JPH03185972A - Display device - Google Patents

Abstract

PURPOSE:To attain optimum phase adjustment by providing a blanking detection circuit for a video signal and a pulse width expansion circuit of a horizontal synchronizing signal, ANDing outputs of both circuits and adjusting the phase of the signal with a pulse width of the AND. CONSTITUTION:A blanking detection circuit 3 detects a horizontal blanking of an inputted RGB signal. On the other hand, a pulse width expansion circuit 4 expands the pulse width of the horizontal synchronizing signal HD till the width is the same as the blanking width. Then an AND gate 5 ANDs the HD signal expanding the pulse width and the blanking signal. When the HD is most advanced, the HD has the same width as the blanking signal and when the HD is most lagged, the blanking signal has the same width as the HD and the phase is detected as the pulse width. An HD phase adjustment circuit 6 is adjusted by using the pulse width to attain the optimum phase adjustment.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a display device for displaying video signals.

Conventional technology display devices are video display terminals such as television tuners, VTRs, video discs, and cameras.

Connections with various peripheral devices such as computers can be considered. In addition, there are various formats of signal interfaces between devices, and for NTSC signals, composite video signals and Y/C separated signals are common, and for high-definition television systems, Y with three-level opening period, P8 ．． PR, R, G, B,
HD and VD signals are often used.

IIB to be Solved by the Invention As mentioned above, signals in various formats are input to the display device from various devices, but the final signal format is R and G.

This becomes a synchronization signal for each video signal of B, HD, and VD.

The problem here is the phase of the synchronization signal with respect to the video signal. If the respective synchronization signals are not at appropriate positions for the horizontal and vertical blanking periods of the video signal, blanking will be displayed on the screen.

For this reason, most display devices have horizontal and vertical phase adjustment functions. However, although it is fine if the incoming signal is of one type and the phase is determined to be one, in reality, as mentioned above, connections with multiple devices are possible, and the phase is often not determined to be of one type. That is, each time the signal is switched, phase adjustment must be performed, which is a hassle.

In view of the above problems, the present invention aims to provide a display device that automatically corrects the phase of horizontal synchronization signals that come in with different phases, and eliminates the need for phase adjustment every time the signal is switched.

Means for Solving the Problems In order to solve the above problems, a display device of the present invention includes a video signal blanking detection circuit and an HD signal pulse width expansion circuit, and an output of the blanking detection circuit; The present invention includes an HD phase adjustment circuit that takes the logical product of the outputs of the pulse width expansion circuit and adjusts the phase of the HD based on the pulse width of the logical product.

Effect of the Invention With the above-described configuration, the present invention can detect the phase of the HD signal relative to the blanking of the video signal and automatically adjust the HD phase.

Example 1 of the present invention below. A display device according to a second embodiment will be described with reference to the drawings.

FIG. 1 is a block diagram of an automatic HD phase adjustment circuit for a display device according to a first embodiment of the present invention. In FIG. 1, l is an RGB signal input terminal, 2 is an HD signal input terminal, 3 is a blanking detection circuit that detects blanking of the RGB signal, 4 is a pulse width expansion circuit that widens the pulse width of the HD signal, and 5 is a 6 is an AND gate that takes the AND of the outputs of the blanking detection circuit 3 and the pulse width expansion circuit 4;
This is an HD phase adjustment circuit that adjusts the HD phase using the output of the ND gate 5.

The operation of the display device configured as above will be explained. First, the blanking detection circuit 3
Detect horizontal blanking of RGB signals. The method will be described in more detail using Figure 2. In FIG. 2, 7 is a clamp circuit, 8 is a comparator that compares each RGB signal clamped by the clamp circuit 7 with a reference voltage 9, and 10 is a logical product of the outputs of the R, G, and B comparators 8. This is an AND gate. The clamped RGB signal is connected to a reference voltage 9 equal to the clamp potential by a comparator 8.
By comparing this, an output can be obtained in which the blanking period is at a low level and the video signal is at a high level during a certain period. Although there is a possibility that the signal becomes low level even during the video signal period, this can be considerably reduced by calculating the logical product of R, G, and B using the AND gate 10. Figure 3(a), (
b) shows an example of RGB signals and a detected blanking signal. On the other hand, the HD signal is R as shown in Figure 3(C).
The blanking of the GB signal can range from the phase shown by the solid line to the phase shown by the broken line. The pulse width of this HD signal is expanded by the pulse width expansion circuit 4 until it becomes the same width as the blanking width (FIG. 3(d)). When the HD signal whose pulse width has been expanded is ANDed with the blanking signal, it becomes a signal with the same width as the blanking signal when the HD is the most advanced, as shown in FIG. 3(e).
When HD is the most delayed, the signal has the same width as HD.

That is, the phase of the HD signal is detected as the pulse width.

Using this pulse width, the HD phase adjustment circuit 6 is adjusted to the optimum phase.

FIG. 4 is a block diagram of an automatic HD phase adjustment circuit of a display device in a second embodiment of the present invention. Fourth
In the figure, 11 is a clamp circuit, 12 is a phase shift circuit that shifts the phase of the HD signal, 13 is a counter that controls the shift amount of the phase shift circuit 12, 14 is a comparator that compares the RGB signal after clamping with a reference voltage, 1
5 is an RS latch, and 16 is a delay circuit.

The operation of the display device configured as above will be explained. Clamp circuit 11 with comparator 14
The RGB signal clamped at 1 is compared with a reference voltage set slightly lower than the clamp potential. If the RGB signal is clamped during the blanking period, the output of the comparator 14 is always at a high level because the clamped RGB signal never becomes lower than the clamp potential.

The HD signal is used as the clamp pulse of the clamp circuit 11, but the phase is gradually delayed by the phase shift circuit 12. The phase shift circuit 12 is controlled by a counter 13. The amount of phase shift is 10 per vertical scanning period.
It is set to about 0 ns. Due to the phase shift of the clamp signal,
Eventually, it will be necessary to clamp the RGB signal other than the blanking period, but in that case, comparator 1
4 occurs, and the output of the comparator 14 falls to a low level. The output of the comparator 14 is input to the set terminal of the RS latch 150.

When the set terminal falls to low level, the output of the RS launch 15 is switched from low level to high level.

The counter 13 is controlled by the output of this RS latch 15. That is, when the output of the RS latch 15 switches to high level, the counter operation is stopped.

By doing this, as soon as the clamp pulse deviates from the blanking period of the RGB signal, the counter stops and the phase shift of the HD signal also stops. Since the output of the phase shift circuit at this time is located at the leading edge of the video portion of the RGB signal, it is moved through the delay circuit 16 to the optimum position during the blanking period. Note that the reset terminal of the RS latch 15 is configured to be reset when the power is turned on and when input signals are switched. With the above configuration, the phase of the HD signal with respect to the RGB signal can always be maintained at an optimal position.

As described above, according to the first and second embodiments, even if the phase of the HD signal with respect to the RGB signal varies somewhat,
Correction can be performed automatically to obtain the optimum phase.

Effects of the Invention As described above, the present invention detects the blanking period of the RGB signal and can automatically adjust the phase of the HD signal so that it is at the optimal position during that period, and the signal is switched. There is no need to perform horizontal phase adjustment every time.

[Brief explanation of drawings]

FIG. 1 is a block diagram of the automatic HD phase adjustment circuit of the display device in the embodiment (2) of the present invention, FIG. 2 is a block diagram of the horizontal blanking detection circuit, and FIG. 3 is a waveform explanation of each part of FIG. 1. 4 are block diagrams of an automatic HD phase adjustment circuit of a display device in a second embodiment. 3...Blanking detection circuit, 4...
Pulse width expansion circuit, 6...HD phase adjustment circuit,
7.11... Clamp circuit, 8,14...
... Comparator, 12 ... Phase shift circuit,
13...Counter 15...RS latch, 16...Delay circuit.

Claims (2)

[Claims] (1) A blanking detection circuit that receives RGB signals as input and detects the horizontal blanking period of the RGB signals, a pulse width expansion circuit that receives HD signals as input and expands the pulse width of the HD signal, and the output of the blanking circuit. and an AND gate that takes the logical product of the output of the pulse width expansion circuit and the output of the pulse width expansion circuit;
HD that adjusts the phase of the HD signal using the output of the ND gate
A display device comprising a phase adjustment circuit. (2) A phase shift circuit that shifts the phase of the HD signal, a counter that controls the phase shift circuit, a clamp circuit that clamps the RGB signal using the output of the phase shift circuit as a clamp pulse, and a reference to the output of the clamp circuit. A display device comprising: a comparator for comparing with a voltage; and an RS latch that uses the output of the comparator as a set pulse, and the counter is controlled by the output of the RS latch.