JPS6248891A - Automatic adjusting circuit for white balance - Google Patents

Abstract

PURPOSE:To perform an effective adjustment on a wide band large output video circuit evading the wasteful loss of power consumption at an output stage by performing a feedback control detecting the cathode current of a cathode-ray tube in a displaying time, etc. by using a non-contact-typed current detecting element. CONSTITUTION:By a current detecting circuit 40 using a Hall element, etc., cathode current DC components only in a spurious pulse period and a blank period by a spurious pulse generating circuit 11 in the display time of a color cathode-ray tube 50 are detected, and a difference voltage between both detecting signals are compared with a reference voltage at a signal conversion circuit 60, forming a control voltage. And through a control circuit 70, a contrast and drive adjusting circuit 20 and a pedestal clamp and amplifier circuit 30 are feedback-controlled to adjust a white balance automatically. By constituting a circuit to detect the cathode current with the non-contact element without performing a detection through a resistor, etc., the big loss of the cathode current especially in a black level can be prevented, thereby evading the loss of power and obtaining the effective and automatic adjustment of the wide band large output video circuit.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a white balance adjustment circuit for a video circuit, and more particularly to an auto white balance adjustment circuit that automatically adjusts white balance and suppresses fluctuations in a wideband video circuit.

[Background of the invention]

Conventionally, an auto white balance adjustment circuit for a video circuit, as shown in FIG.
This is accomplished by detecting the cathode current of the cathode KE of 50 through the resistor R and feeding it back as a voltage value to the white balance control circuit. However, in such a configuration, cathode current flows even at black level, resulting in unnecessary loss of power.

For example, in FIG. 8, the value of the resistor R is set to 12 Ω.

The voltage value of the blanking period (Br, ic) is OV,
The voltage value at black level is 1.3F, and the voltage value at white level is 7. Assuming BV, when the black level is approximately Q, 10m
, 4 At the white level, a current of 0.65 mA flows to the cathode KB. In the current television signal band 3 to 4 MB2, the current Q at black level of 10 mA is not much of a problem, but when applied to a wide band high output video circuit, the cathode current at black level is extremely large. This results in power loss. Conventionally, no consideration has been given to avoiding such losses.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems of the prior art and to provide an automatic white balance adjustment circuit that is effective for wideband, high-output video circuits by using a non-contact current detection element.

[Summary of the invention]

In order to achieve this object, the present invention replaces a detection signal with a part of the display period, detects the DC component of the cathode current by a non-contact current detection element, and combines the DC component of the detected signal with the DC component in advance. The determined reference pressure is compared with the base pressure, and negative feedback control is performed for drive adjustment and cutoff adjustment. This makes it possible to automatically perform cutoff adjustment and drive adjustment.

[Embodiments of the invention]

Embodiments of the present invention will be described below with reference to the drawings.

Figure 1 is a basic block diagram of an auto white balance adjustment circuit according to the present invention, and Figure 2 is a color cathode ray tube (cRr).
) of cathode current IK vs. cando/first grid resistance G
1) It is a diagram showing the voltage between VK and G4%.

In FIG. 1, 10 is a video input terminal, 11 is a pseudo pulse generation circuit, 12 is an addition circuit, 20 is a contrast and drive adjustment circuit, 30 is a video amplification (including DC reproduction),
40 is a current detection circuit (using a non-contact current detection element)
, 50 is a color cathode ray tube (CRT), 6a is a signal conversion circuit, and 70 is a control circuit.

Generally, the cathode current IK versus cathode-01 voltage VK-G+ characteristic of a color cathode ray tube is expressed as shown in FIG. The operating point of the video signal is determined between point A, which is determined from the cutoff characteristics of the cathode ray tube, and point B, where the size of the electron beam shape is set high within a range that does not cause focus deterioration. That is, if the black level (Exco) of the video signal is made to correspond to point A and the white peak level is made to correspond to point B as shown in FIG. 2, the capabilities of the cathode ray tube can be maximized. Therefore, in practice, the following matters are important in adjusting the white balance and obtaining excellent image expression.

(1) Always keep the black level (EKCQ) of the video signal consistent with point A. (2) Always keep the white peak level of the video signal within point B, and adjust R, G, and E so that the white balance matches.
to determine the ratio of

(3) Maximum output should be obtained within a range where the average beam current does not exceed a predetermined current value.

FIG. 1 will be explained in consideration of these three points.

The video signal input to the input terminal 10 is inserted with a pseudo pulse from the pseudo pulse generation circuit 11, is amplified in a video amplification circuit 30 including a contrast adjustment circuit 20 and a DC component regeneration, and passes through a cathode current detection circuit 40. , added to the CRT 500 cathode. The output of this cathode current detection circuit 40 is converted by a signal conversion circuit 60 into a control signal necessary for cutoff adjustment and drive adjustment, and is input to a control circuit 70. The control circuit 70 negatively feeds the output cutoff adjustment control signal to the video amplifier circuit 30 including DC component reproduction, and controls the black level of the video signal to match the cutoff point A. In addition, the control signal for drive adjustment is negatively fed back to the drive adjustment circuit,
Adjust the peak white balance.

In addition, a white peak level 9 is output from the cathode current detection circuit 40, and negative feedback is sent to the contrast adjustment circuit 20 so that this level does not exceed point B.

According to these, υ, the above (11 (21) is satisfied. Also, regarding (3), the average value of the beam current of the conventional cathode ray tube does not exceed the predetermined current value. It can be satisfied if the ABL circuit is applied to both contrast and brightness.Although the present invention does not mention (3), it goes without saying that the average value AEL is used.

Here, a non-contact current detecting element such as a Hall element will be described.

A Hall element is a type of element that can convert a magnetic field into voltage.
Used in current probes, Gauss meters, etc. This Hall element has a first-order advantage.

1. Because it is an electromagnetic transducer, current can be detected without contact in one circuit. Advantageous for medium and wide bandwidth.

2. Good linearity of output voltage versus magnetic flux.

3. Compact and lightweight.

On the other hand, in general, Hall elements 1) Poor temperature characteristics.

2) There is residual voltage.

3) There is variation.

There are drawbacks as mentioned above. However, by improving the manufacturing and management technology for Hall elements, it is possible to obtain Hall elements with excellent temperature characteristics. For example, it is possible to obtain a Hall element with a temperature characteristic of yB (output voltage) of 0.021/'O and a linearity of VH of 0.5% m.

By using such an element, the above drawback 1) can be solved. The problem can also be solved by using a temperature correction circuit used in Gauss meters and the like.

Next is the residual voltage V of the above defect 2). However, this is the current I when the magnetic field is 0. This is the voltage generated at the output terminal when the current is applied to the maximum rated value. This Vo is not related to the linearity of V (voltage of the Hall element) or the performance of the element, but is generally a voltage proportional to the IC. Also, the output voltage V is V=-IC-E+V.

It is expressed as Here, K is the Hall constant + IC is the current flowing through the Hall element, and B is the magnetic flux. This residual voltage V.

can be canceled by the circuit configuration shown in FIG.

FIG. 3 shows a specific example of the current detection circuit in FIG. 1.

FIG. 4 is a waveform diagram for explaining FIG.
1 is a Hall element, and 402 is a magnetic path with magnetic permeability μ.

403 is a constant current source, 404 and 405 are gate signal input terminals, 406 and 407 are gates, 408 is a hold circuit,
409 is a differential amplifier.

In FIG. 3, a signal (FIG. 4 (α)) in which the first line of the input video signal is replaced with a pseudo signal is passed as a cathode current. Magnetic field H (ocI) proportional to this cathode current
are formed concentrically around the cathode wire. This is concentrated on the surface of the Hall element 4010 as magnetic flux B=μH using a magnetic path 402 with magnetic permeability μ. A constant current I is applied to the Hall element 401 from a constant current source 403. , the output voltage VH shown in the above-mentioned equation (1) is obtained due to the Hall effect. Here, the output voltage VH during the BLK period gated by the gate circuit 406 at the timing shown in FIG. 4(h) is "H" because no cathode current is flowing.
This V is the residual voltage.This output is held by the hold circuit 408 for a 1V period (one vertical period).

Further, at the timing shown in FIG. 4(1), that is, at the time of the pseudo signal, the output voltage becomes VH=K-IC-E+Vo. Then, the output of the hold circuit 408 and the pseudo signal which is the output of the gate circuit 407 are transferred to the differential amplifier 4.
09, an output is obtained in which the negative term Vo, that is, the residual voltage is canceled. Therefore, the above point 2) can also be solved.

Regarding the above drawback 3), element variation, when Hall elements are used as audio heads, the element variation can be suppressed to about ±3 dB, and if the manufacturing and management technology of Hall elements is improved. , Kana 9 It is possible to suppress the variation, so drawback 3) can be solved.

In this way, it has been found that by taking advantage of the advantages and overcoming the disadvantages, it is possible to realize a non-contact current detection element that is effective for wide-band, high-output video circuits.

Next, a cutoff adjustment mechanism using this non-contact current detection element will be explained with reference to FIG.

FIG. 5 is a configuration diagram illustrating an automatic cutoff adjustment circuit using the above non-contact current detection circuit constituting the automatic white balance adjustment circuit according to the present invention, in which 61 is a gate circuit, 62 is a hold circuit, and 71 is a voltage source, 72 is a comparator, 111 is a gate, 112 is an inverting circuit, 114
, 115 is an adder, and 116 is a clamp circuit.

In the figure, the signal of the first line of the input video signal applied to the input terminal 10 is transferred to the gate circuit 111 and the inverting circuit 11.
2. cancel via the clamp circuit 116, and instead,
A pseudo pulse from the pseudo pulse generation circuit 11 is inserted.

The DC component of this pseudo pulse is detected by the non-contact current detection circuit 40 shown in detail in FIG. A comparator 72 compares the output with a predetermined basic voltage E of the voltage source 71. The comparator 72 controls the clamp voltage of the pedestal clamp circuit by negative feedback until the detected voltage becomes the same value as the reference voltage E.

As a result, cutoff adjustment can be performed automatically. That is, in the conventional circuit, wasteful current flows during the BLK period to generate a detection signal, whereas in the present invention, the detection signal is inserted into a part of the display period.

This eliminates the need to flow the unnecessary current mentioned above.

Next, a drive adjustment mechanism using a non-contact current detection element will be explained using FIG. 6.

FIG. 6 is a configuration diagram illustrating an automatic drive adjustment circuit using the above non-contact current detection circuit constituting the automatic white balance adjustment circuit according to the present invention, in which 63 is a gate circuit, 64 is a hold circuit, and 73 is a A voltage source, 74 a comparator, and 117 a clamp circuit.

In the same figure, an input video signal applied to an input terminal 10 passes through a clamp circuit 117, and then a gate circuit 111 gates the video signal of the last line, which is then sent to an inverting circuit 117.
12, the pseudo pulse from the pseudo pulse generating circuit 11 is inserted via adders 114 and 115 instead. The DC component of this pseudo pulse is detected by the non-contact current detection circuit 40 shown in detail in FIG.
Hold period (vertical period). This hold circuit 64
The comparator 74 compares the output with a predetermined reference voltage E of the voltage source 73. The comparator 74 performs negative feedback control on the drive adjustment circuit of the contrast and drive adjustment circuit 20 until the detected voltage becomes the same value as the basic voltage E.

In the circuit shown in FIG. 6, drive adjustment can be performed by changing the bias at the first stage of the contrast adjustment circuit, so the negative feedback control described above is based on this bias. As a result, drive adjustment can be performed automatically.

FIG. 7 is a block diagram showing the overall configuration of the auto white balance adjustment circuit according to the present invention, in which the auto white balance adjustment circuit and the automatic drive adjustment circuit shown in FIGS. This is a balance adjustment circuit.

In the figure, the auto white balance adjustment circuit according to the present invention performs cutoff adjustment by replacing pseudo pulses on the first line of the input video signal, and performs drive adjustment by replacing pseudo pulses on the last line of the input video signal. Advantageously, there is no need to flow unnecessary current during the BLK period as in the conventional case.
It is extremely effective when applied to wide-band, high-output video circuits.

〔Effect of the invention〕

As explained above, according to the present invention, unnecessary loss at the output stage can be avoided by performing cutoff and drive adjustment of the video circuit during the display period.
It is possible to provide an automatic white balance adjustment circuit with excellent functions, except for the drawbacks of the prior art described above.

[Brief explanation of the drawing]

Figure 1 shows an auto white rose according to the present invention. Figure 2 is a diagram of the cathode current vs. voltage between the cathode and the first voltage characteristic of a color cathode ray tube, and Figure 5 is the same as Figure 1. A specific example of the current detection circuit, FIG. 4 is a waveform diagram for the explanation in FIG.
Figure 6 shows the present invention. FIG. 7 is a block diagram showing the overall configuration of the auto white balance adjustment according to the present invention; FIG. 8 is a diagram illustrating the automatic drive adjustment circuit. Adjustment circuit 10: Input terminal 11: Pseudo pulse generation circuit

Claims (1)

[Claims] In an auto white balance adjustment circuit for a video circuit having a contrast and drive adjustment circuit, a pedestal clamp and video amplification circuit, and a color cathode ray tube, means for deleting a part of a display period of an input video signal and inserting into the deleted part. a cathode current detection means including a non-contact current detection element for detecting a cathode current of a color cathode ray tube, and a DC component of the cathode current only during a BLK period and a pseudo signal period. means for taking a differential voltage, comparing means for comparing said differential voltage with a reference voltage, and means for feeding back an output of said comparing means to said contrast and drive adjustment circuit, pedestal clamp and video amplifier circuit as a control signal. An automatic white balance adjustment circuit characterized in that it is configured to eliminate cathode current loss at black level.