JP3025793B2 - Oscillation circuit - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a voltage-controlled oscillating circuit in which an oscillating frequency and a duty can be changed by a control voltage input from the outside.

[Prior Art] As an oscillation circuit, there is a circuit shown in FIG. In this circuit, the collector is connected to the power supply Vcc via the resistors R1 and R2,
NPN transistors Q1 and Q2 whose emitters are connected to the ground via load resistors R3 and R4, and a capacitor C1 is connected between the emitters. Is connected to the collector of the transistor Q1, and the output terminal 1 is connected to the collector of the transistor Q2.

In this circuit, transistor Q1 is turned on and Q2
Is turned off, the output voltage V _OUT taken out from the output terminal 1 of the collector of the transistor Q2 becomes high level, and the charge stored in the capacitor C1 is discharged through the resistor R4.

At this time, assuming that the base-emitter voltage of the transistor Q1 is V _BE1 , the emitter potential V _E1 of the transistor Q1 is fixed as V _E1 = V _OUT −V _BE1 (1).

As the discharge proceeds, the emitter potential V _{E2 of the} transistor Q2
The difference between the potential V _E2 and the collector potential of the transistor Q1 (fixed at this time) reaches the threshold voltage V _th2 of the transistor Q2, and V _th2 = V _BE2 (between the base and emitter of the transistor Q2). Voltage), the transistor Q2 turns on, and as a result, the transistor Q1 turns off, and the output voltage V
_OUT is inverted to low level, and the electric charge stored in the capacitor C1 is discharged through the resistor R3. At this time,
The emitter potential V _E2 of the transistor Q2 is fixed as V _E2 = V _OUT −V _CE2 (2). V _CE2 is a saturation voltage between the collector and the emitter of the transistor Q2.

Next, when the emitter potential V _E1 of the transistor Q1 is lower than the collector potential V _{OUT of the} transistor Q2 by the threshold voltage V _th1 between the base and the emitter of the transistor Q1, the transistor Q1 is turned on, the transistor Q2 is turned off, and the output voltage V _OUT goes high, and the above operation is repeated thereafter to continue oscillation. FIG. 3 shows a timing chart of the above oscillation operation.

By the way, in the above oscillation circuit, it is necessary to adjust the values of the resistors R3 and R4 in order to adjust the oscillation frequency or duty, and to lower the oscillation frequency in order to lower the oscillation frequency.
Since it is necessary to increase the value of 4, there is a problem that a high voltage is required for the power supply voltage Vcc.

Therefore, as shown in FIG. 4, the resistance R in FIG.
3 and R4 are changed to NPN transistors Q3 and Q4, a current mirror is configured with transistor Q5 so that the transistors Q3 and Q4 are output sides, and a control voltage V applied to the control terminal 2
There circuit which sets the collector current I ₁ flowing through the transistor Q3, Q4 by _C1. R5 is a resistor that determines the reference current of the current mirror circuit.

In this circuit, the required power supply voltage Vcc is equal to the resistance R1 (or R1
2), the base-emitter voltage (V _BE ) of transistor Q1 (or Q2), and transistor Q3
Since only a value obtained by adding the collector-emitter saturation voltage (V _CE ) of (or Q4) is required, the device operates with a low power supply voltage.

In this circuit, the transistor Q5, I ₁ = current flows determined by _{(V C1 -V BE5) / R5} ··· (3), which is transferred to the transistors Q3 and Q4. V _BE5 is a base-emitter voltage of the transistor Q5. Therefore, the discharge current flowing through the discharge current and the transistor Q4 side through the transistor Q3 of the capacitor C1, are both current that varies with the current I _1, and the control voltage V _C1. Therefore, the oscillation frequency can be controlled by the control voltage _VC1 .

[Problems to be Solved] However, in the oscillation circuit of FIG. 4 described above, since the current flowing through the transistor Q3, Q4 is a common current I _1,
There is a problem that the oscillation frequency can be adjusted, but the duty cannot be adjusted.

An object of the present invention is to provide a voltage-controlled oscillation circuit capable of adjusting the duty as well as the oscillation frequency by adjusting the voltage.

[Means for Solving the Problems] In order to solve the above problems, the present invention provides a power supply system in which collectors of first and second transistors are connected to a first power supply via respective individual resistors. An emitter of the second transistor is connected to a second power supply via a collector and an emitter of the third and fourth transistors, a capacitor is connected between the emitters of the first and second transistors, and
The base of the transistor is connected to the collector of the second transistor, the base of the second transistor is connected to the collector of the first transistor, the collector of the second transistor is connected to the output terminal, and the third, In an oscillation circuit including a reference-side fifth transistor that is current-mirror-connected to the fourth transistor, a sixth transistor is connected in parallel to one of the third and fourth transistors, and the sixth transistor is connected to the fourth transistor. A seventh transistor on the reference side which is connected to the transistor by a current mirror is provided.

[Example] Hereinafter, an example of the present invention will be described. FIG. 1 is a diagram showing a voltage controlled oscillation circuit of one embodiment. The same components as those in FIGS. 2 and 4 are denoted by the same reference numerals, and detailed description thereof will be omitted.

In this embodiment, the control terminal 2 described with reference to FIG.
a current mirror circuit composed of NPN transistors Q6 and Q7, with the collector of output transistor Q6 being the collector of transistor Q4 and the collector of reference transistor Q7 being controlled via resistor R6. 3
Connected to.

In this embodiment, the required power supply voltage Vcc needs to be as low as the circuit shown in FIG.
Current I ₂ flowing through the fixed, same current I ₂ and which flows through the transistor Q3, Q4. The current I ₂ is _{I 2 = (Vcc-V BE5} ) / R5 ··· (4).

However, since the transistor Q6 is connected in parallel to the transistor Q4, if the control voltage applied to the control terminal 3 is V _C2 , the current I ₃ flowing through the transistor Q6 is V _BE6, which is the voltage between the base and the emitter of the transistor Q6. , I ₃ = (V _C2 −V _BE6 ) / R6 (5)

From the above, although the discharge current flowing from the capacitor C1 to the transistor Q3 side is a fixed current I ₂ of As described above, the current flowing through the transistor Q4 and Q6 side "I ₂ + I _3", and
The current changes according to the control voltage V _C2 .

Therefore, this control voltage V _C2, the transistor Q2
You can adjust the time between turning off and on again.
The time from turning off the transistor Q1 to turning it on next is fixed. As a result, the duty of the oscillation output signal can be changed.

In this embodiment, if the power supply side of the resistor R5 is cut off from the power supply line and the control voltage V _C1 is applied thereto as in FIG. 4, the oscillation frequency is adjusted simultaneously with the duty adjustment. Of course, it can also be performed.

[Effects of the Invention] As described above, according to the present invention, since no resistor is connected to the emitter side of the transistor, the required power supply voltage can be set low, and the control voltage can be used to adjust not only the oscillation frequency but also the duty.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of an oscillator circuit according to an embodiment of the present invention, FIG. 2 is a circuit diagram of a conventional circuit, FIG. 3 is a timing chart showing the operation of the oscillator circuit of FIG. 2, and FIG. FIG. 9 is a circuit diagram of a conventional oscillation circuit. 1: Output terminal, 2, 3: Control terminal.

Continuation of front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H03K 3/282

Claims (1)

(57) [Claims] The collectors of the first and second transistors are each connected to a first power supply via a separate resistor, and the emitters of the first and second transistors are connected to the third and fourth transistors, respectively. A collector connected to a second power supply via an emitter, a capacitor connected between the emitters of the first and second transistors, and a base connected to the collector of the second transistor; The base of the second transistor is connected to the collector of the first transistor, the collector of the second transistor is connected to the output terminal, and the fifth transistor on the reference side which is current mirror-connected to the third and fourth transistors. An oscillation circuit including the third transistor, a sixth transistor connected in parallel to one of the third and fourth transistors, and An oscillation circuit comprising a reference-side seventh transistor connected to a mirror.