JPH0546124B2 - - Google Patents

Description

[Detailed description of the invention] (a) Industrial application field The present invention relates to a parabolic wave (quadratic curve waveform) generation circuit used in a deflection circuit of a projection TV receiver or a TV receiver using a large picture tube. It is related to. (b) Prior Art A parabolic wave generation circuit that generates parabolic waves with good waveform symmetry is described in Japanese Patent Laid-Open No. 125217/1983. FIG. 2 is a circuit diagram showing the parabolic wave generation circuit, which includes a first switch 1 that opens and closes in response to a vertical trigger pulse, a constant current source 2, and a switch that is charged in accordance with the constant current from the constant current source 2. It consists of a capacitor 3, a coupling capacitor 4, an integrating circuit 5 , an output terminal 6, and a second switch 7, and is configured to obtain a parabolic wave at the output terminal 6.
When a vertical trigger pulse as shown in FIG. 3A is applied to the first and second switches 1 and 7, the first switch 1 is opened and the second switch 7 is opened during the "L" level period of FIG. 3A. is closed. Then, the capacitor 3 is charged, and the voltage at the upper end A of the capacitor 3 rises as shown in FIG. 3B. Also, during the "H" level period in Figure 3A, the first switch 1 is
is closed and the second switch 7 is opened, so that the capacitor 3 is discharged, and the voltage at its upper end A rapidly drops as shown in FIG. 3B. 2nd switch 7
During the period when the terminal 8 is open, the voltage at the terminal 8 is at the ground level, so a sawtooth wave as shown in FIG. 3C is generated at the terminal 8. The signal shown in Fig. 3C is integrated by the integrating circuit 5 , but at this time, the signal waveform shown in Fig. 3C has the same area above and below the ground level, so the output terminal 6, it is possible to obtain a parabolic wave with good symmetry as shown in Fig. 3 (d). (C) Problems to be Solved by the Invention However, in the circuit shown in FIG. 2, the DC level of the input signal of the integrating circuit 5 must be set equal to the reference voltage (earth level) for integration, and the DC fluctuations in the previous stage must be set equal to the reference voltage (earth level) for integration. A coupling capacitor 4 is necessarily required to prevent this, which has the drawback of increasing the number of elements. Especially IC (integrated circuit)
In this case, the coupling capacitor 4 was attached externally to the IC, which was a problem. In addition, the period of the vertical trigger pulse generally tends to fluctuate, and when a vertical trigger pulse with such a fluctuating period is applied to the circuit shown in Figure 2, the amplitude of the generated sawtooth wave will fluctuate, causing problems in later stages. There was a problem with negative effects. (d) Means for Solving the Problems The present invention has been made in view of the above-mentioned points, and includes a sawtooth wave creation circuit that creates a sawtooth wave with a constant amplitude in response to a vertical trigger pulse, and In a parabolic wave generating circuit consisting of a differential type integrating circuit that integrates the sawtooth wave output from the wave generating circuit and generates a parabolic wave, the reference voltage level of the integrating circuit is set to a level that is 1/2 of the amplitude. It is characterized by (E) Effect According to the present invention, a sawtooth wave having a constant amplitude is created regardless of the period of the vertical trigger pulse, and
Since the reference voltage for integration of the differential type integrating circuit that integrates the sawtooth wave is set to a level that is 1/2 of the amplitude, a parabolic wave with good symmetry can be created. (F) Embodiment FIG. 1 is a circuit diagram showing an embodiment of the present invention.
9 is an RS-FF (RS type flip-flop circuit) that is set in response to a vertical trigger pulse from an input terminal 10; 11 is a charging/discharging capacitor that is charged in response to a constant current from a constant current source 12; 13 is the RS
- A control transistor to which the output of FF9 is applied to the base and controls charging and discharging of the charge/discharge capacitor 11; 14 , a first level shift circuit that level-shifts the sawtooth wave generated at the upper end of the charge/discharge capacitor 11; 15; 1 is a second level shift circuit that level-shifts the reference voltage of the first reference power supply 16;
7 compares the output signals of the first and second level shift circuits 14 and 15, and adjusts the output signal according to the difference.
a comparator for resetting the RS-FF9; 18 is a second reference power supply having a reference voltage (1/2Vref) that is 1/2 of the reference voltage Vref of the first reference power supply 16; 19 ;
20 is a differential amplifier circuit 21 connected between the output terminal 22 and the negative feedback terminal 23 of the differential amplifier circuit 21; capacitor 2
4 and an integrating circuit consisting of a resistor 25, 26 is RS
- A current mirror circuit that operates according to the output of the FF 9, and a transistor 27 that short-circuits the output terminal 22 of the differential amplifier circuit 21 and the negative feedback terminal 23 according to the output signal of the current mirror circuit 26. Next, the operation will be explained. Now, a vertical trigger pulse as shown in Figure 4A is applied to the input terminal 10, and in response to its rise (time _t1 ), RS-FF9 is set, and its output becomes the "L" level as shown in Figure 4B. . Then, since the control transistor 13 is turned off, the constant current from the constant current source 12 flows to the charging/discharging capacitor 11, and the voltage at the upper end A of the charging/discharging capacitor rises as shown in FIG. 4C. The voltage at the upper end A is level-shifted by 2V _BE (V _BE is the voltage between the base and emitter of the transistor) in the first level shift circuit 14 , and is generated at point B as shown in FIG. +).
On the other hand, the reference voltage Vref of the first reference voltage 16 is also
The level shift circuit 15 similarly shifts the level of 2V _BE and applies it to the negative input terminal (-) of the comparator 17. Therefore, the voltage at point A is the reference voltage
When it reaches Vref, the output of the comparator 17 becomes "H" level as shown in Fig. 4, and the RS-FF9
Reset. Then, the output of the RS-FF9 becomes "H" level, and the control transistor 13
is turned on, the charging/discharging capacitor 11 is rapidly discharged, and the voltage at point A drops to the ground level as shown in FIG. 4C. The voltage at point A is the reference voltage
When the voltage drops below Vref, the output of the comparator 17 becomes “L” level again and its output waveform becomes the fourth
It will look like the picture. The sawtooth wave shown in FIG. 4D generated at point B is applied to the integrating circuit 20 via the buffer amplifier 28. A second reference power supply 18 and a third
The voltage (1/ 2Vref +
2V _BE ) is applied, and a voltage equal to that is fed back to the negative input terminal (-), so the level of the negative input terminal (-) is as shown by the two-dot chain line in FIG. 4D. Therefore, during the period _T1 shown in FIG .
At T ₂ the capacitor 24 is discharged. On the other hand, during the period _T3 in which the output of the RS-FF9 is at the "H" level, the transistor 29 is turned on, current flows through the current mirror circuit 26 , and the transistor 27 is turned on. Then, the output terminal 2 of the differential amplifier circuit 21
2 and the negative feedback terminal 23, the integrating circuit 20 stops its integrating operation and becomes a mere buffer amplifier. In other words, the sawtooth wave is not integrated during the period _T3 , and the sawtooth wave is integrated during the periods _T1 and _T2 . The slope of the sawtooth wave is constant, and the voltage level at the positive input terminal (+) of the differential amplifier circuit 21 can be set to exactly 1/2 of the amplitude of the sawtooth wave. As shown in FIG. 4, a parabolic wave whose apex coincides with time _t2 when the capacitor 24 switches from charging to discharging can be obtained. In the embodiment shown in FIG. 1, a single power supply is used, so various level shift circuits are required. However, if two positive and negative power supplies are used, the level shift circuit is not required. (g) Effects of the invention As described above, according to the present invention, parabolic waves with good symmetry can be obtained. In addition, since a coupling capacitor is not required in this case, it is possible to reduce the number of external parts when implementing an IC. Furthermore, according to the present invention, a sawtooth wave can be created according to the edge of the vertical trigger pulse and its amplitude can be made constant, so the amplitude of the parabolic wave can also be made constant.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an embodiment of the present invention, FIG. 2 is a circuit diagram showing a conventional parabolic wave generation circuit,
3A to 3D are waveform diagrams for explaining FIG. 2, and FIGS. 4A to 4F are waveform diagrams for explaining FIG. 1. 9...RS-FF, 11...Charge/discharge capacitor,
12... constant current source, 13... control transistor,
17...Comparator, 18...Second reference power supply,
20... Integrating circuit, 24... Capacitor, 25...
…resistance.

Claims (1)

[Scope of Claims] 1. A flip-flop that inverts in response to a vertical trigger pulse, a sawtooth wave creation circuit that creates a sawtooth wave in response to an output signal of the flip-flop, and a first criterion that determines the amplitude of the sawtooth wave. a power source; a comparator that compares the reference voltage of the first reference power source with the amplitude of the sawtooth wave and inverts the flip-flop according to the difference; and a comparator that integrates the output sawtooth wave of the sawtooth wave generating circuit and generates a parabolic wave. a differential type integrating circuit that generates a voltage, a second reference power source that sets the reference voltage level of one input of the integrating circuit to 1/2 the level of the first reference power source, and a second reference power source that responds to the output signal of the flip-flop. a parabolic wave generating circuit, further comprising inhibiting means for inhibiting operation of the integrating circuit during a period when the sawtooth wave is not generated. 2. The integrating circuit is a differential amplifier circuit having an input terminal to which the second reference power supply is connected, a negative feedback terminal to which the output sawtooth wave of the sawtooth wave generation circuit is applied via a resistor, and an output terminal. and a capacitor connected between the negative feedback terminal and the output terminal, and the inhibiting means is a switch means connected between the negative feedback terminal and the output terminal. A parabolic wave generation circuit according to claim 1.