JPH0455004B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to an oscillation circuit used in electronic control equipment.

Conventional configurations and their problems Conventionally, there is an oscillation circuit that uses a battery as a power source, the oscillation frequency is determined by the product of a capacitor and a resistor, and is configured as a semiconductor IC, as shown in FIG.

In FIG. 1, a current I _O equal to constant current source 1 flows through the collectors of transistors 2-6. Also, the collector currents of transistors 7 and 8 are
Equal to I _O /2.

Now, consider a case where the voltage of capacitor 9, that is, the base voltage of transistor 10, is lower than the base voltage of transistor 11. At this time, transistor 11 operates, transistor 12 is turned on, transistors 13 and 14 are turned on, and transistors 15 to 21 are turned off in an instant. At this time,
All of the current I _O of the transistor 3 as the first current source flows through the resistor 22 and the diode 23, and the base voltage of the transistor 11 becomes (V _BE +R ₁ I _O ).
However, V _BE is the forward voltage of the diode 23, and R ₁ is the resistance value of the resistor 22. Furthermore, in this state, the base of the transistor 10, that is, the potential of the capacitor 9 is charged by the collector current I _O /2 of the transistor 8, which serves as the second current source, since the transistors 19 to 21 are OFF.

In this state, charging of the capacitor 9 progresses, and the potential reaches the base potential of the transistor 11 (V _BE +R ₁ I _O )
At the moment when the voltage becomes higher, transistors 11 to 14
It turns off and transistors 15 to 21 start working.
The sum of the collector currents of transistors 15 and 16 is
Sum of collector currents of transistors 17 and 18 I _O /
2, so if the resistance value of the resistor 24 is equal to the resistance value R ₁ of the resistor 22, the current flowing through the collector of the diode 23 is I _O -I _O /2=I _O /2. Therefore, the base potential of the transistor 11 is
Approximately (V _BE +R ₁ ×I _O /2−R ₁ ×I _O /2)=V _BE . By the way, since the sum of the collector currents of transistors 19 to 21 as the third current source is 3/4 I _O (the current flowing through each of transistors 15 to 21 is 1/4 I _O ), capacitor 9 is a transistor. It is discharged with a current of 1/4 I _O which is the difference between the collector current I _O /2 of 8 and the above-mentioned 4/3 I _O. This discharging changes to charging the moment the potential of the capacitor 9 becomes lower than V _BE , returning to the state described at the beginning, and is repeated. To summarize these, the oscillation period t _O in Figure 1 is expressed by the following formula, where t ₁ is the time when the output V〓 _UT is at low level, t ₂ is the time when it is at high level, and C ₁ is the capacitance of the capacitor. It will be done.

t ₁ = C ₁ × {(V _BE + I _O R ₁ ) − V _BE }/I _O/2 …(1) t ₂ = C ₁ × {(V _BE + I _O R ₁ ) − V _BE }/I _{O /2} …(2) ∴t _O = t ₁ + t ₂ = 6C ₁ R ₁ In other words, the period t _O of the oscillation circuit shown in Figure 1
is a value six times the product of the resistance value R ₁ and the capacitor capacitance value C, regardless of the current I _O of the constant current source.

FIG. 2 shows a time chart of the circuit of FIG. 1. In Figure 2, V ₉ is capacitor 9
The potential of V _OUT indicates the potential of the collector of the transistor 14 . Further, V _H and V _L are as described above, V _H = V _BE + I _O R ₁ and V _L = V _BE , and V _CC indicates the voltage of the power supply V _B.

Incidentally, the oscillation circuit shown in FIG. 1 has a drawback that the voltage between the collector and emitter of the transistor 6 may become almost zero, and the collector current of the transistor 6 no longer flows. That is, during the period _t2 when V _put is at a high level, the transistor 11 is off, and its base potential is V _BE . Therefore, the base potential of transistor 10, that is, the potential of capacitor 9, decreases, and near the end of period _t2 , the base potential of transistor 10 becomes equal to V _BE . At this time, the collector voltage of the transistor 6 becomes (base voltage of the transistor 10 - base-emitter voltage of the transistor 10), which becomes almost zero, and the constant current I _O cannot flow. For this reason, transistors 6, 10, 11, 25, and 26 that make up the differential amplifier operate only with extremely small currents, so even if transistor 11 is turned on, transistors 13 and 14 are inverted because transistor 11 The base potential of will fall further below V _BE . For this reason, according to the calculation formulas 1 and 2 above,
Since the times t ₁ and t ₂ cannot be obtained, this method has the disadvantage that it is particularly inconvenient for circuits where duty is important.

OBJECTS OF THE INVENTION The present invention eliminates these conventional drawbacks and provides an oscillation circuit that has a simple configuration and can ensure an accurate duty ratio.

Composition of the Invention The present invention sets the base potential of a differential amplifier high and makes it possible to set the collector-emitter voltage of its current source transistor to a predetermined value, thereby creating an oscillation circuit that can obtain t ₁ and t ₂ as calculated values. This is what we provide.

DESCRIPTION OF EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 3 is a circuit diagram showing an embodiment of the present invention, and the same parts as in FIG. 1 are given the same numbers. The difference from FIG. 1 is that a resistor 27 is inserted between the base of transistor 11 and the collectors of transistors 15 and 16. At this time, resistance 22,2
Assuming that the resistance values of transistors 4 and 27 are 2R ₂ , R ₂ , and R _{2 ,} respectively, the base voltage of transistor 11 in the present invention is as follows.

(i) When the output V _put is at high level (transistor 11 is OFF).

Since the common collector of transistors 15 and 16 as a fourth current source connected to resistor 27 and the collector of transistor 3 are equal, the collector current I _O of transistor 3 is divided into two equal parts of I _O /2. Therefore, the base potential of the transistor 11 is V _BE +I _O /2·2R ₂ -I _O /2R ₂ =V _BE +I _O /2R ₂ .

(ii) When the output V _put is low level (transistor 11 is on).

At this time, transistors 15 and 16 are off, and the collector current I _O of transistor 3 flows only through resistor 22 and diode 23 . Therefore, the base voltage of transistor 11 is V _BE +
I _O・2R ₂ = V _BE +2I _O R ₂ .

Therefore, in the case of the present invention, when V _put is at a high level, the base potential of transistor 11 is V _BE +
I _O /2R ₂ , which is higher than V _BE in the case of FIG. 1 by I _O /2 R ₂ . Therefore, near the end of the period t ₂ , the base potential of the transistor 10 becomes V _BE +I _O /2R ₂ . Therefore, the collector voltage of transistor 6 is (base potential of transistor 10−base-emitter voltage of transistor 10)=I _O /2R ₂ . That is, in the case of the present invention, the voltage between the collector and emitter of the transistor 6 does not become zero, and the drawbacks described in the conventional example can be eliminated. If this I _O /2R ₂ is set to about 300 mV, the voltage between the collector and emitter of transistor 3 is also ensured at about 0.8 V, and it operates accurately as a constant current source.

By the way, in the case of the present invention, as mentioned above, the output
The base potential of transistor 11 when V _put is at low level and high level is V _BE +2I _O R ₂ and V _BE
+1/2 I _O R ₂ . From this, assuming that the times when the output V _puT is at low level and high level are t ₁ ' and t ₂ ', respectively, the oscillation period t _O ' is expressed by the following equation.

t ₁ ′=C ₂ × {(V _BE +2I _O R ₂ )− (V _BE +1/2I _O R ₂ )}/I _O /2 …(3) t ₂ ′t ₅ =C ₂ × {(V _BE +2I _O R ₂ ) − (V _BE +1/2I _O R ₂ }/I _O /4 …(4) ∴t _O ′=t ₁ ′+t ₂ ′=C ₂ (3R ₂ +6R ₂ )=9C ₂ R ₂ From the above equation, it can be seen that the first
As shown in the figure, it is clear that the oscillation period is determined by the product of the resistor and capacitor, regardless of variations in the constant current source.

Effects of the Invention As described above, the present invention allows the operating point of each transistor to be set accurately even in an oscillation circuit with a low voltage power supply, so it is possible to obtain an oscillation period according to the theoretical formula.

[Brief explanation of the drawing]

Figure 1 is a diagram of a conventional low voltage drive oscillation circuit, Figure 2 is a waveform diagram showing the relationship between its charge/discharge waveform and output.
FIG. 3 is a circuit diagram showing an oscillation circuit in one embodiment of the present invention. V _B ...power supply, 1...constant current source, 10, 11...transistor that constitutes differential amplifier, 27...resistor.

Claims (1)

[Claims] 1 A differential amplifier composed of first and second transistors, a capacitor connected to the base of the first transistor, a diode, and first to third resistors connected in series. a bias circuit in which a base of a second transistor is connected to a connection point between the second and third resistors;
A first resistor connected to a connection point between the first and second resistors.
a second current source connected to a connection point between the capacitor and the base of the first transistor; and a second current source connected to the connection point between the capacitor and the base of the first transistor; a third current source connected to a connection point with the base of the first transistor; and a fourth current source controlled on and off according to the operation of the second transistor and connected to the third resistor. an oscillation circuit that outputs an oscillation output according to charging and discharging of the capacitor.