JP2004320501A - Scanning rate modulating device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a scanning rate modulating device which is equipped in a television receiver capable of receiving signals of a plurality of characteristics for narrowband and wideband or the like, can perform the optimum contour correction according to characteristics of a signal to be inputted and can improve image quality. <P>SOLUTION: Differential processing is performed to a video signal to be inputted from an input terminal 1 by an HPF2. Its output is amplified by a preamplifier circuit 3a or a preamplifier circuit 3b of a preamplifier part 3 and inputted in the final output stage 5. The final output stage 5 drives VM current based on the output of the preamplifier part 3 to a VM coil 6. The number of windings of the VM coil 6 is switched to N or n by a switching circuit 7. Switching of the VM coil 6 and switching of the preamplifier circuit 3a or the preamplifier circuit 3b in the preamplifier part 3 are performed by switching signals from a CPU, etc. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a scanning speed modulating device, and more particularly, to a scanning speed modulating device which modulates a horizontal scanning speed of an electron beam in a television receiver to correct an outline of an image and improve image quality, and is suitably applied to a scanning speed modulating device. is there.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, a method of modulating a horizontal scanning speed has been known as a means for correcting an outline of an image displayed on a television receiver. Here, the modulation of the scanning speed will be briefly described with reference to FIG. FIG. 3A is an example of an image on a tube surface of a cathode ray tube (hereinafter, referred to as a CRT (Cathode Ray Tube)), and FIG. 3B is an enlarged view of the black and white border. FIG. 3C shows a black and white signal level, FIG. 3D shows brightness (luminance), and FIG. 3E shows a horizontal scanning speed. FIG. 3F is an enlarged view of the image after the horizontal scanning speed has been modulated.
[0003]
In the case of the image shown in FIG. 3A, the boundary on the screen is not clear as shown in FIG. 3B due to the rise of the signal shown in FIG. 3C and the focus characteristic of the CRT (particularly the white side). FIG. 3D shows the change in luminance at this time.
[0004]
Therefore, as shown in FIG. 3E, the horizontal scanning speed in the first half of the boundary is increased, and the horizontal scanning speed in the second half is reduced. That is, by modulating the scanning speed, an image as shown in FIG. 3F in which the boundaries on the screen are clear is obtained. This is because, by changing the scanning speed, the number of electrons from the cathode that hits a certain area of the phosphor of the CRT for a certain time changes, and the brightness changes accordingly.
[0005]
As shown in FIG. 3F, in this example, the speed modulation is such that the deterioration of the focus of the signal and the CRT is compensated. However, by further increasing the modulation amount of the scanning speed, the black side of the boundary becomes blacker and the white side becomes blacker. The side can be made whiter, and it becomes possible to obtain outline emphasis.
[0006]
Next, an example method of modulating the scanning speed will be described. FIG. 4 shows an example of the configuration of a conventional scanning speed modulation device. Hereinafter, the scanning speed modulation device shown in FIG. 4 will be described with reference to a waveform diagram shown in FIG. First, a video signal input from an input terminal 11 is first-order differentiated through an HPF (High Pass Filter) 12. For example, in the case of the video signal of the level shown in FIG. 5A, the signal current and voltage after the first differentiation are as shown in FIG. 5B.
[0007]
The output of the HPF 12 is amplified through the preamplifier circuit 13, and the output of the preamplifier circuit 13 is supplied as a drive current to an auxiliary deflection coil (hereinafter, referred to as a VM coil) through a final output stage (VM-OUT) 14.
[0008]
FIG. 6 shows an example of the configuration of the final output stage 14 and the VM coil. That is, in the final output stage 14, the emitter side of the pnp transistor Q1 as the first transistor is connected to the power supply Vcc as the first reference potential. The emitter side of the npn-type transistor Q2 as the second transistor is connected to the ground which is the second reference potential. That is, the collector-emitter paths of the first and second transistors are connected between the first reference potential and the second reference potential.
[0009]
The collector side of the transistors Q1 and Q2 is connected to the ground via the VM coil 6. The description of the resistor, the capacitor and the like is omitted here. By supplying the output of the amplifier 3 to the bases of the transistors Q1 and Q2, a current flowing between the emitter and collector of the transistor Q1 or between the collector and emitter of the transistor Q2 and corresponding to the output of the amplifier 3 is supplied to the VM coil. Is done.
[0010]
As shown in FIG. 7, the VM coils are arranged above and below the grid G4 of the electron gun of the CRT. Therefore, when a current is supplied from the final output stage 14 to the VM coil, the horizontal movement of electrons from the cathode changes due to the Lorentz force caused by the magnetic field generated thereby. For example, when the time (t) is shown on the horizontal axis and the displacement (distance from the horizontal left end on the screen of the CRT) is shown on the vertical axis, the displacement of the signal current shown in FIG. 5B is as shown in FIG. 5C. become.
[0011]
That is, the change in the Lorentz force generated by the first derivative current is just the displacement of the beam, and when this is converted into the velocity, V = dx / dt, so that the second derivative is obtained as shown in FIG. 3E or 5D. Thus, the velocity modulation effect as shown in FIG. 3F is obtained.
[0012]
At present, digital broadcasting has begun in various parts of the world including Japan, and some signal formats having a bandwidth of 30 MHz, such as HD (High Definition) signals, have begun to exist. On the other hand, there is also a terrestrial broadcast of the conventional NTSC (National Television System Committee) system, which is about 4.2 MHz, which is much narrower than the HD signal, and it is necessary to receive and reproduce both signals. is there.
[0013]
Patent Document 1 below discloses a scanning speed modulation device that performs the above-described contour correction by modulating the horizontal scanning speed for two or more different signal bands. Patent Document 2 discloses an electron beam driving magnetic field generation device that can save power.
[0014]
[Patent Document 1]
JP-A-7-135576
[Patent Document 2]
JP-A-7-272639
[Problems to be solved by the invention]
However, the above-described conventional modulation of the scanning speed has the following problems. Number of turns (N) of the VM coil, inductance (L) of the VM coil, correction amount = displacement amount (X), velocity modulation (hereinafter referred to as VM (Velocity Modulation)) current frequency (fi = di / dt), VM The relationship between the voltage (V) at both ends of the coil and the VM current (I) is the square of (1) V = L × di / dt, (2) X∝I × N, (3) L∝N.
[0017]
From the relations (1) to (3), the following can be understood. That is, as the frequency increases, the voltage across the VM coil increases, the dynamic range on the collector side of the transistors Q1 and Q2 shown in FIG. 6 decreases, and the current driving capability of the final output stage 14 decreases. Thus, even if a wideband signal as shown in FIG. 8A is input to the final output stage 14, as shown by the thick line N in FIGS. 8B, 8C, and 8D, a narrow portion in which the VM current does not sufficiently flow in the high-frequency portion. This results in a speed modulation device having band characteristics. 8A shows the frequency characteristics of the input signal of the final output stage 14, FIG. 8B shows the frequency characteristics of the VM coil voltage, FIG. 8C shows the frequency characteristics of the VM coil current, and FIG. 4 shows the frequency characteristics of a quantity.
[0018]
The only way to avoid this, that is, to increase the bandwidth, is to reduce the voltage generated at both ends of the VM coil. For that purpose, the only way is to reduce the inductance of the VM coil, that is, reduce the number of turns of the VM coil. According to the above-mentioned relation (3), when the number of turns of the VM coil is reduced, the voltage drop at that time is effective by the square of the reduced number of turns, so that the effect is large. 8B and 8C indicate frequency characteristics when the number of turns of the VM coil is reduced. However, when the number of windings is reduced, the correction amount X is determined by the multiplication of the current (I) actually flowing through the VM coil and the number of windings (N) of the VM coil according to the above-described relationship (2). Inevitably, as shown by n. Therefore, it has been very difficult to realize a velocity modulation device having a large amount of correction and having a wide band characteristic.
[0019]
Next, the power consumption of the speed modulation device will be described. The power consumption of the speed modulation device is mainly determined by the collector loss (Pc) of the two transistors (Q1 and Q2 shown in FIG. 6) of the final output stage 14. The collector voltages of these two transistors fluctuate according to the respective currents in real time, but are on average about Vcc / 2 irrespective of the number of turns of the VM coil. Since this output stage is a class B amplifier, the emitter voltage of the transistor Q1 is a voltage slightly lower than Vcc, the emitter voltage of the transistor Q2 is very small at 1 V or less, and the average Vce of each transistor is low. Is considered to be approximately Vcc / 2.
[0020]
Since Pc = Vce × Ic, and Vce does not depend on the number of turns of the VM coil as described above, the power consumption of the speed modulator is substantially determined by the VM coil current Ic. Therefore, simply increasing the current of the VM coil greatly increases power consumption. For these reasons, in a television receiver capable of receiving only a narrow-band signal, in order to obtain a necessary correction amount (∝I × N), the number of turns of the VM coil is increased and the consumption of the VM current is reduced. It is common to reduce power.
[0021]
However, as described above, when the number of windings of the VM coil is reduced to widen the band, the amount of correction is reduced, but the only way to improve this is to increase the current. Disadvantageously increases.
[0022]
As described above, the speed modulation device in which the correction amount by the speed modulation is increased is insufficient for the HD signal in terms of the band, and the correction amount is insufficient for the wideband speed modulation device that satisfies the HD signal. Would. In addition, power consumption is increased more than necessary. Therefore, it is difficult to modulate an ideal scanning speed for a plurality of signal characteristics such as a narrow band and a wide band.
[0023]
SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a scanning speed modulation device capable of modulating a scanning speed according to signal characteristics such as a plurality of signal bands and suppressing power consumption and obtaining a sufficient correction amount.
[0024]
[Means for Solving the Problems]
In order to achieve the above object, the invention according to claim 1 includes a differentiating means for differentiating a video signal, an amplifying means for amplifying an output of the differentiating means, and a speed modulation current for generating a speed modulation current based on an output of the amplifying means. Generating means, supplied with a velocity modulation current, an auxiliary deflection coil for modulating the horizontal scanning speed of the electron beam of the cathode ray tube, and switching means for switching the number of turns of the auxiliary deflection coil based on characteristics of a video signal. Is a scanning speed modulation device.
[0025]
According to the scanning speed modulation device of the present invention configured as described above, the voltage appearing at both ends of the auxiliary deflection coil becomes large, and the dynamic range of the speed modulation current generating means for driving the current flowing through the auxiliary deflection coil is insufficient. In such a case, the switching means switches the number of turns of the auxiliary deflection coil based on the characteristics of the video signal, thereby compensating for the insufficient dynamic range and modulating the ideal scanning speed.
[0026]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, a scanning speed modulation device according to an embodiment of the present invention will be described. FIG. 1 shows an example of a configuration of a scanning speed modulation device of a television receiver. The main circuit blocks of the scanning speed modulation device are the same as the scanning speed modulation circuit described with reference to FIG. That is, the scanning speed modulation device according to this embodiment includes an input terminal 1, an HPF 2, an amplification unit 3 including a preamplification circuit, a final output stage 5, a VM coil 6, and the like.
[0027]
The HPF 2 differentiates a video signal input from the input terminal 1, for example, a luminance (Y) signal. In the scanning speed modulation device according to this embodiment, the amplification unit 3 includes a plurality of preamplification circuits. In the example shown in FIG. 1, the amplifying unit 3 has a configuration including a narrow band preamplifier circuit 3a and a wideband preamplifier circuit 3b.
[0028]
The amplifier 3 amplifies the output of the HPF 2 according to the characteristics of each of the preamplifier circuits. In the example shown in FIG. 1, the preamplifier circuit 3a performs amplification for a narrow band and the preamplifier circuit 3b performs amplification for a wide band with respect to the output of the HPF 2. The output of the amplifier 3 is output to the final output stage 5 according to the state of the switch circuit 4 described later.
[0029]
The final output stage 5 generates a current based on the output of the amplifier 3, and supplies the current to the VM coil 6. The final output stage 5 has, for example, a configuration similar to that of FIG. 6 described above.
[0030]
The VM coil 6 is a coil whose number of turns changes according to a state of a switch circuit 7 described later. The VM coil 6 is configured to be switched between, for example, one of N turns for a narrow band and n turns for a wide band (N> n). In the example shown in FIG. 1, one end of the VM coil 6 has a final output. The other end, which is connected to the stage 5 and has N turns for a narrow band, is grounded. Switching between the N-turn for the narrow band and the n-turn for the wide band is performed by the switch circuit 7 controlling the open / short circuit between the n-th turn of the VM coil 6 and the ground.
[0031]
For example, if the number of turns of the VM coil 6 is changed from N to n (N> n) to obtain the same correction amount as before the change, the current flowing through the VM coil 6 needs to be multiplied by N / n. In this case, the above-described switch circuit 4 is switched so that the amplification factor of the amplifier unit 3 becomes N / n times, for example, in synchronization with the switch circuit 7. Thus, it is possible to avoid a shortage of the correction amount due to a decrease in the number of turns of the VM coil 6.
[0032]
The VM coils 6 are provided above and below a grid G4 of a CRT electron gun (not shown). As described with reference to FIG. 7, when the VM current is supplied, the VM coil 6 generates a magnetic field corresponding to the number of turns of the VM coil 6, and the Lorentz force by the magnetic field causes the electron from the cathode to be generated from the cathode. Change the horizontal movement of the. That is, the horizontal scanning speed is modulated. Therefore, in a television receiver provided with this scanning speed modulation device, a good image on which contour correction by the speed modulation effect has been performed can be obtained.
[0033]
The above-described switch circuits 4 and 7 are switched based on a switching signal according to characteristics such as a band of a video signal. This switching signal is controlled by a CPU (Central Processing Unit) or the like included in a television receiver (not shown) based on the signal characteristics, and is supplied to the switch circuit 4 and the switch circuit 7.
[0034]
The determination of the signal characteristics in the CPU or the like is performed, for example, because the horizontal frequency of the wideband HD signal is 33.75 kHz, while the narrowband NTSC video signal is 15.75 kHz. This is done by switching according to.
[0035]
In this speed modulation device, the dynamic range at the final output stage 5, the current capacity that can be passed by the transistors used, and the effect (VM sensitivity) on the actual CRT screen when a current is passed through the VM coil 6. The optimum number of windings and the current value of the VM coil 6 are determined according to various conditions such as.
[0036]
In the example shown in FIG. 1, first, the number of turns N of the VM coil 6 and the voltage gain G1 of the preamplifier circuit 3a are set so that a sufficient band and current can be obtained for a narrowband signal. The correction amount at this time is defined as X1. FIG. 2A shows a relationship between a correction amount and a frequency characteristic when a narrowband signal is received.
[0037]
When the broadband signal is received, the number of turns of the VM coil 6 is reduced to find an ideal number of turns. Assuming that this is n1, then the voltage gain G2 of the preamplifier circuit 3b is set to G1 × N / n1, and under this condition, it is confirmed whether or not there is any amplification deterioration of the high frequency component due to insufficient dynamic range of the final output stage 5. .
[0038]
If there is any deterioration, the number of turns of the VM coil 6 is further reduced and the voltage gain G2 is increased, and finally the ideal number of turns n and the voltage gain G2 for the high-frequency signal are determined. The correction amount at this time is X2. FIG. 2B shows a relationship between a correction amount and a frequency characteristic when a wideband signal is received. In this way, N, n, G1, and G2 are determined, and these optimum values are selected according to the signal band to be received, so that ideal band characteristics are theoretically equivalent to narrowband signals and wideband signals (see FIG. 2 (X1 = X2) can be obtained.
[0039]
As described above, according to the scanning speed modulation apparatus of this embodiment, the switch circuit 7 controls the number of turns of the VM coil 6, and the switch circuit 4 controls the output of the amplifier 3. This makes it possible to modulate the scanning speed according to the signal characteristics, such as narrow band and wide band. For example, when applied to a conventional television receiver having a frequency characteristic capable of receiving only a narrow-band signal, when a narrow-band signal is received, the same frequency characteristic and correction amount as in the related art can be maintained. When a wideband signal is received, the switching circuit 7 reduces the number of turns of the VM coil 6 (equivalently, lowers the L value) to compensate for the insufficient dynamic range and to increase the bandwidth according to the signal band. It is possible to secure an appropriate correction amount. Therefore, in a television receiver capable of receiving both a narrowband signal and a wideband signal, both the narrowband signal and the wideband signal can have good image quality.
[0040]
Further, according to the scanning speed modulation apparatus according to the embodiment, since the scanning speed can be accurately modulated regardless of the signal band, even if a wide band signal is received in the television receiver, the scanning speed modulation device is thin. This makes it possible to enhance image quality such as sharp edge enhancement and reproducibility of details. Also, when a narrow band signal is received, sharpness can be obtained by strong edge enhancement equivalent to a television receiver capable of receiving only a narrow band signal.
[0041]
Also, when a narrow band signal is received, the VM current is automatically reduced compared to when a wide band signal is received, so that a significant reduction in power consumption is possible compared to a configuration without a switch that reduces the number of turns. It is. For example, when VCC supplied to the transistor of the final output stage 5 is 135 V, a VM current of 0.2 A average flows when a wideband signal is received, and the VM current is 80 V when a narrowband signal is received. %, It becomes 21.6 W from 27 W, and the power consumption of 5.4 W is reduced.
[0042]
The present invention is not limited to the embodiment of the present invention described above, and various modifications and applications are possible without departing from the gist of the present invention. For example, in the above-described embodiment, the same correction is obtained for the narrow-band signal and the wide-band signal. However, in practice, the same correction may not always be obtained due to a difference in band or a difference in image formation. (X1 ≠ X2 in FIG. 2). In such a case, the optimum N, n, G1, and G2 may be selected while paying attention to the shortage of the dynamic range of the final output stage 5.
[0043]
Further, when the VM current can flow in a wide band, the correction amount tends to be larger than the theoretical value. Therefore, in the above-described embodiment, both the number of turns of the VM coil 6 and the output of the amplification unit 3 are switched in order to obtain theoretically equivalent or optimal correction. The speed modulation may be performed only by changing the number of turns of No. 6.
[0044]
Further, in the embodiment, the case where two types of signal bands of a narrow band and a wide band signal are received as the types of signal characteristics has been described, but the present invention is not limited to this. For example, even in the NTSC system, there is a DVD (Digital Versatile Disc) having a band almost twice as large as that of terrestrial broadcasting. In addition, even with the same wideband signal, there is a signal having a different horizontal frequency such as a 720p signal (720 lines means progressive). Even in the case of such a difference in signal characteristics, it is possible to provide a plurality of types of outputs of the VM coil 6 and outputs of the amplifying unit 3 and realize an optimum speed modulation for each signal by appropriately selecting the number. .
[0045]
Further, by selecting the number of windings of the VM coil 6 and the gain of the amplifying unit 3 according to not only the band characteristics of the received signal but also the state of the television receiver, an optimum speed modulation characteristic can be obtained. For example, even if the input signal has a narrow band, the television receiver has a dual-screen or multi-screen function and uses these functions when using a compressed video (when the signal band extends inside the apparatus). If you use these functions, you can obtain the speed modulation effect by using the setting to switch to the wide band for the image quality. Improvement can be achieved.
[0046]
The modulation of the speed modulation is open to the user, so that the level of the speed modulation is set to medium or low, or the level is set to low according to the image quality mode or the like. Even if a wideband signal is received in a narrowband state where N is N and the voltage gain of the amplifying unit 3 is G1, if there is enough dynamic range in the final output stage 5 and the wideband can be maintained, the switch By setting the circuit 4 and the switch circuit 7 in a state for a narrow band, power consumption can be reduced.
[0047]
【The invention's effect】
As described above, according to the present invention, by changing the number of turns of the auxiliary deflection coil based on the characteristics of the video signal, it is possible to modulate the scanning speed corresponding to a plurality of video signals having different characteristics. In addition, it is possible to suppress an increase in power consumption. Therefore, it is possible to perform optimal contour correction for a plurality of video signals having different characteristics while suppressing power consumption.
[Brief description of the drawings]
FIG. 1 is a schematic diagram illustrating an example of a configuration of a scanning speed modulation device according to an embodiment of the present invention.
FIG. 2 is a schematic diagram illustrating an example of a relationship between a correction amount and a frequency characteristic when a scanning speed modulation device according to an embodiment of the present invention is used.
FIG. 3 is a schematic diagram for explaining contour correction by modulation of a scanning speed.
FIG. 4 is a schematic diagram illustrating an example of a configuration of a conventional scanning speed modulation device.
FIG. 5 is a schematic diagram for explaining scanning speed modulation.
FIG. 6 is a schematic diagram illustrating an example of a configuration of a final output stage.
FIG. 7 is a schematic diagram for explaining the principle of scanning speed modulation.
FIG. 8 is a schematic diagram illustrating frequency characteristics of the speed modulation device.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Input terminal, 2 ... HPF, 3 ... Amplification part, 3a ... Preamplification circuit (for narrow band), 3b ... Preamplification circuit (for wide band), 4,7 ...・ Switch circuit, 5 ・ ・ ・ Final output stage, 6 ・ ・ ・ VM coil

Claims (3)

A differentiating means for differentiating the video signal,
Amplifying means for amplifying the output of the differentiating means;
Speed modulation current generation means for generating a speed modulation current based on the output of the amplification means,
An auxiliary deflection coil supplied with the velocity modulation current and modulating a horizontal scanning velocity of an electron beam of a cathode ray tube;
Switching means for switching the number of turns of the auxiliary deflection coil to be reduced when the video signal is a wideband signal. 2. The scanning speed modulation apparatus according to claim 1, wherein said amplification means is provided for each characteristic of said video signal, and further comprises switching means for switching outputs of said plurality of amplification means. The speed modulation current generating means includes a collector-emitter path of the first and second transistors connected between the first reference potential and the second reference potential, and a collector connection point of the first and second transistors. 2. The scanning speed modulation apparatus according to claim 1, wherein the auxiliary deflection coil is inserted between the second reference potential point and the second reference potential point.

Images