Abstract:
A duplexer, applying in a cable modem, comprises a first mixer, a band-pass filter and a second mixer, in order to filter MoCA interference signal of downstream signals, a series of steps are carried out, which comprising up-conversion, filtering lower and lower frequency. The duplexer use a synthesizer to provide the local oscillator source to the first mixer and the second mixer according to the channel scan signals and use a channel scan controller to provide the channel scan signal of the local oscillator source to the synthesizer.

Description:
FIELD 
       [0001]    The disclosure relates to cable modem, and particularly to a duplexer and cable modem of using the duplexer. 
       BACKGROUND 
       [0002]    Transmission rates of cable modems based on the DOCSIS3.0 standard has been substantial increased. Furthermore, downstream data transmission band of downstream path has extended from 860 MHz to a 1002 MH. The transmission band is close to Multimedia over Coax Alliance (MoCA), often causing downstream data to be interfered by the MoCA signal. A traditional method of filtering interference signals from the MoCA signal is applied in a LC filter. However, because the frequency band of the downstream path is too close to the frequency band of the MoCA signal and because the filter ability of the LC filter is limited, this results in the interference signal from the MoCA signal not being effectively filtered. Special high-frequency portions of the cable modem downstream data (near 1002 MHz) are still susceptible to interfering MoCA signals, which may lead to an increased data transmission error rate, and may reduces the transmission rate and receiver sensitivity of the cable modem. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0003]    Many aspects of the present embodiments can be better understood with reference to the tracking drawing. The components in the drawing are not necessarily drawn to scale, the emphasis instead being placed upon clearly illustrating the principles of the present embodiments. Moreover, in the drawing, all the views are schematic, and like reference numerals designate corresponding parts throughout the several views. 
           [0004]    A schematic diagram of one embodiment of a cable modem comprises a duplexer as disclosed. 
       
    
    
     DETAILED DESCRIPTION 
       [0005]    The disclosure is illustrated by way of example and not by way of limitation in the figures of the accompanying drawings in which like references indicate similar elements. It should be noted that references to “an” or “one” embodiment in this disclosure are not necessarily to the same embodiment, and such references mean “at least one.” 
         [0006]    The word “module” as used hereinafter, refers to logic embodied in hardware or firmware, or to a collection of software instructions, written in a programming language, such as, for example, JAVA, C, or assembly. One or more software instructions in the modules may be embedded in firmware such as in an EPROM. It will be appreciated that modules may comprise connected logic units, such as gates and flip-flops, and may comprise programmable units, such as programmable gate arrays or processors. The modules described herein may be implemented as either software and/or hardware modules and may be stored in any type of computer-readable medium or other computer storage device. 
         [0007]      FIG. 1  is a schematic diagram of one embodiment of a cable modem  100  comprising a duplexer  10  as disclosed. In one embodiment, the duplexer  10  can include a downstream data channel TX and a upstream data channel RX. The downstream data channel TX includes a first mixer  11 , a band-pass filter  12 , a second mixer  13 , a synthesizer  14  and a channel scan controller  15 . In one embodiment, the cable modem  100  is based on DOCSIS3.0 standard, and a downstream data transmission band of downstream data channel TX can reach 1002 MHz. 
         [0008]    The first mixer  11  up-converts a downstream signal to obtain a first mixed signal and transmits the first mixed signal to the band-pass filter  12 . In one embodiment, a frequency of the downstream signal is defined as F 1 +n*F 0 . A frequency of the first mixed signal is F 1 +F 2 +(m+n)*F 0 , F 1 , F 2  and F 0  are all preset frequency values, where each of m and n is a constant. 
         [0009]    The band-pass filter  12  is connected between the first mixer  11  and the second mixer  13 . The band-pass filter  12  is used for receiving the first mixed signal and filtering interference signals from the mixed signal to obtain a second mixed signal and transmitting the second mixed signal to the second mixer  13 . The second mixed signal is the mixed signal of having filtered the interference signals. In one embodiment, the interference signals of the mixed signal includes a MoCA signal located from 1125 MHz to 1525 MHz. The band-pass filter  12  is a surface acoustic wave (SAW) filter and a center frequency of the band-pass filter  12  is preset as F 1 +F 2 +(m+n)*F 0 . 
         [0010]    The second mixer  13  receives the second mixed signal and reduces a frequency of the second mixed signal to the frequency of the downstream signal to obtain a third mixed signal and transmits the third mixed signal to a modem unit  20  of the cable modem  100  to demodulate. In one embodiment, the third mixed signal is the mixed signal that the frequency of the second mixed signal has reduced to the frequency of the downstream signal, the modem unit  20  demodulates the third mixed signal and transmits to respective external device ( FIG. 1  is not showed). 
         [0011]    The synthesizer  14  is connected to the first mixer  11  and the second mixer  13 , and provides a local oscillator source for the first mixer  11  and the second mixer  13  as needed. 
         [0012]    The first mixer  11  up-converts the frequency (e.g. F 1 +n*F 0 ) of the downstream signal according to the local oscillator source. The second mixer  13  reduces the frequency of the second mixed signal to frequency of the downstream signal according to the local oscillator source. In one embodiment, the frequency of the downstream signal is F 1 +n*F 0 , the frequency of the local oscillator source is F 2 +m*F 0 , F 2  is a preset value, m valued in a preset range parameter. In order to avoid being close to frequency of the MoCA signal, the frequency of the local oscillator source needs to be preset a rational value. 
         [0013]    The channel scan controller  15  is connected to the synthesizer  14  and provides channel scan signal to the synthesizer  14 , and makes the synthesizer  14  provide the local oscillator source to the first mixer  11  and the second mixer  13  according to the channel scan signal. In one embodiment, the channel scan signal is the m of the local oscillator source F 2 +m*F 0 , the range of the channel scan signal is from 0 to 148. 
         [0014]    If the frequency of the downstream signal is F 1 +n*F 0 , m is 148-n, the synthesizer  14  transmits the frequency of the local oscillator source F 2 +(148-n)*F 0  to the first mixer  11  and the second mixer  13 , then the frequency of the third mixed signal is F 1 +F 2 +148 F 0  and filtered by the band-pass filter  12 . 
         [0015]    Furthermore, the cable modem  100  also can be connected to a RF coaxial connector  200 . The upstream data channel RX includes a low-pass filter (LPF). The LPF is used for filtering the upstream signal received by the upstream data channel RX, then the filtered signal by the LPF is transmitted by the RF coaxial connector  200 . 
         [0016]    The foregoing disclosure of the various embodiments has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the present disclosure to the precise forms disclosed. Many variations and modifications of the embodiments described herein will be apparent to one of ordinary skill in the art in the light of the above disclosure. The scope of the present disclosure is to be defined only by the claims appended hereto and their equivalents.