JP2002023870A - Reference voltage circuit and voltage regulator using the reference voltage circuit - Google Patents

Abstract

(57) [PROBLEMS] To provide a reference voltage circuit having low current consumption, short rise and fall times, and low output noise characteristics, and a voltage regulator using the reference voltage circuit. SOLUTION: A voltage at a point A and a voltage at a point B of a reference voltage circuit are compared by a comparator 2, and when the voltage at the point A is higher than the voltage at the point B, a switch SW1 is turned on and a charge is stored in a capacitor C. Charge fast. When charge is accumulated in the capacitor C, A
When the voltage at the point becomes equal to the voltage at the point B, the switch SW1 is turned off. Thereby, even in the reference voltage circuit in which the ripple rejection rate is improved by using the low-pass filter, the rise time of the reference voltage can be shortened, and high-speed operation can be performed. Further, the electric charge accumulated in the capacitor C is forcibly discharged through the switch SW2. This allows the output voltage of the reference voltage circuit to drop quickly,
As a result, current consumption can be reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reference voltage circuit of a voltage regulator used in, for example, a cellular phone, a personal computer, a facsimile apparatus, etc., and more particularly to a technique capable of reducing output noise and having a short rise and fall time. And a reference voltage circuit having a high ripple rejection ratio, and a voltage regulator using the same.

[0002]

2. Description of the Related Art FIG. 4 is a diagram showing a circuit configuration of a conventional general voltage regulator. In the figure,
21 is a reference voltage source, 22 is an error amplifier circuit (differential amplifier circuit), 23 is an output transistor, 24 is an output terminal, R
1 and R2 are resistors. The voltage Vref output from the reference voltage source 21, the output transistor 23 and the resistors R1 and R2
Are detected by the error amplifier circuit 22, and the output transistor 23 is controlled based on the comparison result to stabilize the output voltage Vout to the output terminal 24.

The output voltage Vout at this time is (R1 + R
2) Since it is represented by / R2 * Vref and is proportional to Vref, the fluctuation of Vref directly causes the fluctuation of the output voltage. In order to improve the performance of the voltage regulator, it is necessary to improve the ripple rejection ratio (fluctuation in output voltage with respect to fluctuation in power supply), and Japanese Patent Application Laid-Open No. 8-272461 proposes a configuration therefor.

FIG. 5 is a diagram showing a circuit configuration of an improved voltage regulator proposed in the above-mentioned publication. A low-pass filter 25 including a resistor Rf and a capacitor Cf is provided at the output of a reference voltage source 21. It is a thing. The potential at point b increases with the accumulation of charge in the capacitor Cf, and when the charge is sufficiently accumulated in the capacitor Cf, the potential at point b is stabilized. With this configuration, the ripple rejection of the reference voltage source 21 can be improved, and as a result, the ripple rejection of the voltage regulator can also be improved.

[0005]

In the circuit of FIG. 5, the rise time of the output potential of the reference voltage circuit is determined by the amount of current flowing through the reference voltage source 21. When a conventional reference voltage source of current consumption is used by using a resistor Rf and a capacitor Cf which are sufficiently effective as the low-pass filter 15, several hundred msec is required for rising, and high-speed operation such as communication equipment is required. Not suitable for required applications.

In order to shorten the rise time of the reference potential, it is necessary to increase the amount of current flowing through the reference voltage source 21 or use a capacitor Cf having a small capacitance value. Is increased, the current consumption increases, and when the capacitance Cf having a small capacitance value is used, there is a problem that the performance of the low-pass filter 25 is reduced.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems and to provide a reference voltage circuit having low output current characteristics with low rise time and fall time in addition to low current consumption. To provide a voltage regulator.

More specifically, an object of the present invention is to realize a reference voltage circuit which shortens the rise time of a reference voltage, operates at high speed, and consumes less current. Another object of the present invention is to reduce the current consumption by allowing the output voltage of the reference voltage circuit to drop at a high speed when the power is turned off.

Further, the invention according to claim 3 is a low-pass
The invention according to claim 4 is to provide an effective reference voltage circuit when it is difficult to incorporate a capacitor (C) and a resistor (R) having sufficiently large sizes as a filter in an IC.
It is an object of the present invention to provide a reference voltage circuit capable of improving the characteristics of a low-pass filter.

The invention according to claim 5 provides a reference voltage circuit capable of preventing the operation of the comparator from becoming unstable, and the invention according to claim 6 provides the reference voltage circuit for the charging switch and the discharging switch. It is an object of the present invention to provide a voltage regulator having a low output current characteristic with a short rise time and a fall time in addition to low current consumption. It is an object.

[0011]

In order to achieve the above object, a reference voltage circuit according to a first aspect of the present invention comprises a reference voltage source (1) and a reference voltage source (1) connected to one input terminal (+). ) Is connected via a resistor (R), and the other input terminal (-) is connected to the output of the reference voltage source (1) or a reference voltage source (1 ') different from the reference voltage source. A comparator (2), a charging switch (SW1) and a capacitor (C) connected in series between the first power supply (Vdd) and the second power supply (Vss). The output is connected to the control terminal of the charging switch (SW1), and the charging switch (S
A connection point between W1) and the capacitance (C) is connected to one input terminal (+) of the comparator (2), and a voltage at a connection point between the charging switch (SW1) and the capacitance (C) is output to the output reference voltage (Vout). )
(See FIGS. 1 and 2).

The reference voltage circuit according to claim 2 is the reference voltage circuit according to claim 1, further comprising: a connection point between the charging switch (SW1) and the capacitor (C); and a second power supply (Vss). The reference voltage circuit according to claim 3, further comprising a discharging switch (SW2), a charging switch (SW1), a discharging switch (SW2),
It is characterized in that a resistor (R) or a capacitor (C) is selectively externally provided.

The reference voltage circuit according to a fourth aspect of the present invention is further characterized in that the resistance (R) and the capacitance (C) can be adjusted. The reference voltage circuit according to the fifth aspect further comprises a comparator (2). ) Has hysteresis in the judgment level,
The reference voltage circuit according to claim 6, further comprising a switch for charging (SW1) or a switch for discharging (SW2).
It is characterized by comprising a transistor.

Further, a voltage regulator according to the present invention is provided with the reference voltage circuit according to any one of the first to sixth aspects.

More specifically, in the present invention, by providing a switch (SW1) for rapidly charging electric charges, the rise time of the reference voltage is shortened, and a reference voltage circuit that operates at high speed is realized. Claim 1). Further, in the reference voltage circuit of the present invention, the consumption current is large temporarily only while the charge switch (SW1) for rapidly charging the charge is on, and after the reference voltage rises, the charge switch (SW1). The current consumption can be reduced by turning off the switch (claim 1).

On the other hand, when the reference voltage circuit is turned off, the fall time of the output voltage is determined by the time for discharging (discharging) the charge stored in the capacitor. When the charge stored in the capacitor is discharged only through the reference voltage source or the comparator, the output voltage of the reference voltage circuit cannot fall in a sufficiently short time. Therefore, in the present invention, a discharge switch (SW2) is provided so that the output voltage drop of the reference voltage circuit can be performed at a high speed when the power is turned off, and the current consumption is reduced. 2).

In some cases, it is difficult to incorporate a capacitor (C) and a resistor (R) having sufficiently large sizes as a low-pass filter in an IC. Also, even if it is built in,
The values of the built-in capacitance and resistance cannot be changed later. Similarly, it may be difficult to incorporate a switch into an IC. So resistance, capacity, charge switch,
Alternatively, the discharge switch is selectively externally provided (claim 3). Further, by making the resistance and capacitance values adjustable, the reference voltage circuit of the present invention can be easily realized, and the characteristics of the low-pass filter can be improved (claim 4).

Further, by providing the comparator with a hysteresis in the determination level, the operation of the comparator can be stabilized.

[0019]

FIG. 1 is a configuration diagram for explaining an embodiment of a reference voltage circuit according to the present invention. In the present embodiment, a switch for rapidly charging a capacitor and a switch for discharging at a high speed are provided in a conventional reference voltage circuit using a resistor and a capacitor as shown in FIG. , In which the current consumption is reduced. In the figure, 1 and 1 'are reference voltage sources, 2 is a comparator, R is a resistor, C is a capacitor, and SW1 and SW2 are a charging switch and a discharging switch, respectively.

FIG. 1 shows an improved configuration of a portion of a reference voltage circuit comprising a reference voltage source and a low-pass filter shown in FIG. 5, and the configuration thereafter is omitted because it is the same as that of FIG. The voltage at the point B of the reference voltage circuit of FIG. 1, that is, the output voltage Vout is the error amplifier circuit (differential amplifier circuit) of FIG.
22 is connected to one input terminal (-) of the
It is assumed that a regulator is configured.

First, the operation at the time of startup, that is, at the time of charging will be described with reference to FIG. A of the reference voltage circuit
The voltage at the point and the voltage at the point B are compared by the comparator 2, and while the voltage at the point B is lower than the voltage at the point A, the switch SW1 is turned on, and the charge is rapidly charged and accumulated in the capacitor C. Capacity C
The switch SW1 is turned off when the voltage at the point B becomes equal to the voltage at the point A due to the accumulation of electric charges in the switch SW1.

Thus, even in the reference voltage circuit in which the output noise is reduced by using the low-pass filter including the resistor and the capacitor as shown in FIG. Can be shortened, and high-speed operation can be performed.

Note that the two reference voltage sources 1 and 1 'do not necessarily have to have the same circuit configuration. Furthermore, the output voltages of the two reference voltage sources 1 and 1 'need not necessarily be equal.

In the above embodiment, two reference voltage sources 1
Although the example using お よ び and 'has been shown, similar functions can be achieved using only a single reference voltage source without using two reference voltage sources. FIG. 2 shows an example of such a case. 2, except that the output voltage of the reference voltage source 1 is used as one input of the comparator 2 'and the output voltage of the reference voltage source 1 is used as the other input of the comparator 2' via the resistor R. And has the same effect.

Next, the operation at the time of falling, that is, at the time of discharging (discharging) will be described. When the discharge rate is low, the charge remaining in the capacitor C is an n-channel MOS transistor constituting the comparator 2 (for example, FIG.
There is a problem that the n-channel MOS transistor 11) is turned on in addition to the gate of the n-channel MOS transistor 11) to consume extra current.

In this embodiment, in order to solve this problem,
A switch S is connected between one terminal of the capacitor C and the ground side terminal.
W2 is provided, and the charge stored in the capacitor C is
Through a forcible discharge. As a result, the output voltage of the reference voltage circuit can be rapidly reduced, and as a result, current consumption can be reduced. The timing for turning on the switch SW2 may be the timing for terminating the operation of the reference voltage circuit, for example, the timing for turning off the chip enable signal.

It should be noted that the resistor R, the capacitor C and the switches SW1 and SW2 in FIG. 1 do not necessarily need to be built in the IC, and the same effect can be obtained even if one or all of them are externally mounted on the IC. This makes it possible to use the optimum resistance R, capacitance C, and switches SW1 and SW2, thereby improving the performance of the low-pass filter.

Further, by making the values of the resistor R and the capacitor C adjustable (variable) using, for example, a known laser trimming technique, it becomes possible to use the resistor R and the capacitor C having optimal values. And the performance of the low-pass filter can be improved.

In the above embodiment, the switch SW1 is turned on while the voltage at the point B is lower than the voltage at the point A in FIG.
Although it has been described that the switch SW1 is turned off when the voltage at the point B rises and becomes equal to the voltage at the point A, such a voltage setting causes the following problem.

That is, when the voltage at the point B rises and becomes equal to the voltage at the point A and the switch SW1 turns off, the power supply Vdd
Is not applied, the voltage at the point B is compared with the comparator 2 or the reference power supply 1
For example, when the voltage at the point B falls below the voltage at the point A, the switch SW1 is turned on again by the output of the comparator 2 to increase the voltage at the point A. When the voltage at the point A rises, the switch SW1 is turned off again by the output of the comparator 2. As described above, the ON / OFF repetition of the switch SW1 occurs near the point A voltage and the point B voltage being equal. When the voltage at the point A and the voltage at the point B are equal to each other, the switch SW1 is also affected by noise.
May be frequently switched on and off.

In order to eliminate the above-mentioned repeated ON / OFF phenomenon of the switch SW1 and to stabilize the output, the comparator 2
The hysteresis may be provided for the two input voltage determination levels. FIG. 3 is a diagram showing an example of a circuit configuration in which the determination levels of the two input voltages have hysteresis.

In the figure, 11, 12, 15 are n-channel MOS transistors, and 13, 14, 16, 17 are p-channel MOS transistors.
Channel MOS transistor, n-channel MOS
Transistor 11 and n-channel MOS transistor 12
The gate size (gate width / gate length) of
The gate sizes (gate width / gate length (W / L)) of the channel MOS transistors 13 and 14 are made equal, and the gate sizes (gate width / gate length) of the p-channel MOS transistors 16 and 17 are set. Are the same. Further, the current gain β of the p-channel MOS transistors 13 and 14 is set to be smaller than the current gain β of the p-channel MOS transistors 16 and 17 or the p-channel MOS transistor 1
3, 14, 16 are made smaller than the current gain β of the p-channel MOS transistor 17.

In this configuration, first, at the time of rising, the voltage (input terminal (−)) applied from the reference voltage source 1 ′ to the gate of the n-channel MOS transistor 11 is higher.
From reference voltage source 1 having resistance R and capacitance C to n-channel M
Since the voltage rises faster than the voltage (input terminal (+)) applied to the gate of the OS transistor 12, the n-channel MOS transistor 11 and the p-channel MOS transistor 1
3 and 16 are on, n-channel MOS transistors 12 and
The p-channel MOS transistors 14 and 17 are turned off. At this time, the drain voltage of the n-channel MOS transistor 12 turns on the charging switch SW1 composed of the p-channel MOS transistor via the inverter, and charges the capacitor C at high speed.

By this charging, the gate voltage (input terminal (+)) of the n-channel MOS transistor 12 increases, and n
At the time when the gate voltage becomes equal to the gate voltage of the channel MOS transistor 11, the n-channel MOS transistor 12 is turned on, the p-channel MOS transistors 14, 17 are turned on, and the n-channel MOS transistor 11, p-channel M
The OS transistors 13 and 14 are turned off. When the n-channel MOS transistor 12 is turned on, its drain voltage is reduced, and the switch SW1 is turned off.

At this time, as described above, the p-channel M
The current amplification factor β of the OS transistors 13 and 14 is made smaller than the current amplification factor β of the p-channel MOS transistors 16 and 17 or the p-channel MOS transistors 13 and 1
By making the current gain β of the P.4, 16 smaller than the current gain β of the p-channel MOS transistor 17,
After the gate voltage (input terminal (+)) of the n-channel MOS transistor 12 once becomes high, the p-channel MOS transistor 12 continues to be turned on and charged even if the voltage of the input terminal (+) decreases. Switch SW1 is kept off. In this manner, the operation of the switch SW1 can be stabilized by providing the determination level between the input terminal (+) and the input terminal (-) with hysteresis.

In the above example, the output is switched and the switch SW1 is turned off when the voltage of the input terminal (+) rises to the same voltage as the input terminal (-). However, the input when the output of the comparator is switched is turned off. Terminal (+) and input terminal (-)
Can be set freely.

For example, in FIG. 3, an n-channel MOS transistor 11 and an n-channel MOS
A difference is made in the channel size W / L (width / length) of the gate of the transistor 12, and the voltage of the input terminal (+) is V1
When the potential of the input terminal (−) is V2, V2−V1
Is switched to a predetermined value, the output of the comparator is switched.

As an example, considering the case where the input voltage (-) from the reference voltage source is 3 V and the predetermined value is 0.2 V, the input voltage (-) is raised at the time of rising (when the capacitor C is charged). +) Gradually rises while charging the capacitor C by the voltage from the reference voltage source and the voltage from Vdd via the switch SW1, and when the voltage reaches 2.8V, the output of the comparator 2 switches and the switch SW1 is turned off. . With this configuration,
The voltage difference between the two input terminals for turning off the switch SW1 can be made a desired value, and the design of the reference voltage circuit of the present invention can be given a degree of freedom.

[0039]

According to the present invention, a reference voltage circuit having low current consumption, a short rise time and a short fall time, and low output noise characteristics, and a voltage regulator using the reference voltage circuit can be realized.

More specifically, according to the first aspect of the present invention, it is possible to realize a reference voltage circuit which operates at high speed with a short rise time of the reference voltage and consumes a small amount of current. Further, according to the second aspect of the present invention, the output voltage of the reference voltage circuit can be dropped at a high speed when the power is turned off, and the current consumption can be reduced.

According to the third aspect of the present invention, even when it is difficult to incorporate a capacitor (C), a resistor (R), a switch, and the like having a sufficiently large size as a low-pass filter in an IC, it is possible to provide a low-pass filter. By attaching it, it becomes possible to select the optimal resistance, capacity, switch according to the use conditions,
The performance of the low-pass filter can be improved. Further, according to the fourth aspect of the present invention, since the capacitance (C) and the resistance (R) can be adjusted, a reference voltage circuit capable of improving the characteristics of the low-pass filter can be realized.

According to the fifth aspect of the invention, the reference voltage circuit capable of reliably stabilizing the operation can be realized by providing hysteresis to the judgment level of the two inputs of the comparator. . Further, according to the invention of claim 6, since the charging switch and the discharging switch are MOS transistors, the switches can be built in the IC. By using the voltage circuit, it is possible to realize a voltage regulator having low output noise characteristics which can operate at high speed with low current consumption.

[Brief description of the drawings]

FIG. 1 is a configuration diagram for explaining an embodiment of a reference voltage circuit according to the present invention.

FIG. 2 is a modification of FIG. 1 using only a single reference voltage source.

FIG. 3 is a diagram illustrating an example of a circuit configuration of a comparator in which a determination level of two input voltages has hysteresis.

FIG. 4 is a diagram showing a circuit configuration of a conventional general voltage regulator.

FIG. 5 is a diagram showing a circuit configuration of a conventional improved voltage regulator.

[Explanation of symbols]

 1, 1 ', 21: reference voltage source, 2, 2': comparator, 11 to 17: MOS transistor, 22: error amplifier circuit (differential amplifier circuit), 23: output transistor, 24: output terminal, 25: R, R1, R2, Rf, r, r1, r2, r3: resistance, C, Cf: capacitance,

Claims (7)

[Claims] 1. A reference voltage source, wherein one input terminal is connected to an output of the reference voltage source via a resistor, and the other input terminal is connected to the reference voltage source or a reference voltage source different from the reference voltage source. And a charging switch and a capacitor connected in series between a first power supply and a second power supply. An output of the comparator is connected to a control terminal of the charging switch. A reference voltage circuit, wherein a connection point between the charging switch and the capacitor is connected to the one input terminal of the comparator, and a voltage at the connection point between the charging switch and the capacitor is set as an output reference voltage. . 2. A connection point between the charging switch and a capacitor,
2. The reference voltage circuit according to claim 1, wherein a discharge switch is provided between the reference voltage circuit and the second power supply. 3. The switch for charging, the switch for discharging,
3. The reference voltage circuit according to claim 1, wherein a resistor or a capacitor is selectively built-in or externally mounted. 4. The reference voltage circuit according to claim 1, wherein said resistance or capacitance is adjustable. 5. The reference voltage circuit according to claim 1, wherein a hysteresis is provided to the judgment level of the comparator. 6. The reference voltage circuit according to claim 1, wherein said charging switch or discharging switch is constituted by a MOS transistor. 7. A voltage regulator using the reference voltage circuit according to claim 1. Description: