JPH04273773A - Direct current transmission quantity correcting device - Google Patents

Abstract

PURPOSE:To obtain an optimum video even when a common circuit is used for both TV of CRT and liquid crystal TV. CONSTITUTION:At the time of liquid crystal TV, a switch SW is located at an A side, an input signal inputted to an input edge 1 and the output signal of an amplifier 3 are added by an adder 2 and the output to perform the optimum direct current transmission quantity correction to the liquid crystal TV is outputted to an output edge 4. At the time of CRT-TV, the switch SW is located at a B side, and at the adder 2, the signal where the input signal of the input edge 1 and the output signal of the amplifier 3 are inverted by an inverting circuit 5 is subtracted and the output to perform the direct current transmission quantity correction optimum to the CRT-TV is outputted to an output edge 4.

Description

[Detailed description of the invention]

[Object of the invention]

0002

[Industrial Application Field] This invention is applicable to television (TV).
) and other video signal processing.

0003

2. Description of the Related Art In signal processing in a TV set, radio waves from a broadcasting station are received by a tuner, and the received signals are processed by an audio signal processing circuit and a video signal processing circuit. The audio signal processing circuit extracts only the audio signal, processes it, and then sends the audio signal to the speaker. Further, the video signal processing circuit performs luminance signal processing, color signal processing, and synchronization signal processing. In brightness signal processing, the image quality is adjusted to soft to sharp, amplitude is adjusted, and brightness is adjusted, and a brightness signal is output. In color signal processing, color signals are detected, hue adjusted, and saturation (R
, G, B).

[0004] In synchronization signal processing, horizontal synchronization signal processing and vertical synchronization signal processing are performed after synchronization separation, and a timing signal is output so that when the RGB signal is displayed on a display, the same image as the transmitted signal appears. After performing the signal processing described above, the received signal is displayed on the display.

[0005] In recent years, the same color cathode ray tube CRT
The two-screen TV above is now in the spotlight. This TV has two systems each of a tuner and a video signal processing circuit. Among these, circuits that process signals for large screens operate at a high power supply voltage of 9V or more, and circuits that process signals for small screens operate at a low power supply voltage of 5V or less. Conventionally, signal processing circuits used in small screen TVs are
Since only signal processing circuits for large screens have been developed, signal processing circuits for LCD TVs that operate at low voltage were used. In addition, in TV sets, direct current transmission amount correction is performed regardless of whether the TV is a CRT TV or a liquid crystal TV, in order to increase the apparent contrast.

FIG. 3 shows DC transmission amount correction in the case of CRT. First, we will explain why DC transmission amount correction is necessary for CRTs. Assume that in the case of FIG. 3A without DC transmission amount correction, the large signal of FIG. 3A is input to the signal processing circuit. This signal is processed without DC transmission amount correction (
(DC transmission amount correction 100%) and outputs the large signal shown in (b). When this large signal is transferred to the CRT, the CR
T draws large currents from the power supply for large signals. As a result, the power supply voltage Vcc decreases to the voltage Vd, so that (c
), the DC voltage of the signal decreases. Therefore, C
In the RT output, crushed blacks and a decrease in contrast Cd occur.

[0007] To prevent this, in CRT TVs,
The DC transmission amount is corrected by more than 100%. this,
This will be explained using the case with DC transmission amount correction in FIG. 3(B). Suppose that a large signal of (aa) is input to the circuit. In the circuit,
A pulse is inserted into the horizontal retrace period H/BLK in the direction in which the DC voltage increases, this pulse period is clamped, and a large signal shown in (bb) is output. At this time as well, since a large signal is input to the CRT, the power supply voltage Vcc decreases Vd and the DC voltage of the signal decreases. However, since the pulses inserted in advance for correcting the amount of DC transmission during the horizontal retrace period H and BLK and the drop in power supply voltage cancel each other out, the CRT output does not have any blackout or decrease in contrast (CC). The signal will be as shown in . Therefore, the input signal (aa) can be directly output to the CRT without deterioration.

Next, correction of the DC transmission amount of a liquid crystal TV will be explained using FIG. 4. For LCD TVs, T for CRT
DC transmission amount correction is necessary for reasons other than V. The reason for this will be explained using the case in which there is no DC transmission amount correction in FIG. 4(A). Input the large signal in (d) to the circuit. This is clamped and the signal (e) is output. The panel outputs the signal in (e) as it is, but because the dynamic range of the panel is narrow, whitewashing Cc occurs as shown in (f).

[0009] In order to prevent this, LCD TVs use CR
The DC transmission amount is corrected by 100% or less, which has the opposite polarity to that of the T TV. This will be explained using the case with DC transmission amount correction shown in FIG. 4(B). A large signal (dd) is input to the circuit. In the circuit, a pulse is inserted in the horizontal blanking period H/BLK in a direction in which the DC voltage decreases (DC transmission amount correction is 100% or less). Then, clamp this pulse period (e
Output the large signal e). Since the (ee) signal has been corrected for the DC transmission amount so that it falls within the dynamic range of the liquid crystal panel, it is possible to output the (ff) signal without crushed shadows to the liquid crystal panel.

As mentioned above, CRT TV and liquid crystal T
V performs DC transmission amount correction with different polarities due to different causes to increase the apparent contrast.

However, since the small screen (CRT) of a two-screen TV uses a signal processing circuit for LCD TVs, the polarity of the DC transmission amount correction is reversed, resulting in the whiteout shown in FIG. 3(c). This further accelerates the decline in contrast. Conventionally, in order to reduce this phenomenon, signal processing circuits for small-screen TVs output signals without applying DC transmission amount correction (DC transmission amount correction 100%). However, with this method, the phenomenon shown in FIG. 3(c) occurs, resulting in an unnatural image with crushed shadows and decreased contrast.

0012

[Problem to be Solved by the Invention] Since a signal processing circuit for LCD TVs is used for the small screen of the CRT of a two-screen TV, it is necessary to use the signal processing circuit of the small screen TV without applying DC transmission amount correction. Because the signal was being output, the resulting image was unnatural with crushed blacks and reduced contrast.

The present invention eliminates the above-mentioned drawbacks and reduces the T of CRT.
The purpose of this invention is to perform optimal DC transmission amount correction for both V and liquid crystal TVs.

[Configuration of the invention]

[0015]

[Means for Solving the Problems] The present invention provides a DC transmission amount correction system for adjusting the voltage during the horizontal retrace period, which comprises means for switching the polarity of the voltage applied during the horizontal retrace period. It is characterized by

[0016]

[Operation] By the means described above, one circuit can be connected to the T of a CRT.
It can be used for both V and LCD TVs to produce natural and optimal images.

[0017]

Embodiments Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 shows an embodiment of the present invention. A signal is input to input terminal 1, one to adder 2 and the other to capacitor C1 through resistors R1 and R2. Capacitor C1 integrates the signal and converts it to APL.
(Average Picture Level = signal average value) Detect the voltage. This APL voltage is resistance-divided by R1 and R2 and input to the amplifier 3. in fact,
Since the amplifier 3 is ON only during the horizontal retrace period, the voltage VIN input to the amplifier 3 is (APL voltage - Va) x R
1/(R1+R2)+Va. However, Va
There is a DC potential at input terminal 1, and when there is no signal, input terminal 1
is V1 = Va [V].

The amplifier 3 amplifies and outputs the difference voltage between the amplifier input voltage VIN and the reference voltage V1. Now switch S
Assume that W is connected to A side. Adder 2 adds the input signal and the output signal of amplifier 3. As a result, the adder 2 inserts a pulse in the direction in which the DC voltage decreases as shown in (ee) of FIG. Therefore, when the switch is set to the A side, the optimum DC transmission amount correction for the liquid crystal TV can be performed.

Next, assume that the switch SW is connected to the B side. At this time, the adder 2 adds the input signal and the signal obtained by inverting the output signal of the amplifier 3 using the inverting circuit 5. That is, the adder 2 subtracts the signal of the amplifier 3 from the input signal. As a result, the adder 2 corrects the DC transmission amount by 100% or more as shown in (bb) of FIG. 3, inserts a pulse in the direction of increasing the DC voltage, and outputs a signal to the output terminal 4. Therefore, if the switch SW is set to the B side, the CRT/TV
Optimal DC transmission amount correction can be performed.

FIG. 2 is a circuit diagram specifically configuring the system shown in FIG. The same parts as in FIG. 1 are given the same reference numerals. First, a case will be described in which the control terminal 6 is connected to the power supply Vcc and this circuit is used in a liquid crystal TV. In the switch circuit including transistors Q21 and Q22, since the control terminal 6 is connected to the power supply Vcc, transistor Q22 is turned on and transistor Q21 is turned off. This turns off transistors Q17, Q18, and Q19. A switch consisting of transistors Q7 and Q8 and a transistor Q9
, Q10, transistors Q17 and Q
18 does not draw current, the base voltages of transistors Q7 and Q8 are lowered by the voltage drop across resistor R5, transistors Q7 and Q8 are turned on, and transistors Q9 and Q10 are turned off. Therefore, when the control terminal 6 is at the power supply Vcc, the switches of the transistors Q7 and Q8 operate. In this circuit state, the APL of the input signal input to input terminal 1 is detected by capacitor C1. This APL voltage is resistance-divided by R1 and R2 and amplified by an amplifier including transistors Q1 and Q2. The output current of this amplifier flows from the collector of transistor Q7 to resistor R4 because transistor Q13 is turned on and transistor Q15 is turned off by the horizontal retrace pulse H.BLK. Therefore, the voltage according to APL is approximately (R
4/R3) and added to the input signal at output terminal 4. In this way, direct current transmission amount correction of 100% or less can be performed.

[0022] Also, a case will be described in which the control terminal 6 is set to GND. At this time, the switch made up of transistors Q21 and Q22 is such that transistor Q21 is turned on and Q22 is turned off.
FF. As a result, transistors Q17 and Q18
, Q19 turns ON. This time, transistors Q17 and Q
Since transistor 18 draws current, the bases of transistors Q9 and Q10 become lower than the bases of transistors Q7 and Q8, so transistors Q7 and Q8 are turned off and transistors Q9 and Q10 are turned on. transistor Q
1, the output current of the amplifier Q2 is the horizontal retrace pulse H
- BLK turns on transistor Q14 and turns off transistor Q16, so a current is output from the collector of transistor Q9 and is drawn from resistor R4 via transistors Q12 and Q11. Therefore, the voltage according to APL is approximately (R4 /R3) times, and the voltage at the output terminal 4
Subtract from the input signal with . In this way, it is possible to correct the amount of direct current transmission by 100% or more.

[0023] From the above explanation, it is possible to change the polarity of DC transmission amount correction with one circuit, and whether this circuit is used for either a liquid crystal TV or a PIP (CRT/TV), the optimum DC transmission amount correction can be performed. It can be carried out.

[0024]

[Effects of the Invention] As described above, according to the present invention,
It can be applied to both LCD TVs and CRT TVs with PIP functions.

[Brief explanation of the drawing]

FIG. 1 is a circuit configuration diagram showing an embodiment of the present invention.

FIG. 2 is a circuit diagram specifically showing FIG. 1;

FIG. 3 is a waveform diagram showing DC transmission amount correction in the case of a CRT/TV.

FIG. 4 is a waveform diagram showing DC transmission amount correction in the case of a liquid crystal TV.

[Explanation of symbols]

1……Input end 2... Adder 3……Amplifier 4……Output end 5……Inversion circuit R1, R2...Resistance C1...Capacitor V1...Reference voltage SW...Switch

Claims (1)

[Claims] 1. A DC transmission amount correction system for adjusting a voltage within a horizontal retrace period, comprising means for switching the polarity of a voltage added during the horizontal retrace period. correction device.