JP2009037372A - Constant current circuit and constant voltage circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a constant current circuit and a constant voltage circuit for simultaneously providing a reference voltage and a reference current. <P>SOLUTION: An output Vref of a reference voltage generating circuit 100 is input to the (-) input terminal of an operational amplifier 102; an output voltage Vout of a reference voltage trimming circuit 103 whose total resistance value is not changed with trimming is input to the (+) input terminal of the operational amplifier 102 and both voltage values are compared. An output of the operational amplifier 102 controls the gate of an output transistor 104 so as to virtually short-circuit two inputs of the operational amplifier 102 to set an output voltage Vref1 at a desired value. If the output voltage Vref1 needs to be adjusted, resistors R1, R2 are trimmed. Since the total resistance value is not changed with the trimming, both the constant voltage and the constant current can be stably obtained. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a constant current / constant voltage circuit for generating a constant voltage and generating a constant current that is a reference current (including a bias current) of an oscillator, an error amplifier, a comparator, and the like.

  FIG. 5 is a block diagram showing a configuration of a conventional constant current / constant voltage circuit that includes a reference current generation circuit and supplies the generated reference current (including a bias current) to an oscillator, an error amplifier, a comparator, and the like. As shown in FIG. 5, the conventional constant current / constant voltage circuit includes a reference voltage / reference current generation unit 10 including a reference voltage generation circuit 1, a reference current generation circuit 2, an output buffer 3, and a resistor including resistors 4-6. It consists of The reference voltage / reference current generation unit 10 outputs the reference voltage Vref1 output from the output buffer 3, the reference voltage Vref2 output from the connection point of the resistors 5 and 6, and the reference output from the reference current generation circuit 2. The current ib4 and the bias currents ib1 to ib3 and ib5 are output. The reference voltages Vref1 and Vref2 and the reference current ib4 and the bias currents ib1 to ib3 and ib5 for driving these circuits are output to the output buffer 3 and the oscillator 20. The error amplifier 30, the comparator 40, and the input buffer 50 are supplied. Incidentally, the reference voltage Vref1 is a reference voltage for the input buffer 50, and the reference voltage Vref2 is a reference voltage for the error amplifier 30. The reference current ib4 is a reference current for driving the oscillator 20. The bias current ib1 is the output buffer 3, the bias current ib2 is the error amplifier 30, the bias current ib3 is the input buffer 50, and the bias current ib5 is This is for driving the comparator 40. In the conventional constant current / constant voltage circuit, the reference voltage generation circuit 1 and the reference current generation circuit 2 are separately configured to generate the reference voltages Vref1 and Vref2, the reference current ib4, and the bias currents ib1 to ib3 and ib5 as described above. Has been. Since these reference voltage and reference current (including bias current) serve as a reference for each circuit, it is required that there is no variation with respect to temperature and power supply voltage.

  Conventionally, various circuit configurations have been proposed as circuits for generating a reference voltage and a reference current that satisfy these conditions. For example, constant current / constant voltage circuits such as a reference voltage generation circuit using a depletion MOSFET and a reference voltage generation circuit using a band gap reference circuit using the temperature characteristics of a bipolar transistor are known to those skilled in the art.

In addition to the above, there is also a reference current generation circuit in which an operational amplifier and a current mirror are combined as disclosed in JP-A-2003-177830 (Patent Document 1).
Further, there is an example of a voltage regulator that outputs a voltage adjusted to a constant voltage from the output terminal 5 by trimming the resistor R1 as disclosed in Japanese Patent Laid-Open No. 05-289758 (Patent Document 2).
Japanese Patent Laying-Open No. 2003-177830 (FIGS. 1, 2 and 3) JP 05-289758 A (FIG. 2)

  The conventional constant current and constant voltage circuit shown in FIG. 5 has a low driving capability of the output Vref of the reference voltage generation circuit 1 and it is difficult to freely set a wide voltage range. It is essential to provide the circuit configuration, which causes a problem that the circuit configuration becomes complicated.

The current source circuit disclosed in Patent Document 1 adjusts an external resistor to obtain a desired constant current value, but cannot adjust a reference voltage.
In addition, the voltage regulator disclosed in Patent Document 2 can adjust the reference voltage by trimming the resistor R1, but the resistance value is changed by trimming, so that the resistance voltage is constant even when the voltage of the output terminal 5 is constant. Since the current flowing through R1 and R2 changes, a constant current cannot be obtained.

  An object of the present invention is to provide a constant current / constant voltage circuit capable of solving the above-described problems related to the prior art and obtaining a reference voltage and a reference current simultaneously.

  In order to solve the above-described problems, a constant current / constant voltage circuit according to the present invention includes a reference voltage generating circuit, a reference voltage output buffer, and a constant current / constant voltage circuit having a voltage dividing resistor to be trimmed. The output of the buffer is connected to the gate of a first MOSFET (Metal Oxide Semiconductor Field Effect Transistor), the drain of the first MOSFET is connected to the voltage dividing resistor, and the voltage dividing resistor adjusts the resistance by trimming. The sum of the resistance values is made the same only by changing the voltage dividing ratio, and the voltage dividing by the voltage dividing resistor of the drain voltage of the first MOSFET and the output of the reference voltage generating circuit are supplied to the reference voltage output buffer. And a second MOSFET having the same conductivity type as the first MOSFET is connected in parallel to the first MOSFET, and the current output of the second MOSFET and the drain voltage of the first MOSFET are Characterized by a constant current output and the constant voltage output of respectively the constant current and constant voltage circuit. Note that connecting two (a plurality of) MOSFETs in parallel or connecting them in parallel means connecting the gates and gates (gates) and the sources and sources (sources) of the MOSFETs.

  According to the present invention, since the total resistance value of the trimming circuit does not change even after trimming, even if trimming is performed to relieve the fluctuation of the reference voltage of the reference voltage generation circuit due to process variation, temperature environment change, etc. Both constant voltage and constant current can be obtained.

  Further, since a reference current is generated using a reference voltage output buffer provided at a subsequent stage of the reference voltage generation circuit, it is not necessary to prepare a reference current generation circuit independently, which is advantageous in terms of circuit area.

Hereinafter, the best mode for carrying out the present invention will be described in detail with reference to the drawings. [Embodiment 1]
FIG. 1 is a circuit block diagram showing a configuration of a constant current / constant voltage circuit according to a first embodiment of the present invention. In the constant current / constant voltage circuit of FIG. 1, a reference voltage generation circuit 100, an operational amplifier (OP1) 102, a reference voltage trimming circuit 103 whose total resistance does not change even after trimming, and a generated reference voltage Vref1 Is connected in parallel to the (first) output transistor (QP4) 104 and the (first) output transistor 104 (the source and drain are connected in common, ie, the current mirror circuit is connected to the output terminal (drain)). And a (second) output transistor (QP5) 105 that outputs a current I2 that is a copy of the output current of the output transistor 104 and supplies it to the diode-connected transistor (QN3) 106, and a diode-connected transistor ( A current mirror circuit (QN4) 107 that generates a reference current ib4 based on a current I2 flowing through QN3) 106, and a diode A current mirror circuit (QN5) 108 that generates a reference current ib1 based on the current I2 flowing through the connected transistor (QN3) 106, and a reference current based on the current I2 that flows through the diode-connected transistor (QN3) 106 and a current mirror circuit (QN6) 109 for generating ib2. Although not shown in the figure, the reference currents ib3 and ib5 can be generated by further connecting current mirror circuits in parallel based on the current I2.

  Here, a reference voltage trimming circuit according to an embodiment of the present invention will be described with reference to FIG. As shown in FIG. 3, the reference voltage trimming circuit 103 is mainly configured by connecting a resistor R1 (130) and a resistor R2 (140) in series. The resistor R1 (130) includes a resistor R1a (131) and a resistor R1b ( 132), a resistor R1c (133), a resistor R1d (134), and a resistor R1e (135) are cascaded so that (R1a + R1b + R1c + R1d + R1e) becomes a resistance value of R1, and a resistor R2 ( 140) includes a resistor R2a (141), a resistor R2b (142), a resistor R2c (143), a resistor R2d (144), and a resistor R2e (145), and (R2a + R2b + R2c + R2d + R2e) is a resistor. The resistance value is set to R2. Trimming switches 151, 152, 153, and 154 are provided for the resistor R1b (132), the resistor R1c (133), the resistor R1d (134), and the resistor R1e (135), and the switches 151, 152, 153, and 154 are provided. Control is performed by binary signals applied to the input terminals Zb, Zc, Zd, Ze via the two-stage inverters 171, 172, 173, 174, 175, 176, 177, 178. Similarly, trimming switches 161, 162, 163, and 164 are provided for the resistors R2b (142), R2c (143), R2d (144), and R2e (145), and the switches 161, 162, 163 are provided. 164 is controlled by a binary signal applied to the input terminals Zb, Zc, Zd, Ze via one-stage inverters 171, 173, 175, 177. Note that in the reference voltage trimming circuit 103, the switch provided in the resistor arranged at the same position among the resistors R1 (130) and R2 (140) to be trimmed includes a first-stage inverter and 2 A different binary signal is input as a control signal by the stage inverter, and the resistance value of R1 and R2 is changed by switching so that one is ON and the other is OFF, and the output voltage Vout of the reference voltage trimming circuit is adjusted. . In that case, the resistance values of the resistors arranged at the same position are set to the same value, that is, R1b = R2b, R1c = R2c, R1d = R2d, R1e = R2e, and the resistance of (R1 + R2) before and after trimming The values are always made equal.

The operation of the constant current / constant voltage circuit shown in FIG. 1 will be described. In FIG. 1, a reference voltage generation circuit 100 is configured by a reference voltage generation circuit using a known depletion MOSFET, a bandgap reference circuit, or the like, and the output voltage variation with respect to temperature and power supply voltage is small. The output Vref of the reference voltage generation circuit 100 is input to the − side input terminal of the operational amplifier 102, and the output voltage Vout of the reference voltage trimming circuit 103 shown in FIG. 3 is input to the + side input terminal of the operational amplifier 102. Are compared. Then, the output of the operational amplifier 102 controls the gate of the output transistor 104, whereby the two inputs of the operational amplifier 102 are virtually shorted, and the output voltage Vref1 is set to a desired value. When it is necessary to adjust the output voltage Vref1, the resistors R1 and R2 are trimmed. In the reference voltage trimming circuit 103 shown in FIG. 3, (R1 + R2) is always equal before and after trimming. Therefore, even if trimming for adjusting process variations is performed, the constant current Vref1 can be obtained without affecting the current flowing through the resistor (without changing the current). The output of the operational amplifier 102 that controls the gate of the output transistor 104 is also applied to the gate of the output transistor (QP5) 105. The constant voltage Vref1 is obtained from the output transistor 104 and the resistance value (R1 + R2) of the reference voltage trimming circuit 103 is invariable with respect to the trimming. This means that the current I1 flowing through the reference voltage trimming circuit 103 is a constant current. Means. Therefore, the current I2 flowing through the diode-connected transistor (QN3) 106 also becomes a constant current, and constitutes a constant current source. If the ratio (W / L) of the channel width W to the channel length L of the output transistor (QP4) 104 and the output transistor (QP5) 105 is (W4 / L4) and (W5 / L5), respectively, I2 = I1 × (W5 / L5) / (W4 / L4). Thus, the diode-connected transistor (QN3) 106 and the output transistor (QP5) 105 also constitute a constant current source. A constant current I2 copied from the current I1 flowing through the reference voltage trimming circuit 103 flows through the diode-connected transistor (QN3) 106, and the constant current I2 flowing through the diode-connected transistor (QN3) 106 is copied by the current mirror circuit. Thus, the constant currents ib4, ib1, ib2,... Can be generated. That is, the transistor (QN4) 107, the transistor (QN5) 108, and the transistor (QN6) 108 each form a current mirror circuit with the diode-connected transistor (QN3) 106, thereby flowing to the diode-connected transistor (QN3) 106. Currents ib4, ib1, and ib2 obtained by copying the current I2 can be generated. The transistor (QN4) 107 constituting the (first) current mirror circuit in combination with the transistor (QN3) 106, the transistor (QN5) 108 constituting the (second) current mirror circuit, and the (third) If the dimensional ratio of the transistor (QN6) 108 constituting the current mirror circuit is made the same as that of the transistor (QN3) 106, ib4, ib1, and ib2 can be made the same as the current I2, respectively. The current values of ib4, ib1, and ib2 can be arbitrarily set, and the current for ib4, ib1, and ib2 generated by each current mirror circuit is a reference for operating the oscillator, error amplifier, comparator, etc. shown in FIG. It can be used as a current or a bias current.

Alternatively, the transistor (QN3) 106 to the transistor (QN6) 109 may be omitted, and a constant current / constant voltage circuit that outputs the constant voltage Vref1 and the constant current I2 may be used. In this case, the constant current I2 can be used not only as an input to the current mirror circuit but also as a reference current for various circuits.
[Embodiment 2]
FIG. 2 is a circuit block diagram showing a configuration of a constant current / constant voltage circuit according to the second embodiment of the present invention. In the constant current / constant voltage circuit of FIG. 2, a reference is provided by a differential amplifier and a common source amplifier circuit to which an output of the differential amplifier is input, instead of the operational amplifier 102 according to the first embodiment shown in FIG. A voltage output buffer is configured.

  The circuit shown in FIG. 2 will be described. The reference voltage generation circuit 100 includes a known reference voltage generation circuit using a depletion MOSFET, a band gap reference circuit, and the like, and has a small output voltage variation with respect to temperature and power supply voltage. To be. This point is the same as described in FIG. In the subsequent stage of the reference voltage generating circuit 100, a constant voltage output value is generally set to a desired voltage value, and a current sufficient to drive the subsequent oscillator, error amplifier, comparator, etc. as shown in FIG. In order to ensure supply capability, a reference voltage output buffer 200 comprising a two-stage amplifier of a differential amplifier 210 and a (first) common source amplifier (hereinafter simply referred to as “source ground”) 220, and FIG. A reference voltage trimming circuit 103 is provided which does not change the total resistance value even when trimming is performed. In FIG. 2, a reference voltage trimming circuit 103 includes a resistor R1 (130) and a resistor R2 (140) connected in series, and outputs an output from a connection point between the resistor R1 (130) and the resistor R2 (140). Connected to 210 non-inverting input terminal (IN +). On the other hand, the output Vref of the reference voltage generation circuit 100 is given to the inverting input terminal (IN−) of the differential amplifier 210. Note that a resistor 223 and a capacitor 224 connected between the gate and drain of the transistor 222 constituting the (first) source ground 220 in the drawing prevent the amplifier (reference voltage output buffer 200) from oscillating and operate stably. belongs to.

  The voltage trimming circuit 103 is connected to the output of the reference voltage output buffer 200 (the output of the (first) source ground 220), and the connection point between the resistors R1 (130) and R2 (140) is differential as described above. Feedback is provided to the non-inverting input terminal (IN +) of the amplifier 210. Since the two inputs of the differential amplifier 210 are virtually short-circuited, the non-inverting input terminal voltage and the inverting input terminal voltage are equal, and the voltage across the resistors R1 (130) and R2 (140) (connection point) ) Shows the reference voltage Vref applied to the inverting input terminal. With this Vref, series resistance R1 (130) and resistance R2 (140), the output voltage Vref1 of the reference voltage output buffer 200 becomes Vref1 = Vref × (R1 + R2) / R2, and a constant voltage is obtained. Here, if the value of Vref of the reference voltage generation circuit 100 deviates from the design value due to process variations, a desired voltage value cannot be obtained for Vref1, and thus the resistors R1 and R2 of the voltage trimming circuit 103 are adjusted. Then, adjust Vref1 to a desired constant voltage.

The current I1 flowing through the resistor R1 (130) and the resistor R2 (140) is determined by Vref1 / (R1 + R2), and Vref1 is less dependent on the power supply voltage and temperature, but the resistors R1 and R2 have temperature characteristics. I1 shows temperature characteristics depending on the temperature characteristics of these resistors. Therefore, in order to generate a constant current having a small temperature characteristic, an element having no temperature dependency or a combination of elements that cancels the temperature dependency may be selected as the resistor R1 (130) and the resistor R2 (140).

  In order to adjust the output voltage Vref1, the resistors R1 and R2 are trimmed as described in FIG. As described above, the total resistance value (R1 + R2) of this trimming circuit is always equal before and after trimming. With such a configuration, even if trimming for adjusting process variations is performed, the current I1 flowing through the resistors R1 and R2 is not affected at all, and can be regarded as a constant current source. Thereby, even in the constant current / constant voltage circuit according to the second embodiment shown in FIG. 2, a constant voltage and a constant current can be obtained simultaneously without providing a special constant current source.

  In the above description, the constant current I1 is obtained by the constant current / constant voltage circuit shown in FIG. 2, and the current I1 is the current flowing through the MOSFET (QP1) 221 and MOSFE (QN1) 222 in FIG. This is the difference between Ip1 and In1. Further, the MOSFET (QP1) 221 and the MOSFET (QP3) 202 constitute a current mirror circuit, and the current Ip1 flowing through the MOSFET (QP1) 221 is a constant current ((power supply voltage VDD−MOSFET ( QP3) is a constant current that is substantially equal to (the threshold voltage of 202) / the resistance value of resistor Rb201), and it can be seen that the current In1 flowing through MOSFE (QN1) 222 is also a constant current. Further, MOSFETs (QP2) 231, 231 having gate voltages equal to the gate voltages of MOSFET (QP1) 221 and MOSFET (QN1) 222, respectively, and the dimensions of the MOSFETs being the same as those of MOSFET (QP1) 221 and MOSFET (QN1) 222, respectively. When the second source grounded amplifier 230 composed of the MOSFET (QN2) 232 is connected, the currents Ip2 and In2 flowing through the transistors 231 and 232 of the second source grounded 230 become equal to the currents Ip1 and In1, respectively. It becomes.

  Further, when a diode-connected MOSFET (QN3) 106 is connected between the connection point between the drain terminals of the transistor (QP2) 231 and the transistor (QN2) 232 and GND, the current I2 flowing therethrough is connected to the transistor (QP2) 231 and the MOSFET. Since a current that is the difference between the currents Ip2 and In2 flowing through (QN2) 232 flows, a constant current can be obtained.

  The current I2 flowing through the transistor (QN3) 106 is copied by the current mirror circuits 107, 108, 109... To generate constant currents ib4, ib1, ib2,. The current values of the constant currents ib4, ib1, and ib2 can be arbitrarily set by changing the dimensional ratio of the transistor (QN4) 107, the transistor (QN5) 108, and the transistor (QN6) 109 with respect to the transistor (QN3) 106. Can be used as a reference current or bias current for operating the oscillator, error amplifier, comparator, etc. shown in FIG. The current values of the constant currents ib4, ib1, and ib2 can also be adjusted by adjusting the dimensional ratio of the MOSFET (QP2) 231 and the MOSFET (QN2) 232 to the MOSFET (QP1) 221 and the MOSFET (QN1) 222. . In order to prevent the current I2, the constant currents ib4, ib1, and ib2 from fluctuating even when the power supply voltage VDD fluctuates, the dimensional ratio of the MOSFET (QP2) 231 to the MOSFET (QP1) 221 and the MOSFET (QN1) 222 The dimensional ratio of MOSFET (QN2) 232 should be equal.

In the constant current / constant voltage circuit shown in FIG. 2, the reference current is generated by the reference voltage output buffer 200 including the second source ground 230, and therefore the reference current ib for driving the reference voltage output buffer 200 itself. (This is a current that determines the bias current of the differential amplifier 200, the first source ground 220, and the second source ground 230, as shown in FIG. 2.) A circuit that separately generates a reference current ib Is required. However, since the reference current ib need only be accurate to operate the reference voltage output buffer 200, a simple constant current source using a resistor Rb201 as shown at the left end of FIG. For example, the circuit shown in FIG. 4 can be used as a simple current source circuit when it is desired to suppress fluctuations of the reference current ib with respect to the power supply voltage and temperature. That is, FIG. 4 shows a current source circuit for generating a reference current of the reference voltage output buffer according to the second embodiment of the present invention. The base-emitter voltage VBE (= diode forward voltage) of the NPN transistor (QB1) 301 is shown in FIG. Is applied to the resistor R3 (302), and the current VBE / R3 obtained through the MOSFET (QN7) 303 is passed through the MOSFET (QP3) 304 (same as the MOSFET (QP3) 202 shown in FIG. 2). is there. If such a simple constant current source is used, the current fluctuation with respect to the power supply voltage fluctuation can be made smaller than when the resistor Rb 201 is used without significantly increasing the circuit scale.

1 is a circuit block diagram showing a configuration of a constant current / constant voltage circuit according to a first embodiment of the present invention. It is a circuit block diagram which shows the structure of the constant current and constant voltage circuit which concerns on the 2nd Embodiment of this invention. It is a figure which shows the reference voltage trimming circuit used for the constant current and constant voltage circuit which concerns on embodiment of this invention. It is a figure which shows the current source circuit which produces | generates the reference current of the reference voltage output buffer which concerns on the 2nd Embodiment of this invention. It is a block diagram which shows the structure of the conventional constant current and constant voltage circuit.

Explanation of symbols

100 Reference voltage generator
102 Operational amplifier (OP1)
103 Trimming circuit
104 (first) output transistor
105 (second) output transistor
106 Diode-connected transistor
107 (First) current mirror circuit
108 (second) current mirror circuit
109 (Third) current mirror circuit
200 Reference voltage output buffer
210 Differential Amplifier
220 (First) Common Source Amplifier
230 (second) common source amplifier
301 NPN transistor
302 resistance
303 MOSFET
304 MOSFET

Claims (8)

  In a constant current / constant voltage circuit having a reference voltage generation circuit, a reference voltage output buffer, and a voltage dividing resistor to be trimmed, an output of the reference voltage output buffer is connected to a gate of a first MOSFET, and the first MOSFET The drain of the first MOSFET is connected to the voltage dividing resistor, and even if the resistance of the voltage dividing resistor is adjusted by trimming, only the voltage dividing ratio is changed and the sum of the resistance values is made the same. The voltage divided by the voltage dividing resistor and the output of the reference voltage generation circuit are input to the reference voltage output buffer, and a second MOSFET having the same conductivity type as that of the first MOSFET is connected in parallel to the first MOSFET. And connecting the current output of the second MOSFET and the drain voltage of the first MOSFET to a constant current output and a constant voltage output of the constant current / constant voltage circuit, respectively. Pressure circuit.   In a constant current / constant voltage circuit having a reference voltage generation circuit, a reference voltage output buffer, and a voltage dividing resistor to be trimmed, an output of the reference voltage output buffer is connected to a gate of a first MOSFET, and the first MOSFET The drain of the first MOSFET is connected to the voltage dividing resistor, and even if the resistance of the voltage dividing resistor is adjusted by trimming, only the voltage dividing ratio is changed and the sum of the resistance values is made the same. The voltage divided by the voltage dividing resistor and the output of the reference voltage generation circuit are input to the reference voltage output buffer, and a second MOSFET having the same conductivity type as that of the first MOSFET is connected in parallel to the first MOSFET. A third MOSFET having a conductivity type different from that of the first MOSFET diode-connected to the output of the second MOSFET, a current mirror circuit connected to the third MOSFET, and the current MOSFET Mirror Constant current and constant voltage circuit, characterized in that the flow output and the drain voltage of the first MOSFET and the constant current output and the constant voltage output of each of the constant current and constant voltage circuit.   3. The constant current / constant voltage circuit according to claim 1, wherein a plurality of current mirror circuits are connected in parallel to the third MOSFET.   Even if the resistance is adjusted by the trimming, only the voltage dividing ratio is changed and the total sum of the resistance values is the same. The voltage dividing resistors include a first resistor group composed of a plurality of resistors connected in series, and the first resistor group. A second resistor group consisting of a series connection of resistors having the same number and corresponding resistance values are connected in series, and each of the trimming resistors is provided with a MOSFET capable of short-circuiting both ends thereof, Different binary signals are input to the gates of the two MOSFETs respectively provided in the two corresponding resistors of the first resistor group and the second resistor group, and only one of the corresponding two resistors is input. 4. The constant current / constant voltage circuit according to claim 1, wherein the constant current / voltage circuit is trimmed.   A reference voltage generation circuit, a reference voltage output buffer, and a voltage dividing resistor for dividing the output voltage of the reference voltage output buffer; and the voltage division by the voltage dividing circuit and the output of the reference voltage generation circuit are stored in the reference voltage output buffer The reference voltage output buffer includes a first output stage configured by connecting two complementary MOSFETs in series, and two complementary MOSFETs connected in parallel to the first output stage. A second output stage configured in series; the voltage divider circuit is connected to the first output stage; and a current mirror circuit at a connection point of the two MOSFETs constituting the second output stage Constant current / constant voltage circuit.   The reference voltage output buffer includes a differential amplifier circuit, the differential amplifier circuit and the first output stage constitute a two-stage amplifier circuit, and the first and second output stages are source-grounded amplifier circuits. 6. The constant current / constant voltage circuit according to claim 5, wherein: The voltage dividing resistor that divides the output voltage of the reference voltage output buffer includes a trimming circuit that suppresses output voltage fluctuations due to process variations and the like by adjusting the voltage dividing ratio of the resistance value, and the voltage dividing ratio is maintained even if the resistance is adjusted by trimming. 7. The constant current / constant voltage circuit according to claim 5, wherein the total sum of resistance values is the same only by changing.   The voltage dividing resistor includes a first resistor group composed of a plurality of resistors connected in series, and a second resistor composed of a series connection of resistors having the same number and corresponding resistance values as the first resistor group. The resistors to be trimmed are respectively provided with MOSFETs that can short-circuit both ends of the resistors, and are provided for the corresponding two resistors of the first resistor group and the second resistor group, respectively. 8. The method according to claim 5, wherein different binary signals are inputted to the gates of the two MOSFETs, and only one of the corresponding two resistors is trimmed. The constant current / constant voltage circuit described.

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