JP2011023891A - Tuner for receiving television broadcast signal - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a tuner for receiving a television broadcast signal capable of being made responsive to the PAL system and the SECAM-L system in a VHF low band without degrading fundamental performance. <P>SOLUTION: This tuner 1 for receiving a television broadcast signal capable of receiving television broadcast signals of the PAL system and the SECAM-L system includes: a primary tuning circuit 11 and a secondary tuning circuit 12; and an RF tuning circuit 4 having a coupling inductor L5 for adjusting the degree of coupling between the primary tuning circuit 11 and the secondary tuning circuit 12; and is structured such that, in receiving a television broadcast signal of the SECAM-L system in the VHF low band, the degree of coupling by the coupling inductor of the RF tuning circuit 4 is reduced relative to that in receiving the television broadcast signal of the PAL system. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a television broadcast signal receiving tuner capable of receiving PAL and SECAM television broadcast signals.

  In Europe, the PAL system and the SECAM-L system are adopted as the television broadcast system, and a tuner capable of receiving a television broadcast signal corresponding to the PAL system and the SECAM (L) system has been developed. 2. Description of the Related Art Conventionally, as a television broadcast signal reception tuner that supports the PAL system and the SECAM (L) system, one that switches a circuit configuration between a VHF high band and a VHF low band is known (see, for example, Patent Document 1).

  As shown in FIG. 6, this television broadcast signal receiving tuner 21 includes an antenna tuning circuit 22, an RF amplifier circuit 23, an RF tuning circuit 24, a VHF mixer circuit 25, a VHF local oscillation circuit 26, and an IF tuning. Circuit 27 and switching the circuit configuration of the RF tuning circuit 24 enables reception of VHF high-band and VHF low-band television broadcast signals.

  The RF tuning circuit 24 is a double tuning circuit provided between the RF amplifier circuit 23 and the VHF mixer circuit 25, and includes a primary tuning circuit 31 and a secondary tuning circuit 32. The primary tuning circuit 31 is connected to the output terminal of the RF amplifier circuit 23. The output terminal of the RF amplifier circuit 23 is grounded through a capacitor C31 and a varactor diode VD31. The varactor diode VD31 has a cathode connected to a power supply B31 that outputs a tuning voltage via a resistor R31, and an anode connected to the ground. The cathode of the varactor diode VD31 is connected to a series circuit including inductors L31 and L32 via a capacitor C31.

  The secondary tuning circuit 32 is connected to one end of the inductor L32 of the primary tuning circuit 31. One end of the inductor L32 of the primary tuning circuit 31 is connected to a series circuit including an inductor L33, a capacitor C32, an inductor L34, and a varactor diode VD32. The varactor diode VD32 has a cathode connected to a power supply B31 that outputs a tuning voltage via a resistor R32, and an anode connected to the input terminal of the VHF mixer circuit 25. A connection point between the inductor L34 and the cathode of the varactor diode VD32 is grounded via the varactor diode VD33. The varactor diode VD33 has a cathode connected to a power supply B31 that outputs a tuning voltage via a resistor R32, and an anode connected to the ground.

  The connection point of the inductors L31 and L32 of the primary tuning circuit 31 is connected to the connection point of the inductor L33 and the capacitor C32 of the secondary tuning circuit 32 via the bypass line 33 provided with the switching diodes SD31 and SD32. The switching diode SD31 has an anode connected to the connection point of the inductors L31 and L32, and a cathode connected to the cathode of the switching diode SD32. The switching diode SD32 has an anode connected to the connection point of the inductor L33 and the capacitor C32. The connection point of the cathodes of the switching diodes SD31 and SD32 is grounded via the capacitor C33 and is connected to the switch type power supply 34 via the resistor R33.

  A connection point between the primary tuning circuit 31 and the secondary tuning circuit 32 is grounded through a coupling inductor L35 and a capacitor C34. A connection point between the coupling inductor L35 and the capacitor C34 is connected to the power supply B32. The power source B32 is connected to the collector of the switching transistor T31 via the resistor R34. The switching transistor T31 has a collector connected to the power source B32 via a resistor R34, an emitter grounded, and an ON resistance between the collector and emitter.

  In the RF tuning circuit 24 configured as described above, the switch type power supply 34 and the switching transistor T31 are turned OFF when receiving a VHF high-band television broadcast. As a result, the output voltage output from the power source B32 is applied to the anodes of the switching diodes SD31 and SD32 via the inductors L35, L32 and L33, and the primary tuning circuit 31 and the secondary tuning circuit 32 are connected via the bypass line 33. Conducted. In this case, the primary tuning circuit 31 includes a parallel resonance circuit including the varactor diode VD31 and the inductor L31, and the secondary tuning circuit 32 includes a parallel resonance circuit including the inductor L34 and the varactor diodes VD32 and VD33.

  On the other hand, when receiving a VHF low-band television broadcast, the switch-type power supply 34 and the switching transistor T31 are turned on. When the switch type power supply 34 is turned on, a reverse voltage is applied from the switch type power supply 34 to the cathodes of the switching diodes SD31 and SD32 via the resistor R33. At this time, the forward voltage is applied from the power source B32 to the anodes of the switching diodes SD31 and SD32 via the inductors L35, L32, and L33, but the reverse voltage applied to the switching diodes SD31 and SD32 is more than the forward voltage. Largely, the bypass line 33 is blocked.

  In this case, the primary tuning circuit 31 includes a parallel resonance circuit including the varactor diode VD31 and the inductors L31 and L32. The secondary tuning circuit 32 includes the parallel resonance circuit including the inductors L33 and L34 and the varactor diodes VD32 and VD33. Is done. At this time, the primary tuning circuit 31 and the secondary tuning circuit 32 are coupled in high frequency by the inductor L35. In this way, by switching the circuit configuration of the RF tuning circuit 24 of the television broadcast signal receiving tuner 21, the television broadcast signal of the VHF high band and the VHF low band can be received.

Japanese Patent Laid-Open No. 11-341391

  By the way, the SECAM-L television broadcast signal in the VHF low band is inverted in the frequency of the video signal P and the audio signal S compared to the PAL television broadcast signal. In this case, as shown in FIGS. 7A and 7B, when receiving a VHF low-band PAL television broadcast signal, there is an interference signal UD corresponding to the upper adjacent interference with respect to the audio signal S, and SECAM. When the -L system television broadcast signal is received, a disturbance signal UD corresponding to the lower adjacent disturbance is present with respect to the audio signal S.

  As shown in FIG. 7A, the above-described television broadcast signal receiving tuner 21 is designed so as to attenuate the interference signal UD adjacent to the upper side by giving priority to the basic performance of the PAL system. As shown in (b), the lower adjacent disturbance signal UD cannot be sufficiently attenuated when a SECAM-L television broadcast signal is received. For this reason, the above-mentioned television broadcast signal receiving tuner 21 has no room for the basic performance defined by the EMC resistance or the like, and it has been difficult to absorb variations in the basic performance during mass production.

  The present invention has been made in view of the above points, and an object of the present invention is to provide a television broadcast signal receiving tuner capable of supporting the PAL system and the SECAM-L system in the VHF low band without degrading the basic performance. And

  The television broadcast signal receiving tuner of the present invention is a television broadcast signal receiving tuner capable of receiving PAL and SECAM-L television broadcast signals, and includes a primary tuning circuit, a secondary tuning circuit, the primary tuning circuit, and A double tuning circuit having a coupling inductor for adjusting the coupling degree of the secondary tuning circuit, and when receiving the SECAM-L television broadcast signal in the VHF low band, the double tuning circuit is formed by the coupling inductor. The degree of coupling is smaller than when receiving the PAL television broadcast signal.

  According to this configuration, when the PAL television signal in the VHF low band is received, the degree of coupling by the coupling inductor is greatly adjusted, so that the adjacent adjacent interference signal can be sufficiently attenuated. On the other hand, when receiving a SECAM-L television broadcast signal in the VHF low band, the coupling frequency by the coupling inductor is adjusted to be smaller than when receiving a PAL television broadcast signal in the VHF low band. The bandwidth is narrowed, and the adjacent adjacent interference signal can be sufficiently attenuated. Therefore, in the television broadcast signal receiving tuner corresponding to the PAL system and the SECAM-L system, it is possible to ensure the basic performance defined by the EMC resistance and the like and absorb the variation in the basic performance at the time of mass production.

  The television broadcast signal receiving tuner includes a switch unit that switches between a connection state in which a resistor is connected in parallel to the coupling inductor and a non-connection state in which the resistor is disconnected. An inductor is connected between a connection point between the primary tuning circuit and the secondary tuning circuit and a ground, and the switch unit is configured to receive the coupling when receiving a SECAM-L television broadcast signal in the VHF low band. The resistor is connected to an inductor for use.

  According to this configuration, when a SECAM-L television signal in the VHF low band is received, it is possible to reduce the degree of coupling by the coupling inductor by connecting the resistor in parallel to the coupling inductor.

  In the television broadcast signal receiving tuner according to the present invention, the switch unit includes a collector connected to one end of the coupling inductor, an emitter connected to the other end of the coupling inductor, and an ON resistance between the collector and the emitter. The transistor is turned on when receiving a SECAM-L television broadcast signal in the VHF low band.

  According to this configuration, when a SECAM-L television signal in the VHF low band is received, the transistor is turned on, so that the ON resistance is connected in parallel to the coupling inductor, and the degree of coupling by the coupling inductor is reduced. can do.

  The present invention provides the television broadcast signal receiving tuner, wherein the switch unit is provided between a switching diode having an anode connected to one end of the coupling inductor, a cathode of the switching diode, and the other end of the coupling inductor. The switching diode is turned on when receiving a SECAM-L television broadcast signal in the VHF low band.

  According to this configuration, when the SECAM-L television signal in the VHF low band is received, the switching diode is turned on, so that the resistor is connected in parallel to the coupling inductor, and the coupling degree by the coupling inductor is reduced. can do.

  According to the present invention, it is possible to support the PAL method and the SECAM-L method in the VHF low band without degrading the basic performance.

It is a figure which shows embodiment of the television broadcast signal receiving tuner which concerns on this invention, and is a circuit block diagram of a television broadcast signal receiving tuner. It is a figure which shows embodiment of the television broadcast signal reception tuner which concerns on this invention, and is a figure which shows an example of the response characteristic at the time of the television broadcast signal reception in a VHF low band. It is a figure which shows embodiment of the television broadcast signal receiving tuner which concerns on this invention, and is a figure which shows an example of the video characteristic from a television broadcast signal receiving tuner to the demodulation circuit which is not shown in figure. It is a figure which shows the modification of the television broadcast signal receiving tuner which concerns on this invention, and is a partial block diagram of a television broadcast signal receiving tuner. It is a figure which shows the other modification of the television broadcast signal receiving tuner which concerns on this invention, and is a partial block diagram of a television broadcast signal receiving tuner. It is a figure which shows the prior art example of the television broadcast signal receiving tuner which concerns on this invention, and is a circuit block diagram of a television broadcast signal receiving tuner. It is a figure which shows the prior art example of the television broadcast signal reception tuner which concerns on this invention, and is a figure which shows an example of the response characteristic at the time of the television broadcast signal reception in a VHF low band.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. The television broadcast signal reception tuner according to the embodiment of the present invention reduces the degree of coupling between the primary side tuning circuit and the secondary side tuning circuit when receiving a SECAM-L television broadcast signal in the VHF low band. Thus, the PAL system and the SECAM-L system are made compatible with the basic performance secured. FIG. 1 is a circuit configuration diagram of a television broadcast signal receiving tuner according to an embodiment of the present invention.

  As shown in FIG. 1, a television broadcast signal receiving tuner 1 is compatible with the PAL system and the SECAM (L) system, and includes an antenna tuning circuit 2, an RF amplifier circuit 3, an RF tuning circuit 4, and a VHF. A mixer circuit 5, a VHF local oscillation circuit 6, and an IF tuning circuit 7 are provided. A tuning frequency component is extracted from an antenna tuning circuit 2 from a high-frequency signal received from an antenna element (not shown).

  The high frequency signal that has passed through the antenna tuning circuit 2 is amplified by the RF amplifier circuit 3, and the tuning frequency component is extracted by the RF tuning circuit 4. The high frequency signal that has passed through the RF tuning circuit 4 is input to the VHF mixer circuit 5 together with the local oscillation signal output from the VHF local oscillation circuit 6. The high-frequency signal input to the VHF mixer circuit 5 is multiplied by the local oscillation signal and converted into an intermediate frequency signal. The intermediate frequency signal frequency-converted by the VHF mixer circuit 5 is extracted from the tuning frequency component by the IF tuning circuit 7 and output to the subsequent circuit.

  The television broadcast signal receiving tuner 1 is configured so that the circuit configuration of the RF tuning circuit 4 can be switched when receiving a VHF high-band and VHF low-band television broadcast signal. The RF tuning circuit 4 is a double tuning circuit, and includes a primary tuning circuit 11 connected to the output terminal of the RF amplifier circuit 3 and a secondary tuning circuit 12 connected to the input terminal of the VHF mixer circuit 5. It is configured.

  In the primary tuning circuit 11, the output terminal of the RF amplifier circuit 3 is grounded through the capacitor C1 and the varactor diode VD1. The varactor diode VD1 has a cathode connected to a power supply B1 that outputs a tuning voltage via a resistor R1, and an anode connected to the ground. The cathode of the varactor diode VD1 is connected to a series circuit including inductors L1 and L2 via a capacitor C1.

  The secondary tuning circuit 12 is connected to one end on the ground side of the inductor L <b> 2 of the primary tuning circuit 11. One end of the inductor L2 of the primary tuning circuit 11 is connected to a series circuit including an inductor L3, a capacitor C2, an inductor 4, and a varactor diode VD2. The varactor diode VD <b> 2 has a cathode connected to the power supply B <b> 1 that outputs a tuning voltage via the resistor R <b> 2 and an anode connected to the input terminal of the VHF mixer circuit 5. A connection point between the inductor L4 and the cathode of the varactor diode VD2 is grounded via the varactor diode VD3. The varactor diode VD3 has a cathode connected to a power supply B1 that outputs a tuning voltage via a resistor R2, and an anode connected to the ground.

  The connection point between the inductors L1 and L2 of the primary tuning circuit 11 is connected to the connection point between the inductor L3 and the capacitor C2 of the secondary tuning circuit 12 via the bypass line 13 provided with the switching diodes SD1 and SD2. The switching diode SD1 has an anode connected to the connection point of the inductors L1 and L2, and a cathode connected to the cathode of the switching diode SD2. The switching diode SD2 has an anode connected to a connection point between the inductor L3 and the capacitor C2. The connection point of the cathodes of the switching diodes SD1 and SD2 is grounded via a capacitor C3 and connected to the switch type power supply 14 via a resistor R3.

  A connection point between the primary tuning circuit 11 and the secondary tuning circuit 12 is grounded via a coupling inductor L5 and a capacitor C4. The coupling inductor L5 is a coupling coil that couples the primary tuning circuit 11 and the secondary tuning circuit 12 at a high frequency, and the bandwidth of the reception frequency in the RF tuning circuit 4 depends on the degree of coupling by the coupling coil. Adjusted. The operation of adjusting the degree of coupling of the coupling inductor L5 will be described later.

  One end of the coupling inductor L5 opposite to the ground side is connected to the collector of the switching transistor T1 via the capacitor C5. The switching transistor T1 has a collector connected to the power source B2 via a resistor R4, an emitter grounded, and an ON resistance between the collector and emitter. The connection point between the coupling inductor L5 and the capacitor C4 is connected to the power supply B2.

  In the present embodiment, VHF mixer circuit 5, VHF local oscillation circuit 6, IF tuning circuit 7, switch type power supply 14, and switching transistor T1 are provided in the IC of television broadcast signal receiving tuner 1. Yes. However, the present invention is not limited to this configuration, and these may be provided outside the IC.

  In the television broadcast signal receiving tuner 1 configured as described above, the VHF high-band and VHF low-band television broadcast signals can be received by turning on and off the switch type power supply 14 and the switching transistor T1. Further, the coupling by the inductor L5 for coupling is performed so as to widen the reception frequency bandwidth when receiving the PAL television broadcast signal in the VHF low band and narrow the reception frequency bandwidth when receiving the SECAM-L television broadcast signal. The degree is adjusted.

  Hereinafter, the reception operation by the television broadcast signal reception tuner will be described. When receiving a VHF high-band television broadcast signal, the switch type power supply 14 is turned off and the switching transistor T1 is turned off. With this configuration, a forward voltage is applied from the power source B2 to the anodes of the switching diodes SD1 and SD2 via the inductors L5, L2, and L3, and the primary tuning circuit 11 and the secondary tuning circuit 12 are conducted through the bypass line 13. Is done.

  The primary tuning circuit 11 includes a parallel resonance circuit including the varactor diode VD1 and the inductor L1, and the secondary tuning circuit 12 includes a parallel resonance circuit including the inductor L4 and the varactor diodes VD2 and VD3. A tuning voltage is applied to the cathodes of the varactor diodes VD1, VD2, and VD3 of the two resonant circuits configured as described above, thereby adjusting the tuning frequency of the RF tuning circuit 4 when receiving a VHF high-band television broadcast signal. Is done.

  When receiving a PAL television broadcast signal in the VHF low band, the switch type power supply 14 is turned on and the switching transistor T1 is turned off. When the switch type power supply 14 is turned on, a reverse voltage is applied from the switch type power supply 14 to the cathodes of the switching diodes SD1 and SD2 via the resistor R3. At this time, the forward voltage is applied from the power source B2 to the anodes of the switching diodes SD1 and SD2 via the inductors L5, L2, and L3, but the reverse voltage applied to the switching diodes SD1 and SD2 is more than the forward voltage. The bypass line 13 is cut off.

  With this configuration, the primary tuning circuit 11 and the secondary tuning circuit 12 are coupled in high frequency by the coupling inductor L5. Further, when the switching transistor T1 is turned OFF, the ON resistance of the switching transistor T1 is disconnected from the coupling inductor L5. Thereby, the degree of coupling by the coupling inductor L5 is greatly adjusted. Note that the bandwidth of the reception frequency at this time is set to a bandwidth capable of receiving the desired wave signal of the PAL system in the low band and sufficiently attenuating the interference signal.

  In the primary tuning circuit 11, a parallel resonant circuit is configured by the varactor diode VD1 and the inductors L1 and L2. In the secondary tuning circuit 12, a parallel resonant circuit is configured by the inductors L3 and L4 and the varactor diodes VD2 and VD3. The By applying a tuning voltage to the cathodes of the varactor diodes VD1, VD2, and VD3 of the resonance circuit configured as described above, the tuning frequency of the RF tuning circuit 4 when receiving a PAL television broadcast signal in the VHF low band is reduced. Adjusted.

  When receiving a SECAM-L television broadcast signal in the VHF low band, the switch type power supply 14 is turned on and the switching transistor T1 is turned on. When the switch type power supply 14 is turned on, a reverse voltage is applied from the switch type power supply 14 to the cathodes of the switching diodes SD1 and SD2 via the resistor R3. At this time, the forward voltage is applied from the power source B1 to the anodes of the switching diodes SD1 and SD2 via the inductors L5, L2, and L3, but the reverse voltage applied to the switching diodes SD1 and SD2 is more than the forward voltage. The bypass line 13 is cut off.

  With this configuration, the primary tuning circuit 11 and the secondary tuning circuit 12 are coupled in high frequency by the coupling inductor L5. Further, when the switching transistor T1 is turned ON, the other end of the inductor L5 opposite to the ground side is grounded to the ground via the capacitor C5 and the collector-emitter of the switching transistor T1. Therefore, the ON resistance of the switching transistor T1 is connected in parallel to the coupling inductor L5.

  As a result, the degree of coupling by the coupling inductor L5 is adjusted to be smaller than when receiving a PAL television broadcast signal in the VHF low band. Note that the bandwidth of the reception frequency at this time is set to a bandwidth that can receive the desired signal of the SECAM method in the low band and can sufficiently attenuate the interference signal that is inverted from the PAL method. The

  In the primary tuning circuit 11, a parallel resonant circuit is configured by the varactor diode VD1 and the inductors L1 and L2. In the secondary tuning circuit 12, a parallel resonant circuit is configured by the inductors L3 and L4 and the varactor diodes VD2 and VD3. The By applying a tuning voltage to the cathodes of the varactor diodes VD1, VD2, and VD3 of the resonance circuit configured as described above, the tuning frequency of the RF tuning circuit 4 when receiving a PAL television broadcast signal in the VHF low band is reduced. Adjusted.

  Next, response characteristics between the antenna and the VHF mixer circuit when receiving a television broadcast signal in the VHF low band will be described with reference to FIG. FIG. 2 is a diagram illustrating an example of response characteristics when a television broadcast signal in the VHF low band of the television broadcast signal reception tuner according to the embodiment of the present invention is received. 2, (a) is when receiving a PAL television broadcast signal in this embodiment, (b) is when receiving a SECAM-L television broadcast signal in a comparative example, and (c) is this embodiment. The response characteristics at the time of receiving a television broadcast signal of the SECAM-L system in the form are respectively shown.

  First, response characteristics when a PAL television broadcast signal in the VHF low band is received will be described. When receiving a PAL television broadcast signal in the VHF low band, the switch type power supply 14 is turned on, the switching transistor T1 is turned off, and the primary tuning circuit 11 and the secondary tuning circuit 12 are coupled to each other by a coupling inductor L5. Combined with In this case, the degree of coupling of the coupling inductor L5 is set large, and response characteristics as shown in FIG. 2A are obtained.

  In this response characteristic, the video signal P, the color signal C, and the audio signal S appear in order from the low frequency side to the high frequency side of the reception frequency band, and the disturbance signal UD of the upper adjacent channel is displayed on the high frequency side of the audio signal S. Appears. At this time, the bandwidth of the reception frequency is set to a bandwidth that can receive the video signal P, the color signal C, and the audio signal S and that can sufficiently attenuate the interference signal UD.

  Next, response characteristics when receiving a SECAM-L television broadcast signal in the VHF low band will be described. Here, as a comparative example, a description will be given in comparison with a case where a SECAM-L television broadcast signal is received with the same circuit configuration as when a PAL television broadcast signal in the VHF low band is received. When a SECAM-L television broadcast signal is received in the comparative example, response characteristics as shown in FIG. 2B are obtained.

  In this response characteristic, the desired signal and the interference signal are inverted with respect to the PAL television broadcast signal, and the audio signal S, the color signal C, and the video signal P (for example, 63. 75 MHz), and on the low frequency side of the audio signal S, the interference signal UD (for example, 55.75 MHz) of the lower adjacent channel appears. At this time, in the comparative example, since the bandwidth of the reception frequency is adapted to the PAL system, the influence of the interference signal UD on the audio signal S is increased.

  When 70 dBμV is input to 63.75 MHz (video signal P) and 68 dBμV is input to 55.75 MHz (disturbance signal UD), as shown in FIG. 3A, from the television broadcast signal reception tuner to the demodulation circuit (not shown). The video characteristics are swollen at an intermediate portion from the video signal P to the color signal C. Under this condition, no beat is detected, but there is no margin for the basic performance defined by EMC tolerance or the like. For this reason, the television broadcast signal receiving tuner according to the comparative example cannot absorb variations in basic performance due to mass production or the like.

  On the other hand, in the television broadcast signal receiving tuner 1 according to the present embodiment, the switch type power supply 14 is turned on when the SECAM-L television broadcast signal in the VHF low band is received, and the primary tuning circuit 11 and the secondary tuning are received. The circuit 12 is coupled at a high frequency by a coupling inductor L5. Further, the switching transistor T1 is turned on, and the ON resistance of the switching transistor T1 is connected in parallel to the coupling inductor L5. As a result, the degree of coupling of the coupling inductor L5 is set smaller than when receiving a PAL television broadcast signal, and response characteristics as shown in FIG. 2C are obtained.

  In this response characteristic, compared to the comparative example, the bandwidth of the reception frequency is narrowed and a steep waveform is formed. Also, the audio signal S, the color signal C, and the video signal P (for example, 63.75 MHz) appear in the order from the low frequency side to the high frequency side, and on the low frequency side of the audio signal S, the interference signal UD ( For example, 55.75 MHz) appears. At this time, since the signal level is attenuated on the low frequency side of the reception frequency, the signal level of the disturbing signal UD of the lower adjacent channel is greatly attenuated.

  Then, when 70 dBμV is input to 63.75 MHz (video signal P) and 68 dBμV is input to 55.75 MHz (interference signal UD), as shown in FIG. 3B, from the television broadcast signal reception tuner to the demodulation circuit (not shown). The video characteristics are narrowed from the video signal P toward the color signal C. At this time, the beat detection limit is improved to +6 dBμV with respect to the basic performance defined by EMC tolerance or the like. Therefore, the television broadcast signal receiving tuner according to the present embodiment can absorb variations in basic performance due to mass production or the like.

  As described above, according to the television broadcast signal receiving tuner 1 according to the present embodiment, when the PAL television signal is received, the coupling degree by the coupling inductor L5 is greatly adjusted, so Sufficiently attenuate the signal. On the other hand, when receiving a SECAM-L television broadcast signal in the VHF low band, the coupling degree by the coupling inductor L5 is adjusted to be smaller than when receiving a PAL television broadcast signal in the VHF low band. The frequency band is narrowed, and the adjacent adjacent interference signal is sufficiently attenuated. Therefore, in the television broadcast signal receiving tuner corresponding to the PAL system and the SECAM-L system, it is possible to secure the basic performance defined by the EMC resistance or the like and absorb the variation in the basic performance at the time of mass production.

  In this embodiment, the coupling degree of the coupling inductor is adjusted by the switching transistor having the ON resistance. However, the present invention is not limited to this configuration. Any resistor may be used as long as the resistor is connected in parallel to the coupling inductor. For example, an alternative circuit as shown in FIG.

  In the alternative circuit shown in FIG. 4, a series circuit including a switching diode SD11, a resistor R11, and a capacitor C11 is provided between one end of the coupling inductor L11 opposite to the ground side and the ground. At this time, a power source (not shown) is connected to the connection point between the resistor R11 and the capacitor C11 via the resistor R12. By applying the output voltage from the power supply to the cathode of the switching diode SD11, the resistor R11 is disconnected from the coupling inductor L11. Further, when the application of the output voltage is stopped, the resistor R11 is connected in parallel to the coupling inductor L11.

  As described above, the series circuit of the switching diode SD11 and the resistor R11 can suppress variation in the degree of coupling due to the coupling inductor L11 as compared with the configuration in which the ON resistance in the switching transistor is connected.

  In this embodiment, the coupling degree of the coupling inductor is adjusted by the switching transistor provided in the IC. However, the present invention is not limited to this configuration. As shown in FIG. 5, the coupling degree of the coupling inductor L21 may be adjusted by a switching transistor T21 provided outside the IC. In this case, a capacitor C21 and a switching transistor T21 are provided between one end of the coupling inductor L21 and the ground. The switching transistor T21 has a collector connected to the power source B21 via a resistor R21, and an emitter grounded.

  When the switching transistor T21 is OFF, the coupling inductor L21 is disconnected from the ON resistance of the switching transistor T21. On the other hand, when the switching transistor T21 is turned on, one end of the coupling inductor L21 is grounded to the ground via the capacitor C21 and the collector-emitter of the switching transistor T21, and the coupling inductor L21 is turned on of the switching transistor T21. Connected in parallel with the resistor.

  In this way, even in a configuration in which a switching transistor is provided outside the IC, in the television broadcast signal receiving tuner corresponding to the PAL system and the SECAM-L system, the basic performance defined by the EMC resistance or the like is ensured, It is possible to absorb variations in basic performance during mass production.

  In this embodiment, a resistor is connected in parallel to the coupling inductor by a switching transistor or the like, and the coupling degree by the coupling inductor is set to a SECAM-L system television rather than the PAL system in the VHF low band. Although the configuration is made small when receiving a broadcast signal, it is not limited to this configuration. Any configuration may be used as long as the degree of coupling by the coupling inductor is smaller when receiving a SECAM-L system television broadcast signal than the PAL system in the VHF low band.

  In the present embodiment, the coupling inductor is composed of a coupling coil, but the present invention is not limited to this configuration. As long as the primary tuning circuit and the secondary tuning circuit can be coupled in a high frequency manner, for example, a laminated inductor formed by laminating sheet-like conductor plates, a thin film type constituted by printing a spiral conductor pattern You may comprise with an inductor.

  In the present embodiment, the television broadcast signal receiving tuner corresponding to the PAL and SECAM-L broadcast signals has been described as an example. However, the present invention is not limited to this configuration. The present invention can also be applied to a television broadcast signal receiving tuner corresponding to a television broadcast system in which the frequency of a desired wave signal is inverted. For example, the SECAM-L system and other broadcast systems You may apply to the thing corresponding to.

  The embodiment disclosed this time is illustrative in all respects and is not limited to this embodiment. The scope of the present invention is shown not by the above description of the embodiments but by the scope of the claims, and is intended to include all modifications within the meaning and scope equivalent to the scope of the claims.

  As described above, the present invention has the effect of being able to support the PAL system and the SECAM-L system in the VHF low band without degrading the basic performance, and in particular, the PAL system and the SECAM system television. This is useful for a television broadcast signal receiving tuner capable of receiving a broadcast signal.

1 Television broadcast signal reception tuner 2 Antenna tuning circuit 3 RF amplifier circuit 4 RF tuning circuit (double tuning circuit)
5 VHF Mixer Circuit 6 VHF Local Oscillator 7 IF Tuning Circuit 11 Primary Tuning Circuit 12 Secondary Tuning Circuit 13 Bypass Line 14 Switch Type Power Supply L5, L11, L21 Inductors (Coupling Inductors)
T1, T21 Switching transistor (switch part)
SD11 Switching diode (switch part)
R11 resistor (switch part)

Claims (4)

In a television broadcast signal reception tuner capable of receiving PAL and SECAM-L television broadcast signals,
A double tuning circuit having a primary tuning circuit and a secondary tuning circuit, and a coupling inductor for adjusting a coupling degree of the primary tuning circuit and the secondary tuning circuit;
When receiving the SECAM-L television broadcast signal in the VHF low band, the double tuning circuit has a smaller degree of coupling by the coupling inductor than when receiving the PAL television broadcast signal. John broadcast signal reception tuner. A switch unit that switches between a connection state in which a resistor is connected in parallel to the coupling inductor and a non-connection state in which the resistor is disconnected;
The coupling inductor is connected between a connection point of the primary tuning circuit and the secondary tuning circuit and a ground;
2. The television broadcast signal receiving tuner according to claim 1, wherein the switch unit connects the resistor to the coupling inductor when receiving a SECAM-L television broadcast signal in the VHF low band. The switch unit includes a transistor having a collector connected to one end of the coupling inductor, an emitter connected to the other end of the coupling inductor, and an ON resistance between the collector and the emitter,
3. The television broadcast signal receiving tuner according to claim 2, wherein the transistor is turned on when a SECAM-L television broadcast signal in the VHF low band is received. The switch unit includes a switching diode having an anode connected to one end of the coupling inductor, and a resistor provided between the cathode of the switching diode and the other end of the coupling inductor,
3. The television broadcast signal receiving tuner according to claim 2, wherein the switching diode is turned on when a SECAM-L television broadcast signal in the VHF low band is received.

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