JP2001157128A - Television tuner - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a television tuner by which transmission characteristic in a intermediate audio frequency is made excellent even when an FM transmission signal is received. SOLUTION: An intermediate audio frequency turning circuit 2 is made to tune in-between an intermediate video frequency P and a intermediate audio frequency S in an intermediate frequency band at a time, when a television signal is received and is also made to tune in to the frequency S at a time when FM broadcasting is received.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a television tuner, and more particularly to an intermediate frequency circuit of a television tuner capable of receiving an FM broadcast signal.

[0002]

2. Description of the Related Art A conventional television tuner converts a received television signal into a signal in a television intermediate frequency band as shown in FIG.
Balanced output type mixer 31 for frequency-converting a received FM broadcast signal into a signal of an audio intermediate frequency in an intermediate frequency band
An intermediate frequency tuning circuit 32 that tunes to the intermediate frequency band;
A first trap circuit 33 having one end connected to one end of the intermediate frequency tuning circuit 32, a second trap circuit 34 connected to the other end of the intermediate frequency tuning circuit 32, and coupling capacitors 35 and 36. And an intermediate frequency circuit composed of a balanced input type intermediate frequency amplifier (IF AMP) 37 connected to the other ends of the first trap circuit 33 and the second trap circuit 34.

The intermediate frequency tuning circuit 32 includes a capacitor 32
a and inductors 32b and 32 connected in series to each other
c, and tunes between the video intermediate frequency and the audio intermediate frequency in the intermediate frequency band. Then, an intermediate frequency signal is input to both ends. The power supply voltage Vb applied to the connection point between the inductors 32b and 32c is supplied to the mixer 31 by the inductors 32b and 32c.
c. The first trap circuit 33 is constituted by a parallel tuning circuit including a capacitor 33a and an inductor 33b, and its tuning frequency (trap frequency) is
The frequency S 'is set to be higher than the video intermediate frequency P in the intermediate frequency band by a frequency which is the difference between the video carrier frequency of the television channel to be received and the audio carrier frequency of one adjacent television channel. Further, the second trap circuit 34 includes a capacitor 3
4a and an inductor 34b, and the tuning frequency (trap frequency) is set to an intermediate value by the frequency of the difference between the audio carrier frequency of the receiving television channel and the video carrier frequency of the other adjacent television channel. Audio intermediate frequency S in frequency band
Is set to a frequency P 'which is farther away from P'.

As a result, the transmission characteristics in the intermediate frequency band are as shown in FIG. 9, and these trap frequencies S 'and P' are fixed irrespective of the reception of the television signal and the reception of the FM broadcast signal. .

[0005]

In the conventional television tuner as described above, the tuning frequency of the intermediate frequency tuning circuit is, as shown in FIG. 9, at least a video carrier frequency P and an audio carrier frequency S in the intermediate frequency band. Therefore, the voice carrier frequency S is deviated from the tuning frequency, and the transmission characteristic is such that the level at the voice carrier frequency S is attenuated as compared with the level at the tuning frequency. For this reason, good transmission characteristics can be obtained when receiving a television signal, but the level of the most important audio intermediate frequency is attenuated when receiving an FM broadcast signal, so that good selection characteristics cannot be obtained.
Further, as shown in FIG. 9, since the trap frequencies S ′ and P ′ of the first trap circuit 33 and the second trap circuit 34 are fixed, when the FM broadcast signal is
Good suppression characteristics for broadcast signals cannot be obtained.

The present invention has been made in view of such a problem, and has as its object to provide a television tuner having good transmission characteristics at an audio intermediate frequency even when receiving an FM broadcast signal. .

[0007]

In order to achieve the above object, according to the present invention, a received television signal is frequency-converted into a signal in a television intermediate frequency band, and a received FM broadcast signal is converted into a signal in the intermediate frequency band. A mixer for converting the frequency to an audio intermediate frequency signal, and an intermediate frequency tuning circuit for tuning to the intermediate frequency band, wherein the intermediate frequency tuning circuit, when receiving the television signal, a video intermediate frequency in the intermediate frequency band And the audio intermediate frequency, and can be tuned to the audio intermediate frequency when the FM broadcast is received.

In addition, a first trap circuit and a second trap circuit are connected to the intermediate frequency tuning circuit, and when the television signal is received, the trap frequency of the first trap circuit is set to one of the adjacent television channels. The audio trapping frequency of the second trapping circuit, the trapping frequency of the second trapping circuit is set to the video intermediate frequency of the other adjacent television channel, at the time of receiving the FM broadcast, the trapping frequency of the first trapping circuit, FM received
A frequency difference between a broadcast signal and one FM broadcast signal adjacent to the received FM broadcast signal is set to a frequency apart from the audio intermediate frequency, and a trap frequency of the second trap circuit is set to the received FM broadcast signal. The frequency can be set to a frequency apart from the audio intermediate frequency by a frequency difference between the signal and the other FM broadcast signal adjacent to the received FM broadcast signal.

Further, a first varactor diode for setting a tuning frequency of the intermediate frequency tuning circuit is provided in the intermediate frequency tuning circuit, and the trap frequency of the first trap circuit is set in the first trap circuit. A second varactor diode for setting, a third varactor diode for setting a trap frequency of the second trap circuit is provided in the second trap circuit, and the first varactor diode and the third varactor diode are provided. A common bias voltage is applied to the second varactor diode and the third varactor diode, and the bias voltage can be switched between when the television signal is received and when the FM broadcast is received.

Further, the intermediate frequency tuning circuit, the first trap circuit and the second trap circuit are respectively constituted by parallel tuning circuits, and both ends of the intermediate frequency tuning circuit are provided.
The signal of the intermediate frequency band and the signal of the audio intermediate frequency are input in a balanced state, one end of the first trap circuit is connected to one end of the intermediate frequency tuning circuit, and the other end of the intermediate frequency tuning circuit is connected to the other end of the intermediate frequency tuning circuit. One end of a second trap circuit is connected, and the signal of the intermediate frequency band and the signal of the audio intermediate frequency are output in a balanced state from the other ends of the first trap circuit and the second trap circuit. I do.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a television tuner according to the present invention will be described with reference to FIGS.

FIG. 1 is a circuit diagram of a television tuner showing a first embodiment of the present invention. The television signal received by the high-frequency circuit unit (not shown) is input to the mixer 1 and frequency-converted into an intermediate frequency band signal by an oscillation signal from a local oscillation circuit (not shown). Similarly, the FM broadcast signal received by the high-frequency circuit is frequency-converted into an audio intermediate frequency signal in an intermediate frequency band by an oscillation signal from the local oscillation circuit. These signals are output from the mixer 1 in a balanced state. The frequency-converted intermediate frequency band signal or audio intermediate frequency signal is input to both ends of the intermediate frequency tuning circuit 2.

The intermediate frequency tuning circuit 2 includes a capacitor 2a
And a parallel tuning circuit including inductors 2b and 2c connected in series with each other, and a first varactor diode 2e and a capacitor 2d connected in series with each other. A balanced input type intermediate frequency amplifier (IF AMP) 5 is connected to both ends of the intermediate frequency tuning circuit 2 via DC cut capacitors 6 and 7.

The mixer 1 has inductors 2b and 2c.
The power supply voltage Vb applied to the connection point with the inductor 2b
And 2c. The voltage Vb is applied to the cathode of the first varactor diode 2e via the inductor 2b. The first varactor diode 2
A bias voltage Ve or a voltage of 0 V is applied to the anode of e via the changeover switch 8.

The switching operation of the reception of the television signal and the FM broadcast signal will be described below. When a television signal is received, the anode of the first varactor diode 2e is grounded by the changeover switch 8. Therefore, the voltage Vb is applied as it is to the first varactor diode 2e as a bias voltage. Here, the voltage Vb is also a power supply voltage of the mixer 1, and its voltage value is a relatively large value. Therefore, at the time of receiving a television signal, a relatively large bias voltage is applied to both ends of the first varactor diode 2e, and the capacitance between both ends becomes a relatively small value. At this time, the tuning frequency of the intermediate frequency tuning circuit 2 is set to be an intermediate frequency between the video intermediate frequency P and the audio intermediate frequency S.

On the other hand, when an FM broadcast signal is received, a bias voltage Ve is applied to the anode of the first varactor diode 2e by the changeover switch 8, and a voltage having a difference between the voltage Vb and the voltage of the power supply Ve is applied to both ends thereof. Join. Here, the voltage value of the power supply Ve is set to a value relatively close to the voltage value of the voltage Vb (where Vb> Ve). Therefore, FM
When receiving a broadcast signal, a relatively small bias voltage is applied to both ends of the first varactor diode 2e, and the capacitance between both ends of the first varactor diode 2e has a relatively large value. At this time, the tuning frequency of the intermediate frequency tuning circuit 2 is set to be the audio intermediate frequency S. As a result,
The tuning frequency when receiving a television signal is higher than the tuning frequency when receiving an FM broadcast signal.

Here, the tuning frequency at the time of receiving a television signal depends on the capacitance of the capacitor 2a and the inductor 2b.
, The inductance of the inductor 2c, and the capacitance of the capacitor 2d are set as shown in FIG. 2 in consideration of the capacitance between both ends of the varactor diode 2e. On the other hand, the tuning frequency when receiving an FM broadcast signal is
The value is set as shown in FIG. 3 by the value of the voltage Ve in consideration of the capacitance between both ends of the varactor diode 2e.

As described above, when the television signal is received, the tuning frequency of the intermediate frequency tuning circuit is set to at least a frequency between the video intermediate frequency P and the audio intermediate frequency S in the intermediate frequency band, thereby obtaining the television signal. Good selection characteristics for reception are obtained. When the FM broadcast signal is received, the tuning frequency of the intermediate frequency tuning circuit is set to the audio intermediate frequency S in the intermediate frequency band.
Good selection characteristics for receiving M broadcast signals are obtained.

FIG. 4 is a circuit diagram of a television tuner showing a second embodiment of the present invention. The television signal received by the high-frequency circuit unit (not shown) is input to the mixer 1 and frequency-converted into an intermediate frequency band signal by an oscillation signal from a local oscillation circuit (not shown). Similarly, the FM broadcast signal received by the high-frequency circuit is frequency-converted into an audio intermediate frequency signal in an intermediate frequency band by an oscillation signal from the local oscillation circuit. These signals are output from the mixer 1 in a balanced state.

The converted intermediate frequency band signal or audio intermediate frequency signal is input to both ends of the intermediate frequency tuning circuit 2. The intermediate frequency tuning circuit 2 includes a capacitor 2a,
A parallel tuning circuit composed of inductors 2b and 2c connected in series with each other, and a first varactor diode 2e and a capacitor 2d connected in series with each other. The power supply voltage Vb applied to the connection point between the inductors 2b and 2c is supplied to the mixer 1 via the inductors 2b and 2c.

Each end of the first trap circuit 3 and one end of the second trap circuit 4 are connected to both ends of the intermediate frequency tuning circuit 2. The first trap circuit 3 includes a second varactor diode 3c and a capacitor 3 connected in series with each other.
a, and a parallel tuning circuit including an inductor 3b and a capacitor 3d connected in series to each other. Further, the second trap circuit 4 is configured by a parallel tuning circuit including a third varactor diode 4c and a capacitor 4a connected in series with each other, and an inductor 4b and a capacitor 4d connected in series with each other. A balanced input type intermediate frequency amplifier (IF AMP) 5 is connected to the other ends of the first trap circuit 3 and the second trap circuit 4.

The voltage V is applied to the cathode of the first varactor diode 2e and the cathode of the second varactor diode 3c via the inductor 2b, and to the cathode of the third varactor diode 4c via the inductor 2c.
b is applied. And the first varactor diode 2e
The bias voltage Ve or 0 V is applied to the anode of the second varactor diode 3c and the anode of the third varactor diode 4c via the changeover switch 8.

When receiving a television signal, the changeover switch 8 connects the anodes of the first, second and third varactor diodes 2e, 3c and 4c to ground. Therefore, a relatively large voltage of the power supply Vb is directly applied as a bias voltage to both ends of the first, second, and third varactor diodes 2e, 3c, and 4c. The capacitance between both ends of the diodes 2e, 3c and 4c has a relatively small value. At this time, the tuning frequency of the intermediate frequency tuning circuit 2 is set to at least a frequency between the video intermediate frequency P and the audio intermediate frequency S in the intermediate frequency band, as in FIG.

In the first trap circuit 3, the capacitances of the capacitors 3a and 3d and the inductance of the inductor 3b are appropriately selected while taking into account the capacitance between both ends of the second varactor diode 3c. As shown in the figure, the tuning frequency (trap frequency) is higher than the video intermediate frequency P in the intermediate frequency band by the frequency of the difference between the video carrier frequency of the television channel to be received and the audio carrier frequency of one of the adjacent television channels. (Hereinafter referred to as an audio intermediate frequency of one adjacent television channel) S ′.

In the second trap circuit 4, the capacitances of the capacitors 4a and 4d and the inductance of the inductor 4b are appropriately selected in consideration of the capacitance between both ends of the third varactor diode 4c. As shown in the figure, the tuning frequency (trap frequency) is lower than the audio intermediate frequency S in the intermediate frequency band by the frequency of the difference between the audio carrier frequency in the television channel to be received and the video carrier frequency in the other adjacent television channel. (Hereinafter referred to as the video intermediate frequency of the other adjacent television channel) P ′.

On the other hand, when an FM broadcast signal is received, a bias voltage Ve is applied to the cathodes of the first, second and third varactor diodes 2e, 3c and 4c by the changeover switch 8, so that the power supply Vb is applied to both ends. And the voltage of the power supply Ve. Here, the power supply V
e is relatively close to the voltage value of the power supply Vb (however, V
b> Ve), so that when the FM broadcast signal is received, the first, second and third varactor diodes 2e
, 3c and 4c are applied with a relatively small bias voltage, and the capacitance between the first, second and third varactor diodes 2e, 3c and 4c is relatively large. As a result, the tuning frequency of the intermediate frequency tuning circuit 2 is set to be the audio intermediate frequency S as in FIG.

Further, the trap frequency of the first trap circuit 3 is changed between the received FM broadcast signal and one of the adjacent F broadcast signals.
The frequency S + is set to be higher than the audio intermediate frequency S by a frequency difference from the M broadcast signal. Then, the trap frequency of the second trap circuit 4 is set to a frequency S− that is lower than the audio intermediate frequency S by a frequency difference between the received FM broadcast signal and the other FM broadcast signal adjacent thereto. The frequencies S + and S- are set by the value of the bias voltage Ve in consideration of the capacitance between both ends of the second and third varactor diodes 3c and 4c together with the first varactor diode 2e.

As described above, when the television signal is received, the tuning frequency of the intermediate frequency tuning circuit 2 is set to at least the video intermediate frequency P and the audio intermediate frequency S in the intermediate frequency band.
And the trap frequency of the first trap circuit 3 is set to the audio intermediate frequency S 'of one adjacent television channel, and the trap frequency of the second trap circuit is set to the other adjacent television channel. By setting to the video intermediate frequency P ′ of the television channel, it is possible to obtain good selection characteristics for receiving television signals and suppression characteristics for television signals of adjacent television channels.

When an FM broadcast signal is received, the tuning frequency of the intermediate frequency tuning circuit 2 is set to the audio intermediate frequency S in the intermediate frequency band, and the trap frequency of the first trap circuit 3 is set adjacent to the received FM broadcast signal. One FM to do
A frequency S + that is higher than the audio intermediate frequency S by a frequency difference from the broadcast signal is set, and the trap frequency of the second trap circuit 4 is set to be adjacent to the received FM broadcast signal and the received FM broadcast signal. The frequency S- is set to be lower than the audio intermediate frequency S by a frequency difference from the other FM broadcast signal. This makes it possible to obtain good selection characteristics and adjacent channel suppression characteristics for receiving FM broadcast signals.

FIG. 7 is a circuit diagram of a television tuner showing a third embodiment of the present invention. The difference between the circuit shown in FIG. 7 and the circuit shown in FIG. 4 is that the mixer 9 is an unbalanced output type and the intermediate frequency amplifier (IF AMP) 12 Is an unbalanced input type, and the third trap circuit 11 is constituted by a series tuning circuit.

The signal of the intermediate frequency band or the signal of the audio intermediate frequency output from the mixer 9 in an unbalanced state is input to one end of the intermediate frequency tuning circuit 10. The intermediate frequency tuning circuit 10 includes a parallel tuning circuit including a capacitor 10a, an inductor 10b and a capacitor 10c connected in series with each other, and a fourth varactor diode 10e and a capacitor 10d connected in series with each other. Grounded. Since the intermediate frequency tuning circuit 10 has substantially the same configuration as the intermediate frequency tuning circuit 2 shown in FIG. 4, the operation is the same. Therefore, the description of the operation is omitted. The power supply voltage Vb applied to the connection point between the inductor 10b and the capacitor 10c is supplied to the mixer 9 via the inductor 10b.

The first trap circuit 3 is connected to one end of the intermediate frequency tuning circuit 10. The configuration and operation of the first trap circuit 3 are the same as those shown in FIG. Then, an intermediate frequency amplifier 12 is connected to the other end of the first trap circuit 3. The second trap circuit 11 is composed of a series tuning circuit including a capacitor 11a, a fifth varactor diode 11c, an inductor 11b, and a capacitor 11d connected in series with each other, and the other end is grounded. The capacitor 11 a also serves as a DC cut, and one end thereof is connected to the other end of the first trap circuit 3. Similarly, the capacitor 11d
Also serves as a DC cut, and one end thereof is grounded.

The voltage Vb is applied to the cathode of the fourth varactor diode 10e and the cathode of the second varactor diode 3c via the inductor 10b, and to the cathode of the fifth varactor diode 11c via the inductor 11b. You. And varactor diode 1
The bias voltage Ve or 0 through the changeover switch 8 is connected to the anode of the second varactor diode 3c and the anode of the fifth varactor diode 11c.
A voltage of V is applied.

At the time of receiving a television signal, the changeover switch 8 switches the fourth and second varactor diodes 10
e and 3c have their respective anodes grounded;
The anode of the fifth varactor diode 11c is also grounded. For this reason, a relatively large voltage of the voltage Vb is applied as it is to both ends of the fifth varactor diode 11c as a bias voltage, and the capacitance between both ends of the fifth varactor diode 11c has a relatively small value.

On the other hand, when the FM broadcast signal is received, the bias voltage Ve is applied to the cathodes of the fourth, second and fifth varactor diodes 10e, 3c and 11c by the changeover switch 8, so that the power supply V is applied to both ends.
The voltage of the difference between the voltage of b and the voltage of the power supply Ve is applied. Here, the voltage value of the power supply Ve is set to a value relatively close to the voltage value of the power supply Vb (where Vb> Ve). Therefore, FM
When receiving a broadcast signal, the fifth varactor diode 11c
, A relatively small bias voltage is applied to each end, and the capacitance between both ends becomes a relatively large value. Thus, at the time of receiving a television signal, the fifth varactor diode 1
The capacity between both ends of 1c is reduced, and is increased when receiving an FM broadcast signal.

Here, in the third trap circuit, when receiving a television signal, the capacitors 11a and 11a
By appropriately selecting the capacitance d and the inductance of the inductor 11b while taking into account the capacitance between both ends of the fifth varactor diode 11c, the series tuning frequency (trap frequency) of the other is changed as shown in FIG. The video intermediate frequency P ′ of the adjacent television channel is set.

On the other hand, when receiving the FM broadcast signal, the power supply Ve
By appropriately setting the capacitance between both ends of the fifth varactor diode 11c,
As shown in FIG. 6, the tuning frequency (trap frequency)
Is set to a frequency S− apart from the audio intermediate frequency by a frequency difference between the received FM broadcast signal and the other FM broadcast signal adjacent to the FM broadcast signal.

As described above, according to the present invention, when receiving a television signal, the intermediate frequency tuning circuit 2 or 10
Is set to at least a frequency between the video intermediate frequency P and the audio intermediate frequency S in the intermediate frequency band, and the trap frequency of the first trap circuit 3 is set to the audio intermediate frequency S of one adjacent television channel. '
, And the trap frequency of the second trap circuit 4 or 11 is set to the video intermediate frequency P ′ of the other adjacent television channel, whereby a good selection characteristic for receiving a television signal and an adjacent channel suppression characteristic are obtained. be able to.

At the time of receiving the FM broadcast signal, the tuning frequency of the intermediate frequency tuning circuit 2 or 10 is set to the audio intermediate frequency S in the intermediate frequency band. A frequency S + that is higher than the audio intermediate frequency S by a frequency difference from one adjacent FM broadcast signal is set, and the trap frequency of the second trap circuit 4 or 11 is set to
The frequency S− is set to be lower than the audio intermediate frequency S by a frequency difference between the broadcast signal and the other adjacent FM broadcast signal. This makes it possible to obtain good selection characteristics and adjacent channel suppression characteristics for receiving FM broadcast signals.

[0040]

As described above, the television tuner according to the present invention tunes the intermediate frequency tuning circuit between the video intermediate frequency and the audio intermediate frequency in the intermediate frequency band when receiving a television signal. Since tuning is performed to the audio intermediate frequency during broadcast reception, it is possible to obtain selection characteristics suitable for television signal reception and FM broadcast reception, respectively.

When a television signal is received, the trap frequency of the first trap circuit is set to the audio intermediate frequency of one adjacent television channel, and the trap frequency of the second trap circuit is set to the video frequency of the other adjacent television channel. Set to the intermediate frequency, and at the time of FM broadcast reception, the trap frequency of the first trap circuit is set to a frequency separated from the audio intermediate frequency by a frequency difference from one FM broadcast signal adjacent to the received FM broadcast signal; Since the trap frequency of the second trap circuit can be set to a frequency which is separated from the audio intermediate frequency by a frequency difference from the other FM broadcast signal adjacent to the received FM broadcast signal, the trap frequency can be set at the time of receiving the television signal and at the time of FM signal reception. When receiving a broadcast,
Adjacent channel suppression characteristics suitable for each can be obtained.

Further, a first varactor diode for setting the tuning frequency is provided in the intermediate frequency tuning circuit,
A second varactor diode for setting the trap frequency of the first trap circuit in the first trap circuit, and a third varactor for setting the trap frequency of the second trap circuit in the second trap circuit A diode is provided, and a common bias voltage is applied to the first varactor diode, the second varactor diode, and the third varactor diode, and the bias voltage is switched between when the television signal is received and when the FM broadcast is received. Selection characteristics and adjacent channel suppression characteristics suitable for receiving a television signal and receiving an FM broadcast can be easily selected.

Further, the intermediate frequency tuning circuit, the first trap circuit and the second trap circuit are each constituted by a parallel tuning circuit, and a signal of an intermediate frequency band and a signal of an audio intermediate frequency are provided at both ends of the intermediate frequency tuning circuit. Is input in a balanced state, one end of the first trap circuit is connected to one end of the intermediate frequency tuning circuit, one end of the second trap circuit is connected to the other end of the intermediate frequency tuning circuit, the first trap circuit and In order to output the signal of the intermediate frequency band and the signal of the audio intermediate frequency in a balanced state from the other end of the second trap circuit, all the circuits from the mixer output to the outputs of the first and second trap circuits are balanced circuits. Can be configured.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing one embodiment of a television tuner according to the present invention.

FIG. 2 is a diagram showing transmission characteristics of a television tuner according to the present invention.

FIG. 3 is a diagram showing transmission characteristics of a television tuner according to the present invention.

FIG. 4 is a circuit diagram showing one embodiment of a television tuner according to the present invention.

FIG. 5 is a diagram showing transmission characteristics of a television tuner according to the present invention.

FIG. 6 is a diagram showing transmission characteristics of a television tuner according to the present invention.

FIG. 7 is a circuit diagram showing one embodiment of a television tuner according to the present invention.

FIG. 8 is a circuit diagram showing one embodiment of a conventional television tuner.

FIG. 9 is a diagram illustrating transmission characteristics of a conventional television tuner.

[Explanation of symbols]

 Reference Signs List 1 mixer 2 intermediate frequency tuning circuit 2a capacitor 2b inductor 2c inductor 2d capacitor 2e first varactor diode 3 first trap circuit 3a capacitor 3b inductor 3c second varactor diode 3d capacitor 4 second trap circuit 4a capacitor 4b inductor 4c Third Varactor Diode 4d Capacitor 5 Intermediate Frequency Amplifier 6 Capacitor 7 Capacitor 8 Changeover Switch 9 Mixer 10 Intermediate Frequency Tuning Circuit 10a Capacitor 10b Inductor 10c Capacitor 10d Capacitor 10e Fourth Varactor Diode 11 Second Trap Circuit 11a Capacitor 11b Inductor 11c Fifth varactor diode 11d Capacitor 12 Intermediate frequency amplifier circuit 31 Mixer 32 Intermediate frequency tuning circuit 32a capacitor 32b inductor 32c inductor 33 first trap circuit 33a capacitor 33b inductor 34 second trap circuit 34a capacitor 34b inductor 35 capacitor 36 capacitor 37 intermediate frequency amplifier circuit

 ──────────────────────────────────────────────────続 き Continued on the front page F-term (reference)

Claims (4)

[Claims] A mixer for frequency-converting a received television signal to a signal in a television intermediate frequency band and frequency-converting a received FM broadcast signal to a signal of an audio intermediate frequency in the intermediate frequency band; An intermediate frequency tuning circuit for tuning to an intermediate frequency band, wherein the intermediate frequency tuning circuit is tuned between a video intermediate frequency and an audio intermediate frequency in the intermediate frequency band when the television signal is received, and A television tuner tuned to the audio intermediate frequency upon reception. 2. A first trap circuit and a second trap circuit are connected to the intermediate frequency tuning circuit, and when the television signal is received, the trap frequency of the first trap circuit is set to one of adjacent television channels. An audio intermediate frequency is set, a trap frequency of the second trap circuit is set to a video intermediate frequency of the other adjacent television channel, and when the FM broadcast is received, a trap frequency of the first trap circuit is set to the reception frequency. The FM broadcast signal is set to a frequency separated from the audio intermediate frequency by a frequency difference between the FM broadcast signal and one FM broadcast signal adjacent to the received FM broadcast signal, and the trap frequency of the second trap circuit is received. FM broadcast signal and the received FM
The television tuner according to claim 1, wherein the frequency is set apart from the audio intermediate frequency by a frequency difference from another FM broadcast signal adjacent to a broadcast signal. 3. The intermediate frequency tuning circuit is provided with a first varactor diode for setting a tuning frequency of the intermediate frequency tuning circuit, and the first trap circuit is provided with a trap frequency of the first trap circuit. A second varactor diode for setting, a third varactor diode for setting a trap frequency of the second trap circuit is provided in the second trap circuit, and the first varactor diode and the third varactor diode are provided. The common bias voltage is applied to the second varactor diode and the third varactor diode, and the bias voltage is switched between when the television signal is received and when the FM broadcast is received. Television tuner. 4. The intermediate frequency tuning circuit, the first trap circuit, and the second trap circuit are each constituted by a parallel tuning circuit, and a signal and a signal of the intermediate frequency band are provided at both ends of the intermediate frequency tuning circuit. The signal of the audio intermediate frequency is input in a balanced state, one end of the first trap circuit is connected to one end of the intermediate frequency tuning circuit, and one end of the second trap circuit is connected to the other end of the intermediate frequency tuning circuit. And outputting the signal of the intermediate frequency band and the signal of the audio intermediate frequency in a balanced state from the other ends of the first trap circuit and the second trap circuit. Television tuner.