JP2003332889A - Oscillation circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To stably operate an oscillation circuit by preventing the production yield from lowering due to nonuniformity in production. <P>SOLUTION: A switch S1 is changed-over by a comparator X1, and a switch S2 is changed-over by a comparator X2, so that a capacitor C is charged/ discharged to oscillate the voltage Vc with voltages VH and VL as the vertical peaks. In this case, a negative offset voltage Vofs1 is given when the output is changed from 'H' into 'L' at the non-inverse input side of the comparator X1, and a normally negative offset voltage Vofs2 (<Vofs1) is given to the non-inverse input side of the comparator X2. Thus, a sequence that the comparator X2 is inverted after the inversion of the comparator X1 is surely secured. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a current control type oscillation circuit for generating a sawtooth wave, a triangular wave, a rectangular wave or the like in a semiconductor integrated circuit device (hereinafter referred to as an IC).

[0002]

2. Description of the Related Art Oscillation circuits that generate saw-tooth waves and triangular waves are widely used in devices that control electric power such as power supplies and motors, especially as part of an important configuration of PWM control circuits. The PWM control compares the output state of the control circuit, which is input via a sensor, with the sawtooth wave or triangular wave that serves as a reference, and changes the output duty of the power switching element to supply power that matches the load. This is the control method. This circuit is made into an IC and widely used in terms of accuracy and cost.

As one of the factors that determine the accuracy of this control circuit, there is a reference signal generating circuit that serves as a duty reference. As the reference signal, a sawtooth wave or a triangular wave is often used because of easy duty control. A current control type oscillation circuit as shown in FIG. 4 has been used as a sawtooth wave or triangular wave generation circuit suitable for IC and capable of obtaining required accuracy. This configuration will be described.

A power supply Vcc and an output terminal OUT to which a capacitor C for determining the time constant of a sawtooth wave or a triangular wave is connected.
A current source I1 for charging the capacitor C is connected between and, and another current source I2 for discharging the capacitor C is connected to the ground via a switch S2. The inverting input (−) of the comparator X2 whose output is connected to control the switch S2 is connected to the output terminal OUT,
The non-inverting input (+) is connected to the output of the comparator X1.

The inverting input of the comparator X1 is the reference voltage V
It is connected to the output of the switch S1 that switches between H and VL, and the non-inverting input is connected to the output terminal OUT.
The output of the comparator X1 is connected to the control terminal of the switch S1. The switch S1 is a comparator X
When the output of 1 is "H", the reference voltage VL is selected, and when it is "L", the reference voltage VH is selected. Here, the relationship between the reference voltages VH and VL is set as “VH> VL”. These reference voltages VH and VL and the switch S1 form a reference voltage generating circuit. The relation between the currents of the current sources I1 and I2 is set as "I1 <I2". The switch S2 is a comparator X
When the output of 2 is "H", it is turned on to connect the current source I2 to the ground, and when it is "L", it is turned off to open it.

Next, the operation will be described. In the initial state, it is assumed that the voltage Vc of the output terminal OUT is the ground potential and the higher reference voltage VH is selected as the reference voltage. In this case, the outputs of the comparators X1 and X2 are "L",
The capacitor C is charged by the current from the current source I1. When the charging of the capacitor C progresses and the output voltage Vc exceeds the reference voltage VH, the output of the comparator X1 becomes “H”.
And the switch S1 selects the reference voltage VL, and the non-inverting input of the comparator X2 becomes “H”. Then, the output of the comparator X2 is inverted to "H", the switch S2 is closed, and the electric charge of the capacitor C is discharged by the current source I2. When the discharge of the capacitor C progresses and the voltage of the output voltage Vc decreases and falls below VL, the output of the comparator X1 inverts to "L" again, and the comparator X
The output of 2 is also inverted to "L", so that the capacitor C is charged again. The reference voltage VH is selected by switching the switch S1. By repeating this operation, the output voltage Vc becomes a triangular waveform having the reference voltages VH and VL as upper and lower peaks. When the current sources I1 and I2 are composed of resistors, a sawtooth wave is formed.

FIG. 5 is a circuit which has the same function as that of the oscillation circuit of FIG. 4 and further aims to reduce the number of elements for cost reduction. In order to reduce the number of input elements of the comparator,
The inputs of the two comparators X1 and X2 are connected in parallel. In the oscillator circuit of FIG. 4, the output of the comparator X1 and the output of the switch S1 change in inverse logic, so that the same output should be obtained even if the inverting input of the comparator X2 is connected to the output of the switch S1. Therefore, FIG.
Even if the inverting inputs of the comparators X1 and X2 are commonly connected as described above, the same operation as in FIG. 4 can be expected.

Further, although level shift transistors are added to the comparators X1 and X2 in order to expand the input voltage range (not shown), since the input logic is the same, these are the comparators X1 and X2. Can be shared. That is, with the configuration of FIG. 5, at least two transistors can be eliminated.

[0009]

However, in the configuration shown in FIG. 5, since the reference voltage switching by the comparator X1 and the charging / discharging of the capacitor C by the comparator X2 are independently performed, the comparator X1 may be affected by disturbance or comparator offset. When the switching of (1) is delayed much later than the comparator X2, the comparator X1 does not switch, and the capacitor C is charged and discharged only by switching the comparator X2 without switching the reference voltage. As a result, the output voltage Vc may continue to change in a narrow range around the reference voltage, and the sawtooth wave or the triangular wave may not be output.

In actuality, during mass production of a product employing this circuit, the distribution range of the offset of the comparator is widened due to manufacturing variations, which causes the sawtooth wave or triangular wave oscillator circuit not to operate and the output voltage thereof. However, there are many oscillation circuits that are stable at the voltage value at the end of the waveform, which causes a problem that product yield is deteriorated.

An object of the present invention is to solve the above problems and to provide an oscillation circuit which secures stable operation while keeping the advantage of the circuit shown in FIG. 5 which can be constituted by a small number of elements.

[0012]

According to a first aspect of the present invention, a reference voltage circuit for switching and outputting one of a high reference voltage and a low reference voltage and an output of the reference voltage circuit is connected to an inverting input. One end of a capacitor whose other end is grounded is connected to the inverting input, and when the output becomes “H”, the voltage of the reference voltage circuit is switched to the low reference voltage, and when it becomes “L”, the voltage of the reference voltage circuit is changed to the above-mentioned A first comparator for switching to a high reference voltage, a first current source connected between one end of the capacitor and a power supply, and a second current source connected between one end of the capacitor and ground via a switch , The output of the reference voltage circuit is connected to the inverting input, one end of the capacitor is connected to the non-inverting input, the switch is turned on when the output becomes “H”, and the switch is turned on when the output becomes “L”. In the oscillation circuit and a second comparator to off, the first when an output of said first comparator is switched from "H" to "L" 1
The first negative offset voltage is applied to the non-inverting input side of the comparator and the second negative offset voltage smaller than the first negative offset voltage is applied to the non-inverting input side of the second comparator at all times. The oscillator circuit is characterized by that.

According to a second aspect of the present invention, in the oscillator circuit according to the first aspect, the first comparator includes first and second transistors of a first conductivity type that are differentially connected, and the first and second transistors. A third transistor of a second conductivity type, the collector of which is connected to the collector of the first transistor;
A collector and a base of the transistor are connected to each other, and a base of the second transistor is connected to a base of the third transistor, and the second comparator is differentially connected. First and fifth conductive type fifth and sixth transistors, a second conductive type seventh transistor whose collector is connected to the collector of the fifth transistor, and collector of the sixth transistor And a base connected to the base of the seventh transistor and an eighth transistor of the second conductivity type connected to the base of the seventh transistor. The reference power supply circuit includes first and second transistors connected between a power supply and ground. And a collector and an emitter are connected between a common connection point of the first and second resistors and ground, and a base is connected to a common connection point of the collectors of the first and third transistors. It was made from the second conductive type ninth transistor of said switch base the fifth, seventh
Of a second conductivity type tenth transistor connected to a common collector connection point of the second collector and having a collector connected to the second current source, wherein the bases of the first and fifth transistors are the first and second transistors. Connected to a common connection point of the resistors, the bases of the second and sixth transistors are connected to one end of the capacitor, and the seventh transistor has a larger emitter area than the eighth transistor. The oscillator circuit is characterized by.

According to a third aspect of the present invention, in the oscillator circuit according to the second aspect, the seventh and eighth transistors are replaced with transistors having the same emitter area, and the emitter of the eighth transistor is a second transistor. The oscillator circuit is characterized in that the resistor 3 is connected.

The invention according to claim 4 is the invention according to claim 2 or 3.
The eleventh transistor of the first conductivity type for level shifting is connected between the bases of the first and fifth transistors and a common connection point of the first and second resistors in the oscillator circuit described in the above. The level shift first between the bases of the second and sixth transistors and one end of the capacitor.
The oscillating circuit is characterized in that the twelfth conductive type transistor is connected.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION The above-mentioned problem is caused by the influence of the offset voltage or the like of the comparator X1.
The reason is that the comparator X2 operates before the output of the above-mentioned does not change and the reference voltage is not switched, and as a result, the reference voltage is not switched. In order to solve this problem, the operation timing of the comparator X2 must be the same at the upper and lower ends of the oscillation waveform.
It may be configured to occur after 1.

Therefore, first, at the upper end of the oscillation waveform, a negative input from the beginning with respect to the non-inverting input (+) of the comparator X2 is ensured so that the output change of the comparator X2 with respect to the change of the output voltage Vc is surely delayed as compared with the comparator X1. The offset voltage Vofs2 may be provided. At this time, the comparators X1 and X2 may have several meters due to manufacturing variations.
Since an input offset voltage of about V may generally exist, the offset voltage Vofs2 is set to several mV to several tens of mV in order to cancel it and obtain a sufficient margin for the operation of the comparator X1. To do.

The offset voltage Vofs2 acts at the lower end of the oscillation waveform in the opposite manner to the upper end, that is, the output of the comparator X2 is changed first.
Therefore, at the lower end, the negative offset Vofs1 may be provided to the non-inverting input (+) side of the comparator X1 only when the output of the comparator X1 switches from "H" to "L". At that time, the offset voltage Vofs1 is set to the offset voltage V
By setting the value of several mV to several tens of mV larger than ofs2, it is possible to cancel manufacturing variations and offset voltage Vofs2.

With such a configuration, the output inversion of the comparator X2 operates after the output inversion of the comparator X1 and a correct reference voltage can be always selected corresponding to the output of the comparator X2. It is possible to prevent erroneous operation due to variations in the timing of the comparator operation and stabilize the operation of the current control type oscillation circuit. This will be described in detail below.

FIG. 1 is a block diagram showing the configuration of an oscillator circuit according to an embodiment of the present invention. X1 and X2 are comparators,
Vofs2 is a reference voltage that represents the input offset voltage applied to the non-inverting input side of the comparator X2, VH is a reference voltage that determines the upper peak of the oscillation waveform, VL is a reference voltage that determines the lower peak of the oscillation waveform, and S1 is the reference voltage. A switch that switches VH and VL by external logic input,
C is a capacitor, I1 and I2 are current sources for supplying a charging / discharging current to the capacitor C, S2 is a switch for turning on / off the connection of the current source I2 to the ground, and Vc is an oscillation output voltage of this circuit. The reference voltages VH and VL and the switch S1 form a reference voltage generating circuit.

The oscillator circuit of FIG. 1 operates as follows. As an initial value, it is assumed that the switch S1 selects the reference voltage VH side, and the output voltage Vc is zero, that is, the ground potential. Further, the switch S1 operates so as to select the reference voltage VH when the output of the comparator X1 is "L" and the reference voltage VL when the output of the comparator X1 is "H". Further, the switch S2 is configured to connect the current source I2 to the ground when the output of the comparator X2 is “H” and open it when the output of the comparator X2 is “L”.

At this time, since the reference voltage VH is input to the inverting input and the output voltage Vc, that is, the ground potential is input to the non-inverting input, the inputs of the comparators X1 and X2 are both "L", Since the current source I2 is not connected, the capacitor C is charged by the current source I1. When the output voltage Vc rises as the capacitor C is charged and exceeds the reference voltage VH, the output of the comparator X1 becomes "H" and the switch S1 selects the reference voltage VL.

At this time, since the input voltage of the non-inverting input of the comparator X2 is reduced by the offset voltage Vofs2, the non-inverting input of the comparator X2 has not reached the reference voltage VH and the output of the comparator X2 is still. “L”, the switch S2 is open, and the capacitor C is continuously charged. Switch S1
When the output of is determined as the reference voltage VL and input to the inverting input of the comparator X2, the voltage of the non-inverting input of the comparator X2 becomes higher than the voltage of the inverting input, and the output of the comparator X2 becomes “H”. , Switch S2 is closed and capacitor C is discharged.

Next, when the output voltage Vc drops as the capacitor C is discharged, the non-inverting input voltage is reduced by the offset voltage Vofs2 in the comparator X2, but the output is " Since the input voltage is reduced by the negative offset Vofs1 larger than Vofs2 only when switching from “H” to “L”, the non-inverting input of the comparator X1 changes the voltage VL before the non-inverting input of the comparator X2. Below, the output of the comparator X1 becomes “L”, and the switch S1 selects the voltage VH. At this time, in the comparator X2, since the input voltage is increased more than the comparator X1 by the offset voltage difference (Vofs1−Vofs2), the non-inverting input of the comparator X2 does not reach the reference voltage VL, and the comparator X2 has a non-inverting input. The output still holds "H", short-circuiting the switch S2, and continuing discharging from the capacitor C. The output of the switch S1 is the reference voltage VH
When the input is input to the inverting input of the comparator X2, the voltage of the non-inverting input of the comparator X2 becomes lower than that of the inverting input, the output of the comparator X2 becomes “L”, the switch S2 opens, and the capacitor S2 opens. C changes from discharge to charge.

Through this series of operations, the output voltage Vc has an oscillation waveform with a maximum peak value of VH and a minimum peak value of VL.

FIG. 2 shows an example in which the oscillation circuit of FIG. 1 is concretely configured in a semiconductor integrated circuit. The outputs of the comparator X2 having the negative offset voltage Vofs2 of FIG. 1 and the output of the comparator X1 are "H". → A negative offset Vof is applied to the non-inverting input side of the comparator X1 only when switching to "L".
The comparator X1 having s1 is realized in a circuit without using an external reference voltage.

Bipolar transistors PNP2, PNP
4, NPN1 and NPN2 form the comparator X1 of FIG. 1, and bipolar transistors PNP5, PNP6 and N
PN3 and NPN4 form a comparator X2. The transistors PNP2 and PNP5 are the inverting input elements, and the transistors PNP4 and PNP6 are the non-inverting input elements. Vcc is connected to the power supply that operates this circuit. The transistors NPN1 and NPN2, and the transistors NPN3 and NPN4 form a current mirror circuit that serves as a load of the differential circuit. Transistor PN
P1, PNP3 and current source I3 are comparators X1, X
2 is a component element of both, and is a transistor PNP1
Is connected to the inverting input side of both comparators for common level shifting, the transistor PNP3 is connected to the non-inverting input side for common level shifting, and the current source I3 biases two sets of differential circuits including the transistor PNP2 and the like. It is connected as a current source to supply.

In this circuit, the reference voltage input to the comparator X1 is the power supply voltage Vcc and the resistors R1, R2 and R3.
It is obtained by resistance-dividing with, etc., and the transistor NPN5 is used as a switch for switching the resistance division. When the output voltage Vc is low, the transistor NPN5 is turned off through the differential circuit, and as a result, the comparator X1,
The voltage input to the base of the transistor PNP1 corresponding to the inverting input of X2 corresponds to the reference voltage VH, and is given by VH = VccR2 / (R1 + R2).

At this time, the transistor NPN6 functions as a switch controlled by the output of the comparator X2 and is off. Therefore, the capacitor C is charged and the output voltage Vc rises. Output voltage V
When c exceeds the reference voltage VH, the transistor NPN5 is turned on, and the voltage input to the base of the transistor PNP1 switches to the voltage corresponding to the reference voltage VL. The reference voltage VL is VL = Vcc · (R2 · R3) / (R1 · R2 + R1 · R
3 + R2 ・ R3) + Vce _NPN5・ (R1 ・ R2) / (R1
・ R2 + R1 ・ R3 + R2 ・ R3) Vce _NPN5 is a collector-emitter voltage of the transistor NPN5.

At this time, R3 is considerably smaller than R1 and R2.
Since it is usually set in advance, the reference voltage V
The formula for L is VL≈Vce_NPN5 Becomes

By the switching of the comparators X1 and X2, the output voltage Vc drops, and when it falls below the reference voltage VL, the transistor NPN5 is turned off. At that time, the comparator X1 has the following description. A large negative offset Vofs1 is generated.

First, when the transistor NPN5 is in the ON state
Collector current Ic_NPN5Is Ic_NPN5= (Vcc-Vce_NPN5) / R1 And is usually set to several μA to several tens of μA. Also,
Transistor NPN5 is used as a switch in the saturation region
Therefore, its collector-emitter voltage Vce _NPN5But
It is about 0.1V. Bipolar transistor
If Vce is small, current amplification factor h_feBecame smaller rapidly
When Vce is about 0.1V, it has h
_feIs about 10. Therefore, the collector current Ic_NPN5
Is 10 μA, the base current Ib_NPN5Is only 1 μA
Will be needed.

Normally, the output of a differential circuit using an active load such as the comparator X1 is switched when the collector currents of both input transistors become equal. Therefore, the transistor PNP2, and in that the collector current Ic _PNP2 = Ic _PNP4 of pNP4, the transistor N
Since PN1 and NPN2 are current mirrors, Ic _PNP
2 = Ic _NPN1 .

However, the transistor NPN5 is Vce
To maintain _NPN5 = 0.1V is required base current Ib _NPN5 of Ic _{NPN 5/10,} the base current Ib _NPN5 is below than the required amount, Vce _NPN5 increases. Vce _NPN5
Is increased, the reference voltage VL is increased. With the output voltage Vc falling, the reference voltage VL
Therefore, the positive feedback is applied, and finally, when the base current Ib _NPN5 falls below the required amount, the comparator X1 is switched and the transistor NPN5 is turned off.

The relationship between the input potential difference Vid the collector current Ic of the differential circuit can be expressed as _{Ic NPN1 / Ic PNP2 = exp (} Vid / Vt). Note that Vt is a thermal voltage. Here, that the base current Ib _NPN5 is below 1 .mu.A, i.e., the current points difference Ic _{NPN 1} and Ic _PNP2 is 1 .mu.A or less, Ic _{NPN 1} = 2 .mu.A, when the Ic _PNP2 = 3 .mu.A, Vid
Is about -10.5 mV. That is, the comparator X
1 is only when the output switches from "H" to "L",
An offset Vofs1 of about -10.5 mV occurs.

Further, in this circuit, the comparator X
The size of the transistor NPN4 of the current mirror circuit, which serves as a load of the differential circuit forming the circuit 2, is smaller than NPN3. Even if the base voltages of the transistors PNP5 and PNP6 are at the same level, the collector current of NPN3 is N.
It is larger than that of PN4 and is not in equilibrium. Transistors PNP5 and PN required to balance this
The voltage applied to the input of P6 is the input offset voltage Vofs2
Which is given by the equation: Vofs2 = Vt · ln (n / 1). Here, Vt is a thermal voltage, n is a current ratio of NPN4 to NPN3 when the same base-emitter voltage is applied to the transistors NPN3 and NPN4, and n is smaller than 1.

From this, the comparator X2 converts the input voltage into the offset voltage Vof given by the above equation.
It can be explained that the circuit of FIG. 2 has the same function as the circuit of FIG. Actually, n is set to 0.8 in the semiconductor integrated circuit, and as a result, about -5.7 mV is given as the offset voltage Vofs2. This value is
As described above, the offset variation range of the differential element due to manufacturing is set to about 3 mV. The offset voltage Vofs2 is Vofs1.
Is a smaller value.

In the internal circuit of the IC, in order to adjust the current ratio of the transistors in this way, for example, to reduce the current of the transistor NPN4 below the reference element, the emitter area of the transistor NPN4 is laid out smaller than the reference transistor. Since it can be easily realized, there is almost no effect on cost, and the problem can be solved and stable operation can be realized without impairing the advantage of FIG. 1 or 5 that can be realized with a small number of elements. It will be possible.

FIG. 3 shows an example of a circuit in which the offset voltage Vofs2 of FIG. 1 is realized by another method. Offset voltage Vofs2
Are the transistors NPN3, N as described in FIG.
In the current mirror circuit composed of PN4, it can be realized by making the current of the transistor NPN4 smaller than that of the transistor NPN3. Therefore, in FIG. 3, the emitter areas of the transistors NPN3 and NPN4 are made the same, and the resistor R4 is inserted in the emitter of the transistor NPN4. This circuit includes transistors NPN3 and N
Since the relation of the collector current of PN4 cannot be expressed by an algebraic expression,
The value of the resistor R4 needs to be obtained by numerical calculation from the required offset voltage. However, since the resistor can be changed more easily than the transistor size, there is an advantage that the offset amount can be easily adjusted due to changes in manufacturing variations.

[0040]

As described above, according to the present invention,
It has an advantage that it can be configured as a current control type oscillation circuit with a small number of elements, and has a merit that it can prevent a decrease in yield due to manufacturing variations and can operate stably.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of an oscillator circuit of the present invention.

FIG. 2 is a circuit diagram embodying the oscillation circuit of FIG.

FIG. 3 is a circuit diagram in which the oscillation circuit of FIG. 1 is embodied separately.

FIG. 4 is a block diagram of a conventional oscillator circuit.

FIG. 5 is a block diagram of another conventional oscillation circuit.

[Explanation of symbols]

X1, X2: Comparator VL, VH: Reference voltage S1, S2: Switch I1, I2, I3: Current source C: Capacitor

Continued front page    (72) Inventor Kazuyuki Miyajima             2-1, 1-1 Fukuoka, Kamifukuoka City, Saitama Prefecture             Inside the Kawagoe Manufacturing Co., Ltd. F term (reference) 5J043 AA00 AA14 EE00 FF03 FF07                       GG01 GG02 GG08

Claims (4)

[Claims] 1. A reference voltage circuit for switching and outputting one of a high reference voltage and a low reference voltage, and one end of a capacitor whose output is connected to an inverting input and whose other end is grounded to a non-inverting input. Is connected, and when the output becomes “H”, the voltage of the reference voltage circuit is switched to the low reference voltage,
When it becomes “L”, a first comparator that switches the voltage of the reference voltage circuit to the high reference voltage, a first current source connected between one end of the capacitor and a power supply, and between one end of the capacitor and ground. The second current source connected via a switch is connected to the inverting input of the output of the reference voltage circuit, the non-inverting input is connected to one end of the capacitor, and the switch is turned on when the output becomes “H”. West,
In an oscillation circuit including a second comparator that turns off the switch when it becomes “L”, when the output of the first comparator switches from “H” to “L”, the first comparator is turned off. A first negative offset voltage is applied to the inverting input side, and a second negative offset voltage smaller than the first negative offset voltage is always applied to the non-inverting input side of the second comparator. Oscillation circuit. 2. The oscillator circuit according to claim 1, wherein the first comparator includes first and second transistors of a first conductivity type which are differentially connected, and a collector of the first transistor. A third transistor of the second conductivity type having a collector connected thereto, and a second transistor of the second conductivity type having a collector and a base connected to the collector of the second transistor and a base connected to the base of the third transistor. The second comparator includes a fifth transistor and a fifth transistor of the first conductivity type which are differentially connected, and a second transistor whose collector is connected to the collector of the fifth transistor. And a collector and a base of the sixth transistor are connected to the collector and the base of the sixth transistor, the base of which is connected to the base of the seventh transistor. Consists of a eighth transistor, the reference power supply circuit, a first power and is connected between ground,
A collector and an emitter are connected between the second resistor and a common connection point of the first and second resistors and the ground, and the base is the first and second resistors.
A ninth transistor of the second conductivity type connected to the common collector connection point of the third transistor, wherein the switch has a base connected to the fifth and seventh collector common connection points, and a collector connected to the third common transistor. A second conductive type tenth transistor connected to a second current source, wherein bases of the first and fifth transistors are connected to a common connection point of the first and second resistors, 2. The oscillator circuit, wherein the bases of the sixth and sixth transistors are connected to one end of the capacitor, and the emitter area of the seventh transistor is set larger than that of the eighth transistor. 3. The oscillator circuit according to claim 2, wherein the seventh and eighth transistors are replaced with transistors having the same emitter area, and a third resistor is connected to the emitter of the eighth transistor. An oscillation circuit characterized by the above. 4. The oscillation circuit according to claim 2, wherein a first level shift circuit is provided between the bases of the first and fifth transistors and a common connection point of the first and second resistors. The eleventh transistor of conductivity type is connected, and the twelfth transistor of the first conductivity type for level shifting is connected between the bases of the second and sixth transistors and one end of the capacitor. Characteristic oscillation circuit.