JP3461668B2 - Tuner - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention particularly relates to a UHF tuner antenna input in a so-called combination tuner in which a VHF tuner and a UHF tuner are housed in one shield case. The present invention relates to a tuner suitable for application to a circuit.

[0002]

2. Description of the Related Art A conventional tuner will be described with reference to FIGS. Here, FIG. 4 is a UH in a conventional tuner.
The antenna input circuit of the F tuner is shown together with the peripheral circuits, and FIG. 5 is an equivalent circuit for explaining the operation. Further, FIG. 6 shows a UHF tuner in a conventional tuner.
The characteristics of the antenna input circuit of
It is a characteristic view shown with the characteristic of the antenna input circuit of the UHF tuner in the antenna.

In FIG. 4, of the television signals input to the antenna input terminal 1, the U signal received by the UHF tuner 2 is U.
The HF band television signal is guided to a UHF band tuning circuit (hereinafter, simply referred to as a tuning circuit) 4 via a switch diode 3, and a desired frequency is selected by the tuning circuit 4 and F
It is amplified by a UHF high-frequency amplifier circuit (hereinafter, simply referred to as an amplifier circuit) 6 including ET5 and sent to a mixing circuit or the like in the subsequent stage not shown. Similarly, of the television signals input to the antenna input terminal 1, a television signal in the VHF band (actually including the low frequency portion of the UHF band) is desired by the VHF tuner tuning circuit 7a of the VHF tuner 7. Is selected, and the selected signal is amplified by the VHF high frequency amplifier circuit 7b. Here, the part from the antenna input terminal 1 to the front of the amplifier circuit 6 will be referred to as an antenna input circuit for convenience. The tuning circuit 7a of the VHF tuner 7 also includes a varactor diode (not shown) for tuning, and this varactor diode has the same tuning voltage as the tuning voltage applied from the terminal TU to the varactor diode 10 of the UHF tuner 2. The voltage is supplied, and the terminal TU receives VHF when receiving UHF.
The tuning voltage is always applied regardless of the reception of HF.

The tuning circuit 4 basically comprises two tuning coils 8 and 9 connected in series, and a voltage variable capacitance diode (hereinafter referred to as a varactor diode) connected in parallel to the tuning coils 8 and 9. It is composed of 10 and. The tuning voltage supplied to the cathode of the varactor diode 10 from the terminal TU via the power feeding resistor 11 causes U
It is tuned to a desired frequency in the HF band. The capacitor 12 connected in series to the varactor diode 10 and the coil 13 connected in parallel are for setting the variable range of the tuning frequency by the varactor diode 10.

The switch diode 3, which is inserted between the antenna input terminal 1 and the tuning circuit 4, has its both ends connected to terminals VB and UB through feeding resistors 14 and 15, respectively. Then, the UHF band television signal selected by the tuning circuit 4 has a small capacity (approximately 2 Pf) coupling capacitor 16
Is input to the first gate (hereinafter, simply referred to as the gate 1) which is the input end of the FET 5. One end of a coil 17 is connected to the gate 1 and the other end is grounded at a high frequency by a capacitor 18. This coil 17 is
A parallel resonance circuit is configured with the input capacitance (approximately 2Pf) of the ET5, and the peaking coil is set so that its resonance frequency is near the lower end of the UHF band. A power feeding resistor 19 is connected between the other end of the coil 17 and the terminal UB. Further, a resistor 20 is connected between the gate 1 of the FET 5 and the connection point between the coil 8 and the coil 9, and a bias voltage is applied to the gate 1 of the FET 5 by the resistor 20 and the feeding resistor 19. ing. The resistor 20 also functions as a damper resistor of the tuning circuit 4.

In the above construction, the tuner is U-shaped.
When receiving HF band TV signals (hereinafter simply referred to as UH
At the time of receiving F, the switching voltage to the terminal UB (usually the same as the power supply voltage supplied to the tuner,
(Referred to simply as voltage) and UHF tuner 2
Power supply voltage to other circuits not shown in the figure
Ground. This turns on switch diode 3.
(Conducted) to guide the TV signal from the antenna input terminal 1 to the tuning circuit 4, and the FETs are connected by the resistors 19 and 20.
Bias voltage is supplied to the gate 1 of No. 5. On the other hand,
When the receiver receives a VHF band television signal (hereinafter, simply referred to as VHF reception), the power supply voltage is applied to a circuit (not shown) in the VHF tuner 7 and the same switching voltage is applied to the terminal VB. Then, the terminal UB is grounded. As a result, the switch diode 3 is turned off (non-conducting) to prevent the television signal from the antenna input terminal 1 from entering the tuning circuit 4, and the gate 1 of the FET 5 is prevented from being biased. I have to.

Therefore, the antenna input circuit becomes an equivalent circuit as shown in FIG. 5 both when receiving UHF and when receiving VHF. However, in FIG. 5, the switch diode of FIG.
The distinction between conduction and non-conduction of the terminal 3 is not shown. And
The frequency response characteristic (transmission characteristic) of this antenna input circuit when receiving VHF is VH in the varactor diode 10.
Since the same tuning voltage is applied both during F reception and during UHF reception, the curves shown in A and B of FIG. 6 are obtained similarly to the frequency characteristics during UHF reception. Here, the curve A of FIG. 6 has a VHF tuner of approximately 295 MHz.
It is a frequency characteristic when (A1 of curve A) is received. The tuning voltage at this time is also applied to the varactor diode 10 of the tuning circuit 4 of the UHF tuner 2, and this voltage causes the tuning circuit 4 to have a frequency of approximately 700 MHz (A in curve A).
It is in tune with 2). A2 of the curve A is the frequency characteristic of the antenna tuning circuit (not shown) of the VHF tuner 7,
This is the UHF tuner 2 via the antenna input terminal 1.
It appears on the antenna input circuit side of. Similarly, in the case of the curve B, when the VHF is received, the VHF tuner 7 is almost 3
This is the frequency characteristic when tuning to 43 MHz (B1 of curve B). At this time, the tuning circuit 4 of the UHF tuner 2
Is tuned to approximately 855 MHz (B2 of curve B). In FIG. 5, the variable capacitance 21 is shown as an equivalent capacitance by the varactor diode 10, the correction capacitor 12, and the correction coil 13 in FIG. The capacitor 22 shown by the dotted line shows the input capacitance of the FET 5.

[0008]

In the conventional tuner described above, the power supply voltage is not applied to the amplifier circuit 5 at the time of VHF reception, so that the power supply voltage is applied to the drain (D) of the FET 5. It has not been. Further, no bias voltage is applied to the gate 1. Therefore, the reverse transfer characteristic from the output end of the FET 5 to the input end (drain to gate 1) is deteriorated (a signal is easily transferred in the reverse direction). On the other hand, this kind of combination tuition
As the size of the UHF tuner 2 is further reduced, the UHF tuner 2 and the VHF tuner 7 are arranged close to each other in one case.
Therefore, it is unavoidable that the signal leaks from the circuit of the tuner in one operating state to the circuit of the tuner in the other non-operating state.

Under these circumstances, for example, VHF
When receiving, when the VHF tuner 7 is tuned to a high-band high channel, the local oscillator circuit (not shown) of the VHF tuner 7 oscillates at 350 MHz to 400 MHz (US-specified CATV channel 40). Before and after, I received it with the VHF tuner). The local oscillator circuit generates high-level harmonics. Of these, focusing on the second harmonic, its frequency is approximately 700 MHz to 8 MHz.
It becomes 00. This harmonic easily leaks to the UHF tuner 2 arranged close to the VHF tuner 7,
When leaking to the tuner 2, the FET 5 of the amplifier circuit 6 is transmitted in the reverse direction. And VHF tuner 7 is 300MHz
When receiving ˜350 MHz, the tuning circuit 4 of the UHF tuner 2 is tuned to approximately 700 MHz to 855 MHz (see FIG. 6). Therefore, the second harmonic transmitted in the reverse direction of the FET 5 is this tuning. There is a problem that the circuit easily transmits and reaches the antenna input terminal 1, where it is radiated into the air as unnecessary radiation.

On the other hand, a UHF band television signal entering the antenna input terminal 1 enters a mixing circuit (not shown) of the VHF tuner 7 via the tuning circuit 4, the amplifier circuit 6 including the FET 5, and the like. However, there is a problem that an unwanted interference signal is generated in this mixing circuit. That is, for example, a UHF band television signal is 700 MHz to 855 M.
In the case of Hz, these frequencies easily propagate the tuning circuit 4 and also the amplifier circuit 6. Although the amplifier circuit 6 is in a non-operating state, the television signal passing through the amplifier circuit 6 leaks to the adjacent VHF tuner 7. If any of the TV signal frequencies leaked to the VHF tuner 7 is close to a frequency higher by an intermediate frequency than the harmonic of the oscillation frequency of the local oscillation circuit (not shown) of the VHF tuner 7 being received,
There is a problem in that the mixing circuit of the VHF tuner 7 (not shown) mixes this harmonic wave and frequency-converts it to an intermediate frequency and outputs it, which becomes an interference signal. Therefore, an object of the present invention is not necessary because such a signal leaks from one tuner (for example, VHF tuner 7) circuit to the other tuner (for example, UHF tuner 2) circuit. Radiation is emitted from the antenna as radiation, or conversely, a signal from the antenna leaks to one tuner (eg, VHF tuner 7) via the other tuner (eg, UHF tuner 2). do it,
Therefore, it is necessary to solve the problem of generating unnecessary interference signals.

[0011]

Therefore, a tuner of the present invention is a VHF tuner having a VHF band tuning circuit,
And a UHF tuner having a UHF band tuning circuit,
For the VHF band tuning circuit and the UHF band tuning circuit
Share the tuning voltage to set each tuning frequency.
Applied to the tuning frequency of the UHF band tuning circuit.
When receiving the UHF tuner at one of the tuning voltages
Lower than when receiving the VHF tuner and
Note Oscillation signal output from the local oscillator circuit of the VHF tuner
The frequency of the second harmonic is less than or equal to the frequency of the second harmonic.

In addition, a high voltage is provided in the next stage of the UHF band tuning circuit.
A frequency amplifier circuit is provided to adjust the UHF band tuning circuit and the high frequency band.
The frequency amplification circuit is coupled with a switch diode, and the V
Conducts the switch diode when receiving the HF tuner
The input capacitance of the high-frequency amplifier circuit in the UHF band.
Added to the tuning circuit.

[0013] Further, when receiving the VHF tuner, it conducts.
The high frequency amplification circuit through the switch diode
Bias voltage is applied to the
The degree of amplification of the high frequency amplifier circuit is received by the UHF tuner.
It was lower than the amplification degree at time.

[0014]

[0015]

[0016]

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of the present invention will be described with reference to FIGS. Here, FIG. 1 shows a tuner UHF antenna input circuit to which the present invention is applied together with peripheral circuits, and FIG. 2 is an equivalent circuit at the time of receiving UHF.
Is an equivalent circuit at the time of receiving VHF. In these figures, the same parts as those of the prior art are designated by the same reference numerals and the description thereof will be omitted.

In FIG. 1, a conventional coupling capacitor 1 is provided between one end (anode) of a varactor diode 10 for tuning frequency tuning and a gate 1 which is an input end of the FET 5.
Instead of 6, a DC blocking capacitor 25 and a switch diode 26 are connected in series. One end (anode) of the switch diode 26 is connected to the terminal VB through the power feeding resistor 27, and the other end (cathode) is connected to the gate 1 of the FET 4 and the coil 17 and the resistor. Two
It is also connected to 0.

In FIG. 1, when UHF is received, the switch diode 3 is rendered conductive and the switch diode 26 is rendered non-conductive by the voltage applied to the terminal UB, and the resistors 19 and 20 divide the voltage. The compressed voltage is applied to the gate 1 of the FET 5 as a bias voltage. On the other hand, at the time of receiving VHF, the switch diode 3 becomes non-conductive due to the voltage applied to the terminal VB, and a current flows through the switch diode 26 through the power feeding resistor 27 to become conductive, so that the gate 1 of the FET 5 is biased. Voltage is applied. At this time, the bias voltage applied to the gate 1 may be set to be the same as the bias voltage applied at the time of receiving UHF, or may be different. In this embodiment, the FET4 at the time of receiving UHF
The power feeding resistor 27 is set so that the amplification degree is lower than the normal amplification degree.

An equivalent circuit of the antenna input circuit of FIG. 1 at the time of receiving UHF is shown in FIG. Here, the variable capacitance 2
The capacitor 28 between 1 and the coil 17 represents the inter-terminal capacitance when the switch diode 26 is not conducting. Generally, the capacitance between terminals is 1 to 2 Pf when a reverse bias is applied to the diode to make it non-conductive.
It has a suitable value as a coupling capacitor with the high frequency amplifying circuit 6 of F, and can perform the same function as the coupling capacitor 16 between the conventional tuning circuit 4 and the amplifying circuit 6. FIG. 2 is the same as FIG. 5 showing an equivalent circuit of the conventional antenna input circuit at the time of receiving UHF, and the relationship between the tuning frequency and the tuning frequency is also the same.

On the other hand, when VHF is received, the switchdio
When the gate 26 is turned on, its equivalent circuit is shown in FIG. 3, and the tuning circuit 4 and the FETs of the amplifier circuit 6 are directly connected without a coupling capacitor. And the coil 17 and FE
Since the parallel resonance frequency due to the input capacitance 22 of T5 is in the vicinity of the lower end of the UHF band, the coil 1 is used in the high UHF band region.
Since the reactance of No. 7 becomes larger than the reactance of the input capacitance 22 of the FET 5, it can be ignored. Therefore, it is the same as the input capacitance 22 of the FET 5 being connected in parallel to the variable capacitance 21. Therefore, the tuning frequency of the tuning circuit 4 is lowered. In addition, the conventional coupling capacitor 1
Since there is no equivalent to 6, tuning circuit 4 and FET 5
By directly connecting the two, the matching condition between the two is broken and the transmission level is lowered. In this way, the frequency can be made different by simply connecting the amplifier circuit 6 to the tuning circuit 4 by the switch diode 26, and the circuit configuration becomes simple. Since the frequency is made different in the tuning circuit of the antenna input circuit, a signal which interferes from the outside is prevented from entering the tuning circuit and thereafter, so that leakage is reduced.

This state is shown in the curves C and D in FIG.
Is. Curve C is the characteristic of the tuning circuit 4 of the UHF tuner 2 when the VHF tuner 7 is tuned to 295 MHz, in which case the tuning circuit 4 of the UHF tuner 2 tunes to approximately 650 MHz, And the level is also A2
It is 15 dB lower than that (X in FIG. 6). The curve D is the characteristic of the tuning circuit 4 of the UHF tuner 2 when the VHF tuner 7 is tuned to 343 MHz. In this case, the tuning circuit 4 of the UHF tuner 2 is approximately 750 MHz.
It is tuned to and the level is 15 dB better than the conventional B2.
It is decreasing (X in FIG. 6). As described above, when the tuning frequency of the tuning circuit 4 of the UHF tuner 2 during VHF reception is lowered, the frequency shifts, and the antenna input terminal 1
The interference signal from is difficult to enter the tuning circuit 4, and
Since the transmission level is also lowered, a disturbing signal that slightly enters the tuning circuit 4 becomes difficult to be transmitted to the amplifier circuit 6 at the next stage. As a result, the interfering signal does not leak to the VHF tuner 2, and therefore the interfering signal is not generated in the mixing circuit (not shown) of the VHF tuner.

Further, when VHF is received, the switch diode 26 is turned on to apply a bias voltage to the gate 1 of the FET 5. Therefore, the FET of the amplifier circuit
In No. 5, the signal is less likely to be transmitted in the opposite direction (from the output side to the input side) as compared to when the bias voltage is not applied. Therefore, even if the harmonic of the oscillation frequency of the local oscillator circuit (not shown) of the VHF tuner 7 leaks to the UHF tuner 2, the harmonic is not transmitted to the input side of the amplifier circuit 6, and therefore, via the antenna input terminal 1. It is not emitted in the air.

As described above, in this embodiment, the tuning frequency of the tuning circuit 4 of the UHF tuner 2 is set to U
V should be set lower when VHF is received than when HF is received.
The harmonics of the oscillation frequency from the local oscillation circuit of the HF tuner 7 are prevented from leaking to the antenna input terminal 1, and the interfering signal among the signals input from the antenna input terminal 1 is UHF. Although it is difficult to transmit the tuning circuit 4 of the tuner 2, the present invention is not limited to this. For example, conversely, the tuning frequency of the tuning circuit 4 is increased in the case of VHF reception as compared with the case of UHF reception. May be. In short, V
The tuning frequency of the tuning circuit 4 of the UHF tuner 2 may be different from the frequency of the harmonic wave from the local oscillation circuit of the HF tuner 7 so that it is difficult to transmit. Further, in the same way, the tuning frequency of the tuning circuit 7a of the VHF tuner 7 is changed to
The harmonics of the oscillation frequency from the local oscillation circuit (not shown) of the UHF tuner 2 are set to be lower or higher when receiving UHF than when receiving VHF, and the harmonics of the oscillation frequency are tuned through the tuning circuit 7a of the VHF tuner 7 to the antenna. Leakage to the input terminal 1 may be prevented, and an interfering signal of the signals input from the antenna input terminal 1 may be difficult to transmit to the tuning circuit 7a of the VHF tuner 72. Further, although the embodiment of the present invention has been described by changing the tuning frequency of the tuning circuit 4 of the antenna input circuit, double tuning between the amplifier circuit 6 and the mixing circuit connected to the subsequent stage of the amplifier circuit 6 is performed. The same effect can be obtained when applied to a circuit.

Further, in the present invention, the same tuning voltage is applied to the tuning circuit 4 of the UHF tuner 2 and the tuning circuit 7a of the VHF tuner 7, and the relationship of their tuning frequencies cannot be changed. Also in this case, the tuning frequency of the tuning circuit 4 can be easily changed by connecting / disconnecting the switch diode 26 with the U / V switching voltage from the terminal VB or UB.

[0026]

As described above, the tuner of the present invention is U
The tuning frequency of the HF band tuning circuit is set to the same tuning voltage.
Than when receiving the UHF tuner
Local oscillator circuit of VHF tuner while lowering during reception
Below the frequency of the second harmonic of the oscillation signal output from
As a result, the 2nd harmonic is transmitted through the UHF band tuning circuit.
Is not output to the antenna.

[0026]

As described above, according to the tuner of the present invention, the tuning frequency of the tuning circuit of one tuner at the time of reception of one tuner and the tuning frequency of the tuner at the time of reception of the other tuner. Since the tuning frequency of the circuit is made different, a signal interfering with the other tuner is externally transmitted via the tuning circuit of the other tuner.
That the harmonics leaked from the local oscillation circuit of the other tuner to the one tuner are radiated from the antenna via the tuning circuit of the one tuner without leaking to the tuner. Disappears.

In addition, the high frequency is added to the next stage of the UHF band tuning circuit.
UHF band tuning circuit and high frequency amplifier circuit
And are connected by a switch diode to receive the VHF tuner.
When the signal is received, the switch diode is turned on and the high frequency amplifier circuit
Since the input capacitance is added to the UHF band tuning circuit,
Adjust the tuning frequency to VHF tuner than when receiving UHF tuner.
It can be lowered when receiving a message.

In addition, when the VHF tuner is received, it is conducted.
Bias to high frequency amplifier circuit via switch diode
Applying a voltage to increase the high frequency amplifier circuit by bias voltage
The width is lower than the amplification when receiving the UHF tuner.
As a result, the 2nd harmonic leaks to the output side of the high frequency amplifier circuit.
Even if it leaks, it becomes difficult for the high-frequency amplifier circuit to transmit in the opposite direction,
The level output to the antenna is even lower. Also, V
Since the amplification level decreases when receiving the HF tuner,
The level of the output UHF band television signal is low.
As a result, interference in the latter stage is less likely to occur.

[0029]

[0030]

[0031]

[Brief description of drawings]

FIG. 1 is an antenna input circuit in a tuner of the present invention.

FIG. 2 is an equivalent circuit of the antenna input circuit of the tuner of the present invention when receiving UHF.

FIG. 3 is an equivalent circuit of the antenna input circuit of the tuner of the present invention when receiving VHF.

FIG. 4 is an antenna input circuit of a conventional tuner.

FIG. 5 is an equivalent circuit of an antenna input circuit of a conventional tuner.

FIG. 6 is a characteristic diagram of an antenna input circuit.

[Explanation of symbols]

1 Antenna input terminal 2 UHF tuner 3.26 switch diode 4 UHF band tuning circuit 5 FET 6 UHF high frequency amplifier circuit 7 VHF tuner 7a VHF band tuning circuit 7b VHF high frequency amplifier circuit 8.9.13.17 coil 10 Varactor diode 11.14.15.19.27 Power supply resistance 12 capacitors 16.28 Coupling capacitor 18 Grounding capacitor 20 resistance 21 Variable capacity 22 Input capacity 25 DC blocking capacitor

Claims (3)

(57) [Claims] 1. A VHF tuner having a VHF band tuning circuit.
And a UHF tuner having a UHF band tuning circuit
And a tuning circuit for the VHF band and a tuning circuit for the UHF band.
Tuning to set each tuning frequency in the circuit
Apply a common voltage to the tuning circuit of the UHF band tuning circuit.
The UHF tuner at the tuning voltage having the same wave number
Lower when receiving the VHF tuner than when receiving
Output from the local oscillator circuit of the VHF tuner together with
The frequency is less than the frequency of the second harmonic of the oscillation signal
And the tuner. 2. A high frequency wave is provided at the next stage of the UHF band tuning circuit.
An amplifier circuit is provided, and the UHF band tuning circuit and the high frequency wave are provided.
The amplifier circuit is coupled with a switch diode, and the VHF
When receiving the tuner, turn on the switch diode.
The input capacitance of the high frequency amplifier circuit is set to the tuning circuit of the UHF band.
The chew according to claim 1, which is added to the road.
Na. 3. Conducting when receiving the VHF tuner
To the high-frequency amplifier circuit via the switch diode
Applying a bias voltage, the bias voltage
The degree of amplification of the frequency amplifier circuit when receiving the UHF tuner
3. The degree of amplification is lower than that in the above.
The tuner described in.