference voltage Vref, and it is possible to realize a constant voltage for the voltage of the connecting route between the third current source  11  and the NMOS transistor  12 . As a result, it is possible to improve the symmetry of the differential circuit  2 , and it is possible to decrease the offset voltage of the output voltage Vout. 
     For the LDO regulator  1  shown in  FIG. 5 , it is preferred that the second current source  9  and the third current source  11  have the same electric characteristics, and that the broadband control transistor  7  and the NMOS transistor  12  also have the same electric characteristics. 
     Also, in the LDO regulator  1  shown in  FIG. 5 , instead of connecting one end of each of the output capacitor Cout and the phase compensating capacitor Ci 1  to the ground line Vss, one may also adopt a scheme in which they are connected to a stable voltage route with a low impedance. In addition, the phase compensating circuit  4  may be omitted. 
     As shown in  FIG. 5 , the NMOS transistor  12  is added to the LDO regulator  1  shown in  FIG. 4 . However, one may also adopt a scheme in which the third current source  11  and the NMOS transistor  12  are added to the LDO regulator  1  to have a symmetric configuration shown in  FIG. 3 . 
     (Embodiment 5) 
     In Embodiment 5 to be explained below, it is possible to perform fine adjustment of the phase margin. 
       FIG. 6  is a circuit diagram illustrating the internal constitution of the LDO regulator  1  according to Embodiment 5. The same reference numbers as those in the above in FIG.  5  are used in  FIG. 6  when referring to the same features and, in the following, only the different features will be explained. 
     In the LDO regulator  1  shown in  FIG. 6 , in addition to the constitution shown in  FIG. 5 , there is a phase compensating capacitor Ci 3  (third capacitor) connected between the gate of the broadband control transistor  7  and the source of the NMOS transistor  12 . The capacitance of the phase compensating capacitor Ci 3  should be selected to be much smaller than the capacitance of the phase compensating capacitor Ci 1 , such as a capacitance value smaller by two or more orders of magnitude than that of the latter. By arranging the phase compensating capacitor Ci 3 , it is possible to perform fine adjustment of the phase margin. 
       FIG. 7  is a circuit diagram illustrating a modified circuit of  FIG. 6 . Here, one end of the phase compensating capacitor Ci 3  is connected to the drain of the NMOS transistor  12  instead of its source. Just as in  FIG. 6 , in the case of  FIG. 7 , too, by arranging a phase compensating capacitor Ci 3 , it is possible to perform fine adjustment of the phase margin. 
     For the LDO regulator  1  shown in  FIG. 6  and  FIG. 7 , it is preferred that the second current source  9  and the third current source  11  have the same electrical characteristics, and that the broadband control transistor  7  and the NMOS transistor  12  have the same electrical characteristics. In addition, instead of connecting one end of each of the output capacitor Cout and the phase compensating capacitor Ci 1  to the ground line Vss, one may also adopt a scheme in which they are connected to a stable voltage route with a low impedance. In addition, the phase compensating circuit  4  may be omitted. 
     As shown in  FIG. 6  and  FIG. 7 , the phase compensating capacitor Ci 3  is added to the LDO regulator  1  shown in  FIG. 5 . However, one may also adopt a scheme in which a phase compensating capacitor Ci 3  for fine adjustment of the phase margin is added to all of the LDO regulators  1  having the third current source  11 . 
     (Embodiment 6) 
     In Embodiment 6 to be explained below, the differential circuit  2  has a folded cascade type of configuration. 
     In the LDO regulator  1  shown in  FIG. 1  through  FIG. 7 , as an example, the differential circuit  2  includes a pair of NMOS transistors M 1 , M 2 . However, when the input voltage VIN becomes as low as 1.5 V or lower, the reference voltage Vref also decreases, so that the NMOS transistor cannot be used in the differential circuit  2 . In such a case, one may adopt a constitution in which the differential circuit  2  has a folded cascade type of constitution, in which a pair of PMOS transistors M 1 , M 2  are set. 
       FIG. 8  is a circuit diagram illustrating the internal constitution of the LDO regulator  1  according to Embodiment 6. The same reference numbers as those in the above in  FIG. 7  are used in  FIG. 8  when referring to the same features and, in the following, only the different features will be explained. 
     The differential circuit  2  in the LDO regulator  1  shown in  FIG. 8  has a folded cascade type of constitution, and it has a pair of PMOS transistors M 1 , M 2 . A second current mirror circuit  21  including a pair of NMOS transistors M 5 , M 6  is connected between the differential circuit  2  and the first current mirror circuit  3  including a pair of PMOS transistors M 3 , M 4 . The pair of differential output lines  10  of the second current mirror circuit  21  are connected to a fourth current source  22  and a fifth current source  23 . 
     The broadband control transistor  7  and the second current source  9  are connected in series between one line of the pair of differential output lines  10  between the first current mirror circuit  3  and second current mirror circuit  21  and the ground line Vss, and the phase compensating capacitor Ci 1  is connected in parallel with the second current source  9 . 
     The NMOS transistor  12  and the third current source  11  are connected in series between the other line of the pair of differential output lines  10  and the ground line Vss. The phase compensating capacitor Ci 1  for fine adjustment of the phase margin is connected between the drain of the NMOS transistor  12  and the output voltage line Vout. 
     Because the pair of PMOS transistors M 1 , M 2  are set in the differential circuit  2 , even when the reference voltage Vref is a constant voltage of about 1.2 V, it is still possible to perform the comparison operation free of problems, and it is possible to generate a low voltage as the output voltage line Vout. 
     One end of each of the second through fifth current sources  9 ,  11 ,  22  and  23 , one end of the phase compensating capacitor Ci 1 , one end of the voltage dividing circuit  6 , and one end of the output capacitor Cout are all connected to the ground line Vss. Also, one end of the first current source  8 , one end of the first current mirror circuit  3 , one end of the phase compensating circuit  4 , and the source of the output-stage transistor  5  are all connected to the input voltage VIN. 
       FIG. 9  is a circuit diagram illustrating a modified example of  FIG. 8 . The LDO regulator  1  shown in  FIG. 9  has the characteristic feature that one end of the phase compensating capacitor Ci 1  for fine adjustment of the phase margin is connected to the source of the NMOS transistor  12  instead of its drain. 
     Just as in  FIG. 8 , for the LDO regulator  1  shown in  FIG. 9 , because it has the folded cascade type of constitution, a stable operation can be performed even when the input voltage VIN is a low voltage. 
     For the LDO regulator  1  shown in  FIG. 8  and  FIG. 9 , it is preferred that the second current source  9  and the third current source  11  have the same electric characteristics, the fourth current source  22  and the fifth current source  23  have the same electrical characteristics, and the broadband control transistor  7  and the NMOS transistor  12  have the same electrical characteristics. Also, instead of connecting one end of each of the output capacitor Cout and the phase compensating capacitor Ci 1  to the ground line Vss, they may also be connected to a stable voltage route with a low impedance. In addition, the phase compensating circuit  4  may be omitted. 
     The LDO regulator  1  shown in  FIG. 8  and  FIG. 9  has a phase compensating capacitor Ci 3  for fine adjustment of the phase margin. However, it may also be omitted. 
     (Embodiment 7) 
     In Embodiment 7 to be explained below, the electroconductive type of the transistors in the LDO regulator  1  is inverted to that in Embodiments 1 through 6, and the circuit connection configuration is also inverted. 
       FIG. 10  is a circuit diagram illustrating the internal constitution of the LDO regulator  1  according to Embodiment 7. The electroconductive type of the transistors in the LDO regulator  1  shown in  FIG. 10  is inverted to the electroconductive type of the transistors in the LDO regulator  1  shown in  FIG. 6 . In addition, the connection configuration of the circuit between the input voltage line VIN and the ground line Vss is also inverted. The same keys as those for the transistors shown in  FIG. 6  are adopted in  FIG. 10 , too, although the electroconductive type should be inverted for them. 
     In the LDO regulator  1  shown in  FIG. 10 , one end of each of the first through third current sources  8 ,  9 ,  11 , one end of the phase compensating capacitor Ci 1 , one end of the voltage dividing circuit  6 , one end of the output capacitor Cout, and one end of the load resistor Rload are all connected to the input voltage line VIN. Also, one end of the first current mirror circuit  3  including a pair of NMOS transistors M 1 , M 2 , one end of the phase compensating circuit  4 , and the source of the output-stage transistor  5  are all connected to the ground line Vss. 
     In addition, the LDO regulator  1  shown in  FIG. 10  has the following parts: the differential circuit  2  including a pair of PMOS transistors M 1 , M 2 , the broadband control transistor  7  made of PMOS transistor, the second current source  9  and the phase compensating capacitor Ci 1  connected in parallel between the source of the broadband control transistor  7  and the input voltage line VIN, the PMOS transistor  12  connected to the symmetric position of the broadband control transistor  7 , the third current source  11  connected between the source of the transistor  12  and the input voltage line VIN, and the phase compensating capacitor Ci 1  for fine adjustment of the phase margin. 
       FIG. 11  is a circuit diagram illustrating a modified example of  FIG. 10 . It has the differential circuit  2  of the folded cascade type. For the LDO regulator  1  shown in  FIG. 11 , the electroconductive type of the transistors is inverted to that of the transistors in the LDO regulator  1  shown in  FIG. 8 , and the connection configuration of the circuit is also inverted. 
     For the LDO regulator  1  shown in  FIG. 11 , one end of each of the second through fifth current sources  9 ,  11 ,  22 ,  23 , one end of voltage dividing circuit  6 , and one end of the output capacitor Cout are all connected to the input voltage line VIN. Also, one end of the first current source  8 , one end of the first current mirror circuit  3  including a pair of NMOS transistors M 3 , M 4 , one end of the phase compensating capacitor Ci 1 , and one end of the phase compensating circuit  4  are connected to the ground line Vss. 
     The LDO regulator  1  shown in  FIG. 11  has the following parts: the differential circuit  2  including a pair of NMOS transistors M 1 , M 2 , the first current source  8  connected between the differential circuit  2  and the ground line Vss, the second current mirror circuit  21  including a pair of PMOS transistors M 5 , M 6  connected to the pair of differential output lines  10  of the differential circuit  2 , the first current mirror circuit  3  including a pair of NMOS transistors M 3 , M 4  connected to the second current mirror circuit  21 , the second current source  9  and the broadband control transistor  7  connected in series between the input voltage line VIN and the drain of the PMOS transistor M 6 , the phase compensating capacitor Ci 1  connected between the source of the broadband control transistor  7  and the ground line Vss, and the third current source  11  and the PMOS transistor  12  connected in series between the input voltage line VIN and the drain of the PMOS transistor M 5 . 
     For the LDO regulator  1  shown in  FIG. 10  and  FIG. 11 , it is preferred that the second current source  9  and the third current source  11  have the same electric characteristics, and that the broadband control transistor  7  and the NMOS transistor  12  have the same electrical characteristics. Instead of connecting one end of each of the output capacitor Cout and the phase compensating capacitor Ci 1  to the ground line Vss, one may also adopt a scheme in which they are connected to a stable voltage route with a low impedance. In addition, the phase compensating circuit  4  may be omitted. 
     As shown in  FIG. 10 , the gate of the broadband control transistor  7  may be connected to the output voltage Vout. In addition, in  FIG. 10 , the PMOS transistor  12  may be omitted. In addition, in  FIG. 10 , PMOS transistor  12  and the third current source  11  may be omitted as well. Also, in  FIG. 10  and  FIG. 11 , the phase compensating capacitor Ci 3  may also be omitted. 
     (Embodiment 8) 
     In Embodiment 8 to be explained below, the reference voltage on the low voltage side of the LDO regulator  1  is at a negative voltage level. 
       FIG. 12  is a circuit diagram illustrating the LDO regulator  1  according to Embodiment 8. The LDO regulator  1  shown in  FIG. 12  has a circuit constitution similar to that shown in  FIG. 2 . However, the reference voltage on the low voltage side is not the ground voltage; instead, it is a negative voltage (=−VIN 2 ). 
     For the LDO regulator  1  shown in  FIG. 12 , two types of input voltages VIN 1 , VIN 2  are input to it. Among them, one becomes the input voltage line VIN 1  on the higher voltage side, and the other becomes the input voltage line (=−VIN 2 ) on the lower voltage side. 
     The first current source  8  is connected between the differential circuit  2  including a pair of NMOS transistors M 1 , M 2  and the negative side input voltage line (=−VIN 2 ). The broadband control transistor  7  and the second current source  9  are connected in series between the drain of the NMOS transistor M 2  and the negative side input voltage line (=−VIN 2 ). Also, the voltage dividing circuit  6  and the load resistor Rload are connected in parallel between the output voltage line Vout and the negative side input voltage line (=−VIN 2 ). In addition, the phase compensating capacitor Ci 1  is connected between the source of the broadband control transistor  7  and the gate of the NMOS transistor M 1 . 
       FIG. 13  is a circuit diagram illustrating a modified example with respect to that shown in  FIG. 12 . The LDO regulator  1  shown in  FIG. 13  differs from that shown in  FIG. 12  in that one end of the phase compensating capacitor Ci 1  is connected to the positive side input voltage line VIN 1  instead of the gate of the broadband control transistor  6 ; at the same time, the positive side input voltage line VIN 1  is set at the ground voltage level. 
     The voltage level of the negative side input voltage line of the LDO regulator  1  shown in  FIG. 13  is at −(VIN 1 +VIN 2 ), and the operation can be carried out at a voltage lower than that in  FIG. 12 . 
     The LDO regulator  1  shown in  FIG. 12  and  FIG. 13  works in the same way and has the same effects as those of the LDO regulator  1  shown in  FIG. 2  except that the voltage level of the negative side input voltage line is set at a negative voltage lower than the ground voltage. 
     For the LDO regulator  1  shown in  FIG. 12  and  FIG. 13 , the voltage of the negative side electrode of the output capacitor Cout and the phase compensating capacitor Ci 1  may also be connected to a stable voltage route with a low impedance instead of setting at the voltage shown in  FIG. 12  and  FIG. 13 . In addition, the phase compensating circuit  4  may be omitted. 
     In  FIG. 12  and  FIG. 13 , the gate of the broadband control transistor  7  may be connected to the output voltage line Vout. In  FIG. 12  and  FIG. 13 , the third current source  11  may be added to form a symmetric constitution just as in  FIG. 4 . In addition, in order to further improve the symmetry, the NMOS transistor  12  may be added just as in  FIG. 5 . Also, as shown in  FIG. 12  and  FIG. 13 , the phase compensating capacitor Ci 3  as shown in  FIG. 6  and  FIG. 7  may be added, too. 
     (Embodiment 9) 
     In Embodiment 9 to be explained below, the electroconductive type of the broadband control transistor  7  is inverted to that in Embodiment 1. 
       FIG. 14  is a circuit diagram illustrating the LDO regulator  1  according to Embodiment 9. Different from the LDO regulator  1  shown in  FIG. 2 , the LDO regulator  1  shown in  FIG. 14  has a different connection configuration of the broadband control transistor  7 , the second current source  9  and the phase compensating capacitor Ci 1 . The broadband control transistor  7  shown in  FIG. 14  is a PMOS transistor; the second current source  9  is connected between its source and the input voltage line VIN, and a phase compensating capacitor Ci 1  is connected between its source and the ground line Vss. 
     In this way, even when the broadband control transistor  7  is made of a PMOS transistor, the same effect in forming a broader band as in  FIG. 2  can be realized. 
     Just as in  FIG. 2 , in the case of the LDO regulator  1  shown in  FIG. 14 , too, in order to adjust the offset, it is preferred that the size ratio of the transistors M 1 , M 2  or the size ratio of the pair of transistors M 3 , M 4  in the current mirror circuit  3  be changed. 
     In addition, for the LDO regulator  1  shown in  FIG. 14 , instead of connecting one end of the output capacitor Cout and the phase compensating capacitor Ci 1  to the ground lines Vss, they may also be connected to a stable voltage route with a low impedance. In addition, the phase compensating circuit  4  may be omitted. 
     Similarly, the broadband control transistor  6  made of NMOS transistor explained in the aforementioned embodiments may be substituted by a PMOS transistor. 
       FIG. 15  is a circuit diagram illustrating a modified example with respect to  FIG. 6 . The LDO regulator  1  shown in  FIG. 15  has the following parts: the second current source  9  and the broadband control transistor  7  connected in parallel between the input voltage line VIN and the gate of the NMOS transistor M 2 , the third current source  11  and the PMOS transistor  12  connected in series between the input voltage line VIN and the gate of the NMOS transistor M 1 , and the phase compensating capacitor Ci 1  connected between the drain of the NMOS transistor M 1  and the gate of the NMOS transistor M 2 . The gate of the broadband control transistor  7  is connected to the gate of the NMOS transistor M 2 , and the gate of the PMOS transistor  12  is connected to the gate of the NMOS transistor M 1 . 
     For the LDO regulator  1  shown in  FIG. 15 , it is preferred that the second current source  9  and the third current source  11  have the same electrical characteristics, and that the broadband control transistor  7  and the PMOS transistor  12  have the same electrical characteristics. Also, instead of connecting of an end of each of the output capacitor Cout and the phase compensating capacitor Ci 1  to the ground line Vss, they may also be connected to a stable voltage route with a low impedance. In addition, the phase compensating circuit  4  may be omitted. 
     As shown in  FIG. 14  and  FIG. 15 , the gate of the broadband control transistor  7  may also be connected to the output voltage line Vout. Also, as shown in  FIG. 15 , the PMOS transistor  12  may be omitted. Also, as shown in  FIG. 15 , the connecting site of the phase compensating capacitor Ci 3  is not limited to that shown in the figure, and the phase compensating capacitor Ci 3  may be added in  FIG. 14 . 
       FIG. 16  is a circuit diagram illustrating a modified example with respect to  FIG. 8 . The LDO regulator  1  shown in  FIG. 16  has a folded cascade type of constitution. The second current source  9  and the broadband control transistor  7  are connected in series between the input voltage line VIN and the drain of the PMOS transistor M 4 . The third current source  11  and the PMOS transistor  12  are connected in series between the input voltage line VIN and the drain of the PMOS transistor M 3 . The phase compensating capacitor Ci 1  is connected between the source of the broadband control transistor  7  and the ground line Vss. The phase compensating capacitor Ci 3  is connected between the drain of the PMOS transistor M 3  and the gate of the broadband control transistor  7 . 
     In the LDO regulator  1  shown in  FIG. 16 , it is preferred that the second current source  9  and the third current source  11  have the same electrical characteristics, the fourth current source  22  and the fifth current source  23  have the same electrical characteristics, and the broadband control transistor  7  and the NMOS transistor  12  have the same electrical characteristics. Also, instead of connecting one end of each of the output capacitor Cout and the phase compensating capacitor Ci 1  to the ground line Vss, they may also be connected to a stable voltage route with a low impedance. In addition, the phase compensating circuit  4  may be omitted. 
     In the LDO regulator  1  shown in  FIG. 17  and  FIG. 18  shown below, the electroconductive type is inverted to that of the broadband control transistor  7  of the LDO regulator  1  shown in  FIG. 15  and  FIG. 16 , and the connection configuration between the input voltage line VIN and the ground line Vss is also inverted. 
     In the LDO regulator  1  shown in  FIG. 17 , there are the following parts: the broadband control transistor  7  and the second current source  9  connected in series between the drain of the PMOS transistor M 2  in the differential circuit  2  and the ground line Vss, the phase compensating capacitor Ci 1  connected between the gate of the broadband control transistor  7  and the ground line Vss, the NMOS transistor  12  and the third current source  11  connected in series between the drain of the PMOS transistor M 1  and the ground line Vss, and the phase compensating capacitor Ci 3  connected between the drain of the NMOS transistor  12  and the gate of the broadband control transistor  7 . 
     For the LDO regulator  1  shown in  FIG. 17 , it is preferred that the second current source  9  and the third current source  11  have the same electrical characteristics, and that the broadband control transistor  7  and the PMOS transistor have the same electrical characteristics. Also, instead of connecting one end of each of the output capacitor Cout and the phase compensating capacitor Ci 1  to the input voltage line VIN or the ground line Vss, they may also be connected to a stable voltage route with a low impedance. In addition, the phase compensating circuit  4  may be omitted. 
     The LDO regulator  1  shown in  FIG. 18  has the following parts: the broadband control transistor  7  and the second current source  9  connected in series between the drain of the NMOS transistor M 4  in the second current mirror circuit  21  and the ground line Vss, the phase compensating capacitor Ci 1  connected in parallel with the second current source  9 , the NMOS transistor  12  and the third current source  11  connected in series between the drain of the NMOS transistor M 3  and the ground line Vss, and the phase compensating capacitor Ci 3  connected between the drain of the NMOS transistor  12  and the gate of the broadband control transistor  7 . 
     For the LDO regulator  1  shown in  FIG. 18 , it is preferred that the second current source  9  and the third current source  11  have the same electrical characteristics, the fourth current source  22  and the fifth current source  23  have the same electrical characteristics, and the broadband control transistor  7  and the NMOS transistor  12  have the same electrical characteristics. Also, instead of connecting one end of each of the output capacitor Cout and the phase compensating capacitor Ci 1  to the input voltage line VIN or the ground line Vss, they may also be connected to a stable voltage route with a low impedance. In addition, the phase compensating circuit  4  may be omitted. 
     As shown in  FIG. 17 , the PMOS transistor  12  may be omitted. In addition, the third current source  11  may be omitted as well. In addition, as shown in  FIG. 17 , the gate of the broadband control transistor  7  may be connected to the output voltage line Vout. In addition, as shown in  FIGS. 16 to 18 , the phase compensating capacitor Ci 3  may be omitted. In addition, the connecting site of the phase compensating capacitor Ci 3  is not limited to what is shown in the figure. 
     As in the aforementioned Embodiments 2 to 9, just as in Embodiment 1, because there are the broadband control transistor  7 , the second current source  9  and the phase compensating capacitor Ci 1 , it is possible to instantly amplify the high frequency signal superposed on the output voltage Vout, it is possible to realize a broader band, and a ceramic capacitor can be used as the output capacitor Cout. 
     In the aforementioned embodiments, an explanation has been made on the examples in which all of the transistors are MOS transistors that are formed on a chip. In alternative embodiments, it is also possible to use bipolar transistors. 
     For the LDO regulator  1  according to various embodiments, it may be adopted in combination with a switching regulator (containing a DC-DC converter) that carries out the switching operation. That is, after DC voltage conversion is carried out for increasing or decreasing the voltage by the switching regulator, in the LDO regulator  1 , the output voltage Vout with a small voltage difference between the input/output voltages is generated and a load with significant variation in the load current, such as CPU or the like, may be connected thereto. 
     In the aforementioned embodiments, the divided voltage Vdiv obtained by dividing the output voltage Vout by the voltage dividing circuit  6  is fed back to the differential circuit  2 . However, the voltage dividing circuit  6  is not a necessary constitution, and the output voltage Vout may also be fed back to the differential circuit  2  directly. In this case, the output voltage Vout is input to the gates of the transistor M 2  and the broadband control transistor  7  in the differential circuit  2 . That is, one may also adopt a scheme in which a voltage related to the output voltage Vout is applied on the various gates of the transistor M 2  in the differential circuit  2  and the broadband control transistor  7 . 
     While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Indeed, the novel embodiments described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the embodiments described herein may be made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the inventions.