Abstract:
A termination/attenuation network applies to an input of a set-top box a MOCA channel signal having a narrow band of frequencies and included in RF signals having a wide band of frequencies received via a cable from a satellite antenna. The network includes a pair of series resistors and a parallel resistor coupled to a junction terminal between the pair of series resistors in a T-shaped configuration. A series-pass band-pass filter (L1, C2) bypasses the pair of series resistors and a parallel band stop filter (L 2,  C 1 ) decouples the parallel resistor at the frequency band of the MOCA channel signal for selectively reducing attenuation at the frequency band of the MOCA channel signal.

Description:
FIELD OF THE INVENTION 
       [0001]    The invention relates to a radio frequency (RF) filter forming a termination. 
       BACKGROUND OF THE INVENTION 
       [0002]    Many home entertainment devices not only include the capability to communicate with other devices in a home network but also include the ability to receive and/or process available media content from a plurality of sources, including a plurality of providers. The sources and providers may include, but are not limited to, satellite service, cable service, and free to home over the air terrestrial service. The services may operate in the same or different radio frequency (RF) ranges and may use the same or different transmission formats or protocols. The devices for receiving the services often include, but are not limited to, set-top boxes, gateways, televisions, home computers, and the like. 
         [0003]    The operation of home entertainment devices is further complicated by the inclusion of home networking functions in the devices. Many of these devices use a home networking that shares the transmission medium such as cable with the incoming transmission system from the service providers. One such example is a multimedia over cable alliance (MOCA) home network system that operates from an RF signal provided by a cable in a frequency spectrum of 950 MHz-1050 MHz. The frequency spectrum, 950 MHz-1050 MHz, is unused by the other signal transmission systems. Examples of other signal transmission systems would be satellite down link frequencies from 1250 to 2150 MHz, broadcast television from 174 to 805 MHz and certain control frequencies from 2.3 to 2.4 MHz that are all contained in the same cable together with the MOCA RF signal. 
         [0004]    Return loss is a measurement of how well the impedance of a load, including, for example, a filter that is driven from the signal contained in the cable, is matched to the characteristic impedance of the cable. The return loss is a number associated with a corresponding interface that is calculated from the reflection caused at the corresponding interface as a result of an impedance mismatch. The return loss is usually expressed as a ratio in decibels (dB). 
         [0005]    The above mentioned filter may be a band-pass filter that passes the MOCA band signals and blocks the passage of signals at frequencies outside the MOCA band contained in the same cable along with the MOCA band signals. It may be desirable to avoid significant input return loss with respect to each signal that is contained in the same cable containing the MOCA band signals. Ideally, it may be desirable to provide a termination to the cable, for example, 75 ohms that matches the characteristic impedance of the cable for each signal within the frequency spectrum that is contained in the same cable including the MOCA band signals. 
         [0006]    Typical practice is to design diplex, triplex or higher order L-C filters to divide the frequency bands. A corresponding termination such as a 75 ohm resistor would be coupled to an output of each of the filters. However, these filters are complex having a relatively large number of parts and require a corresponding filter for each of the frequency bands of the corresponding RF signals, not just for the RF signal at the band such as MOCA. 
         [0007]    It is also well known to utilize a resistive network commonly referred to as “pad” for providing a terminating resistance over a wide frequency band. For example, a 6 dB pad will provide a −12 dB or better return loss S 11  even in the extreme case in which an output terminal of the pad is either an open or short circuit. However, utilizing such a resistive pad downstream the input of a receiver would, undesirably, degrade the noise figure by 6 dB. 
         [0008]    In carrying out an advantageous feature, the 6 dB pad is supplemented with relatively simple band-pass filter such that the desired frequency band, for example, of the MOCA home network system can be subjected, advantageously, to lower attenuation while RF signals at the range of frequencies that excludes the MOCA band are attenuated more and terminated with the resistive pad that provides improved impedance matching. 
       SUMMARY 
       [0009]    An advantageous termination network coupled in operation to an input of a band-pass filter includes a first resistor coupled to a second resistor to form a voltage divider for voltage dividing a first radio frequency (RF) input signal that is applied to the filter input. It also includes a first resonant circuit responsive to the first RF input signal for controlling a magnitude of a second RF input signal developed at the filter input. The magnitude of the second RF input signal is controlled in a manner to increase the second RF input signal, when the first RF input signal is at a resonant frequency of the first resonant circuit, relative to when the first RF input signal is outside a range of frequencies that includes the resonant frequency. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]      FIG. 1  illustrates a home network that includes a band-pass filter/termination, embodying advantageous aspects; 
           [0011]      FIG. 2  illustrates a detailed schematics of a first embodiment of the band-pass filter/termination of  FIG. 1 ; 
           [0012]      FIG. 3  illustrates a graph showing the selectivity or S-parameter S 21  of a stand-alone band-pass filter that is included in the band-pass filter/termination of  FIG. 2 ; 
           [0013]      FIG. 4  illustrates a graph showing the return loss or S-parameter S 11  of a stand-alone band-pass filter that is included in the band-pass filter/termination of  FIG. 2 ; 
           [0014]      FIG. 5  illustrates a graph showing the selectivity or S-parameter S 21  of the band-pass filter/termination of  FIG. 2 ; 
           [0015]      FIG. 6  illustrates a graph showing the return loss or S-parameter S 11  of the band-pass filter/termination of  FIG. 2 ; 
           [0016]      FIG. 7  illustrates a detailed schematics of a second embodiment of the band-pass filter/termination of  FIG. 1 ; 
           [0017]      FIG. 8  illustrates a graph showing the selectivity or S-parameter S 21  of the band-pass filter/termination of  FIG. 7 ; and 
           [0018]      FIG. 9  illustrates a graph showing the return loss or S-parameter S 11  of the band-pass filter/termination of  FIG. 7 . 
       
    
    
     DETAILED DESCRIPTION 
       [0019]      FIG. 1  illustrates a block diagram of an embodiment of a system  100  for providing home entertainment media content in a home, or end user, network. The media content, originating from a content provider, is provided through an external network receiving device  130  and also through an external network receiving device  120  to a hybrid coupler or combiner  110 . The media content may be provided using any one of the standard transmission protocols and standards for content delivery (e.g., Advanced Television Systems Committee (ATSC) A/53, digital video broadcast (DVB)-Cable (DVB-C), DVB-Satellite (DVB-S), or DVB-Terrestrial (DVB-T)). For example, external network receiving device  120  receives the media content via a satellite antenna dish  201 . Combiner  110  is also connected to a Multimedia over Cable Alliance (MOCA) network device  140  via a radio frequency (RF) transmission line  110   a  having a characteristic impedance of, for example, 75 OHM and via a combination of a band-pass filter and a termination network referred to herein as a band-pass filter/termination  115 , embodying an advantageous feature. Combiner  110  may be connected to other devices, not shown, via, for example, an RF transmission line  110   b.    
         [0020]    In particular, combiner  110  provides a routing arrangement for an output signal  120   a  of external network receiving device  120  that is applied to devices in the home or user network such as MOCA device  140  in conjunction with signals that operate in the MOCA network. Combiner  110  is conventional and may include active or passive circuit elements to combine the input signals from the various sources into a corresponding combined output signal in each of transmission lines  110   a  and  110   b,  for example, into a combined output signal Vout in transmission line  110   a.  MOCA device  140  may be controlled by the user to convert one or more of the program content from device  130  or  120  into a MOCA output at the MOCA frequency spectrum of 950 MHz-1050 MHz, in a manner not shown in details, for use with other MOCA devices on the network. The converted MOCA signal, not shown, is applied back to combiner  110  to form an RF signal Vouta at the MOCA frequency spectrum of 950 MHz-1050 MHz. Consequently, combined output signal Vout in transmission line  110   a  also contains RF signal Vouta at the MOCA frequency spectrum of 950 MHz-1050 MHz. As a result, RF signal Vout, as well as other outputs of combiner  110 , such as, for example, those signals, not shown, that are developed on line  110   b,  will also contain all original signals, for example, satellite down link frequencies from 1250 to 2150 MHz, broadcast television frequencies from 174 to 805 MHz and certain control frequencies from 2.3 to 2.4 MHz referred to collectively as a signal Voutb. In addition, signal Vout also contains internally generated MOCA RF signal Vouta. For combiner  110  to function properly, it may be desirable to provide terminating impedance with a value close to the characteristic impedance of the combiner and of the coaxial cables, for example, 75 ohms as mentioned before. 
         [0021]      FIG. 2  illustrates a more detailed circuit diagram of band-pass filter/termination  115  of  FIG. 1 , embodying advantageous features. Similar symbols and numerals in  FIGS. 1 and 2  indicate similar items or functions. In  FIG. 2 , an advantageous termination portion  116  included in band-pass filter/termination  115  includes a first end terminal  304  of a resistor R 1 , referred to herein as an input port  1  of band-pass filter/termination  115 , that is coupled to a signal carrying conductor, not shown, of transmission line  110   a  of  FIG. 1 . In transmission line  110   a  signal Vout that includes signals Vouta and Voutb is developed. Resistor R 1  of  FIG. 2  has a second end terminal forming a junction terminal  302  with a resistor R 3 . A second end terminal of resistor R 3  is coupled in series with a parallel resonant circuit  303  having a second terminal that is coupled to a common conductor G of transmission line  110   a  of  FIG. 1 . Parallel resonant circuit  303  includes an inductor L 2  coupled in parallel with a capacitor C 1 . Thus, resistor R 3  and parallel resonant circuit  303  is tuned to resonate at a frequency, for example, 1000 MHz that is within the MOCA band of frequencies, 950 MHz-1050 MHz, of signal Vouta. Consequently, parallel resonant circuit  303  forms high impedance or a band-stop filter at the frequencies within the MOCA band of frequencies of signal Vouta. As a result, resistor R 3  has only a minimal effect on attenuation of termination band-pass filter/termination  115  at the frequencies within the MOCA band of frequencies of signal Vouta. A resistor R 2  has a first end terminal in common with junction terminal  302 . 
         [0022]    A series resonant circuit  306  includes an inductor L 1  coupled in series with a capacitor C 2 . Series resonant circuit  306  is coupled between a second terminal  305  of resistor R 2  and terminals  304  and in parallel with series coupled resistors R 1  and R 2 . Series resonant circuit  306  is also tuned to resonate at a frequency, for example, 1000 MHz that is within the MOCA band of frequencies, 950 MHz-1050 MHz, of signal Vouta. Consequently, series resonant circuit  306  forms a low impedance or a band-pass filter at the frequencies within MOCA band of frequencies, 950 MHz-1050 MHz, of signal Vouta in a manner to bypass the signal path formed by series coupled resistors R 1  and R 2 . The result is that resistors R 1  and R 2  have only a minimal attenuation effect at the frequencies within the MOCA band of frequencies, 950 MHz-1050 MHz, of signal Vouta. 
         [0023]    Advantageously, series resonant circuit  306  forms high impedance at the frequencies within the frequency spectrum of signal Voutb that excludes MOCA signal Vouta. Thus, with respect to signal Voutb at the frequencies within the frequency spectrum that is non-overlapping with the MOCA band of frequencies, 950 MHz-1050 MHz, of signal Vouta, resistors R 1  and R 2  dominate the impedance formed between terminals  304  and  305  for attenuating signal Voutb. Advantageously, the bypassing effect of series resonant circuit  306  does not significantly diminish the desirable attenuation of signal Voutb. 
         [0024]    On the other hand, parallel resonant circuit  303  forms low impedance at the frequencies within the frequency spectrum of signal Voutb. Thus, with respect to the frequencies within the frequency spectrum of signal Voutb that are non-overlapping with or excluding the MOCA band of frequencies, 950 MHz-1050 MHz, of signal Vouta, resistors R 1  and R 3  form a substantially resistive attenuating voltage divider. The result is that, with respect to signal Voutb, the combination of resistors R 1 , R 2  and R 3  that are coupled in a T-shaped configuration, advantageously, effectively forms a so-called Tee attenuator. Thus, advantageously, signal Vouta is coupled to terminal  305  of  FIG. 2  without being significantly attenuated; whereas, advantageously, non-MOCA signal Voutb that needs to be suppressed at terminal  305  is attenuated by the combination of resistors R 1 , R 2  and R 3 . The inclusion of resonant circuits  306  and  303 , advantageously, negates the attenuation of the resistive pad formed by the combination of resistors R 1 , R 2  and R 3  in the desired MOCA band of 950 to 1050 MHz. Adjusting the ratio of the inductance to capacitance, L/C ratio, in each of resonant circuits  306  and  303  can produce a desired pass band characteristic from 950 to 1050 MHz. 
         [0025]    The values of the following components of termination portion  116  of band-pass filter/termination  115  of  FIG. 2  are, as follows: 
         [0026]    R 1 =24 Ohm 
         [0027]    R 2 =24 Ohm 
         [0028]    R 3 =99 Ohm 
         [0029]    L 1 =36 nH 
         [0030]    L 2 = 8 . 2  nH 
         [0031]    C 1 =3.3 pF 
         [0032]    C 2 =0.68 pF 
         [0033]    Terminal  305  of resistor R 2 , forming an output terminal of termination portion  116  also forms, in common, an input terminal, referred to as port  1 -SP 1  of a band-pass filter SP 1 . Band-pass filter SP 1  has an output referred to herein as a port  2 -SP 1  of band-pass filter SP 1 . Port  2  of band-pass filter SP 1  forms, in common, an output port of band-pass filter/termination  115 . 
         [0034]    Band-pass filter SP 1  passes with low attenuation the signal at the frequencies spectrum of the MOCA band of frequencies, 950 MHz-1050 MHz, of signal Vouta. On the other hand, band-pass filter SP 1  blocks or attenuates signals at frequencies within the frequency spectrum of signal Voutb that are non-overlapping with the MOCA band of frequencies, 950 MHz-1050 MHz, of signal Vouta. An example of such filter may be an LTCC device such as a prior art filter made by MURATA, LFB321CG00M8D792. LTCC is an abbreviation of Low Temperature Co-fired Ceramics. High purity ceramics used in the industrial world are also called “fine ceramics.” Among fine ceramics, LTCC is classified as electronic ceramics which are used as electronic materials. Such filter provides low attenuation and good impedance match with respect to the MOCA 950 to 1050 MHz band of signal Vouta. However, input port  1 -SP 1  of band-pass filter SP 1  generally forms input impedance that, disadvantageously, is significantly different at different frequencies over the frequency spectrum of signal Voutb. Other filter types may, instead, be employed such as conventional L-C types or SAW devices.  FIG. 3  illustrates a graph showing a selectivity or S-parameter S 21  of stand-alone band-pass filter SP 1  of  FIG. 2 . S-parameter S 21  of  FIG. 3  represents a ratio of the power received at port  2 -SP 1  of band-pass filter SP 1  of  FIG. 2  relative to the power input at port  1 -SP 1  of band-pass filter SP 1 . A broken line  3   a  of  FIG. 3  represents a specification limit requirement for S-parameter S 21  of band-pass filter/termination  115  of  FIG. 2  that is better than minus  50  decibel (db) at frequencies below 800 MHz. By way of an example, S-parameter S 21  of −55 db is better than S-parameter S 21  of −50 db. A broken line  3   b  of  FIG. 3  represents a specification limit requirement for S-parameter S 21  of band-pass filter/termination  115  of  FIG. 2  that is better than minus 5 db at the MOCA frequency band. By way of an example, S-parameter S 21  of −3 db is better than S-parameter S 21  of −5 db. A broken line  3   c  of  FIG. 3  represents a specification limit requirement for S-parameter S 21  of band-pass filter/termination  115  of  FIG. 2  that is better than minus 55 db at frequencies between 1250 MHz and 2150 MHz. 
         [0035]      FIG. 4  illustrates a graph showing the return loss or S-parameter S 11  of stand-alone band-pass filter SP 1  of  FIG. 2 . S-parameter S 11  of  FIG. 4  represents a ratio of the power reflected from port  1 -SP 1  of band-pass filter SP 1  of  FIG. 2  relative to the power input at port  1 -SP 1 . A broken line  4   a  of  FIG. 4  represents a specification limit requirement for S-parameter S 11  of band-pass filter/termination  115  of  FIG. 2  that is better than minus 8 db at frequencies below 800 MHz. A broken line  4   b  of  FIG. 4  represents a specification limit requirement for S-parameter S 11  of band-pass filter/termination  115  of  FIG. 2  that is better than minus 10 db at the MOCA frequency band. A broken line  4   c  of  FIG. 4  represents a specification limit requirement for S-parameter S 11  of band-pass filter/termination  115  of  FIG. 2  that is better than minus 10 db at frequencies between 1250 MHz and 2150 MHz. By way of an example, S-parameter S 11  of −12 db is better than S-parameter S 11  of −10 db. 
         [0036]    Assume, hypothetically, that stand-alone band-pass filter SP 1  of  FIG. 2  is coupled to transmission line  110   a  of  FIG. 1  without interposing termination portion  116  between transmission line  110   a  and stand-alone band-pass filter SP 1 . In this case, as demonstrated in the graph of  FIG. 4 , the specification limits of lines  4   a  and  4   c  would, disadvantageously, not be met. 
         [0037]      FIG. 5  illustrates a graph showing the selectivity or S-parameter S 21  of band-pass filter/termination  115  of  FIG. 2  that includes both termination portion  116  and band-pass filter SP 1 . S-parameter S 21  of  FIG. 5  represents the power received at port  2  of band-pass filter/termination  115  of  FIG. 2  relative to the power input at port  1  that is at terminal  304  of band-pass filter/termination  115  of  FIG. 2 . A broken line  5   a  of  FIG. 5 , a broken line  5   b  and a broken line  5   c  represent the same specification limit requirements of broken lines  3   a,    3   b  and  3   c,  respectively, of  FIG. 3 . As shown in  FIG. 5 , S-parameter S 21  of band-pass filter/termination  115  of  FIG. 2  meets the specification limit requirements, advantageously, even better than in  FIG. 3 . 
         [0038]      FIG. 6  illustrates a graph showing the return loss or S-parameter S 11  of band-pass filter/termination  115  of  FIG. 2  that includes both termination portion  116  and band-pass filter SP 1 . S-parameter S 11  of  FIG. 6  represents the power reflected from port  1  of band-pass filter/termination  115  of  FIG. 2  relative to the power input at port  1  of band-pass filter/termination  115 . A broken line  6   a  of  FIG. 6 , a broken line  6   b  and a broken line  6   c  represent the same specification limit requirements of broken lines  4   a,    4   b  and  4   c,  respectively, of  FIG. 4 . As shown in  FIG. 6 , S-parameter  511  of band-pass filter/termination  115  of  FIG. 2  meets the specification limit requirements, advantageously, better than in  FIG. 4 . As shown in  FIG. 6 , band-pass filter/termination  115  of  FIG. 2  fully meets the required impedance matching except in a narrow range of frequencies between 1250 MHz and about 1400 MHz. 
         [0039]      FIG. 7  illustrates a circuit diagram of improved band-pass filter/termination  115 ′ of  FIG. 1 , embodying another advantageous feature. Similar symbols and numerals in  FIGS. 1 and 2 and 7 , except for the addition of a prime symbol, ′, in  FIG. 7 , indicate similar items or functions. In a termination portion  116 ′ of band-pass filter/termination  115 ′ of  FIG. 7 , a capacitor Cfix′ is coupled in parallel with an inductor L 1 ′ forming an addition relative to filter/termination  115  of  FIG. 2 . The inclusion of capacitor Cfix′ provides a transfer function or transmission” zero” below 950 MHz. The combination of capacitors Cfix′ and C 2 ′ resonate with inductor L 1 ′ at 1000 MHz. The ratio of the capacitance of capacitor Cfix′ to that of capacitor C 2 ′ can be adjusted to improve the impedance matching at 800 MHz and below. Also, an inductor Lfix′ is coupled in series with a parallel resonant circuit  303 ′ that includes an inductor L 2 ′ for resonating with capacitor C 1 ′ above 1000 MHz. Whereas, inductor L 2 ′ and capacitor C 1 ′ resonate at approximately 1000 MHz. The addition of inductor Lfix′ provides a transfer function or transmission “zero” above 1050 MHz. The ratio of the inductance of inductor Lfix′ to that of inductor L 2 ′ can be adjusted to improve the impedance matching at 1250 MHz and above. 
         [0040]    The values of the components of termination portion  116 ′ of band-pass filter/termination  115 ′ of  FIG. 7  are, as follows: 
         [0041]    R 1 ′24 Ohm 
         [0042]    R 2 ′=24 Ohm 
         [0043]    R 3 ′=99 Ohm 
         [0044]    L 1 ′=18 nH 
         [0045]    L 2 ′=5.6 nH 
         [0046]    Lfix′=12 nH 
         [0047]    C 1 ′=4.3 pF 
         [0048]    C 2 ′=0.82 pF 
         [0049]    Cfix′=0.56 pF 
         [0050]      FIG. 8  illustrates a graph showing the selectivity or S-parameter S 21  of band-pass filter/termination  115 ′ of  FIG. 7  that includes band-pass filter SP 1 ′. S-parameter S 21  of  FIG. 8  represents the power received at port  2  of band-pass filter/termination  115 ′ of  FIG. 7  relative to the power input at port  1  that is at terminal  304 ′ of band-pass filter/termination  115 ′ of  FIG. 7 . A broken line  8   a  of  FIG. 8 , a broken line  8   b  and a broken line  8   c  represent the same specification limit requirements of broken lines  5   a,    5   b  and  5   c,  respectively, of  FIG. 5 . As shown in  FIG. 8 , S-parameter S 21  of band-pass filter/termination  115 ′ of  FIG. 7  fully meets the specification limits. 
         [0051]      FIG. 9  illustrates a graph showing the return loss or S-parameter S 11  of band-pass filter/termination  115 ′ of  FIG. 7 . S-parameter S 11  of  FIG. 9  represents the power reflected from port  1  of band-pass filter/termination  115 ′ of  FIG. 7  relative to the power input at port  1  of band-pass filter/termination  115 ′. A broken line  9   a  of  FIG. 9 , a broken line  9   b  and a broken line  9   c  represent the specification limit requirements of broken lines  6   a,    6   b  and  6   c,  respectively, of  FIG. 6 . As shown in  FIG. 9 , S-parameter S 11  of band-pass filter/termination  115 ′ of  FIG. 7 , advantageously, fully meets the specification limits.