JPS58125991A - Receiving circuit of television signal - Google Patents

Abstract

PURPOSE:To perform an automatic switch between the black/white and color pictures, by displaying a color or balck/white video in response to the detected potential at a prescribed section of a back porch of the luminance signal of a color input signal. CONSTITUTION:The input video signal is clamped 1, and its DC potential is fixed. Then the back porch of a synchronizing signal is sampled by a sample holding circuit 2 and then smoothed 3. In this case, if a TCM signal is applied as an input, the absolute level of the pedestal is fixed at 0V by a clamping circuit 1 to obtain +0.35V. In case a black/white TV siganl is applied as an input, the smoothed output is set at 0V. This smoothed output is compared 4 with the reference voltage 5, and a switch 8 is driven by the output of comparison. As a result, no color signal is delivered when a black/white signal is supplied, and a base band color signal is delivered via a color processing circuit 7 when the TCM signal is supplied.

Description

Detailed Description of the Invention The present invention provides a television signal (hereinafter referred to as TCM signal) in which a compressed color signal is superimposed on a back porch of a luminance signal in a time division manner.
The present invention also relates to a television signal receiving circuit for receiving a black and white television signal.

NTfSC: l' One-way color information t 3.58MH
Since it is modulated in z, the standards for the transmission path are strict in terms of wideband, delay time, two-line crosstalk, DG, and DPζb. Therefore, there is a conventional method in which color information is time-compressed and superimposed on a luminance signal in a time-division manner to perform color transmission.

That is, the TCM signal is obtained by time-compressing the color signal, applying a standard voltage to the back porch of the luminance signal, and superimposing it. By doing this, the p transmission band becomes a difference between black and white signals compared to the NTSC system, which frequency multiplexes color signals, and the above-mentioned restrictions on the transmission path are relaxed, making it possible to transmit color signals on the transmission path for black and white signals. Become. The TCM signal transmitter compresses the time axis and superimposes the next color signal on the back porch of the so-called luminance signal, which is only the black and white component of the color signal to be transmitted. Here, the color signals R-Y and B-Y are sent alternately every other line. The reference potential of the back porch is that the amplitude of the luminance signal is lVpp.
In this case, a level that is 0.35V closer to white than the pedestal level is selected. The demodulation section time-expands this color signal, matches the relative time timing with the luminance signal, and reproduces the original signal again.

Conventional TCM receivers assume that the input signal is sent from the TCM transmitter, but TCM signals sometimes use a black-and-white television transmission path, so black-and-white television signals generated from a regular black-and-white camera, etc. It may also be applied to the receiver. When this black-and-white signal is applied to a conventional TCM receiver, time expansion processing is performed on the back porch portion of the signal as if it were superimposed with a compressed color signal, and a color signal that does not originally exist is reproduced, and this is reproduced as a color signal. In the following cases, there is a drawback that an image with completely different content from the original signal is produced.

An object of the present invention is to provide a television signal receiving circuit that can automatically switch between black and white and color.

The television signal receiving circuit of the present invention receives as an input signal a black and white television signal and a color signal obtained by subjecting the back porch to time axis compression and superimposing a baseband color signal, and receives the back porch of this input signal. When it is determined that the potential detected in the determined interval is equal to or higher than the predetermined potential, the input signal is assumed to be the color signal and is demodulated from that signal, and the next color signal is used to display a color image, and the detected nine potentials are demodulated from that signal. When it is determined that the input signal is lower than the predetermined potential, demodulation of the color signal is prohibited, assuming that the input signal is the black-and-white television signal, and a black-and-white image is displayed.

Next, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 shows a block diagram of an embodiment of the present invention.

A good signal applied to the input terminal 6 is clamped by a clamp circuit 1 to fix the DC potential of the signal.

Next, the sample holding circuit 2 samples the back porch of the synchronizing signal, and the smoothing circuit 3 smooths this sample. At this time, if a TCM signal is added as an input, +0.35V is obtained by fixing it to the absolute level of the pedestal, 0■, using the aforementioned clamp circuit. Figure 2 0,
0 shows the TCM signal and back porch sampling pulse. When a normal black and white television signal is input, the relationship between the signal and the sampling pulse is as shown in Figure 2, however, and the smoothed output is Ov. The output of the smoothing circuit 3 is compared with a predetermined reference voltage 5 in a comparator circuit 4 to drive a switch 8.

As a result, when the black and white signal is applied, the switch 8 is opened and no black signal is output. When the input signal is a TCM signal, a baseband color signal is regenerated in the color expansion processing circuit 7 and applied to the switch 8, and then passed through the comparison circuit 4 and the switch 8#'i.
When closed, a baseband color signal appears at the output terminal 9. This signal is applied to a color encoder or the like. The above operation makes it possible to receive both black and white signals and TCM signals as input signals.

According to the present invention, even if the input to the TCM signal receiving section changes to normal black and white, the color image is automatically switched to the black and white image.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a television receiver circuit according to the present invention;
FIG. 2 is a waveform diagram showing the operation of FIG. 1. 1...Clamp circuit, 2...Sample holding circuit, 3-...Smoothing circuit, 4...Comparison circuit, 5...Standard Voltage, 6... Input terminal, 7... Color processing circuit, 8... Switch, 9... Output terminal, 10... Compressed color signal.

Claims (1)

[Claims] A black-and-white television signal and a color signal obtained by superimposing a time-axis compressed baseband color signal on the back porch are received as input signals, and the potential detected in a determined section of the back porch of this input signal is equal to or higher than a predetermined potential. When it is determined that the input signal is the color signal, a color signal demodulated from that signal is used to display a color image, and when the cocoon weight is detected and the subsequent potential is determined to be below the predetermined potential, the input signal is the color signal. The present invention is characterized in that the demodulation of the color signal is prohibited as it is a black-and-white television signal, and a black-and-white television signal is displayed. Television signal receiving circuit.