JPH08140119A - Satellite television receiver picture quality display device - Google Patents

Abstract

PURPOSE: To enable accurate display even at the time of NTSC standard television signal and MUSE signal reception on the received picture quality display device for a satellite broadcasting receiver. CONSTITUTION: A MUSE signal outputted from an FM demodulation circuit 13 is inputted to a band pass filter 14 and the noise extracted there is amplified by an amplifier 15 and inputted to a sample-and-hold(S/H) circuit 17 after its noise level is detected by a detection circuit 16. A key pulse deciding circuit 32 inputs a key pulse and decides whether it is NTSC standard television signal reception or MUSE signal reception, the time constant of the detection circuit 16 is controlled, besides, the sampling pulse of the S/H circuit 17 is switched and during a clamp level term in which no signal is transmitted at the time of MUSE signal reception, a noise detection output signal is sampled.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a satellite broadcast receiver,
In particular, the present invention relates to a received image quality display device of a satellite television receiver that can be useful for the angle of installation of an antenna by displaying the quality of received radio waves.

[0002]

2. Description of the Related Art In satellite broadcasting, radio waves in the microwave band are transmitted as television signals (NTSC standard television signals, M
(USE signal) frequency-modulates, radiates a radio wave from a geostationary satellite, and converges the radio wave on the ground with a BS antenna 81 such as a parabolic antenna, and then uses a BS converter 82 including an ultra-low noise amplifier to shift to a 1 GHz band. Convert frequency. The output signal from the BS converter 82 is subjected to signal processing such as channel selection and FM demodulation in an indoor BS tuner 84 using a coaxial cable 83, and a video signal and an audio signal are output, which are input to a TV receiver 85. To be done.

In order to obtain a high quality image, it is necessary to increase the SN ratio of the demodulated video signal. Since the SN ratio (signal level to noise level ratio) of the demodulated video signal is proportional to the CN ratio (carrier level to input noise level ratio) of the received signal, it is necessary to take a large CN ratio. In order to increase the CN ratio, it is necessary to use a lower noise BS converter to reduce the noise level and to use a higher gain BS antenna to increase the carrier level. As for the gain of the BS antenna, a high gain antenna of about 35 dBi is usually used in the direct reception system, so that the half-value angle is about 2 degrees, and the directivity of the antenna is extremely strong. Therefore, it is necessary to properly install the antenna in order to obtain a higher CN ratio.

Therefore, various display devices have been devised so far for the purpose of confirming that the received image quality is kept good and for improving the accuracy of the direction when the antenna is installed. To give an example, first
As a conventional example of the above, a CN ratio measuring method and apparatus as disclosed in JP-A-61-274495 has been proposed.

This is a signal obtained by multiplexing a television signal (NTSC standard television signal, MUSE signal) and another signal as in satellite television broadcasting and FM-modulating the main carrier, and then the main carrier power C and within the transmission frequency band. Is a measuring method and apparatus for detecting the noise power N included in the above and the CN ratio by detecting in the intermediate frequency band. Originally, in the CN ratio measurement, the television signal (NTSC standard television signal and M
It is difficult to know only the noise power in the band from the FM modulated signal such as the USE signal), but the image information is transmitted including the vertical blanking period of the video signal of the television signal and the period in the vicinity thereof. When the sideband is generated by the other signal according to the frequency band of the main carrier and the multiplexing form of the television signal and the other signal in the period not performed, the frequency of the sideband signal in the period The CN ratio is obtained from the noise power N obtained by extracting the noise component of the frequency band excluding the band.

A CN ratio measuring device based on this method will be described with reference to the drawings. FIG. 9 shows an FM signal of satellite television broadcasting during a period in which image information is not transmitted, including a vertical blanking period of the video signal of the television signal and a period in the vicinity thereof, which is a period for detecting noise power in the CN ratio measuring method. Represents the spectral distribution, the main carrier signal component 1
And upper and lower sideband spectra 2, 3, 4, and 5 due to the audio subcarrier signal (5.772772 MHz). FM in the frequency bands 6, 7, 8 and 9 between these spectra
There are no spectral components that form the modulated wave.

FIG. 10 shows a CN ratio measuring device. In FIG. 10, 70 is a first intermediate frequency signal input terminal for satellite broadcasting from the BS converter, 71 is a frequency converter that converts the input signal into a constant intermediate frequency that is easy to process in the measuring device, 72 is an intermediate frequency amplifier, Reference numeral 73 is an amplitude detector for the main carrier level C, 74 is a signal level display section for displaying the level of the main carrier power C detected by the main carrier level detector, 7
Reference numeral 5 is a bandpass filter for extracting a noise component from the intermediate frequency signal, 78 is a switching circuit for switching the noise component extracted by the bandpass filter 75, 7
6 is a frequency detector for demodulating a television sync signal,
Reference numeral 77 is a switching signal generator for generating a switching signal from the television signal synchronizing signal obtained by the frequency detector 26, 79 is an amplitude detector for the noise power N output from the switching circuit 78, and 80 is an amplitude for the noise power N. It is a noise level display unit that displays the level of noise power N detected by the detector.

Input terminal 7 for the first intermediate frequency signal of satellite broadcasting
The satellite broadcast FM signal input from 0 is the frequency converter 7
1 and converted to a constant intermediate frequency which is easy to process in the measuring device. The output signal of the frequency converter 71 is input to the intermediate frequency amplifier 72, is amplified to a required level, and is limited to the bandwidth required to measure the signal level and noise level. The required bandwidth here means the minimum bandwidth required to demodulate the television synchronizing signal for forming the signal for switching only the noise component extraction time described above in the switching signal generator 77. However, the band of the noise extraction bandpass filter 75 may be included in the bandwidth.

By the way, the minimum required bandwidth required for demodulating a television sync signal varies depending on the emphasis applied to the video signal before modulation, the superposition of energy diffusion signals, and the content of the video signal. Considering this, it is about 4 MHz. Also, by setting the band of the intermediate frequency amplifier 72 to a position including the signal spectrum 1 and the band 6 in which only the noise component exists in the FM spectrum of the satellite television broadcast shown in FIG. Will contain the various required signals. The output of the intermediate frequency amplifier 72 is amplitude-detected by the amplitude detector 73 for displaying the signal level, and is displayed on the signal level display unit 74, and the signal level applied to the signal input terminal 70 is corresponded thereto. I am able to read it as a level. The output of the intermediate frequency amplifier 72 is also supplied to a band pass filter 75 for noise extraction and a frequency detector 76 for demodulating a television sync signal.

During the noise extraction time, the band pass filter 75 is matched with the frequency at the center of the frequency band 6 shown in FIG. 9, and its pass band width is 0.2 to 1.0.
MHz is appropriate. The output of the band pass filter 75 is switched by the switch circuit 78 in response to the switching signal formed by the frequency detector 76 and the switching signal generator 77 so that only the noise component extraction time is taken out. Pass filter 7
Only the internal noise component of the output of 5 is extracted.

The noise component thus extracted is detected and rectified by the amplitude detector 79. This amplitude detector 7
9 has an integrating function to convert the detected rectified output into a DC voltage. This DC voltage output is displayed on the noise level display unit 8
The noise level converted into the noise level included in the 27 MHz band of the signal under measurement applied to the input signal terminal 70 is displayed.

On the other hand, as a second conventional example, Japanese Patent Application Laid-Open No. 1-17
A satellite television receiver image quality display device as disclosed in Japanese Patent No. 5487 has been proposed. As shown in FIG. 11, the noise component is extracted from the baseband signal of the FM demodulation output and detected to obtain an output proportional to the noise power to obtain the video SN ratio, which is converted to correspond to the CN ratio. By doing so, it is a device that indicates the good reception image quality. The operation of the second conventional example shown in FIG. 11 will be described below with reference to the drawings.

FIG. 11 shows an example of the prior art of a satellite television receiver image quality display device, 11 is a 1stIF input terminal for inputting a signal by connecting a coaxial cable from a BS converter, and 12 is a channel from many channels. A channel selection circuit for selecting the signal of, an FM demodulator, a bandpass filter 14 for extracting only a noise component from the FM demodulation output, an amplifier circuit 15 for amplifying the extracted noise as much as necessary for detection, and a reference numeral 16 A detection circuit for detecting the magnitude of noise power, 40 is a video signal processing circuit for an NTSC standard TV signal with an FM demodulation output as an input, and 42 is a video signal processing circuit for superimposing a noise detection output signal from the detection circuit on a video signal. An on-screen display circuit for enabling on-screen display on the receiver, and 43 is a video signal output terminal to the television receiver.

The reception signal input to the 1stIF input terminal 11 is selected by the channel selection circuit 12 and F by the FM demodulation circuit 13.
After the M demodulation, the video signal processing circuit 40 for the NTSC standard television signal removes the audio subcarrier signal, de-emphasis, removes the energy spread signal to obtain the video signal, and then the information such as channel display and volume display is turned on. After being superimposed on the video signal in the screen circuit 42, it is output from the video signal output terminal 43. The circuit operation up to now is included in the function of a normal BS tuner.

When the FM demodulated signal is an NTSC standard television signal, its spectrum is as shown in FIG. In FIG. 12, 90 is a video luminance component, and 9
1 is a 3.58 MHz color subcarrier, 92 is 5.7272
The 72 MHz audio subcarrier and 93, 94 are harmonics of the color subcarrier. The noise demodulated by FM demodulation generally has a noise power as the frequency increases, as is generally called triangular noise as shown in FIG.

Generally, the frequency band of the demodulation output of the FM demodulator of the BS tuner is 50 Hz to 8.1 MHz.
It is only to the extent that higher frequencies are not guaranteed. However, in recent years, the FM demodulation circuit has been made into an IC, and the demodulation frequency characteristic has been stabilized and the performance has been improved.
Almost flat frequency characteristics have been obtained even in a wide band of about MHz. Therefore, the bandpass filter 14 for extracting only the noise component excluding the demodulated signal component has a center frequency of about 8.1 MHz and a bandwidth of 1M.
Hz or center frequency is about 11MHz, bandwidth is 1
It is desirable to select around MHz.

The noise extracted by the band-pass filter 14 is amplified by the amplifier 15 to a level sufficient for detection by the detection circuit 16 using a diode, and is input to the detection circuit 16 and detected. Since the output level (S) of the video signal is 0.714Vp-p and is set to a constant value, if the detected noise level (N) is displayed in inverse proportion, the SN ratio of the video signal can be displayed. . When the output level amplifier of the video signal has no non-linear amplification effect, the detection output sharply increases when the CN ratio of the input signal is changed and the CN ratio deteriorates as shown in FIG.

This is because in the case of satellite broadcasting, since FM is used to modulate the video signal, a so-called threshold phenomenon occurs at a CN ratio of about 9 dB or less, and the noise level of the demodulation output sharply increases. To be Therefore, the SN ratio rapidly deteriorates. When the detection output as shown in FIG. 14 is displayed as it is, the linearity of the display output with respect to the change of the CN ratio is poor, and the range of the CN ratio that can be displayed is limited. Therefore, it is necessary to devise an amplifier, and if a nonlinear amplification effect is applied to the gain of the amplifier so that the noise amplitude does not exceed a certain value, the linearity of the noise detection output with respect to the CN ratio is improved. become that way. By this device, the SN ratio of the video signal can be obtained and converted so as to correspond to the CN ratio.

The detection output proportional to the noise power obtained by the detection circuit 16 is input to the on-screen display circuit 42, superposed on the video signal, and output from the video signal output terminal 43 to the television receiver. By displaying with, it becomes possible to display an amount corresponding to the CN ratio.

Further, if the detected output is input to the voltmeter and displayed, it can be used for adjusting the direction of the BS antenna.

[0021]

The problems of the above-mentioned conventional example will be described below.

In the first conventional example, a television signal (NTSC standard television signal, MU) like satellite television broadcasting is used.
The main carrier power C and the noise power N included in the transmission frequency band are measured in the intermediate frequency band and C
A measuring method and apparatus for obtaining the N ratio, and in measuring the carrier wave and noise power thereof, the fact that there is no spectrum of the modulation component due to the signal in the image during the vertical blanking period of the image signal is utilized. This method measures the carrier power and the accompanying noise power directly from the intermediate frequency signal, and in principle can measure the CN ratio accurately and is an excellent method.

However, when the noise power N is detected, the noise in the frequency band is used by using a narrow band pass filter having a center frequency near the center frequency of the intermediate frequency signal and a bandwidth of 0.2 to 1.0 MHz. It is necessary to extract the ingredients. Since the center frequency of the intermediate frequency signal in the BS tuner is 134 MHz or 402 MHz, it is difficult to manufacture a bandpass filter with a very small ratio band with high frequency accuracy, and the frequency accuracy directly affects the CN ratio detection accuracy. To do.

Further, in order to detect the noise component extracted in this frequency band, the detection circuit needs to operate in the intermediate frequency band of high frequency. However, there are technical problems such as instability of the narrow band intermediate frequency and insufficient detection sensitivity in high frequency operation. Further, in order to avoid such a technical problem, adding a new frequency converter to the BS tuner in order to lower the intermediate frequency for the CN ratio measurement has a problem of increasing the cost.

On the other hand, in the second conventional example, a device showing good reception image quality is obtained by extracting a noise component from the baseband signal of the FM demodulation output of satellite television broadcasting and detecting it to obtain an output proportional to the noise power. is there. When the television signal is an NTSC standard television signal, the band pass filter for extracting the noise component in this device is a television signal component, that is, a video luminance signal component, a color subcarrier, and a harmonic wave of 2 times and 3 times of that and an audio sub Since the carrier wave component and its harmonics are removed and only the noise component is taken out, the center frequency is about 8.1 MHz and the bandwidth is 1 MH.
About z or center frequency about 11MHz, bandwidth 1M
It is desirable to select around Hz.

Generally, the frequency band of the demodulation output of the FM demodulator of the BS tuner is 50 Hz to 8.1 MHz.
To the extent that no higher frequencies are guaranteed. However, in recent years, the FM demodulation circuit has been made into an IC, and the FM demodulation characteristic has been stabilized and the performance has been improved. Therefore, a substantially flat demodulation frequency characteristic can be obtained even in a wide band of about 12 MHz. Is coming. This is shown in FIGS. 4 and 5.

4 and 5 show the spectrum of the baseband signal after the FM demodulation when the FM-modulated signal by the MUSE signal is received. FIG. 4 shows the spectrum when the frequency of the video signal is high, and FIG. A spectrum is shown when the frequency of the video signal is low. As shown in FIGS. 4 and 5, when the baseband MUSE signal has a frequency band of the signal up to about 8.1 MHz, and a harmonic component exists at a frequency of 8.1 MHz or more depending on the content of the video signal. There is. In the case of a signal having such a spectral distribution, it becomes impossible to extract only noise power with the noise extraction bandpass filter.

Next, FIG. 7 shows the relationship between the noise detection output voltage and the CN ratio when the second conventional example of the satellite television receiver image quality display device is operated with the MUSE signal.
00 is a noise detection output voltage-to-CN ratio characteristic when the frequency of the video signal is high, and 101 is a noise detection output voltage-to-CN ratio characteristic when the frequency of the video signal is low. As shown in FIG. 7, in the region where the CN ratio is high, the noise detection output signal level changes depending on the content of the video signal even if the input CN ratio does not change, which causes a problem that the error in image quality display increases. It was

In view of the above problems, the present invention is capable of technically easily displaying the reception CN ratio of a satellite television broadcast receiver, and is capable of receiving an MU when receiving an NTSC standard television signal.
It is an object of the present invention to provide a reception image quality display circuit that can accurately display both when receiving an SE signal.

[0030]

A satellite television receiver image quality display apparatus according to the first invention for solving the above-mentioned problems,
An FM demodulator for demodulating a satellite television signal, an NTSC standard television signal obtained by demodulating by the FM demodulator or a bandpass filter for extracting a noise component from a MUSE baseband signal, and an amplifier for amplifying the noise component, A detection circuit that has a control terminal that receives the output of the amplifier as input and switches the time constant to two types, detects the magnitude of the noise component, a sample hold circuit that holds the output of the noise detection circuit by a key pulse, and the key pulse. The key pulse; and Connect the output of the presence / absence judgment circuit to the control terminal of the noise detection circuit, and When an NTSC standard television signal is not input, the time constant of the noise detection circuit is increased to detect the amount of noise power, and the sample and hold circuit is always in the sampling state. On the other hand, when receiving a MUSE signal to which a key pulse is input, The time constant of the noise detection circuit is set to be smaller than the key pulse period, and MUSE is set.
While detecting the magnitude of the noise component during the signal clamp level period, the sample and hold circuit samples the output signal of the noise detection circuit only during the key pulse period,
It is in the hold state outside the key pulse period. The output signal of the sample hold circuit thus obtained is input to the drive circuit and the received image quality is on-screen at both the reception of the NTSC standard television signal and the reception of the MUSE signal by the level display means showing the good reception image quality. The feature is that it can be displayed.

The satellite television receiver image quality display device according to the second aspect of the present invention comprises an FM demodulator for demodulating a satellite television signal and noise from an NTSC standard television signal or MUSE baseband signal obtained by demodulating by the FM demodulator. A band pass filter for extracting a component, an amplifier for amplifying the noise component, a detection circuit for detecting the magnitude of the noise component with the output of the amplifier as an input, and an NTSC standard television signal with an output signal of the FM demodulator as an input NT when receiving
A pulse generation circuit for generating a pulse synchronized with a horizontal sync signal of an SC standard television signal, a sample hold circuit for holding the output of the noise detection circuit by a pulse or a key pulse from the pulse generation circuit, and a key pulse by integrating the key pulse. Of a sampling pulse switching circuit that switches the sampling pulse of the sample-hold circuit according to the output signal of the determination circuit, and the output of the sample-hold circuit as an input corresponding to the output level of the sample-hold circuit. A driving circuit for displaying the level of the received image quality, and at the time of receiving an NTSC standard television signal in which no key pulse is input, the output signal of the determination circuit is used to output the output of the pulse generation circuit as a sampling pulse of the sample hold circuit. The output signal of the noise detection circuit is sampled in synchronism with the horizontal sync period of the NTSC standard television signal, and is put in the hold state outside the horizontal sync period, while the output of the judgment circuit is received when the MUSE signal to which the key pulse is input is received. A key pulse is used as the sampling pulse of the sample and hold circuit by the signal, the output signal of the noise detection circuit is sampled only during the key pulse period, and the hold state is held outside the key pulse period.
The output signal of the sample-hold circuit thus obtained is input to the drive circuit and is displayed by the level display means showing the goodness of the received image quality, when the NTSC standard television signal is received, M
It is characterized in that the received image quality can be displayed on-screen both when receiving the USE signal.

[0032]

The above-described structure of the present invention provides the following functions.

The satellite television signal, which is an intermediate frequency signal FM-modulated by the MUSE signal or the NTSC standard television signal, is FM demodulated by the FM demodulator. From this FM demodulator, MUSE signal or NTSC standard television signal, B
A demodulation output component consisting of a demodulation noise component that changes depending on the S antenna input level is output.

When the FM demodulated signal is an NTSC standard television signal, its video signal and audio signal are frequency-division multiplexed, and its spectrum is 4.5 MHz.
Video luminance component with frequency band up to 3.58MH
The color subcarrier of z, the voice subcarrier of 5.727272 MHz, and the harmonics of the color subcarrier.
On the other hand, the spectrum of the output of the FM demodulator at the time of receiving the MUSE signal has the frequency band of the signal up to 8.1 MHz,
Moreover, an unnecessary spectrum appears at a frequency of 8.1 MHz or higher depending on the content of the video signal. This unnecessary spectrum is generated when the video signal is converted into a signal having a high frequency component, and is considered to be a harmonic component of the video signal. By the way, the MUSE signal is a video signal, an audio signal, a clamp level period (key pulse period), and other control signals are transmitted by time division multiplexing. Therefore, in the key pulse period where no information is sent, no signal component or the above-mentioned unnecessary spectrum appears.

The output of the FM demodulator is input to a bandpass filter and noise power is extracted. The noise power extracted by the bandpass filter is amplified to a sufficient level by the amplifier and then detected by the noise detection circuit, and the output of the noise detection circuit is input to the sample hold circuit.

Whether the FM demodulated signal is an NTSC standard television signal or a MUSE signal is determined by a determination circuit that determines the presence or absence of a key pulse. The output signal of this determination circuit determines when the NTSC standard television signal is received and when the MU signal is received.
The noise detection circuit and the sample hold circuit are controlled when the SE signal is received. The control methods in the respective inventions are as follows.

In the first invention, when no key pulse is input, that is, when an NTSC standard television signal is received,
When the pass frequency band of the band pass filter for extracting the noise component is within the guaranteed frequency of the FM demodulator, and the demodulation signal component is removed and only the noise component is extracted,
There is little change in the output of the noise detection circuit due to changes in the video signal when the CN ratio is high. Therefore, by the output of the judgment circuit,
The noise detection circuit is controlled so as to increase its time constant, and the noise component extracted by the bandpass filter is smoothed to output a DC component as the magnitude of the noise component, and a sample hold circuit after the noise detection circuit. Are always controlled to the sampling state.

On the other hand, when a key pulse is input, that is, when a MUSE signal is received, the video signal is set no matter which frequency within the guaranteed frequency of the FM demodulator is set as the pass frequency band of the band pass filter for extracting the noise component. Because of the harmonics of, it is not possible to always extract only the noise component as in the NTSC standard television signal. Therefore, among the outputs of the noise detection circuit, the sample hold circuit samples only the noise detection circuit output in the period of the key pulse in which no signal is transmitted, and the sample hold circuit operates to hold it in other periods. By doing so, the magnitude of only the noise component can be equivalently detected.

Therefore, by the output of the judgment circuit, the noise detection circuit is controlled so that its time constant is a key pulse and a time constant smaller than the period, and the magnitude of the noise component during the key pulse period is detected from the output of the band pass filter. The sample and hold circuit after the noise detection circuit is controlled so as to sample the output of the noise detection circuit during the key pulse period and hold it during the other period. This suppresses the fluctuation of the noise detection output signal due to the change of the MUSE video signal.

In the second invention, the time constant of the noise detection circuit is not changed by the NTSC standard television signal and the MUSE signal, but the output signal of the FM demodulator is used as an input and the NTSC standard television signal is received. Is provided with a pulse generation circuit for generating a pulse synchronized with the horizontal synchronization signal, and the output of the determination circuit for the presence / absence of the key pulse is used as the sampling pulse of the sample / hold circuit when the NTSC standard television signal without the key pulse is received. The difference between the video signals in the first invention is selected by selecting the output of the pulse generation circuit, sampling the output signal of the noise detection circuit during the horizontal synchronizing period of the NTSC standard television signal, and holding it outside the horizontal synchronizing period. Even if the fluctuation of the output of the noise detection circuit due to It is.

On the other hand, when the MUSE signal to which the key pulse is input is received, the key pulse is selected as the sampling pulse of the sample hold circuit by the output signal of the judgment circuit, and the output signal of the noise detection circuit is sampled only during the key pulse period. It is in the hold state outside the key pulse period. This suppresses the fluctuation of the noise detection output signal due to the change of the MUSE video signal.

With respect to the bandpass filter for extracting the noise power, in the first invention, the noise component in the key pulse period having no video information is extracted when the MUSE signal is received. In the key pulse period in which no information is transmitted during the sampling period, the signal component and the harmonic component do not exist in the frequency domain, so that the center frequency and bandwidth of this band pass filter can be freely selected. However, the demodulation noise component in the FM demodulation output generally increases in noise voltage as the demodulation frequency increases, as is commonly called triangular noise. Therefore, the higher the frequency of the bandpass filter, the larger the noise voltage. Also NT
Considering the reception of SC standard television signals, a bandpass filter for extracting only noise components excluding demodulated signal components has a center frequency of about 8.1 MHz and a bandwidth of 1 MH.
About z or center frequency about 11MHz, bandwidth 1M
It is desirable to select around Hz.

On the other hand, the bandpass filter according to the second aspect of the invention extracts noise components in the horizontal sync signal period or the key pulse period in which there is no video information when receiving the MUSE signal or the NTSC standard television signal. However, since the sampling period of the noise detection output is a period during which no information is transmitted, the center frequency of this bandpass filter, since the signal component and the harmonic component do not exist when the period is viewed in the frequency domain, Bandwidth is freely selectable. However, the demodulation noise component in the FM demodulation output generally increases in noise voltage as the demodulation frequency increases, as is commonly called triangular noise. Therefore, the higher the frequency of the bandpass filter, the larger the noise voltage is obtained. It is desired to be as high as possible within the guaranteed frequency of the FM demodulator.

The output level of the FM-demodulated NTSC standard television signal is 1 Vp-p and the output signal level of the MUSE signal is 0.4 Vp-p.
The SN ratio of the TSC standard television signal and the MUSE signal is D according to the magnitude of the noise voltage detected as described above.
It is inversely proportional to the C output. Therefore, it is possible to judge whether the reception performance is good or bad by converting this DC output into a value proportional to the SN ratio. By superimposing this DC output on the television signal by the level display means, it is demodulated on the screen. It is possible to display the SN ratio of the video signal.

The relationship between the SN ratio of the demodulated NTSC standard television signal and the MUSE signal and the CN ratio of the received signal is expressed by the following equation.

[0046]

[Equation 1]

The above (Equation 1) is the NTSC standard television of Japan.
Applying the specifications of satellite broadcasting, I _FN= 21 dB, I
_EMP= 2.9 dB, MUSE high-definition TV guard
Applying the specifications of star broadcasting, I_FN= 12.5 dB, I
_EMP= 9.5 dB. According to (Equation 1), the SN ratio and C
Since the N ratio has a proportional relationship, it depends on the direction change of the antenna.
If the antenna gain changes and C changes, the SN ratio changes.
If you display the SN ratio on the TV image,
It can be used for direction adjustment when the antenna is installed.

[0048]

【Example】

(Embodiment 1) First, an embodiment of the first invention will be described with reference to the drawings. FIG. 1 is a satellite television receiver image quality display device showing a first embodiment of the present invention. In FIG. 1, 11 is a 1stIF input terminal for connecting a coaxial cable from a BS converter to input a signal, 12 is a channel selection circuit for selecting a 1-channel signal from a number of channels, 13 is an FM demodulator, and 14 is an FM. A bandpass filter for extracting only noise components from the demodulated output, 15 is an amplifier circuit for amplifying the extracted noise as much as necessary for detection, 1
6 is a noise detection circuit for detecting the magnitude of noise power,
20 diodes, 21 and 22 capacitors, and 2
It is a radiation detection circuit composed of three resistors.

Reference numeral 17 is a sample hold circuit to which the output of the detection circuit is input, 30 is a MUSE decoder, and 31 is FIG.
An amplifier circuit for amplifying a key pulse input from the MUSE decoder to a level capable of driving the sample hold circuit, 32 is a circuit for determining the presence or absence of a key pulse,
It is composed of resistors 33 and 35, a capacitor 34, and a transistor 36. Reference numeral 37 denotes an output terminal of the key pulse determination circuit, which is connected to the noise detection circuit 16 and has a high impedance when there is a key pulse and a low impedance when there is no key pulse. The time constant of the 16 noise detection circuits can be changed.

40 is an NTSC standard television signal processing circuit,
Reference numeral 60 is an on-screen display circuit for superimposing the noise amount detection output signal from the sample hold circuit on the MUSE type video signal and displaying it on the television receiver. 42 is the noise amount detection output signal from the sample hold circuit NTSC type. On-screen display circuit for superimposing on the video signal of the above and displaying on the television receiver, 61 is a MUSE video signal output terminal on which the noise amount detection signal is superposed, 43 is an NTSC video signal output on which the noise amount detection signal is superposed It is a terminal.

The operation of the satellite television receiver image quality display device configured as described above will be described below. First, the received signal input to the 1st IF input terminal 11 of the BS tuner is tuned by the channel selection circuit 12, and the MUSE signal obtained by FM demodulation by the FM demodulation circuit 13 and the NTSC standard television signal are respectively MUSE decoder 30, After the video signal is obtained by the NTSC standard television signal processing circuit 40, information such as channel display and audio signal display is displayed on the on-screen display circuit 6 of the MUSE video signal.
0, NTSC video signal on-screen display circuit 4
After being superimposed on the video signal in 2, the video signal is output from the MUSE video signal output terminal 61 and the NTSC video signal output terminal 43. The circuit operation up to now is included in the functions of an ordinary MUSE high-definition television and an NTSC standard television satellite broadcast receiver.

When the FM demodulated signal is an NTSC standard television signal, its video signal and audio signal are frequency-division multiplexed, and its spectrum is as shown in FIG. 90 is a video luminance component having a frequency band up to 4.5 MHz, 91 is a 3.58 MHz color subcarrier, 92 is a 5.727272 MHz audio subcarrier, and 93, 94 are harmonics of the color subcarrier. On the other hand, M
The spectrum of the USE signal is shown in FIGS.

FIG. 4 shows the spectrum when the frequency of the video signal is high, and FIG. 5 shows the spectrum when the frequency of the video signal is low. As shown in FIGS. 4 and 5, the baseband MUSE signal has a frequency band of the signal up to about 8.1 MHz, and depending on the content of the video signal, it may be 8.1.
It is shown that an unnecessary spectrum appears at frequencies above the video signal band up to MHz. This unnecessary spectrum is generated when the video signal is converted into a signal having a high frequency component, and is considered to be a harmonic component of the video signal. By the way, the MUSE signal is, as shown in FIG. 6, a video signal, an audio signal, a clamp level period which is a period of a key pulse,
Other control signals are sent by time division multiplexing.

Therefore, during the period of the key pulse in which no information is transmitted, no signal component or the above-mentioned unnecessary spectrum appears at a frequency of 8.1 MHz or higher. The satellite television image quality display device of the first invention utilizing the characteristics of the NTSC standard television signal and the MUSE signal operates as follows.

MUS output from the 13 FM demodulation circuit
The E signal or the NTSC standard television signal is input to 14 band pass filters, and noise components are extracted. By the way, the frequency band of the noise component to be extracted can be considered as follows.

At the time of receiving the MUSE signal, the noise power level detected by the 16 noise detection circuit is sampled and held during the key pulse period, during which no information is transmitted by the 17 sample and hold circuit. It suffices for the bandpass filter 14 to be capable of extracting the noise power during the key pulse period. By the way, in the period of this key pulse, since its signal component and its harmonic component do not exist in the frequency domain, the center frequency and bandwidth of this band pass filter can be freely selected. But,
When receiving an NTSC standard television signal, it is necessary to remove only the noise component from the demodulated signal component in the FM demodulated spectrum of FIG. 12, and the demodulation noise component in the FM demodulation output is demodulated as generally known as triangular noise. Since the noise voltage increases as the frequency increases, the higher the pass band of the band pass filter within the guaranteed frequency range of the FM demodulator, the larger the noise voltage. For this reason, it is desirable that the 14 band pass filters have a center frequency of about 8.1 MHz and a bandwidth of about 1 MHz or a center frequency of about 11 MHz and a bandwidth of about 1 MHz.

The noise extracted by the band-pass filter 14 is amplified by the amplifier 15 to a level sufficient for detection by the detection circuit 16 using a diode, and is input to the detection circuit 16 and detected. When the amplifier has no non-linear amplification effect, the detection output sharply increases when the CN ratio of the input signal is changed and the CN ratio deteriorates as shown in FIG. In the case of satellite broadcasting, the FM ratio is used to modulate the video signal, so the CN ratio is about 9 dB.
It is considered that the so-called threshold phenomenon occurs in the following and the noise level of the demodulation output sharply increases. When the detection output as shown in FIG.
The linearity of the display output with respect to the change in the ratio is poor, and the range of the CN ratio that can be displayed is limited. For this reason, it is necessary to devise an amplifier, and the nonlinearity to the CN ratio of the detection output is improved by giving a nonlinear amplification effect to the gain of the amplifier and decreasing the gain when the noise amplitude exceeds a certain value. It looks like 15.

The noise power amplified by the 15 amplifier circuits is 1
6 is input to the noise detection circuit. This noise detection circuit has 2
0 diode, 21 and 22 capacitor, and 23
This is a detection circuit of the radiation line composed of the resistance of. The output terminal of the key pulse determination circuit of 37 is connected to the capacitor of 22. When there is a key pulse, it becomes high impedance, and when there is no key pulse, it becomes low impedance.
The time constants of the 16 noise detection circuits can be changed when the C standard television signal is received and when the MUSE signal is received. NTSC
3 whether standard TV signal reception or MUSE signal reception
This is performed using the key pulse shown in FIG. 3 which is output from the MUSE decoder of 0 when the MUSE signal is received. When no key pulse is input, that is, when an NTSC standard television signal is received, the pass frequency band of the band pass filter for extracting the noise component of 14 is F of 13 as shown above.
The center frequency is set to about 8.1 MHz, the bandwidth is set to about 1 MHz or the center frequency is set to about 11 MHz and the bandwidth is set to about 1 MHz so that only the noise component can be taken out within the guaranteed frequency of the M demodulator. By selecting, the change in the output of the 16 noise detection circuits due to the change in the video signal at the high CN ratio is small. Therefore, when the key pulse is not input, the transistor 36 of the determination circuit of 32 is turned on and the output terminal of 37 becomes low impedance. Therefore, the noise detection circuit of 16 is controlled to increase its time constant and the amplification of 15 is amplified. The noise component that is the output of the circuit is smoothed and the DC component as the magnitude of the noise component is output.

On the other hand, when a key pulse is input, that is, when a MUSE signal is received, no matter what frequency the pass frequency band of the band pass filter of 14 is set within the guaranteed frequency of the FM demodulator of 13, the video signal of N because of harmonics
It is not possible to always extract only the noise component as in the TSC standard television signal. Therefore, of the 16 noise detection circuit outputs, only the noise detection circuit output during the key pulse period during which no signal is transmitted is sampled by the 17 sample hold circuit and held during the other periods. By operating the above, it is possible to equivalently detect the magnitude of only the noise component. Therefore, when a key pulse is input, the transistor 36 of the determination circuit of 32 is turned off and the output terminal of 37 becomes high impedance, so that the noise detection circuit of 16 has its time constant sufficiently smaller than the period of the key pulse. As a result, the 16 noise detection circuits can be controlled sufficiently to respond during the key pulse period of the MUSE signal, and the magnitude of the noise component during the key pulse period can be accurately detected.

The noise detection output signal proportional to the noise power obtained by the noise detection circuit of 16 is input to the sample hold circuit of 17. This sample and hold circuit is 25
Of analog switches, 26 capacitors, and 27 buffer amplifiers. When the NTSC standard television signal is received, the key pulse for turning on / off the analog switch of 25 is not input, so that the sample hold circuit of 17 always operates in the sampling state. On the other hand, at the time of receiving the MUSE signal, the 25 analog switches are turned on / off by the key pulse output from the 31 key pulse amplification circuit, the output of the 16 noise detection circuit is sampled during the key pulse period, and held during the other periods. Controlled.

By detecting the presence or absence of the key pulse in this way, the reception of the NTSC standard television signal and the MUSE signal is detected, and by controlling the noise detection circuit and the sample hold circuit based on the determination, only the NTSC standard television signal is obtained. Without displaying MUSE, the image quality display does not fluctuate due to changes in the video signal. FIG. 8 shows the relationship between the noise detection output voltage and the CN ratio of the output of the sample hold circuit 17 at the time of receiving the MUSE signal. 102 is the noise detection output voltage vs. CN ratio characteristic when the frequency of the video signal is high, and 103 is It is a noise detection output voltage-to-CN ratio characteristic when the frequency of the video signal is low. As shown in FIG. 8, the fluctuation of the noise detection output signal level due to the contents of the video signal in the region where the CN ratio is high is not seen, and the error of the image quality display is eliminated.

As the sampling period of the 17 sample and hold circuits at the time of receiving the MUSE signal, the audio signal,
The same effect can be obtained in the data transmission period.

The noise detection signal output through the sample hold circuit 17 is superimposed on each video signal by the MUSE signal on-screen display circuit of 60 and the NTSC standard television signal on-screen display circuit of 42 and output from the output terminal. When the standard television signal and the MUSE signal are received, the amount corresponding to the CN ratio can be displayed on the television receiver.

(Embodiment 2) Next, an embodiment of the second invention will be described with reference to the drawings. FIG. 2 is a satellite television receiver image quality display device showing a first embodiment of the present invention.

In FIG. 2, 11 is a 1stIF input terminal for connecting a coaxial cable from a BS converter to input a signal, 12 is a channel selection circuit for selecting one channel signal from many channels, 13 is an FM demodulator, 14 is FM
A bandpass filter that extracts only noise components from the demodulation output, 15 is an amplification circuit for amplifying the extracted noise as much as necessary for detection, 16 is a noise detection circuit that detects the magnitude of noise power, and a diode of 20 It is a radiation detection circuit composed of capacitors 21 and 22 and resistors 23.

Reference numeral 17 is a sample and hold circuit which receives the output of the detection circuit, 30 is a MUSE decoder, and 31 is an MU.
An amplification circuit for amplifying the key pulse input from the SE decoder to a level capable of driving the sample hold circuit,
Reference numeral 32 denotes a circuit for determining the presence / absence of a key pulse, which includes resistors 33,
35 and a condenser 34. 40 is N
TSC standard television signal processing circuit, 41 a pulse generation circuit for generating a pulse synchronized with a horizontal synchronizing signal of an NTSC standard television signal, 50 a sampling pulse switching circuit for switching sampling pulses to a sample and hold circuit 17 and 60 and sample and hold An on-screen display circuit for superimposing a noise amount detection output signal from the circuit on a MUSE type video signal and displaying it on a television receiver.
2 is an on-screen display circuit for superimposing the noise amount detection output signal from the sample hold circuit on the NTSC system video signal and displaying it on the television receiver, 61 is a MUSE system video signal output terminal on which the noise amount detection signal is superposed , 43 are NTSC video signal output terminals on which a noise amount detection signal is superimposed.

The operation of the satellite television receiver image quality display device configured as described above will be described below.

First, the received signal input to the 1st IF input terminal 11 of the BS tuner is selected by the tuning circuit 12,
The MUSE signal obtained by FM demodulation in the FM demodulation circuit 13 and the NTSC standard television signal are obtained by the MUSE decoder 30 and the NTSC standard television signal processing circuit 40, respectively, and then information such as channel display and audio signal display is obtained. Is superposed on the video signal in the on-screen display circuit 60 for the MUSE video signal and the on-screen display circuit 42 for the NTSC video signal, and then output from the MUSE video signal output terminal 61 and the NTSC video signal output terminal 43. The circuit operation up to now is a normal MU
It is included in the functions of the SE system high-definition television and the NTSC standard television satellite broadcast receiver.

When the FM demodulated signal is an NTSC standard television signal, its video signal and audio signal are frequency division multiplexed, and its spectrum is as shown in FIG. 90 is a video luminance component having a frequency band up to 4.5 MHz, 91 is a 3.58 MHz color subcarrier, 92 is a 5.727272 MHz audio subcarrier, and 93, 94 are harmonics of the color subcarrier. On the other hand, M
The spectrum of the USE signal is shown in FIGS. FIG. 4 shows the spectrum when the frequency of the video signal is high, and FIG. 5 shows the spectrum when the frequency of the video signal is low. As shown in FIGS. 4 and 5, the baseband MUSE signal has a frequency band of the signal up to about 8.1 MHz, and is unnecessary at a frequency higher than the video signal band up to 8.1 MHz depending on the content of the video signal. It shows that a spectrum appears. This unnecessary spectrum is generated when the video signal is converted into a signal having a high frequency component, and is considered to be a harmonic component of the video signal.

By the way, in the MUSE signal, as shown in FIG. 3, the clamp level period which is the period of the key pulse, NT
In the SC standard television signal, no information is transmitted during the period of the horizontal synchronizing signal, so that the signal components and their harmonics as shown in FIGS. 4, 5 and 12 do not appear. Utilizing this property, the present invention operates as follows.

MUS output from the 13 FM demodulation circuit
The E signal or the NTSC standard television signal is input to 14 band pass filters, and noise components are extracted. By the way, the frequency band of the noise component to be extracted can be considered as follows.

At the time of receiving the MUSE signal, the noise power level detected by the 16 noise detection circuit is sampled and held by the 17 sample and hold circuit during the key pulse period during which no information is transmitted. At the time of receiving the television signal, the pulse output from the pulse generating circuit of 41 is used to sample and hold during the period of the horizontal synchronizing signal period. It suffices if the noise power in the horizontal synchronizing signal period can be extracted. By the way, in the period of the key pulse and the horizontal synchronizing signal, the signal component and the harmonic component thereof do not exist in the frequency domain, so that the center frequency and the bandwidth of the band pass filter can be freely selected.

However, the demodulation noise component in the FM demodulation output generally increases in noise voltage as the demodulation frequency increases, as is generally called triangular noise, so that the pass band of the band pass filter is within the guaranteed frequency range of the FM demodulator. The higher the value is, the larger the noise voltage is obtained.

The noise extracted by the band-pass filter 14 is amplified by the amplifier 15 to a level sufficient for detection by the detection circuit 16 using a diode, and input to the detection circuit 16 for detection. When the amplifier has no non-linear amplification effect, the detection output sharply increases when the CN ratio of the input signal is changed and the CN ratio deteriorates as shown in FIG. In the case of satellite broadcasting, the FM ratio is used to modulate the video signal, so the CN ratio is about 9 dB.
It is considered that the so-called threshold phenomenon occurs in the following and the noise level of the demodulation output sharply increases. When the detection output as shown in FIG.
The linearity of the display output with respect to the change in the ratio is poor, and the range of the CN ratio that can be displayed is limited. For this reason, it is necessary to devise an amplifier, and the nonlinearity to the CN ratio of the detection output is improved by giving a nonlinear amplification effect to the gain of the amplifier and decreasing the gain when the noise amplitude exceeds a certain value. It looks like 15.

The noise power amplified by the amplifier circuit of 15 is 1
6 is input to the noise detection circuit. This noise detection circuit has 2
It is a radiation detection circuit composed of a diode of 0, a capacitor of 21, and a resistance of 23, and detects the magnitude of a noise component. Now, the output of the detection circuit of 16 is 17
In the sample hold circuit, the signal is sampled in the period of the key pulse in which no signal is transmitted and the period of the horizontal synchronizing signal. Therefore, the 16 noise detection circuits can accurately detect the magnitude of noise components in the key pulse period and the horizontal synchronizing signal period by making the time constants sufficiently smaller than the sampling period so that they can respond.
Key pulse duration of MUSE signal is 17usec, NTSC
The horizontal synchronizing signal of the standard television signal is 4.7 usec, and the period of the horizontal synchronizing signal is shorter. Therefore, it is necessary to make the time constant sufficiently small in accordance with the period of the horizontal synchronizing signal of the NTSC standard television signal.

The noise detection output signal proportional to the noise power obtained by the 16 noise detection circuit is input to the 17 sample hold circuit. This sample and hold circuit is 25
Of analog switches, 26 capacitors, and 27 buffer amplifiers. The sampling pulse of the sample hold circuit of 17 is a sampling pulse switching circuit of which the pulse synchronized with the key pulse output from the key pulse amplifying circuit of 31 and the horizontal synchronizing signal of the NTSC standard television signal output from the pulse generating circuit of 41 is 50. In the above, the output of the 32 key pulse presence / absence determination circuit supplies the key pulse when the MUSE signal is received and the pulse output from the 41 pulse generation circuit when the NTSC standard television signal is received.

When the MUSE signal is received, the outputs of the 16 noise detection circuits are sampled during the key pulse period, and the holding operation is performed during the period other than the key pulse period. When the NTSC standard television signal is received, the horizontal synchronizing signal period is received. The outputs of 16 noise detection circuits are sampled and operated so as to be in the hold state during the period other than the horizontal synchronizing signal.

By thus determining the presence or absence of the key pulse, the reception of the NTSC standard television signal and the MUSE signal is detected, and the sampling pulse of the sample and hold circuit is controlled based on the determination, whereby the NTSC
There is no change in the image quality display due to the change in the video signal not only when receiving the standard TV signal but also when receiving MUSE. Figure 8 is MUS
The relationship between the noise detection output voltage and the CN ratio of the output of the sample hold circuit 17 at the time of receiving the E signal is shown.
Reference numeral 2 is a noise detection output voltage-to-CN ratio characteristic when the frequency of the video signal is high, and 103 is a noise detection output voltage-to-CN ratio characteristic when the frequency of the video signal is low. As shown in FIG. 8, the fluctuation of the noise detection output signal level due to the contents of the video signal in the region where the CN ratio is high is not seen, and the error of the image quality display is eliminated.

The sampling period of the 17 sample-hold circuits when receiving the MUSE signal is provided in the audio signal and data transmission period of the MUSE signal, and the sampling period of the 17 sample-hold circuits when receiving the NTSC standard television signal is The same effect can be obtained even if it is provided in the vertical synchronizing signal period of the NTSC standard television signal.

The noise detection signal output through the sample hold circuit 17 is superimposed on each video signal by the MUSE signal on-screen display circuit of 60 and the NTSC standard television signal on-screen display circuit of 42 and output from the output terminal. When the standard television signal and the MUSE signal are received, the amount corresponding to the CN ratio can be displayed on the television receiver.

[0081]

As described above, the present invention is provided with the determination circuit for detecting the presence or absence of the key pulse, and controls the time constant of the noise detection circuit and the sampling pulse of the sample hold circuit when the NTSC standard television signal or the MUSE signal is received. By performing the control described above and displaying the noise detection signal obtained in such a manner as to correspond to the CN ratio, the reception image quality can be displayed when the NTSC standard television signal and the MUSE signal are received.

Further, the present invention is a reception image quality display device using baseband signal processing, which can be easily realized.
There are great practical effects.

[Brief description of drawings]

FIG. 1 is a block diagram of a satellite television receiver image quality display device according to a first embodiment of the present invention.

FIG. 2 is a block diagram of a satellite television receiver image quality display device according to a second embodiment of the present invention.

FIG. 3 is a diagram showing a keyed AFC pulse when receiving a MUSE signal.

FIG. 4 is a spectrum diagram of an FM demodulation output when a MUSE signal having a high video signal frequency is received.

FIG. 5 is a spectrum diagram of an FM demodulation output when a MUSE signal having a high video signal frequency is received.

FIG. 6 is a transmission signal configuration diagram of a MUSE signal.

FIG. 7 is a diagram showing that the relationship between the noise detection output voltage and the CN ratio changes due to a change in the video signal of the MUSE signal in the conventional example.

FIG. 8 is a diagram showing that the relationship between the noise detection output voltage and the CN ratio does not change even when the video signal of the MUSE signal changes when the MUSE signal is received according to the present invention.

FIG. 9 is a spectrum distribution diagram in a period in which image information is not transmitted, including a vertical blanking period of a video signal of a satellite television broadcast signal FM-modulated by an NTSC standard television signal and a period in the vicinity thereof.

FIG. 10 is a block diagram showing an example of a conventional CN ratio measuring device.

FIG. 11 is a block diagram showing an example of a conventional satellite television receiver image quality display device.

FIG. 12 is a spectrum diagram of FM demodulation output when an NTSC standard television signal is received.

FIG. 13 is a noise spectrum diagram in FM demodulation output.

FIG. 14 is a diagram showing a relationship between a noise detection output voltage and a CN ratio when an amplifier having no non-linear amplification effect is used.

FIG. 15 is a diagram showing a relationship between a noise detection output voltage and a CN ratio when an amplifier having a non-linear amplification action is used.

FIG. 16 is a conceptual diagram of a satellite television broadcast receiver image quality device.

[Explanation of symbols]

11 1stIF signal input terminal from BS converter 12 Channel selection circuit for selecting 1 channel signal from a large number of channels 13 FM demodulator 14 Bandpass filter 15 for extracting noise components 15 Amplifier circuit 16 Detection circuit 17 Sample and hold circuit 30 MUSE decoder 31 Key pulse amplification circuit 32 Key pulse presence / absence judgment circuit 37 Key pulse judgment circuit output terminal 60 MUSE system signal on-screen display circuit 40 NTSC standard TV signal video signal processing circuit 41 NTSC standard TV signal receiving sampling pulse generation circuit 42 NTSC standard TV signal On-screen display circuit 61 MUSE high-definition TV video signal output terminal 43 NTSC standard TV signal video signal output terminal

Claims (2)

[Claims] 1. An FM demodulator for demodulating a satellite television signal,
A bandpass filter for extracting a noise component from an NTSC standard television signal or a MUSE baseband signal obtained by demodulating by the FM demodulator, an amplifier for amplifying the noise component, and a time constant for switching an output of the amplifier as an input. A detection circuit having a control terminal for detecting the magnitude of a noise component, a sample hold circuit for holding the output of the noise detection circuit by a key pulse, a determination circuit for integrating the key pulse to determine the presence or absence of a key pulse, The output of the sample-hold circuit is used as an input, and a level display means that indicates the quality of the received image by the drive circuit corresponding to the output level of the sample-hold circuit is provided, and the output of the determination circuit is connected to the control terminal of the noise detection circuit. , The noise detection circuit when receiving NTSC standard TV signals without key pulse input The time constant of the noise detection circuit is set to a value larger than that of the key pulse during the reception of the MUSE signal to which the key pulse is input, while the sample hold circuit is always in the sampling state while detecting the magnitude of the noise power. Make MUS smaller
In addition to detecting the magnitude of the noise component during the clamp level period of the E signal, the sample hold circuit samples the output signal of the noise detection circuit only during the key pulse period, and holds it outside the key pulse period. Satellite TV receiver Image quality display device. 2. An FM demodulator for demodulating a satellite television signal,
A bandpass filter for extracting a noise component from an NTSC standard television signal or a MUSE baseband signal obtained by demodulating by the FM demodulator, an amplifier for amplifying the noise component, and a magnitude of the noise component with the output of the amplifier as an input. A detection circuit for detecting a signal and an output signal of the FM demodulator as an input, and when receiving an NTSC standard television signal, an NTSC signal is received.
A pulse generation circuit for generating a pulse synchronized with a horizontal synchronizing signal of a standard television signal, a sample hold circuit for holding the output of the noise detection circuit by a pulse or a key pulse from the pulse generation circuit, and a key pulse by integrating the key pulse. Of a sampling pulse switching circuit that switches the sampling pulse of the sample-hold circuit according to the output signal of the determination circuit, and the output of the sample-hold circuit as an input corresponding to the output level of the sample-hold circuit. A driving circuit for displaying the level of the received image quality, and when an NTSC standard television signal without a key pulse input is received, the output signal of the judgment circuit is used to output the output of the pulse generation circuit as a sampling pulse of the sample hold circuit. The output signal of the noise detection circuit is sampled in synchronism with the horizontal sync period of the NTSC standard television signal, and is put in the hold state outside the horizontal sync period, while the MUSE signal receiving the key pulse is received, the output of the judgment circuit is output. According to a signal, a key pulse is used as a sampling pulse of the sample and hold circuit, an output signal of the noise detection circuit is sampled only during a key pulse period, and a hold state is set outside the key pulse period. .