JP3524351B2 - Television tuner - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a television tuner, and more particularly, to a television capable of receiving a US TV broadcast that effectively reduces interference received from an FM radio broadcast when receiving the sixth channel of a US TV broadcast. Regarding John Tuner.

[0002]

2. Description of the Prior Art In US TV broadcasting, the frequency band assigned to the sixth channel is 82 to 88 MHz, and the audio carrier frequency thereof is set to 87.75 MHz. Further, in the US FM radio broadcasting, there is a broadcasting of a frequency f _FM whose assigned frequency band is 88 to 108 MHz and which is close to the frequency band of the sixth channel of TV broadcasting.

If the received electric field strength of the FM radio broadcast of the frequency f _FM is relatively large, the T-channel of the sixth channel
When V broadcasting is received, noise occurs in the reproduced sound,
Beats appear in the video.

For this reason, in a known television tuner for receiving US TV broadcasting, an F signal is input to the reception signal input terminal.
An M trap circuit is connected, and the received signal of frequency f _FM is attenuated by this trap circuit.

Here, FIG. 3 is a block diagram including a partial circuit diagram showing an example of the configuration of the known television tuner.

As shown in FIG. 3, a known television tuner has a high pass filter (HPF) 61 and an F
M trap circuit 32 and antenna (ANT) tuning circuit 6
2, a high frequency amplifier circuit (RFAMP) 63, a high frequency double tuning circuit 64, a mixing circuit (MIX) 65, and a PLL 6
8, a resistance ground circuit 38, and a buffer diode 39
An input terminal 69 and an output terminal 70.

The FM trap circuit 32 is composed of a switching diode 32 ₁ , an inductor 32 ₂ and capacitors 32 ₃ and 32 ₄ , and is a high frequency double tuning circuit 6
4 is variable capacitance diodes 64 ₁ and 64 ₂ , inductors 64 _{3 to} 64 ₇ , and capacitors 64 _{8 to} 64.
_10, the switching diode 64 _11, 64 _12, and the resistor 64 _13, 64 _14, consists coupling capacitor 64 _15, 64 _16., PLL 68 is the tuning voltage terminal TU, comprises a band switching terminal BS2, BS3, BS4 The resistance ground circuit 38 is composed of resistors 38 ₁ and 38 ₂ and a bypass capacitor 38 ₃ .

The known television tuner of the above construction operates as follows.

In the received signal applied to the input terminal 69, unnecessary high frequency components are removed by the high pass filter 61, and the FM radio broadcasting frequency component close to the sixth channel is attenuated by the FM trap circuit 32 as described later. Then, the received signal of the desired channel is selected in the antenna tuning circuit 62. Next, the received signal is amplified in the high frequency amplifier circuit 63, the received signal of the desired channel is further selected in the high frequency double tuning circuit 64, and the selected received signal is mixed with the local oscillation signal in the mixing circuit 65 to be an intermediate frequency signal. The converted intermediate frequency signal is derived from the output terminal 70.

When any one of the 2 to 6 channel TV broadcasts in the VHF low band is selected, PLL6
A positive voltage is output from the band switching terminal BS3 of 8 and the switching diodes 64 ₁₁ and 64 ₁₂ are output by this positive voltage.
Since the high frequency double tuning circuit 64 turns off the inductors 64 ₃ and 64 because the buffer diode 39 and the buffer diode 39 are turned off.
₄ , inductors 6 together with capacitors 64 ₈ and 64 ₉
4 _{5 to} 64 ₇ and the capacitor 64 ₁₀ are inserted and connected. At this time, a tuning voltage is output from the tuning voltage terminal TU of the PLL 68, this tuning voltage is applied to the variable capacitance diode 64 ₁ via the resistor 64 ₁₃ and the inductor 64 _3, and at the same time via the resistor 64 ₁₄ and the inductor 64 _4. The high frequency double tuning circuit 64 is tuned to the selected TV broadcast by adjusting the capacitances of the variable capacitance diodes 64 ₁ and 64 ₂ in addition to the variable capacitance diode 64 ₂ .

On the other hand, 7 to 13 in the VHF high band
PLL when selecting one of the TV broadcasting channels
A positive voltage is output from the band switching terminal BS2 of 68, and the switching diodes 64 ₁₁ , 64 are generated by this positive voltage.
_{Since the 12} and the buffer diode 39 are turned on respectively, the high frequency double tuning circuit 64 includes the inductors 64 _{5 to} 6
4 ₇ and the circuit part consisting of the capacitor 64 ₁₀ are short-circuited,
Inductors 64 ₃ 64 ₄ Capacitors 64 ₈ 64 ₉
Only the connected form. Also at this time, a tuning voltage is output from the tuning voltage terminal TU of the PLL 68, the tuning voltage is applied to the variable capacitance diode 64 ₁ via the resistor 64 ₁₃ and the inductor 64 ₃ , and the resistor 64 _{14 is also applied.}
And the variable capacitance diode 64 ₂ via the inductor 64 ₄
In addition, since the capacitances of the variable capacitance diodes 64 ₁ and 64 ₂ are adjusted, the high frequency double tuning circuit 64 is tuned to the selected TV broadcast.

The band switching terminal BS4 of the PLL 68
, A positive voltage equal to the power supply voltage is output only when TV broadcast of the sixth channel is selected.

When a TV broadcast other than the sixth channel is selected, the positive voltage output from the band switching terminal BS3 of the PLL 68 is directly applied to the FM trap circuit 32 or the band switching terminal BS2 of the PLL 68.
The positive voltage output from the buffer diode 39 is applied to the FM trap circuit 32, and the switching diode 32 ₁ , the inductor 32 ₂ , and the resistance ground circuit 38 are provided.
The switching diode 32 ₁ is turned on, and the FM trap circuit 32 is bypassed and does not function as a trap circuit.

On the other hand, when the TV broadcast of the sixth channel is selected, as described above, the FM trap circuit 32 is used.
Although a positive voltage is applied to the anode of the switching diode 32 ₁ of the switching diode 32 ₁ , the positive voltage output from the band switching terminal BS4 is applied to the cathode of the switching diode 32 ₁ via the resistor 38 ₁ and the inductor 32 ₂ , so that switching is performed. The diode 32 ₁ turns off. At this time, the FM trap circuit 32 becomes a parallel resonant circuit including the inductor 32 ₂ , the capacitors 32 ₃ and 32 ₄ ,
The parallel resonance circuit attenuates the reception signal of the FM radio broadcast near the frequency band of the sixth channel.

[0015]

Since the known television tuner has the FM trap circuit 32 inserted and connected to the reception signal input terminal when the TV broadcast of the sixth channel is selected, the TV tuner of the sixth channel is not connected. The TV broadcast received signal is input after being attenuated on the high frequency side. Therefore, in order to compensate for this attenuation, the inductors 64 ₅ and 64 _{6 are} adjusted in the sixth channel so that the high frequency double tuning circuit 64 has a wide characteristic on the high frequency side. This characteristic also affects the adjacent fifth channel, and interference is likely to occur when receiving the fifth channel broadcast. Therefore, the high frequency double tuning circuit 64 must adjust to an intermediate characteristic between the two characteristics different between these two channels,
It was not possible to obtain sufficient characteristics.

Further, in the known television tuner, the FM trap circuit 32 is inserted and connected,
Even when the FM trap circuit 32 is not functioning as a trap circuit, the high-frequency amplifier circuit 6 is used so that the noise figure deteriorates or the insertion loss of the FM trap circuit 32 is commensurate.
There is also a problem that the gain of 3 must be increased.

The present invention solves these problems all at once, and its purpose is to adjust the high-frequency double-tuned circuit to ideal characteristics in the sixth channel, thereby reducing insertion loss and noise figure. Is to provide a lesser television tuner.

[0018]

In order to achieve the above-mentioned object, a television tuner of the present invention comprises a high frequency double tuning circuit having a tuning variable capacitance diode, and a television of the sixth channel in the United States. At the time of receiving a broadcast, the tuning variable capacitance diode of at least one of the high frequency double tuning circuits is provided with a means for adding an additional bias voltage, which makes the capacitance of the variable capacitance diode larger than that when only the tuning voltage is applied, together with the tuning voltage. ing.

According to the above-mentioned means, the frequency response characteristic of the high frequency double tuning circuit moves to the lower frequency side when receiving the US 6th channel TV broadcast, and becomes an interference without using the FM trap circuit. It is possible to effectively attenuate the reception signal of FM radio broadcasting.

[0020]

BEST MODE FOR CARRYING OUT THE INVENTION In a preferred embodiment of the present invention, a television tuner includes a high frequency double tuning circuit having a tuning variable capacitance diode, is capable of receiving a television broadcast of a US channel, and is a sixth channel. When receiving the television broadcast of, the additional bias voltage, which makes the capacitance of the variable capacitance diode larger than that when only the tuning voltage is applied, is added to the tuning variable capacitance diode of at least one of the high frequency double tuning circuits together with the tuning voltage. Is.

In one of the embodiments of the present invention, the additional bias voltage is a divided voltage obtained by dividing the switching voltage output from the band switching terminal of the PLL with a resistance circuit.

In another of the embodiments of the present invention, the tuning variable capacitance diode has a tuning voltage applied to the cathode and an additional bias voltage applied to the anode.

According to the embodiment of the present invention, when receiving the TV broadcast of the 6th channel in the United States, a tuning voltage for applying a predetermined tuning capacitance is applied to the tuning variable capacitance diode of the high frequency double tuning circuit. At the same time, since the additional bias voltage that makes the capacitance of the variable capacitance diode larger than that when only the tuning voltage is applied, the frequency response characteristic of the high frequency double tuning circuit in the sixth channel depends on only the predetermined tuning voltage. From the frequency response characteristics, it is possible to move to the low frequency side and effectively attenuate the reception signal of the FM radio broadcast which becomes an interfering wave.

When receiving a TV broadcast other than the sixth channel, a tuning voltage that gives a predetermined tuning capacitance is applied to the tuning variable capacitance diode of the high frequency double tuning circuit, and no additional bias voltage is applied. Therefore, the high frequency double tuning circuit can obtain the frequency response characteristic only by the predetermined tuning voltage.

[0025]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram including a partial circuit diagram showing the configuration of an embodiment of a television tuner according to the present invention.

As shown in FIG. 1, the television tuner of this embodiment includes a high pass filter (HPF) 1 and
Antenna (ANT) tuning circuit 2 and high frequency amplifier circuit (R
FAMP) 3, high frequency double tuning circuit 4, mixing circuit (M
IX) 5, a PLL 8, a resistance voltage dividing circuit 7, an input terminal 9, and an output terminal 10. The input end of the high-pass filter 1 is connected to the input terminal 9, and the output end is connected to the input end of the antenna tuning circuit 2. The high frequency amplifier circuit 3 has an input end connected to the output end of the antenna tuning circuit 2 and an output end connected to the input end of the high frequency double tuning circuit 4. The mixing circuit 5 has an input terminal connected to the output terminal of the high frequency double tuning circuit 4 and an output terminal connected to the output terminal 10.

The high frequency double tuning circuit 4 includes variable capacitance diodes 4 ₁ and 4 ₂ , inductors 4 _{3 to} 4 ₇ , capacitors 4 _{8 to} 4 ₁₀ and switching diodes 4 ₁₁ and 4 _12.
And resistors 4 ₁₃ and 4 ₁₄ and coupling capacitors 4 ₁₅ and 4 ₁₆ and
It is composed of two resistance voltage dividing circuits 7, 7. The cathode of the variable capacitance diode 4 ₁ has the coupling capacitor 4
The input terminal of the high frequency double tuning circuit 4 and the one terminal of the inductor 4 ₃ are connected via ₁₅ respectively, and the anode is connected to one resistance voltage dividing circuit 7. Variable capacitance diode 4
_The cathode ₂ is connected to the output end of the high frequency double tuning circuit 4 and one end of the inductor 4 ₄ via the coupling capacitor 4 ₁₆ , and the anode is connected to the other resistance voltage dividing circuit 7. The inductors 4 ₃ and 4 ₄ are inductively coupled to each other, and the other end of the inductor 4 ₃ is connected to one end of the inductor 4 ₅ via the capacitor 4 ₈ and the tuning voltage terminal TU of the PLL ₈ via the resistor 4 _13. , Inductor 4
₄ of the other end is connected to the tuning voltage terminal TU of PLL8 through one end and the resistor 4 ₁₄ of the inductor 4 ₆ through the capacitor 4 _9. The inductors 4 ₅ and 4 ₆ are inductively coupled to each other, and one end of the inductor 4 ₅ is connected to the band switching terminal BS2 of the PLL 8 via the switching diode 4 ₁₁ and is directly connected to the band switching terminal BS3 and the other end is connected. The other end of inductor 4 ₆ and inductor 4 ₇
Is connected to the band switching terminal BS2 of the PLL 8 via the switching diode 4 ₁₂ , and the inductor 4 ₆ is directly connected to the band switching terminal BS.
Connected to 3. The other end of the inductor 4 ₇ is connected to the ground point via the capacitor 4 ₁₀ .

On the other hand, the resistance voltage dividing circuit 7 includes resistors 7 ₁ and 7 ₂
And the bypass capacitor 7 ₃ , and the other resistance voltage dividing circuit 7 includes resistors 7 ₄ and 7 ₅ and a bypass capacitor 7 3.
It consists of ₆ and. One end of the resistor 7 ₁ is connected to the anode of the variable capacitance diode 4 ₁ , one end of the resistor 7 ₂ and one end of the bypass capacitor 7 ₃ , and the other end is the PLL.
8 band switching terminal BS4. Resistance 7 ₂
And the other end of the bypass capacitor 7 ₃ are connected to the ground point. One end of the resistor 7 ₄ is connected to the anode of the variable capacitance diode 4 ₂ and one end of the resistor 7 ₅ and one end of the bypass capacitor 7 ₆ , respectively, and the other end is PL
It is connected to the band switching terminal BS4 of L8. Resistance 7
The other end of _{5 and} the other end of the bypass capacitor 7 ₆ are respectively connected to the ground point.

The PLL 8 has a tuning voltage terminal TU and band switching terminals BS2, BS3, BS4, and the tuning voltage terminal TU transfers the capacitance of the variable capacitance diodes 4 ₁ , 4 ₂ to the TV broadcast channel to be received. A tuning voltage for setting the capacitance according to the generated voltage is generated, and the band switching terminal BS2 is set to VHF.
When receiving a high band TV broadcast, a positive voltage for turning on the switching diodes 4 ₁₁ and 4 ₁₂ is generated, and the band switching terminal BS3 is connected to the VHF low band TV.
When receiving the broadcast, switching diodes 4 ₁₁ , 4
A positive voltage for turning off ₁₂ is generated, and the band switching terminal BS4 applies a positive voltage for applying an additional bias voltage to the variable capacitance diodes 4 ₁ , 4 ₂ only when receiving the TV broadcast of the sixth channel. Occur.

The television tuner of this embodiment having the above-described structure operates as follows.

The high-pass filter 1 removes unnecessary low-frequency components from the reception signal applied to the input terminal 9, and the antenna tuning circuit 2 selects the reception signal of the desired channel. Next, the received signal is amplified in the high frequency amplifier circuit 3, the received signal of the desired channel is further selected in the high frequency double tuning circuit 4, and the selected received signal is mixed with the local oscillation signal in the mixing circuit 5 to obtain the intermediate frequency signal. The signal is converted into a signal, and the intermediate frequency signal is derived from the output terminal 10.

Here, 2 in the VHF low band
Or when you select any of the 6 TV channels,
A positive voltage is output from the band switching terminal BS3 of the PLL8, and the switching diode 4 ₁₁ ,
4 ₁₂ is turned off, so high frequency double tuning circuit 4
Are inductors 4 ₃ and 4 ₄ and capacitors 4 ₈ and 4 ₉ ,
The three inductors 4 _{5 to} 4 ₇ and the capacitor 4 ₁₀ are inserted and connected. At this time, the tuning voltage terminal T of the PLL 8
A tuning voltage is output from U, and this tuning voltage is applied to the variable capacitance diode 4 ₁ via the resistor 4 ₁₃ and the inductor 4 ₃ and to the variable capacitance diode 4 ₂ via the resistor 4 ₁₄ and the inductor 4 _4. , The capacitances of the variable capacitance diodes 4 ₁ and 4 ₂ are adjusted, so that the high frequency double tuning circuit 4 is tuned to the selected TV broadcast.

On the other hand, 7 to 13 in the VHF high band
PLL when selecting one of the TV broadcasting channels
A positive voltage is output from the band switching terminal BS2 of 8 and the switching diodes 4 ₁₁ and 4 ₁₂ are turned on by the positive voltage, so that the high frequency double tuning circuit 4 includes inductors 4 _{5 to} 4 ₇ and a capacitor 4 _10. Circuit parts are short-circuited, inductors 4 ₃ 4 ₄ capacitors 4 ₈ 4
Only ₉ will be connected. Also at this time, a tuning voltage is output from the tuning voltage terminal TU of the PLL 8, and this tuning voltage is applied to the variable capacitance diode 4 ₁ via the resistor 4 ₁₃ and the inductor 4 ₃ as well as via the resistor 4 ₁₄ and the inductor 4 ₄ . Te is added to the variable capacitance diode 4 _2, so to adjust the respective capacitance of the variable capacitance diode 4 _1, 4 _2, the high-frequency double tuned circuit 4 is tuned to a TV broadcast that is selected.

Here, when a television broadcast other than the sixth channel is selected, the band switching terminal B of the PLL 8 is selected.
Since the ground voltage is output to S4, the anodes of the variable capacitance diodes 4 ₁ and 4 ₂ become the ground voltage by the resistors 7 ₂ and 7 ₅ , respectively. Therefore, the variable capacitance diode 4
The capacitances of ₁ and 4 ₂ are the variable capacitance diode 4 from the tuning voltage terminal TU of the PLL 8 via the resistor 4 ₁₃ and the inductor 4 _3.
It is set by the tuning voltage applied to the cathode of ₁ through the tuning voltage terminal TU of the PLL 8 via the resistor 4 ₁₄ and the inductor 4 ₄ to the cathode of the variable capacitance diode 4 ₂ .

On the other hand, when the TV broadcast of the sixth channel is selected, the positive voltage output from the band switching terminal BS4 is divided by the resistance voltage dividing circuit 7, and this divided voltage is used as the additional bias voltage and the variable capacitance. It is added to the anodes of the diodes 4 ₁ , 4 ₂ . At the same time, the tuning voltage obtained at the tuning voltage terminal TU of the PLL 8 is applied to the cathode of the variable capacitance diode 4 ₁ via the resistor 4 ₁₃ and the inductor 4 ₃ and to the variable capacitance via the resistor 4 ₁₄ and the inductor 4 _4. The capacitances of the variable capacitance diodes 4 ₁ and 4 ₂ respectively added to the cathode of the diode 4 ₂ become the capacitances set by the tuning voltage and the additional bias voltage, and the high frequency double tuning circuit has a frequency response characteristic based on only the tuning voltage. The frequency response characteristic moves to the lower frequency side than that, and the received signal of the FM radio broadcast, which becomes an interfering wave, is attenuated.

FIG. 2 is a characteristic diagram showing a frequency response characteristic at the time of receiving the sixth channel in the high frequency double tuning circuit of the television tuner of the present embodiment. The frequency of a known television tuner using the FM trap circuit. It shows the response characteristics together with the frequency response characteristics of the television tuner that does not use the FM trap circuit.

In FIG. 2, the vertical axis is the output level, the horizontal axis is the frequency, the curve (solid line) a is that of the television tuner of this embodiment, and the curve (dashed line) b is the FM trap circuit. The curve (dotted line) c of the known television tuner is the frequency response characteristic obtained by applying only the tuning voltage to the variable capacitance diodes 4 ₁ and 4 ₂ .

As shown by the curve a in FIG. 2, the frequency response characteristic a at the time of receiving the sixth channel in the television tuner of this embodiment, that is, the variable capacitance diodes 4 ₁ , 4
_The frequency response characteristic obtained by adding the tuning voltage and the additional bias voltage to ₂ in comparison with the frequency response characteristic c obtained by applying only the tuning voltage to the variable capacitance diodes 4 ₁ and 4 ₂ is As a result, the signal is moved to the lower frequency side as a whole, and as a result, the received signal of FM radio broadcasting is 1% less than that when no additional bias voltage is applied.
It is attenuated as much as 0 db.

Further, according to the frequency response characteristic a at the time of receiving the sixth channel in the television tuner of the present embodiment, even when compared with the response characteristic b of the known television tuner using the FM trap circuit, The received signal of the FM radio broadcast is attenuated by about 7 dB more than the response characteristic b of the known television tuner using the FM trap circuit. ing.

As described above, according to the television tuner of this embodiment, when the sixth channel TV broadcast is received, the variable capacitance diodes 4 ₁ , 4 of the high frequency double tuning circuit 4 are received.
The frequency response characteristic of the sixth channel in the high frequency double tuning circuit 4 was moved to the low frequency side from the frequency response characteristic when only the tuning voltage was applied by adding the additional bias voltage together with the predetermined tuning voltage to ₂ . Since the frequency response characteristic is changed, it is possible to effectively attenuate the reception signal of the FM radio broadcast, which is the interfering wave of the sixth channel reception, without providing the FM trap circuit at the reception signal input end. Further, the adjustment of the new frequency response characteristic is sufficient if the additional bias voltage is adjusted, so that the adjustment becomes easier than the case of using the FM trap circuit.

In the above embodiment, the tuning voltage and the additional bias voltage are applied to the variable capacitance diodes 4 ₁ ,
4 has been illustratively described that in addition to both of the _2, additional bias voltage according to the present invention, the variable capacitance diode 4 _1, 4 ₂
However, when the degree of attenuation of the received signal of the FM radio broadcast may be small, it may be added to either _{one of} the variable capacitance diodes 4 ₁ and 4 ₂ .

Further, in the above-mentioned embodiment, an example in which the tuning voltage is applied to the cathodes of the variable capacitance diodes 4 ₁ and 4 ₂ and the additional bias voltage is applied to the anode thereof has been described, but the tuning voltage and the additional bias according to the present invention are described. The mode for applying the voltage is not limited to such an example, and the tuning voltage may be applied to the anode and the additional bias voltage may be applied to the cathode, or both the tuning voltage and the additional bias voltage may be superposed. It may be added to the cathode or the anode.

Further, in the above embodiment, the positive voltage applied to the resistance voltage dividing circuit 7 when the sixth channel is selected is P
Although the example of obtaining from the band switching terminal BS4 of the LL8 has been described, the means for obtaining such a positive voltage according to the present invention is not limited to the case of obtaining from the band switching terminal BS4 of the PLL8, and is not limited to channel selection. Other means may be used as long as they can be switched accordingly.

[0045]

As described above, according to the present invention, when the sixth channel of US television broadcasting is received, a predetermined tuning voltage is applied to the tuning variable capacitance diode of the high frequency double tuning circuit, and Since the additional bias voltage that makes the capacitance of the variable capacitance diode larger than that when only the tuning voltage is applied, the frequency response characteristic of the sixth channel in the high frequency double tuning circuit is the frequency response characteristic when only the predetermined tuning voltage is applied. Changes to a new frequency response characteristic that attenuates the carrier frequency component of FM radio broadcasting, and it is possible to effectively attenuate the reception signal of FM radio broadcasting that becomes an interfering wave without using an FM trap circuit. In addition, the adjustment for obtaining a new frequency response characteristic is sufficient if the additional bias voltage is adjusted. Compared with the case of using a wrap circuit,
The effect is that the adjustment becomes easy.

Further, according to the present invention, since the FM trap circuit is not used, there is an effect that insertion loss does not occur and noise figure does not decrease.

[Brief description of drawings]

FIG. 1 is a block diagram including a partial circuit diagram showing a configuration of an embodiment of a television tuner according to the present invention.

FIG. 2 is a sixth example of the television tuner of this embodiment.
It is a frequency response characteristic characteristic figure of the high frequency double tuning circuit at the time of channel reception.

FIG. 3 is a block diagram including a partial circuit diagram showing an example of the configuration of a known television tuner.

[Explanation of symbols]

1 High Pass Filter (HPF) 2 Antenna (ANT) Tuning Circuit 3 High Frequency Amplifier Circuit (RFAMP) 4 High Frequency Double Tuning Circuit 4 ₁ , 4 ₂ Variable Capacitance Diode 5 Mixing Circuit (MIX) 7 Resistor Voltage Dividing Circuit 8 PLL 9 Input Terminal 10 Output terminal

─────────────────────────────────────────────────── ─── Continuation of front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) H04N 5/44

Claims (3)

(57) [Claims] 1. A high-frequency double-tuning circuit having a tuning variable-capacitance diode, capable of receiving a television broadcast of a US channel, and capable of receiving a sixth-channel television broadcast, A television tuner, wherein an additional bias voltage for increasing the capacitance of the variable capacitance diode is applied to at least one of the tuning variable capacitance diodes together with the tuning voltage as compared with the case where only the tuning voltage is applied. 2. The television tuner according to claim 1, wherein the additional bias voltage is a divided voltage obtained by dividing the switching voltage output from the band switching terminal of the PLL with a resistance circuit. . 3. The tuning variable capacitance diode has a cathode to which a tuning voltage is applied and an anode to which the additional bias voltage is applied.
Television tuner described in.