JP2005157616A - Reference voltage generating circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a reference voltage generating circuit which generates a fixed voltage regardless of fluctuations in temperature or the like, operates with lower power consumption and is excellent in stability. <P>SOLUTION: The reference voltage generating circuit includes:a band gap regulator equipped with a tree and a hand gap type reference voltage source for inputting the output currents of a current source to be driven by a voltage on the tree to be generated when currents are running through the tree, and for generating a reference voltage, and configured to drive the tree according to the generated reference voltage; a start circuit having a function to drive the tree instead of driving the tree with the reference voltage; and a control current source for supplying the output currents to the start circuit in order to validate the function of the start circuit, and for controlling the output currents according to the output voltage of the hand gap regulator in an analog status. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a reference voltage generation circuit that outputs a constant voltage regardless of variations in temperature or the like, and more particularly to a reference voltage generation circuit that operates with lower power consumption.

A bandgap reference voltage source or a bandgap reference is frequently used for a reference voltage generation circuit that outputs a constant voltage regardless of variations in temperature or the like. The operating principle of these circuits is that the temperature between the base and emitter of a bipolar transistor having a negative temperature characteristic and the voltage V _t having a positive temperature characteristic (= kT / q: k, q is a constant, T is an absolute temperature) A voltage with a characteristic of zero is output. An example of a band gap reference is disclosed in Japanese Patent Laid-Open No. 10-143265.
Japanese Patent Laid-Open No. 10-143265

  In many cases, the band gap type reference voltage source is used with a so-called start circuit added in order to promptly shift to a normal operation state when the power is turned on. When the initial voltage is generated by the starting circuit, the driving by the voltage is chained internally to reach a stable state. When the stable state is reached, driving by the starting circuit is not necessary for operation. Therefore, it can be said that the starting current after such an operation should be reduced in terms of power saving.

  Note that the above document discloses a bandgap reference for reducing power consumption by reducing the current in the starting circuit after starting. However, since the starting current is controlled to be turned on / off at the time of starting / operating, it is conceivable that the returning operation is not necessarily generated from the starting circuit when the output voltage as the reference voltage generating circuit is disturbed for some reason. In this case, there is a problem in terms of stability as a reference voltage generation circuit.

  The present invention has been made in consideration of the above circumstances, and in a reference voltage generation circuit that outputs a constant voltage regardless of fluctuations in temperature or the like, the reference voltage operates with lower power consumption and has excellent stability. An object is to provide a generation circuit.

  In order to solve the above-described problems, a reference voltage generation circuit according to the present invention includes a tree and an output current of a current source driven by a voltage on the tree generated when a current flows through the tree. A band gap regulator having a band gap type reference voltage source for generating a voltage and driving the tree by the generated reference voltage; and driving the tree by the reference voltage instead of driving the tree A starting circuit having a function of supplying an output current to the starting circuit in order to enable the function of the starting circuit, and the output current being controlled in an analog manner by an output voltage of the band gap regulator And a source.

  That is, the starting circuit has a function of driving the tree constituting the band gap regulator, and a current for driving is supplied from the control current source. The output current of the control current source is controlled in an analog manner by the output voltage of the band gap regulator. With such a configuration, the bandgap regulator is initially activated by the voltage generated by the starter circuit driving the tree of the bandgap regulator. On the way to the stable state, the output current of the control current source is reduced in an analog manner by the output voltage of the band gap regulator.

  Therefore, the power consumption during the operation after stabilization can be reduced by the decrease in the output of the control current source. Also, since the output current of the control current source is controlled in an analog manner by the output voltage of the band gap regulator, if the voltage output by the band gap regulator varies due to some factor, the starting circuit will be adjusted accordingly. Since it starts to work again and is energized, it is possible to return to stable output more quickly.

  According to the reference voltage generating circuit of the present invention, a current to the starting circuit that drives the tree constituting the band gap regulator at the time of starting is supplied from the control current source, and the control current source is analogized by the output voltage of the band gap regulator. Since the output current is controlled, the operation with lower power consumption and excellent stability can be obtained.

  As an embodiment of the present invention, the control current source is a p-channel MOS transistor whose source is connected to a positive voltage as viewed from the ground level, and the output current of the control current source is the p-channel MOS transistor In order to control the output current of the control current source, which is a drain current, a node on which the reference voltage of the band gap regulator is generated is connected to a gate of the p-channel MOS transistor, and the band gap regulator generates The reference voltage may be approximately 1.2 V when viewed from the ground level when stable.

  This is a configuration example for outputting a positive voltage as a reference voltage (stabilized voltage) output. Although approximately 1.2 V is a voltage corresponding to a so-called band gap voltage of silicon, this voltage is supplied to the gate of the p-channel MOS transistor when stable. A voltage of 0V to 1.2V is sometimes applied to this gate.

  Here, when the reference voltage generated by the bandgap regulator is supplied to the gate of the p-channel MOS transistor at the time of stabilization, the p-channel MOS is set so that the drain current of the p-channel MOS transistor becomes substantially zero. The threshold voltage of the transistor can be set. In this way, the drain current of the p-channel MOS transistor at the time of stability is almost zero, which is most preferable in terms of power saving.

  As an embodiment, the control current source is an n-channel MOS transistor whose source is connected to a negative voltage as viewed from the ground level, and the output current of the control current source is the drain of the n-channel MOS transistor In order to control the output current of the control current source, the node from which the reference voltage of the band gap regulator is generated is connected to the gate of the n-channel MOS transistor, and the band gap regulator generates the current. The reference voltage may be approximately −1.2 V when viewed from the ground level when stable. This is a configuration example for outputting a negative voltage as a reference voltage (stabilized voltage) output. Except for the negative voltage, it can be considered as above.

  Also in this case, when the reference voltage generated by the bandgap regulator is supplied to the gate of the n-channel MOS transistor at the time of stabilization, the n-channel MOS transistor has a drain current of almost zero. The threshold voltage of the MOS transistor can be set. This is most preferable in terms of power saving.

  As an embodiment, the band gap regulator, the starter circuit, and the control current source may be integrated and built on the same semiconductor chip. According to such a configuration, a circuit with superior functionality can be provided on a single chip.

  Based on the above, embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing a configuration of a reference voltage generating circuit according to an embodiment of the present invention. As shown in the figure, the reference voltage generating circuit includes a band gap regulator 11, an output terminal 12, a starting circuit 13, and a control current source 14.

  The band gap regulator 11 has one tree, a current source driven by a voltage generated in the tree, and a band gap type reference voltage source into which an output current of the current source flows. The reference voltage generated in the reference voltage source is output to the output terminal 12. Further, the tree is driven by the generated reference voltage, and is internally connected so that a current flows through the tree. The band gap regulator 11 operates when a current flows between the power supply VCC and the ground.

  The start circuit 13 is a circuit that temporarily drives the tree so that a current flows through the tree in the bandgap regulator 11 when the power supply VCC rises (at the start). In order to validate this function of the starting circuit 13, the current output of the control current source 14 is supplied to the starting circuit 13. The control current source 14 outputs a current toward the starting circuit 13 when the power supply VCC rises. The voltage output of the band gap regulator 11 is supplied to the control input of the control current source 14.

  According to the reference voltage generating circuit having such a configuration, the output current of the control current source 14 is controlled in an analog manner by the output voltage generated by the band gap regulator 11. Therefore, the band gap regulator 11 starts to rise due to the voltage in the band gap regulator 11 generated by the start circuit 13 driving the tree in the band gap regulator 11 at the beginning. As the voltage generated by 11 reaches the reference voltage, the output current of the control current source 14 decreases in an analog manner. Therefore, the power consumption during the operation after stabilization can be reduced by the decrease in the output of the control current source 14. Further, when the voltage output from the bandgap regulator 11 decreases due to some external factor, the control current source 14 and the start circuit 13 start to work again according to the degree, and are energized. Return can be achieved.

  FIG. 2 is a diagram showing an example of a specific circuit diagram of the configuration shown in FIG. In FIG. 2, the same reference numerals are given to components corresponding to the components shown in FIG. 1. That is, a p-channel MOS transistor Q9 is used for the control current source 14, and the starting circuit 13 is composed of bipolar transistors Q1 and Q4 and a resistor R2. The band gap regulator 11 includes a band gap type reference voltage source 11a and a tree 11b. The band gap type reference voltage source 11a includes a bipolar transistor Q3 as a current source, bipolar transistors Q6, Q7, and Q8, and resistors R5, R6, and R8 that are supplied with current from the current source and generate a reference voltage. Circuit. The tree 11b includes a bipolar transistor Q2 constituting a current mirror circuit with the bipolar transistor Q3, and a bipolar transistor Q5 and a resistor R3 connected thereto.

  The transistor Q1 of the starting circuit 13 is diode-connected, and a resistor R2 is connected in series thereto. When power supply VCC rises and current Id is supplied from the drain of MOS transistor Q9 to transistor Q1 and resistor R2, a voltage is generated at the base and collector of transistor Q1, and transistor Q4 is turned on by this voltage. As a result, the tree 11b is driven. At this time, the current path of the tree 11b is Q2 → Q4 → R3. By driving this tree 11b, a voltage is generated at the base and collector of Q2, and as a result, current is output from the collector of Q3 which is one transistor of the current mirror circuit and the current source of the band gap type reference voltage source 11a. The

In the circuit constituted by Q6, Q7, Q8, R5, R6, and R8, a reference voltage is generated by the current from the collector of Q3. Here, the emitter size of Q7 is N times. The voltage at the output terminal 12 is initially 0V, but the voltage V _beQ8 + R5 · I _cQ7 is generated by the current from Q3. This voltage is calculated as V _beQ8 + V _t (lnN · R5 / R8) under the condition that R5 and R6 are equal, V _beQ6 and V _beQ8 are equal, and the collector current and emitter current of the transistor are equal. be able to. V _t = kT / q (k is Boltzmann constant, q is electron charge, T is absolute temperature), V _be is a base-emitter voltage, and I _c is a collector current. From the form of V _beQ8 + V _t (lnN · R5 / R8), this voltage is the sum of negative and positive temperature characteristics, and changes in temperature by setting N and R5 / R8 appropriately It can be seen that the accuracy is high without fluctuation. Specifically, this voltage can be set to approximately 1.2 V, for example.

  When such a reference voltage is generated at the output terminal 12, Q5 having the base connected to the reference voltage is turned on, and Q4 differentially connected to Q5 is turned off. Thereafter, the voltage output at the output terminal 12 as described above continues by establishing the current path of the tree 11b by turning on Q5. The voltage generated at the output terminal 12 rises from 0 V to, for example, 1.2 V and stabilizes at the time of starting.

  The MOS transistor Q9 which is the control current source 14 is initially turned on by applying VCC between the source and the drain due to such a voltage change of the output terminal 12, and reaches the time when the output of the output terminal 12 is stabilized and is in the first on state. As a result, the drain current Id decreases. This is a characteristic of a MOS transistor due to a decrease in the gate-source voltage Vgs. Thus, the drain current Id of the MOS transistor Q9 decreases when the reference voltage generation circuit is stable (during normal operation). At this time, if the threshold voltage of the MOS transistor Q9 is set so that the voltage at the stable output terminal 12 is turned off when the voltage is supplied to the gate of the MOS transistor Q9, the power reduction is effective. Most preferred. The threshold voltage of the MOS transistor can generally be set by controlling the manufacturing process.

For reference, the drain current Id of a MOS transistor generally operating in the saturation region can be expressed as Id = (1/2) × μ × Cox × (W / L) × (Vgs−Vth) ² . Here, μ is the carrier mobility, Cox is the gate capacitance per unit area, W is the gate width, L is the channel length, and Vth is the threshold voltage. Assuming that the voltage of the output terminal 12 at the time of stability is 1.2 V and the power supply voltage VCC = 5 V, the threshold voltage Vth of the MOS transistor Q9 for substantially turning off the MOS transistor Q9 at the time of stability is 3 .8V. In practice, it is preferable to set with an allowance in consideration of variations in VCC.

  Further, the following can be said from the viewpoint of a change in impedance of the MOS transistor Q9. In general, the impedance z between the source and drain of a MOS transistor can be expressed as z = 1 / gm = 1 / (∂Id / ∂Vgs) = L / (μ × Cox × W × (Vgs−Vth)). Here, gm is a mutual conductance. Therefore, in order to increase the impedance after stabilization of the output voltage and reduce the drain current, it is conceivable to design an element (device) so that W is small or L is large.

  The specific operating current value of each transistor in the circuit diagram of FIG. 2 can be determined in various ways according to the device to be applied. Recently, there is a need for a circuit that generates a reference voltage with very little power consumption mainly in portable devices. In that case, there can be a design in which the entire circuit shown in FIG. In any case, if the MOS transistor Q9 does not substantially output current when it is stable, the overall power reduction amount can be about 20%.

  In the configuration of FIG. 2 described above, NPN type or PNP type bipolar transistors are used as the transistors Q1, Q4, Q5, Q2, and Q3. Instead, n-channel MOS transistors or p-channel MOS transistors are used instead. Can also be used. When such a modification is made, in the case of the circuit shown in FIG. 2, the entire reference voltage generation circuit can be integrated on a single chip by using, for example, a BiCMOS process.

  5 and 6 are diagrams showing comparative examples for the configurations and circuits shown in FIGS. 1 and 2, respectively. In FIG. 5 and FIG. 6, the same components as those shown in FIG. 1 and FIG. As can be seen from the description in FIGS. 1 and 2 above, in the configuration shown in FIGS. 5 and 6, the current source 14 </ b> A is provided instead of the control current source 14. Current from source 14A flows. Therefore, the power consumption is larger than that of the embodiment of the present invention shown in FIGS.

  FIG. 3 is a block diagram showing a configuration of a reference voltage generation circuit according to an embodiment of the present invention different from the embodiment shown in FIG. As shown in the figure, the reference voltage generating circuit includes a band gap regulator 21, an output terminal 22, a starting circuit 23, and a control current source 24. The difference from that shown in FIG. 1 is that it corresponds to the case where the power supply voltage (= VEE) is negative. Regarding the functions and operations of the band gap regulator 21, the start circuit 23, and the control current source 24, except that the power supply voltage is negative, the band gap regulator 11, the start circuit 13, and the control current source 14 shown in FIG. It is the same. Therefore, the same effect as the embodiment shown in FIG. 1 can be obtained.

  FIG. 4 is a diagram showing an example of a specific circuit diagram of the configuration shown in FIG. In FIG. 4, constituent elements corresponding to the constituent elements shown in FIG. Here, the band gap regulator 21 includes a band gap type reference voltage source 21a and a tree 21b. At the element level, the elements corresponding to the elements shown in FIG. That is, p-channel MOS transistor Q9 is replaced with n-channel MOS transistor q9, each NPN transistor is replaced with each PNP transistor, and each PNP transistor is replaced with each NPN transistor. The configuration shown in FIG. 4 is the same as the operation by replacing the positive power supply VCC in FIG. 2 with the negative power supply VEE. The stable voltage output to the output terminal 22 can be set to −1.2 V, for example. The same applies to the other features, modifications, and descriptions described in FIG.

The block diagram which shows the structure of the reference voltage generation circuit which concerns on one Embodiment of this invention. The figure which shows the example of the concrete circuit diagram of the structure shown in FIG. The block diagram which shows the structure of the reference voltage generation circuit which concerns on embodiment of this invention different from embodiment shown in FIG. The figure which shows the example of the concrete circuit diagram of the structure shown in FIG. The figure which shows the comparative example with respect to the structure shown in FIG. The figure which shows the comparative example with respect to the circuit shown in FIG.

Explanation of symbols

  11, 21 ... band gap regulator, 11 a, 21 a ... band gap type reference voltage source, 11 b, 21 b ... tree, 12, 22 ... output terminal, 13, 23 ... start circuit, 14, 24 ... control current source, 14 A ... current source.

Claims (6)

And a band gap type reference voltage source for generating a reference voltage by receiving an output current of a current source driven by a voltage on the tree generated by a current flowing through the tree. A band gap regulator configured to drive the tree with a reference voltage
A starting circuit having a function of driving the tree instead of driving the tree by the reference voltage;
A control current source for supplying an output current to the starter circuit to enable the function of the starter circuit and for controlling the output current in an analog manner by an output voltage of the bandgap regulator. Reference voltage generation circuit. The control current source is a p-channel MOS transistor whose source is connected to a positive voltage as viewed from the ground level;
The output current of the control current source is the drain current of the p-channel MOS transistor;
In order to control the output current of the control current source, a node where the reference voltage of the bandgap regulator is generated is connected to a gate of the p-channel MOS transistor,
The reference voltage generation circuit according to claim 1, wherein an output voltage of the band gap regulator generated by the band gap regulator is approximately 1.2 V when viewed from the ground level when stable. The control current source is an n-channel MOS transistor whose source is connected to a negative voltage as viewed from the ground level;
The output current of the control current source is the drain current of the n-channel MOS transistor;
In order to control the output current of the control current source, a node where the reference voltage of the bandgap regulator is generated is connected to a gate of the n-channel MOS transistor,
The reference voltage generation circuit according to claim 1, wherein the reference voltage generated by the bandgap regulator is approximately −1.2 V when viewed from the ground level when stable.   When the reference voltage generated by the bandgap regulator is supplied to the gate of the p-channel MOS transistor at the stable time, the p-channel MOS transistor is set so that the drain current of the p-channel MOS transistor becomes substantially zero. 3. The reference voltage generating circuit according to claim 2, wherein a threshold voltage is set.   When the reference voltage generated by the bandgap regulator is supplied to the gate of the n-channel MOS transistor at the stable time, the n-channel MOS transistor is set so that the drain current of the n-channel MOS transistor becomes substantially zero. 4. The reference voltage generating circuit according to claim 3, wherein a threshold voltage is set.   2. The reference voltage generating circuit according to claim 1, wherein the band gap regulator, the starting circuit, and the control current source are integrated on the same semiconductor chip.

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