JPH11234355A - Satellite broadcasting receiver - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a satellite broadcasting receiver capable of easily and accurately receiving the signals of a desired transmission rate. SOLUTION: Fixed type low-pass filters 23 and 25 for noise elimination are provided between an I/Q demodulator 9 and an A/D converter 10. Also, switching circuits 21 and 22 for switching the state of transmitting I/Q demodulation output through the low-pass filters 23 and 25 to the A/D converter 10 and the state of transmitting it to the A/D converter 10 by through circuits 24 and 25 without passing it through the low-pass filters 23 and 25 are provided.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a satellite broadcast receiving apparatus such as a satellite broadcast receiving tuner.

[0002]

2. Description of the Related Art At present, digital satellite broadcasting has begun to be broadcast at various transmission rates around the world. For example, in Japan, 20 to 30 Msps (symbol per sec.
Broadcasting at the symbol rate of ond) was the mainstream, but broadcasting at a low transmission rate such as 1 to 6 Msps has recently started. The low transmission rate in this area is also adopted for communication within a company.

FIG. 18 shows a configuration of a conventional satellite broadcast receiving tuner. In the figure, 1 is an input terminal,
2 is an RF circuit for performing RF amplification, 3 is an attenuator for stabilizing the gain of the received signal, 4 is a tracking or image filter for removing the influence of signals on adjacent channels and the like, 5 is a received RF signal and a local signal. A mixer for mixing the oscillation signals and outputting an IF signal having a frequency difference therebetween, a local oscillation circuit section 6, and a PLL circuit 7 for controlling the local oscillation frequency.

[0004] Reference numeral 8 denotes an IF band-pass filter for passing an IF signal output from the mixer 5;
A W (surface acoustic wave) filter is used. Reference numeral 9 denotes an I / Q demodulator for demodulating an I signal and a Q signal from the IF signal, and the output is transmitted to a QPSK demodulator 11 through an A / D converter 10.

In this conventional satellite broadcast tuner (first conventional example), a SAW filter of an IF band-pass filter having a bandwidth matching a signal having a high transmission rate is used, and a signal having a high transmission rate is also used. Low signals were also received without discrimination (ie, without making circuit changes).

In the second conventional example, two SAW filters having different bandwidths are prepared as SAW filters.
They were switched and used. Further, in the third conventional example, a tuner for receiving a high transmission rate signal and a tuner for receiving a low transmission rate signal are prepared. FIG. 19 shows the characteristics of the SAW filter.
A SAW filter for receiving an Msps modulated signal (that is, a bandwidth of about 30 MHz), and (b) is a SAW filter for receiving a 20 Msps modulated signal (that is, a bandwidth of about 20 MHz).
Filter.

[0007]

However, in the first conventional example, it is good to receive a signal with a high transmission rate, but it is possible to cut noise in an unnecessary band when receiving a signal with a low transmission rate. As a result, the output signal of the filter becomes a very noisy signal.

In the second conventional example and the third conventional example,
There is a restriction on the type of SAW filter, and it is difficult to obtain a filter that matches a desired band, and it is not possible to continuously or multi-steply change the signal, so that a desired signal cannot be received. In addition, there is a problem that the cost is high.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and has as its object to provide a satellite broadcast receiving apparatus capable of easily and accurately receiving a signal having a desired transmission rate.

[0010]

According to the first aspect of the present invention, a fixed low-pass filter for removing noise is provided between an I / Q demodulator and an A / D converter. Switching means for switching between a state in which the I / Q demodulated output is transmitted to the A / D converter through the low-pass filter and a state in which the I / Q demodulated output is transmitted to the A / D converter without passing through the low-pass filter is provided. I do.

According to such a configuration, when a low transmission rate signal is received, an unnecessary noise can be attenuated by operating the low-pass filter. On the other hand, when a high transmission rate signal is received, the high transmission rate signal can be passed by disabling the low pass filter and passing the signal through.

Further, according to the present invention, a variable low-pass filter for removing noise is provided between the I / Q demodulator and the A / D converter so that an arbitrary transmission rate signal can be received. Features. According to this configuration, the low transmission rate signal and the high transmission rate signal can be properly received only by changing the band characteristic of the low-pass filter.

[0013] The invention according to claim 3 is characterized in that a band-pass filter capable of changing a pass band of an intermediate frequency signal including an I signal and a Q signal by a control signal is provided. In this configuration, for example, when a variable capacitance diode is provided as a component of the filter, the pass characteristic of the filter is varied by varying the DC voltage applied to the variable capacitance diode.

According to a fourth aspect of the present invention, in the satellite broadcast receiving apparatus according to any one of the first to third aspects, the filter is switched or changed by an open collector port of an IC having an IIC bus built in a tuner. It is characterized in that it is performed using output. In this configuration, since "1" and "0" can be selectively latched in the open collector port, the output can be used to selectively set the filter to two bands. When the outputs of a plurality of open collector ports are used, the number of bands that can be switched can be increased because the switching data has a plurality of bits.

According to a fifth aspect of the present invention, in the satellite broadcast receiving apparatus according to the first or second aspect, a fifth-order or higher-order filter is used as the low-pass filter. By using a high-order low-pass filter like this,
Cut-off characteristics become steep.

[0016]

FIG. 1 shows a first embodiment of the present invention. In the figure, the same parts as those of the conventional example shown in FIG. Here, the IF bandpass filter 8 has a fixed characteristic S
An AW filter (other band pass filter may be used), and its characteristic is, for example, 30 Mps as shown in FIG.
p band.

In this embodiment, the I / Q demodulator 9 and the A / D
A low-pass filter, a through circuit, and a circuit for switching between the low-pass filter and the through circuit are provided in both the I and Q signal paths between the converter 10 and the converter 10. That is, the I signal path includes a low-pass filter 23, a through circuit 24, and a switching circuit 21, and the Q signal path includes a low-pass filter 25, a through circuit 26, and a switching circuit 22. The low-pass filters 23 and 25 have the characteristic (low band) shown in FIG. On the other hand, the through circuits 24 and 26 pass the I and Q signals as they are, and their pass bands are as shown in FIG.

FIG. 8 shows a specific configuration of the low-pass filter 23. The low-pass filter 25 has the same configuration. Input terminal 70 receives an I signal from an I signal terminal of I / Q demodulator 9. 71 and 76 are coupling capacitors. The output terminal 77 is connected to the input terminal of the A / D converter 10. The low-pass filter 23 includes an inductance coil 82 and capacitors 80 and 81. This is a third-order low-pass filter. Reference numerals 72 to 75 denote switching diodes forming the switching circuit 21, which are turned on / off by a control voltage (switching voltage) input to a terminal 78. A power supply terminal 79 receives the power supply voltage Vcc. 83, 84 and 85 are DC cut capacitors.

When a high-level voltage is applied to the terminal 78, the diodes 72 and 74 are turned on, and the diodes 73 and 75 are turned off.
Then, the low-pass filter 23 operates and the through circuit 24 does not operate. Conversely, when a low level voltage is input to the terminal 78, the diodes 73 and 75 are turned on,
74 turns OFF, the low-pass filter does not operate, and the through circuit 24 operates. Low-pass filter 23
Instead of the fifth-order elliptic filter 90 shown in FIG.
Is preferable because the fall becomes a steep characteristic like α to β in FIG. Further, it may be of a higher order. In FIG. 12, the horizontal axis represents frequency f and the vertical axis represents gain.

Next, FIG. 3 shows a second embodiment of the present invention. In the figure, the same parts as those in the first embodiment of FIG. 1 are denoted by the same reference numerals. In the second embodiment, the low-pass filters 31 and 32 are continuously variable. Thereby, as shown in FIG.
A plurality of bands can be realized as shown by d. FIG. 10 shows a configuration example of these low-pass filters for the low-pass filter 31.
Shown in

In FIG. 10, reference numeral 60 denotes an input terminal.
69 is an output terminal. 61 and 68 are coupling capacitors, 65 is a control voltage input terminal, 66 is a bypass capacitor, and 67 is a resistor. Low-pass filter 3
1 is an inductance coil 62 and a variable capacitance diode 6
3, 64. The capacitance value of the variable capacitance diodes 63 and 64 changes according to the value of the DC voltage input to the terminal 65, and thereby the cutoff frequency of the low-pass filter 31 changes.

In the second embodiment (FIG. 3), the switching circuits 21 and 22 and the through circuit 24 as in the first embodiment are used.
Since 26 is unnecessary, the circuit configuration is simplified. In addition, the characteristics can be changed to a plurality of characteristics as shown in FIG. Further, since the band can be continuously varied, signals of any transmission rate can be received.

FIG. 5 shows a third embodiment. This embodiment is substantially the same as the embodiment of FIG. 1 except that the switching voltages of the switching circuits 21 and 22 (terminal 78 in FIG.
To the PLL circuit 7 (integrated circuit)
It is characterized by the point obtained from. The circuit shown in FIG.
In the embodiment, the switching voltage is controlled by an operation switch 96 by providing a circuit as shown in FIG. 14 externally and connecting its output terminal 95 to a terminal 78 in FIG.

That is, when the switch 96 is turned on, a high-level voltage is applied from the terminal 95 to the terminal 78, the low-pass filters 23 and 25 are activated, and the switch 9 is turned on.
When the terminal 6 is turned off, the low level voltage is changed from the terminal 95 to the terminal 7.
8, the through circuits 24 and 26 are activated instead of the low-pass filters 23 and 25.

However, in FIG. 5 (third embodiment), a switching voltage is obtained from an IC having an existing PLL circuit 7 without adding an external circuit. This IC 200 is shown in FIG. The IC 200 is an IC having an IIC bus line 210, and this bus line 210 is connected to an external microcomputer 218 via a terminal 208 (the part between the terminal 208 and the computer 218 is also an IIC bus line). On the other hand, the microcomputer 218 receives a command from the tuning operation unit 219.

The output of the local oscillation circuit 6 (see FIG. 1) constituted by a VCO (voltage controlled oscillator) is input from a terminal 201 to a phase comparator 203. On the other hand, this phase comparator 20
Reference numeral 3 designates a reference oscillation signal from the reference voltage oscillator 205, which is frequency-divided by the frequency divider 207 into N. The comparison output is output from the terminal 202 through the low-pass filter 204 and supplied to the local oscillation circuit 6 as a control voltage.

Reference numeral 206 denotes a crystal oscillator. The microcomputer 218 outputs frequency-divided data according to a channel-selection command from the channel-selection operation unit 219, and outputs the frequency-divided data through the IIC bus.
07. Since this frequency-divided data is latched on the IC 200 side, the IIC bus becomes empty after the latch. In this empty state, other data is sent from the microcomputer 218 to the IC and the open collector port 211 is sent.
To 214 can be set to either "1" or "0". 214 to 217 are terminals corresponding to the ports 211 to 214.

A circuit 209 receives data from the microcomputer and controls and sets the ports 211 to 214. Therefore, the switching circuits 21 and 22 can be controlled using any one of these ports 211 to 214. That is, in the third embodiment of FIG. 5, the low-pass filters 23 and 25 are switched using a circuit (hardware) provided in a satellite broadcast tuner.
Specifically, the switching is handled by a microcomputer program (software).

Next, in the fourth embodiment shown in FIG.
The bandpass filter 8 is made variable. In this case, for example, a bandpass filter 8 as shown in FIG. 11 is used without using a SAW filter. This filter comprises a capacitor 106 and inductance coils 102, 10
4 and variable capacitance diodes 103 and 105.

100 is an input terminal, 108 is an output terminal, 1
01 and 107 are coupling capacitors, 110 is a bypass capacitor, and 109 is a control terminal for inputting a control voltage. Coil 102 and variable capacitance diode 1
The resonance characteristic 03 is a characteristic as shown by a dotted line A in FIG. 13, and the resonance characteristic of the coil 104 and the variable capacitance diode 105 is a characteristic as shown by a dotted line B in FIG. Become. This C is the pass characteristic of the band pass filter 8.

By varying the voltage input to the terminal 109, the bandpass characteristic can be continuously varied.
Each characteristic can be set as shown in FIG.
In the fourth embodiment, since various characteristics can be formed unlike a conventional SAW filter, a signal having a desired transmission rate can be appropriately received with a simple configuration.

When continuously varying the low-pass filter of FIG. 3 (FIG. 10) or continuously varying the band-pass filter of FIG. 6 (FIG. 11), the volume 97 as shown in FIG.
Can be realized by connecting to the outside, but in the case of switching according to the receiving channel, multi-stage switching can be realized by externally connecting a circuit as shown in FIG.
In these circuits, + B indicates a DC power supply.

In FIG. 16, VR1 to VR4 are variable resistors, S1 to S4 are switches for switching the outputs of the variable resistors VR1 to VR4, and 300 is an output terminal. The switching of the switches is performed by the decoder 301 decoding the tuning data from the microcomputer 302 output in response to the tuning operation of the tuning operation unit 303, and turning on only the switch corresponding to the tuning among the switches S1 to S4. It is done by doing. Also, the decoders 301, 302,
Ports 211 and 2 in FIG.
It is also possible to switch the switches S1 to S4 using the 14 data.

[0034]

As described above, according to the present invention, for example, in a satellite broadcast tuner, a signal having a normal transmission rate (high transmission rate in this case) of a signal of 20 to 30 Msps and a signal having a low transmission rate of 1 to 6 Mspsp are used. The signal can be received by a tuner of one package, so that there is no need to use different dedicated tuners as in the related art, which is advantageous in that it is convenient and inexpensive.

[Brief description of the drawings]

FIG. 1 is a block circuit diagram of a satellite broadcast tuner according to a first embodiment of the present invention.

FIG. 2 is a diagram showing pass band characteristics of the low-pass filter.

FIG. 3 is a block circuit diagram of a satellite broadcast tuner according to a second embodiment of the present invention.

FIG. 4 is a diagram showing pass band characteristics of the low-pass filter.

FIG. 5 is a block circuit diagram of a satellite broadcast tuner according to a third embodiment of the present invention.

FIG. 6 is a block circuit diagram of a satellite broadcast tuner according to a fourth embodiment of the present invention.

FIG. 7 is a diagram showing band characteristics of the band-pass filter.

FIG. 8 is a configuration diagram of a low-pass filter used in the tuners according to the first and third embodiments.

FIG. 9 is a configuration diagram of a fifth-order elliptic filter that can be used in a tuner according to the first embodiment or the third embodiment;

FIG. 10 is a configuration diagram of a low-pass filter used in the tuner of the second embodiment.

FIG. 11 is a configuration diagram of an IF bandpass filter used in the tuner of the fourth embodiment.

FIG. 12 is a diagram showing a difference in characteristics between a third-order low-pass filter and a fifth-order elliptic filter.

FIG. 13 is a characteristic diagram of an IF bandpass filter.

FIG. 14 is a configuration diagram of a circuit that supplies a switching voltage for switching a low-pass filter of a tuner according to the first embodiment or the third embodiment;

FIG. 15 is a configuration diagram of a circuit that supplies a voltage for continuously switching a filter characteristic of a tuner according to the second embodiment or the fourth embodiment;

FIG. 16 is a configuration diagram of a circuit that supplies a voltage for switching a filter characteristic of a tuner in a stepwise manner in the second embodiment, the fourth embodiment, or the like.

FIG. 17 is a block circuit diagram of an integrated circuit device having an IIC bus including a PLL circuit;

FIG. 18 is a block circuit diagram of a conventional satellite broadcast tuner.

FIG. 19 is a characteristic diagram of a SAW filter used therein.

[Explanation of symbols]

 Reference Signs List 8 IF band pass filter 9 I / Q demodulator 10 A / D converter 23, 25 Low pass filter 31, 32 Variable low pass filter 200 IIC bus IC 211-214 port

Claims (5)

[Claims] A fixed low-pass filter for removing noise is provided between an I / Q demodulator and an A / D converter, and an I / Q demodulated output is transmitted to the A / D converter through the low-pass filter. A satellite broadcast receiving apparatus provided with switching means for switching between a state and a state of transmitting to the A / D converter through without passing through the low-pass filter. 2. A satellite broadcast receiving apparatus wherein a variable low-pass filter for noise removal is provided between an I / Q demodulator and an A / D converter so that an arbitrary transmission rate signal can be received. . 3. A satellite broadcast receiving apparatus provided with a band-pass filter capable of changing a pass band of an intermediate frequency signal including an I signal and a Q signal by a control signal. 4. The satellite according to claim 1, wherein said filter is switched or varied using an output of an open collector port of an IC having an IIC bus built in a tuner. Broadcast receiver. 5. The satellite broadcast receiving apparatus according to claim 1, wherein a fifth-order or higher-order filter is used as said low-pass filter.