This application claims the benefit of Taiwan application Serial No. 107103693, filed Feb. 1, 2018, the subject matter of which is incorporated herein by reference.
The invention relates to a satellite television, and more particularly to a user-terminal television signal receiving apparatus in a frequency division full-duplex satellite television system.
A dish antenna for satellite television is usually shared by multiple television sets in a same building.
If a frequency division full-duplex system structure is used, following signals are configured to be simultaneously transmitted at different frequency bands through the cable 130: television signals sent by the front-end circuit 120 to the television signal receiving apparatus 140, communication signals (e.g., informing the television signal receiving apparatus 140 of an exclusive frequency band the television signals belongs to or the foregoing system related information after the television signal receiving apparatus 140 has been activated) sent by the dish antenna 110 to the television signal receiving apparatus 140, and request signals (e.g., the foregoing registration request or channel selection request) sent by the television signal receiving apparatus 140 to the dish antenna 110. For example, in a current satellite television system, the television signals sent by the front-end circuit 120 are carried in a frequency band near 1 GHz, the communication signals sent by the dish antenna 110 to the television signal receiving apparatus 140 are carried in a frequency band near 6.5 MHz, and the request signals sent by the television signal receiving apparatus 140 to the dish antenna 110 are carried in a frequency band near 4.5 MHz. An example using the above frequency allocation is described below.
A diplexer 142, a command parsing circuit 143 and a television signal parsing circuit 144 are a receiving circuit in the television signal receiving apparatus 140. The diplexer 142 may be considered as including two band-pass filters (BPF) 142A and 142B, which respectively keep a 6.5 MHz analog communication signal to the command parsing circuit 143 and a 1 GHz analog television signal provided to the television signal processing circuit 144. The 6.5 MHz analog communication signal entering the command parsing circuit 143 is sequentially converted to a digital signal by an analog-to-digital converter (ADC) 143A, down-converted to a baseband signal by a first frequency down conversion circuit 143B, filtered by a low-pass filter 143C to remove high-frequency noise, and undergoes content parsing by a decoder 143D. The 1 GHz analog television signal entering the television signal processing circuit 144 is first down-converted to a baseband signal by a second frequency down conversion circuit 144A, converted to a digital signal by an ADC 144B, and undergoes other image processing processes.
Among the three types of signals transmitted through the cable 130, the carrier frequency of the television signals is higher, whereas the carrier frequencies of the communication signals and the request signals are lower and are close to each other. As shown in
The invention is directed to a circuit structure for a television signal receiving to solve the above issues.
A television signal receiving apparatus cooperating with a front-end circuit in a frequency division full-duplex satellite television system is provided according to an embodiment of the present invention. The front-end circuit provides a television signal and a communication signal. The television signal receiving apparatus includes a request generating circuit, a command parsing circuit and a television signal processing circuit. The request generating circuit includes an information processing circuit, a mixer, a digital-to-analog conversion circuit and a multi-node low-pass filter (LPF). The information processing circuit generates a string of data bits representing a request signal. The mixer mixes the string of data bits to generate a mixing result. The digital-to-analog conversion circuit performs digital-to-analog conversion on the mixing result to generate an analog request signal. The multi-node LPF has a first terminal, a second terminal and a third terminal. The first terminal receives the analog request signal, the second terminal is electrically coupled to the command parsing circuit, and the third terminal is electrically coupled to the front-end circuit. The multi-node LPF filters out high-frequency signals coupled from the first terminal and the third terminal to the second terminal, and further filters out high-frequency signals coupled from the first terminal to the third terminal. A cut-off frequency of the multi-node LPF is associated with a frequency of the analog request signal and a frequency at which the front-end circuit provides the communication signal. The command parsing circuit is electrically coupled to the second terminal of the multi-node LPF, receives a filtered signal from the second terminal, and processes and parses the filtered signal. The television signal processing circuit receives and processes the television signal from the front-end circuit.
The above and other aspects of the invention will become better understood with regard to the following detailed description of the preferred but non-limiting embodiments. The following description is made with reference to the accompanying drawings.
It should be noted that, the drawings of the present invention include functional block diagrams of multiple functional modules related to one another. These drawings are not detailed circuit diagrams, and connection lines therein are for indicating signal flows only. The interactions between the functional elements/or processes are not necessarily achieved through direct electrical connections. Further, functions of the individual elements are not necessarily distributed as depicted in the drawings, and separate blocks are not necessarily implemented by separate electronic elements.
The television signal receiving apparatus 300 is connected to a front-end circuit (e.g., the circuit 120 in
The request generating circuit 310 includes an information processing circuit 311, a mixer 312, a digital-to-analog conversion circuit 313, and a multi-node low-pass filter (LPF) 314. When a request is to be sent to the front-end circuit, the information processing circuit 311 provides a string of data bits representing the request signal to the mixer 312 and to the digital-to-analog conversion circuit 313 to generate an analog request signal carried at 4.5 MHz. As shown in
Thus, the cut-off frequency of the multi-node LPF 314 may be determined according to the frequency of the request signal (from the digital-to-analog conversion circuit 313) and the frequency of the communication signal (from the front-end circuit to the television signal receiving apparatus 300). In an example where the frequency of the request signal is 4.5 MHz and the frequency of the communication signal is 6.5 MHz, the cut-off frequency of the multi-node LPF 314 may be set to block signals higher than 8 MHz from coupling to the second node T2 and the third node T3.
As shown in
Under the effect of the multi-node LPF 314, the signal ST2 at the second node T2 does not include the television signal sent by the front-end circuit to the television signal receiving apparatus 300. However, the signal ST2 nonetheless includes two carrier signals, which are respectively the request signal carried at 4.5 MHz and the communication signal carried at 6.5 MHz. The first down conversion circuit 332 down converts by means of mixing according to the carrier frequency (6.5 MHz) of the communication signal, such that the communication signal in the signal ST2 is shifted to around the baseband (having a 0 frequency) and 13 (=6.5+6.5) MHz on the spectrum. On the other hand, the 4.5 MHz request signal in the signal ST2 is shifted to around −2 (=4.5-6.5) MHz and 11 (=4.5+6.5) MHz on the spectrum. To obtain the baseband communication signal after the frequency down conversion, the digital LPF 333 needs to filter out the above signals at −2 MHz, 11 MHz and 13 MHz, particularly the −2 MHz signal, which is closest to the baseband. It is seen from the above description that, the cut-off frequency of the digital LPF 333 is associated with a frequency difference between the request signal and the communication signal. In practice, the number of taps of the digital LPF 333 may be appropriately set to reinforce the attenuation effect on the −2 MHz signal.
On the other hand, the BPF 320 filters the signals to provide the 1 GH television signal to the television signal processing circuit 340. The television signal carried at 1 GHz inputted to the television signal processing circuit 340 is sequentially shifted to baseband by a second down conversion circuit 341, and then is converted to a digital signal by an analog-to-digital conversion circuit 342, and undergoes other image processing processes. It should be noted that, the image processing procedure of the television signal is common knowledge to one person skilled in the art, and shall be omitted herein.
As seen from the above embodiments, it is not necessary to apply diplexer in the television signal receiving apparatus 300 as in the prior art. Instead, it is configured to have the request generating circuit 310 and the command parsing circuit 330 share one multi-node LPF. Thus, the television signal receiving apparatus 300 eliminates the issue a diplex implemented by a costly chip of the prior art.
While the invention has been described by way of example and in terms of the preferred embodiments, it is to be understood that the invention is not limited thereto. On the contrary, it is intended to cover various modifications and similar arrangements and procedures, and the scope of the appended claims therefore should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements and procedures.
Number | Date | Country | Kind |
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107103693 | Feb 2018 | TW | national |