JP3801845B2 - Television tuner - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a television tuner that effectively improves the interference received from FM signals and the interference received from intermediate frequency band signals.
[0002]
[Prior art]
FIG. 3 shows a configuration of a conventional television tuner (hereinafter simply referred to as a tuner). In FIG. 3, the television signal input to the input terminal 31 is input to the FM trap circuit 34 through the CB trap circuit 32 and the IF trap circuit 33.
The CB trap circuit 32 is composed of a series resonance circuit, and attenuates the civil band in the 27 MHz band. The IF trap circuit 33 is composed of a parallel resonant circuit, and attenuates, for example, an intermediate frequency band of a television of the US specification.
[0003]
The FM trap circuit 34 is configured by a parallel resonance circuit including an inductance element 34a and a capacitor 34b, and attenuates, for example, an FM broadcast band of US specifications.
A first switch diode 35 is connected in parallel to the FM trap circuit 34 via a DC cut capacitor 36. The cathode of the first switch diode 35 is grounded via a resistor 37 and is connected to the first terminal 38 in a direct current manner. A voltage for turning off the first switch diode 35 is applied to the first terminal 38.
The television signal that has passed through the FM trap circuit 34 is input to the input tuning circuit 39.
[0004]
The input tuning circuit 39 includes a second switch diode 39a for switching to tune to the high band or low band of the VHF band, a varactor diode 39b for changing the tuning frequency, and the like. The cathode of the second switch diode 39a is connected to the anode of the first switch diode 35 in a direct current manner and is grounded by a resistor 39c. Further, it is connected to the second terminal 40 in a direct current manner. A voltage for turning off the second switch diode 39 a is applied to the second terminal 40.
The anode of the second switch diode 39 a is connected to the third terminal 42. A voltage for applying the second switch diode 39 a is applied to the third terminal 41.
[0005]
The anode of the varactor diode 39 b is grounded in a direct current manner, and the cathode is connected to the fourth terminal 42. A voltage (tuning voltage) for changing the capacitance value of the varactor diode 39b is applied to the fourth terminal. A high frequency amplifier circuit 43 is connected to the next stage of the input tuning circuit 39. A mixing circuit (not shown) for frequency conversion is provided in the subsequent stage of the high frequency amplifier circuit 43.
[0006]
In the above configuration, when receiving a high-band channel of the US specification VHF band, a voltage is applied to the first terminal 38 and the third terminal 41 without applying a voltage to the second terminal 40. . Then, the first switch diode 35 is turned off and the second switch diode 39a is turned on. As a result, the FM trap circuit 34 attenuates the FM broadcast band.
The input tuning circuit 39 is tuned to the high band, and the tuning frequency is adjusted to the frequency of the desired channel by the tuning voltage applied to the fourth terminal 42. Here, the frequency of the high-band channel is twice that of the FM broadcast band. However, since the FM trap circuit 34 functions, it is not disturbed by the FM broadcast signal.
[0007]
Also, when receiving a channel whose frequency is closest to the FM broadcast band among the low-band channels (for example, channel 6 in the US specification), the first terminal 38 is not applied with a voltage to the third terminal 41. And a voltage is applied to the second terminal 40. Then, the first switch diode 5 and the second switch diode 9a are turned off. As a result, the FM trap circuit 4 functions, the input tuning circuit 39 is tuned to the low band, and the tuning frequency is adjusted to the frequency of the desired channel by the tuning voltage applied to the fourth terminal 42.
[0008]
When receiving a low-band channel other than the channel closest to the FM broadcast band, a voltage is applied to the second terminal 40 without applying a voltage to the first terminal 38 and the third terminal 41. Apply. Then, the first switch diode 5 is turned on and the second switch diode 39a is turned off. As a result, the FM trap circuit 34 becomes invalid, and a CATV signal transmitted using the FM broadcast band can also be received. The input tuning circuit 9 is tuned to a low band channel.
[0009]
[Problems to be solved by the invention]
As is apparent from FIG. 3, the conventional tuner has an IF trap circuit and an FM trap circuit provided independently, which increases the number of parts used, increases the part cost, and further reduces the size. It was an obstacle.
[0010]
Therefore, the television tuner of the present invention aims to effectively attenuate the intermediate frequency band and FM broadcast band of the television by reducing the number of parts used in the trap circuit.
[0011]
[Means for Solving the Problems]
In order to solve the above problems, a television tuner of the present invention includes a high-frequency amplifier circuit that amplifies a VHF-band television signal, and a signal interposed between the input terminal of the television signal and the high-frequency amplifier circuit. A trap circuit for attenuation, wherein the trap circuit is an inductance element, a varactor diode connected in series to the inductance element, and a first circuit connected in parallel to a series circuit of the inductance element and the varactor diode. A capacitor, and when receiving an adjacent channel whose frequency is closest to the FM broadcast band and a double frequency channel that matches twice the frequency of the FM broadcast band , a reverse bias voltage is applied to the varactor diode to The trap frequency of the trap circuit is set to be within the FM broadcast band, and When receiving another channel other than the near-channel and the double frequency channel is set to be within an intermediate frequency band trap frequency of the television of the trap circuit by turning on the varactor diode.
[0012]
The proximity channel is a US-specific channel 6 and the double frequency channel is a US-specific high-band channel.
[0014]
A second capacitor was connected to the varactor diode.
[0015]
A switch diode provided between the trap circuit and the high-frequency amplifier circuit, which is turned on when receiving a high-band channel of the VHF band and turned off when receiving a low-band channel; An input tuning circuit that tunes to the frequency of the channel to be switched, a first terminal that is DC connected to the anode of the switch diode, a second terminal that is DC connected to the cathode of the switch diode, and the varactor A third terminal connected to the cathode of the diode in a direct current manner, and grounding the cathode of the varactor diode via a first resistor, and connecting the anode to the cathode of the switch diode and the second terminal. Connect to DC and ground through a second resistor to receive the proximity channel Applies a voltage to the second terminal and the third terminal, and when receiving the double frequency channel, applies a voltage to the first terminal and the third terminal, When receiving, a voltage was applied only to the second terminal.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 shows a circuit diagram of a television tuner (hereinafter simply referred to as a tuner) of the present invention. In FIG. 1, an input end 1 of a television signal is connected to each end of a first trap circuit 3 and a second trap circuit 4 via a DC cut capacitor 2. The first trap circuit 3 is composed of a series resonance circuit of a capacitor 3a and an inductance element 3b, one end of which is grounded, and serves as a CB trap circuit for attenuating a civil band in the 27 MHz band. A connection point between the capacitor 3a and the inductance element 3b is grounded by the first resistor 5 and is connected to the first terminal 6 in a direct current manner.
[0017]
The second trap circuit 4 includes an inductance element 4a and a first varactor diode 4b connected in series to each other, and a first capacitor connected in parallel to the series circuit of the inductance element 4a and the first varactor diode 4b. 4c and a parallel resonant circuit including a second capacitor 4d connected in parallel to the first varactor diode 4b.
[0018]
A connection point between the inductance element 4 a and the first capacitor 4 c is connected to the input terminal 1 and to the inductance element 3 b of the first trap circuit 3. As a result, the cathode of the first varactor diode 4b is DC-grounded by the first resistor 5 and further connected to the first terminal 6 by DC. The first varactor diode 4b is turned off when a voltage is applied to the first terminal 6, and turned on when no voltage is applied.
[0019]
The parallel resonance frequency of the second trap circuit 4 is low when the first varactor diode 4b is turned on, and is high because it is reverse-biased and has a capacity when it is turned off. Therefore, the parallel resonance frequency when turned on is set to be an intermediate frequency band of television, for example, between 41 MHz and 47 MHz in the US specification (between 54 MHz and 60 MHz in the Japanese specification).
Further, the parallel resonance frequency when turned off is set to be an FM broadcast band, for example, between 88 MHz and 108 MHz in the US specification (between 76 MHz and 90 MHz in the Japanese specification).
Therefore, the second trap circuit 4 is a frequency switching type trap circuit.
[0020]
An input tuning circuit 7 is provided on the output side of the second trap circuit 4.
The input tuning circuit 7 is switched so as to tune to the high band channel or low band channel of the VHF band, and the switching diode 7a for switching and three inductance elements 7b connected in series as shown in the figure. 7c, 7d, an inductance element 7f connected in series to the inductance element 7b via a DC cut capacitor 7e, a second varactor diode 7g for changing the tuning frequency, and the like. The connection point between the inductance elements 7b and 7c is connected to the anode of the first varactor diode 4b.
[0021]
The inductance element 7d is grounded by the DC cut capacitor 7h and grounded by the second resistor 8. It is also connected to the second terminal 9. The cathode of the switch diode 7a is connected to the connection point between the inductance element 7b and the DC cut capacitor 7e, and the cathode is connected to the connection point between the inductance elements 7c and 7d via the DC cut capacitor 7i and the third terminal. 10 and further grounded by a resistor 11. As a result, the cathode of the switch diode 7a is connected in direct current to the anode of the first varactor diode 4a. A voltage for turning off the switch diode 7a is applied to the second terminal 9, and a voltage for turning on the third terminal 10 is applied.
[0022]
A connection point between the DC cut capacitor 7e and the inductance element 7f is grounded by the resistor 12. The cathode of the second varactor diode 7 g is connected to the other end of the inductance element 7 f and the anode is connected to the fourth terminal 13. A voltage (tuning voltage) for changing the capacitance value of the second varactor diode 7g is applied to the fourth terminal 13.
A high frequency amplifier circuit 14 is connected to the next stage of the input tuning circuit 7, and a mixing circuit (not shown) is provided after the high frequency amplifier circuit 14.
[0023]
In the above configuration, when receiving a channel whose frequency is closest to the FM broadcast band (herein referred to as a close channel, which is a low band channel 6 in the US specification), the third terminal 10 is not applied with a voltage, A voltage is applied to one terminal 6 and the second terminal 9. In this case, since the resistance values of the first resistor 5 and the second resistor 8 are set so that the first varactor diode is reverse-biased, both the first varactor diode 4b and the switch diode 7a are turned off. To do. As a result, the parallel resonance frequency of the first trap circuit 4 is within the FM broadcast band, and the total transmission characteristics of the first trap circuit 3 and the second trap circuit 4 are as shown by the solid line A in FIG. The characteristics are attenuated in the civil band (indicated by CB) and the FM broadcast band (indicated by FM). Since the channel 6 is separated from the intermediate frequency band (indicated by IF), the channel 6 is not subjected to the interference wave reception by a signal existing in this frequency band even if the intermediate frequency band is not attenuated.
On the other hand, the input tuning circuit 7 is tuned to the low band when the switch diode 7 a is turned off, and the tuning frequency is adjusted to the frequency of the channel 6 by the tuning voltage applied to the fourth terminal 13.
[0024]
Next, when receiving a channel in which the frequency of the channel to be received is twice the frequency of the FM broadcast band (herein referred to as a double frequency channel, which corresponds to all high-band channels in the US specification) A voltage is applied to the first terminal 6 and the third terminal 10 without applying a voltage to the second terminal 9. Then, the first varactor diode is turned off and the switch diode 7a is turned on. Therefore, the total transmission characteristic in this case is also as shown by the solid line A in FIG. Even in this case, the double frequency channel is separated from the intermediate frequency band, so that it is not disturbed even if the intermediate frequency band is not attenuated.
The input tuning circuit 7 is tuned to the high band when the switch diode 7a is turned on, and the tuning frequency is adjusted to the tuning voltage applied to the fourth terminal 13 to the frequency of the high band receiving channel.
[0025]
Next, when receiving a channel other than the adjacent channel (herein referred to as another channel, and a low-band channel other than channel 6 (channel 2 to channel 5) corresponds to this), the first terminal 6 and the third channel are received. A voltage is applied to the second terminal 9 without applying a voltage to the terminal 10. Then, the first varactor diode 4b is turned on and the switch diode 7a is turned off. Therefore, the overall transmission characteristic is attenuated in the civic band and the intermediate frequency band and is not attenuated in the FM broadcast band as shown by a dotted line B in FIG. Therefore, it is possible to receive a CATV signal transmitted using the FM broadcast band. Further, even if the channel is transmitted by AIR (normal television signal), the interference wave due to the FM broadcast signal is not a problem because it is away from the FM broadcast band.
[0026]
In the second trap circuit 4 of the present invention, the number of inductance elements, capacitors, and resistors to be used is one less than that of the conventional one.
Since the second capacitor 4d is connected in parallel to the first varactor diode 4a, it is easy to match the parallel resonance frequency of the second trap circuit 4 to the intermediate frequency band and the FM broadcast frequency band.
[0027]
【The invention's effect】
As described above, the television tuner of the present invention includes the signal attenuation trap circuit interposed between the input end of the television signal and the high frequency amplifier circuit, and the trap circuit includes the inductance element, the inductance, and the inductance circuit. A varactor diode connected in series to an element, and a first capacitor connected in parallel to a series circuit of the inductance element and the varactor diode, the adjacent channel having the frequency closest to the FM broadcast band, wherein by applying a reverse bias voltage to the varactor diode set a trap frequency of the trap circuit so that the FM broadcast band when receiving a double frequency channel that matches the twice the frequency of the FM broadcast band, wherein When a channel other than the adjacent channel and the double frequency channel is received When the varactor diode is turned on and the trap frequency of the trap circuit is set to be in the intermediate frequency band of the television , the trap frequency is set to the FM broadcast band when the varactor diode is reverse-biased. In addition, it can be adjusted to the intermediate frequency band when turned on, and the trap frequency required by the receiving channel can be properly used by one trap circuit, so the number of parts used can be reduced and the cost can be reduced. . It also contributes to miniaturization.
[0028]
Further, since the proximity channel is the US specification channel 6 and the double frequency channel is the US specification high band channel, the US specification television tuner can be configured at low cost.
[0030]
In addition, since the second capacitor is connected to the varactor diode, it is easy to match the trap frequency to the FM broadcast band and the intermediate frequency band.
[0031]
In addition, the first terminal connected to the anode of the switch diode of the input tuning circuit is connected to the anode, the second terminal connected to the cathode of the switch diode and connected to the cathode of the varactor diode. A third terminal is provided, and when receiving a proximity channel, a voltage is applied to the second terminal and the third terminal, and when receiving a double frequency channel, a voltage is applied to the first terminal and the third terminal. When the other channel is received, the voltage is applied only to the second terminal, so that the varactor diode can be reverse-biased when the adjacent channel and the double frequency channel are received, and the other channel is received. Sometimes the varactor diode can be turned on.
[Brief description of the drawings]
FIG. 1 is a circuit diagram of a television tuner of the present invention.
FIG. 2 is a transmission characteristic diagram of the television tuner of the present invention.
FIG. 3 is a circuit diagram of a conventional television tuner.
[Explanation of symbols]
1 Input Terminal 2 DC Cut Capacitor 3 First Trap Circuit 3a Capacitor 3b Inductive Element 4 Second Trap Circuit 4a Inductive Element 4b First Varactor Diode 4c First Capacitor 4d Second Capacitor 5 First Resistor 6 First One terminal 7 Input tuning circuit 7a Switch diodes 7b, 7c, 7d, 7f Inductance elements 7e, 7h, 7i DC cut capacitor 7g Second varactor diode 8 Second resistor 9 Second terminal 10 Third terminal 11, 12 Resistor 13 Fourth terminal 14 High frequency amplifier circuit

Claims (4)

A high frequency amplifier circuit for amplifying a VHF band television signal, and a signal attenuation trap circuit interposed between the input terminal of the television signal and the high frequency amplifier circuit,
The trap circuit includes an inductance element, a varactor diode connected in series to the inductance element, and a first capacitor connected in parallel to a series circuit of the inductance element and the varactor diode. When receiving the closest channel and the double frequency channel that matches the double frequency of the FM broadcast band , a reverse bias voltage is applied to the varactor diode to set the trap frequency of the trap circuit to the FM broadcast. The varactor diode is turned on when receiving a channel other than the adjacent channel and the double frequency channel so that the trap frequency of the trap circuit falls within the intermediate frequency band of the television. that it is set to Television tuner for the butterflies.   2. The television tuner according to claim 1, wherein the adjacent channel is a US-specific channel 6 and the double frequency channel is a US-specific high-band channel.   The television tuner according to claim 1, wherein a second capacitor is connected to the varactor diode. A channel that is provided between the trap circuit and the high-frequency amplifier circuit and has a switch diode that is turned on when receiving the high-band channel of the VHF band and turned off when receiving the low-band channel. An input tuning circuit that tunes to the frequency of the switch diode, a first terminal connected to the anode of the switch diode in a direct current, a second terminal connected to the cathode of the switch diode in a direct current, and the varactor diode A third terminal connected to the cathode in a direct current manner, the cathode of the varactor diode is grounded via a first resistor, and the anode is connected to the cathode of the switch diode and the second terminal in a direct current manner. When receiving the adjacent channel by connecting to and grounding via a second resistor When a voltage is applied to the second terminal and the third terminal and the double frequency channel is received, a voltage is applied to the first terminal and the third terminal and the other channel is received. 4. The television tuner according to claim 2, wherein a voltage is applied only to the second terminal.

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