JPH10276068A - Ring oscillator - Google Patents

Abstract

(57) [Problem] To provide a ring oscillator that suppresses a decrease in oscillation frequency when a power supply voltage becomes low. SOLUTION: An odd number of inverters IV1 to IV2n +
1, a resistor R, a first capacitor CAP1, a second capacitor CAP2, one end of which is the other end of the resistor R, and the other end of which is the first capacitor CAP1.
When the first power supply voltage Vcc is close to the rated value, the resistance value is negligibly small when the first power supply voltage Vcc is close to the rated value, and the resistance value increases as the first power supply voltage Vcc decreases. One variable resistor Tr1, Tr2, one end is connected to the other end of the resistor R, and the other end is connected to the other end of the second capacitor CAP2, respectively, and can be ignored when the first power supply voltage Vcc is near the rated value. Low resistance value
It has second variable resistors Tr3 and Tr4 whose resistance values increase as the first power supply voltage Vcc decreases.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ring oscillator, and more particularly, to a ring oscillator that suppresses a decrease in oscillation frequency when a power supply voltage is reduced, and reduces fluctuations in the oscillation frequency with respect to a change in the power supply voltage.

[0002]

2. Description of the Related Art FIG. 4 shows a circuit configuration diagram of a conventional ring oscillator. The ring oscillator of this conventional example is cascaded, and an odd number (2n +) in which the output of the last inverter IV2n + 1 is supplied to the input of the first inverter IV1.
1) Inverters IV1 to IV2n + 1 and a resistor R
, A first capacitor CAP1, and a second capacitor CAP
2 and an inverter IVo as an output driver that receives the output of the last inverter IV2n + 1 and outputs it as an output signal OUT. Note that one end of the resistor R is connected to the output of the second-stage inverter IV2, and the other end of the resistor R is connected to the input of the third-stage inverter IV3. The other end of the resistor R is connected to the other end of the first capacitor CAP1 having one end connected to the power supply voltage Vcc, and the other end of the second capacitor CAP2 having one end connected to the ground potential GND. I have.

In the conventional ring oscillator having such a configuration, the oscillation frequency f of the output signal OUT depends on the capacitances of the first and second capacitors CAP1 and CAP2 and the first and second capacitors CAP1 and CAP.
2 largely depends on the currents I1 and I2 for charging. For this reason, when the power supply voltage Vcc decreases, the first capacitor C
The drive current capability of the inverter that charges the AP1 and the second capacitor CAP2 decreases, and the charging currents I1 and I2 decrease, so that the oscillation frequency f of the output signal OUT decreases. FIG. 5 shows a change in the oscillation frequency f with respect to a change in the power supply voltage Vcc obtained by measurement in the ring oscillator of the conventional example. The dependence of the oscillation frequency on the power supply voltage, in which the oscillation frequency f decreases as the power supply voltage Vcc decreases, clearly appears.

[0004]

As described above, in the above-mentioned conventional ring oscillator, when the power supply voltage Vcc decreases, the charging currents I1 and I2 of the first capacitor CAP1 and the second capacitor CAP2 decrease. There has been a situation where the oscillation frequency f of the signal OUT decreases. A ring oscillator is used, for example, to periodically drive a charge pump circuit to generate a boost power supply or the like.However, when a conventional ring oscillator is used, when a power supply voltage decreases, the ring oscillator is used. There has been a situation in which the current capability of the step-up power supply also decreases because the oscillation frequency also decreases.

The present invention has been made in view of the above-mentioned conventional circumstances, and suppresses a decrease in the oscillation frequency when the power supply voltage becomes low, thereby reducing the fluctuation of the oscillation frequency with respect to a change in the power supply voltage. The purpose of the present invention is to provide an improved ring oscillator.

[0006]

In order to solve the above-mentioned problems, a ring oscillator according to the present invention comprises an odd number of inverters connected in cascade, the output of the last inverter being supplied to the input of the front inverter, and one end. Is a resistor connected to the output of the inverter of an arbitrary stage, the other end is connected to the input of the next stage of the inverter, one end is connected to the capacitor connected to the second power supply, and one end is connected to the other end of the resistor. And a variable resistor whose ends are respectively connected to the other ends of the capacitors, the resistance value is small when the voltage of the first power supply is near the rated value, and the resistance value increases with the decrease in the voltage of the first power supply. It is provided with.

Further, in the ring oscillator according to the present invention, in the variable resistor, the first diffusion layer is connected to the other end of the resistance, the second diffusion layer is connected to the other end of the capacitor, and the gate is connected to the second diffusion layer. It has a first conductivity type transistor connected to one power supply.

Further, in the ring oscillator according to the present invention, in the variable resistor, the first diffusion layer is connected to the other end of the resistance, the second diffusion layer is connected to the other end of the capacitor, and the gate is connected to the second end of the capacitor. And a second conductivity type transistor connected to two power sources.

Further, the ring oscillator of the present invention has an odd number of cascade-connected inverters whose last stage inverter output is supplied to the front stage inverter input, one end of which is connected to the output of the arbitrary stage inverter, and the other end of which is connected to the other end. , A resistor connected to the input of the next stage of the inverter, a first capacitor connected at one end to the first power supply, a second capacitor connected at one end to the second power supply, and a resistor connected at one end to the second power supply. The other end is connected to the other end of the first capacitor. When the voltage of the first power supply is near the rated value, the resistance value is small, and the resistance value decreases as the voltage of the first power supply decreases. And a first variable resistor having one end connected to the other end of the resistor and the other end connected to the other end of the second capacitor.
When the power supply voltage is near the rated value, the resistance value is small,
A second variable resistor whose resistance value increases as the voltage of the first power supply decreases.

In the ring oscillator according to the present invention, the first variable resistor is configured such that a first diffusion layer is connected to the other end of the resistor, and a second diffusion layer is connected to the other end of the first capacitor. A gate having a first first-conductivity-type transistor that is turned on by the supply of the voltage of the first power supply, wherein the second variable resistor has a second diffusion layer at the other end of the resistance, and a first diffusion layer Are respectively connected to the other ends of the second capacitors,
The semiconductor device includes a second first conductivity type transistor having a gate connected to the first power supply.

Further, in the ring oscillator according to the present invention, the first variable resistor includes a first diffusion layer connected to the other end of the resistance, a second diffusion layer connected to one end of the first capacitor, and a gate. Has a first second conductivity type transistor connected to the second power supply, wherein the second variable resistor has a second diffusion layer at the other end of the resistance, and a first diffusion layer at the other end of the second variable resistance. A second second conductivity type transistor connected to one end of each of the two capacitors and having a gate connected to the second power supply.

The ring oscillator of the present invention has a configuration in which a variable resistor is connected between a resistor and a capacitor. First
When the power supply voltage is high (close to the rated value), the resistance value of the variable resistor is negligibly small and performs the same operation as the conventional ring oscillator. When the first power supply voltage is small, the current for charging the capacitor is small. However, the resistance value of the variable resistor increases as the first power supply voltage decreases, so that the voltage drop due to the resistance component affects the variable resistance. That is, the rise or fall delay due to the decrease in the first power supply voltage at the connection point of the resistor and the variable resistor is reduced as compared with the conventional ring oscillator, and as a result, the ring oscillator associated with the decrease in the first power supply voltage Of the oscillation frequency is suppressed, and the fluctuation of the oscillation frequency with respect to the change of the power supply voltage can be reduced.

In the ring oscillator according to the present invention, the first variable resistor and the second variable resistor are connected between the resistor and the first capacitor and between the resistor and the second capacitor, respectively. The first power supply voltage is large (it is near the rated value)
In this case, the resistance values of the first variable resistor and the second variable resistor are negligibly small, and the operation is the same as that of the conventional ring oscillator. When the first power supply voltage is small,
Although the current for charging the first capacitor and the second capacitor decreases, the resistance value of the first variable resistor and the second variable resistor increases with the decrease in the first power supply voltage. As a result, the rise or fall delay due to the decrease in the first power supply voltage at the connection point between the resistor and the first variable resistor and the second variable resistor is reduced as compared with the conventional ring oscillator. A decrease in the oscillation frequency of the ring oscillator due to a decrease in the power supply voltage is suppressed, and a variation in the oscillation frequency with respect to a change in the first power supply voltage can be reduced.

Further, in the ring oscillator according to the present invention, the variable resistor, the first variable resistor and the second variable resistor may be the on-resistance of the first conductivity type transistor or the on-resistance and the second conductivity type of the first conductivity type transistor. It is desirable to use a combined resistance of the on-resistance of the transistor. That is, when the first power supply voltage is high (near the rated value), the resistance value of the on-resistance is negligibly small, and when the first power supply voltage decreases, the resistance value of the on-resistance is reduced. Has the property of increasing. In order to set the output of the ring oscillator to a balanced duty ratio, the first variable resistor and the second variable resistor are formed by combining the on-resistance of the first conductivity type transistor and the on-resistance of the second conductivity type transistor. It is desirable that

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of a ring oscillator according to the present invention will be described below in detail with reference to the drawings. FIG. 1 is a circuit configuration diagram of a ring oscillator according to one embodiment of the present invention.

In FIG. 1, the ring oscillator of this embodiment is cascaded, and the last inverter IV2n + 1 is connected.
(2n + 1) inverters IV1 to IV2n + 1 whose output is supplied to the input of the front-stage inverter IV1
, A resistor R, a first capacitor CAP1, a second capacitor CAP2, and first pass transistors Tr1 and Tr1.
2, the second pass transistors Tr3 and Tr4, and an inverter IVo as an output driver that receives the output of the last inverter IV2n + 1 and outputs the output signal OUT. When the oscillation frequency of the ring oscillator is, for example, about 10 [MHz], the resistance R is 5 [kΩ] and the first capacitor CAP1
The second capacitor CAP2 may have a value of several [pF].

One end of the resistor R is connected to a second-stage inverter IV2.
The other end of the resistor R is connected to the input of the third-stage inverter IV3. The first pass transistors Tr1 and Tr2 have their source electrodes connected to the other end of the resistor R and their drain electrodes connected to one end of the first capacitor CAP1, respectively, and are turned on by supplying the second power supply voltage GND to the gate electrodes. First P-channel transistor T
r1 and a first N-channel transistor Tr2 whose source electrode is connected to the other end of the resistor R, whose drain electrode is connected to one end of the first capacitor CAP1, and which is turned on by supplying the first power supply voltage Vcc to the gate electrode. Configuration.

The second pass transistors Tr3 and T3
r4 is a second P-channel transistor Tr3 whose drain electrode is connected to the other end of the resistor R, whose source electrode is connected to one end of the second capacitor CAP2, and which is turned on by the supply of the second power supply voltage GND to the gate electrode; The electrode is at the other end of the resistor R, and the source electrode is at the second capacitor CA.
A second N-channel transistor Tr4 is connected to one end of P2 and is turned on by the supply of the first power supply voltage Vcc to the gate electrode.

Next, the operation of the ring oscillator of this embodiment will be described. FIG. 2 is an operation explanatory diagram of the circuit portion of the resistor R, the first capacitor CAP1, the second capacitor CAP2, the first pass transistors Tr1 and Tr2, and the second pass transistors Tr3 and Tr4 of the ring oscillator of the present embodiment. FIG. 2A shows the first power supply voltage Vc.
FIG. 2B is an explanatory diagram when the first power supply voltage Vcc is small when c is large (close to the rated value).

First, the operation when the first power supply voltage Vcc is high (close to the rated value) will be described with reference to FIG. In this case, the first pass transistor Tr1
And Tr2 and the second pass transistors Tr3 and Tr4 are sufficiently turned on, so that the voltage drop due to the on-resistance component can be ignored with respect to the first power supply voltage Vcc. Is equivalent to the circuit shown on the right side of FIG. That is, when the first power supply voltage Vcc is large, the operation of the ring oscillator of the present embodiment is the same as that of the conventional ring oscillator (FIG. 4).

Next, the operation when the first power supply voltage Vcc is small will be described with reference to FIG. In this case, in this case, the first pass transistors Tr1 and Tr1
2, and the voltage drop due to the on-resistance component of the second pass transistors Tr3 and Tr4 increases with the decrease of the first power supply voltage Vcc, and cannot be ignored for a small first power supply voltage Vcc. The circuit portion is the equivalent circuit shown on the right side of FIG. That is, the on-resistance components Ron1 of the first pass transistors Tr1 and Tr2 are connected between the node N, which is the connection point between the other end of the resistor R and the input of the third-stage inverter IV3, and one end of the first capacitor CAP1.
However, the on-resistance components Ron2 of the second pass transistors Tr3 and Tr4 are equivalently connected between the node N and one end of the second capacitor CAP2.

That is, when the first power supply voltage Vcc is small, the first capacitor CAP1 and the second capacitor CA
Although the current for charging P2 decreases, the first power supply voltage Vc
The first pass transistor Tr1 increases as c decreases
And Tr2, and the voltage drop due to the on-resistance components of the second pass transistors Tr3 and Tr4,
The delay of the rise or fall due to the decrease of the first power supply voltage Vcc at the potential of the node N is reduced as compared with the conventional ring oscillator. That is,
The decrease in the oscillation frequency of the ring oscillator due to the decrease in the first power supply voltage Vcc is reduced as compared with the conventional example.

As described above, in the ring oscillator of the present embodiment, the resistor R and the first pass transistor Tr1,
The delay of the rise or fall due to the decrease of the first power supply voltage Vcc at the connection point N between Tr2 and the second pass transistors Tr3 and Tr4 is reduced as compared with the conventional ring oscillator, and as a result, the first power supply voltage Vc
c can be suppressed from lowering the oscillation frequency of the ring oscillator due to the lowering of the first power supply voltage Vcc of the oscillation frequency.
Can be reduced.

The ring oscillator is used, for example, to periodically drive a charge pump circuit to generate a boosted power supply or the like. However, when a conventional ring oscillator is used, the power supply voltage becomes smaller. Since the oscillation frequency of the ring oscillator has also been reduced, the current capability of the step-up power supply has also been reduced. However, if the ring oscillator of the present embodiment is used, a decrease in the oscillation frequency can be reduced even when the power supply voltage is reduced, so that a reduction in the current capability of the boosted power supply at a low power supply voltage can be reduced. still,
Since the reduction in the current capability of the boost power supply can be reduced, an increase in the capacitor area for securing the current capability, that is, an increase in the boost circuit area can be suppressed.

[0025]

As described above, according to the ring oscillator of the present invention, the decrease in the oscillation frequency when the power supply voltage becomes low is suppressed, and the fluctuation of the oscillation frequency with respect to the change in the power supply voltage is reduced. be able to.

[Brief description of the drawings]

FIG. 1 is a circuit configuration diagram of a ring oscillator according to one embodiment of the present invention.

FIG. 2 illustrates a resistance, a first capacitor, a second capacitor, a first pass transistor, and a second capacitor of the ring oscillator according to the embodiment.
FIG. 2 is an explanatory diagram of the operation of the circuit portion of the pass transistor, and FIG.
2A is an explanatory diagram when the first power supply voltage is high (it is near the rated value), and FIG. 2B is an explanatory diagram when the first power supply voltage is low.

FIG. 3 is an explanatory diagram illustrating the power supply voltage dependence of the oscillation frequency in the ring oscillator of the present invention.

FIG. 4 is a circuit configuration diagram of a conventional ring oscillator.

FIG. 5 is an explanatory diagram illustrating the power supply voltage dependence of the oscillation frequency in a conventional ring oscillator.

[Explanation of symbols]

IV1 to IV2n + 1, IVo: inverter, R: resistor, CAP1: first capacitor, CAP2: second capacitor, Tr1, Tr2: first pass transistor, Tr
3, Tr4: second pass transistor, Tr1: first P-channel transistor, Tr2: first N-channel transistor, Tr3: second P-channel transistor, Tr4 ...
First N-channel transistor, Vcc ... first power supply voltage,
GND: second power supply voltage (ground potential), N: node, Ro
n1, Ron2: ON resistance, OUT: Output signal.

Claims (6)

[Claims] 1. An odd number of inverters which are cascaded and the last inverter output is supplied to the first inverter input, one end of which is the output of an arbitrary stage inverter, and the other end of which is the next stage of the inverter. A resistor connected to the input, a capacitor connected at one end to the second power supply, one end connected to the other end of the resistor, the other end connected to the other end of the capacitor, and a voltage of the first power supply A variable resistor having a resistance value which is small when the value is near the rated value, and whose resistance value increases as the voltage of the first power supply decreases. 2. The variable resistor, wherein a first diffusion layer is connected to the other end of the resistor, a second diffusion layer is connected to the other end of the capacitor, and a gate is connected to the first power supply. 2. The ring oscillator according to claim 1, further comprising a first conductivity type transistor. 3. The variable resistor has a first diffusion layer connected to the other end of the resistor, a second diffusion layer connected to the other end of the capacitor, and a gate connected to the second power supply. 3. The ring oscillator according to claim 2, further comprising a second conductivity type transistor. 4. An odd number of inverters which are cascade-connected and the output of the last stage inverter is supplied to the input of the front stage inverter; one end is connected to the output of the arbitrary stage inverter, and the other end is connected to the next stage of the inverter. A resistor connected to the input, a first capacitor connected to the first power supply at one end; a second capacitor connected at one end to the second power supply; one end connected to the other end of the resistor; A first variable resistor connected to the other end of the first capacitor, the resistance value being small when the voltage of the first power supply is near the rated value, and the resistance value increasing as the voltage of the first power supply decreases And one end is connected to the other end of the resistor, and the other end is connected to the other end of the second capacitor. When the voltage of the first power supply is near the rated value, the resistance is small, The resistance value increases as the voltage decreases Ring oscillator and a second variable resistor. 5. The first variable resistor has a first diffusion layer connected to the other end of the resistance, a second diffusion layer connected to the other end of the first capacitor, and a gate connected to the first power supply. A first transistor of a first conductivity type connected to the second variable resistor, wherein a second diffusion layer is provided at the other end of the resistor, and a first diffusion layer is provided at the other end of the second capacitor. 5. The ring oscillator according to claim 4, further comprising a second transistor of a first conductivity type connected to each other and having a gate connected to said first power supply. 6. The first variable resistor, wherein a first diffusion layer is connected to the other end of the resistance, a second diffusion layer is connected to one end of the first capacitor, and a gate is connected to the second power supply. Wherein the second variable resistor has a second diffusion layer connected to the other end of the resistor, and a first diffusion layer connected to one end of the second capacitor. The ring oscillator according to claim 5, further comprising a second second conductivity type transistor having a gate connected to said second power supply.