CN1528086A - combined tuner for terrestrial and satellite broadcasting - Google Patents

Abstract

A combined tuner for receiving ground waves and satellite waves, the tuner comprising: a satellite frequency output portion for receiving satellite waves, a ground frequency output portion for receiving ground waves, a first switch device for selectively inputting an RF signal output via the satellite frequency output portion or the ground frequency output portion in response to a control signal, an IF signal forming device for forming an IF signal, a second switch device for selectively inputting the IF signal, and a low-pass filter for selectively filtering ground waves or satellite waves from a second IF signal output via the second switch device.

Description

Combo tuner for terrestrial and satellite radio

technical field

The present invention relates to a tuner, and more particularly, to a combined tuner for terrestrial and satellite broadcasting, which allows a viewer to selectively receive terrestrial broadcasting or satellite broadcasting using a single device.

Background technique

Generally, a tuner is driven with two conversion types, for example, a single conversion type and a double conversion type. A single conversion type tuner outputs an intermediate frequency (IF) signal. A double conversion type tuner amplifies and synthesizes a first intermediate frequency (IF) signal to convert the first IF signal into a second IF signal while performing detection. These double conversion type tuners are further classified into ground wave tuners and satellite wave tuners.

Meanwhile, it is a common way to convert the broadcast signal into an IF signal and simultaneously complete the detection procedure of the converted IF signal, so as to improve the frequency selectivity.

Fig. 1 is a block diagram of a conventional double conversion type terrestrial tuner.

Referring to FIG. 1, a double conversion type terrestrial tuner 1 includes an AGC (Automatic Gain Controller) 2, a tracking filter 3, an RF amplifier 4, an RF filter 5, a first mixer 6, a first local oscillator 7, First PLL 8, first IF filter 9, first IF amplifier 10, second mixer 11, second local oscillator 12, second PLL 13, second IF filter 14.

In detail, the AGC 2 automatically controls the gain so that even if a radio frequency (RF) signal having a frequency range of 44 to 860 MHz induced and input from the antenna is changed in magnitude, the output of the image signal is always maintained at a constant level.

The tracking filter 3 removes noise contained in the RF signal received by the antenna, and passes only the RF signal corresponding to the desired frequency band.

The RF amplifier 4 amplifies the RF signal passing through the tracking filter 3 .

The RF filter 5 selects a desired RF component from the signal amplified by the RF amplifier 4 .

The first mixer 6 synthesizes the RF component selected in the RF filter 5 with the oscillation frequency generated by the first local oscillator 7, thereby outputting a first IF signal. When a channel is selected, the first local oscillator 7 generates a certain oscillation frequency according to the control voltage of the first PLL 8 and outputs the generated oscillation frequency to the first mixer 6. The first PLL (Phase Locked Loop) 8 outputs a control voltage to the first local oscillator 7 according to external control if there is spare channel data inside.

The first IF filter 9 passes only a desired IF component in the first IF signal output from the first mixer 6 .

The first IF amplifier 10 amplifies the first IF signal output from the first filter 9 .

The second mixer 11 synthesizes the first IF signal amplified by the first IF amplifier 10 and the oscillation frequency signal generated by the second local oscillator 12 to output a second IF signal. When a channel is selected, the second local oscillator 12 relies on the second PLL 13 to generate a certain oscillation frequency, and outputs the generated oscillation frequency to the second mixer 11 simultaneously. The second PLL outputs a control voltage to the second local oscillator 12 by means of external control if there is spare channel data in it.

The second IF filter 14 passes only a signal having a desired bandwidth among the second IF signals output from the second mixer 11 .

When the double conversion type tuner 1 as described above selects a desired channel among the ground wave signals introduced from the antenna (ANT), the desired channel is controlled and selected by the first PLL 8, and the signal corresponding to the desired channel passes through the first PLL 8. The frequency converter 6 and the first IF filter 9 will up-convert the oscillating frequency to an IF of 1038 MHz, and at the same time pass through the second mixer 11 and the second IF filter 14 to down-convert the oscillating frequency to a final 44 MHz IF.

Meanwhile, the double conversion type satellite wave tuner has the same structure as the conventional ground wave tuner, but differs from the conventional ground wave tuner in the frequency conversion method and the target frequency for frequency down conversion.

However, if these conventional double-conversion type ground wave tuners and satellite tuners are applied to a single device, it is required to separately apply respective tuners suitable for the ground wave tuner and the satellite electric wave tuner, thereby reducing the manufacturing cost. Difficulties in reducing.

Meanwhile, since a ground wave tuner and a satellite electric wave tuner are respectively used in the electronic wave receiver market positioned for continuous miniaturization, the volume increases, which is a considerable problem.

Contents of the invention

SUMMARY OF THE INVENTION The present invention is to solve the foregoing problems, and aims to provide a combined tuner for terrestrial and satellite broadcasting capable of receiving both terrestrial and satellite electric waves.

In order to achieve the above objects and other advantages, the combined tuner for terrestrial and satellite broadcasting provided herein includes: a double-conversion tuner including a first antenna, an AGC, a first amplifier, a first low-pass filter, a first A mixer, a first local oscillator, a first PLL, a bandpass filter, a second amplifier, a second mixer, a second local oscillator and a second PLL; for receiving satellite radio waves and outputting certain A satellite frequency output section of a frequency signal; a first switching device which is switched by a control signal input from the outside to select and output an RF signal input from the first antenna or an RF signal output from the satellite frequency output section using the AGC; a second switch means, which are switched together with the first switching means to selectively provide the second IF signal output from the second mixer; the second low-pass filter is used to pass only the second IF signal corresponding to the output from the second switching means ground wave band in the signal; meanwhile the third low-pass filter is used to only pass the frequency corresponding to the satellite wave band in the second IF signal output from the second switching device.

According to another aspect of the present invention, there is provided a combined tuner for terrestrial and satellite broadcasting, comprising: a double-conversion tuner including a first antenna, an AGC, a first amplifier, a first low-pass filter, a first A mixer, a first local oscillator, a first PLL, a bandpass filter, a second amplifier, a second mixer, a second local oscillator and a second PLL; used to receive satellite radio waves and output a certain The satellite frequency output part of the frequency signal; the first switch means is used for selectively outputting the second IF signal input from the second mixer or the RF signal output from the satellite frequency output part by an external control signal; the second switch means, which operates in conjunction with the first switching means while selectively providing the second IF signal output from the first switching means; the second low-pass filter for passing only a ground wave band frequency; and a third low pass filter for passing only a satellite wave band frequency corresponding to the second IF signal output from the second switching means.

According to another aspect of the present invention, a combined tuner for terrestrial and satellite broadcasting is provided, comprising: a ground frequency output section mainly comprising a ground wave antenna for receiving ground waves; a satellite frequency output portion of a satellite electric wave antenna; a first switch means for selectively providing a frequency output from the ground wave output portion or the satellite frequency output portion; and second switch means constituted at a rear end of the first switch means, A low pass filter for selectively supplying the signal which has passed through the first switching means to a ground wave and a satellite electric wave.

Description of drawings

FIG. 1 is a block diagram showing a conventional double conversion type terrestrial tuner;

Figure 2 is a block diagram showing a preferred embodiment of a combined tuner for terrestrial and satellite broadcasting according to the present invention; and

Fig. 3 is a block diagram showing another preferred embodiment of a combined tuner for terrestrial and satellite broadcasting according to the present invention.

best practice

Hereinafter, a preferred embodiment of a combined tuner for terrestrial and satellite broadcasting according to the present invention will be described with reference to FIG. 2 .

FIG. 2 is a block diagram showing a preferred embodiment of a combined tuner for terrestrial and satellite broadcasting according to the present invention.

With reference to Fig. 2, the combination tuner 100 that is used for terrestrial and satellite broadcasting comprises the first antenna (ANT1), the second antenna (ANT 2), AGC 101, the first amplifier 102, the first low-pass filter 103, the first Mixer 104, first local oscillator 105, first PLL 106, bandpass filter 107, second amplifier 108, second mixer 109, second local oscillator 110, second PLL 111, second Three mixers 112, a third local oscillator 113, a third PLL 114, a first switch 115, a second switch 116, a second low-pass filter 117, and a third low-pass filter 118.

In more detail, the first antenna (ANT 1) receives ground waves corresponding to frequency bands ranging from 44 to 860 MHz, and the second antenna (ANT 2) receives satellite electric waves corresponding to frequency bands ranging from 950 to 2150 MHz .

The third mixer 112 synthesizes the RF signal input from the second antenna (ANT 2 ) and the oscillation frequency input from the third local oscillator 113 into a satellite radio wave to output a certain intermediate frequency (IF) signal. The IF signal output from the third mixer 112 preferably has a frequency of 479.5 MHz.

The third local oscillator 113 generates a certain oscillation frequency using a control voltage input from the third PLL 114 storing channel data, and outputs the generated oscillation frequency to the third mixer 112. The third PLL 114 receives the feedback voltage of the third local oscillator 113, and thereby outputs the control voltage to the third local oscillator 113.

The first switch 115 has a fixed terminal "a" connected to the output of the first antenna (ANT 1), a fixed terminal "b" connected to the output of the third mixer 112, and a working terminal. The working end of the first switch 115 is switched by an external control signal, so that the IF signal output from the third mixer 112 is selected accordingly and the selected IF signal is output to the AGC 101. At the same time, the first switch 115 is switched by the QAM or QPSK control of the system, and at the same time, the working terminal thereof is changed in combination with the second switch 116 .

The AGC 101 is connected to the working end of the first switch 115 to automatically control the gain so that even if the magnitude of the RF signal input through the first switch 115 varies, the signal can be output at a constant value. The first amplifier 102 amplifies the RF signal passing through the AGC 101. The low pass filter 103 passes only the RF signal components of 860 MHz or less in the RF signal amplified by the first amplifier 102 .

The first mixer 104 synthesizes the RF signal selected by the first low-pass filter 103 with the oscillation frequency input from the first local oscillator 105 to increase the frequency of the RF signal to a first IF signal having a frequency of 1038 MHz and output it simultaneously converted IF signal. When a channel is selected, the first local oscillator 105 generates an oscillation frequency according to a control voltage supplied from the first PLL 106 to output the oscillation frequency to the first mixer 104. The first PLL 106 receives the output voltage fed back from the first local oscillator 105 to provide and output a control voltage to the first local oscillator 105 according to the magnitude of the output voltage.

The bandpass filter 107 passes only frequencies according to a desired band in the first intermediate frequency output from the first mixer 104 . The second amplifier 108 is connected to the output terminal of the band-pass filter 107 to amplify the signal output from the band-pass filter 107 .

The second mixer synthesizes the first IF signal amplified by the second amplifier 108 with the oscillation frequency input from the second local oscillator 110 to output a second IF signal having a frequency of 45 MHz. When a channel is selected, the second local oscillator 110 generates an oscillation frequency according to the control voltage of the second PLL 111 to output the generated oscillation frequency to the second mixer 109. The second PLL 111 receives the output voltage fed back from the second local oscillator 110 to output a control voltage to the second local oscillator 110 according to the magnitude of the output voltage.

The working terminal of the second switch 116 is connected to an output terminal of the second mixer 109, the fixed terminal "a" is connected to an input terminal of the second low-pass filter 117, and the fixed terminal "b" is connected to the third One input of low pass filter 118. The second switch is switched according to an external control signal to selectively supply the second IF signal output from the second mixer 109 to the second low pass filter 117 or the third low pass filter 118 . Here, the second switch 116 is switched according to the control of QAM or QPSK of the system.

The second low-pass filter 117 passes only the frequency having a bandwidth suitable for receiving ground waves among the second intermediate frequencies output from the second switch 116, and the third low-pass filter 118 passes only the first intermediate frequency output from the second switch 116. Among the two intermediate frequencies, there is a frequency suitable for receiving satellite radio waves.

In detail, the second low-pass filter 117 passes only frequencies with a bandwidth of 10 MHz, and the third low-pass filter passes only frequencies with a bandwidth of 45 MHz.

Meanwhile, more precisely, the bandwidth is the width of a frequency band used to transmit data provided by the transmission-side provider. It is preferable to use SPS (symbol speed per second) instead of bandwidth in a more precise definition, but since SPS and bandwidth are similar to each other, bandwidth is used for convenience of description, which is also used in the following description.

Hereinafter, the operation of a preferred embodiment of the combined tuner for terrestrial and satellite broadcasting according to the present invention will be specifically described with reference to FIG. 2 .

First, when it is required to receive broadcasting signals for ground waves, the QAM or QPSK of the system respectively connects the working terminals of the first switch 115 and the second switch 116 with their fixed terminals "a".

Simultaneously, the initial states of the first and second switches 115 and 116 are set as the state in which the working ends of the first and second switches 115 and 116 are connected to the fixed terminals "a" of the first and second switches 115 and 116 is allowed.

The RF signal introduced through the first antenna (ANT 1) assumes a tuned waveform when passing through the first switch 115, AGC 101, first amplifier 102 and first low-pass filter 103. Then, when passing through the first mixer 104, the RF signal is upconverted to a first intermediate frequency (1038 MHz). By the band-pass filter 107 , only frequencies having a desired bandwidth in the first intermediate frequency output from the first mixer 104 pass through the band-pass filter 107 .

The signal is then amplified when passed through the second amplifier 108 and down-converted to a second intermediate frequency (45 MHz) when passed through the second mixer 109 . Then, only frequencies with a bandwidth of 10 MHz pass through the second switch 116 and the second low-pass filter 117 .

Conversely, when reception of broadcast signals for satellite airwaves is required, the QAM or QPSK of the system connects the working terminals of the first and second switches 115 and 116 to the fixed terminals "b" of the first and second switches 115 and 116 stand up.

Then, the RF signal introduced through the second antenna (ANT 2) is destroyed when passing through the third mixer 112, so that only the signal having a frequency of 479.5 MHz is passed through the working end of the first switch 115 and the fixed terminal "b" Input to AGC 101.

Thereafter, after the signal goes through the frequency up step and the frequency down step, only a frequency having a bandwidth of 45 MHz suitable for satellite electric waves is output through the third low pass filter 117 when the second switch 116 is switched.

Thus, by using many switches on a single tuner structure and switching the switches, terrestrial and satellite electric wave signals input via respective antennas are selectively introduced into the circuit while detection procedures are performed by the single structure. The bandwidths of the terrestrial and satellite waves are selected by different low pass filters 117 and 118 via the second mixer 109 . According to the aforementioned structure and operation using a pair of switches on a single tuner structure, the effect of simultaneously receiving ground waves and satellite waves can be produced.

Fig. 3 is a block diagram showing another preferred embodiment of a combined tuner for terrestrial and satellite broadcasting according to the present invention.

Referring to Fig. 3, the combined tuner 200 for terrestrial and satellite broadcasting comprises the tenth antenna (ANT 1), AGC 201, the tenth amplifier 202, the tenth low-pass filter 203, the tenth mixer 204, the tenth Ten local oscillator 205, tenth PLL 206, bandpass filter 207, twentieth amplifier 208, twentieth mixer 209, twentieth local oscillator 210, twentieth PLL 211, twentieth Antenna (ANT 2), thirtieth mixer 212, thirtieth local oscillator 213, thirtieth PLL 214, tenth switch 215, twentieth switch 216, twentieth low-pass filter 217, and A thirtieth low pass filter 218 .

In detail, the tenth antenna (ANT 1) receives ground waves corresponding to frequency bands ranging from 44 to 860 MHz.

The AGC 201 is connected to the working end of the tenth switch 115 to automatically control the gain so that even if the magnitude of the RF signal input from the tenth antenna (ANT 1) is varied, the image signal can be output at a constant value. The tenth amplifier 202 amplifies the RF signal passing through the AGC 201. The tenth low pass filter 203 passes only an RF signal having a frequency of 860 MHz or less among the RF signals amplified by the tenth amplifier 202 .

The tenth mixer 204 synthesizes the RF signal selected by the tenth low-pass filter 203 with the oscillation frequency input from the tenth local oscillator 105 to increase the frequency of the RF signal to the first IF of 1038MHz and simultaneously outputs the frequency-increased after the IF signal. The tenth local oscillator 205 generates an oscillation frequency according to a control voltage supplied from the tenth PLL 206 to output the oscillation frequency to the tenth mixer 204 when one channel is selected. The tenth PLL 206 receives the output voltage fed back from the tenth local oscillator 205 to output a control voltage according to the magnitude of the output voltage.

The band-pass filter 207 passes only frequencies corresponding to a desired band in the first intermediate frequency output from the tenth mixer 204 . The twentieth amplifier 208 is connected to one output terminal of the bandpass filter 207 to amplify the signal output from the twentieth amplifier 208 .

The twentieth mixer 209 synthesizes the first IF signal amplified by the twentieth amplifier 208 and the oscillation frequency input from the twentieth local oscillator 210 to output a second IF of 45 MHz. The twentieth local oscillator 210 generates an oscillation frequency according to the control voltage of the twentieth PLL 211 to output the generated oscillation frequency to the twentieth mixer 209 when one channel is selected. The twentieth PLL 211 receives the output voltage fed back from the twentieth local oscillator 210 to output a control voltage to the twentieth local oscillator 210 according to the magnitude of the output voltage.

Meanwhile, the twentieth antenna (ANT 2) receives satellite radio waves in the frequency range of 950 to 2150MHz.

The thirtieth mixer 213 synthesizes the RF signal received from the twentieth antenna (ANT 2 ) with the oscillation frequency input from the thirtieth local oscillator 213 to output an intermediate frequency (IF) of 45 MHz.

The thirtieth local oscillator 213 generates an oscillation frequency according to a control voltage input from the thirtieth PLL 214 to output the generated oscillation frequency to the thirtieth mixer 212. The thirtieth PLL 214 receives the output voltage fed back from the thirtieth local oscillator 213 to output the control voltage to the thirtieth local oscillator 213.

The tenth switch 215 has a fixed terminal "a" connected to the output terminal of the twentieth mixer 209, and a fixed terminal "b" connected to the output terminal of the thirtieth mixer 212. By the above-mentioned structure of the tenth switch 215, the working end of the tenth switch 215 is controlled and converted by an external control signal, so that the second IF output from the twentieth mixer 209 or an output from the thirtieth mixer 312 The IF is selected and the selected IF is output to the twentieth switch 216 . Here, the tenth switch 215 is switched by the control of QAM or QPSK of the system, and its working terminal is changed in combination with the twentieth switch 216 .

The twentieth switch 216 has a fixed terminal "a" connected to the working end of the tenth switch 215, a fixed terminal "a" connected to the input terminal of the twentieth low-pass filter 217, and a fixed terminal "b" connected to to the input of the thirtieth low-pass filter 218. The twentieth switch 216 is switched by means of an external control signal to selectively supply the second IF signal output from the twentieth mixer 209 or the IF signal output from the thirtieth mixer 212 to the twentieth low-pass filter 217 or a thirtieth low-pass filter 218. Here, the twentieth switch 216 is switched according to the control of QAM or QPSK of the system, especially, the tenth switch 215 and the twentieth switch 216 work in combination.

The twentieth low-pass filter 217 passes only the frequency with 10 MHz bandwidth (BW) in the second intermediate frequency output from the twentieth switch 216, and the thirtieth low-pass filter 218 passes only the frequency with the second intermediate frequency output from the twentieth switch 216. The output IF frequency is 45MHz bandwidth.

Hereinafter, another preferred embodiment of a combined tuner for terrestrial and satellite broadcasting according to the present invention will be described in detail with reference to FIG. 3 .

First, when reception of broadcast signals for ground waves is required, QAM or QPSK of the system connects the working terminals of the tenth switch 215 and the twentieth switch 216 to their fixed terminals "a", respectively. At this time, the initial states of the tenth and twentieth switches 215 and 216 are set to the working ends of the tenth and twentieth switches 215 and 216 and the fixed terminals "a" of the tenth and twentieth switches 215 and 216. "Connected state is allowed.

Then, the RF signal introduced through the tenth antenna (ANT 1) constitutes a tuned waveform while sequentially passing through the AGC 201, the tenth amplifier 202 and the tenth low-pass filter 203. Afterwards, the tuned RF signal is up-converted to the first intermediate frequency (1038 MHz) when passing through the tenth mixer 204 . Then, the bandpass filter 207 passes only frequencies having a desired bandwidth among the tenth intermediate frequencies output from the tenth mixer 204 .

Thereafter, this signal is amplified when passing through the twentieth amplifier 208 and then down-converted to an intermediate frequency (45 MHz) when passing through the twentieth mixer 209 . Then, only frequencies having a bandwidth of 10 MHz corresponding to the ground wave pass through the twentieth switch 216 and the twentieth low-pass filter 217 .

Conversely, when required to receive broadcast signals for satellite waves, the system's QAM or QPSK connects the operating terminals of the tenth and twentieth switches 215 and 216 to the fixed terminals "b" of the tenth and twentieth switches 215 and 216 "connect them.

Then, the RF signal introduced through the twentieth antenna (ANT 2) is destroyed while passing through the thirtieth mixer 212, so that only a signal having a frequency of 45 MHz passes through the working terminal of the tenth switch 215 and the fixed terminal "b" output to the twentieth switch 216.

Due to the above operation, the IF signal via the twentieth switch 216 is filtered by the thirtieth low-pass filter 218 so that only frequencies having a bandwidth of 45 MHz corresponding to satellite electric waves pass through the thirtieth low-pass filter 217 .

Thus, by using many switches on a single tuner structure and switching the switches, the terrestrial and satellite electric wave signals input through the respective antennas are selectively introduced into the circuit, and the tuner allows the second output from the twentieth mixer. The second IF or the IF output from the thirtieth mixer is passed through different low-pass filters so that both ground waves and satellite waves can be received.

Meanwhile, the above specific embodiments can be reviewed from other aspects. In other words, the tuner includes a ground frequency output section, which is a set of elements for receiving ground waves and outputting the received ground waves, and a satellite frequency output section, which is for receiving satellite electric waves and outputting received ground waves. A set of components for satellite radio output. Also, the first and second switching means are included in the tuner so that received signals output from the ground frequency output section and the satellite frequency output section are filtered by respective low-pass filters and the filtered signals are output, thus , can describe the structure of the tuner as a whole.

As described above, according to the combined tuner for terrestrial and satellite broadcasting of the present invention, terrestrial waves and satellite electric waves can be received by a single tuner, so that manufacturing cost and product size can be reduced.

Industrial Applicability

As previously provided, a combination tuner for terrestrial and satellite broadcasts provides the ability to receive both terrestrial and satellite waves by adding a simple pair of switches to the single tuner structure.

Also, the circuit structure of the tuner is simplified to reduce the volume of the radio wave receiver, so that the tuner of the present invention allows for a closer approach in miniaturization of the radio wave receiver.

Further, the tuner of the present invention allows simultaneous reception of ground waves and satellite electric waves by a single electric wave receiver, thereby reducing manufacturing costs.

Claims (19)

1. A combined tuner for terrestrial and satellite broadcasting, comprising: a double-conversion tuner comprising a first antenna, an AGC, a first amplifier, a first low-pass filter, a first mixer, a first local oscillator, a first PLL, a band-pass filter, a second amplifier, a second mixer, a second local oscillator and a second PLL; Satellite frequency output part for receiving satellite radio waves and outputting certain frequency signals; a first switching device which is switched by a control signal input from the outside to select and output an RF signal input from the first antenna or an RF signal output from the satellite frequency output section using the AGC; the second switching means is switched along with the first switching means to selectively provide the second IF signal output from the second mixer; a second low pass filter for passing only frequencies corresponding to the ground wave band in the second IF output from the second switching means; and The third low pass filter is used to pass only frequencies corresponding to the satellite electric wave band in the second IF output from the second switching means. 2. The combined tuner according to claim 1, wherein the second low pass filter passes only frequencies with a bandwidth of 10 MHz. 3. The combined tuner according to claim 1, wherein the third low pass filter passes only frequencies with a bandwidth of 45 MHz. 4. The combination tuner according to claim 1, wherein the satellite frequency output section comprises: A second antenna for receiving satellite waves; A third mixer for synthesizing the RF signal input from the second antenna with the oscillation frequency to output a certain frequency; a third local oscillator for generating a certain oscillation frequency according to a control voltage input from the outside and outputting the generated oscillation frequency to the third mixer; and A third PLL for outputting a control voltage to a third local oscillator. 5. The combined tuner according to claim 1, wherein the satellite frequency output part outputs a signal having a frequency of 479.5 MHz. 6. The combined tuner according to claim 1, wherein the first low pass filter passes only RF signals of 860 MHz or less. 7. The combined tuner according to claim 1, wherein the first switching means has a first fixed connection terminal formed at the output terminal of the first antenna, a second fixed terminal formed at the output terminal of the satellite frequency output section, and according to an external The control signal is connected to the working terminal on the AGC. 8. A combined tuner according to claim 1, wherein the second switching means has an operating terminal formed on the output of the second mixer, a first fixed terminal formed on the second low-pass filter, and connected to The second fixed terminal of the third low-pass filter, the second switching means is switched according to an external control signal to selectively supply the second IF signal output from the second mixer to the second low-pass filter or third low pass filter. 9. The composite tuner according to claim 1, wherein the first switching means and the second switching means are switched according to the control of QAM or QPSK of the system. 10. A combined tuner for terrestrial and satellite broadcasting, comprising: a double-conversion tuner comprising a first antenna, an AGC, a first amplifier, a first low-pass filter, a first mixer, a first local oscillator, a first PLL, a band-pass filter, a second amplifier, a second mixer, a second local oscillator and a second PLL; Satellite frequency output part for receiving satellite radio waves and outputting certain frequency signals; first switching means for selectively outputting the second IF signal input from the second mixer or the RF signal output from the satellite frequency output section by an external control signal; the second switching device operates in conjunction with the first switching device and selectively provides a second IF signal output from the first switching device; a second low pass filter for passing only frequencies corresponding to the ground wave band in the second IF output from the second switching means; and The third low pass filter is used to pass only frequencies corresponding to the satellite electric wave band in the second IF output from the second switching means. 11. The combined tuner as claimed in claim 10, wherein the second low pass filter passes only frequencies with a bandwidth of 10 MHz. 12. The combined tuner as claimed in claim 10, wherein the third low pass filter passes only frequencies with a bandwidth of 45 MHz. 13. The combination tuner of claim 10, wherein the satellite frequency output section comprises: A second antenna for receiving satellite waves; A third mixer for synthesizing the RF signal input from the second antenna with the oscillation frequency to output a certain frequency; a third local oscillator for generating a certain oscillation frequency according to an external control voltage and outputting the generated oscillation frequency to the third mixer; and A third PLL for outputting a control voltage to a third local oscillator. 14. The combined tuner as claimed in claim 10, wherein the satellite frequency output part outputs an IF of 45 MHz. 15. The combined tuner as claimed in claim 10, wherein the first low pass filter passes only RF signals having a frequency of 860 MHz or less. 16. A combined tuner as claimed in claim 10, wherein the first switching means has a first fixed terminal formed at the output of the second mixer, a second fixed terminal formed at the output of the satellite frequency output section, and constitutes at the working end of the output of the second switching device. 17. A combined tuner as claimed in claim 10, wherein the second switching means has an operating terminal formed at the first switching means, a first fixed terminal formed at the second low-pass filter, and a first fixed terminal formed at the second low-pass filter. The second fixed terminal at the three low-pass filter, the second switching device is switched according to the external control signal to selectively output the second IF signal output from the second mixer or the IF signal output from the satellite frequency output section Provided to the second low-pass filter or the third low-pass filter. 18. The composite tuner as claimed in claim 10, wherein the first switching means and the second switching means are switched according to control of QAM or QPSK of the system. 19. A combined tuner for terrestrial and satellite broadcasting comprising: The ground frequency output part mainly includes a ground wave antenna for receiving ground waves; The satellite frequency output part mainly includes a satellite radio antenna for receiving satellite radio waves; the first switch means for selectively providing the frequency output from the ground wave output section or the satellite frequency output section; and A second switching device is formed at the rear end of the first switching device for selectively supplying a signal having passed through the first switching device to a low-pass filter suitable for ground waves and satellite electric waves.

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