JPH11341373A - Tuner for receiving digital broadcasting - Google Patents

Abstract

PROBLEM TO BE SOLVED: To simplify and miniaturize a front end part in a reception system and to reduce cost by using a direct conversion system at the receiving of digital satellite broadcasting and using an up-down conversion system at the time of receiving a digital CATV/ground broadcasting. SOLUTION: A first local oscillator 316 is controlled so as to oscillate at a frequency almost equal to those of the RE signals of the digital satellite broadcasting tuned by turning signals from a PLL circuit 317 and is used for directly converting the RE signals to baseband signals at the receiving of the digital satellite broadcasting. At the receiving of the digital CATV/ground broadcasting, it is used for up-converting the RE signals of the digital CATV/ ground broadcasting which is inputted to a mixer 206 to intermediate frequency(IF) signals. At the receiving of the digital CATV/ground broadcasting, the frequency of the IF signals inputted to an I/Q orthogonal detector 300 becomes the same as that of an RF signal frequency in digital satellite broadcasting reception.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a tuner for receiving digital broadcasts such as satellite (BS) broadcasts, cable television (CATV) broadcasts, and terrestrial broadcasts.

[0002]

2. Description of the Related Art Conventionally, when receiving each digital broadcast of BS broadcast, CATV broadcast and terrestrial broadcast, a dedicated tuner for receiving each broadcast is prepared, and a dedicated tuner for digital broadcast to be received is selected. I switched and received. The configuration of the receiving tuner dedicated to each digital broadcast in this case will be described with reference to FIGS.

FIG. 3 shows a circuit configuration of a conventional receiving tuner dedicated to digital satellite broadcasting. First, a digital satellite broadcast high-frequency signal (hereinafter referred to as "R") received and input to an input terminal 1 via a parabolic antenna (not shown).
F signal) is amplified by the RF amplifier 3 through the high-pass filter 2 and is amplified by an RF-automatic gain control circuit (hereinafter, referred to as an F-signal).
A tracking band pass filter 5 whose pass band changes in conjunction with a local oscillation frequency selected by a phase locked loop circuit (hereinafter, referred to as a “PLL circuit”) 8 via an “AGC circuit” 4. After the components have been filtered, they are input to a first mixer 6. During this time, the R
In the F-AGC circuit 4, the level of the RF signal received and input to the input terminal 1 is controlled by the control output signal of the AGC circuit 12 so that the level of the input signal to the subsequent I / Q quadrature detector 25 becomes a predetermined level. Is controlled. The AGC circuit 12 connects the RF-AGC circuit 4 and an intermediate frequency (IF) -AGC amplifier 11 described later so that the AGC reduction changes linearly according to the control voltage applied from the control input terminal 13. To control.

In the first mixer 6, a PLL circuit 8
A local oscillation signal of the first local oscillator 7 selected based on channel data previously stored in a microcomputer (not shown) is mixed with the RF signal, and the selected local oscillation signal is mixed. A first intermediate frequency (hereinafter, referred to as “IF”) signal having a frequency that is the difference between the frequency and the RF signal frequency is output. The first IF signal output from the first mixer 6 is amplified by an IF amplifier 9 and then amplified by a surface acoustic wave (SAW) filter 10.
And is input to the I / Q quadrature detector 25 via the IF-AGC amplifier 11. The first IF signal input to the I / Q quadrature detector 25 is split into two and input to the two second mixers 14 and 19. In the second mixer 14, the oscillation signal of the second local oscillator 24 oscillating at a frequency substantially equal to the first IF signal is mixed with the first IF signal, and the local oscillation signal frequency and IF The signal is converted to a baseband signal having a frequency different from the signal frequency. On the other hand, in the second mixer 19, the oscillation signal obtained by shifting the oscillation signal of the second local oscillator 24 by 90 degrees and the first IF signal are mixed, and
The signal is converted into a baseband signal having a frequency that is the difference between the oscillation signal frequency and the IF signal frequency that have been phase shifted. Then, the I and Q signals having a phase difference of 90 degrees from each other converted into baseband signals are respectively supplied to the amplifiers 15 and 20.
Is band-limited by the low-pass filters 16 and 21 via
After being amplified by the baseband amplifiers 17 and 22, they are output from the I signal output terminal 18 and the Q signal terminal 23 and input to a QPSK demodulation circuit (not shown).

FIG. 4 shows a circuit configuration of a conventional receiving tuner dedicated to digital terrestrial broadcasting. First, an RF signal in the VHF / UHF band input from the input terminal 101 via an antenna (not shown) is combined with an RF signal in the UHF band via the high-pass filter 102 and a VHF signal.
Band RF signal. And RF in VHF band
The signal is input to the input tuning circuit 103 and the RF-AGC circuit 10.
4, the RF signal in the UHF band is input to the first mixer 111 via the RF amplifier 105 and the output tuning circuit 106, and the RF signal in the UHF band is input to the input tuning circuit 10 like the RF signal in the VHF band.
7. The signal is input to the first mixer 113 via the RF-AGC circuit 108, the RF amplifier 109, and the output tuning circuit 110. During this time, the input tuning circuits 103 and 107 and the output tuning circuits 106 and 110 select a desired channel based on channel data previously stored in a microcomputer (not shown).
The desired channel frequency can be obtained by tuning to the RF signal frequency by the tuning signal of the L circuit 115. Further, the RF-AGC circuit 10 by the AGC circuit 119 is used.
4, 108 and an IF-AGC amplifier 118 described later are controlled in the same manner as the control of the above-mentioned receiving tuner (FIG. 3) dedicated to digital satellite broadcasting. Thus, the first mixer 111/113 to which the RF signal in the VHF / UHF band tuned to the desired channel frequency is inputted,
The local oscillation signal of the frequency selected by the PLL circuit 115 output from the local oscillator 112/114 of the
F signal and a first IF having a difference frequency between the selected local oscillation signal frequency and the RF signal frequency.
A signal is output. The first IF signal output from the first mixer 111/113 is amplified by the first IF amplifier 116 for VHF / UHF band, and then band-limited by the band-pass filter 117, so that the IF-AGC amplifier After being amplified at 118, it is input to the second mixer 121.

[0006] When receiving a VHF band or UHF band, in order to prevent interference between the VHF band and the UHF band, an RF signal in the VHF band is received.
UHF band circuit section (circuits 107 to 110, 113, 11
When the operation of 4) is stopped and the RF signal of the UHF band is being received, the circuit section of the VHF band (the circuits 103 to 106, 11
1, 112) is stopped.

The first I input to the second mixer 121
The F signal is supplied to the first IF in the second mixer 121.
The signal and the second local oscillation signal of the second local oscillator 122 are mixed, and a second intermediate frequency (I) having a frequency equal to the difference between the first IF signal frequency and the second local oscillation signal frequency.
F) Converted to a signal. The second IF signal converted by the second mixer 121 is amplified by a second IF amplifier 123 and an unnecessary harmonic component is removed by a band-pass filter 124. Similarly to the tuner (FIG. 3), the signals are input to the I / Q quadrature detector 125, converted into baseband signals of I and Q signals having a phase difference of 90 degrees, and converted into I signal terminals 126 and Q signal terminals 127. And output to a QPSK demodulation circuit (not shown).

FIG. 5 shows a conventional digital CATV.
1 shows a circuit configuration of a broadcast-only receiving tuner. First, an RF signal of a digital CATV broadcast is input from an input terminal 201 via a cable (not shown). The input RF signal is supplied to an input tuning circuit 202, RF
-The signal is input to the first mixer 206 via the AGC circuit 203, the RF amplifier 204, and the output tuning circuit 205. During this time, the input tuning circuit 202 and the output tuning circuit 205 use a tuning signal of the first PLL circuit 208 for selecting a desired channel based on channel data stored and held in a microcomputer (not shown) in advance. , The desired channel frequency can be obtained in synchronization with the RF signal frequency. Further, the RF-AGC circuit 203 using the AGC circuit 217 and an IF-
The control of the AGC amplifier 216 is performed in the same manner as the control of the receiving tuner (FIG. 3) dedicated to digital satellite broadcasting.

Thus, in the first mixer 206 to which the RF signal tuned to the desired channel frequency is input, the first PL output from the first local oscillator 207 is output.
The local oscillation signal selected by the L circuit 208 and the RF signal
The signal is mixed, and a first IF signal having a difference frequency between the selected local oscillation signal frequency and the RF signal frequency is output. The first IF signal output from the first mixer 206 is band-limited by the band-pass filter 209, amplified by the first IF amplifier 210, and further input to the second mixer 211. A local oscillation signal of a second local oscillator 212 selected by a second PLL circuit 213 for selecting a desired channel based on channel data previously stored in a microcomputer (not shown); The first IF signal is mixed and converted to a second IF signal having a frequency that is the difference between the second local oscillation frequency and the first IF signal frequency. The second IF signal converted by the second mixer 211 is
Is amplified by the IF amplifier 214 of the band pass filter 2
After unnecessary high frequency components are removed at 15, the RF-A
The level is adjusted by the GC circuit 216 and the third mixer 219
Is input to Thereafter, as in the case of the above-described reception tuner dedicated to digital terrestrial broadcasting (FIG. 4), the third mixer 219
The third IF signal converted by the above is amplified by an IF amplifier 221, after which unnecessary harmonic components are removed by a band-pass filter 222, input to an I / Q quadrature detector 223, and 90 degrees from each other. Are converted into baseband signals of I and Q signals having a phase difference of?, And output from an I signal terminal 224 and a Q signal terminal 225, and input to a QPSK demodulation circuit (not shown).

[0010]

As described above, BS /
When receiving CATV / terrestrial digital broadcasting,
Since each dedicated broadcast tuner for receiving each digital broadcast is required, the whole receiving system becomes complicated and large, and a relatively large space is required and the cost increases. is there. Digital satellite broadcasting is 950-2150 MHz, digital CA
50 to 860 MHz for TV and digital terrestrial broadcasting
Since the receiving frequency of each digital broadcast is wide, as described in
A local oscillator having a variable range of 0 to 2150 MHz is required, and there is a problem that it is very difficult to simplify, downsize, and supply such a local oscillator at low cost. In view of the above, the present invention aims at simplifying and reducing the size of the front-end unit in each digital broadcast receiving system, reducing the cost, and enabling digital broadcast of BS / CATV / terrestrial waves to be received by one unit. It is an object (object) to provide a receiving tuner.

[0011]

According to a first aspect of the present invention, a first local oscillator oscillates a digital satellite broadcast RF signal received and input to a digital satellite broadcast reception input terminal at the same frequency as the RF signal frequency. In an I / Q quadrature detector controlled by an oscillation signal of an oscillator, a direct conversion into two baseband signals of an I signal and a Q signal having a phase difference of 90 degrees from each other is performed, and digital CATV broadcast and digital terrestrial broadcast reception are performed. The digital CATV broadcast RF signal and the digital terrestrial broadcast RF signal received and input to the common input terminal are up-converted by changing the oscillation frequency of the first local oscillator and converted into an intermediate frequency signal, The intermediate frequency signal is controlled by an oscillation signal of a second local oscillator oscillating at the same frequency as the intermediate frequency. / In Q quadrature detector, together 9
A digital broadcast receiving tuner is characterized in that it is directly converted into two baseband signals of an I signal and a Q signal having a phase difference of 0 degree.

According to a second aspect of the present invention, in the first aspect of the present invention, a common input terminal for sharing the digital satellite broadcast receiving input terminal and a digital CATV broadcast and digital terrestrial broadcast receiving common input terminal is provided. In addition, a switching circuit for distributing a high-frequency signal received and input to the common input terminal into a digital satellite broadcast high-frequency signal and a digital CATV broadcast and a digital terrestrial broadcast high-frequency signal is provided.

According to a third aspect of the present invention, in the first or second aspect of the present invention, the oscillating operation of the second local oscillator is stopped when digital satellite broadcasting is received.

According to a fourth aspect of the present invention, in the third aspect of the present invention, there is provided a digital satellite broadcasting receiving digital
It is characterized in that each front end unit for receiving V broadcast and digital terrestrial broadcast and the I / Q quadrature detector are housed in the same chassis.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a digital broadcast receiving tuner according to the present invention will be described below in detail with reference to FIGS. FIG. 1 shows a digital broadcast receiving tuner according to a first embodiment of the present invention. First, at the time of receiving digital satellite broadcasting, an RF signal (frequency range of 950 to 2150 MHz) received and input from a parabolic antenna (not shown) to a digital satellite broadcasting receiving input terminal 1 via a coaxial cable passes through a high-pass filter 2. RF-AG amplified by RF amplifier 3
After passing through the C circuit 4, unnecessary frequency components are filtered by the tracking band pass filter 5 whose pass band changes in conjunction with the local oscillation signal frequency selected by the PLL circuit 317, / Q quadrature detector 3
00 is input. During this time, the RF-AGC circuit 4 controls the input level to the mixer 304/309 described later by the AGC circuit 321 controlled by the control voltage applied to the control input terminal 322 together with the AGC amplifier described later to a predetermined level. Controlled.

The RF signal input to the I / Q quadrature detector 300 is supplied to an amplifier 302 and an AGC amplifier 303.
After being amplified in the mixers 304/3, respectively.
09 and in this mixer 304/309,
PLL circuit 317 based on channel data stored and held in a microcomputer (not shown) in advance.
Phase difference between the local oscillation signal (having substantially the same frequency as the RF signal frequency) of the first local oscillator 316 and the local oscillation signal obtained by shifting the phase of the local oscillation signal by 90 degrees. Is mixed with the two local signals with That is, in the mixer 304, the local oscillation signal of the first local oscillator 316 and the RF signal are mixed,
A local oscillation signal that is directly converted into a first baseband signal having a frequency that is a difference between the local oscillation signal frequency and the RF signal frequency, and a 90-degree phase-shifted phase of the local oscillation signal in the mixer 309; The RF signal is mixed and directly converted to a second baseband signal having a frequency that is the difference between the local oscillation signal frequency shifted by 90 degrees and the RF signal frequency. Each of the I and Q signals having a phase difference of 90 degrees and directly converted to the first and second baseband signals is amplified by amplifiers 305 and 310, and then output from an I / Q quadrature detector 300. Low-pass filters 306, 31
1 and the baseband amplifiers 307 and 312
After that, the signal is output from the I signal output terminal 308 and the Q signal terminal 313 and input to a QPSK demodulation circuit (not shown). The low-pass filters 306 and 311
Is the leakage of local signals output from the first local oscillator 316 and a second local oscillator 315 described below to the outside, the I signal output terminal 308 and the Q signal terminal 31.
3 is inserted in order to prevent the leakage of the sampling reference signal from the QPSK demodulation circuit (not shown) connected to the subsequent stage.

Next, during digital CATV / terrestrial broadcast reception, an RF signal (frequency range of 50 to 860 MHz) input to the digital CATV / terrestrial broadcast reception input terminal 201 via an antenna and a cable is input. The signal is input to a mixer 206 via a tuning circuit 202, an RF-AGC circuit 203, an RF amplifier 204, and an output tuning circuit 205, mixed with a local oscillation signal provided from a first local oscillator 316, and An IF signal having a frequency different from the local oscillation signal frequency is output. During this time, in the input tuning circuit 202 and the output tuning circuit 205, a first PLL circuit 317 for selecting a desired channel based on channel data previously stored in a microcomputer (not shown).
By using the tuning signal, a desired channel frequency can be obtained by tuning to the RF signal frequency. Also, RF-AG
The C circuit 203 is controlled by the AGC circuit 321 as in the case of receiving the digital satellite broadcast described above.

The first local oscillator 316 is controlled by the tuning signal from the PLL circuit 317 so as to oscillate at a frequency substantially equal to that of the tuned digital satellite broadcast RF signal during the above-mentioned digital satellite broadcast reception. The RF
The signal is used to directly convert the signal into a baseband signal. When digital CATV / terrestrial broadcasting is received, the digital CATV /
It is used to up-convert a terrestrial broadcast RF signal into an intermediate frequency (IF) signal. That is, the reception frequency range of the digital satellite broadcast RF signal is usually 950
２2150 MHz, and the reception frequency range of the RF signal of digital CATV / terrestrial broadcasting is usually 50 to 860.
MHz, when receiving the digital satellite broadcast, the first local oscillator 316 uses the tuning signal of the PLL circuit 317 to output the RF signal frequency (950 to 950) of the digital satellite broadcast.
2150 MHz), but it is controlled to oscillate at a frequency substantially equal to that of the digital CATV / terrestrial broadcast.
It is controlled to oscillate at 10 MHz. Then, the frequency controlled as described above (1000 to 18)
The local oscillation signal of 10 MHz) is input to the mixer 206 via the switching circuit 318 and the local oscillation amplifier 319, and is mixed with the RF signal of digital CATV / terrestrial broadcasting, whereby the RF signal is up-converted and the local oscillation signal is up-converted. The frequency of the difference between the oscillation signal frequency and the RF signal frequency (950 M
Hz).

The IF signal thus converted passes through the band-pass filter 209, is amplified by the intermediate frequency amplifier 210, and is switched via the switching circuit 301 to the I / O signal.
The signal is input to the Q quadrature detector 300. I / Q quadrature detector 3
00 is input to the amplifier 302 and the AGC
After being amplified by the amplifier 303, it is divided and input to the two mixers 304/309. Then, in the mixer 304, a local oscillation signal of a second local oscillator (fixed oscillator) 315 oscillating at a fixed oscillation frequency (substantially the same as the IF signal frequency (950 MHz)) and the IF signal are mixed, A local oscillation signal, which is directly converted into a first baseband signal having a frequency of a difference between the local oscillation signal frequency and the IF signal frequency, and in which the local oscillation signal is shifted by 90 degrees in a mixer 309; The IF signal is mixed and directly converted to a second baseband signal having a frequency that is the difference between the local oscillation signal frequency shifted by 90 degrees and the IF signal frequency. Each of the I and Q signals having a phase difference of 90 degrees and converted into the first and second baseband signals is amplified by amplifiers 305 and 310, and then output from an I / Q quadrature detector 300, and output from a low-pass Filters 306, 31
1 and the baseband amplifiers 307 and 312
After that, the signal is output from the I signal output terminal 308 and the Q signal terminal 313 and input to a QPSK demodulation circuit (not shown).

As described above, the frequency of the IF signal input to the I / Q quadrature detector 300 at the time of receiving digital CATV / terrestrial broadcasting becomes the same (950 MHz) as the RF signal frequency at the time of receiving digital satellite broadcasting. Because
The I / Q quadrature detector 300 can be used commonly when receiving digital satellite broadcasting and receiving digital CATV / terrestrial broadcasting. In this embodiment, the oscillation frequency of the first local oscillator 316 is set to 10
The intermediate frequency (IF) is controlled to 950 MHz by controlling the frequency to 00 to 1810 MHz.
Since the frequency is the difference between the signal and the oscillation frequency of the first local oscillator 316, the frequency can be freely set within the variable frequency range of the first local oscillator 316. In this case, the oscillation frequency of the second local oscillator 315 also needs to be set according to the set intermediate frequency (IF).

Next, switching in the case of receiving digital satellite broadcasting or digital CATV / terrestrial broadcasting will be described. In FIG. 1, 301, 314, and 318
Are controlled by a switching control signal supplied to a switching control terminal 320, respectively, for digital satellite broadcasting or digital CAT.
This is a switching circuit that is switched when receiving V / terrestrial broadcasting. That is, at the time of digital satellite broadcast reception, the switching circuit 301 inputs the digital satellite broadcast RF signal input to the digital satellite broadcast reception input terminal 1 to the I / Q quadrature detector 300 and receives digital CATV / terrestrial broadcast reception. Sometimes, it is a switching circuit for inputting an intermediate frequency (IF) signal obtained by up-converting an RF signal of digital CATV / terrestrial broadcasting to the I / Q quadrature detector 300. Further, the switching circuit 314 provides a function for receiving digital satellite broadcasts.
The local oscillation frequency signal of the first local oscillator 316 is
A switching circuit for inputting the signal to the quadrature detector 300 and for inputting the local oscillation frequency signal of the second local oscillator 315 to the I / Q quadrature detector 300 at the time of digital CATV / terrestrial broadcast reception. Further, the switching circuit 318 controls the digital CATV / terrestrial broadcasting at the time of reception.
A switching circuit for inputting a local oscillation frequency signal of the first local oscillator 316 to a mixer 206 that up-converts an RF signal of terrestrial broadcasting and converts it into an intermediate frequency (IF) signal.

According to the above circuit configuration, the first local oscillator 316 is an oscillator that oscillates at an oscillation frequency (950-2150 MHz) for directly converting an RF signal of digital satellite broadcast when receiving digital satellite broadcast. When receiving digital CATV / terrestrial broadcasts, it can be used as an oscillator that oscillates at an oscillation frequency (1000 to 1810 MHz) for up-converting the RF signal. It can be used as a local oscillator when receiving wave broadcasting. Also, the first local oscillator 316 has an oscillation frequency of 950 to 2150
Since it is good in the range of MHz, it is relatively easy to design and can be supplied at low cost.

FIG. 2 shows a digital broadcast receiving tuner according to a second embodiment of the present invention. In this embodiment, the input terminal for digital satellite broadcast reception and the input terminal for digital CATV / terrestrial broadcast reception are shared to form one input terminal 323, and the digital satellite broadcast is switched inside the tuner by switching of the switching circuit 324. And an RF signal for digital CATV / terrestrial broadcasting. Further, the switching circuit 324 includes:
In conjunction with the other switching circuits 301, 314, and 318, they are controlled by a switching control signal applied to a switching control terminal 320. The RF signal of digital satellite broadcasting or RF signal of digital CATV / terrestrial broadcasting switched by the switching circuit 324 is converted in the same manner as the circuit operation shown in FIG.
The signals are output from the I signal output terminal 308 and the Q signal terminal 313 as I and Q signals having a phase difference of 0 degree, and are input to a QPSK demodulation circuit (not shown).

According to the second embodiment described above,
Since the RF signals of digital satellite broadcasting and digital CATV / terrestrial broadcasting are switched and distributed before the RF amplifiers 3 and 204, the RF signals of each digital broadcast due to harmonic spurious generated by the RF amplifiers 3 and 204 are transmitted. Interference is less likely to occur. Also, one input terminal 323
By using a common reception system such as a condominium, even when digital broadcasts are rearranged in frequency and transmitted by a single cable, etc., connection is easy and digital work is easy to install. A broadcast receiving tuner can be realized.

Incidentally, in the first and second embodiments of the present invention shown in FIGS. 1 and 2, the first local oscillator 316
Is used to convert an RF signal input to the I / Q quadrature detector 300 into a baseband signal when receiving digital satellite broadcasting, and upconverts the RF signal when receiving digital CATV / terrestrial broadcasting. And a second local oscillator 315,
Used only for digital CATV / terrestrial broadcast reception,
Since it is used to convert the RF signal input to the I / Q quadrature detector 300 into a baseband signal, the second local oscillator 315 can be stopped when digital satellite broadcasting is received. Therefore, it is possible to eliminate the influence on the I / Q detection operation due to the mutual interference between the oscillation signal of the first local oscillator 316 and the oscillation signal of the second local oscillator 315 at the time of receiving the digital satellite broadcast, and perform the normal operation. This eliminates the need to provide sufficient shielding for both local oscillators and electrically isolate them. Digital CA
First local oscillator 31 during reception of TV / terrestrial broadcasting
The variable range of the oscillation frequency of 6 is 1000 to 1810 MHz
Since it is out of the range of 1900 MHz, which is twice as high as the fixed oscillation frequency 950 MHz of the second local oscillator 315, the influence of the harmonic component of the oscillation frequency of the second local oscillator (fixed oscillator) 315 is reduced. I will not receive it.

[0026]

As described above, according to the tuner for digital broadcast reception according to the present invention, the direct conversion method is used when digital satellite broadcasts are received, and the digital C
By using the up-down conversion method when receiving ATV / terrestrial broadcasting, one local oscillator can be shared for direct conversion and up-conversion, and the I / Q quadrature detector can be shared, simplifying the circuit configuration. Thus, it is possible to obtain a digital broadcast receiving tuner capable of reducing the number of parts and reducing the size. Also, in terms of electrical performance, despite the fact that the local oscillator and the I / Q quadrature detector are shared, there is almost no interference between RF signals of digital broadcasting due to harmonic spurious and the like, and normal operation can be achieved. A tuner for digital broadcast reception that can be obtained can be obtained. Further, at the time of receiving a digital satellite broadcast, the second local oscillator, which is a fixed oscillator, can be stopped, so that the first local oscillator signal and the second local oscillator signal interfere with each other, and
Since the / Q operation is not adversely affected, all circuits can be housed in the same chassis, and a digital broadcast receiving tuner that can be further downsized and simplified can be obtained.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a digital broadcast receiving tuner according to a first embodiment of the present invention.

FIG. 2 is a circuit diagram showing a digital broadcast receiving tuner according to a second embodiment of the present invention.

FIG. 3 is a circuit configuration of a conventional receiving tuner dedicated to digital satellite broadcasting.

FIG. 4 is a circuit configuration of a conventional receiving tuner dedicated to digital terrestrial broadcasting.

FIG. 5 is a circuit configuration diagram of a conventional receiving tuner dedicated to digital CATV broadcasting.

[Explanation of symbols]

 2: High-pass filter 3, 204: RF amplifier 4, 203: RF-AGC circuit 5: Tracking bandpass filter 202: Input tuning circuit 205: Output tuning circuit 206: Mixer 209: Bandpass filter 210: IF amplifier 300: I / Q quadrature detectors 304, 309 mixers 305, 310 amplifier 315 second local oscillator (fixed oscillator) 316 first local oscillator 317 phase locked loop (PLL) circuit 301, 314, 318, 324 ... Switching circuit 320 ... Switching signal terminal 321 ... AGC circuit 322 ... AGC control terminal

Claims (4)

[Claims] An I / Q controlled by an oscillation signal of a first local oscillator which oscillates a digital satellite broadcast RF signal received and input to a digital satellite broadcast reception input terminal at the same frequency as the RF signal frequency. In the quadrature detector, while directly converting into two baseband signals of an I signal and a Q signal having a phase difference of 90 degrees from each other, a digital signal received and input to a common input terminal for digital CATV broadcast and digital terrestrial broadcast reception is provided. CATV broadcast RF
The signal and the RF signal of digital terrestrial broadcasting are up-converted by changing the oscillation frequency of the first local oscillator and converted into an intermediate frequency signal, and the intermediate frequency signal is oscillated at the same frequency as the intermediate frequency. In an I / Q quadrature detector controlled by an oscillation signal of a second local oscillator, a digital signal is directly converted into two baseband signals of an I signal and a Q signal having a phase difference of 90 degrees from each other. Tuner for broadcast reception. 2. A shared input terminal for sharing the digital satellite broadcast receiving input terminal and a digital CATV broadcast and digital terrestrial broadcast receiving common input terminal, and a high-frequency signal received and input to the shared input terminal. To
2. The digital broadcast receiving tuner according to claim 1, further comprising a switching circuit for distributing the digital satellite broadcast high-frequency signal and the digital CATV broadcast and digital terrestrial broadcast high-frequency signal. 3. The tuner for digital broadcast reception according to claim 1, wherein an oscillation operation of said second local oscillator is stopped when receiving digital satellite broadcasts. 4. A method for receiving digital satellite broadcasts and digital C
The digital broadcast receiving tuner according to claim 3, wherein each of the front-end units for receiving ATV broadcasting and digital terrestrial broadcasting and the I / Q quadrature detector are housed in the same chassis.