JPH05299982A - Ring oscillator - Google Patents

Abstract

PURPOSE:To obtain a ring oscillator by which an output always having a constant oscillation frequency is generated regardless of the change of a temperature. CONSTITUTION:This device is equipped with the odd number of invertors 1A having a pair of different conductive MOS transistors 11 and 12 and a resistor elements 13 or 14 connected between the main electrode of at least one of the pair of MOS transistors 11 and 12, that is, a drain or a source and a power terminal and having no temperature dependency or whose resistance value is decreased as a temperature is increased.

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 in particular, for example, in a semiconductor device, in the case of obtaining a signal having a constant cycle without temperature dependence, or in the case of obtaining a signal in which the cycle becomes shorter as the temperature rises. The present invention relates to a ring oscillator suitable for use in.

[0002]

2. Description of the Related Art FIG. 3 is a circuit diagram showing a conventional ring oscillator. In the figure, 1 is an inverter that inverts the phase of an input signal, 2 is an inverter that is connected to the inverter 1 and that inverts the phase of its output signal, and 3 is that the output signal of the inverter 2 is supplied to one input end and the other input end In the NAND circuit to which a timer-on signal S _T is supplied from the outside, the output signal of the NAND circuit 3 is fed back to the input side of the inverter 1. The operation / non-operation of the ring oscillator is substantially determined by the timer-on signal S _T as the oscillation operation control signal of the ring oscillator supplied to the other input terminal of the NAND circuit 3.

FIG. 4 shows an example of the specific circuit of FIG. 3, in which the inverter 1 is a P-channel type MOS transistor 1.
1 and N-channel type MOS transistor 12, P
Channel type MOS transistor 11 and N channel type MO
The gates and drains of the S transistors 12 are commonly connected, the source of the P-channel type MOS 11 is connected to the positive power supply terminal Vcc, and the source of the N-channel type MOS transistor 12 is grounded.

The inverter 2 comprises a P-channel type MOS transistor 21 and an N-channel type MOS transistor 22, and the gates and drains of the P-channel type MOS transistor 21 and the N-channel type MOS transistor 22 are commonly connected. The common connection point of the gates is the P-channel type MOS transistor 11 and the N-type.
The drains of the channel-type MOS transistors 12 are connected to a common connection point. The source of the P-channel MOS transistor 21 is connected to the positive power supply terminal Vcc,
The source of the channel type MOS transistor 22 is grounded.

The NAND circuit 3 comprises P-channel type MOS transistors 31 and 32 and N-channel type MOS transistors 33 and 34, and the gates and drains of the P-channel type MOS transistor 31 and the N-channel type MOS transistor 33 are commonly connected. The common connection point of the gates is connected to the common connection point of the drains of the P-channel MOS transistor 21 and the N-channel MOS transistor 22.

Further, the P-channel type MOS transistor 31
Is connected to the positive power supply terminal Vcc, and the source of the N-channel type MOS transistor 33 is an N-channel type M
It is grounded via the source-drain of the OS transistor 34. The source and drain of the P-channel MOS transistor 32 are the P-channel MOS transistor 31.
Connected in parallel to the source-drain of a P-channel MO
The common connection point between the drains of the S transistor 31 and the N-channel MOS transistor 33 is a P-channel MOS transistor.
Transistor 11 and N-channel MOS transistor 1
2 is connected to the common point of each gate. Then, the timer-on signal S _T is supplied to the gates of the P-channel type MOS transistor 32 and the N-channel type MOS transistor 34.

Next, the operation of FIG. 4 will be described with reference to FIG. When the timer-on signal S _T supplied to the gates of the P-channel type MOS transistor 32 and the N-channel type MOS transistor 34 is at a low level as shown in FIG. 5A, the P-channel type MOS transistor 32 is turned on. , N-channel MOS transistor 34
Is turned off and the ring oscillator is in a non-operating state, and at this time, the output signals S ₂ , S ₃ and S ₁ of the inverters 1 and 2 and the NAND circuit 3 are respectively in FIG. 5 (c), (d) and (b). ), It is always low level, high level and high level.

Next, the P-channel MOS transistor 3
2 and the timer-on signal S _T supplied to the gates of the N-channel MOS transistor 34 becomes high level as shown in FIG. 5A, the P-channel MOS transistor 32 is turned off and the N-channel MOS transistor 34 is turned off.
Turns on, and the ring oscillator becomes active. Then, when the signal S ₁ becomes low level as shown in FIG. 5B almost in synchronization with the rising of the timer-on signal S _T , the P-channel MOS transistor 1 of the inverter 1 is
1 is turned on and the N-channel MOS transistor 12 is turned off, so that a high level output signal S ₂ as shown in FIG. 5C is obtained at the output side of the inverter 1.

This output signal S ₂ is supplied to the inverter 2 at the next stage, whereby the P-channel type MO of the inverter 2 is supplied.
The S-transistor 21 is turned off, the N-channel type MOS transistor 22 is turned on, and the output side of the inverter 2 is shown in FIG.
A low level output signal S ₃ as shown in (d) is obtained. This output signal S ₃ is supplied to the NAND circuit 3 in the next stage, whereby the P-channel type MOS transistor 31 of the NAND 3 is turned on and the N-channel type MOS transistor 3 is turned on.
3 is turned off, and a high level output signal S ₁ as shown in FIG. 5B is obtained at the output side of the NAND circuit 3. Thus, the signals S ₁ , S ₂ , S ₃ transmit their respective changes,
High level and low level are repeated at regular intervals. This state is called the oscillation (operating state) of the ring oscillator.

FIG. 6 shows a simulation result of the temperature dependence of the oscillation period in the conventional ring oscillator having the structure shown in FIG. Here, the size of the MOS transistor of each inverter is P-channel type MOS.
Transistor gate length is 60μm, gate width is 4μ
m, N-channel MOS transistor has a gate length of 12
The simulation results are for 0 μm, a gate width of 4 μm, and a power supply voltage Vcc of 5V.

From this result, the temperature is from 0 ° C to 80 ° C.
Change to 5.6, the oscillation period of the ring oscillator changes to 5.6.
It can be seen that there is a large change from 3 μs to 8.05 μs. That is, for example, if the period of the signals S _{1 to} S ₃ at a certain temperature lower than 80 ° C. is as shown in FIG. 5, the period of these signals S _{1 to} S ₃ is 8
As the temperature rises toward 0 ° C, it becomes longer.

[0012]

Since the conventional ring oscillator is constructed as described above, the ring oscillator is affected by the temperature dependence of the P-channel type MOS transistor and the N-channel type MOS transistor forming the inverter and the NAND circuit. The oscillation cycle changes, and when the oscillation cycle of this ring oscillator is used especially for refreshing DRAM, for example, the cycle of the refresh characteristic becomes longer as the temperature becomes higher, and the refresh characteristic becomes worse as the temperature becomes higher. On the other hand, there was a problem that it worked disadvantageously.

The present invention has been made to solve the above problems, and an object thereof is to obtain a ring oscillator which has little temperature dependence on the oscillation period or has a shorter oscillation period as the temperature rises. And

[0014]

A ring oscillator according to a first aspect of the present invention is provided with a pair of transistors having different conductivity types, a transistor connected between at least one main electrode of the pair of transistors, and a power supply terminal. It is provided with an odd number of inverters each having a resistance element which has no resistance or whose resistance value becomes smaller as the temperature rises.

A ring oscillator according to a second aspect of the present invention is connected between a pair of transistors having different conductivity types and a main electrode of at least one of the pair of transistors and a power supply terminal, and has a smaller resistance value as the temperature rises. In this case, an odd number of inverters are provided, each of which has a resistance element that becomes smaller as the temperature becomes higher or becomes higher, and the resistance value of the resistance value is larger than the ON resistance of the transistor.

[0016]

According to the invention of claim 1, when the on-resistance of the transistor is not negligible with respect to the resistance value of the resistance element, the on-resistance of the transistor is originally
Since it has the property of increasing with increasing temperature,
In such a case, as each resistance element, one having a characteristic that the resistance value becomes smaller as the temperature rises is used. When the on-resistance of the transistor is negligible with respect to the resistance value of the resistance element, the temperature dependence of the circuit is substantially determined by the resistance element temperature dependence. A resistance element having no temperature dependence is used. This will, in any case,
It is possible to obtain a ring oscillator that can generate an output with a constant oscillation period regardless of changes in temperature.

According to the second aspect of the invention, when the on resistance of the transistor is negligible with respect to the resistance value of the resistance element, the resistance value decreases as the temperature of the resistance element increases. Use the one that shows the characteristics. Alternatively, when the on resistance of the transistor is not negligible with respect to the resistance value of the resistance element, a resistance element having a characteristic that the resistance value becomes smaller as the temperature rises is used. Increase the ratio of the element value to the on-resistance of the transistor. Thus, in any case, it is possible to obtain a ring oscillator that can generate an output in which the oscillation cycle becomes shorter as the temperature becomes higher.

[0018]

EXAMPLES Example 1. An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a circuit diagram showing an embodiment of the present invention. The parts corresponding to those in FIG. 4 are designated by the same reference numerals, and detailed description thereof will be omitted. In FIG. 1, 1A is an inverter that inverts the phase of an input signal, 2A is an inverter that is connected to the inverter 1A and that inverts the phase of its output signal, 3A
Is a NAND circuit in which the output signal of the inverter 2A is supplied to one input terminal and the timer-on signal S _T from the outside is supplied to the other input terminal.
Is output to the input side of the inverter 1A. The operation / non-operation of the ring oscillator is substantially determined by the timer-on signal S _T as the oscillation operation control signal of the ring oscillator supplied to the other input terminal of the NAND circuit 3A.

The inverter 1A includes a P-channel type MOS transistor 11 and an N-channel type MOS transistor 12.
And a resistance element 13 that exhibits little temperature dependence or that the resistance value decreases as the temperature rises.
And 14, and is a P-channel MOS transistor 1
The gates and drains of the 1 and N-channel MOS transistors 12 are commonly connected. The source of the P-channel type MOS 11 is connected to the positive power supply terminal Vcc via the resistance element 13, and the source of the N-channel type MOS transistor 12 is grounded via the resistance element 14.

The inverter 2A includes a P-channel type MOS transistor 21 and an N-channel type MOS transistor 22.
And a resistance element 23 that exhibits little temperature dependence or a characteristic that the resistance value decreases as the temperature rises.
And 24, and is a P-channel MOS transistor 2
The gates and drains of the 1 and N-channel MOS transistors 22 are commonly connected. The common connection point of the gates is connected to the common connection point of the drains of the P-channel MOS transistor 11 and the N-channel MOS transistor 12. Also, P channel type M
The source of the OS transistor 21 is connected to the positive power supply terminal Vcc via the resistance element 23, and the source of the N-channel MOS transistor 22 is grounded via the resistance element 24.

The NAND circuit 3A has almost no temperature dependence with the P-channel type MOS transistors 31 and 32 and the N-channel type MOS transistors 33 and 34, or has a characteristic that the resistance value becomes smaller as the temperature rises. P-channel type MOS composed of the resistance elements 35 and 35 shown
Transistor 31 and N-channel MOS transistor 3
Each gate and each drain of 3 are commonly connected. The common connection point of the gates is connected to the common connection point of the drains of the P-channel MOS transistor 21 and the N-channel MOS transistor 22.

Further, the P-channel type MOS transistor 31
Is connected to the positive power supply terminal Vcc through the resistance element 35, and the source of the N-channel type MOS transistor 33 is the source of the N-channel type MOS transistor 34.
It is grounded via the drain and the resistance element 36. The source-drain of the P-channel type MOS transistor 32 is connected in parallel to the source-drain of the P-channel type MOS transistor 31.
1 and the common connection point of the drains of the N-channel type MOS transistor 33 is the P-channel type MOS transistor 11
And N-channel MOS transistor 12 are connected to a common point of their respective gates. Then, the timer-on signal S _T as the oscillation operation control signal of the ring oscillator is supplied to the gates of the P-channel type MOS transistor 32 and the N-channel type MOS transistor 34.

In this embodiment, when the on-resistance of the MOS transistor is not negligible with respect to the resistance value of each resistance element, the on-resistance of the MOS transistor originally increases as the temperature rises. In such a case, each resistance element having a characteristic that the resistance value becomes smaller as the temperature rises is used, and the resistance value of each resistance element is different from that of the MOS transistor. When the on-resistance is negligible, the temperature dependence of the circuit is substantially determined by the resistance element temperature dependence, so in such a case, each resistance element having no temperature dependence should be selected. Shall be used. Here, as the resistance element showing the characteristic that the resistance value becomes smaller as the temperature becomes higher, for example, a resistance element made of polysilicon or polycide can be considered.

Next, the operation will be described. The basic operation that the ring oscillator oscillates is the same as that of the conventional example, and therefore its explanation is omitted. In this embodiment, as described above, the resistance elements 13 and 14, 23 and 24 are connected to the sources of the MOS transistors 11 and 12, 21 and 22, respectively, and the resistance element 35 is connected to the source of the MOS transistor 31. In addition, the resistance element 36 is connected to the source of the MOS transistor 33 via the MOS transistor 34.
When the on-resistance of the transistor is not negligible, even if the on-resistance of each MOS transistor increases as the temperature rises, the resistance value of each resistance element decreases as the temperature rises. The temperature dependence of the MOS transistor is substantially offset by the temperature dependence of the corresponding resistance element, and the circuit as a whole has no temperature dependence. As a result, the cycle of each output of the inverters 1A, 2A and the NAND circuit 3A is always constant regardless of the temperature.

Further, when the on-resistance of the MOS transistor is negligible with respect to the resistance value of each resistance element, each resistance element which does not have temperature dependence is used as described above, so that the circuit as a whole is used. Becomes independent of temperature. As a result, also in this case, the inverter 1A,
The cycle of each output of 2A and NAND circuit 3A is always constant regardless of temperature.

FIG. 2 is a diagram showing a simulation result of temperature dependence of the ring oscillator having the circuit configuration as shown in FIG. 2, waveform a, for example represents a transition of at signal S ₃ of the waveform to a temperature 0 ° C, the waveform b represents the transition of the waveform of the in the signal S _3, for example, temperature 27 ° C and 80 ° C, Therefore, in the cycle of the signal S ₃ , the temperature is 0 ° C,
It can be seen that there is almost no difference at the three points of 27 ° C and 80 ° C. In addition, although this simulation is not shown, similar results were obtained for the other signals S ₁ and S ₂ .

As described above, in this embodiment, it is possible to obtain a ring oscillator which can always generate an output having a constant oscillation period irrespective of a change in temperature. For example, a reference potential generating circuit of a DRAM using a charge pump. It is useful for such purposes.

Example 2. In the first embodiment, when the on resistance of the MOS transistor is negligible with respect to the resistance value of each resistance element, the resistance value of each resistance element decreases as the temperature increases. As shown in the figure, or if the on resistance of the MOS transistor is not negligible with respect to the resistance value of each resistance element, the resistance value decreases as the temperature of each resistance element increases. It is also possible to use those exhibiting characteristics and increase the ratio of the value of each resistance element to the ON resistance of the MOS transistor at that time.

By using such a resistance element,
In any of the embodiments, it is possible to obtain a ring oscillator that can generate an output in which the oscillation cycle becomes shorter as the temperature rises, and particularly, in a semiconductor device that requires a shorter refresh cycle as the temperature rises, for example, a DRAM.
It is useful for refreshing etc.

In each of the above embodiments, the case where the resistance element is inserted into all of the MOS transistors has been described, but if a desired cycle can be obtained with respect to a predetermined temperature dependence in the entire circuit. It is not necessary to insert resistance elements in all MOS transistors. A NOR circuit may be used instead of the NAND circuit.

[0031]

As described above, according to the invention of claim 1,
An inverter having a pair of transistors having different conductivity types and a resistance element connected between at least one main electrode of the pair of transistors and a power supply terminal and having no temperature dependence or a resistance element having a smaller resistance value as the temperature rises. Since it has an odd number of capacitors, it is possible to obtain a ring oscillator that can always generate an output having a constant oscillation period irrespective of temperature changes, and is useful, for example, in a reference potential generating circuit of a DRAM using a charge pump. The effect is that

According to the second aspect of the present invention, a pair of transistors having different conductivity types are connected between at least one main electrode of the pair of transistors and the power supply terminal, and the resistance becomes smaller as the temperature rises. Since the resistance value becomes smaller as the temperature becomes higher or the temperature becomes higher, and an odd number of inverters having resistance elements having a large proportion of the resistance value to the ON resistance of the transistor are provided, the oscillation cycle becomes shorter as the temperature becomes higher. It is possible to obtain a ring oscillator capable of generating a noise, and it is particularly useful for refreshing a semiconductor device, such as a DRAM, which requires a shorter refresh cycle as the temperature rises.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention.

FIG. 2 is a diagram for explaining the operation of one embodiment of the present invention.

FIG. 3 is a configuration diagram showing a conventional ring oscillator.

FIG. 4 is a circuit diagram showing a specific example of FIG.

FIG. 5 is a waveform diagram for explaining the operation of the conventional example.

FIG. 6 is a diagram for explaining the operation of a conventional example.

[Explanation of symbols]

 1A, 2A Inverter 3A NAND circuit 11,12 MOS transistor 13,14 Resistor 21,22 MOS transistor 23,24 Resistor 31-34 MOS transistor 35,36 Resistor

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[Procedure amendment]

[Submission date] December 10, 1992

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0016

[Correction method] Change

[Correction content]

[0016]

According to the invention of claim 1, when the on-resistance of the transistor is not negligible with respect to the resistance value of the resistance element, the on-resistance of the transistor is originally
Since it has the property of increasing with increasing temperature,
In such a case, as each resistance element, one having a characteristic that the resistance value becomes smaller as the temperature rises is used. When the on-resistance of the transistor is negligible with respect to the resistance value of the resistance element, the temperature dependence of the circuit is substantially determined by the resistance element temperature dependence. A resistance element having no temperature dependence is used. This will, in any case,
Regardless of changes in temperature, always Ru can be obtained ring oscillator capable of generating an output having a constant oscillation period.

[Procedure Amendment 2]

[Document name to be amended] Statement

[Name of item to be corrected] 0027

[Correction method] Change

[Correction content]

As described above, in this embodiment, it is possible to obtain a ring oscillator which can always generate an output having a constant oscillation cycle regardless of a change in temperature. For example, a reference cycle generation circuit of a DRAM using a charge pump. It is useful for such purposes.

[Procedure 3]

[Document name to be amended] Statement

[Correction target item name] 0031

[Correction method] Change

[Correction content]

[0031]

As described above, according to the invention of claim 1,
An inverter having a pair of transistors having different conductivity types and a resistance element connected between at least one main electrode of the pair of transistors and a power supply terminal and having no temperature dependence or a resistance element having a smaller resistance value as the temperature rises. Since it has an odd number of ring oscillators, it is possible to obtain a ring oscillator that can always generate an output having a constant oscillation period regardless of changes in temperature. For example, it is useful as a reference period generation circuit of a DRAM using a charge pump. The effect is that

Claims (2)

[Claims] 1. A pair of transistors having different conductivity types,
An odd number of inverters having a resistance element that is connected between at least one main electrode of the pair of transistors and a power supply terminal and has a resistance value that does not depend on temperature or that becomes higher as the temperature rises are provided. Ring oscillator to 2. A pair of transistors having different conductivity types,
It is connected between at least one of the main electrodes of the pair of transistors and the power supply terminal, and the resistance value becomes smaller as the temperature rises, or becomes smaller as the temperature rises, and the resistance value becomes smaller than the on-resistance of the transistor. A ring oscillator comprising an odd number of inverters having a large proportion of resistance elements.