JPH0155633B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION In television broadcasting, the present invention aims to eliminate ghost interference caused by receiving direct waves directly from a transmitting antenna and reflected waves delayed and reflected by buildings etc. using the same antenna. The present invention relates to a ghost measuring device for measuring a quantity.

Video radio waves are received at a receiving point as a composite signal in which a direct wave and a ghost wave with a certain amplitude, phase, and delay time are added at high frequency. To measure the amplitude, phase, and delay time of a ghost wave from a received composite signal, generate two carrier waves with the same frequency as the received signal but with a phase difference of 90 degrees, and then Each performs synchronous detection to obtain an in-phase signal component and a quadrature signal component. Among the in-phase signal components and quadrature signal components, a period of approximately 1/2H (approximately 30 μS) from the leading edge of the vertical synchronization pulse shown in FIG. 1 is subjected to analog-to-digital conversion (A/D conversion). The amplitude, phase, and delay time of the ghost wave are determined from the A/D converted data, and the amount of ghost interference waves at the receiving point is measured.

In-phase signal components and quadrature signal components obtained by synchronously detecting a composite signal in which ghost waves are added at high frequencies have various waveforms depending on the amplitude and phase of the ghost waves. Figure 2 a, b, c, and d show the in-phase signal components obtained by synchronously detecting the received signal with a carrier wave having the same frequency and phase as the received signal. It shows an enlarged waveform during the D conversion period. Note that FIG. 1 shows the waveform of the leading edge portion of the vertical synchronizing pulse of the television synchronizing signal, and the vertical synchronizing pulse includes six cutting pulses having a small time width. In the case of a ghost wave with a phase having a higher level than the leading edge of the vertical synchronization pulse as shown in Figures 2a and b, the level changes variously depending on the amplitude of the ghost wave, and the A/
There is a possibility that the output voltage will be out of the range of D conversion, and accurate A/D conversion cannot be performed.

Furthermore, in a circuit that handles television signals, the DC component of the signal is lost due to AC coupling, and the DC level of the vertical synchronizing pulse shown in FIG. 1 fluctuates as the image changes, making accurate A/D conversion impossible.

The object of the present invention is to perform reliable A/D conversion by regenerating the DC component for image changes and various ghost waves during a period of approximately 1/2H from the leading edge of the vertical synchronizing pulse.

The configuration of one embodiment of the present invention is shown in FIG. In the figure, a signal input to a signal input terminal 6 is input to a delay circuit 4 and a peak hold circuit 1. The output of the delay circuit 4 is input to one side of the inverting and adding circuit 5. The synchronizing signal input to the signal input terminal 7 is transmitted to the peak hold circuit 1 by the television circuit 3.
and generates timing pulses necessary for the sample and hold circuit 2. Sample hold circuit 2
The output of is inputted to the other side of the inverting and adding circuit 5.
By inputting the peak level of the vertical synchronizing pulse shown in FIG. 1 and a signal obtained by delaying the vertical synchronizing pulse by a certain time to the inverting and adding circuit 5, the DC component of the synchronizing pulse is regenerated and output to the signal image terminal 8. be done.

The operation of the above circuit configuration will be explained with reference to the timing chart shown in FIG. Pulse b is generated in synchronization with the vertical synchronizing pulse shown in FIG. 1, which is repeated every field, and before the A/D conversion period shown in FIG. With this pulse, the peak value up to that point is reset, and the first wave a of the vertical synchronization pulse, which is extracted from the A/D conversion period, is held at its peak. After that, sample and hold is performed using pulse c, which is delayed by _t1 from pulse b. The signal obtained at the signal output terminal 8 by applying the vertical synchronizing pulse d delayed from t ₁ by the delay circuit 4 and the DC voltage V ₁ obtained by sample-holding the peak of the first wave vertical synchronizing pulse to the inverting and adding circuit 5 is as follows. As shown by f, the DC component is regenerated in a period of 1/2H from the leading edge of the vertical synchronizing pulse. Further, if there is a ghost wave at a level higher than the rising edge of the leading edge of the vertical synchronizing pulse shown in FIG. 1, DC reproduction is performed at that level. The timing chart in FIG. 4 shows that the DC component is also regenerated for the second wave, which is lower than the first wave with respect to the reference voltage.

The present invention has the above-described configuration, and according to the present invention, it is possible to reproduce the DC component of image changes and various ghost waves, and to have the effect of accurately measuring the amount of ghost interference waves.

[Brief explanation of drawings]

Figure 1 is a waveform diagram of the leading edge portion of the vertical synchronization pulse of the television synchronization signal, Figures 2 a to d are enlarged waveform diagrams of Figure 1 due to the difference in phase when there is a ghost wave, and Figure 3 is a block diagram of a DC regeneration circuit of a ghost measurement device according to an embodiment of the present invention;
Figures 4a to 4f are timing charts of the same device. 1...Peak hold circuit, 2...Sample hold circuit, 3...Timing circuit, 4...Delay circuit, 5
...Inverting addition circuit, 6... Signal input terminal, 7... Timing circuit input terminal, 8... Signal output terminal.

Claims (1)

[Claims] 1 The first signal from the leading edge of the vertical synchronization pulse of the signal obtained by synchronously detecting the above input wave and a carrier wave of the same frequency as the input wave modulated by a television signal having a video signal, a synchronization signal, and an audio signal. A peak hold circuit detects the peak of the measured waveform in the period up to the cutting pulse, a sample hold circuit samples and holds the output of this peak hold circuit, and delays the measured waveform until after the sample hold start point of the sample hold circuit. A delay circuit and a means for inverting and adding the output of the sample and hold circuit and the output of the delay circuit constitute a DC regeneration circuit, and the peak value of the measurement waveform is always fixed at a constant reference voltage, thereby generating an analog signal. A ghost measurement device characterized by performing digital conversion.