JPH01238279A - Velocity modulation circuit - Google Patents

Abstract

PURPOSE:To stabilize contour correction by suppressing a signal level by an automatic gain control signal in case a differential signal outputted from a primary differentiation circuit comes excessive in a velocity modulation circuit which corrects the contour of a video displayed on a cathode-ray tube by modifying the electron beam scanning speed of the cathode-ray tube. CONSTITUTION:A video signal SV is differentiated in the primary differentiation circuit 2, and thus obtained differential signal SH is inputted to a velocity modulation output circuit 12, and the circuit 12 so modifies the scanning speed of the cathode-ray tube that velocity-modulated output signal SL2 generated in itself corresponds to the waveform of the signal SH. In the title circuit 20 which is constituted as mentioned above, the automatic gain control circuit 21 is inserted newly between the primary differentiating circuit 12 and the circuit 12, so that a differential signal SH outputted from the circuit 2, if its level comes excessive, the level is controlled to come within the suitable operating range of the circuit 12 by the circuit 21. As a result, the contour correction processing is stabilized.

Description

DETAILED DESCRIPTION OF THE INVENTION A. Field of Industrial Application The present invention relates to a speed modulation circuit, and is particularly applicable to a speed modulation circuit for cathode ray tubes.

B. Summary of the Invention The present invention provides a speed modulation circuit that corrects the outline of an image displayed on a cathode ray tube by changing the electron beam scanning speed of the cathode ray tube. When the signal becomes excessive, stable contour correction can be performed by suppressing the signal level using an automatic gain control circuit.

C. Prior Art Conventionally, in image receiving devices using cathode ray tubes, a speed modulation circuit was used to emphasize the outline of the video signal to prevent the outline of the image on the display screen from becoming blurred. (Special Publication No. 54-2768)
Publication No. 4, Special Publication No. 54-27fj85, Special Publication No. 5
4-27686).

That is, as shown in FIG. 4, the speed modulation circuit 10 inputs the video signal Sv through the preamplifier circuit 1 to the first-order differentiator circuit 2 and differentiates it, thereby obtaining the signal Sv as shown in FIG. 5(A). , when the brightness suddenly changes at time points t1 and t2, the signal level rises in a pulse-like manner at the contour portion, and the waveform at the tip changes to have a rounded shape (Fig. 5). B)), and after amplifying this correction signal SH with a predetermined gain in the amplifier circuit 3, it is sent to the speed modulation output circuit 4 as an output signal S0.

The speed modulation output circuit 4 performs speed modulation processing on the output signal S0, obtains a drive signal SLI, and sends this to the speed modulation coil.

The velocity modulation coil LVM is provided before or after the deflection yoke of a cathode ray tube (not shown), and in addition to the main deflection scanning by the deflection yoke, it generates a magnetic field perpendicular to the horizontal scanning direction of the electron beam by a drive signal SLI. By generating , the horizontal scanning speed of the electron beam is accelerated or decelerated, thereby making it possible to give a visually clear impression of the boundaries between bright and dark areas of the image.

For example, when trying to express the boundary between bright and dark areas in an image, the brightness of the beam spot is determined by a video signal Sv whose signal level changes according to changes in the boundary, as shown in FIG. 5(A). , the brightness on the display screen changes as shown by the broken line waveform L1 in FIG. 6, but such a brightness change gives a visually slow impression, resulting in The image becomes indistinct with blurred outlines.

In contrast, a speed modulation coil LVN is used to increase the scanning speed of the electron beam at the boundary portion where the bright area changes to the dark area, and to slow down the scanning speed of the electron beam at the boundary area where the dark area changes to the bright area. By modulating the scanning speed of the electron beam as shown in FIG. 6, the image displayed on the display screen can be made even clearer by emphasizing the outline of the image as shown by the solid waveform L2 in FIG.

D Problems to be Solved by the Invention However, in practice, when the frequency characteristics of the input signal are unstable, such as a television broadcast wave signal, the frequency characteristics of the preamplifier circuit 1 and the first-order differential circuit 2 are unstable. Depending on the situation, the level of the correction signal SN output from the first-order differentiator circuit 2 may become excessive, and if this is left unchecked, an excessive power supply current will be drawn into the speed modulation output circuit 4. (e.g. transistor) may be damaged.

In order to solve this problem, conventionally, the power supply current ■ is supplied from the current source VCC. A method has been adopted in which the power supply current Ic is limited by inserting a current limiting circuit 5 into the circuit that draws the current Ic.

However, in this case, when the current limiting circuit 5 operates, the waveform at the tip of the drive signal SLI is flattened as shown in FIG. There was an unavoidable problem that the image would become extremely thick and unnatural.

The present invention has been made in consideration of the above points, and it is an object of the present invention to propose a speed modulation circuit that does not cause unnatural contour correction even when an excessively large correction signal is generated.

E Means for Solving Problem E To solve this problem, in the present invention, the video signal Sv is differentiated in the first-order differentiator circuit 2, and the differentiated signal 5N
(SF) is input to the speed modulation output circuit 12, and the speed modulation output circuit 12 changes the scanning speed of the electron beam of the cathode ray tube so as to correspond to the differential waveform of the differential signal 5N (SF). In the speed modulation circuit 20 that corrects the outline of the image displayed on the cathode ray tube by obtaining SL2, an automatic gain control circuit 21 is inserted between the first-order differentiation circuit 2 and the speed-modulation output circuit 12, and the first-order differentiation When the differential signal SH output from the circuit 2 becomes excessive, the automatic gain control circuit 21 suppresses the signal level within an appropriate operating range of the speed modulation output circuit 12.

By inserting the automatic gain control circuit 21 between the F-action first-order differentiator circuit 2 and the speed modulation output circuit 12, when the eight differential signals output from the first-order differentiator circuit 2 become excessive, they can be speed-modulated. The output circuit 12 can be controlled within an appropriate operating range, thereby stably modulating the scanning speed of the electron beam.

G example An embodiment of the present invention will be described in detail below with reference to the drawings.

In FIG. 1, in which parts corresponding to those in FIG. Send to.

Here, the automatic gain control circuit 21 receives the correction signal S.

The speed modulation output circuit 12 has a gain control amplifier circuit 11 that amplifies and sends out an output signal S, and a drive detection circuit 13 that controls the gain of the output signal S. When the peak detection signal Sp and the average value detection signal S^ are obtained, the drive detection circuit 1
3 detects the signal levels of the peak detection signal S2 and the average value detection signal SA, and sends gain control signals SCI and SCZ such that the signal levels fall within a proper operating range to the gain control amplifier circuit 11 to adjust the gain. Take control.

That is, the gain control amplifier circuit 11, as shown in FIG. , C4 and power supply V
8 and bias resistance R%, R5 and base resistance R7, R1
It consists of a negative side amplifier circuit AMPN consisting of 1, and is shown in FIG.
The correction signal SH (Fig. 3 (B)) obtained by differentiating the video signal Sv as shown in A) in the first-order differentiator circuit 2 is converted into positive and negative signals through capacitors C1 and C2 connected to the input terminal a. It is input to the side amplifier circuit AMP and the input side transistors QI and Q of AMPH.

Thus, the positive side amplifier circuit AMPP amplifies the positive component of the correction signal SN and sends it as an output signal S via the output resistor R9, and the negative side amplifier circuit AMPP x
The negative component of the correction signal SH is amplified and sent as an output signal SF via the output resistor R1l+.

The speed modulation output circuit 12 is composed of transistors Q and Q, resistors R1 to R11l, and capacitors C1 to C3, and when the positive or negative output from the gain control amplifier circuit 11 is received at the base of the transistor Q, A positive or negative current is passed through the speed modulation coil LVH via the capacitors C1 and C4.

Here, the speed modulation output circuit 12 is the gain control signal width circuit 1
The output signal SF output from 1 is the peak detection signal SP
is applied to the differentiating circuit 14 (consisting of a capacitor C6 and a resistor RI) of the drive detection circuit 13 for differentiation, and then sent to the base of a transistor Q7, as well as a smoothing circuit consisting of a resistor R3 and a capacitor C5, and a voltage dividing resistor R1'. l,
The average value detection signal SA obtained by R1° is sent to the base of the transistor Q and the transistor Q connected in parallel.

The collectors of the transistors Q and Q are connected to the base of the transistor Q3 which is connected to the bias power supply (the midpoint of the connection between the resistors R1 and R6) through the resistor R2°, and the output voltage is connected to the positive and negative amplifier circuits AMP. , and AMP,
is applied to the bases of transistors Q9 and QIO, which connect resistors Rit and R2t to the input ends of the transistors Q9 and QIO.

In the above configuration, for example, the correction signal S is shown in FIG.
), and when there is an increasing tendency, the transistor Q is turned on.

At this time, the transistor Q-, whose base is connected to the collector of the transistor Q1, is turned on, so that the transistor Q, whose base is connected to the emitter of the transistor Q, is turned off.

Therefore, the gain control signal Set is in a floating state, and the correction signal SH input via the capacitor C1 is directly transmitted to the transistor Q of the positive side amplifier circuit A M P p.
, and Qt, and is sent out as an output signal S via resistor R9.

On the other hand, when the human input signal is in the positive portion shown in FIG. 3(B) and has a decreasing tendency, the transistors Q and C
8 turns off and the base voltage of the transistor increases, causing Q and Q.

turns on and works. As a result, current flows into the gain control signal SCI, which lowers the base voltage of the transistor C2, and the signal level of the output signal S decreases by being biased to the voltage determined by the voltage division ratio of the resistors R1 and R21. .

Further, when the input signal is a negative component shown in FIG. 3(B), the gain control signal Sc! is activated by the transistor QI6. is applied to the transistor Q4 to control the bias voltage at the base of the transistor Q4.
A similar effect is obtained in the negative side amplifier circuit A M P M formed by C4 and A M P M .

Furthermore, when performing gain control using the average value detection signal S, the average value detection signal SA is sent to the transistor Q, and the transistors Qa, Q9, Ql. A similar effect can be obtained by controlling .

Thus, when an excessive current is about to flow through the speed modulation output circuit 12 due to the output signal SF, the amplitude of the correction signal SN (Fig. 3 (B)) is controlled and the waveform becomes as shown by the solid line in Fig. 3 (C1). Output signal S.

(Such amplitude control is called coring level control), and by suppressing excessive current, it is possible to protect the circuit elements of the speed modulation output circuit 12, and at the same time, as described above with respect to FIG. 5(C). As shown, the drive signal St
It is possible to prevent the waveform at the tip of the Z from being flatly clipped, thereby preventing unnatural contour correction from occurring.

According to the above configuration, even if an excessive correction signal is generated, the output signal S can be suppressed by providing the automatic gain control circuit 21, and thus stable contour correction can be performed.

Particularly in the case of the above embodiment, by controlling the gain using the average value detection signal SA, the average output of the speed modulation output circuit 12 can be kept within an appropriate range, and thus the output of the speed modulation output circuit 12 can be stabilized. can be converted into

In addition, by controlling the gain using the peak detection signal S, it is possible to control the amplitude of the drive signal while maximizing the amplification factor of the speed modulation output circuit 12 within an appropriate range.

In addition, in the above-mentioned embodiment, a case was described in which the peak detection signal S and the average value detection signal SA are used together to control the gain, but the present invention is not limited to this, and only one of them may be used.

Further, in the above embodiment, the gain is controlled by coring level control, but the present invention is not limited to this, and even if amplitude control (gain control) as shown in FIG. 3 (C2) is performed, A similar effect can be obtained.

Further, in the above-described embodiment, a case was described in which a speed modulation coil LV was used as the speed modulation means, but the present invention is not limited to this, and the present invention is not limited to this. The same effect can be obtained even if it is applied to other speed modulation means, such as speed modulation.

H Effects of the Invention As described above, according to the present invention, by inserting an automatic gain control circuit between the first-order differentiator circuit and the speed modulation output circuit, the differential signal output from the first-order differentiator circuit becomes excessive. In this case, this can be suppressed within the appropriate operating range of the speed modulation output circuit, and thus stable contour correction can be performed.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing one embodiment of the present invention, and FIG.
The figure is a circuit diagram showing the speed modulation circuit of the embodiment, Fig. 3 is a signal waveform diagram for explaining the circuit diagram, Fig. 4 is a block diagram showing a conventional example, and Fig. 5 is a signal waveform for explaining contour correction. 6 are characteristic curve diagrams showing the relationship between scanning position and brightness. 1... Preamplifier circuit, 2... Bow order differential circuit, 10120... Speed modulation circuit, 11...
... Gain control amplifier circuit, 12 ... Speed modulation output circuit, 13 ... Drive detection circuit, LVM.
... Speed modulation coil, SP ... Peak detection signal, SA ... Average value detection signal, Sc1. S
ex...Gain control signal.

Claims (1)

[Claims] A video signal is differentiated in a first-order differentiating circuit, the differentiated signal is input to a speed modulation output circuit, and the speed modulation output circuit adjusts the electrons of the cathode ray tube so as to correspond to the differential waveform of the differential signal. In a speed modulation circuit that corrects the outline of an image displayed on the cathode ray tube by obtaining a speed modulation output signal that changes the scanning speed of the beam, a An automatic gain control circuit is inserted, and when the differential signal output from the first-order differential circuit becomes excessive, the automatic gain control circuit suppresses the signal level to an appropriate operating range of the speed modulation output circuit. A speed modulation circuit characterized by: