JP3100994B2 - Receiving level display circuit in satellite broadcasting receiver - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[Object of the Invention]

[0002]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reception level display circuit for a satellite broadcast receiver having a function of receiving a signal transmitted from a broadcasting satellite and displaying the reception level.

[0003]

2. Description of the Related Art In a satellite broadcast (hereinafter abbreviated as a BS broadcast), an image service is provided using an FM-modulated signal. When receiving this BS broadcast, the receiving condition is greatly affected by the orientation of the receiving antenna such as a parabola.
It must be controlled so that the receiving antenna is always correctly pointed at the broadcasting satellite. Therefore, a BS broadcast receiver generally has a function of displaying the reception level of a received signal. As a method of displaying the reception level,
For example, a method of displaying a reception level using a noise level of a channel on which broadcasting is performed with respect to a noise level of a channel on which broadcasting is not performed as a reference level, or an AGC (automatic transmission control) of a BS tuner. Gain control) There is a method of displaying the reception level based on the output signal of the circuit.

FIG. 3 is a system diagram for explaining a method of displaying the two reception levels in a satellite broadcast receiver.
A 12 GHz band BS signal transmitted from a broadcasting satellite is received by a receiving antenna 1 which is, for example, a parabolic antenna, and is transmitted to a 1G band by a BS converter 2 (outdoor unit).
And converted into a first intermediate frequency signal (hereinafter, referred to as a BS-IF signal).
Supplied to The BS-IF signal is amplified by the high-frequency amplifier circuit 3a and then mixed with a local oscillation signal from a local oscillator 3b to which a tuning control signal of an external input circuit (not shown) is supplied by a mixer 3c. (2) A PLL (Ph) composed of a phase comparator (not shown), a voltage controlled oscillator, a low-pass filter, etc.
case Locked Loop) -FM detection circuit 3d
Supplied to

The second intermediate frequency signal is FM-demodulated and restored to a baseband signal by the PLL-FM detection circuit 3d.
Based on the output signal of the PLL-FM detection circuit 3d, the output of the second converter 3 of the tuner is kept constant.
An AGC output signal for adjusting the gain of the signal received by the receiving antenna 1 is supplied to the high frequency amplifier circuit 3a. Here, the AGC output signal is substantially proportional to the level of the input signal, that is, the level of the BS-IF signal.
After the GC output signal is converted into a digital signal by the A / D converter 4, the signal is supplied to a display circuit (not shown), and the display circuit displays the reception level of the input signal based on the signal. However, when the level of the input signal is low,
Since the second converter 3 operates in the maximum gain state up to the region where AGC is applied, the AGC output signal does not change. Therefore, the display of the reception level of the display circuit becomes constant and does not change.

The above-mentioned baseband signal is supplied to a QDPSK demodulation block 6 via a buffer (buffer) 5, and the QDPSK demodulation block 6 is subjected to four-phase DPSK (four-phase differential phase modulation) from the baseband signal. The audio subcarrier signal is separated and demodulated and supplied to an audio processing system including a PCM decoder (not shown). Further, the baseband signal is also supplied via a buffer 5 to an energy dispersal removal block 7, which removes the energy spread signal from the baseband signal to reproduce a video signal, and performs de-emphasis at the next stage. The circuit 8 restores the emphasized high-frequency component of the video signal and supplies it to a video processing system including a Y / C separation circuit (not shown).

As means for determining the reception level, in addition to the means for determining based on the level of the AGC output signal, the noise level when the broadcast is actually received is determined based on the noise level of the channel on which the broadcast is not performed. It is also conceivable to carry out based on the level ratio. In particular,
Since the BS broadcast signal is FM-modulated, it is possible in principle to use the C / N ratio (C: carrier signal level, N: noise signal level), but the carrier signal and the noise signal have the same frequency. In practice, it is difficult to determine the reception level from the C / N ratio because the signal is high and the modulation is applied. Therefore, it is preferable to obtain the noise level ratio from the baseband signal demodulated by the second converter 3. .

In FIG. 3, the baseband signal is passed through a buffer 9 to a narrow band-pass filter BPF1.
0, where a high-frequency component of the baseband signal, for example, a signal of 10.7 MHz (noise detection frequency) is extracted and amplified by the amplifier 11 and then supplied to the noise detection circuit 12 to be supplied with the noise signal. RMS detection is performed. Then, the detected signal is supplied to the A / D converter 1 in the next stage.
After being converted into a digital signal in step 3, the signal is supplied to a display circuit (not shown), and based on this signal, the reception level of the input signal is displayed by the following method.

The BS supplied to the second converter 3
The level of the IF signal varies significantly depending on the direction of the receiving antenna and the length of the connection cable. Therefore, the noise level of a channel that does not change according to the direction of the receiving antenna and the length of the connection cable and is not broadcast is set to the reference level. The ratio between the reference level and the noise level of the channel on which broadcasting is being performed is considered to change almost in the same manner as the change in the C / N ratio of the BS broadcast signal because the noise level changes according to the reception state. This ratio can be used as an indication of the reception level of the input radio wave.

However, in this method, when the level of the received input signal is low, the above ratio is equal to the BS-IF.
Although it is proportional to the signal, when the input signal level increases, the output of the second converter 3 becomes an output to which AGC is applied, and due to the influence of noise inherent in the second converter 3,
The reception level display becomes constant and does not change. In addition, since the noise detection frequency is set to 10.7 MHz as described above, the reception level of the input signal is indicated by the level of the color subcarrier signal under the influence of a harmonic three times higher than the color subcarrier signal 3.58 MHz. The displayed value changes.

As described above, when the input level of the BS broadcast signal is displayed, the noise level of the channel on which broadcasting is not performed is defined as the noise level of the channel on which broadcasting is not performed. In the method using, the reception level display becomes constant and does not change when the input level of the input signal becomes high. On the other hand, in the method using the AGC output signal of the second converter, the reception level is low when the input level of the input signal is low. There is a disadvantage that the level display is constant and does not change.

[0012]

As described above, the reception level display circuit of the conventional satellite broadcast receiver broadcasts data with respect to the reference level based on the noise level of the channel on which the broadcast is not performed. In the method using the noise level ratio of the input channel, when the input level of the input signal is high, while in the method using the AGC output signal, when the input level of the input signal is low, the input signal is low. Has a disadvantage that the reception level display becomes constant and does not change and cannot be used as a reception level display circuit. The present invention has been made to solve such a conventional problem. The input level of an input signal can be displayed over a wide range from a small signal to a large signal, and the reception level of the input signal can be displayed. An object of the present invention is to provide a reception level display circuit in a satellite broadcast receiver that can accurately indicate a reception level without being affected by other signal components such as a subcarrier signal.

[Structure of the Invention]

[0014]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention provides a high-frequency amplifier circuit which converts the frequency of an input radio wave received from a satellite from a satellite by an outdoor converter. And a second converter including an AGC circuit for controlling a gain. The reception level display circuit in the satellite broadcast receiver converts the signal to an intermediate frequency, demodulates the signal, and outputs a baseband signal. Extracting means for extracting a noise signal from an output signal of the extracting means, a detection signal from the noise detecting means at the time of receiving a channel on which satellite broadcasting is not performed, and satellite broadcasting. A first display indicating a reception level of the input radio wave based on a ratio with a detection signal from the noise detection means at the time of reception of the channel. Together to create the over data, the AGC
A display data generating means for generating second display data indicating a reception level of the input radio wave based on an AGC output signal level of the circuit; and selecting the first display data when the AGC output signal level is within a predetermined value. And selecting means for selecting the second display data when the AGC output signal level exceeds a predetermined value, and display means for displaying a reception level of the input radio wave based on the display data output from the selection means. It is provided.

[0015]

A channel on which satellite broadcasting is not performed is selected, a signal of a predetermined frequency is extracted from the baseband signal by the extracting means, and the signal is subjected to noise detection by the noise detecting means. Then, the detected signal is supplied to the display data generating means as a noise level. Similarly, a channel on which satellite broadcasting is performed is selected, and its noise level is supplied to the display data generating means, so that the noise level of the channel on which satellite broadcasting is not performed and the noise level of the channel on which satellite broadcasting is performed are performed. First display data is created by obtaining a ratio with the noise level. At the same time, the AG from the AGC circuit
The second display data is created from the C output signal, and the first display data is selected by the selecting means when the AGC output signal level is within the set value, while when the AGC output signal level exceeds the set value, the first display data is selected. Select the second display data. Then, based on these display data, the display means displays the reception level of the input radio wave.

[0016]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a system diagram showing one embodiment of a reception level display circuit in a satellite broadcast receiver according to the present invention. As a conventional reception level display method, a reception level is displayed by using a noise level of a channel on which broadcasting is not performed as a reference level and a noise level of a channel on which broadcasting is performed with respect to the reference level ( The first
FIG. 3 shows a method of displaying a reception level based on an output signal of an AGC circuit of a BS tuner (hereinafter, referred to as a second method). It was explained in. This embodiment is a combination of the first and second methods. In the system diagram shown in FIG.
The output signals of the noise detection circuit 12 and the PLL-FM detection circuit 3d are supplied to A / D conversion input ports 14a and 14b of the control microcomputer 14, respectively, and the output signals of the control microcomputer 14 are supplied to a display circuit (not shown). The points are different.

Here, the control microcomputer 14 creates display data of the reception level based on the output signals of the noise detection circuit 12 and the PLL-FM detection circuit 3d, as well as the AGC output stored in a RAM (not shown) in advance. The display method of the reception level is switched from the first method to the second method based on the set value of the signal level. The control microcomputer 14 reads out tuning data from a RAM by a channel selection signal supplied from an external input circuit such as a remote controller (not shown), and controls the tuning circuit including the local oscillator 3b and the mixer 3c based on the data. Supply signal. Further, as described above, the detection frequency of the noise signal detected by the noise detection circuit 12 has been selected to be 10.7 MHz by the narrow-band band-pass filter BPF10 in the related art. The detection wave frequency is selected to be 9 MHz.

Assuming that the demodulation band of the second converter 3 is ideally 27 MHz, the baseband output is 1 MHz.
It will output up to 3.5 MHz. The color subcarrier frequency of the video signal is 3.58.
MHz, the frequency of the second harmonic is 7.
The frequency of 16 MHz and the third harmonic is 10.74 MHz. Then, in the case of the MUSE system in Hi-Vision, baseband output is performed up to 8.1 MHz. Therefore, in order to prevent the influence of other signal components in the baseband signal on the noise signal as described above, it is necessary to select a noise detection frequency between 8.1 MHz and 10.74 MHz. In this embodiment, 9 MHz is selected as the noise detection frequency. The configuration other than the above is the same as that of the above-described conventional example. Corresponding elements and portions are denoted by the same reference numerals, and description thereof will be omitted.

Next, the operation of the above embodiment will be described with reference to the flowchart shown in FIG. First, a non-broadcasting channel is selected from currently receiving broadcasting channels (step S1). Specifically, a signal for selecting a channel on which broadcasting is not performed by an external input circuit such as a remote controller (not shown) is transmitted to the control microcomputer 1.
4 The control microcomputer 14 reads out tuning data corresponding to the signal from the RAM, and sends a tuning control signal based on the data to the local oscillator 3b and the mixer 3c.
To select a channel on which broadcasting is not performed. Subsequently, a 9-MHz frequency component is extracted by a narrow-band band-pass filter 10 from a signal of a channel on which broadcasting is not performed, which is output from the second converter 3, and the signal is subjected to noise detection by a noise detection circuit 12, The effective value of the signal is supplied to the A / D conversion input port 14b, converted into a digital signal, and read into the RAM as a noise level (step S2).

Then, by the same operation as described above, the channel is re-selected from the non-broadcasting channel to the broadcasting channel again (step S3), and the baseband signal output from the second converter 3 is re-selected. The 9 MHz frequency component is subjected to noise detection by the noise detection circuit 12, and its effective value is supplied to the A / D conversion input port 14b, converted into a digital signal, and read into the RAM as a noise level (step S4). Further, an AGC output signal for adjusting the gain (gain) of the signal received by the receiving antenna 1 based on the output signal of the PLL-FM detection circuit 3d is supplied to the A / D conversion input port 14a and converted into a digital signal. Then, it is read into the RAM as the AGC output signal level (step S5). Next, it is determined whether or not the AGC output signal level exceeds a set value previously stored in the RAM (step S6). When the answer is NO, that is, when the AGC output signal level is within the set value, the noise level of the non-broadcast channel obtained in step S2 and the noise level obtained in step S4 are stored in the RAM. The ratio between the two is determined from the noise level of the broadcasted channel and display data is created from the ratio (step S7). Then, the display data is supplied to a display circuit (not shown), and the display circuit displays the reception level of the input radio wave of the channel on which the broadcast is being performed based on the display data (step S9).

On the other hand, if the answer to step S6 is YES, that is, if the AGC output signal level exceeds the set value, the input signal level becomes high and the output of the second converter 3 becomes AGC output.
, And the influence of the noise inherent to the second converter 3, the reception level display by the first method becomes constant and does not change. Therefore, sensitivity correction data is created based on the AGC output signal. (Step S
8) The sensitivity correction data is added to the reception level display data obtained by the first method to correct the display data (step S7). Then, the corrected display data is supplied to a display circuit, and the display circuit displays the reception level of the input radio wave of the channel on which the broadcast is being performed based on the corrected display data (step S9).

As described above, according to this embodiment, when the input signal level is low, the noise detection frequency is set to 9M.
Hz, the first method is based on the ratio of the noise level of the broadcasting channel to the noise level of the non-broadcasting channel without being affected by signal components such as the color subcarrier signal. Displays the reception level of the input radio wave. When the input signal level increases, the second
Switching to the second method of displaying the reception level of the input radio wave based on the AGC output signal of converter 3 and displaying the reception level. Therefore, the reception level of the input radio wave of good quality can be displayed without being affected by other signal components such as the chrominance subcarrier signal, from the input level of the BS broadcast signal to the small signal to the large signal. In this embodiment, the case where the reception level display circuit according to the present invention is applied to a satellite broadcast receiver has been described, but it goes without saying that this reception level display circuit can be applied to a communication satellite receiver.

[0023]

As described above in detail, according to the present invention, as a method of displaying the reception level of the input signal, the noise level of the channel not broadcasting and the noise level of the channel broadcasting are performed. A method based on the ratio of
The method based on the output signal of the AGC circuit of the BS tuner is switched by the selection means based on the output signal level of the AGC circuit, so that the input level of the input signal can be changed over a wide range from a small signal to a large signal. There is an excellent effect that the reception level of a high-quality input radio wave can be displayed without being affected by other signal components such as a subcarrier signal.

[Brief description of the drawings]

FIG. 1 is a system diagram showing one embodiment of a reception level display circuit in a satellite broadcast receiver according to the present invention.

FIG. 2 is a flowchart illustrating the operation of a reception level display circuit in the satellite broadcast receiver of FIG. 1;

FIG. 3 is a system diagram of a satellite broadcast receiver illustrating two conventional reception level display methods.

[Description of Signs] 3 ... second converter, 3d ... PLL-FM detection circuit, 10 ... band-pass filter, 12 ... noise detection circuit, 14 ... control microcomputer.

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Noriyuki Miyazaki 3-3-9 Shimbashi, Minato-ku, Tokyo Toshiba Audio Video Engineering Co., Ltd. (56) References JP-A-62-29223 (JP, A) JP-A-1-317727 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H04B 1/16 H04B 17/00 G01S 3/38

Claims (1)

(57) [Claims] 1. A high-frequency amplifier circuit for converting the frequency of an input radio wave received from a satellite received by a receiving antenna by an outdoor converter, and an AGC for controlling the gain of the high-frequency amplifier circuit
Extracting means for extracting a signal of a predetermined frequency from the baseband signal in a reception level display circuit in a satellite broadcast receiver which converts the signal to an intermediate frequency with a second converter including a circuit and demodulates the signal to output a baseband signal. When,
A noise detection unit that detects a noise signal from an output signal of the extraction unit; a detection signal from the noise detection unit when receiving a channel on which satellite broadcasting is not performed; First display data indicating the reception level of the input radio wave is created based on the ratio of the detection signal from the noise detection means to the detection signal.
Display data generating means for generating second display data indicating the reception level of the input radio wave based on the AGC output signal level of the C circuit; and, when the AGC output signal level is within a predetermined value, the first display data. Selection means for selecting the second display data when the AGC output signal level exceeds a predetermined value; and display means for displaying the reception level of the input radio wave based on the display data output from the selection means. A reception level display circuit in a satellite broadcast receiver, comprising: