JPH02111167A - Parabolic wave generating section - Google Patents

Abstract

PURPOSE:To eliminate the need for a coupling capacitor and a switch in a signal line by applying peak detection to a sawtooth wave and using a voltage in response to a peak detection output for a reference voltage of an integration circuit. CONSTITUTION:A capacitor 13 for peak detection is connected to an emitter of a transistor(TR) 23 to apply peak detection to an applied sawtooth wave. When a charging voltage of the capacitor 13 reaches a reference voltage of a reference power supply 41 of a comparator circuit 40 or over, a discharge circuit 42 is driven to discharge the electric charge in the capacitor 13 automatically thereby controlling the circuit such that the said charge voltage reaches the said prescribed value or below even if the voltage is an excessive value. Thus, a parabolic wave with excellent waveform symmetry is generated without requiring a coupling capacitor or a switch in the signal line path.

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of Industrial Application The present invention is directed to the application of parabolic waves (
This relates to a quadratic curve waveform generation circuit.

(b) Prior Art A parabolic wave generation circuit capable of generating parabolic waves is described in Japanese Patent Application Laid-Open No. 125217/1983. FIG. 2 is a circuit diagram showing the parabolic wave generation circuit described in FIG. A capacitor (
3), an integrating circuit (4) that integrates the signal generated at the upper end A of the capacitor (3), and an output terminal (5).

A vertical drive pulse as shown in FIG. 3(a) is applied to the switch (1)
), the switch (1) opens and closes accordingly, and a sawtooth wave as shown in FIG. 3(b) is obtained at the upper end A.

Therefore, if the signal shown in FIG. 3(b) is integrated by the integrating circuit (4), a parabolic wave can be obtained at the output terminal (5).

By the way, as the integrating circuit shown in FIG. 2, an integrating circuit using a differential amplifier circuit is generally used, and its reference voltage is the third
Average DC level of the signal in Figure (B) (a in Figure 3 (B))
is set to However, since the center time tl of the sawtooth wave in FIG. 3(b) is later than the time t1 at which the average DC level and the sawtooth wave intersect, the charging/discharging time of the capacitor built in the integrating circuit is There was a problem in that the time at the center of the sawtooth wave and the time at the center of the parabolic wave did not match. Therefore, a device that solves such problems is described in FIG. 3 of the above-mentioned publication.

FIG. 5 is a circuit diagram showing the parabolic wave generation circuit described in FIG. 3 of the above-mentioned publication. A capacitor (3) that is charged according to a constant current from a constant current source (2), a coupling capacitor (4), and an integrating circuit (RITO).
It consists of an output terminal (6) and a second switch (7), and is configured to obtain a parabolic wave at the output terminal (6).The vertical trigger pulse as shown in Fig. 6 (a) is used as the first switch. And if the voltage is incorrectly applied to the second switches (1) and (7),
"L" level period in Figure 6 (a), first switch (1)
is opened and the second switch (7) is closed. Then, the capacitor (3) is charged, and the capacitor (3)
The voltage at the upper end A increases as shown in FIG. 6(b). or,
The first switch (
1) 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. 6(b). Second switch (7
) is open, the voltage at the terminal (8) is at the ground level, so a sawtooth wave as shown in FIG. 6(c) is generated at the terminal (8). Then, the signal in Figure 6 (C) is integrated by the integrating circuit (A), but at that time, the signal waveform in Figure 6 (C) has an upper area and a lower area with the ground level as the boundary. Since they are equal, the output terminal (6) is
It is possible to obtain parabolic waves with good symmetry, such as

(c) Problems to be Solved by the Invention However, the circuit shown in FIG. 5 requires a coupling capacitor (4) and cannot be constructed as a direct connection type, making it unsuitable for IC implementation. Furthermore, since the second switch (7) is inserted directly into the signal path, noise is generated during switching, which is a problem.

(d) Means for Solving the Problems The present invention has been made in view of the above points, and includes a sawtooth wave creation circuit that creates a sawtooth wave in response to a vertical trigger pulse, and a sawtooth wave creation circuit. a differential type integrating circuit that integrates the output sawtooth wave of the output sawtooth wave and generates a parabolic wave; a peak detection circuit that peak-detects the output sawtooth wave of the sawtooth wave generation circuit; and an output voltage of the peak detection circuit. a discharge circuit that compares the reference voltage of a reference power supply and discharges the charge charged in the capacitor in the peak detection circuit according to the difference, and discharges the charge charged in the capacitor in the peak detection circuit according to the difference, and The feature is that the reference voltage of the circuit is set. (According to the present invention) Since the sawtooth wave is peak-detected and the voltage corresponding to the peak detection output is used as the reference voltage of the integrating circuit, a coupling capacitor or switch is not required in the signal path. It is possible to create a desired parabolic wave without having to do so. or,
According to the present invention, when the value of the peak detection output increases to a predetermined value or more, the capacitor in the peak detection circuit is charged
Since the load is discharged, even if the frequency of the input vertical trigger pulse increases or changes, it is possible to respond immediately and obtain an appropriate detection output.

(v) Embodiment Figure 1 is a circuit diagram showing an embodiment of the present invention, in which (6) is a control transistor (8) to which a vertical trigger pulse is applied to the base from an input terminal (7), and a constant current A sawtooth wave generation circuit consisting of a charge/discharge capacitor (10) supplied with a constant current from a source (9), (11) a level shift circuit for level shifting the sawtooth wave generated at point B, (12) (13) is a second level shift circuit that further level-shifts the level-shifted sawtooth wave from the first rubel shift circuit (11); A capacitor (14) is a third level shift circuit for level shifting the sawtooth wave, and (15) is a first and second level shift circuit built in the third level shift circuit (14). A voltage dividing circuit consisting of resistors (16> and (17), (18) is connected between the differential amplifier circuit (19) and the output terminal and negative input terminal (-) of the differential amplifier circuit (19). An integrating circuit (40) consisting of a capacitor (20) connected to the capacitor (20) and a resistor (21) connected at one end to the capacitor (20) compares the voltage at point C with the reference voltage of the reference power supply (41). A comparison circuit (42) is a discharge circuit that discharges the charge of the capacitor (13) according to the output signal of the comparison circuit (40).

Next, the operation will be explained. Now, when a vertical trigger pulse as shown in FIG. 4(a) is applied to the input terminal (7), the control transistor (8
) is turned off, the constant current from the constant current source (9) flows to the charging/discharging capacitor (1o), and the voltage at the upper end B of the charging/discharging capacitor (10) gradually increases. Trigger pulse rH.

During the level period, the control transistor <8) is on, so
The charge/discharge capacitor <10) discharges rapidly. Therefore, a sawtooth wave as shown in Fig. 4 (b) is obtained at point B, and +4vll! (However, vo
(forward voltage of the PN junction) is level-shifted. The level-shifted sawtooth wave is transferred to the second level shift circuit (
12) to the base of the transistor (22) and to the base of the transistor (23). Since the capacitor (13) for peak detection is connected to the emitter of the transistor (23), the applied sawtooth wave is peak detected and converted into a DC voltage.Here, the sawtooth wave at point B If the maximum amplitude of the wave is ■, then
The voltage V (C) at point C is V (C) - v, + 3 Vll++ ...
. . . (1), and is expressed as the -dotted chain line C in Fig. 4 (c).

Also, at the point which is the emitter of the transistor (22) -
■. A level-shifted sawtooth wave is obtained, and the maximum value of the amplitude of the sawtooth wave V(D)max is V())rlla
X= Vs+ 3 Vllt ””””’ (2
), and the minimum value V(D)ff1in is V(D)mt
n=3 Vsx・・・・・・・・・・・・・・・
...(3), as shown by the solid line in Figure 4 (c).

The aforementioned voltage obtained at point C is level-shifted by -V and lI by the transistor (24), and then divided by the voltage dividing circuit (15). When the resistance values of the first and second resistors (16) and (17) constituting the voltage dividing circuit (15) are set equal, the voltage at point E is V. is, V<t) = 1/2Vs+ 2 Vat...group...
... (4), as shown by the solid line E in Figure 4 (c). Since the voltage v(l!,) is further level-shifted by the transistor (25), the voltage at point F is V(,,, Vry)-1/2Vs+Vsp +++++m+m*
+ (5), as shown by the solid line F in FIG. 4(C).

On the other hand, the sawtooth wave obtained at the point is caused by the transistor (26)
Since the level is shifted by -2Vo in (27), the maximum value V(Q)fflaX of the voltage V(o) at point G is V(c)
llnaX-Vs+Vit “””””old・” (
6), and the minimum value V(o)min is V (G)min = V my, ...
・・・・・・・・・・・・・・・・・・ 7) This is shown as the dotted line G in FIG. 4(C).

Here, as is clear from equations (5), (6), and (7), the solid line F in FIG. 4(c) is exactly 172 with respect to the amplitude of point BG.

The sawtooth wave G in Figure 4 (C) generated at point G is applied to the negative input terminal (-) of the integrating circuit (-), and the voltage F in Figure 4 (C) generated at point F is its Applied to the positive input terminal (+). Therefore, during the period T1 in FIG. 4(C), current flows in the direction shown in the capacitor (20) constituting the integrating circuit (18), and the capacitor (20) is charged, and during the period T, the capacitor (20) is charged. (20) is discharged.

Furthermore, during the period T of FIG. 4(c), the switch (28) is closed in response to the vertical trigger pulse of FIG. 4(a), so the integration operation is stopped.

The slope of the sawtooth wave G in FIG. 20) The amount of charge and discharge can be made the same.

Therefore, the output terminal (29) of the integrating circuit (18) has a fourth
As shown in Figure (d), a parabolic wave whose apex coincides with the time t when the capacitor (20) switches from charging to discharging can be obtained.

Now, the above explanation is based on the case where the frequency of the vertical trigger pulse that can be applied to the input terminal (7) is 60 Hz in the CNT SC system), and the case where the signal is at a regular frequency (hereinafter referred to as synchronization). However, the frequency of the vertical trigger pulse may change and become lower when switching channels or turning on the power (hereinafter referred to as asynchronous time).

For example, in the case of an asynchronous state when the power is turned on, the "L" level period of the vertical trigger pulse becomes longer, so that the amplitude of the sawtooth wave generated at point B becomes larger than that in the synchronous state. Then, the charging voltage of the capacitor (13) also increases accordingly. From this state, when the deflection circuit system becomes stable and synchronized, the large charge in the capacitor (13) cannot be discharged because the discharge path is formed only at the base of the transistor (24). This takes a long time, and there is a fear that it will take a long time to obtain the correct peak detection output. in general,
If such a problem occurs, a resistor is connected in parallel to the capacitor (13) to cause the desired discharge. However, in the peak detection circuit shown in FIG. 1, if the discharge current is large, the correct peak detection output tFt cannot be obtained, and such a method cannot be used.

Therefore, in the present invention, the capacitor (13)
When the charging voltage exceeds the reference voltage of the base 4 power supply (41) of the comparator circuit (40), the discharge circuit (42) is driven to automatically discharge the charge of the capacitor (13), and the charging voltage is excessively high. Even if the value reaches the predetermined value, it is immediately controlled to be below the predetermined value. Fig. 7 is a circuit diagram showing a specific example of the circuit, and (30) is the transistor (23) at the time of synchronization.
reference power supplies (31a) to (31c) that generate a voltage equal to the maximum amplitude V of the sawtooth wave applied to the base of the
is the base 4 (diode for level shifting the voltage) of the reference power supply (30); (32) is the base of the diode (30);
It is a discharge transistor connected to one end H of 1a) to (31c) and whose emitter is connected to point C via a discharge resistor (33). Note that circuit elements that are the same as those in FIG. 1 are given the same reference numerals. Now, assuming that the state is synchronous, the voltage at point C, which is the upper end of the capacitor (13), is < V, + 3 V + as is clear from equation (1).
+t. The voltage at point H is Vs+3V++! Therefore, the discharge transistor (32) is off. Therefore, the voltage at point C remains the same as it is at the transistor (24).
is applied to If this state becomes an asynchronous state, the voltage at point C increases while the transistor (23) is on. Then, the discharge transistor (32) is turned on, and current from the emitter of the transistor (23) flows through the discharge resistor (33) and the discharge transistor (32). Then, when the transistor (23) turns off, the charge in the capacitor (13) is transferred to the discharge resistor (
33) and the discharge transistor (32).

Therefore, the voltage at point C is between the capacitor (13) and the discharge resistor (
33>, gradually decreases to the original value, that is, V
It drops to s+3VB. Therefore, even if the next synchronization state occurs, the normal peak detection output (Vs + 3 V
BI+) Wotora'/Ji, 2. It can be applied to the evening (24) and (7) bases, and the response of peak detection can be made good.

(G) Effects of the Invention As described above, according to the present invention, a parabolic wave with good waveform symmetry can be created without requiring a coupling capacitor or switch in the signal path. Furthermore, according to the present invention, even when the input vertical trigger pulse changes from an asynchronous state to a synchronous state, it is possible to immediately obtain an appropriate peak detection output. A desired parabolic wave can be created immediately.

[Brief explanation of drawings]

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, and Figs. 3 (a) and (b) are for explanation of Fig. 2. Waveform diagram of Fig. 4 (
A) to (D) are waveform diagrams for explaining Fig. 1, Fig. 5 is a circuit diagram showing a conventional parabolic wave generation circuit, and Figs. 6 (A) to (D) are explanations of Fig. 5. waveform diagram for use in
and FIG. 7 are circuit diagrams showing specific circuit examples of the present invention. (6)...Sawtooth wave creation circuit, (11)...Second
Level shift circuit, (12)...Second level shift circuit, (13)...Detection capacitor, (14)
...Third level shift circuit, (18)...Integrator circuit. Figure Figure Figure 4'''j Tl□T2→ Tri Figure 6 Figure 7

Claims (4)

[Claims] (1) a sawtooth wave creation circuit that creates a sawtooth wave in response to a vertical trigger pulse; a differential integration circuit that integrates the output sawtooth wave of the sawtooth wave creation circuit to generate a parabolic wave; A peak detection circuit that peak-detects the output sawtooth wave of the sawtooth wave creation circuit, and compares the output voltage of the peak detection circuit with a reference voltage of a reference power supply, and adjusts the capacitor in the peak detection circuit according to the difference. 1. A parabolic wave generation circuit comprising: a discharging circuit for discharging charges charged in a parabolic wave generating circuit, and a reference voltage of the integrating circuit is set according to an output voltage of the peak detection circuit. (2) When synchronizing the reference voltage of the reference power supply in the discharge circuit (
2. The parabolic wave generation circuit according to claim 1, wherein the voltage is set to a value equal to the output voltage of the peak detection circuit (when a regular vertical trigger pulse is applied). (3) The discharge circuit is comprised of a PNP transistor whose base is connected to a reference power source and whose emitter is connected to one end of a capacitor in the peak detection circuit via a resistor. The parabolic wave generation circuit described in . (4) Claims 1, 2, and 3 further include a voltage dividing circuit that divides the output voltage of the peak detection circuit into 1/2 and applies the divided voltage to the integrating circuit as a reference voltage. The parabolic wave generation circuit described in .