Patent Publication Number: US-7215183-B2

Title: Reference voltage generator circuit

Description:
RELATED APPLICATIONS 
   This application claims priority to Japanese Patent Application No. 2004-200560 filed Jul. 7, 2004 which is hereby expressly incorporated by reference herein in its entirety. 
   BACKGROUND 
   1. Technical Field 
   The present invention relates to a reference voltage generator circuit, particularly a reference voltage generator circuit including a band gap circuit. 
   2. Related Art 
   A band gap circuit has been used widely various kinds of semiconductor circuits. The band gap circuit is capable of generating voltage with extremely small temperature reliance by taking advantage of a difference in voltage-current characteristics created when two diodes different in size are coupled. 
   However, the band gap circuit essentially has two stable output voltage points, namely, a normal operating point and a stopping point. If the output voltage becomes stabilized at the stopping point, it is possible that the band gap circuit does not start. 
   On this account, there is a band gap-based reference voltage generator circuit having a startup circuit so as to bring the output voltage back to one at the normal operating point. The startup circuit is a circuit that brings the output voltage of the band gap circuit back to the normal operating point by forcefully supplying a starting current to the band gap circuit in order to prevent the output voltage from reaching to the stopping point (e.g., see M. Waltari, K. Halonen, “Reference Voltage Driver for Low-Voltage CMOS A/D Converters,” Proceedings of ICECS 2000, Vol. 1, pp. 28–31, 2000). 
     FIG. 4  shows an example of a conventional band gap-based reference voltage generator circuit. As shown in  FIG. 4 , the band gap-based reference voltage generator circuit is a band gap circuit  101  with a startup circuit  102  added thereto. The startup circuit  102  monitors an output voltage OUT at an output terminal of the band gap circuit  101 , and, when the output voltage OUT is the voltage at the normal operating point, a transistor  111  turns on while transistors  112  and  113  stay off. In contrast, when the output voltage OUT is at the stopping point, the transistor  111  turns off while the transistors  112  and  113  turn on, and, as a result, transistors  114  and  115  turn on, and, thereby, a predetermined current Ia is supplied to a line  116 . With the supply of the predetermined current Ia to the line  116 , the output voltage OUT rises and reaches to the normal operating point. 
   As described, the conventional startup circuit  102  brings back the output voltage OUT from the stopping point to the normal operating point by supplying the current Ia in an amount necessary for the startup to the band gap circuit  101 . However, even after the band gap-based reference voltage generator circuit has started, a current Ib keeps flowing to a transistor  117  which is coupled in series with the transistor  111  of the startup circuit  102 . It is not desirable that the current Ib continue to flow to the transistor  117  even after the band gap-based reference voltage generator circuit has started when considering reducing electric consumption. 
   In view of these issues, the present invention aims to provide a reference voltage generator circuit which enables to reduce electric consumption. 
   SUMMARY 
   The reference voltage generator circuit of the invention includes: a band gap circuit that outputs a predetermined voltage to an output terminal; a plurality of current mirror circuits, a gate electrode of at least one of which being coupled with one current path, and a gate electrode of at least another one of which being coupled with an other current path, and which are further coupled with the band gap circuit so as to supply an output current to the output terminal corresponding to a current flowing in either the one or the another current path; and a control unit that detects an output voltage of the output terminal of the band gap circuit and that controls a current flowing in at least the one or the other current path corresponding to the detected output voltage. 
   The reference voltage generator circuit of the invention includes: a band gap circuit that outputs a predetermined voltage to an output terminal and a startup circuit, wherein the startup circuit includes: a plurality of current mirror circuits, a gate electrode of at least one of which being coupled with one current path, and a gate electrode of at least another one of which being coupled with an other current path; and which are further coupled with the band gap circuit so as to supply an output current to the output terminal corresponding to a current flowing in either the one or the other current path; and a control unit that detects an output voltage of the output terminal of the band gap circuit and that controls a current flowing in at least one or the other current path corresponding to the detected output voltage. 
   With these compositions, it is possible to realize the reference voltage generator circuit that enables to reduce electric consumption. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a circuit diagram of a reference voltage generator circuit of a first embodiment of the invention. 
       FIG. 2  is a circuit diagram of a reference voltage generator circuit of a second embodiment of the invention. 
       FIG. 3  is a circuit diagram of a reference voltage generator circuit of a third embodiment of the invention. 
       FIG. 4  is a circuit diagram of a conventional band gap-based reference voltage generator circuit. 
   

   DETAILED DESCRIPTION 
   In the following, embodiments of the invention will be described with reference to the accompanying drawings. 
   First Embodiment 
   First, based on  FIG. 1 , a composition of the reference voltage generator circuit of the present embodiment will be described.  FIG. 1  is a circuit diagram of a reference voltage generator circuit  1  of the first embodiment of the invention. 
   In  FIG. 1 , a band gap circuit  11  includes: a P-channel MOS transistor  21 , resistors  22 ,  24 , and  25 , a PNP bipolar transistor  23 , and a plurality of PNP bipolar transistors  26 . A drain electrode (hereinafter referred to simply as drain) of the transistor  21  is coupled to the emitter of the PNP bipolar transistor  23  via the resistor  22 . That is, the transistor  21 , the resistor  22 , and the transistor  23  are connected in series. Also, the drain of the transistor  21  is coupled commonly with the emitters of the plurality of PNP bipolar transistors  26 . In other words, a series circuit composed of the resistor  22  and the transistor  23  and a series circuit composed of the resistors  24  and  25  and the plurality of PNP bipolar transistors  26  are connected in parallel. A connection point of the transistor  22  and the transistor  23  is coupled to an inversing input (−) of a comparator circuit  27  which is an operational amplifier. A connection point of the resistors  24  and  25  is coupled to a non-inverting input (+) of the comparator circuit  27 . Additionally, resistance values of the resistors  22  and  24  are the same. An output of the comparator circuit  27  is coupled to a gate electrode (hereinafter referred to simply as gate) of the transistor  21 . With this composition, a predetermined output voltage OUT such as 1.2V, for example, is output to the output terminal of the band gap circuit  11  coupled to the drain of the transistor  21 . 
   In contrast, a startup circuit  12  has an N-channel MOS transistor  31  as a control unit, as will be described later, in which the gate of the transistor  31  is coupled to the output terminal of the band gap circuit  11 . The startup circuit  12  contains a multistage current mirror circuit  32  consisting of a plurality of current mirror circuits connected in series in multiple stages.  FIG. 1  shows a case of three-staged current mirror circuits connected in series. A first stage current mirror circuit  33  is composed of two P-channel MOS transistors  33   a  and  33   b  coupled with and mirroring each other. A second stage current mirror circuit  34  is composed of two N-channel MOS transistors  34   a  and  34   b  coupled with and mirroring each other. A third stage current mirror circuit  35  is composed of two N-channel MOS transistors  35   a  and  35   b  coupled with and mirroring each other. In short, the multistage current mirror circuit  32  includes a plurality of current mirror circuits connected in series. 
   The source electrode (hereinafter referred to simply as source) of the transistor  33   a  is coupled to a wire that supplies power source voltage (e.g., 3V). The drain of the transistor  33   a  is coupled to the drain of the transistor  34   a . The source of the transistor  34   a  is coupled to the drain of the transistor  35   a . The drain of the transistor  34   a  is coupled to the drain of the transistor  31 . The gate of the transistor  35   a  is coupled to the source of the transistor  34   a  and the drain of the transistor  35   a . The source of the transistor  35   a  is coupled to a ground voltage supply wire. 
   In contrast, the source of the transistor  33   b  is coupled to a power source voltage supply wire. The drain of the transistor  33   b  is coupled to the gate of the transistor  33   a  and the gate of the transistor  33   b  and, further, to the gate of a P-channel MOS transistor  37 . The source of the transistor  37  is coupled to a power source voltage supply wire. The drain of the transistor  37  is coupled to the drain of the transistor  21 , that is, to the output terminal of the band gap circuit  11 . The drain of the transistor  33   b  is coupled to the drain of the transistor  34   b  via a resistor  36 . A connection point of the resistor  36  and the drain of the transistor  34   b  is coupled to the gates of the transistors  34   a  and  34   b . The source of the transistor  34   b  is coupled to the drain of the transistor  35   b . In other words, the gate and the drain of the transistor  35   a  are electrically coupled to the drains of the transistors  33   a  and  31 . The source of the transistor  35   b  is coupled to a ground voltage supply wire. 
   Thus, the multistage current mirror circuit  32  includes a first current path flowing through the transistors  33   a ,  34   a , and  35   a  and a second current path flowing through the transistors  33   b ,  34   b , and  35   b . The transistor  37  supplies an output voltage corresponding to the current flowing in the second current path to the output terminal of the band gap circuit  11 . 
   Next, operations of the circuit of  FIG. 1  will be described. 
   First, when the power source voltage is applied to the reference voltage generator circuit  1 , the transistor  31 , which is the control unit, detects the output voltage OUT at the output terminal of the band gap circuit  11 . When the output voltage OUT is 0V, that is, at the stopping point, the transistor  31  which is the control unit is turned off. At this point, a power source voltage is being applied to the multistage current mirror circuit  32 , and, therefore, a predetermined current is flowing in the two current paths. Consequently, since a current Ic corresponding to the current flowing in these current paths is supplied to the output terminal of the band gap circuit  11  from the transistor  37 , a potential of the output voltage OUT rises gradually. As the potential of the output voltage OUT rises to 1.2V, that is, to the normal operating point, the transistor  31  turns on, and, as a result, a potential at a connection point P 1  of the transistors  33   a  and  34   a  becomes 0 (zero). When the potential at the connection point P 1  becomes 0, the current, of all the currents flowing in the multistage current mirror circuit  32 , which flows through the connection point P 1  flows more to the transistor  31  than to the transistor  34   a . Therefore, each transistor inside the multistage current mirror circuit  32  turns off and no current flows to the transistor  37 . 
   As described, when the output voltage OUT is at the stopping point immediately after the power source voltage has been supplied to the reference voltage generator circuit, and as the transistor  31  controls the current flowing in one of the two current paths of the multistage current mirror circuit  32 , the startup circuit  12  supplies a predetermined current to the band gap circuit  11  so as to raise the output voltage OUT to the voltage of the normal operating point. Thereafter, when the transistor  31  controls the current flowing in one of the two current paths of the multistage current mirror circuit  32 , no current flows in any of the transistors inside the multistage current mirror circuit  32  or in the transistor  37 . Therefore, it is possible, as a result, to reduce the electric consumption once the startup circuit  12  starts. 
   Further, when the voltage of the output voltage OUT is at the normal operating point immediately after the power source voltage has been applied to the reference voltage generator circuit, the transistor  31  is turned on, and the potential at the connection point P 1  becomes 0. Therefore, the current, of all the currents flowing in the multistage current mirror circuit  32 , which flows through the connection point P 1  flows more to the transistor  31  than to the transistor  34   a . Consequently, each transistor inside the multistage current mirror circuit  32  turns off, and no current flows to the transistor  37 . 
   As thus described, even if the output voltage OUT is at the normal operating point, when the transistor  31  controls the current flowing in one of the two current paths of the multistage current mirror circuit  32 , no current flows to any of the transistors inside the multistage current mirror circuit  32  or to the transistor  37 , and, as a consequence, it becomes possible to reduce the electric consumption once the startup circuit  12  starts. 
   As described, with the first embodiment, it is possible to realize the reference voltage generator circuit which enables to reduce electric consumption. 
   Second Embodiment 
   Next, a composition of the reference voltage generator circuit of the second embodiment will be described.  FIG. 2  is a circuit diagram of the reference voltage generator circuit of the second embodiment. The reference voltage generator circuit of the second embodiment differs from the reference voltage generator circuit of the first embodiment in that there are a fewer current mirror circuits in the startup circuit of the second embodiment than those of the first embodiment. The same reference numerals are used here for the same composition elements as those of the first embodiment, and explanations thereof shall be omitted. 
   As shown in  FIG. 2 , one difference between the reference voltage generator circuit of the second embodiment and that of the first embodiment is that there is no current mirror circuit  34  in  FIG. 2  as is in the multistage current mirror circuit  32  in  FIG. 1 . However, the rest of the composition elements are identical. 
   Operations of the circuit of  FIG. 2  are approximately the same as those of the circuit of  FIG. 1 , in that when voltage of the output voltage OUT is at the stopping point, the transistor  31  turns to an off state. Here, because a power source voltage is being applied to the multistage current mirror circuit  32   a , a predetermined current is flowing therein. Accordingly, because the current Ic is supplied from the transistor  37  to the output terminal of the band gap circuit  11 , a potential of the output voltage OUT rises gradually. As the potential of the output voltage OUT rises and reaches to a predetermined voltage, the transistor  31  turns on, and a potential at a connection point P 2  of the transistors  33   a  and  35   a  becomes 0 (zero). When the potential at the connection point P 2  becomes 0, a current, of all currents flowing in the current mirror circuit  32   a , which flows through the connection point P 2  flows more to the transistor  31  than to the transistor  35   a . Therefore, the transistors inside the multistage current mirror circuit  32   a  turn off, and, consequently, no current flows to the transistor  37 . As a result, it becomes possible to reduce the electric consumption once the startup circuit  12   a  starts. 
   Further, when the output voltage OUT is at the normal operating point, the transistor  31  turns to an on state quite similarly to the circuit of  FIG. 1 . Consequently, because the potential at the connection point P 2  becomes 0, the current, of all the currents flowing in the current mirror circuit  32   a , which flows through the connection point P 2  flows more to the transistor  31  than to the transistor  35   a , and, therefore, the transistors inside the current mirror circuit  32   a  turn off. Consequently, because no current flows to the transistor  37 , it is possible, as a result, to reduce the electric consumption once the startup circuit  12   a  starts. 
   As thus described, it is possible with the second embodiment to realize the reference voltage generator circuit which enables to reduce electric consumption. 
   Third Embodiment 
   Next, a composition of the reference voltage generator circuit of the third embodiment will be described.  FIG. 3  is a circuit diagram of the reference voltage generator circuit of the third embodiment. The reference voltage generator circuit of the third embodiment has the same startup circuit  12  as that of the first embodiment but differs in the band gap circuit. The same reference numerals are used here for the same composition elements as those of the first embodiment, and explanations thereof shall be omitted. 
   As shown in  FIG. 3 , the reference voltage generator circuit of the third embodiment has a band gap circuit different from that in the circuit of  FIG. 1 . A band gap circuit  11   a  of  FIG. 3  is a band gap circuit to be used when the power source voltage is low. With the band gap circuit  11   a , the power source voltage is as low as 1V, for example, and the output voltage OUT of the output terminal is as low as 0.6V. 
   The band gap circuit  11   a  includes a series circuit composed of a P-channel MOS transistor  41  and a resistor  42  coupled to the drain of the transistor  41 . The drain of the transistor  41  is coupled to one terminal of the resistor  42 . The source of the transistor  41  is coupled to a power source voltage supply wire, and the other terminal of the resistor  42  is coupled to a ground potential supply wire. The drain of the transistor  41  is coupled to the output terminal of the band gap circuit  11   a  and to the gate of the transistor  31 . 
   The band gap circuit  11   a  further includes: P-channel MOS transistors  43  and  47 , resistors  44 ,  45 , and  48 , a PNP bipolar transistor  49 , and a plurality of PNP bipolar transistors  46 . 
   The source of the transistor  43  is coupled to a power source voltage supply wire. The drain of the transistor  43  is coupled to a ground potential supply wire via the resistor  44 . The drain of the transistor  43  is further coupled commonly to emitters of the plurality of PNP bipolar transistors  46  via the resistor  45 . Each base and each collector of the plurality of transistors  46  is coupled to each ground potential supply wire. 
   The drain of the transistor  47  is coupled to one terminal of resistor  48  and the emitter of the PNP bipolar transistor  49 . The source of the transistor  47  is coupled to a power source voltage supply wire. The other terminal of the resistor  48  and the base and collector of the transistor  49  are coupled to ground potential supply wires. 
   In addition, the band gap circuit  11   a  further includes a comparator circuit  50  which is an operational amplifier. The drain of the transistor  37  of the startup circuit  12  and the drain of the transistor  47  are coupled to the inverting input (−) of the comparator circuit  50 , and the drain of the transistor  43  is coupled to the non-inverting input (+) of the comparator circuit  50 . The output of the comparator circuit  50  is coupled to the gate of the transistor  47 , the gate of the transistor  43 , and to the gate of the transistor  41 . With this composition, the output voltage OUT of the transistor  41  can be maintained at a fixed voltage. 
   The composition of the startup circuit  12  is identical to the startup circuit  12  of the first embodiment. 
   Operations of the circuit of  FIG. 3  are approximately the same as those of the circuit of  FIG. 1 . The only differences are that the transistor  37  supplies an output current via the comparator circuit  50  by controlling the gate of the transistor  41  and that the band gap circuit  11   a  is a band gap circuit whose power source voltage is low. 
   Accordingly, with the reference voltage generator circuit of the third embodiment, it also is possible to reduce the electric consumption once the startup circuit  12  starts. 
   With the reference voltage generator circuit of the above-described embodiments of the invention, the electric consumption can be reduced upon starting the startup circuit  12 . 
   The invention is not limited to the embodiments as hereinbefore described, and various alterations and modifications are possible within the gist of the invention.