JP2001339619A - Device for canceling sand-castle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To allows to perform at least synchronized separation of a composite synchronizing signal regardless of the presence or absence of a sand-castle pulse. SOLUTION: This device for canceling a sand-castle has an input buffer 1, which receives a composite synchronizing signal on which a sand-castle pulse selectively superimposed, and a waveform shaping circuit, which leaves a blanking signal component of the sand-castle pulse and eliminates a level of forming a clamp signal component of the composite synchronizing signal put out from the input buffer 1 and generates the composite synchronizing signal with a synchronizing pulse delayed by a predetermined time from a rising of the blanking signal component. Further, this device has an output control means CNT, which detects that the composite synchronizing signal put out from the input buffer 1 has exceeded a reference pedestal level and outside supplying the composite synchronizing signal from the waveform shaping circuit WS instead of the input buffer 1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a video display for demodulating a PAL video signal based on a composite synchronizing signal, and more particularly to a sandcastle canceling device for canceling a sandcastle pulse superimposed on the composite synchronizing signal.

[0002]

2. Description of the Related Art A video display is configured to receive a composite synchronization signal supplied together with a video signal, for example, and to demodulate the video signal based on the composite synchronization signal.
The composite synchronization signal is a signal having portions called front porch and back porch before and after the synchronization pulse as shown in FIG.

In recent years, a composite synchronizing signal on which a sandcastle pulse is superimposed is mainly used for demodulating a video signal mainly in a video display dedicated to the PAL system. This sandcastle pulse is composed of a blanking signal and a clamp signal synchronized with the synchronization pulse shown in FIG. The composite synchronizing signal is called a composite ternary signal when such a sandcastle pulse is superimposed.

[0004]

Since a general video display performs synchronization separation processing and chroma / gamma correction processing using a general-purpose demodulation IC, such a composite ternary signal does not overlap a sandcastle pulse. If it is input in the same way as the synchronization signal, it will malfunction. More specifically, synchronization separation cannot be performed, and signal clamping cannot be performed because the clamp signal exists at the back porch position of the composite synchronization signal.

[0005] It is an object of the present invention to provide a sandcastle canceling apparatus that can at least separate synchronization from a composite synchronization signal regardless of the presence or absence of a sandcastle pulse in order to solve the above-mentioned problem.

[0006]

According to the present invention, an input buffer for receiving a composite synchronization signal on which a sandcastle pulse is selectively superimposed, and a sandcaster pulse for the composite synchronization signal output from the input buffer are provided. A waveform shaping circuit for removing a level serving as a clamp signal component while leaving a blanking signal component to generate a composite synchronization signal having a synchronization pulse delayed by a predetermined time from the rise of the blanking signal component, and an output from an input buffer unit An output control unit for detecting that the composite synchronization signal has exceeded the reference pedestal level, and externally outputting the composite synchronization signal output from the waveform shaping circuit instead of the composite synchronization signal output from the input buffer unit at the time of this detection; The sandcastle cancellation apparatus provided with this is provided.

In this sandcastle canceling device,
The waveform shaping circuit removes the level serving as the clamp signal component while leaving the blanking signal component of the sandcastle pulse from the composite synchronization signal output from the input buffer unit, and removes the synchronization pulse delayed by a predetermined time from the rise of the blanking signal component. Generate a composite synchronization signal. The output control unit detects that the composite synchronization signal output from the input buffer unit has exceeded the reference pedestal level, and at the time of this detection, the composite synchronization signal output from the input buffer unit was output from the waveform shaping circuit instead of the composite synchronization signal output from the input buffer unit. Output the composite synchronization signal to the outside. That is, when the sandcastle pulse is superimposed on the composite synchronization signal, the sandcastle pulse is automatically removed. Therefore, a general-purpose demodulation IC can be used to perform the synchronization separation processing and the chroma / gamma correction processing of the composite synchronization signal regardless of the presence or absence of the sandcastle pulse.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A sandcastle canceling apparatus according to one embodiment of the present invention will be described below with reference to the drawings. This sandcastle cancellation device is mainly P
It is incorporated in a video display that demodulates the video signal of the AL system based on the composite synchronization signal. Figure 2 shows the composite synchronization signal.
As shown in FIG. 5, the signal has portions called a front porch and a back porch before and after the synchronization pulse, and is further selectively overlapped with a sandcastle pulse. The sandcastle pulse is composed of a blanking signal and a clamp signal synchronized with the synchronization pulse shown in FIG. The sandcastle cancellation device is used for synchronous separation processing and chroma /
It is used for selectively canceling a sandcastle pulse superimposed on a composite synchronization signal at a stage prior to a general-purpose demodulation IC that performs gamma correction processing.

FIG. 1 shows the configuration of the sandcastle canceling device. This sandcastle cancellation device,
An input terminal IN for receiving the composite synchronization signal as described above, an input buffer 1 for current-amplifying the composite synchronization signal supplied from this input terminal, and a blanking signal component of a sandcastle pulse for the composite synchronization signal output from the input buffer 1. , A waveform shaping circuit WS that removes the level serving as a clamp signal component and generates a composite synchronization signal having a synchronization pulse delayed by a predetermined time from the rise of the blanking signal component.
And detecting that the composite synchronizing signal output from the input buffer 1 exceeds the reference pedestal level VF, and upon detecting this, the composite synchronizing signal output from the waveform shaping circuit WS instead of the composite synchronizing signal output from the input buffer 1 An output control unit CNT that externally outputs a signal.

The waveform shaping circuit WS includes, for example, an input buffer 1
Comparator 2, inverted comparator 2 connected to
, And a mono-multivibrator 4 connected to the delay buffer 3. The output control unit CNT includes a comparator 5 connected to the input buffer 1, an inverter 6 connected to the comparator 5, a switch 7 connected between the input buffer 1 and the output terminal OUT, and controlled by the comparator 5 via the inverter 6, and A switch 8 is connected between the monomultivibrator 4 and the output terminal OUT and is directly controlled by the comparator 5.

In output control unit CNT, comparator 5 compares the level of the composite synchronization signal output from input buffer 1 with reference pedestal level VF. When it is detected that the level of the composite synchronization signal is equal to or lower than the reference pedestal level VF, the comparator 5 determines that the sandcastle pulse is not superimposed on the composite synchronization signal and outputs a low-level output signal. This output signal is inverted by the inverter 6 to turn on the switch 7 and supplied to the switch 7, and is also directly supplied to the switch 8 to turn off the switch 8. As a result, the composite synchronization signal output from the input buffer 1 is output from the output terminal OU.
Externally output via T. When it is detected that the level of the composite synchronization signal is higher than the reference pedestal level VF, the comparator 5 determines that the sandcastle pulse is superimposed on the composite synchronization signal, and outputs a high-level output signal. I do. This output signal is inverted by the inverter 6 to turn off the switch 7 and supplied to the switch 7, and is also directly supplied to the switch 8 to turn on the switch 8. As a result, the composite synchronization signal output from the waveform shaping circuit WS is output from the output terminal OUT.
Is output externally via

In the waveform shaping circuit WS, the inverting comparator 2 compares the level of the composite synchronizing signal output from the input buffer 1 with the blanking signal level VC of the sandcastle pulse, and leaves the blanking signal component. The clamp signal component exceeding the blanking signal level VC is removed. The delay buffer 3 includes an integrator for integrating the composite synchronization signal inverted and output from the inverting comparator 2 and a buffer for amplifying the integrated value of the integrator, and a predetermined time has elapsed from the falling timing of the blanking signal. Sometimes configured to output a trigger pulse. The predetermined time is determined with reference to the phase of the synchronization pulse of the normal composite synchronization signal on which the sandcastle pulse is not superimposed. The mono multivibrator 4 generates a composite synchronizing signal having a synchronizing pulse falling at the timing when the trigger pulse is input from the delay buffer 3. This synchronization pulse has a pulse width of 4.7 μs defined by the standard. In the sandcastle canceling device according to the above-described embodiment, the waveform shaping circuit WS removes the level serving as the clamp signal component from the composite synchronization signal output from the input buffer 1 while leaving the blanking signal component of the sandcastle pulse. A composite synchronization signal having a synchronization pulse delayed by a predetermined time from the rise of the ranking signal component is generated. The output control unit CNT detects that the composite synchronizing signal output from the input buffer 1 exceeds the reference pedestal level, and outputs from the waveform shaping circuit WS instead of the composite synchronizing signal output from the input buffer 1 at the time of this detection. And outputs the composite sync signal to the outside. That is, when the sandcastle pulse is superimposed on the composite synchronization signal, the sandcastle pulse is automatically removed. Therefore, a general-purpose demodulation IC can be used to perform the synchronization separation processing and the chroma / gamma correction processing of the composite synchronization signal regardless of the presence or absence of the sandcastle pulse.

[0013]

As described above, according to the present invention, it is possible to provide a sandcastle canceling apparatus capable of performing at least synchronization separation from a composite synchronization signal regardless of the presence or absence of a sandcastle pulse.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a configuration of a sandcastle cancellation device according to an embodiment of the present invention.

FIG. 2 is a waveform diagram showing a conventionally known general composite synchronization signal and a sandcastle pulse superimposed on the composite synchronization signal.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Input buffer 2 ... Inverting comparator 3 ... Delay buffer 4 ... Mono-multivibrator 5 ... Comparator 6 ... Inverter 7 ... Switch 8 ... Switch WS ... Waveform shaping circuit CNT ... Output control part

Claims (1)

[Claims] An input buffer for receiving a composite synchronization signal on which a sandcastle pulse is selectively superimposed, and a clamp signal for the composite synchronization signal output from the input buffer while leaving a blanking signal component of the sandcastle pulse. And a waveform shaping circuit for generating a composite synchronization signal having a synchronization pulse delayed by a predetermined time from the rise of the blanking signal component, and a composite synchronization signal output from the input buffer unit being a reference pedestal level. And an output control unit that externally outputs a composite synchronization signal output from the waveform shaping circuit in place of the composite synchronization signal output from the input buffer unit at the time of this detection. Sandcastle canceling device.