CN101931794B - Band switching circuit and its related satellite TV system - Google Patents

Abstract

The invention relates to a band switching circuit and a related satellite television system thereof. Specifically, the band conversion circuit comprises a band-pass filter, a band-stop filter, a first power divider, a local oscillator, a mixer, a switching circuit, a high-pass filter, a second power divider and a low-pass filter. The band-pass filter and the band-stop filter respectively filter the input signal after frequency reduction to generate a first filtered signal and a second filtered signal. The first power divider is coupled to the band-stop filter. The mixer is coupled to the first power divider and the local oscillator. The switching circuit is coupled to the first power divider and the mixer. The high pass filter is coupled to the switching circuit. The second power divider is coupled to the band-pass and high-pass filters. The low pass filter is coupled to the second power divider. The invention can simplify the circuit, reduce the whole size of the product, save the cost, reduce the transmission loss of signals, improve the signal quality of the product, directly realize mass production on a production line and improve the manufacturing yield of the product.

Description

Band switching circuit and its related satellite TV system

technical field

The invention relates to a band conversion circuit and its related satellite TV system, in particular to a band conversion circuit and its related satellite TV system which can improve signal quality and product manufacturing yield.

Background technique

Satellite communication systems have the characteristics of broadband and large coverage, and are widely used in the fields of detection, military, telecommunication networks, data and mobile communications. For ground users of the satellite communication system, an antenna, a satellite down-converter (Low-noise Block Down-converter, LNB) and a demodulator are required to receive satellite signals. After the satellite signal is received by the antenna, it is down-converted to an intermediate frequency signal by the satellite down-converter, and finally demodulated by the demodulator to generate a playback signal, which is output to user devices, such as TVs.

Please refer to FIG. 1 and FIG. 2. FIG. 1 is a schematic diagram of a down-frequency satellite signal 100 on the frequency spectrum, and FIG. 2 is a schematic diagram of the down-frequency satellite signal 100 shown in FIG. 1 after being processed by a band conversion circuit 200. . As shown in FIG. 1, the down-converted input signal 100 includes a first data signal DS1 located in a first frequency band FB1, a second data signal FB2 located in a second frequency band FB2, and a first data signal located in a third frequency band FB3. Three data signals DS3, wherein the third frequency band FB3 is higher than the second frequency band FB2, and the second frequency band FB2 is higher than the first frequency band FB1.

Since the current receiver (such as the narrow-band receiver 240) can only receive the data signals of the second frequency band FB2 and the third frequency band FB3, but cannot receive the first data signal DS1 located in the first frequency band FB1, it must be narrow-band If a band conversion circuit 200 is added to the input end of the frequency receiver 240, then all data signals can be selectively received in sections. As shown in FIG. 2, through the control of a selection signal SEL1, the band conversion circuit 200 can select to output the first output signal 210 or the second output signal 220 to the narrowband receiver 240, wherein the first output signal 210 contains The second data signal DS2 of FB2 and the third data signal DS3 located in the third frequency band FB3, and the second output signal 220 includes the second data signal DS2 located in the second frequency band FB2 and the first data signal located in the third frequency band FB3 DS1 (after upscaling).

Please refer to FIG. 3 , which is a schematic structural diagram of a conventional B-band conversion circuit 300 . As shown in Figure 3, the B-band conversion circuit 300 includes a first power divider 310, a first high-pass filter HPF1, a second power divider 320, a band-pass filter BPF1, a low-pass filter LPF1, a Mixer 330 , a local oscillator 340 , a second high-pass filter HPF2 , a third power divider 350 , a switching circuit 360 , a microcontroller 370 and a second low-pass filter LPF2 . It can be known from FIG. 3 that the B-band conversion circuit 300 receives the down-frequency satellite signal 100 shown in FIG. The output signal 220 is sent to a back-end narrowband receiver (not shown in the figure).

The B-band conversion circuit 300 shown in FIG. 3 is a product currently available on the market, but the realized circuit structure is relatively complicated. Therefore, how to improve signal quality, simplify circuits and save costs has become one of the important topics in this design field.

Contents of the invention

Therefore, one of the objectives of the present invention is to provide a band conversion circuit and related satellite TV system to solve the above problems.

The invention discloses a band conversion circuit for receiving a down-frequency input signal, the down-frequency input signal includes a first data signal in a first frequency band, a second data signal in a second frequency band and A third data signal in a third frequency band, and the third frequency band is greater than the second frequency band and the second frequency band is greater than the first frequency band. The band conversion circuit includes a band-pass filter, a band-stop filter, a first power divider, a local oscillator, a mixer, a switching circuit, a high-pass filter, a second power divider and a low pass filter. The bandpass filter performs bandpass filtering on the down-converted input signal to generate a first filtered signal, wherein the first filtered signal includes the second data signal in the second frequency band. The band-stop filter performs band-stop filtering on the down-converted input signal to generate a second filtered signal, wherein the second filtered signal includes the first data signal in the first frequency band and the first data signal in the first frequency band. The third data signal in the third frequency band. The first power splitter is coupled to the band-stop filter, and is used for generating a first split signal and a second split signal according to the second filtered signal. The local oscillator provides a local oscillator signal. The mixer is coupled to the first power divider and the local oscillator, and is used for adjusting the frequency of the second split signal according to the local oscillator signal, so as to generate an up-frequency second split signal. The switching circuit is coupled to the first power splitter and the mixer, and is used to select one of the first split signal and the up-converted second split signal according to a selection signal, and output an output signal . The high-pass filter is coupled to the switching circuit for performing a high-pass filtering operation on the output signal to generate a third filtered signal. The second power divider is coupled to the band-pass filter and the high-pass filter, and is used for combining the first filtered signal and the third filtered signal to generate a combined signal. The low-pass filter is coupled to the second power divider for performing a low-pass filtering operation on the combined signal to generate a fourth filtered signal.

The present invention also discloses a band conversion circuit for receiving a down-frequency input signal, and the down-frequency input signal includes a first data signal in a first frequency band and a second data signal in a second frequency band and a third data signal located in a third frequency band, and the third frequency band is greater than the second frequency band and the second frequency band is greater than the first frequency band. The band conversion circuit includes a band-pass filter, a band-rejection filter, a first power divider, a local oscillator, a mixer, a switching circuit, a high-pass filter and a second power divider. The bandpass filter performs bandpass filtering on the down-converted input signal to generate a first filtered signal, wherein the first filtered signal includes the second data signal in the second frequency band. The band-stop filter performs band-stop filtering on the down-converted input signal to generate a second filtered signal, wherein the second filtered signal includes the first data signal in the first frequency band and the first data signal in the first frequency band. The third data signal in the third frequency band. The first power splitter is coupled to the band-stop filter, and is used for generating a first split signal and a second split signal according to the second filtered signal. The local oscillator provides a local oscillator signal. The mixer is coupled to the first power divider and the local oscillator, and is used for adjusting the frequency of the second split signal according to the local oscillator signal, so as to generate an up-frequency second split signal. The switching circuit is coupled to the first power splitter and the mixer, and is used to select one of the first split signal and the up-converted second split signal according to a selection signal, and output an output signal . The high-pass filter is coupled to the switching circuit for performing a high-pass filtering operation on the output signal to generate a third filtered signal. The second power divider is coupled to the band-pass filter and the high-pass filter, and is used for combining the first filtered signal and the third filtered signal to generate a combined signal. Wherein the band switching circuit is a B-band switching circuit.

The invention also discloses a satellite television system. The satellite TV system includes a low-noise frequency reducer, a band conversion circuit and a satellite integrated receiving decoder. The low-noise frequency reducer receives a satellite signal, and performs frequency reduction and amplification to generate a frequency-reduced satellite signal. The frequency-reduced satellite signal includes a first data signal located in a first frequency band, and a signal located in a second frequency band. A second data signal and a third data signal in a third frequency band, and the third frequency band is greater than the second frequency band and the second frequency band is greater than the first frequency band. The band conversion circuit is coupled to the low-noise down-converter for receiving the down-frequency satellite signal. The band conversion circuit includes a band-pass filter, a band-stop filter, a first power divider, a local oscillator, a mixer, a switching circuit, a high-pass filter, a second power divider and a low pass filter. The bandpass filter performs bandpass filtering on the down-converted input signal to generate a first filtered signal, wherein the first filtered signal includes the second data signal in the second frequency band. The band-stop filter performs band-stop filtering on the down-converted input signal to generate a second filtered signal, wherein the second filtered signal includes the first data signal in the first frequency band and the first data signal in the first frequency band. The third data signal in the third frequency band. The first power splitter is coupled to the band-stop filter, and is used for generating a first split signal and a second split signal according to the second filtered signal. The local oscillator provides a local oscillation signal. The mixer is coupled to the first power divider and the local oscillator, and is used for adjusting the frequency of the second split signal according to the local oscillator signal, so as to generate an up-frequency second split signal. The switching circuit is coupled to the first power splitter and the mixer, and is used to select one of the first split signal and the up-converted second split signal according to a selection signal, and output an output signal . The high-pass filter is coupled to the switching circuit for performing a high-pass filtering operation on the output signal to generate a third filtered signal. The second power divider is coupled to the band-pass filter and the high-pass filter, and is used for combining the first filtered signal and the third filtered signal to generate a combined signal. The low-pass filter is coupled to the second power divider for performing a low-pass filtering operation on the combined signal to generate a fourth filtered signal. The satellite integrated receiver decoder is coupled to the band conversion circuit for receiving and decoding the fourth filtered signal.

The band conversion circuit involved in the present invention can simplify the circuit (for example, reduce the number of power dividers and filters), thereby reducing the overall size of the product and saving costs. And because the number of components of the band conversion circuit is small, the transmission loss of the signal can be reduced, so as to improve the signal quality of the product. In addition, components such as a power divider, a mixer, a local oscillator, a switching circuit, and a microcontroller can be implemented on the same integrated circuit, and the integrated circuit can be mass-produced directly on the production line, thereby improving the manufacturing yield of the product.

Description of drawings

FIG. 1 is a schematic diagram of a frequency spectrum of a down-frequency satellite signal.

FIG. 2 is a schematic diagram of the down-frequency satellite signal shown in FIG. 1 after being processed by a band conversion circuit.

FIG. 3 is a schematic structural diagram of a known B-band conversion circuit.

FIG. 4 is a schematic structural diagram of an embodiment of the band conversion circuit of the present invention.

FIG. 5 is a schematic diagram of the frequency spectrum of each signal shown in FIG. 4 .

FIG. 6 is a schematic diagram of the first embodiment of the satellite TV system of the present invention.

FIG. 7 is a schematic diagram of a second embodiment of the satellite TV system of the present invention.

Description of main component symbols:

100 down-converted satellite signal SS2 second split signal

DS1 First Data Signal SS22 Upconverted Second Split Signal

DS2 Second Data Signal LOS1 Local Oscillator Signal

DS3 third data signal fo oscillation frequency

FB1 first frequency band S _OUT output signal

FB2 Second frequency band SEL1, SEL11 selection signal

FB3 The third frequency band V1 Power supply

240 Narrowband receiver FS3 3rd filtered signal

300 B-band conversion circuit CS1 combined signal

200, 400, 620 band conversion circuit FS4 4th filtered signal

BPF1, BPF11 bandpass filter 210 first output signal

BSF11 Band stop filter 220 Second output signal

HPF1, HPF2, HPF11 High Pass Filter 600, 700 Satellite TV System

LPF1, LPF2, LPF11 Low Pass Filter 610 Low Noise Frequency Reducer

310, 320, 350, 410, 450 power splitter 630 satellite integrated receiver decoder

330, 430 Mixer 640 Cable

340, 440 Local Oscillator 720 Multiplexer

360, 460 Switching circuit 720A Input port

370, 470 Microcontroller 720B Output port

FS1 The first filtered signal IM1, IM2 Image signal

FS2 Second filtered signal CS2 Combined down-frequency satellite signal

SS1 First separation signal

Detailed ways

Please refer to FIG. 4 , which is a schematic structural diagram of an embodiment of a band conversion circuit 400 of the present invention. As shown in Figure 4, the band conversion circuit 400 includes (but not limited to) a band-pass filter BPF11, a band-stop filter (band-stop filter) BSF11, a first power divider 410, a mixer 430, a The local oscillator 440 , a switching circuit 460 , a microcontroller 470 , a high pass filter HPF11 , a second power divider 450 and a low pass filter LPF11 . The band conversion circuit 400 is used for receiving a down-converted input signal, such as the down-converted satellite signal 100 shown in FIG. 1 . In this embodiment, the first frequency band FB1 is 250-750 MHz, the second frequency band FB2 is 950-1450 MHz, and the third frequency band FB3 is 1650-2150 MHz, but the present invention is not limited thereto. Please note that the band conversion circuit 400 can be applied to a satellite TV system, but the present invention is not limited thereto, and can also be applied to other products.

Please also refer to FIG. 5 , which is a schematic diagram of the frequency spectrum of each signal shown in FIG. 4 . Firstly, a filtering operation is performed on the down-frequency satellite signal 100 by using the band-pass filter BPF11 and the band-stop filter BSF11 respectively, so as to generate a first filtered signal FS1 and a second filtered signal FS2, wherein the first A filtered signal FS1 includes the second data signal DS2 located in the second frequency band FB2, and the second filtered signal FS2 includes the first data signal DS1 located in the first frequency band FB1 and the third data signal DS3 located in the third frequency band FB3 . The first power splitter 410 is coupled to the band-stop filter BSF11, and generates a first split signal SS1 and a second split signal SS2 according to the second filtered signal FS2, wherein the first split signal SS1 and the second split signal SS2 The signal components and distribution positions on the frequency spectrum are the same as those of the second filtered signal FS2, but the power of both is smaller than that of the second filtered signal FS2.

Next, the local oscillator 440 provides a local oscillator signal LOS1 to the mixer 430, and the mixer 430 adjusts the frequency of the second split signal SS2 according to the local oscillator signal LOS1 to generate an up-frequency second split signal SS22. In this embodiment, the oscillation frequency fo of the local oscillation signal LOS1 is 2400 MHz as an example, but this is not a limiting condition of the present invention. Therefore, after the mixer 430 mixes the local oscillation signal LOS1 and the second split signal SS2, the second split signal SS2 will be boosted from the original frequency (for example, the center frequency of the second split signal SS2 is fs). to the frequency (fo+fs), and generate a mirror signal of the second split signal SS2 at the frequency (fo-fs), as shown in the up-converted second split signal SS22 of FIG. 5 . In other words, the mixer 430 here is to up-convert the first data signal DS1 originally located in the first frequency band FB1 to the third frequency band FB3 . Next, the switching circuit 460 is coupled to the first power divider 410 and the mixer 430, and is used for selecting one of the first split signal SS1 and the up-converted second split signal SS22 according to a selection signal SEL11, and output an output signal S _OUT .

In addition, the microcontroller 470 is coupled to the switching circuit 460 and the local oscillator 440 for providing a selection signal SEL11 to control how the switching circuit 460 performs signal switching, and to provide a power supply V1 to the local oscillator 440 . When the switch circuit 460 selects to output the second split signal SS22 which has been up-converted as the output signal S _OUT , the microcontroller must simultaneously provide the supply power V1 to the local oscillator 440 so that it can operate normally; and when the switch circuit 460 selects When outputting the first separation signal SS1 as the output signal S _OUT , the microcontroller 470 can turn off the power supply V1 to save the power consumption of the local oscillator 440 . The high-pass filter HPF11 is coupled to the switching circuit 460, and is used to perform a high-pass filtering operation on the output signal S _OUT (that is, the first separated signal SS1 or the up-converted second separated signal SS22) to generate a third filtered Rear signal FS3. That is to say, the high-pass filter HPF11 only allows signals higher than the third frequency band FB3 to pass through, as shown in the third filtered signal FS3 in FIG. 5 .

Afterwards, the second power divider 450 is coupled to the band-pass filter BPF11 and the high-pass filter HPF11 for combining the first filtered signal FS1 and the third filtered signal FS3 to generate a combined signal CS1. Finally, the low-pass filter LPF11 is coupled to the second power divider 450 for performing a low-pass filtering operation on the combined signal CS1 to generate a fourth filtered signal FS4. Since the low-pass filter LPF11 only allows the signals below the first frequency band FB1, the second frequency band FB2 and the third frequency band FB3 to pass through, the signals higher than the third frequency band FB3 generated by the mixer 430 can be filtered out, as shown in FIG. 5 as shown in the fourth filtered signal FS4. That is to say, the fourth filtered signal FS4 includes the second data signal DS2 located in the second frequency band FB2 and the third data signal DS3 located in the third frequency band FB3 (that is, the first output signal 210 ), or includes a data signal located in the second frequency band The second data signal DS2 of FB2 and the first data signal DS1 of the third frequency band FB3 (ie, the second output signal 220 ).

In short, the band conversion circuit 400 receives the down-frequency satellite signal 100 shown in FIG. For the narrowband receiver at the back end (not shown in the figure).

Please note that in this embodiment, the low-pass filter LPF11 is set in the band conversion circuit 400. If the back-end narrow-band receiver has been equipped, it is only allowed to include the first frequency band FB1, the second frequency band FB2 and the third frequency band FB3. The low-pass filter or band-pass filter through which the signal passes, the low-pass filter LPF11 is an optional element, and can also be omitted or replaced by other components that can achieve the same purpose. Then the band converting circuit 400 can be a B-band converting circuit (B-band converter), but this is not a limiting condition of the present invention. Please note that in other embodiments, the selection signal SEL11 can also be provided by the user (for example, the user makes a selection through a remote controller), and the microcontroller 470 is also an unnecessary component.

It is worth noting that, since the first power divider 410, the mixer 430, the local oscillator 440, the switching circuit 460, and the microcontroller 470 occupy a small area in this embodiment, they can be easily implemented in on the same integrated circuit. In this way, the integrated circuit can be mass-produced directly on the production line, thereby improving the manufacturing yield of the product.

The band conversion circuit 400 disclosed in this embodiment has the following advantages: simple circuit, low cost, can improve the signal quality of the product, and achieve the purpose of product modularization (chip). The band conversion circuit 400 uses four filters and two power dividers. In this way, the purpose of reducing the size of the product and saving costs can be achieved. Moreover, since the number of components of the band conversion circuit 400 is small, the transmission loss of the signal can be reduced, and the signal quality of the product can be further improved. In addition, the band conversion circuit 400 can implement components such as the first power divider 410, the mixer 430, the local oscillator 440, the switching circuit 460, and the microcontroller 470 on the same integrated circuit, and directly mass-produce this on the production line. Integrated circuits, thereby improving the manufacturing yield of products.

Generally speaking, the B-band conversion circuit is used together with a low-noise block down-converter (LNB) and an integrated receiver-decoder (IRD). Among them, the output signal of the low-noise frequency reducer includes: Ka Lo-band signal falling at 250-750MHz (also known as B-band (BBand) signal), Ku-band signal falling at 950-1450MHz and falling at 1650MHz ~2150MHz Ka Hi-band signal (also known as A band (A band) signal). The input frequency range of the satellite integrated receiver decoder only includes 950-2150MHz, so the Ka Lo-band signal must be up-converted (from 250-750MHz to 1650-2150MHz) through the B-band conversion circuit before it can Received Ka Lo-band signal.

Please refer to FIG. 6 , which is a schematic diagram of a first embodiment of a satellite TV system 600 of the present invention. As shown in FIG. 6 , the satellite TV system 600 includes a low-noise downconverter 610 , a band conversion circuit 620 and a satellite integrated receiver decoder 630 . The low noise down-converter 610 receives a satellite signal, and performs down-conversion and amplification to generate a down-frequency satellite signal, such as the down-frequency satellite signal 100 shown in FIG. 1 . The band conversion circuit 620 is coupled to the low-noise downconverter 610 through a cable 640 to receive the down-frequency satellite signal, and the band conversion circuit 620 can be composed of the band conversion circuit 400 shown in FIG. 4 (or the band conversion circuit 400 Variation embodiment) to achieve. The satellite integrated receiver decoder 630 is coupled to the band conversion circuit 620, and is used to receive and decode the signal (such as the fourth filtered signal FS4) output by the band conversion circuit 620. The satellite integrated receiver decoder 630 here is the aforementioned Mentioned narrowband receivers.

Please refer to FIG. 7 , which is a schematic diagram of a second embodiment of a satellite TV system 700 of the present invention. The structure of the satellite TV system 700 of FIG. 7 is similar to the satellite TV system 600 of FIG. 6 , the difference between the two is that the satellite TV system 700 also includes a multi-switch (multi-switch) 720 coupled to the low-noise frequency reducer 610 and the band conversion circuit 620. The multiplexer 720 has a plurality of input ports 720A and a plurality of output ports 720B, wherein the plurality of input ports 720A are used to receive the down-converted satellite signal and a plurality of image signals (such as IM1, IM2) and combine them to generate a The combined down-converted satellite signal (eg, CS2 ) is combined, and one of the plurality of output ports 720B distributes the combined down-converted satellite signal CS2 to the band conversion circuit 620 . In other words, through the multiplexer 720 , the combined down-frequency satellite signal CS2 can be distributed to several users at the same time for their use.

The above-mentioned embodiments are only used to illustrate the technical features of the present invention, and are not intended to limit the scope of the present invention. As can be seen from the above, the present invention provides a band conversion circuit and related satellite TV system. The band conversion circuit can simplify the circuit (such as reducing the number of power dividers and filters), thereby reducing the overall size of the product and saving costs. And because the number of components of the band conversion circuit is small, the transmission loss of the signal can be reduced, so as to improve the signal quality of the product. In addition, components such as a power divider, a mixer, a local oscillator, a switching circuit, and a microcontroller can be implemented on the same integrated circuit, and the integrated circuit can be mass-produced directly on the production line, thereby improving the manufacturing yield of the product.

The above descriptions are only preferred embodiments of the present invention, and all equivalent changes and modifications made according to the scope of the patent application of the present invention shall fall within the scope of the present invention.

Claims (20)

1. band switching circuit; In order to receive a reduced frequency input signal; Said reduced frequency input signal comprises one first data-signal that is positioned at one first frequency range, one the 3rd data-signal that is positioned at one second data-signal of one second frequency range and is positioned at one the 3rd frequency range; And said the 3rd frequency range is higher than said second frequency range and said second frequency range is higher than said first frequency range, and said band switching circuit comprises:

One band pass filter is used for carrying out a bandpass filtering and moves on said reduced frequency input signal, filters the back signal to produce one first, and wherein said first filters the back signal comprises said second data-signal that is positioned at said second frequency range;

One band stop filter; Being used for carrying out a bandreject filtering moves on said reduced frequency input signal; Filter the back signal to produce one second, wherein said second filters the back signal comprises said first data-signal that is positioned at said first frequency range and said the 3rd data-signal that is positioned at said the 3rd frequency range;

One first power divider is coupled to said band stop filter, is used for filtering the back signal according to said second and produces one first separation signal and one second separation signal;

One local oscillator is used to provide a local oscillated signal;

One frequency mixer is coupled to said first power divider and said local oscillator, is used for adjusting according to said local oscillated signal the frequency of said second separation signal, to produce raising frequency second separation signal;

One switches circuit, is coupled to said first power divider and said frequency mixer, is used for coming from said first separation signal and said second separation signal of raising frequency, to select one of which according to a selection signal, and exports signal;

One high pass filter is coupled to said commutation circuit, is used for carrying out a high-pass filtering and moves on said output signal, filters the back signal to produce one the 3rd;

One second power divider is coupled to said band pass filter and said high pass filter, is used for merging said first and filters back signal and said the 3rd filtration back signal, to produce a combined signal; And

One low pass filter is coupled to said second power divider, is used for carrying out a LPF and moves on said combined signal, filters the back signal to produce one the 4th.

2. band switching circuit as claimed in claim 1, wherein said first frequency range drops on 250～750MHz, and said second frequency range drops on 950～1450MHz, and said the 3rd frequency range drops on 1650～2150MHz.

3. band switching circuit as claimed in claim 1, the wherein said the 4th filters the back signal comprises said second data-signal that is positioned at said second frequency range and said the 3rd data-signal that is positioned at said the 3rd frequency range.

4. band switching circuit as claimed in claim 1, the wherein said the 4th filters the back signal comprises said second data-signal that is positioned at said second frequency range and said first data-signal that is positioned at said the 3rd frequency range.

5. band switching circuit as claimed in claim 1 also comprises a microcontroller, is coupled to said commutation circuit and said local oscillator, is used to provide said selection signal and gives said commutation circuit, and provide a power supply to said local oscillator.

6. band switching circuit as claimed in claim 5, wherein said first power divider, said local oscillator, said frequency mixer, said commutation circuit and said microcontroller are arranged on the same integrated circuit.

7. band switching circuit as claimed in claim 1, said band switching circuit are applied in the satellite TV system, and wherein said reduced frequency input signal is a reduced frequency satellite-signal.

8. band switching circuit; In order to receive a reduced frequency input signal; Said reduced frequency input signal comprises one first data-signal that is positioned at one first frequency range, one the 3rd data-signal that is positioned at one second data-signal of one second frequency range and is positioned at one the 3rd frequency range; And said the 3rd frequency range is higher than said second frequency range and said second frequency range is higher than said first frequency range, and said band switching circuit comprises:

One band pass filter is used for carrying out a bandpass filtering and moves on said reduced frequency input signal, filters the back signal to produce one first, and wherein said first filters the back signal comprises said second data-signal that is positioned at said second frequency range;

One band stop filter; Being used for carrying out a bandreject filtering moves on said reduced frequency input signal; Filter the back signal to produce one second, wherein said second filters the back signal comprises said first data-signal that is positioned at said first frequency range and said the 3rd data-signal that is positioned at said the 3rd frequency range;

One first power divider is coupled to said band stop filter, is used for filtering the back signal according to said second and produces one first separation signal and one second separation signal;

One local oscillator is used to provide a local oscillated signal;

One frequency mixer is coupled to said first power divider and said local oscillator, is used for adjusting according to said local oscillated signal the frequency of said second separation signal, to produce raising frequency second separation signal;

One switches circuit, is coupled to said first power divider and said frequency mixer, is used for coming from said first separation signal and said second separation signal of raising frequency, to select one of which according to a selection signal, and exports signal;

One high pass filter is coupled to said commutation circuit, is used for carrying out a high-pass filtering and moves on said output signal, filters the back signal to produce one the 3rd; And

One second power divider is coupled to said band pass filter and said high pass filter, is used for merging said first and filters back signal and said the 3rd filtration back signal, to produce a combined signal.

9. band switching circuit as claimed in claim 8, wherein said first frequency range drops on 250～750MHz, and said second frequency range drops on 950～1450MHz, and said the 3rd frequency range drops on 1650～2150MHz.

10. band switching circuit as claimed in claim 8 also comprises a microcontroller, is coupled to said commutation circuit and said local oscillator, is used to provide said selection signal and gives said commutation circuit, and provide a power supply to said local oscillator.

11. band switching circuit as claimed in claim 10, wherein said first power divider, said local oscillator, said frequency mixer, said commutation circuit and said microcontroller are arranged on the same integrated circuit.

12. band switching circuit as claimed in claim 8, said band switching circuit are applied in the satellite TV system, wherein said reduced frequency input signal is a reduced frequency satellite-signal.

13. band switching circuit as claimed in claim 12, said band switching circuit are a B band switching circuit.

14. a satellite TV system comprises:

One lnb; In order to receive a satellite-signal; And carry out frequency reducing and amplify to produce a reduced frequency satellite-signal; Said reduced frequency satellite-signal comprises one first data-signal that is positioned at one first frequency range, one the 3rd data-signal that is positioned at one second data-signal of one second frequency range and is positioned at one the 3rd frequency range, and said the 3rd frequency range is higher than said second frequency range and said second frequency range is higher than said first frequency range;

One band switching circuit is coupled to said lnb, and in order to receive said reduced frequency satellite-signal, said band switching circuit comprises:

One band pass filter is used for carrying out a bandpass filtering and moves on said reduced frequency satellite-signal, filters the back signal to produce one first, and wherein said first filters the back signal comprises said second data-signal that is positioned at said second frequency range;

One band stop filter; Being used for carrying out a bandreject filtering moves on said reduced frequency satellite-signal; Filter the back signal to produce one second, wherein said second filters the back signal comprises said first data-signal that is positioned at said first frequency range and said the 3rd data-signal that is positioned at said the 3rd frequency range;

One first power divider is coupled to said band stop filter, is used for filtering the back signal according to said second and produces one first separation signal and one second separation signal;

One local oscillator is used to provide a local oscillated signal;

One frequency mixer is coupled to said first power divider and said local oscillator, is used for adjusting according to said local oscillated signal the frequency of said second separation signal, to produce raising frequency second separation signal;

One switches circuit, is coupled to said first power divider and said frequency mixer, is used for coming from said first separation signal and said second separation signal of raising frequency, to select one of which according to a selection signal, and exports signal;

One high pass filter is coupled to said commutation circuit, is used for carrying out a high-pass filtering and moves on said output signal, filters the back signal to produce one the 3rd;

One second power divider is coupled to said band pass filter and said high pass filter, is used for merging said first and filters back signal and said the 3rd filtration back signal, to produce a combined signal; And

One low pass filter is coupled to said second power divider, is used for carrying out a LPF and moves on said combined signal, filters the back signal to produce one the 4th; And

One satellite Integrated Receive Decoder is coupled to said band switching circuit, in order to receive said the 4th filtration back signal and to decode.

15. satellite TV system as claimed in claim 14 also comprises:

One variable connector device; Be coupled between said lnb and the said band switching circuit; Have a plurality of input ports and a plurality of output port; Said a plurality of input port is used for receiving said reduced frequency satellite-signal and a plurality of signal of video signal and merges to produce one and merges back reduced frequency satellite-signal, and one of them distributes to said band switching circuit with said merging back reduced frequency satellite-signal said a plurality of output ports.

16. satellite TV system as claimed in claim 14, wherein said first frequency range drops on 250～750MHz, and said second frequency range drops on 950～1450MHz, and said the 3rd frequency range drops on 1650～2150MHz.

17. satellite TV system as claimed in claim 14, the wherein said the 4th filters the back signal comprises said second data-signal that is positioned at said second frequency range and said the 3rd data-signal that is positioned at said the 3rd frequency range.

18. satellite TV system as claimed in claim 14, the wherein said the 4th filters the back signal comprises said second data-signal that is positioned at said second frequency range and said first data-signal that is positioned at said the 3rd frequency range.

19. satellite TV system as claimed in claim 14 also comprises a microcontroller, is coupled to said commutation circuit and said local oscillator, is used to provide said selection signal and gives said commutation circuit, and provide a power supply to said local oscillator.

20. satellite TV system as claimed in claim 19, wherein said first power divider, said local oscillator, said frequency mixer, said commutation circuit and said microcontroller are arranged on the same integrated circuit.

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