JPH06196977A - Voltage controlling oscillation circuit - Google Patents

Abstract

PURPOSE:To provide a voltage controlling oscillation circuit capable of obtaining stable oscillation even when power supply voltage or temperature is changed. CONSTITUTION:The voltage controlling oscillation circuit has a current source 6 for allowing a current proportional to power supply voltage connected to a DC power supply to flow, a capacitor 7 connected between the output of a current source and GND, the 1st and 2nd comparators 3, 4 having opened collector outputs, the 1st and 2nd resistors 1, 2 serially connected between the power supply and the output of the 2nd comparator 4, and a diode 5 and constituted so that the inverted inputs of the two comparators 3, 4 and the anode of the diode 5 are connected a node between the capacitor 7 and the current source 6, the output of the 1st comparator 3 and th non-inverted input of the 2nd comparator 4 are connected to a node between the serially connected resistors 1, 2 and the cathode of the diode 5 is connected to the output of the 2nd comparator 4.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a voltage controlled oscillator circuit having an oscillation frequency proportional to a control voltage.

[0002]

2. Description of the Related Art A conventional voltage controlled oscillator circuit requires correction for changes in power supply voltage and temperature in order to stabilize the oscillation frequency, and many parts and highly accurate parts are required for these corrections. I was trying.

[0003]

Since the conventional voltage controlled oscillator circuit requires a large number of parts and parts with high accuracy as described above, there are problems such as an increase in cost and an increase in shape. there were.

The present invention provides a voltage controlled oscillator circuit capable of suppressing fluctuations in the oscillation frequency due to fluctuations in the power supply voltage as much as possible with a small number of parts, and suppressing fluctuations due to temperature only to the influence of the voltage drop of the diode. With the goal.

[0005]

The first means of the present invention for achieving the above object is to provide a current source, which is connected to a direct current power source, for supplying a current proportional to a power source voltage, an output of the current source, and a GND. With a capacitor connected between
It has first and second comparators having an open collector output, two resistors connected in series between a power supply and the output of the second comparator, and one diode, and has a capacitor and a current source. The inverting inputs of the two comparators and the anode of the diode are connected to the connection point, and the output of the first comparator and the non-inverting input of the second comparator are connected to the connection point of the resistors connected in series. The cathode of the diode is connected to the output of the second comparator, and the oscillation frequency is changed by the voltage applied to the non-inverting input of the first comparator.

A second means of the present invention is, in addition to the first means, a diode connected to a current source in series.

[0007]

According to the first means of the present invention, the fluctuation of the oscillation frequency due to the fluctuation of the power supply voltage can be suppressed as much as possible with a small number of parts, and the fluctuation due to the temperature can be suppressed only by the influence of the voltage drop of the diode. Further, since the number of parts is small, the cost and shape can be suppressed.

Further, in the second means of the present invention, by connecting the current source in series with the diode, the first
In addition to the function of the means described above, the oscillation waveform can be made into a triangular wave, so that it can be applied to a wider range of applications.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT An embodiment of the first means of the present invention will be described with reference to FIGS. A current source 6 which flows a current proportional to a power source voltage connected to a DC power source, a capacitor 7 connected between the output of the current source 6 and GND, and first and second comparators 3 having open collector outputs, 4, power supply and the second comparator 4
Has first and second resistors 1 and 2 and a diode 5 connected in series between the outputs of the two, and at the connection point of the capacitor 7 and the current source 6, the two comparators 3, 4 is connected to the anode of the diode 5, and the output of the first comparator 3 and the non-inverting input of the second comparator 4 are connected to the connection point of the resistors 1 and 2 connected in series. The cathode of the diode 5 is connected to the output of the second comparator 4, and the oscillation frequency is changed by changing the voltage applied to the non-inverting input of the first comparator 3.

The first resistor 1 and the current source 6 are connected to the power supply voltage VDD, and the control voltage Vc is input to the non-inverting input of the first comparator 3. The oscillation output Vf outputs the voltage of the capacitor.

Next, the operation of the above circuit will be described. In the initial state, the capacitor 7 is in a discharged state, and the control voltage V
It is assumed that c is lower than the power supply voltage VDD. At this time, the output terminals of the first comparator 3 and the second comparator 4 maintain a high impedance state, and the potential VA at the connection point of the first resistor 1 and the second resistor 2 becomes equal to the power supply voltage VDD. There is. The current source 6 supplies a direct current IC proportional to the power supply voltage VDD, and the direct current IC charges the capacitor 7. When the voltage of the capacitor 7 rises and becomes higher than the control voltage VC, the output of the first comparator 3 shifts from high impedance to low impedance, and the potential VA at the connection point of the first resistor 1 and the second resistor 2 becomes It becomes GND potential instantly. At this time, the output of the second comparator 4 is also inverted and the discharge of the capacitor 7 is started. When the potential of the capacitor 7 becomes lower than the control voltage VC, the first comparator 3
Output returns to high impedance state. Since the output of the second comparator 4 has a low impedance, the potential VA has a value obtained by dividing the power supply voltage VDD by the first resistor 1 and the second resistor 2.

When the potential of the capacitor 7 drops and becomes equal to VA, the output of the second comparator 4 becomes the high impedance state again, and the charging of the capacitor 7 is restarted.

FIG. 2 shows the voltage waveform of each part. The potential Vf of the capacitor 7 linearly rises by the constant current supplied from the current source 6 and reaches the control voltage VC. At this time, VA is immediately reduced to GND from the state of being equal to the power supply voltage VDD, the capacitor 7 is discharged, and Vf is reduced. When the capacitor 7 starts discharging, VA is the first resistance 1, the second
When the voltage Vf becomes equal to the voltage VA 'divided by the resistor 2 and the voltage Vf becomes equal to the voltage VA', the voltage VA 'becomes equal to the power supply voltage VDD. Oscillation continues by repeating this operation. The control of the oscillation frequency is controlled by the value of the control voltage VC.

FIG. 3 shows an embodiment when actually configured as a circuit. In FIG. 3, 11 is the first resistance, and 12
Is a second resistor, 13 is a first comparator, and 14 is a second resistor.
, 15 is a first diode, 16 is a capacitor, 17 is a third resistor, 18 is a fourth resistor, 19 is a fifth resistor, 20 is a transistor, and 21 is a second diode. The first resistor 11 is connected to the power supply voltage VDD, and the control voltage is input to the non-inverting input of the first comparator 13. The oscillation output outputs the voltage of the capacitor 16. In the circuit of FIG. 3, the current source of the circuit of FIG. 1 is composed of a resistor, a diode and a transistor.
The resistor 17 is for limiting the input current of the second comparator 14.

The current value of the current source, that is, the emitter current of the transistor 20 is proportional to the voltage across the fourth resistor 18, and the voltage across the fourth resistor 18 is proportional to the power supply voltage VDD. That is, the direct current IC generated by the current source is proportional to the power supply voltage. In addition, the temperature characteristic of the base-emitter voltage of the transistor is the same as that of the second diode 2
Since it is canceled by 1, the DC current IC of the current source is not affected by temperature.

When the power supply voltage VDD fluctuates, the control voltage V
If C is generated by resistance voltage division of the power supply voltage VDD, the DC current IC of the current source, the potential of VA, and the control voltage VC are proportional to the power supply voltage VDD. Therefore, the oscillation frequency does not change. In addition, when the temperature changes, the control voltage V
Since C and VA are generated by resistance voltage division, the influence due to temperature is canceled and the control voltages VC and VA are not influenced by temperature. Therefore, the direct current IC and the control voltages VC and VA
Is stable with respect to temperature changes, so fluctuations in the oscillation frequency are also stable. Next, an embodiment of the second means of the present invention will be described with reference to FIGS. In FIG. 4, 31 is a first resistor, 32 is a second resistor, and 33 is a first resistor.
Is a comparator, 34 is a second comparator, 35 is a diode, 36 is a first current source, 37 is a capacitor, and 38 is a second current source. The first resistor 31 and the first current source 36 are connected to the power supply voltage VDD, and the control voltage is input to the non-inverting input of the first comparator 33. The oscillation output is the voltage of the capacitor 37.

When the capacitor 37 discharges, the discharge current is limited by the second current source 38, so that the oscillation waveform can be a triangular wave as shown in the operation waveform of FIG.

FIG. 5 shows the voltage waveform of each part. The potential Vf of the capacitor 37 is linearly increased by the direct current IC supplied from the first current source 36 and reaches the control voltage VC. At this time, VA is equal to the power supply voltage VDD,
It instantly drops to GND and the capacitor 37 starts discharging. At this time, since the discharge current of the capacitor 37 is determined by the second current source 38, Vf linearly decreases. When the capacitor 37 starts discharging, VA becomes the potential VA 'divided by the first and second resistors 31 and 32, and when Vf becomes equal to VA', VA 'becomes equal to the power supply voltage VDD.

Oscillation continues by repeating this operation. Also, by changing the value of the direct current generated by the first and second current sources,
It is possible to easily generate a triangular wave having different falling dv / dt.

[0020]

According to the first means of the present invention, it is possible to construct a voltage controlled oscillator circuit which is stable against temperature changes and power supply voltage changes with a small number of parts, and it is possible to keep costs low. The circuit shape can also be reduced.

According to the second means of the present invention, in addition to the effect of the first means, the oscillation waveform can be made into a triangular wave,
By changing the value of the DC current generated by the two current sources, it is possible to easily generate a triangular wave having different dv / dt of rising and falling.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of a first means of a voltage controlled oscillator circuit of the present invention.

[Fig. 2] Same operation waveform diagram

FIG. 3 is a circuit diagram showing an embodiment when the circuit is actually configured as a circuit.

FIG. 4 is a circuit diagram showing an embodiment of a second means of the voltage controlled oscillator circuit of the present invention.

[Fig. 5] Same operation waveform diagram

[Explanation of Codes] 1/11/3 1st resistance 2/12/3 2nd resistance 3/1 3/3 1st comparator 4/1 4/34 2nd comparator 5/1 5/21/35 diode 6・ 36 ・ 38 Current source 7 ・ 16 ・ 37 Capacitor 17 Third resistance 18 Fourth resistance 19 Fifth resistance 20 Transistor 22 Sixth resistance

Claims (2)

[Claims] 1. A first and second comparator having an open collector output, a current source connected to a direct current power source and flowing a current proportional to a power source voltage, a capacitor connected between an output of the current source and GND. And two resistors and one diode connected in series between the power source and the output of the second comparator, and the inversion of the two comparators at the connection point of the capacitor and the current source. The input of the diode is connected to the anode of the diode, the output of the first comparator and the non-inverting input of the second comparator are connected to the connection point of the resistors connected in series, and the cathode of the diode is connected to the second Connected to the output of the first comparator and changing the voltage applied to the non-inverting input of the first comparator changes the oscillation frequency. Oscillation circuit. 2. The voltage controlled oscillator circuit according to claim 1, wherein a current source is connected in series with the diode.