JP2641259B2 - Convergence circuit - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a display device using a cathode ray tube, such as a projection display, a high-definition television, and a high-definition display, and more particularly to a convergence circuit thereof. It is.

[Conventional technology]

As a display device using a cathode ray tube, for example,
In a projection display, R (red), G
The three projection tubes (cathode ray tubes) and projection lenses respectively corresponding to (green) and B (blue) are positioned adjacent to each other in the horizontal direction, and the three-color image is projected and synthesized on one screen to form a color image. It has gained.

FIG. 6 is an explanatory diagram showing an image projected on a screen in a general projection type display.

In FIG. 6, 20 is a projection lens, 21 is a screen,
ω is the slope of blue light relative to green light. In FIG. 6, a projection tube to be arranged before the projection lens 20 is omitted.

As shown in FIG. 6, since the R and B images are projected from an oblique direction, a trapezoidal distortion (hereinafter, referred to as trapezoidal distortion) is generated based on the principle of projective geometry.

Generally, a projection type display is provided with a convergence circuit in order to correct such a trapezoidal distortion.

As a conventional convergence circuit, for example,
A configuration as shown in the figure is disclosed in Japanese Utility Model Publication No. 58-7750.

FIG. 7 is a circuit diagram showing a conventional convergence circuit.

In FIG. 7, 1 is a correction voltage generation circuit (GEN), 2
Is a negative feedback power amplifier, 3 is a convergence yoke (hereinafter referred to as CY), 4 is a projection tube, and 5 is a current detection resistor.

FIG. 8 is a waveform diagram showing a voltage waveform of a main part of FIG.

8, (a) shows the output voltage waveform of the correction voltage generating circuit 1, (b) shows the output voltage waveform of the power amplifier 2,
Shown respectively. Further, the T _H is the horizontal period, T _r is the horizontal blanking period, T _S is a horizontal scanning period, respectively.

Correction voltage generating circuit 1 shown in FIG. 7, for example, when a projection tube 4 is scanning the upper part of the screen, as the correction voltage E _1, Figure 8, such as (a), the horizontal period (T _H) A sawtooth voltage is output every time.

On the other hand, the current detection resistor 5 detects the current flowing through CY3 and performs negative feedback to the power amplifier 2.

Power amplifier 2, so that the voltage waveform is negatively fed back from the current detection resistor 5 is equal to the correction voltage E _1, the output voltage
By controlling the E _2, it is applied to CY3. As a result, the output voltage E ₂
Is a pulse-like waveform almost as shown in FIG. 8 (b) due to the differential action of the inductor component of CY3.

By the way, in the conventional convergence circuit as shown in FIG. 7, the power consumed by the power amplifier 2 has a horizontal period (T _H ) of about 10 μsec, which is a high speed (four times as fast as a normal television). In the case of a projection type display for display, it reaches about 20 W per color and about 60 W in total of R, G and B colors.

[Problems to be solved by the invention]

As described above, in the conventional convergence circuit, since the power consumed by the power amplifier is large, the amount of heat generated due to the power consumption is large, and as a result, the internal temperature in the display device increases. However, there is a problem that the reliability is reduced. Further, in order to lower the internal temperature, it is necessary to newly provide a cooling means or the like, and therefore, there is a problem that the price increases.

The object of the invention is to solve the above-mentioned problems of the prior art,
An object is to provide a convergence circuit with low power consumption.

[Means for solving the problem]

In order to achieve the above object, as a convergence circuit in a projection display device using a cathode ray tube, in the present invention, a convergence correction deflection coil provided in the cathode ray tube, and a convergence correction voltage for generating a convergence correction voltage Generating means, power amplifying means for amplifying the convergence correction voltage from the convergence correction voltage generating means, and a current output from the power amplifying means, and passing a high-frequency component including a horizontal scanning frequency component among them. A high-pass capacitor to be supplied to the convergence correction deflection coil, and a resistance means for guiding and supplying a low frequency component and a DC component of the current output from the power amplification means to the convergence correction deflection coil; Deflection coil for convergence correction Current detection resistance means for detecting a current flowing through the power detection means as a voltage, and a negative feedback circuit for negatively connecting the voltage detected by the current detection resistance means to the power amplification means, the power amplification means, the resistance means, A convergence correction deflection coil, a current detection resistor, and a negative feedback circuit form a DC loop gain circuit, and the high-pass capacitor and the convergence correction deflection coil form a series resonance circuit at the horizontal scanning frequency. A convergence circuit was constructed.

Further, in this convergence circuit, a low-pass filter for extracting a low-frequency component and a DC component of the current output from the power amplifying means in a path connecting the resistance means and the convergence correcting deflection coil; An amplifier configured to amplify the power of the output of the low-pass filter and a choke coil are connected in this order.

[Action]

At both ends of the high-pass capacitor, a potential difference having a polarity opposite to that of the potential difference at both ends of the convergence correction coil is generated for a high-frequency component including a horizontal scanning frequency component. Thus, the peak-to-peak value of the output voltage of the power amplifier, expressed as the combination of these two potential differences, can be reduced compared to the peak-to-peak value of the potential difference across the convergence correction coil. . Therefore, the power supply voltage to be supplied to the power amplifier can be reduced, and the power consumption can be reduced.

〔Example〕

 FIG. 1 shows a first embodiment of the present invention.

In FIG. 1, reference numeral 1 denotes a correction voltage generation circuit (GEN). As is well known, in this part, a horizontal period sawtooth is multiplied by a vertical period sawtooth to obtain a composite correction waveform. 2 is a power amplifier. 3 is CY, 5 is
This is a current detection resistor for detecting and feeding back the CY current. 6
Is a newly added capacitor, and 7 is a resistor for securing a finite current loop gain. In addition, other general projector components are omitted from FIG.

In the present embodiment, when the same CY current flows as in the prior art, the peak-to-peak value (hereinafter, referred to as the voltage) output from the power amplifier 2 is obtained by series resonance of the capacitor 6 and the inductor of the CY3. pp value) can be small.

Here, the current output from the power amplifier 2 includes a horizontal scanning frequency (53 kHz in this embodiment) and its high frequency component (that is, a high frequency component) and a vertical scanning frequency (60 Hz in this embodiment) and its high frequency. Component (ie, low frequency component; about
(Corresponding to a frequency range of 1 kHz or less) and 2 kHz. The DC component and the low-frequency component current are supplied to the YC3 via the resistor 7, and the high-frequency component current is Is supplied to CY3 via the capacitor 6.

That is, by reducing the pp value of the high-frequency component voltage in the output voltage from the power amplifier 2 by the series resonance of the capacitor 6 and the inductor of the CY3,
The power supply voltage supplied to the power amplifier 2 can be reduced.

 Hereinafter, a specific description will be given.

In the figure, the element values of 3, 5, 6, 7, L _1, when the _{r 1, C 1, R 2} , its specific numerical example, the horizontal scanning frequency of about 53k Hz
In the case of

The concept of selecting the values of C ₁ and R ₂ is described below.

First, considering the case of R ₂ = ∞, qualitatively,
The waveform of each part is as shown in FIG. In FIG. 2, the solid line corresponds to the case where the upper part of the screen is scanned, and the dotted line corresponds to the case where the lower part of the screen is scanned.

In FIG. (A), E ₁ corresponds to the output voltage E ₁ of the power amplifier 2 of FIG. 1, the waveform is based on negative feedback operation, the current detection resistor _{5 (r 1), CY3 (} L 1 ) And the waveform of the current flowing through the capacitor 6 (C ₁ ). In response to this E _1, CY3
The potential E ₂ (the potential difference between both ends of the current detection resistor 5 can be ignored) at the connection point between (L ₁ ), the capacitor 6 (C ₁ ), and the resistor 7 (R ₂ ) has a waveform as shown in FIG. Becomes The second
In FIG. (B), V _op indicates an amplitude value above 0V, and V _ob indicates an amplitude value below 0V.

The potential difference between both ends of the capacitor 6 (C ₁ ) in FIG.
E ₃ −E ₂ ), and its waveform is as shown in FIG. 2 (c). This is obtained by integrating the waveform of the E _1. Finally the output voltage E ₃ of the power amplifier 2 in the, E ₂ + (E ₃ -
From E ₂ ), the waveform is obtained as shown in FIG. 2 (d). In comparison Figure 2 (d) and a second view (b), as is apparent, the pp value of E _3, is reduced to approximately half the pp value of E _2.

Therefore, under the condition that a similar CY current is passed, a power supply voltage that covers the pp value of E ₂ is conventionally required, whereas in the present embodiment, a power supply voltage that covers the pp value of E ₃ is used. As a result, the power supply voltage can be reduced by about half compared with the related art, and the power consumption can be reduced by half.

Omitted quantitative details computation process, when the horizontal scanning frequency and f _H, so as to satisfy the following condition of Equation (series resonance condition of the capacitor 6 and CY3), when selecting the values of C _1, second pp value of E ₃ shown in FIG. (d) is of E ₂ shown in FIG. 2 (b)
It can be about half the pp value.

(2πf _H ) ² · L ₁ · C ₁ ≒ 1 In FIG. 1, the value of R ₂ is a resonance composed of CY 3 (L ₁ ), capacitor 6 (C ₁ ), and resistor 7 (R ₂ ). The Q value of the circuit is chosen to be between about 0.5 and 10.

If the Q value is too small, the function of the capacitor 6 (C ₁ ) is lost. If the Q value is excessive, a slight DC current will cause a large potential difference across the resistor 7 (R ₂ ),
The dynamic range of the power amplifier 2 is lost.

Therefore, this embodiment can be said to be suitable when a large correction in the DC or low frequency region is not required.

Next, a method suitable for a case where a large correction is required in a DC or low frequency region will be described.

 First, the concept is shown in FIG.

In the figure, 1, 2, 3, and 5 are the same as those in FIG. In addition, 8 is a high-frequency matching circuit (HF). 9 is a low frequency matching circuit (LF).

The problem in the configuration of FIG. 1, that is, the problem of insufficient dynamic range of the power amplifier 2 for low frequency components, is as follows.
This is overcome by converting the power supply voltage or impedance level by the matching circuits shown at 8 and 9 in FIG.

FIG. 4 shows a second embodiment of the present invention based on the concept shown in FIG.

In the figure, 1,2,3,5,6 are the same as those already described in FIG. The capacitor 6 is a high-frequency matching circuit 8 shown in FIG.
, Choke coil 10, resistor 11, small power amplifier 1
2, the resistor 13, the capacitor 14, and the resistor 15 correspond to the low frequency matching circuit 9.

In FIG. 4, the element values of 3, 6, 5, 10, 11, 13, 14, and 15 are represented by L ₁ , C ₁ , r ₁ , L ₀ , r ₀ , R ₀ , R ₀ , C ₀ , and R ₁ . Specific numerical examples are shown below.

The operation of FIG.

First, a high-frequency component current flows through the capacitor 6 (C ₁ ) to the inductance L ₁ of CY 3. At this time, since the choke coil 10 (L ₀ ) has high impedance, the shunt loss to the choke coil 10 (L ₀ ) is small.

Next, the current of the DC component and the low frequency component is
(R ₀ ), a low-pass filter composed of a capacitor 14 (C ₀ ) and a resistor 15 (R ₁ ), and then a low-voltage power supply (±
5V) through a small power amplifier 12
(R ₀ ), and is supplied to CY3 (L ₁ ) via the choke coil 10 (L ₀ ). Here, the choke coil 10 (L ₀₎ resistors connected in series 11 (r ₀₎ is representative of the loss of the choke coil 10 (L ₀₎ itself. Since the impedance of the capacitor 6 (C ₁ ) is high with respect to the low-frequency signal, the shunt loss of the current of the DC component and the low-frequency component in the direction of the capacitor 6 (C ₁ ) is small.

In FIG. 4, a resistor 13 (R ₀ ), a capacitor 14
The low-pass filter composed of (C ₀ ) and the resistor 15 (R ₁ ) is for attenuating high-frequency components. In addition, resistance 15 (R ₁ )
Is to prevent the amount of delay of the feedback loop from becoming excessive, thereby preventing the loop from hunting. To prevent hunting from appearing at the top of the screen immediately after vertical retrace, not shown in FIG.
It is effective to add a series connection element of a 5 mμF capacitor and a 3 kΩ resistor in parallel at both ends of (R ₀ ).

Now, the low-frequency shunt effect unique to the present embodiment is as follows.

Conventionally, a power of about 0.5 A was supplied from the power amplifier 2 of the 24 V power supply, so that a power loss of about 12 W was required. In contrast, in the present embodiment, the power can be supplied from the 5 V power supply of the small power amplifier 12. , Power loss can be reduced to about 2.5W.

 FIG. 5 shows a third embodiment of the present invention.

In the figure, 1,3,5,6,10 are the same as those in FIG. In addition, in this embodiment, a power amplifier having a power supply of ± 5 V is used as the power amplifier 2. However, since the power supply amplitude is insufficient as it is, the transformer 16 steps up to about 5 times with a turns ratio of 1: 5. I do.

The capacitor 6 (C ₁ ) and the capacitor 17 pass a high-frequency component current through the transformer 16 and supply the current to CY3. In addition, resistors 18, 19 connected in parallel to these
Is for avoiding loop hunting in the intermediate frequency region, and has the same purpose as the resistor 15 in FIG.

Current of the low-frequency component is supplied to CY3 via the choke coil 10 (L _0).

Specific numerical examples are as follows when the horizontal scanning frequency is 53 kHz.

The effect of this embodiment is almost the same as that of the second embodiment described above. However, in this embodiment, a transformer 16 is used instead of requiring no separate power supply.

In the description of each embodiment, the convergence circuit has been described for only one channel. Actually, it is necessary to use at least four channels, that is, red for left and right and up and down, and blue for left and right and up and down. Therefore, the power consumption reduction effect is approximately 40 W in the first embodiment, and approximately 80 W in the second or third embodiment.

In the above description, the present invention has been described as being applied to a projection type display. However, the present invention is also effective when applied to a direct-view tube type ultra-high definition display.

In the case of ordinary television, the horizontal scanning frequency is about 16
Since the frequency is as low as 2 kHz and the upper limit of the high frequency of the vertical scanning frequency is close to about 2 kHz, the application of the present invention is slightly difficult.However, in a high definition television and a high definition display with a horizontal scanning frequency of about 32 kHz or more, The present invention is easily applicable.

〔The invention's effect〕

Conventionally, the power amplifier used in the convergence circuit was simply designed and used as a broadband amplifier, and the power consumption was large.On the other hand, in the present invention, the frequency band to be processed by the power amplifier is vertical scanning. Focusing on the fact that it can be separated into a low frequency band of about 2 kHz or less consisting of a frequency and its high frequency and direct current, and a high frequency band consisting of the horizontal scanning frequency and its harmonics, by matching each frequency band, This has the effect of reducing power consumption to less than half.

[Brief description of the drawings]

1 is a circuit diagram showing a first embodiment of the present invention, FIG. 2 is a waveform diagram showing a voltage waveform of a main part of FIG. 1, and FIG. 3 requires a large correction in a DC or low frequency region. FIG. 4 is a block diagram showing a basic configuration of a convergence circuit according to the present invention, FIG. 4 is a circuit diagram showing a second embodiment of the present invention, FIG. 5 is a circuit diagram showing a third embodiment of the present invention, Sixth
FIG. 7 is an explanatory view showing an image projected on a screen in a general projection type display, FIG. 7 is a circuit diagram showing a conventional convergence circuit, and FIG. 8 is a waveform showing a main part voltage waveform of FIG. FIG. DESCRIPTION OF SYMBOLS 1... Correction voltage generation circuit 2... Power amplifier 3... Convergence yoke 5... Current detection resistor 6.
Capacitor, 7 ... resistance.

 ────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Miyuki Ikeda 292 Yoshida-cho, Totsuka-ku, Yokohama-shi, Kanagawa Pref. New Media Factory, Hitachi, Ltd.

Claims (2)

(57) [Claims] 1. A convergence circuit in a projection display device using a cathode ray tube, comprising: a convergence correction deflection coil provided in the cathode ray tube; convergence correction voltage generation means for generating a convergence correction voltage; Power amplifying means for amplifying the convergence correction voltage from the convergence correction voltage generating means, and a current output from the power amplifying means are input, and high-frequency components including a horizontal scanning frequency component thereof are passed therethrough, and the convergence correction is performed. High-pass capacitor means for supplying to the deflecting coil, resistance means for guiding and supplying a low-frequency component and a DC component of the current output from the power amplifying means to the convergence correcting deflection coil, and The current flowing through the deflection coil is And a negative feedback circuit for negatively connecting the voltage detected by the current detection resistance means to the power amplification means, the power amplification means, the resistance means, and a convergence correction deflection coil. A DC loop gain circuit is formed by the current detection resistor means and the negative feedback circuit, and the series resonance circuit at the horizontal scanning frequency is formed by the high-pass capacitor means and the convergence correction deflection coil. And a convergence circuit. 2. The convergence circuit according to claim 1, wherein a low-frequency component and a DC component of a current output from said power amplifying means are provided in a path connecting said resistance means and a convergence correcting deflection coil. A convergence circuit comprising: a low-pass filter for extracting the output of the low-pass filter; amplifying means for power-amplifying the output of the low-pass filter; and choke coil means connected in this order.