JP2696883B2 - Sawtooth wave generation circuit - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sawtooth wave generating circuit applied to generate a sawtooth wave for vertical deflection of a graphic display monitor.

[Summary of the Invention]

According to the present invention, in the sawtooth wave generating circuit for generating the sawtooth wave for the vertical deflection circuit by the Miller integrating circuit, the reference voltage source is connected to one input terminal of the first operational amplifier constituting the Miller integrating circuit, An output terminal of the first operational amplifier is connected to one input terminal of a second operational amplifier constituting a non-inverting amplifier through a low-pass filter, and an output terminal of the second operational amplifier is connected to the first operational amplifier. The first input terminal of the second operational amplifier is feedback-connected to the other input terminal via a capacitor, and the first input terminal is connected to the other input terminal of the second operational amplifier via a capacitor.
The saw-tooth wave is taken out from the output terminal of the operational amplifier to obtain a saw-tooth wave having a stable amplitude and from which the DC component is removed, and a circuit which is very fast to be stabilized when the power is turned on is realized. .

[Conventional technology]

The easiest way to obtain a sawtooth wave for vertical deflection is
This is to use the Miller integration circuit shown in the figure. In FIG. 3, a parallel circuit of a capacitor 22 and a switch 23 is inserted between an inverting input terminal and an output terminal of an operational amplifier indicated by 21, an output terminal 24 is derived, and a non-inverting input terminal of the operational amplifier is grounded, The inverting input terminal is connected to a negative voltage source 26 via a resistor 25. The switch 23 is turned on by a vertical synchronization pulse. The Miller integrating circuit outputs a saw-tooth wave having a slope determined by the values of the capacitor 22, the resistor 25 and the voltage source 26 at the time of resetting when the switch 23 is turned on as shown in FIG.
Occurs at 24.

Therefore, the configuration shown in FIG. 3 has a drawback that the amplitude of the output signal fluctuates due to a change in the vertical deflection frequency and a variation in the values of the integrating capacitor 22 and the resistor 25. Also, because the output signal has a DC component,
It is necessary to cut the direct current component by the capacitor coupling. However, if the capacitance of the coupling capacitor is too small, the linearity of the sawtooth wave is impaired. On the other hand, if the capacitance is too large, it takes too much time until the power becomes stable when the power is turned on.

In order to solve the above-mentioned drawbacks, a sawtooth wave generating circuit shown in FIG. 5 has been put to practical use. In FIG. 5, 1
The Miller integrator circuit is constituted by the operational amplifier shown by.
That is, a parallel circuit of the capacitor 2 and the switch 3 is inserted between the inverting input terminal and the output terminal of the operational amplifier 1, the output terminal 4 is led out, and the inverting input terminal is connected to the negative power supply via the resistor 5 such as -12 [V ] Is supplied to the power supply terminal 6 to be supplied. The non-inverting input terminal of the operational amplifier 1 is connected to the power supply terminal 6 via the resistor 7 and is grounded via the Zener diode 8. This Zener diode 8
The negative peak value of the output signal-
E1 (see FIG. 6) is determined.

The output signal of the Miller integrating circuit is peak-detected by a rectifying circuit including diodes 27 and 28, a capacitor 29 and a resistor 30, and is supplied to a non-inverting input terminal of an operational amplifier 33. The connection point of the diodes 27 and 28 is connected to the positive power supply terminal 32 via the resistor 31.
It is connected to the. The two diodes 27 and 28 are used to cancel the forward voltage drop.

A feedback resistor 34 is inserted between the inverting input terminal and the output terminal of the operational amplifier 33. Also, a positive power supply voltage, for example,
A series circuit of a resistor 37 and a Zener diode 38 is inserted between a power supply terminal 36 to which V is applied and ground, and a connection point of the resistor 37 and the Zener diode 38 is connected to the inverting input terminal of the operational amplifier 33 via the resistor 35. I have. The positive peak value + E2 (see FIG. 6) of the output signal is determined by the Zener voltage + E2 of the Zener diode 38. That is, in the circuit configuration of FIG. 5, the difference voltage between the level at which the output signal is peak-detected and the Zener voltage of the Zener diode 38 is determined by the operational amplifier.
The signal is amplified by 33 and fed back to the inverting input terminal of the operational amplifier 1 via the resistor 39, and is controlled so that the positive peak value of the output signal becomes equal to + E2.

According to the configuration shown in FIG. 5, as shown in FIG. 6, a saw-tooth wave having a constant amplitude is obtained even when the DC component is zero and the vertical deflection frequency changes.

[Problems to be solved by the invention]

In the configuration shown in FIG. 5, the amplitude or the DC component slightly fluctuates due to the imbalance of the absolute values of the Zener voltages of the Zener diodes 8 and 38 or the difference in the temperature characteristics of the diodes 27 and 28. There is a problem that a movement of about several mm occurs on the monitor screen due to the fluctuation. Further, since the output signals are detected by the diodes 27 and 28, the capacitance of the capacitor 29 cannot be reduced. This is because if the capacitance of the capacitor 29 is reduced, the rectified output supplied to the operational amplifier 33 has a ripple, and the ripple is amplified and fed back by the operational amplifier 33, so that the quality of the sawtooth wave is significantly deteriorated. Because of the large capacity of the capacitor 29, it took several seconds to stabilize when the power was turned on.

Therefore, an object of the present invention is to generate a saw-tooth wave having a constant amplitude irrespective of the vertical frequency, to almost completely remove the DC component, and to stabilize the power supply at a very high speed, Another object of the present invention is to provide a saw-tooth wave generating circuit capable of simultaneously performing S-shaped correction.

[Means for solving the problem]

According to the present invention, in a sawtooth wave generating circuit for generating a sawtooth wave for a vertical deflection circuit by a mirror integrating circuit, a reference voltage source is connected to one input terminal of a first operational amplifier constituting the mirror integrating circuit, An output terminal of the first operational amplifier is connected to one input terminal of a second operational amplifier constituting a non-inverting amplifier through a low-pass filter, and an output terminal of the second operational amplifier is connected to the first operational amplifier. A feedback connection is made to the other input terminal and a feedback connection is made to the other input terminal of the second operational amplifier via a capacitor, so that a sawtooth wave is extracted from the output terminal of the first operational amplifier. This is a sawtooth wave generation circuit.

[Action]

The DC component passed through the low-pass filters 9 and 10 is amplified by the non-inverting amplifier 11 and is fed back to the operational amplifier 1. Therefore, the operation is performed so that the DC component is zero, that is, the areas of the positive half wave and the negative half wave of the sawtooth wave are equal to each other. As a result, control is performed so that the positive peak value of the sawtooth wave becomes constant. The negative peak value of the sawtooth wave is determined by the reference power supply 8. Therefore, the problem of imbalance of the Zener diode does not occur, and the amplitude is stabilized regardless of the vertical frequency. In addition, the ripples included in the outputs of the low-pass filters 9 and 10 are fed back, so that the S-shaped correction can be performed. In this case, since ripples may occur, the value of the capacitor 10 of the low-pass filters 9 and 10 can be reduced, and the time until the operation is stabilized when the power is turned on can be shortened.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings. In FIG. 1, a Miller integrating circuit is constituted by the operational amplifier indicated by 1. That is, the capacitor 2 and the switch 3 are connected between the inverting input terminal and the output terminal of the operational amplifier 1.
And an output terminal 4 is derived, and an inverting input terminal is connected via a resistor 5 to a power supply terminal 6 to which a negative power supply, for example, -12 [V] is supplied. The operational amplifier 1
Is connected to the power supply terminal 6 via the resistor 7 and grounded via the Zener diode 8.
By the Zener voltage -E1 of the Zener diode 8,
The negative peak value -E1 (see FIG. 2A) of the output signal is determined. An output signal of the Miller integrating circuit is supplied to a non-inverting input terminal of the operational amplifier 11 through a low-pass filter including a resistor 9 and a capacitor 10. A series circuit of a capacitor 12 and a resistor 13 is connected between the inverting input terminal of the operational amplifier 11 and its output terminal, and the inverting input terminal is grounded via a resistor 14. The output signal of the operational amplifier 11 is fed back to the inverting input terminal of the operational amplifier 1 via the resistor 15.

 An example of each specific value of the circuit element is shown below.

Capacitor 2: 0.1 [μF] Resistance 5: 68 [kΩ], Resistance 9: 1 [MΩ] Capacitor 10: 0.47 [μF] Capacitor 12: 0.47 [μF] Resistance 13: 1 [MΩ] Resistance 14: 100 [kΩ] Resistance 15: 100 [kΩ] In one embodiment of the present invention, when the switch 3 is turned on by the vertical synchronization pulse, the output signal drops to the value of the Zener voltage -E1. Next, the level of the output signal gradually increases toward the positive peak value. This output signal is smoothed by a low-pass filter including a resistor 9 and a capacitor 10 until the output signal becomes substantially DC. Operational amplifier
11 performs an amplifying operation with a gain of approximately ∞ for a DC component because a DC cut capacitor 12 is inserted in the negative feedback path. Therefore, the DC voltage obtained at the output terminal of the operational amplifier 11 is fed back to the inverting input terminal of the operational amplifier 1 via the resistor 15, so that the DC component becomes infinitely zero, that is, the negative of the sawtooth wave And the area of the positive half-wave is equal to the area of the positive half-wave. As a result, control is performed so that the positive peak value + E3 (see FIG. 2A) of the sawtooth wave becomes constant. In this embodiment, the amplitude is determined only by the Zener voltage E1 of the Zener diode 8.

Further, a small amount of ripple remains after being integrated by the resistor 9 and the capacitor 10. This ripple has a parabolic waveform as shown in FIG. 2B. The amount of this ripple is calculated by the operational amplifier 11. (Where R13 is the value of the resistor 13 and R14 is the value of the resistor 14), is superimposed on the DC component, and is fed back to the Miller integrating circuit. Since the parabolic wave is integrated by the Miller integrating circuit, the saw-tooth wave taken out to the output terminal 4 has been subjected to the S-shaped correction as shown by the broken line in FIG. 2A. The amount of this S-shaped correction is determined by the resistance 9, the capacitor 10, the resistance 13
And the value of the resistor 14 can be adjusted. If the values of these circuit elements are properly selected, no adjustment is possible.

Note that a battery may be used instead of the Zener diode 8. Instead of a negative power supply,
A positive power supply may be used to form a sawtooth wave having a slope opposite to that of the above-described embodiment.

〔The invention's effect〕

According to the present invention, the amplitude can be stabilized irrespective of the vertical deflection frequency with a simple circuit configuration as compared with the conventional circuit configuration shown in FIG. Further, in the present invention, ripples may be placed on the output of the low-pass filter, so that the value of the capacitor constituting the low-pass filter can be reduced, and the time required for stabilization at the time of turning on the power can be shortened. Further, according to the present invention, since the S-shape correction can be performed at the same time, it is not necessary to provide a separate integration circuit, and the number of circuit components can be greatly reduced. Furthermore, in the present invention, what is important for the stabilization of the amplitude and the DC component is only the reference voltage determined by the Zener diode 8, and the accuracy of the stabilization of the amplitude and the DC component is increased without being affected by other components. Can be.

[Brief description of the drawings]

FIG. 1 is a connection diagram of one embodiment of the present invention, FIG. 2 is a waveform diagram used for explaining the operation of one embodiment of the present invention, FIGS. 3 and 4 are connection diagrams of a Miller integrating circuit and output waveforms thereof. 5 and 6 are a connection diagram of a conventional sawtooth wave generating circuit and a diagram showing an output waveform thereof. Description of main reference numerals in the drawings 1,11: operational amplifier, 3: switch, 4: output terminal, 6: power supply terminal, 8: zener diode, 9, 10: resistor and capacitor constituting low-pass filter.

Claims (1)

(57) [Claims] 1. A sawtooth wave generating circuit for generating a sawtooth wave for a vertical deflection circuit by a Miller integrating circuit, wherein a reference voltage source is connected to one input terminal of a first operational amplifier constituting the Miller integrating circuit. An output terminal of the first operational amplifier is connected to one input terminal of a second operational amplifier constituting a non-inverting amplifier through a low-pass filter, and an output terminal of the second operational amplifier is connected to the first operational amplifier. A feedback connection is made to the other input terminal of the first operational amplifier, and a feedback connection is made to the other input terminal of the second operational amplifier via a capacitor, so that a sawtooth wave is extracted from the output terminal of the first operational amplifier. A saw-tooth wave generating circuit characterized in that: