JPS62102688A - Reception circuit for fm television signal - Google Patents

Abstract

PURPOSE:To eliminate a energy spread signal by controlling an amplitude of a triangle wave in response to the magnitude and direction of displacement of a demodulated output caused by a triangle wave of an energy spread signal and adding the result to a demodulation signal or a video signal in an opposite phase. CONSTITUTION:A synchronizing separator circuit 10 extracts a vertical synchronizing pulse from a video signal or a sound signal of a video band, the pulse is frequency- divided into 1/2 by a frequency division circuit 11 and the result is fed to a triangle wave generating circuit 12. Further, a vertical synchronizing pulse signal branched by the circuit 10 is fed to a sample-and-hold circuit 13 sampling and holding a high and a low voltage of a triangle wave of an energy spread signal appearing at the demodulation output of an FM demodulation circuit 4 synchronously with the pulse signal. The difference between the high and low voltages of the energy spread signal extracted by the circuit 13 is detected by a difference detection circuit 14. Then an amplitude control circuit 15 connected to a triangle wave generating circuit 12 controls the amplitude of the triangle wave in response to the difference and the output of the circuit 15 is added to a demodulation signal by an adder circuit 16 to eliminate the energy spread signal.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to the configuration of a receiving circuit suitable for receiving FM television broadcasts such as satellite broadcasts.

[Background of the invention]

In satellite broadcasting, an FM modulation method is used to transmit television signals, and a triangular wave energy spread signal is used to reduce the peak voltage of a carrier wave when there is no signal. To receive this broadcast, it is necessary to remove the energy spread signal from the video signal. Figure 1 shows the configuration of a general satellite broadcasting receiver. FM converted to UHF band by a first heterodyne receiving circuit (not shown) located outdoors
The television signal is converted into a VHF band signal by a second heterodyne receiving circuit consisting of a mixing circuit 1 and a local oscillation circuit 6 whose oscillation frequency changes according to the tuning voltage generated by the tuning circuit 2, and then FM demodulated. The demodulated signal is demodulated in a circuit 4, and one of the demodulated signals is split into two, and one is demodulated and output as an audio signal in an audio demodulation circuit 5. In addition to the demodulated signal, there is a video processing circuit 9 consisting of a low-pass filter circuit 6, a de-emphasis circuit 7, and a clamp circuit 8.
is input to obtain a video signal. Conventionally, the energy spread signal was removed by a clamp circuit 8. However, the Technical Report of the Television Society, RE78-14. PP15~20゜197
Peak clamping, which is often used as described in "Energy spread signal for satellite television broadcasting and its removal method" by Yoshino and Zenichi in June 1988, tends to cause waveform distortion called sag in the vertical synchronization waveform, and this sag If it is too large, it may cause the television receiver to lose synchronization.

Pay television broadcasting has recently become popular in the United States. In order to prevent eavesdropping, this broadcast transforms the television signal so that it cannot be received by ordinary television receivers. A scrambling method is used that allows only television receivers with a built-in receiving circuit to receive images. Conventionally, a representative example of this scrambling method is described as a pay TV decoder on pages 41 to 54 of the February 1981 issue of Radio Electronics, but it generally suppresses horizontal and vertical synchronization pulse signals. A method is used in which synchronization pulse information is included in the audio signal, making it impossible for ordinary television receivers to synchronize.

When this scrambling method is performed by satellite broadcasting,
Furthermore, in order to reproduce the television signal to which the energy diffusion signal has been added and subjected to these displacements, various processing must be performed after the energy diffusion signal is completely removed. Therefore, it is impossible to use a conventional clamp circuit that uses a synchronization pulse signal included in a video signal to remove an energy spread signal.

[Purpose of the invention]

The purpose of the present invention is to eliminate the above-mentioned drawbacks of the prior art, remove the spread signal from TV No. 23718 on which a low frequency spread signal is superimposed, output a video signal without sag, etc., and always maintain stable operation. The purpose is to provide a circuit for

[Summary of the invention]

In order to achieve the above object, the present invention extracts a vertical synchronization pulse from a video signal or an audio signal, divides the extracted vertical synchronization pulse, and uses the frequency-divided synchronization pulse to generate the same signal as an energy spread signal. It generates a triangular wave with a periodicity, extracts the demodulated output of the vertical sync pulse signal portion of the video signal in synchronization with the frequency-divided sync pulse, detects the displacement of the demodulated output caused by the triangular wave of the energy diffusion signal, and calculates the displacement. The energy spread signal is removed by controlling the imaging width r of the triangular wave generated by the first wave according to the magnitude and direction, and adding the demodulated signal or the first range signal t in the opposite phase.

[Embodiments of the invention]

Hereinafter, the present invention will be explained in detail according to embodiments shown in the drawings. FIG. 2 shows an embodiment of the present invention.

The demodulated signal output of the FM demodulation circuit 4 is input to the video processing circuit 9 via the adder circuit 16, the output of the video processing circuit 9 is branched, and the vertical synchronization pulse signal is taken out by the synchronization separation circuit 10. The vertical synchronizing pulse signal whose frequency is divided by one and divided into ten thousand by the division (b) path 11 is branched, and the vertical synchronizing pulse signal is connected to a triangular wave generating circuit 12 that generates a triangular wave in synchronization with the divided vertical synchronizing pulse. The energy extracted by the sampling and holding circuit 13 is supplied to a sampling and holding circuit 15 that samples and holds the peak and trough voltages of the triangular wave of the energy spread signal appearing in the demodulated output of the FM demodulation circuit 4 in synchronization with the FM demodulation circuit 4. The difference between the peak and valley voltages of the spread signal is detected by the difference detection circuit 14, and the amplitude of the triangular wave is controlled by the amplitude control circuit 15 connected to the triangular wave generation circuit 12 according to the difference. The output is added to the demodulated signal by an adder circuit 16.

FIG. 3 is a diagram showing an example of the operation and configuration of the sampling/holding circuit 16 and the difference detection circuit 14. The sampling/holding circuit 13 samples the demodulated output of the FM demodulation circuit 4 at peaks 180 and troughs 190 of the triangular wave 170 generated by the triangular wave generating circuit, and circuit A of the sampling/holding circuit 16 operates at the troughs 180. mountain 180
The voltage obtained by operating circuit B is supplied to a difference detection circuit 14, for example, a differential amplifier, and the difference is determined. Now, if the detected voltage 200 is in the state of waveform (a), the output 21 of the difference detection circuit 31 will be a voltage proportional to the difference on the positive side as shown in voltage (a)', and the detected voltage 200 will be in the state shown in waveform (a). In the case of waveform (b), an output on the negative side of voltage (b)' is obtained, and in this way, the direction and magnitude of the triangular wave of the energy diffusion signal included in the video signal are obtained. In this example, the trough 19Q of the triangular wave 170.

Sampled at the timing of mountain 180, but mountain 18
0. The valley 190 may be used, and the polarity of the input and output of the 1+ difference detection circuit 14 is not limited to this. The amplitude control circuit 15 is
According to the output of the difference detection circuit 14, the triangular wave generation circuit 12
The amplitude of the generated triangular wave can be varied continuously from the positive polarity to the negative polarity, and can be easily realized using the circuit shown in FIG. 4, for example. The triangular wave generated by the triangular wave generating circuit 12 is input to the terminal 22, branched, and inputted to the negative input terminal of the differential amplifier 25, the other of the branched triangular waves is input to the variable gain amplifier 24, and the output of the variable gain amplifier 24 is is input to the positive input terminal of the differential amplifier 23, and the difference detection circuit 1
4 is input to the variable gain terminal 25 of the variable gain amplifier 24. When signals of the same strength are input to the positive and negative input terminals of the differential amplifier 25, there is no output, but the input to the positive input terminal, that is, the output of the variable gain amplifier 24, is different from the input signal to the negative input terminal. When the amplitude of the triangular wave output from the differential amplifier 23 changes from high to low, the amplitude of the triangular wave output from the differential amplifier 23 changes from large to small and from positive to negative.

In this embodiment, the vertical synchronizing pulse is obtained from the output of the video processing circuit 9, but it is not limited to this and may be obtained anywhere after the adding circuit 16.

FIG. 5 shows another embodiment of the present invention. When the synchronous pulse signal information is included in the audio signal in a scrambled television signal, the output of the audio demodulation circuit 5 is branched, and the pulse separation circuit 26 separates the synchronous pulse signal information contained in the audio signal. A vertical synchronizing pulse signal is generated from the separated information by the vertical synchronizing pulse generating circuit 27, and is supplied to the frequency dividing circuit 11, which is configured in the same manner as in the previous embodiment. Further, the descrambling circuit 28 normalizes the transformed video signal. In scrambled television signals, the 4M pulse signal is suppressed or not present at all, but the synchronization pulse part is fixed at a certain level, so the energy spread signal is synchronized with the vertical synchronization pulse signal. Therefore, the sample and hold circuit can extract the peak and trough voltages of the triangular wave of the energy diffusion signal, and the energy diffusion signal can be removed by the above means. An example is shown. The same reference numerals as in FIGS. 2 and 5 indicate the same functional blocks. In this embodiment, conventional television broadcasting and scrambled television broadcasting are used together, and the descrambling circuit 2 has an input and an output that are short-circuited during conventional broadcasting, and when scrambled broadcasting is used. The descrambling operation is performed, and these discrimination signals are outputted to the signal line 29. The switch 6o switches between the outputs of the synchronization separation circuit 1o and the vertical synchronization pulse generation circuit 27 using a signal on the signal line 29.

In the case of conventional broadcasting, the vertical synchronizing pulse of the video signal is removed. In the case of scrambled broadcasting, the triangular wave of the energy spread signal is removed using the information of the synchronizing pulse signal contained in the audio signal.

In addition, in the embodiments of FIGS. 2 and 3, an example was described in which the information of the synchronization pulse signal is included in the audio signal, but the invention is not limited to this, and the information of the synchronization pulse signal may take a signal form other than a video signal, It is clear that by demodulating or decoding it, the synchronization pulse signal can be recovered and the energy spread (g) removed by the method of the invention.

In addition, although the synchronization of the energy diffusion signal has been described above with a period twice that of the vertical synchronization pulse signal, it is also possible to synchronize with the vertical synchronization pulse signal at other periods by changing the division ratio of the frequency divider circuit 11. It is clear that this can be done.

〔Effect of the invention〕

As described above, according to the present invention, a vertical synchronizing pulse is extracted from a video signal or an audio signal, the frequency of the extracted vertical synchronizing pulse is divided, and an energy diffusion signal is generated from the frequency-divided synchronizing pulse. Generates a triangular wave with the same period, and outputs the demodulated output of the vertical synchronizing pulse signal portion of the video signal in synchronization with the frequency-divided synchronizing pulse, detects the displacement of the demodulated output caused by the triangular wave of the energy spread signal, and detects the displacement. By controlling the amplitude of the generated triangular wave according to the magnitude and direction of the signal and adding it to the demodulated signal or video signal in the opposite phase, the energy spread signal can be sufficiently removed and a good signal without sag etc. can be obtained. Video signal output can be obtained, and
Even in a scrambled FM television signal in which the synchronization pulse signal in the video signal is suppressed, good energy spread signal removal characteristics can be obtained.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a conventional FM television signal receiving circuit, FIG. 2 is a block diagram showing the first embodiment of the present invention, and FIG. 3 is a diagram showing a sampling hold circuit and a difference detection circuit of the present invention. 4 is a block diagram showing an amplitude control circuit of the present invention, FIG. 5 is a block diagram showing a second embodiment of the present invention, and FIG. 3 is a block diagram showing a third embodiment of the present invention. It is a diagram. 10... Synchronization separation circuit 11... Branch circuit 12.
・Triangular wave generation circuit

Claims (2)

[Claims] (1) A mixing circuit that receives a high frequency FM television signal and a local oscillation signal from a local oscillation circuit and outputs a low frequency FM television signal, and a mixing circuit that demodulates the low frequency FM television signal and generates a first signal. a first demodulation circuit that outputs
A video processing circuit that inputs a first signal and outputs a second signal consisting of a video signal, and a second demodulation circuit that inputs the first signal and outputs a third signal. The receiving circuit includes at least one synchronization separation circuit that separates a synchronization pulse signal from the first signal, second signal, or third signal and generates a vertical synchronization pulse signal, and the vertical synchronization pulse output from the synchronization separation circuit. A frequency dividing circuit that divides the signal, a triangular wave generating circuit that generates a triangular wave synchronized with the output signal of the frequency dividing circuit, and a first
The output of the sampling and holding circuit and the triangular wave output of the triangular wave generation circuit are input to the sampling and holding circuit, and the amplitude and polarity of the inputted triangular wave are controlled and output according to the output signal of the sampling and holding circuit. 1. An FM television signal receiving circuit comprising: an amplitude control circuit; and means for adding an output signal of the amplitude control circuit to an output of a first demodulation circuit or an output of a video processing circuit. (2) In the FM television signal receiving circuit according to claim 1, the first synchronization separation circuit receives the first signal or the second signal, and the second synchronization separation circuit receives the third signal. synchronous separation circuit, and means for switching the outputs of the first synchronous separation circuit and the second synchronous separation circuit according to a specific signal included in the first signal or the second signal. Features: FM television signal receiving circuit.