JPH084383B2 - Voltage converter - Google Patents

Description

TECHNICAL FIELD The present invention relates to a voltage conversion device for outputting a constant voltage using a charge pump circuit.

(Prior Art) Conventionally, as a technique in such a field, for example, there has been a technique as shown in FIG. 2 and FIG. Hereinafter, the configuration will be described.

FIG. 2 is a block diagram showing a configuration example of a conventional voltage conversion device.

This voltage converter is a device that supplies a stable and constant voltage to the load circuit 1, and is connected between the power supply voltage VCC and the ground potential VSS to output the oscillation signal S. The ring oscillator circuit 10
And a reference voltage generation circuit 11 which is similarly connected between the power supply voltage VCC and the ground potential VSS and outputs the reference voltage Vr. The charge pump circuit 12 is connected to the output sides of both circuits 10 and 11. The charge pump circuit 12 is a circuit which boosts the reference voltage Vr to a predetermined voltage Vg based on the oscillation signal S, and includes MOS transistors 13 and 14 and a capacitor 15 which are connected in series through the node N on the power supply voltage VCC side. ing. The MOS transistors 13 and 14 have a function as a diode in the forward direction with respect to the power supply voltage VCC, and the gate of one of the MOS transistors 13 is connected to the output side of the reference voltage generation circuit 11 and the other MOS transistor. The gate of the transistor 14 is connected to the output side of the ring oscillator 10 via the capacitor 15.

Output side of charge pump circuit 12 and reference voltage generation circuit 11
A clamp circuit 16 made up of a MOS transistor is connected between the output side of and. The clamp circuit 16 is a circuit that clamps the maximum amplitude value of the output voltage Vg of the charge pump circuit 12 to a constant level. An output MOS transistor 17 that outputs the output voltage Vo is connected to the power supply voltage VCC side, and the gate of the output MOS transistor 17 is connected to the charge pump circuit 12. Output MOS transistor 17
Has a threshold voltage Vt (<Vr), and the load circuit 1 is connected between the output side and the ground.

 Next, the operation will be described.

For example, when a positive power supply voltage VCC is applied, the ring oscillator circuit 10 outputs an AC oscillation signal S having an amplitude value between the power supply voltage VCC and the ground potential VSS (= OV) and supplies it to the charge pump circuit 12. The reference voltage generation circuit 11 generates a reference voltage Vr having a small current capacity and supplies it to the charge pump circuit 12. This reference voltage Vr has a relationship of VSS <Vr <VCC.

When the oscillation signal S is at VSS level, the charge pump circuit 12 has a power supply voltage VCC → MOS transistor 13 → capacitor 15
The charging voltage V1 is stored in the capacitor 15 through the route of, and when the oscillation signal S rises from the VSS level to the VCC level, the voltage obtained by adding the rising voltage V2 and the charging voltage V1.
Vg is output to the gate side of the output MOS transistor 17 through the node N → MOS transistor 14. Then the clamp circuit
16 clamps the maximum amplitude value of the output voltage Vg output from the charge pump circuit 12 so that Vg = Vr + Vt. This output voltage Vg
The conduction state of the output MOS transistor 17 is controlled by
An output voltage Vo (= Vr) having a large current capacity and a constant voltage value is output from the output MOS transistor 17 and supplied to the load circuit 1.

FIG. 3 is a block diagram showing a configuration example of another conventional voltage conversion device.

In this voltage conversion device, the threshold voltage V between the power supply voltage VCC side and the ring oscillator circuit 10 in the device of FIG.
A MOS transistor 20 having t (<Vr) is connected,
The circuit configuration is such that the gate of the MOS transistor 20 is connected to the output side of the reference voltage generation circuit 11. Therefore, the ring oscillator circuit 10 has a potential (Vr-Vt) and a ground potential VSS.
The alternating oscillation signal S having an amplitude value between the two is output and supplied to the charge pump circuit 12. In this voltage conversion device, even if the power supply voltage VCC fluctuates, the amplitude of the oscillation signal S is constant without being affected thereby, and stable voltage conversion can be performed.

(Problems to be Solved by the Invention) However, the apparatus having the above configuration has the following problems.

In the voltage converter of FIG. 2, the ring oscillator circuit 10
Since the oscillation signal S has an amplitude value between the power supply voltage VCC and the ground potential VSS, when the power supply voltage VCC changes, the amplitude value of the oscillation signal S also changes. Therefore, there is a problem that the efficiency of the charge pump circuit 12 changes and stable voltage conversion is difficult.

Further, in the voltage converter of FIG. 3, since the oscillation signal S of the ring oscillator circuit 10 has an amplitude value between the potential (Vr-Vt) and the ground potential VSS, the charge pump circuit due to the fluctuation of the power supply voltage as described above. Although the problem of change in efficiency of 12 can be eliminated, since the amplitude value of the oscillation signal S is small, the drive capability of the charge pump circuit 12 is small and the power supply voltage is low.
If VCC is low or the potential (Vr-Vt) is low, the operation of the ring oscillator circuit 10 becomes difficult, and stable voltage conversion cannot be performed.

The present invention solves the problems of the prior art by solving the problems of the change in efficiency of the charge pump circuit due to power supply voltage fluctuation, the reduction in efficiency of the charge pump circuit, and the poor low voltage operation margin of the ring oscillator circuit. A conversion device is provided.

(Means for Solving Problems) In order to solve the above problems, the present invention controls the conduction state of an output transistor by the output of a charge pump circuit that converts a reference voltage into a predetermined voltage based on an oscillation signal. In a voltage conversion device that outputs a constant voltage, a constant current circuit to which a power supply voltage is applied to generate a reference voltage and supply it to the charge pump circuit, and an amplitude value between the reference voltage of the constant current circuit and a ground potential are And an oscillator circuit for generating the oscillation signal and supplying the oscillation signal to the charge pump circuit.

(Operation) According to the present invention, since the voltage conversion device is configured as described above, the constant current circuit outputs the reference voltage having a constant current value. The oscillator circuit connected in series to the constant current circuit works to suppress the fluctuation of the reference voltage and keep it constant, and outputs an oscillation signal having a constant amplitude value in a wide power supply voltage region. With this reference voltage and the oscillation signal, the charge pump circuit can perform stable voltage conversion.
Therefore, the above problems can be eliminated.

(Embodiment) FIG. 1 is a block diagram showing the configuration of a voltage converter according to an embodiment of the present invention.

This voltage conversion circuit has a stable constant voltage Vo as in the past.
Is a device for supplying the load circuit 20 with the constant current circuit 30 and the ring oscillator circuit 4 between the power supply voltage VCC and the ground potential VSS.
0 is connected in series, and the charge pump circuit 50 is connected to the output side of the constant current circuit 30 and the output side of the ring oscillator circuit 40.
Is connected. A clamp circuit 60 and an output MOS transistor 70 are connected to the output side of the charge pump circuit 50.

The constant current circuit 30 is a circuit that outputs a reference voltage Vr having a small current capacity and a constant current value.For example, MOS transistors 31 and 32 are connected in parallel on the power supply voltage VCC side, and both MOS transistors 31 and 32 are connected. Is commonly connected, and the gate is connected to the ground via a resistor 33 having a large resistance value. The constant current circuit 30 operates as an error amplifier, outputs a constant current reference voltage Vr, and supplies it to the ring oscillator circuit 40 and the charge pump circuit 50.

The ring oscillator circuit 40 has a reference voltage Vr and a ground potential VSS.
It is a circuit that outputs an alternating current oscillation signal S having an amplitude value between 3 and 3 between the output side of the constant current circuit 30 and the ground.
Complementary MOS transistors (hereinafter referred to as CMOS) 41,4
2, 43 is connected in parallel, and the input and output sides of the respective CMOS 41, 42, 43 are connected to each other.

The charge pump circuit 50 is a circuit that converts the reference voltage Vr into a predetermined voltage Vg based on the oscillation signal S as in the conventional case.
MOS transistors 51,5 connected in series on the power supply voltage VCC side
2 and a capacitor 53, one MOS transistor 51
The gate of is connected to the output side of the constant current circuit 30,
The gate of the other MOS transistor 52 is connected to the output side of the ring oscillator circuit 40 via the capacitor 53. A node N, which is a connection point between the MOS transistors 51 and 52, is connected to the gate of the MOS transistor 52.

The clamp circuit 60 outputs the output voltage Vg of the charge pump circuit 50.
Of the charge pump circuit 50 and the constant current circuit 30. The MOS transistor 61 is connected between the output side of the charge pump circuit 50 and the output side of the constant current circuit 30. It functions as a diode in the forward direction from the output side of the circuit 50 toward the output side of the constant current circuit 30.

Output MOS connected to the output side of the charge pump circuit 50
The transistor 70 has a threshold voltage Vt, its source is connected to the power supply voltage VCC side, its gate is connected to the output side of the charge pump circuit 50, and its drain is connected to the load circuit 20 side. It is a transistor that outputs Vo and supplies it to the load circuit 20.

The operation of the voltage conversion device configured as described above will be described with reference to FIGS. 4 and 5. Note that FIG. 4 is a voltage-current characteristic diagram of the ring oscillator circuit 40, in which the horizontal axis represents applied voltage and the vertical axis represents current consumption. FIG. 5 is an output voltage characteristic diagram of the constant current circuit 30, with the horizontal axis representing the power supply voltage VC.
The reference voltage Vr, which is the output, is taken on the vertical axis C.

For example, when a positive power supply voltage VCC is applied, the constant current circuit 3
As shown in FIG. 5, 0 indicates the reference voltage value that the output reference voltage Vr rises when the power supply voltage VCC is a small value, and is saturated when the power supply voltage VCC is above a certain power supply voltage value. Normally, the power supply voltage VCC is set within the range of the saturated reference voltage value, so the constant current circuit 30 outputs a substantially constant reference voltage Vr regardless of fluctuations in the power supply voltage VCC, which is the ring oscillator circuit.
40 and the charge pump circuit 50.

The ring oscillator circuit 40 outputs an alternating oscillation signal S having an amplitude value between the applied reference voltage Vr and the ground potential VSS (= OV), and supplies it to the clamp circuit 50. Here, the ring oscillator circuit 40 uses the applied reference voltage Vr.
Is almost constant, an oscillation signal S having a substantially constant amplitude value is output. Furthermore, this ring oscillator circuit 40
As shown in FIG. 4, when the applied reference voltage Vr increases, the consumption current also increases. Therefore, when the applied voltage Vr increases, the consumption current increases and the reference voltage Vr decreases. To work. Therefore, the constant reference voltage Vr is always supplied to the charge pump circuit 50.

In the charge pump circuit 50, when the oscillation signal S is at the VSS level, the charging voltage is stored in the capacitor 53 through the route of the power supply voltage VCC → MOS transistor 51 → capacitor 53, and the oscillation signal S changes from the VSS level to the Vr level. When changing, the changed voltage is added to the charging voltage to output the output voltage Vg through the route of capacitor 53 → node N → MOS transistor 52, and the output voltage Vg is supplied to the gate of the output MOS transistor 70. At this time, the output voltage Vg is
As a result, the voltage is clamped to the potential (Vr + Vt), so that the voltage Vg = Vr + Vt is applied to the output MOS transistor 70. As a result, the conduction state between the source and the drain of the output MOS transistor 70 is controlled, and the output voltage Vo (= Vr) having a large current capacity and a constant voltage value is output from the drain and supplied to the load circuit 20.

 The present embodiment has the following advantages.

Oscillation signal S for driving the charge pump circuit 50
Since the amplitude value and the period are almost constant regardless of the power supply voltage VCC, the operation is stable against the fluctuation of the power supply voltage VCC.

The maximum amplitude value of the oscillation signal S is equivalent to the reference voltage Vr and there is no loss corresponding to the transistor threshold Vt as in the conventional FIG. 3, so that the efficiency of the charge pump circuit 50 is not reduced. At the same time, since the ring oscillator circuit 40 also has no loss of the threshold voltage Vt, it operates stably even with a lower power supply voltage or a reference voltage set value.

Since the ring oscillator circuit 40 also changes the current consumption according to the change in the applied voltage, the entire device exhibits almost constant power consumption regardless of the fluctuation of the power supply voltage VCC.

The present invention is not limited to the illustrated embodiment, and various modifications can be made. The following are examples of such modifications.

(I) The ring oscillator circuit 40 is used as the oscillator circuit.
However, it is also possible to configure this circuit 40 with elements other than CMOS 41, 42, 43, or to replace the ring oscillator circuit 40 with another oscillator circuit having the characteristics shown in FIG. Is.

(Ii) The constant current circuit 30, the charge pump circuit 50, the clamp circuit 60, and the output MOS transistor 70 can be configured using elements other than MOS transistors, or they can be replaced with circuits of other configurations. is there.

(Effects of the Invention) As described in detail above, according to the present invention, the constant current circuit and the oscillator circuit are connected in series between the current voltage and the ground voltage. The output reference voltage can be held constant, and stable voltage conversion can be performed in a wide power supply voltage region.

[Brief description of drawings]

FIG. 1 is a block diagram of the configuration of a voltage converter showing an embodiment of the present invention, FIGS. 2 and 3 are block diagrams of a conventional voltage converter, and FIG. 4 is a voltage of the ring oscillator circuit of FIG. A current characteristic diagram and FIG. 5 are output voltage characteristic diagrams of the constant current circuit of FIG. 20 …… load circuit, 30 …… constant current circuit, 40 …… ring oscillator circuit, 50 …… charge pump circuit, 60 …… clamp circuit, 70 …… output MOS transistor, S …… oscillation signal, VCC …… power supply Voltage, Vo ... Output voltage, Vr ... Reference voltage, VSS ... Ground potential.

Claims (1)

[Claims] 1. A voltage converter that outputs a constant voltage by controlling the conduction state of an output transistor by the output of a charge pump circuit that converts a reference voltage into a predetermined voltage based on an oscillation signal. A constant current circuit for generating and supplying the charge pump circuit to the charge pump circuit, and an oscillator circuit for generating an oscillation signal having an amplitude value between a reference voltage of the constant current circuit and a ground potential and supplying the oscillation signal to the charge pump circuit. A voltage conversion device comprising: