JPH04369195A - Satellite television broadcast receiver - Google Patents

Abstract

PURPOSE:To reproduce a pattern in an excellent way without reception of flicker disturbance caused by nonlinearity of an amplifier even in the case of a satellite television broadcast in which a large level of an energy spread signal superimposed onto a video signal is high. CONSTITUTION:A radio wave from a satellite is received and selected and the result is given to a band pass filter 6, in which FM demodulation is implemented and from which a video signal is obtained. The video signal onto which a large energy spread signal superimposed is inputted to a 1st clamp circuit 8 at a low level, in which the energy spread signal is eliminated to provide a margin to a dynamic range of a post-stage amplifier 9, and a 2nd clamp circuit 10 keeps DG, DP of a post-stage amplifier 11 in an excellent state. Thus, even in the case of a satellite television broadcast, in which a level of the energy spread signal superimposed onto the video signal is high, distortion due to nonlinearity of the amplifiers is considerably reduced and a pattern is reproduced in an excellent way without reception of flicker disturbance.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a satellite television broadcast receiver used for receiving satellite television broadcasts from communication satellites and broadcasting satellites.

0002

[Prior Art] In recent years, services using communication satellites (CS) have been expanding, and satellite TV broadcast receivers used for purposes such as video distribution and reception of TV broadcasts using satellites are basically is equivalent to one intended for receiving television broadcasts from a broadcasting satellite, and has a configuration as shown in FIG.

In FIG. 3, reference numeral 1 denotes an input terminal for inputting a first intermediate frequency signal;
A 2 GHz band radio wave is frequency-converted to a 1 GHz band by a down converter, and a first intermediate frequency signal guided indoors via a coaxial cable is applied. Reference numeral 2 denotes a channel selection circuit that selects a channel from among a large number of first intermediate frequency signals and receives one channel. 3 is a band pass filter that passes only one wave of the output signal of the tuning circuit 2; 4 is an FM demodulator that demodulates the FM signal that is the output signal of the bandpass filter 3; A de-emphasis circuit 5 de-emphasizes the detection output signal which is the output of the FM demodulator 4. 6 is a low-pass filter circuit that passes only the video signal. A first amplifier 20 amplifies the output signal of the low-pass filter circuit 6. A clamp circuit 21 removes the energy spread signal contained in the output signal of the first amplifier 20. A second amplifier 22 amplifies the output signal of the clamp circuit 21. A video output terminal 12 outputs the output signal of the second amplifier 22. 13 is an audio signal processing circuit which outputs an audio signal from the detection output signal which is the output of the FM demodulator 4; 14 and 15 are audio signal output terminals, and the audio signal processing circuit 1
Outputs the output signal of 3.

[0004] The operation of the satellite television broadcasting receiver configured as described above will be explained below. Input terminal 1 receives 12 GHz from the satellite received by the antenna.
The frequency of radio waves in the band is converted to a 1 GHz band by a down converter, and a first intermediate frequency signal guided indoors via a coaxial cable is applied. A channel selection circuit 2 selects this signal from among a large number of first intermediate frequency signals and receives one channel. Only one wave of the signal tuned by the tuning circuit 2 is passed through the bandpass filter 3. The bandpass filter 3 includes S
An AW filter or the like is commonly used. FM demodulator 4
demodulates the selected FM signal and obtains a detection output signal. In the audio signal processing circuit 13, the detection output signal is 5.7M.
After demodulating the QPSK modulated audio signal on the Hz subcarrier and performing PCM demodulation processing, the digital signal is converted to an analog signal by a D/A converter, and the audio signal is converted to an analog signal via a low-pass filter. Audio signal output terminals 14, 15
Output to. Further, the detection output signal of the FM demodulator 4 is input to a de-emphasis circuit 5, and the frequency characteristic of the signal pre-emphasized on the transmitting side is flattened by the de-emphasis circuit 5. The signal flattened by the de-emphasis circuit 5 is input to a low-pass filter circuit 6, and only the video signal is passed through the low-pass filter circuit 6 and output.

[0005] In the spectrum of the FM wave modulated by the video signal, the energy is concentrated around the frequency corresponding to the pedestal level and synchronization signal level, which have a large time rate among the video signal level, and the power peaks there. Become. Since this peak interferes with microwave lines for telephones and the like, WARC-BS stipulates that the power flux density of satellite broadcast waves should be reduced by 22 dB in a bandwidth of about 4 kHz. This is called energy diffusion, and is realized by superimposing a triangular wave synchronized with the frame period of the video signal on the video signal. In the case of satellite television broadcast by a broadcasting satellite, the frequency shift of the energy spread signal is 600 kHz p-p, and the repetition frequency of the energy spread signal is 15 Hz. Furthermore, since the frequency shift of the main carrier wave is 17 MHzp-p, the level of the energy diffusion signal superimposed on the video signal 1Vp-p is 0.11Vp-p, considering the pre-emphasis applied to the video signal. FIG. 4 shows a video signal on which an energy spread signal is superimposed in the case of television broadcasting by a broadcasting satellite. (Reference: Satellite Broadcasting Receiver (Part 2 Desirable Performance) Radio Technology Association) On the other hand, in recent years, it has been planned to perform television broadcasting using communication satellites. In this case, it is communication, so
The conditions are even stricter than those for satellite broadcasting. In television broadcasting by Japan's communication satellites, the frequency deviation of the energy spread signal is from 2MHzp-p to 3MHz.
The repetition frequency of the energy diffusion signal is a triangular wave of about 30 Hz. Also, since the frequency shift of the main carrier wave varies depending on the satellite, the level of the energy spread signal superimposed on a 1Vp-p video signal is approximately 0.5V at maximum, considering the pre-emphasis applied to the video signal.
It will be about pp. FIG. 5 shows a video signal on which an energy spread signal is superimposed in the case of television broadcasting by a communication satellite.

[0006] After being FM demodulated, de-emphasized and passed through a low-pass filter, the energy spread signal remains superimposed on the video signal, and if the screen is reproduced as it is, it will experience flicker-like interference.

[0007] The first amplifier 20 receives the output signal of the low-pass filter circuit 6 as an input, amplifies it to a level of a video signal excluding the energy spread signal portion, and outputs the amplified signal up to 2Vp-p. The clamp circuit 21 removes the energy spread signal superimposed on the video signal and applies a DC bias to the second amplifier 22. The second amplifier 22 is
It is a buffer circuit with a voltage gain of 1, and the clamp circuit 21
By setting a good DC bias for DG and DP, a video signal of 1Vp-p is output from the video output terminal 12 with a terminal value of 75Ω.

[0008]

[Problems to be Solved by the Invention] However, with the above configuration, the level of the energy diffusion signal superimposed on a 1Vp-p video signal is approximately 0.5Vp-p at maximum in television broadcasting by a communication satellite. When receiving television broadcasts from satellites, the peak-to-peak value of the video signal on which the energy spread signal is superimposed is larger than that from broadcasting satellites, and distortion occurs due to the nonlinearity of the first amplifier. . Due to this distortion, even if the energy diffusion signal could be completely removed by the clamp circuit, there was a problem in that the reproduced screen would receive a flicker-like disturbance.

The present invention solves the above-mentioned conventional problems, and eliminates flicker-like interference caused by the nonlinearity of the amplifier even in television broadcasting by communication satellites in which the level of the energy spread signal superimposed on the video signal is high. ,
The purpose of the present invention is to provide a satellite television broadcasting receiver that reproduces the screen well.

0010

[Means for Solving the Problem] In order to achieve this object, the satellite television broadcasting receiver of the present invention has a first intermediate frequency signal obtained by receiving and frequency converting radio waves from a satellite as an input signal. a bandpass filter that uses the output of the station circuit and the tuning circuit as input and passes only the desired FM signal;
An FM demodulator that receives the output signal of the bandpass filter as input, a de-emphasis circuit that uses the detected output signal of the FM demodulator as input and de-emphasizes the pre-emphasized signal on the transmitting side, and a video image that uses the output of the de-emphasis circuit as input. a low-pass filter circuit that passes only the signal; a first amplifier that inputs and amplifies the output of the low-pass filter circuit; and a first clamp circuit that uses the output of the first amplifier as input and clamps the signal; a second amplifier that uses the output of the first clamp circuit as an input to amplify the signal; a second clamp circuit that uses the output of the second amplifier as the input and clamps the signal; and a second amplifier that uses the output of the second clamp circuit as the input. It is characterized by being equipped with a buffer amplifier that amplifies the signal.

[0011]

[Operation] According to the above-described structure, even when receiving television broadcasting by a communication satellite, the present invention inputs a video signal superimposed with a larger energy diffusion signal than that of a broadcasting satellite into the first clamp circuit at a low level, thereby generating energy. The level of the energy spread signal superimposed on the video signal is increased by removing the spread signal, leaving some margin in the dynamic range of the downstream amplifier, and maintaining good DG and DP of the downstream amplifier using the second clamp circuit. Even in television broadcasting by communication satellites, distortion caused by amplifier nonlinearity is greatly reduced.
This allows the screen to be reproduced well without flicker-like interference.

0012

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

In FIG. 1, 1 is an input terminal for a first intermediate frequency signal. 2 is a tuning circuit, 3 is a band pass filter, 4 is an FM demodulator, 5 is a de-emphasis circuit, 6 is a low pass filter circuit, 13 is an audio signal processing circuit, 14
, 15 are audio signal output terminals, which are the same as the configuration shown in FIG. 3. A first amplifier 7 amplifies the output signal of the low-pass filter circuit 6. A first clamp circuit 8 removes the energy spread signal contained in the output signal of the first amplifier 7. A second amplifier 9 amplifies the output signal of the first clamp circuit 8. A second clamp circuit 10 performs DC regeneration of the output signal of the second amplifier 9 and applies a DC bias to the buffer amplifier 11. A buffer amplifier 11 buffers and amplifies the output signal of the second clamp circuit 10. A video output terminal 12 outputs a video signal which is an output signal of the buffer amplifier 11. The operation of the satellite broadcasting receiver configured as described above will be explained using FIG. 1. First, a first intermediate frequency signal is applied to the input terminal 1, which is a 12 GHz band radio wave received by an antenna from a satellite, frequency-converted to 1 GHz band by a down converter, and then guided indoors via a coaxial cable. A channel selection circuit 2 selects this signal from among a large number of first intermediate frequency signals and receives one channel. Only one wave of the signal tuned by the tuning circuit 2 is passed through the bandpass filter 3. As the bandpass filter 3, a SAW filter or the like is generally used. The FM demodulator 4 demodulates the selected FM signal and obtains a detected output signal. The audio signal processing circuit 13 demodulates the QPSK modulated audio signal onto a 5.7 MHz subcarrier from the detection output signal, performs PCM demodulation processing, and then converts the digital signal into an analog signal using a D/A converter. Then, the audio signal is outputted to audio signal output terminals 14 and 15 via a low-pass filter. Further, the detection output signal of the FM demodulator is input to the de-emphasis circuit 5, and the signal pre-emphasized on the transmitting side is sent to the de-emphasis circuit 5.
The frequency characteristics are flattened back to their original state by passing through the signal. The signal whose frequency characteristics have been flattened by the de-emphasis circuit 5 is input to a low-pass filter circuit 6, where only the video signal is passed and output. The first amplifier 7 amplifies the output video signal of the low-pass filter circuit 6 to a level necessary for the operation of the first clamp circuit 8 and outputs the amplified signal.

The first clamp circuit 8 removes the energy diffusion signal superimposed on the video signal by a clamping operation, and outputs the video signal. The second amplifier 9
The output signal level of the clamp circuit 8 is amplified to 2Vp-p and output. The second clamp circuit 10 performs DC regeneration and applies a DC bias to the buffer amplifier 11. The buffer amplifier 11 is a buffer circuit with a voltage gain of 1,
The second clamp circuit 10 sets a DC bias that provides good DG and DP, and outputs a 1Vp-p video signal from the video output terminal 12 with a terminal value of 75Ω.

An example of a clamp circuit used for the first clamp circuit 8 and the second clamp circuit 10 is shown in FIG. In FIG. 2, 31 is an input signal terminal into which a signal is input;
2 is a capacitor whose one end is connected to the input signal terminal 31, 33 is an output signal terminal, 34 is a DC power supply, 35 is a base connected to the DC power supply 34, and an emitter is connected to the capacitor 32.
a transistor connected to the other end and the output signal terminal 33;
36 is a power terminal. The DC component of the input signal input to the signal input terminal 31 is cut by the capacitor 32 . Due to changes in the amplitude of the input signal, the difference between the voltage on the side of the capacitor 32 connected to the signal output terminal 33 and the DC power supply 34, that is, the base voltage of the transistor 35, increases.
When the emitter voltage becomes greater than 0.6V, the transistor 35 becomes conductive, the capacitor 32 is charged, and at the signal output terminal 33, the DC potential of the negative peak value of the input signal is approximately 0.6V from the DC power supply 4. Clamped to a lower voltage.

As described above, according to the present embodiment, there is a tuning circuit which takes as an input signal the first intermediate frequency signal obtained by receiving radio waves from a satellite and converting the frequency thereof, and a tuning circuit which takes as an input the output of the tuning circuit. A bandpass filter that passes only the desired FM signal, and an F that receives the output signal of the bandpass filter as input.
An M demodulator, a de-emphasis circuit that uses the detected output signal of the FM demodulator as input and de-emphasizes the signal pre-emphasized on the transmitting side, and a low-pass filter that uses the output of the de-emphasis circuit as input and passes only the video signal. a first amplifier that receives and amplifies the output of the low-pass filter circuit; a first clamp circuit that uses the output of the first amplifier as input and clamps the signal;
A second circuit amplifies the signal by using the output of the clamp circuit as input.
By providing an amplifier, a second clamp circuit that takes the output of the second amplifier as input and clamps the signal, and a buffer amplifier that uses the output of the second clamp circuit as input and buffers and amplifies the signal, it is possible to superimpose it on the video signal. Even in the case of TV broadcasting by communication satellites, where the level of the energy diffusion signal is high, the video signal on which the energy diffusion signal, which is higher than that of the broadcasting satellite, is superimposed is input to the first clamp circuit at a low level to remove the energy diffusion signal. The second clamp circuit determines the operating point of the buffer amplifier to maintain good DG and DP, greatly reducing the influence of non-linearity of the amplifier and eliminating flicker-like effects. The screen can be reproduced well without interference.

[0017]

Effects of the Invention As described above, the present invention provides a tuning circuit whose input signal is a first intermediate frequency signal obtained by receiving and frequency-converting radio waves from a satellite, and a desired tuning circuit whose input signal is the output of the tuning circuit. A band-pass filter that passes only the FM signal of the band-pass filter, an FM demodulator that receives the output signal of the band-pass filter, and a de-emphasis system that de-emphasizes the pre-emphasized signal on the transmitting side using the detected output signal of the FM demodulator as input. a low-pass filter circuit that receives the output of the de-emphasis circuit as an input and passes only the video signal; a first amplifier that receives the output of the low-pass filter circuit as an input and amplifies it; and the output of the first amplifier as an input. a first clamp circuit that clamps a signal as an input, a second amplifier that uses the output of the first clamp circuit as an input and amplifies the signal, and a second clamp circuit that uses the output of the second amplifier as an input and clamps the signal. By providing a buffer amplifier that uses the output of the second clamp circuit as an input to buffer and amplify the signal, the effects of nonlinearity of the amplifier can be minimized even in TV broadcasting by communication satellites where the level of the energy diffusion signal superimposed on the video signal is high. It is possible to realize an excellent satellite television broadcasting receiver that can significantly reduce the amount of noise caused by flickering and reproduce the screen well without flicker-like interference.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a satellite television broadcast receiver according to an embodiment of the present invention.

[Figure 2] Circuit diagram of clamp circuit

[Figure 3] Block diagram of a conventional satellite TV broadcast receiver

[Figure 4] Waveform diagram of a video signal superimposed with an energy spread signal with a frequency shift of 600kHzp-p

[Figure 5] Waveform diagram of a video signal superimposed with an energy spread signal with a frequency shift of 3MHzp-p

[Explanation of symbols]

1 Input terminal 2 Tuning circuit 3 Bandpass filter 4 FM demodulator 5 De-emphasis circuit 6 Low pass filter circuit 7 First amplifier 8 First clamp circuit 9 Second amplifier 10 Second clamp circuit 11 Buffer amplifier 12 Video signal output terminal 13 Audio signal processing circuit 14, 15 Audio signal output terminal 20 First amplifier 21 Clamp circuit 22 Second amplifier 31 Input signal terminal 32 Capacitor 33 Output signal terminal 34 DC power supply 35 Transistor

Claims (1)

[Claims] Claim 1: A tuning circuit that receives as an input signal a first intermediate frequency signal obtained by receiving radio waves from a satellite and converting the frequency; and passing only a desired FM signal using the output of the tuning circuit as an input. a bandpass filter; an FM demodulator receiving the output signal of the bandpass filter;
a de-emphasis circuit that takes as input the detection output signal of the M demodulator and de-emphasizes the signal pre-emphasized on the transmitting side; a low-pass filter circuit that takes the output of the de-emphasis circuit as input and passes only the video signal; a first amplifier that receives the output of the low-pass filter circuit as an input and amplifies the signal; a first clamp circuit that uses the output of the first amplifier as the input and clamps the signal;
a second amplifier that uses the output of the first clamp circuit as an input to amplify the signal; a second clamp circuit that uses the output of the second amplifier as the input to clamp the signal; and an output of the second clamp circuit. A satellite television broadcast receiver with a buffer amplifier that amplifies the signal as input.