Patent Publication Number: US-2011051015-A1

Title: Television signal receiving tuner

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     The present invention contains subject matter related to and claims priority to Japanese Patent Application JP 2009-194359 filed in the Japanese Patent Office on Aug. 25, 2009, the entire content of which is incorporated herein by reference. 
     BACKGROUND 
     1. Technical Field 
     The present disclosure relates to a television signal receiving tuner. More particularly, the present disclosure relates to a television signal receiving tuner available for a tuner that receives a digital television signal and an analog television signal. 
     2. Related Art 
     As shown in  FIG. 11 , as one example, an existing television signal receiving tuner  101  mainly includes a mixer circuit  103 , a trap circuit  105  and a first intermediate frequency amplifying circuit  104 . 
     The mixer circuit  103  is provided inside a chip IC  102  to convert a frequency signal of a reception channel regarding a digital television signal or an analog television signal into an intermediate frequency signal. A second intermediate frequency amplifying circuit  108  is connected to an output terminal of the mixer circuit  103  to amplify the intermediate frequency signal output from the mixer circuit  103 . 
     The trap circuit  105  is provided outside the chip IC  102  and is connected between the mixer circuit  103  and the first intermediate frequency amplifying circuit  104  to attenuate a frequency band adjacent to an intermediate frequency signal based on an analog television signal to be received. At the time of receiving the digital television signal, the function of the trap circuit  105  is invalidated by the conduction of a switching element  107  connected in parallel to the trap circuit  105 . 
     The first intermediate frequency amplifying circuit  104  is provided inside the chip IC  102 , and for example is a gain control amplifier. Further, the first intermediate frequency amplifying circuit  104  is connected to the rear stage of the trap circuit  105 . A third intermediate frequency amplifying circuit  109  is connected between the trap circuit  105  and the first intermediate frequency amplifying circuit  104 . When the third intermediate frequency amplifying circuit  109  individually outputs respective intermediate frequency signals based on the digital television signal and the analog television signal, the intermediate frequency signal based on the analog television signal is output to an AIF  114 . The intermediate frequency signal based on the digital television signal input to the first intermediate frequency amplifying circuit  104  through a SAW filter  113  is further amplified together with a control signal received from an IF-AGC (an intermediate-frequency automatic gain control circuit) through an AGC terminal  115 , and then is output to DIFs  116  and  117 . 
     Furthermore, in the existing television signal receiving tuner  101 , since a digital and analog integrated demodulation IC is used, both the digital television signal and the analog television signal may be extracted from the DIFs  116  and  117 . Japanese Unexamined Patent Application Publication No. 2001-157128 is an example of the related art. 
     However, in the existing television signal receiving tuner  101 , when both the trap circuit  105  and the first intermediate frequency amplifying circuit  104  effectively operate, since impedance changes suddenly due to the characteristics of the trap circuit  105  that attenuates a narrow band, a high frequency signal generated at the time of the output of the first intermediate frequency amplifying circuit  104  serves as an unnecessary noise source, so that ripples (wave-like undulation occurring in signals) and parasitic oscillation of the first intermediate frequency amplifying circuit  104  may occur with respect to signals output from the DIFs  116  and  117 . 
     Hereinafter, the above phenomena will be described in detail. When the frequency of the intermediate frequency signal passing through the trap circuit  105  is outside a resonant frequency of the trap circuit  105 , since the trap circuit  105  is low impedance, the trap circuit  105  is in a pass-through state as surrounded by a dot line of  FIG. 12 , so that the intermediate frequency signal may pass through the trap circuit  105  as shown in  FIG. 12 . 
     On the other hand, when the frequency of the intermediate frequency signal passing through the trap circuit  105  is equal to or approximates to the resonant frequency of the trap circuit  105 , since the trap circuit  105  is high impedance, the trap circuit  105  is in an open state as surrounded by a dot line of  FIG. 13 , so that the intermediate frequency signal may not theoretically pass through the trap circuit  105  as shown in  FIG. 13 . Further, when a weak electric field is applied to the first intermediate frequency amplifying circuit  104 , since gain of the first intermediate frequency amplifying circuit  104  is maximized, high frequency noise N may be generated in the trap circuit  105  from a conductive line between an output terminal of the first intermediate frequency amplifying circuit  104  and the DIFs  116  and  117 . As a result, intrusion of the high frequency noise N discharged from the trap circuit  105  in the open state occurs and unnecessary returning occurs between the input and output of the first intermediate frequency amplifying circuit  104 . Thus, as described above, the high frequency signal generated at the time of the output of the first intermediate frequency amplifying circuit  104  serves as the unnecessary noise source, so that the ripples and the parasitic oscillation of the first intermediate frequency amplifying circuit  104  may occur with respect to signals output from the DIFs  116  and  117  as shown in  FIG. 14 . 
     Consequently, in the existing television signal receiving tuner  101 , since the above problems occur when using the first intermediate frequency amplifying circuit  104  while the trap circuit  105  is operating, it may be impossible to use the trap circuit  105  at the time of receiving an analog television signal, so that it may not be possible to satisfy required analog reception characteristics. 
     SUMMARY 
     According to a first aspect of the invention, there is provided a television signal receiving tuner including: a mixer circuit configured to convert a frequency signal of a reception channel regarding a digital television signal or an analog television signal into an intermediate frequency signal; a first intermediate frequency amplifying circuit connected to a rear stage of the mixer circuit; a trap circuit connected between any one of an output terminal of the mixer circuit and an input terminal of the first intermediate frequency amplifying circuit and a ground, and configured to attenuate a frequency band, which is adjacent to the intermediate frequency signal based on the analog television signal, on a basis of an attenuation point; and a tuned circuit connected between the output terminal of the mixer circuit and the input terminal of the first intermediate frequency amplifying circuit to tune the intermediate frequency signal by employing the attenuation point or a frequency band approximating to the attenuation point as a tuning point. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a circuit diagram illustrating a television signal receiving tuner according to an embodiment of the invention. 
         FIG. 2  is a circuit diagram illustrating a tuned circuit and a trap circuit according to an embodiment and a graph illustrating frequency characteristics thereof. 
         FIG. 3  is a circuit diagram illustrating a case in which a frequency of an intermediate frequency signal passing through a trap circuit is outside an attenuation point in a television signal receiving tuner according to an embodiment. 
         FIG. 4  is a circuit diagram illustrating a case in which a frequency of an intermediate frequency signal passing through a trap circuit is equal to an attenuation point in a television signal receiving tuner according to an embodiment. 
         FIG. 5  is a graph illustrating wide frequency characteristics in a television signal receiving tuner according to an embodiment. 
         FIG. 6  is a circuit diagram illustrating a state in which a switching element is in a conductive state in a tuned circuit and a trap circuit according to an embodiment. 
         FIG. 7  is a graph illustrating frequency characteristics of a digital television signal in a television signal receiving tuner according to an embodiment. 
         FIG. 8  is a graph illustrating frequency characteristics of an analog television signal and a digital television signal in a television signal receiving tuner according to an embodiment. 
         FIG. 9  is a graph locally illustrating frequency characteristics of a digital television signal in a television signal receiving tuner according to an embodiment. 
         FIG. 10  is a circuit diagram illustrating one example of a television signal receiving tuner according to another embodiment of the invention. 
         FIG. 11  is a circuit diagram illustrating one example of an existing television signal receiving tuner. 
         FIG. 12  is a circuit diagram illustrating a case in which a frequency of an intermediate frequency signal passing through a trap circuit is outside an attenuation point in an existing television signal receiving tuner. 
         FIG. 13  is a circuit diagram illustrating a case in which a frequency of an intermediate frequency signal passing through a trap circuit is equal to an attenuation point in an existing television signal receiving tuner. 
         FIG. 14  is a graph illustrating wide frequency characteristics in an existing television signal receiving tuner. 
     
    
    
     DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     Hereinafter, an embodiment of a television signal receiving tuner in accordance with the invention will be described. 
     As shown in  FIG. 1 , the television signal receiving tuner  1  according to the present embodiment includes a mixer circuit  3 , a first intermediate frequency amplifying circuit  4 , a trap circuit  5  and a tuned circuit  6 . Preferably, the television signal receiving tuner  1  according to the embodiment further includes two second intermediate frequency amplifying circuits  8  and  9 , and a SAW filter  13 . In addition, the mixer circuit  3 , the first intermediate frequency amplifying circuit  4 , and the second intermediate frequency amplifying circuits  8  and  9  are provided inside a tuner IC  2 , and other circuits including the trap circuit  5 , the tuned circuit  6  and the SAW filter  13  are provided outside the tuner IC  2 . 
     The mixer circuit  3  converts a frequency signal of a reception channel regarding a digital television signal and an analog television signal into an intermediate frequency signal. When the second intermediate frequency amplifying circuit  8  is connected between the mixer circuit  3  and the tuned circuit  6 , it is preferable that another intermediate frequency amplifying circuit  18  provided outside the tuner IC  2  is connected between the second intermediate frequency amplifying circuit  8  and the mixer circuit  3 . 
     The first intermediate frequency amplifying circuit  4  is connected to the rear stage of the mixer circuit  3  through at least the trap circuit  5  and the tuned circuit  6 , preferably, the two second intermediate frequency amplifying circuits  8  and  9  and the SAW filter  13 . Furthermore, two DIFs  16  and  17  are connected to an output terminal of the first intermediate frequency amplifying circuit  4  to output an intermediate frequency signal based on the digital television signal. Preferably, the first intermediate frequency amplifying circuit  4  is a gain control amplifier. In such a case, preferably, an IF-AGC (an intermediate-frequency automatic gain control circuit) provided outside the tuner IC  2  is connected to the first intermediate frequency amplifying circuit  4  through an AGC terminal  15 . 
     The trap circuit  5  attenuates a frequency band, which is adjacent to an intermediate frequency signal based on an analog television signal, on the basis of an attenuation point. In the trap circuit  5  according to the embodiment, the attenuation point is set to a frequency of a low frequency side or a frequency, which is lower than the frequency of the low frequency side, in a frequency band based on a required intermediate frequency signal. In this regard, the trap circuit  5  is connected between an input terminal of the first intermediate frequency amplifying circuit  4  and a ground  10 . 
     Preferably, the trap circuit  5  is configured such that a trap function thereof is validated at the time of receiving the analog television signal and the trap function thereof is invalidated at the time of receiving the digital television signal. As one example of such a trap circuit  5 , preferably, the trap circuit  5  according to the embodiment includes a parallel connection circuit  53  and a second capacitor  54 . The parallel connection circuit  53  includes a first inductor  51  and a first capacitor  52  connected in parallel to each other, and the second capacitor  54  is serially connected between one end  53   a  of the parallel connection circuit  53  and the ground  10 . The one end  53   a  of the parallel connection circuit  53  is connected to an input terminal  6   a  of the tuned circuit  6  through a switching element  7 . Furthermore, the other end  53   b  of the parallel connection circuit  53  is connected to an output terminal  6   b  of the tuned circuit  6 . 
     The switching element  7  connected to the trap circuit  5  according to the embodiment is in a conductive state only at the time of receiving the digital television signal. For example, when the switching element  7  is a diode, a circuit  11  that performs DC output is provided at an anode side of the switching element  7  and a circuit  12  including any one of DC output and the ground is provided at the other end  53   b  of the parallel connection circuit  53 , so that the switching element  7  is formed. 
     The tuned circuit  6  tunes the intermediate frequency signal by employing the attenuation point of the trap circuit  5  or a frequency band approximating to the attenuation point as a tuning point. In the tuned circuit  6  according to the embodiment, the tuning point is set to be a frequency higher than the attenuation point of the trap circuit  5  and exist in a low frequency side of the frequency band based on the required intermediate frequency signal. The tuned circuit  6  is connected between an output terminal of the mixer circuit  3  and the input terminal of the first intermediate frequency amplifying circuit  4 . Furthermore, an AIF  14  that outputs an intermediate frequency signal based on the analog television signal is connected to the output terminal  6   b  of the tuned circuit  6  through the second intermediate frequency amplifying circuit  9  or is directly connected to the output terminal  6   b  of the tuned circuit  6  when the second intermediate frequency amplifying circuit  9  is not connected. 
     Preferably, the tuned circuit  6  according to the embodiment, for example, includes a third capacitor  61 , a fourth capacitor  62  and a second inductor  63 . In such a case, the third capacitor  61  and the fourth capacitor  62  are serially connected between the input terminal  6   a  and the output terminal  6   b  of the tuned circuit  6 , and the second inductor  63  is serially connected between a connection point between the third capacitor  61  and the fourth capacitor  62  and the ground  10 . 
     According to the embodiment, preferably, the two second intermediate frequency amplifying circuits  8  and  9  are used. Preferably, the second intermediate frequency amplifying circuit  8  is connected between the mixer circuit  3  and the tuned circuit  6 , and the second intermediate frequency amplifying circuit  9  is connected between the tuned circuit  6  and the first intermediate frequency amplifying circuit  4 . However, the second intermediate frequency amplifying circuit  8  or  9  may be connected only to any one of between the mixer circuit  3  and the tuned circuit  6  and between the tuned circuit  6  and the first intermediate frequency amplifying circuit  4 . 
     Preferably, the SAW filter  13  is connected between the second intermediate frequency amplifying circuit  9 , which is provided at the rear stage of the tuned circuit  6 , and the first intermediate frequency amplifying circuit  4 . However, when the second intermediate frequency amplifying circuit  9  is not provided in the television signal receiving tuner  1  according to the embodiment, the SAW filter  13  is preferably connected between the tuned circuit  6  and the first intermediate frequency amplifying circuit  4 . 
     Next, the operation of the television signal receiving tuner  1  according to the embodiment will be described. 
     In the television signal receiving tuner  1  according to the embodiment, as shown in  FIGS. 1 and 2 , the tuned circuit  6  and the trap circuit  5  are connected between the mixer circuit  3  and the first intermediate frequency amplifying circuit  4 . Furthermore, the trap circuit  5  is connected between the input terminal of the first intermediate frequency amplifying circuit  4  and the ground  10  through the tuned circuit  6 . Thus, in the case of frequencies other than the resonant frequency (attenuation point) of the trap circuit  5 , since the trap circuit  5  is low impedance, the trap circuit  5  is in a pass-through state as surrounded by a dot line of  FIG. 3 , so that the intermediate frequency signal can pass through the trap circuit  5  as shown in  FIG. 3 . On the other hand, when the frequency of the intermediate frequency signal passing through the trap circuit  5  is equal to or approximates to the resonant frequency (attenuation point) of the trap circuit  5 , since the trap circuit  5  is high impedance, the trap circuit  5  is in a ground state as surrounded by a dot line of  FIG. 4 , so that the intermediate frequency signal flows to the ground  10  connected to the trap circuit  5  as shown in  FIG. 4 . 
     As described above, in the television signal receiving tuner  1 , since one end of the trap circuit  5  is grounded, a signal line including the trap circuit  5  can be prevented from serving as an antenna at the resonant point of the trap circuit  5 . As a result, as shown in  FIG. 5 , the occurrence of unnecessary returning and ripple can be avoided in the first intermediate frequency amplifying circuit  4  provided at the rear stage of the trap circuit  5 . Moreover, when a gain control amplifier is used as the first intermediate frequency amplifying circuit  4 , since there is no need for concern about the unnecessary returning and ripples, gain adjustment of the intermediate frequency signal can be easily performed and gain of the intermediate frequency signal based on the digital television signal can be increased. 
     In addition, in the television signal receiving tuner  1  according to the embodiment, the tuning point of the tuned circuit  6  is set to be equal to or approximate to the attenuation point of the trap circuit  5 . According to the embodiment, the attenuation point of the trap circuit  5  is set to a frequency lower than a frequency of a low frequency side in a frequency band based on the required intermediate frequency signal as indicated by a dotted line ( 3 ) in the graph at the right side of  FIG. 2 . The tuning point of the tuned circuit  6  is set to a frequency higher than the attenuation point of the trap circuit  5  and exist in the low frequency side in the frequency band based on the required intermediate frequency signal as indicated by a dotted line ( 2 ) in the graph at the right side of  FIG. 2 . As a result, as indicated by a solid line ( 4 ) in the graph at the right side of  FIG. 2 , gain of the intermediate frequency signal based on the analog television signal, which has passed through the tuned circuit  6  and the trap circuit  5  and has been excessively attenuated by the trap circuit  5 , can be rapidly increased in the required intermediate frequency band. 
     That is, one end of the trap circuit  5  according to the embodiment is grounded, and reduction of the gain of the intermediate frequency band caused by the attenuation characteristics of the trap circuit  5  is compensated by the tuned circuit  6 , so that the digital television signal and the analog television signal can be received and required analog characteristics can be achieved at the time of receiving the analog television signal. 
     Moreover, in the trap circuit  5  according to the embodiment, the trap function of the trap circuit  5  is validated at the time of receiving the analog television signal and is invalidated at the time of receiving the digital television signal. In detail, as shown in  FIG. 1 , the switching element  7  connected to the trap circuit  5  according to the embodiment is in the conductive state only at the time of receiving the digital television signal, so that the presence or absence of the operation of the trap circuit  5  can be determined according to the type of signals. For example, when the switching element  7  is in the conductive state, since the tuned circuit  6  and the trap circuit  5  form an equivalent circuit as shown in  FIG. 6 , the frequency characteristics thereof are changed from characteristics indicated by a dotted line to characteristics indicated by a solid line as shown in  FIG. 7 . As described above, in the television signal receiving tuner  1  according to the embodiment, the intermediate frequency signal based on the weak output digital television signal can be prevented from being attenuated by the trap circuit  5 . 
     That is, at the time of receiving the analog television signal, the switching element  7  is allowed to be in a non-conductive state, so that frequency characteristics including a trap operation as indicated by a solid line of  FIG. 8  can be achieved. At the time of receiving the digital television signal, the switching element  7  is allowed to be in a conductive state, so that frequency characteristics excluding the trap operation as indicated by a dotted line of  FIG. 8  can be achieved. 
     Furthermore, a dotted line of  FIG. 9  represents band characteristics of the existing television signal receiving tuner  101  and a solid line of  FIG. 9  represents band characteristics of the television signal receiving tuner  1  according to the embodiment. When a diode is selected as the switching element  7  and is allowed to be in a conductive state, as compared with the existing television signal receiving tuner  101 , the band of the digital television signal can be limited by the diode, so that only the required intermediate frequency band can be easily achieved as shown in  FIG. 9 . 
     In addition, in the trap circuit  5  according to the embodiment, as shown in  FIG. 1 , the parallel connection circuit  53 , the second capacitor  54  and the ground  10  are serially connected to one another. The input terminal  6   a  of the tuned circuit  6  is connected to the one end  53   a  of the parallel connection circuit  53  through the switching element  7 , and the output terminal  6   b  of the tuned circuit  6  is connected to the other end  53   b  of the parallel connection circuit  53 . That is, with a simple configuration, the trap circuit  5  suitable for the television signal receiving tuner  1  according to the embodiment can be formed. 
     Meanwhile, in the tuned circuit  6  according to the embodiment, as shown in  FIG. 1 , the second inductor  63  is serially connected between the connection point between the third capacitor  61  and the fourth capacitor  62 , which are serially connected to each other, and the ground  10 . This is because the one end  53   a  and the other end  53   b  of the parallel connection circuit  53  in the trap circuit  5  are connected to the input terminal  6   a  and the output terminal  6   b  of the tuned circuit  6 , respectively. That is, with a simple configuration, the tuned circuit  6  suitable for the television signal receiving tuner  1  according to the embodiment can be formed. 
     Moreover, since the television signal receiving tuner  1  according to the embodiment includes the two second intermediate frequency amplifying circuits  8  and  9 , the gain of the intermediate frequency signal can be easily increased. Furthermore, since the television signal receiving tuner  1  according to the embodiment includes the SAW filter  13 , the intermediate frequency signal based on the digital television signal can be easily selected and extracted from the signal output from the circuit provided at the rear stage of the tuned circuit  6 . 
     That is, according to the television signal receiving tuner  1  of the embodiment, the mixer circuit  3  converts the digital television signal and the analog television signal into the intermediate frequency signal, and the signal line including the trap circuit  5  is prevented from serving as an antenna at the resonant point of the trap circuit  5  provided at the rear stage of the mixer circuit  3 , so that the occurrence of unnecessary returning can be avoided in the first intermediate frequency amplifying circuit  4  provided at the rear stage of the trap circuit  5 . Furthermore, the intermediate frequency signal based on the analog television signal, which has been attenuated by the trap circuit  5 , is tuned by the tuned circuit  6 , so that the gain of the intermediate frequency signal can be rapidly increased. As a result, the digital television signal and the analog television signal can be received and required analog characteristics can be achieved at the time of receiving the analog television signal. 
     In addition, the present disclosure is not limited to the above-described embodiment. That is, various modifications can be made if necessary. 
     For example, according to another embodiment, as shown in  FIG. 10 , the trap circuit  5  may be connected between the output terminal of the mixer circuit  3  and the ground  10 . In such a case, the one end  53   a  of the parallel connection circuit  53  of the trap circuit  5  is connected to the output terminal  6   b  of the tuned circuit  6  through the switching element  7 , and the other end  53   b  thereof is connected to the input terminal  6   a  of the tuned circuit  6 . 
     Furthermore, according to the previous embodiment, the tuned circuit  6  is provided in order to improve the analog reception characteristics. However, only for the purpose of preventing oscillation of the first intermediate frequency amplifying circuit  4  and the like, the tuned circuit  6  may be removed from the television signal receiving tuner  1  according to the embodiment. 
     It should be understood by those skilled in the art that various modifications, combinations, sub-combinations and alterations may occur depending on design requirements and other factors insofar as they are within the scope of the appended claims or the equivalents thereof.