JP3128394B2 - Oscillator circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an oscillation circuit having less jitter of an oscillation output signal, and more particularly to an oscillation circuit suitable for use in a horizontal oscillation circuit incorporated in a horizontal deflection circuit in a TV receiver.

[0002]

2. Description of the Related Art As shown in JP-A-63-155958, there is known a horizontal oscillation circuit included in a horizontal deflection circuit. The horizontal oscillation circuit oscillates at the horizontal synchronization signal frequency in the video signal, and is included in a so-called horizontal AFC circuit loop. Generally, a horizontal oscillation circuit formed into an IC compares the voltage between both ends of a capacitor charged and discharged with a constant current and two reference voltages, high and low, and compares the voltage between both ends of the capacitor with the two reference voltages. By changing with time, an oscillation output signal is obtained from between both ends of the capacitor.

[0003]

By the way, recently, a dispress apparatus for displaying an image such as a graphic or a character on a cathode ray tube has become widespread, but this apparatus also requires a horizontal oscillation circuit similar to a TV receiver. . In a display device, since there are many still images, small fluctuation in the horizontal direction of the image becomes a problem. This is called so-called horizontal jitter, and it has been clarified that this occurs because the value of the reference voltage in the horizontal oscillation circuit slightly changes due to resistance noise or the like.

[0004]

SUMMARY OF THE INVENTION The present invention has been made in view of the above points, and has as its object a capacitor for charging and discharging, a constant current source for charging the capacitor, a resistor for level switching and a resistor for level setting. A variable reference voltage source including a diode, capable of outputting first and second reference voltages; comparing a level of an output voltage of the capacitor with an output voltage of the variable reference voltage source; When the voltage becomes lower than the first reference voltage, the output voltage of the variable reference voltage source is switched to a second reference voltage higher than the first reference voltage, and the output voltage of the capacitor is changed to the second reference voltage. A first comparator for first switching an output voltage of the variable reference voltage source when the output voltage of the variable reference voltage source becomes higher than a voltage of the variable reference voltage source; A second comparator for discharging the capacitor when an output voltage is higher than a second reference voltage output from the variable reference voltage source, and obtaining an oscillation output signal from the capacitor. .

[0005]

According to the present invention, a diode (P
(N junction), the inversion level of the first comparator becomes constant, and an oscillation output signal of a constant frequency is obtained.

[0006]

FIG. 1 is a circuit diagram showing an embodiment of the present invention.
(1) is a charge / discharge capacitor, (2) is a constant current source for charging the capacitor (1), (3) is a variable reference voltage having a diode group (4) for level setting and changing to binary. A level comparison between the output voltage of the capacitor (1) and the value of the variable reference voltage source (5), and the value of the variable reference voltage source (5) according to the comparison result. A first method for switching to a value side different from the output voltage of the capacitor (1);
A comparator (6) for comparing the level of the value of the variable reference voltage source (5) with the output voltage of the capacitor (1);
The second comparator discharges the capacitor (1) according to the comparison result.

Now, it is assumed that the charging / discharging capacitor (1) in FIG. 1 is not sufficiently charged from the constant current source (2), and the voltage at the point A is correspondingly low. The voltage at point A is point B
If the voltage is sufficiently lower than the voltage of the first comparator (3), the first transistor (7) constituting the first comparator (3) is off, and the second transistor (8) is on. In this state, the voltage at the point C becomes the power supply voltage (+ V _cc ) level, and the voltage at the point B accordingly becomes + V _cc − (n + 1) V _BE (where n is the number of diodes in the diode group (4), V _BE is the forward voltage of the PN junction.) On the other hand, since the voltage at the point A is lower than the voltage at the point B, the transistor (9) of the second comparator (6) is off. .

This state corresponds to time t ₁ in FIG. 2. When charging of the capacitor (1) proceeds from this point, the voltage at the point A gradually increases. When the voltage at point A exceeds the voltage at point B (time t ₂ ), the voltage at point C drops from the power supply voltage level. Then, the voltage at the point B decreases by the reduced amount, and the difference between the voltages at the points A and B increases. Therefore, the voltage level at the point C further decreases, and the point B
Voltage drops again. That is, in the first comparator (3), a positive feedback loop is formed, and the first transistor (7) is turned on and the second transistor (8) is turned off immediately.
Then, the voltage of point _{C, + V CC -I O R 1} ( except, I _O
The current value of the constant current source (10), R ₁ is the resistance of the resistor (11). ), And the voltage at point _{B, + V CC -I O R} 1
− (N + 1) V _BE .

Therefore, the voltage at the point A becomes sufficiently higher than the voltage at the point B, the transistor (9) is turned on, and the charge / discharge capacitor (1) is discharged at a constant current. When the discharge of the charging / discharging capacitor (1) proceeds and the voltage at the point A decreases and becomes equal to or lower than the voltage at the point B (time t ₃ ), positive feedback occurs again in the first comparator (3) and immediately the first transistor (7)
Is turned off, and the second transistor (8) is turned on. This state is the above-described initial state, and thereafter, the same operation is repeated.

As a result, a sawtooth oscillation output signal is obtained at point A. In the circuit of FIG. 1, the voltage at the point B that determines the inversion timing (t ₂ ) of the first comparator (3) can be set by the diode group (4). Therefore, a reference voltage with much less noise than that determined by a resistor or the like can be obtained, and an oscillation output signal without jitter can be obtained.

[0011]

As described above, according to the present invention, it is possible to provide an oscillation circuit capable of obtaining an oscillation output signal with less jitter.

[Brief description of the drawings]

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

FIG. 2 is a waveform chart for explaining FIG. 1;

[Explanation of symbols]

 (1) Capacitor (2) Constant current source (3) First comparator (6) Second comparator

Claims (1)

(57) [Claims] 1. A first and a second transistor having a common charge and discharge capacitor, a constant current source for charging the capacitor, and an emitter connected in common.
And one end is connected to the collector of the first transistor and the other end is
A resistor connected to a power supply and the base are connected to the first transistor.
A third transistor connected to the collector of the
The other end is the emitter of the third transistor and the other end is the emitter of the third transistor.
A diode connected to the base of the two transistors;
A current source connected to the other end of the diode,
A variable reference voltage source capable of outputting the first and second reference voltages
And a fourth comparator in which the voltage of the variable reference voltage source is applied to a base.
The transistor and the fourth transistor share an emitter.
And the output voltage of the capacitor is applied to the base.
A fifth transistor, and the fourth and fourth commonly connected transistors.
And the constant current circuit connected to the emitter of the fifth transistor
And a second comparator comprising more a road, an output voltage of said capacitor and said variable reference voltage source of the voltage
And the output voltage of the capacitor is
When the voltage is lower than the voltage of the variable reference voltage source, the first transistor is turned off.
Turn off, turn on the third transistor, and set the variable reference voltage
The voltage of the source is determined by the level setting diode.
Switching to the first reference voltage and the fifth transistor of the second comparator
The capacitor is turned off, the capacitor is charged with a constant current, and the output voltage of the capacitor becomes the voltage of the variable reference voltage source.
When it becomes higher, the first transistor is turned on and the second transistor is turned on.
A third transistor is turned off and the voltage of the variable reference voltage source
Is determined by the diode and the resistor from a first reference voltage.
To the second reference voltage, and the fifth transistor of the second comparator
And turn on the capacitor, and replace the capacitor with the fifth transistor.
An oscillation output signal is obtained from the capacitor by discharging a constant current through the oscillation circuit.