Abstract:
A loading-adjustable RF switch matrix circuit includes a first output unit for selectively outputting at least one RF signal, at least one signal switching module, and a detecting module coupled to the first output unit and the signal switching module. The signal switching module includes a first loading unit for adjusting the loading of the RF switch matrix circuit; a first switch unit coupled to the RF signal, the first loading unit and the first output unit for controlling the RF signal coupled to the first loading unit or the first output unit. If the detecting module detects that the first output unit is not coupled to a first external device, the first switch unit couples the RF signal to the first loading unit.

Description:
BACKGROUND OF INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to an RF switch matrix circuit and driving method thereof, and more particularly, to a loading-adjustable RF switch matrix circuit and driving method thereof.  
         [0003]     2. Description of the Prior Art  
         [0004]     Due to the rapid development of wireless communication systems, wireless devices offering great convenience are widely used in daily communications. With wireless devices, people are able to exchange information, share experiences, and communicate with each other anytime and anywhere. Because of the wide usage of wireless devices, a broad range of new wireless products are being developed. As indicated by Brunner, et al. in U.S. Pat. No. 5,754,118, an RF switch matrix is applied to wireless communication such as digital satellite broadcasting (DSB) and digital video broadcasting (DVB).  
         [0005]     Please refer to  FIG. 1 .  FIG. 1  is a schematic diagram of a prior art RF switch matrix circuit. The RF switch matrix circuit  100  is a 4×2 RF switch matrix circuit comprising: a plurality of switches  100   a ; a plurality of input nodes IN-A, IN-B, IN-C and IN-D; and a plurality of output nodes OUT- 1  and OUT- 2 . A plurality of RF signals RF a , RF b , RF c , and RF d  are inputted into the input nodes IN-A, IN-B, IN-C and IN-D respectively, and then chosen by the plurality of switches  100   a . The RF signal RF 1  of output node OUT- 1  could be one of the RF signals RF a , RF b , RF c , or RF d . The other RF signal RF 2  of output node OUT- 2  could be one of the RF signals RF a , RF b , RF c , or RF d . Generally speaking, the output nodes OUT- 1  or OUT- 2  in the RF switch matrix circuit  100  can further be coupled to the outside set-top box (STB) through outside amplifiers.  
         [0006]     For the RF switch matrix circuit  100 , the STB can be taken as a loading resistance having a specific impedance such as 75 ohms. When one of the output nodes OUT- 1  or OUT- 2  does not couple to the outside STB, the output loading of the RF switch matrix circuit  100  will change. This change of output loading will further affect the plurality of switches  100   a  inside the RF switch matrix circuit  100 , and finally cause bad isolation between the plurality of switches  100   a . For example, if the plurality of switches  100   a  choose RF signals RF a  and RF d  to become output signals through proper control and a user does not connect an STB to the output node OUT- 1 , the RF signal RF a  will couple to output node OUT- 2  through switches  100   a  inside the RF switch matrix circuit  100 , and therefore interfere with the RF signal RF d  of output node OUT- 2 .  
       SUMMARY OF INVENTION  
       [0007]     One objective of the claimed invention is therefore to provide an RF switch matrix circuit and driving method of adjusting an inner circuit to control loading when the outside loading changes, to solve the above-mentioned problems.  
         [0008]     According to an exemplary embodiment of the claimed invention, a loading-adjustable RF switch matrix circuit is disclosed comprising a first output unit for selectively outputting at least one RF signal; at least one signal switching module; and a detecting module coupled to the first output unit and the signal switching module. The signal switching module comprises a first loading unit for adjusting the loading of the RF switch matrix circuit; and a first switch unit coupled to the RF signal, the first loading unit, and the first output unit, for controlling the RF signal to connect to the first loading unit or the first output unit. If the detecting module detects the first output unit does not connect to the first outside device, the first switch unit will couple the RF signal to the first loading unit.  
         [0009]     According to another exemplary embodiment of the claimed invention, a driving method is disclosed. The RF switch matrix circuit comprises a first output unit for selectively outputting at least one RF signal. The driving method comprises the following steps: providing a first loading unit for adjusting the loading of the RF switch matrix circuit; and detecting whether the first output unit connects to a first outside device. If the detecting result is that the first output unit does not connect to the first outside device, the RF signal will couple to the first loading unit rather than the first output unit.  
         [0010]     The present invention RF switch matrix circuit has a plurality of loading units. When one of the output units of the RF switch matrix circuit does not connect to an outside device, the RF signal originally coupled to an output unit through a switch unit will couple to a loading unit through a switch unit. This can avoid the bad isolation from outside loading change. Therefore the present invention RF switch matrix circuit can substantially improve the quality of output signals.  
         [0011]     These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings. 
     
    
     BRIEF DESCRIPTION OF DRAWINGS  
       [0012]      FIG. 1  is a schematic diagram of a prior art RF switch matrix circuit.  
         [0013]      FIG. 2  is a circuit diagram of a RF switch matrix circuit according to an embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION  
       [0014]     Please refer to  FIG. 2 .  FIG. 2  shows a circuit diagram of an RF switch matrix circuit according to an embodiment of the present invention. In this embodiment, the RF switch matrix circuit  200  is a 4×2 RF switch matrix circuit, which can be applied to wireless communication systems such as digital satellite broadcasting (DSB) and digital video broadcasting (DVB). Please note that the above mentioned 4×2 RF switch matrix circuit is one embodiment, and the present invention is not limited to 4×2 RF switch matrix circuits. For example, it can also be applied to a 4×4 RF switch matrix circuit. The RF switch matrix circuit  200  comprises: a plurality of signal switching modules  202 ,  204 ,  206  and  208 ; a plurality of output units  210  and  212 ; a detecting module  214 ; and a 4:16 decoder  216 . The signal switching modules  202 ,  204 ,  206  and  208  all have the same circuit function and structure. The signal switching module  202  comprises a plurality of switch units  222  and  224 , and a plurality of loading units  226  and  228 . The signal switching module  204  comprises a plurality of switch units  232  and  234 , and a plurality of loading units  236  and  238 . The signal switching module  206  comprises a plurality of switch units  242  and  244 , and a plurality of loading units  246  and  248 . Finally, the signal switching module  208  comprises a plurality of switch units  252  and  254 , and a plurality of loading units  256  and  258 . Additionally, as shown in  FIG. 2 , in this embodiment the RF switch matrix circuit  200  utilizes an amplifier to apply to output units  210  and  212 , and utilizes a resistance to apply to loading units  226 ,  228 ,  236 ,  238 ,  246 ,  248 ,  256  and  258 . The function of each element in the RF switch matrix circuit  200  is detailed below.  
         [0015]     Signal switching modules  202 ,  204 ,  206  and  208  selectively couple the RF signals RF a , RF b , RF c  and RF d  to output units  210  and  212  or to loading units  226 ,  228 ,  236 ,  238 ,  246 ,  248 ,  256  and  258 . Loading units  226 ,  228 ,  236 ,  238 ,  246 ,  248 ,  256  and  258  are then utilized to adjust loading of the RF switch matrix circuit  200  to improve the isolation of switch units  222 ,  224 ,  232 ,  234 ,  242 ,  244 ,  252  and  254  when outside loading changes. The detailed description will be discussed later. A 4:16 decoder  216  is utilized to control signal switching modules  202 ,  204 ,  206  and  208  to choose two of the RF signals RF a , RF b , RF c  or RF d  to couple to output units  210  and  212  according to the plurality of selecting signals S 1 , S 2 , S 3  and S 4 . If the outputs of output units  210  and  212  connect to an outside device such as the STB, the output units  210  and  212  can get bias voltages V 1 , and V 2  from the corresponding outside devices. In other words, bias voltages V 1 , and V 2  can enable output units  210  and  212  to amplify the selected RF signals to output RF signals RF 1  and RF 2  to the outside device. The detecting module  214  is coupled to output units  210  and  212  to detect whether bias voltages V 1 , and V 2  exist in output units  210  and  212  to determine if outside devices (not shown) are connected to the RF switch matrix circuit  200 . As mentioned above, the needed bias voltages V 1 , and V 2  of output units  210  and  212  are applied by outside devices. For example, if the detecting module  214  does not successfully detect the existence of bias voltage V 1 , the detecting module  214  then determines that the output of output unit  210  does not connect to one of the outside devices.  
         [0016]     The function of the RF switch matrix circuit  200  is now described in greater depth. If the RF switch matrix circuit  200  only selects RF signal RF a  from RF signals RF a , RF b , RF c  and RF d  to be the output signal, the 4:16 decoder  216  drives switch units  222  and  224  to make RF signal RF a  able to connect to both output units  210  and  212  through switch units  222  and  224  according to selecting signals S 1 , S 2 , S 3  and S 4 . The other switch units  232 ,  234 ,  242 ,  244 ,  252  and  254  couple RF signals RF b , RF c  and RF d  to corresponding loading units  236 ,  238 ,  246 ,  248 ,  256  and  258 . Take switch unit  222  as an example; node A and node B connect to each other at this moment. When the output of output unit  220  connects to an outside device and the output of output unit  210  does not connect to an outside device, the detecting module  214  detects that the bias voltage V 1 , of output unit  210  is smaller than a predetermined value. Therefore, when the bias voltage V 1 , of output unit  210  is near ground level, the detecting module  214  determines the output of output unit  210  does not connect to an outside device. If the detecting module  214  detects that the bias voltage of output unit  220  is larger than a predetermined value, when the bias voltage V 1 , of output unit  210  is near to the supply voltage of the outside device, the detecting module  214  determines the output of output unit  220  connects to an outside device. At the same time, the detecting module  214  has determined the output of output unit  210  does not connect to an outside device, so the detecting module  214  outputs a detecting signal to switch unit  222 , which corresponds to the output unit  210  selected by the 4:16 decoder  216 , in order to drive the switch unit  222  coupling RF signal RF a  to loading unit  226 . To switch unit  222 , node A and node C connect to each other at this moment.  
         [0017]     In this embodiment, loading units  226 ,  228 ,  236 ,  238 ,  246 ,  248 ,  256  and  258  are all resistances, and their resistance values correspond with the outside device connected to the RF switch matrix circuit  200 . In other words, to the RF switch matrix circuit  200 , if the equivalent impedance of the outside device is 75 ohms, loading units  226 ,  228 ,  236 ,  238 ,  246 ,  248 ,  256  and  258  are implemented with a resistance whose value is 75 ohms. When the output of output unit  210  does not actually connect to an outside device, the loading unit  226  is utilized to be an outside device to provide a proper impedance for improving the isolation of switch unit  222  when outside loading changes. In other words, when switch unit  222  couples the RF signal RF a  to the loading unit  226 , the RF signal RF a  flowing through switch unit  222  does not interference with another RF signal RF a  flowing through output unit  212 .  
         [0018]     Looking at another operation example, if the RF switch matrix circuit  200  selects RF signals RF a  and RF c  from RF signals RF a , RF b , RF c  and RF d  to be output signals, the 4:16 decoder  216  drives switch units  222  and  244  to make the RF signals RF a  and RF c  able to connect switch units  222  and  244  to output units  210  and  212  respectively, according to selecting signals S 1 , S 2 , S 3  and S 4 . The other switch units  224 ,  232 ,  234 ,  242 ,  252  and  254  couple RF signals RF a , RF b , RF c  and RF d  to corresponding loading units  228 ,  236 ,  238 ,  246 ,  256  and  258 .  
         [0019]     However, when the outputs of output units  220  and  210  do not actually connect to an outside device, the detecting module  214  will detect that the bias voltage of the output unit  210  is near ground level. Because the detecting module  214  determines the output of output unit  210  does not connect to an outside device at this moment, the detecting module  214  will output a detecting signal to switch unit  222 , which corresponds to the output unit  210  selected by the 4:16 decoder  216 , for driving switch unit  222  to couple the RF signal RF a  to the loading unit  226 . The loading unit  226  is utilized to be an outside device to provide a proper impedance for improving the isolation of switch unit  222  when outside loading changes. In other words, when switch unit  222  couples the RF signal RF a  to the loading unit  226 , the RF signal RF a  flowing through switch unit  222  does not interfere with another RF signal RF a  flowing through output unit  212 .  
         [0020]     Please note that the other operations of switch units  232 ,  234 ,  244 ,  252  and  254  are the same as the above mentioned switch unit  226 ,  224  and  242 . They all couple RF signals RF a , RF b , RF c  and RF d  to the corresponding loading units  236 ,  238 ,  248 ,  256  and  258  according to the detecting signal of the detecting module  214 . Further discussion is omitted for the sake of brevity.  
         [0021]     Compared with the prior art, the present invention RF switch matrix circuit has a plurality of loading units. When one of the output units of the RF switch matrix circuit does not connect to an outside device, the RF signal originally coupled to an output unit through a switch unit will couple to a loading unit through a switch unit. This can avoid bad isolation from outside loading changing. Therefore the present invention RF switch matrix circuit can substantially improve the quality of output signals.  
         [0022]     Those skilled in the art will readily observe that numerous modifications and alterations of the device and method may be made while retaining the teachings of the invention. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of the appended claims.