JP2000040971A - In-vehicle TV receiver - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce only secondary harmonics of a locally oscillated output in an antenna input terminal at receiving of a UHF channel by providing a trap, which attenuates n-th degree harmonics of locally oscillated frequency of a tuner. SOLUTION: Television radio waves received by a television antenna 1 are tuned in and selected by a tuner 2. GPS radio waves received by a GPS antenna 7 are subjected to signal processing by a navigation device 8. An LC trap 9, which tunes in to a double frequency of a local frequency of a UHF 56 channel and attenuates the frequency, is provided between the antenna connection terminal (a) of a television receiver and the antenna input terminal (b) of the tuner 2. Thus, it prevents the secondary harmonics of a locally oscillated frequency of the tuner 2, which becomes the cause of GPS receiving interference from being radiated from the antenna 1. The trap 9 is constructed by serially connecting a capacitor and an inductor between a television signal line and a GND pattern.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a GPS (Global P
The present invention relates to an in-vehicle monitor and a general in-vehicle television receiver having a television receiving function used for displaying an image of a navigation system using an ositioning system.

[0002]

2. Description of the Related Art FIG. 6 is a block diagram of a conventional GPS navigation system. In the figure, 1 is a television
Antenna, 2 is a tuning / tuning tuner, 3 is a tuning control microcomputer, 4 is a video demodulation circuit, 5 is a signal switching circuit, 6
Is a display, 7 is a GPS antenna, and 8 is a navigation device.

A television wave received by a television antenna 1 is tuned and tuned by a tuner 2 controlled by a tuning control microcomputer 3, and detected and tuned by a video demodulation circuit 4.
After demodulation, a television image is displayed on a display 6 such as a liquid crystal panel via a signal switching circuit 5. On the other hand, the GPS radio wave received by the GPS antenna 7 is signal-processed by the navigation device 8, and the navigation device 8 outputs the processing result as a video signal and supplies it to the signal switching circuit 5. As a result, for example, the current position of the own vehicle can be displayed on a map screen every moment.

When an in-vehicle monitor having a television reception function of a domestic channel is used for displaying images of the GPS navigation system, when the UHF 56 channel is selected, the local oscillation frequency of the tuner at that time becomes 788 MHz. Since the local oscillation output contains harmonics, the second harmonic is 788 MHz × 2 =
1576 MHz, which is the frequency of GPS radio waves of 1755.42 MHz
And almost match. In addition, since GPS radio waves are originally weak,
If there is a signal such as a local oscillation second harmonic of the UHF 56 channel whose level is large and the frequency matches, a signal is masked by this signal, a normal GPS radio wave cannot be received, and the current position cannot be calculated. Is a fatal obstacle for

That is, when a UHF television channel is received during operation of the GPS navigation system, the harmonics twice as high as the local oscillation frequency of the tuner almost coincide with the frequency of the GPS signal. Cause the navigation function to be impaired. In reality, the generation of harmonics of the local oscillation frequency of the tuner is unavoidable, so it is necessary to reduce the local harmonic level of 56 channels by some means in order not to disturb the weak GPS signal. .

[0006] There is a passive method for preventing the reception of 56 channels during the GPS operation, but there is a case where the system is inconvenient. Therefore, an aggressive method for fundamentally reducing harmonics is desired. However, the problem is how to reduce it. Conventionally, this has generally been addressed by strengthening the shield of the tuner.

Therefore, conventionally, a PLL (Phase Lo
In addition to employing the tuner 2 having a built-in cked loop) circuit, the shield of the tuner is strengthened so that leakage of local oscillation output including harmonics is reduced as much as possible as a whole.

[0008]

SUMMARY OF THE INVENTION However, PLL
Even when a function requiring a local oscillation output can be enclosed in a tuner housing by employing a tuner having a built-in circuit, it is difficult to reduce the leakage of the local oscillation output to a required level or less. Therefore, in a system in which the PLL circuit is outside the tuner housing, it is even more difficult to reduce GPS reception interference due to leakage of local oscillation output.

However, as can be seen from FIG. 6, since the television antenna 1 for television reception is also a radiation antenna for unnecessary harmonics of the local oscillation output, the local oscillation output appearing at the antenna input terminal of the television receiver is obtained. Reducing only the unwanted harmonic level of the GPS could be an effective measure of GPS interference.

Therefore, an object of the present invention is to attenuate harmonics of a local oscillation frequency of a tuner that interfere with GPS reception. More specifically, an object is to reduce only the second harmonic of the local oscillation output at the antenna input terminal at the time of receiving the UHF 56 channel.

[0011]

According to the present invention, an on-vehicle television receiver according to the present invention comprises a 1 / n (n = n) of a GPS carrier between an antenna input terminal of a tuner and an antenna connection terminal of the television receiver.
A trap for electrically attenuating an nth harmonic of a local oscillation frequency of the tuner, which is a frequency close to a positive integer). According to the present invention,
Solving the fatal problem of GPS reception interference, which occurs when the nth frequency of the GPS carrier is close to the nth harmonic of the local oscillation frequency of the tuner, with a trap for eliminating harmonics alone Because you can
A large effect can be produced with a simple circuit configuration with a small number of parts.

Second, the trap comprises a capacitor and an inductor connected between a GND and an antenna signal line connecting an antenna input terminal of the tuner and an antenna connection terminal of the television receiver. I do. Thus, the trap has a simple circuit configuration with a small number of components.

Thirdly, the trap is constituted by a chip capacitor mounted on a circuit board and an inductor by a strip line formed on the circuit board. As described above, only a chip capacitor is provided as a mounting component on a circuit board, and the circuit configuration is simple with a small number of components.

Fourth, the trap is formed by a capacitor formed by a wiring pattern facing the television signal line formed on a circuit board with an insulator interposed therebetween, and a trip line of the wiring pattern. And an inductor. In the case of the present invention, a trap can be formed only by wiring, and the circuit configuration is simple with a small number of components.

Fifth, the trap has a local oscillation frequency of the UHF 56 channel in the Japanese domestic broadcast.
It is characterized in that the frequency corresponding to the second harmonic is attenuated. In particular, it is possible to cope with the local oscillation frequency of the UHF 56 channel which is remarkable as GPS reception interference.

[0016]

FIG. 1 shows a block diagram according to a first embodiment of the present invention in comparison with a conventional example. Although the description of the portion equivalent to that of FIG. 6 of the conventional example is omitted, the present invention is different from the conventional example in that it is synchronized with the antenna connection terminal a of the television receiver.
The trap 9 corresponding to the second harmonic of the local oscillation output of the UHF 56 channel in television broadcasting for Japan is provided between the tuner 2 and the antenna input terminal b of the tuning tuner 2. The trap frequency is, of course, 1576 MHz.

That is, the present invention tunes the frequency between the antenna connection terminal a of the television receiver and the antenna input terminal b of the tuning / tuning tuner 2 to twice the local oscillation frequency of the UHF 56 channel, LC to attenuate this frequency
A trap is provided to prevent the second harmonic of the local oscillation frequency of the tuner, which causes GPS reception interference, from being radiated from the television antenna via the antenna input terminal.

The LC trap is composed of a series circuit of a capacitor and an inductor. Specifically, a TV signal line connecting the antenna connection terminal a and the antenna input terminal b of the tuner 2 is provided on a circuit board built in the TV receiver. GN formed on the circuit board like this signal line
It is composed of a strip / wiring line between the D pattern and a capacitor. The details will be described below.

FIG. 3 shows an equivalent circuit as an example of the LC trap. The trap is connected to antenna connection terminal a and tuner 2
In this configuration, an LC trap 9 in which a capacitor C and an inductor L are electrically connected in series is interposed between a TV signal line that electrically connects the antenna input terminal b of FIG. This LC trap functions as a series resonance circuit, tunes to a frequency of 1576 MHz which is twice the local oscillation frequency of the UHF 56 channel, and attenuates this frequency.

The local oscillation frequency f of the UHF 56 channel
= 788 MHz. Therefore, the frequency of the second harmonic is given by the following equation.

[0021]

(Equation 1)

The values of the capacitor C and the inductor L are
“2f” in Equation 1 is set to be 1576 MHz.

As a specific example of this trap, FIG. 4 is a plan view on a circuit board built in a television receiver for a vehicle. As shown in FIG. 4, a trap of a series resonance circuit is constituted by a chip capacitor C and an inductor L by a strip line in the middle of a television signal line surrounded by a GND pattern. The chip capacitor C is mounted so as to straddle a terminal (thick line in the figure) formed on the television signal line and a terminal (thick line in the figure) formed at the end of the strip line sandwiched between two GND patterns. Is done. On the other hand, the inductor is arranged so that the strip line is sandwiched by the GND pattern, and the length L and the width W of the strip line are set by the following formula to obtain the inductance.

[0024]

(Equation 2)

By using a strip line as the inductor, the variation in inductance can be minimized, the influence of interference with peripheral discrete components can be minimized, and further, there is no need to mount components and the cost is advantageous. become. In addition, a small chip capacitor is used as the capacitor C and the layout shown in the figure is used. In the case of a system that does not require a trap, the capacitor is not mounted, so that the electric influence on the TV signal line is almost eliminated. It can be eliminated.

Further, the capacitor may be constituted by a wiring pattern formed on a circuit board, and the capacitor is formed by a different wiring pattern opposed to a television signal line formed on the circuit board via an insulator. Alternatively, an LC trap may be constituted by a capacitor formed by wiring and an inductor formed by a strip line of a wiring pattern. Other than this, the capacitor C
Is formed by a wiring pattern formed on a circuit board in parallel with a television signal line at an insulated gap, or by forming a television signal line on one surface side of a circuit board to form an insulating circuit. Obviously, the present invention can be realized in various forms, such as forming with a wiring pattern formed on the back side of the circuit board with the board interposed.

FIG. 5 is a diagram showing an example of characteristics obtained by using a strip line trap as shown in FIG. Local oscillation second harmonic 15 of UHF 56 channel
Although the attenuation at 76 MHz was about 10 dB in the past, it increased to about 40 dB in the present invention, and the GPS reception interference can be greatly reduced even as a result of actually performing UHF 56 channel TV reception during operation of the navigation system. It was confirmed that characteristics that could be used above were obtained.

FIG. 2 shows another embodiment of the present invention. In this case, between the RF switch circuit 10 provided for the diversity reception of the television and the tuning / tuning tuner 2, the harmonic trap 9 having the same configuration as in the first embodiment is provided.
Is inserted. The other configuration is the same as that of the first embodiment.

The GPS reception disturbance countermeasure of the present invention is a method of obtaining an effect by a trap provided on a television signal line. Therefore, as can be seen from FIG. 5, an adverse effect on a television reception band far away from the trap frequency is obtained. Is nothing.

In the above embodiment, it is assumed that the problem at the time of receiving the UHF 56 channel is solved. However, the frequency of 1 / n (n = positive integer) of the GPS carrier is n of the local oscillation frequency of the tuner. The present invention can be applied to any channel as long as it is close to the second harmonic.

[0031]

As described above, according to the present invention, the GP
Solving the fatal problem of GPS reception interference, which occurs when the 1 / nth frequency of the S carrier is close to the nth harmonic of the local oscillation frequency of the tuner, with a trap for eliminating harmonics alone Therefore, a great effect can be produced with a simple circuit configuration with a small number of parts.

[Brief description of the drawings]

FIG. 1 is a block diagram of a GPS navigation system of the present invention.

FIG. 2 shows another embodiment of the present invention.

FIG. 3 is an equivalent circuit diagram of a trap unit.

FIG. 4 is a specific configuration example of a wrap.

FIG. 5 is an example of a passband characteristic of an antenna terminal.

FIG. 6 is a block diagram of a conventional GPS navigation system.

[Explanation of symbols]

 1. TV antenna 2. Tuner for tuning and tuning 3. Microcontroller for tuning control 4. Video demodulation circuit 5. Signal switching circuit 6. Display 7. 7. GPS antenna Navigation device 9. RF switch circuit

Claims (5)

[Claims] 1. A 1 / nth of a GPS carrier is provided between an antenna input terminal of a tuner and an antenna connection terminal of a television receiver.
An in-vehicle television receiver, wherein a trap for attenuating an nth harmonic of a local oscillation frequency of the tuner, which is a frequency close to (n = positive integer), is electrically connected. 2. The device according to claim 1, wherein the trap comprises a capacitor and an inductor connected between an antenna signal line connecting an antenna input terminal of the tuner and an antenna connection terminal of the television receiver, and GND. Item 4. The on-vehicle television receiver according to item 1. 3. The on-vehicle vehicle according to claim 2, wherein said trap comprises a chip capacitor mounted on a circuit board and an inductor formed by a strip line formed on the circuit board. TV receiver. 4. The trap is formed by a capacitor formed by a wiring pattern facing the television signal line formed on a circuit board with an insulator interposed therebetween, and a trip line of the wiring pattern. 3. The on-vehicle television receiver according to claim 2, wherein the television receiver comprises an inductor. 5. The on-vehicle television receiver according to claim 1, wherein the trap attenuates a frequency corresponding to a second harmonic of a local oscillation frequency of UHF 56 channel in the Japanese domestic broadcasting.