JP2000224068A - Electronic device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the disturbance to a digital demodulating section in an electronic device, in which an on-vehicle car navigation set and a television receiver is integrally provided by reducing the higher harmonics of locally oscillated signals. SOLUTION: A serial resonance circuit 34 composed of a capacitor 32 and an inductance 33 is connected to one side of a tank circuit 31, and the resonant frequency of the resonance circuit 34 is matched to the secondary higher harmonic of an oscillation frequency when a specific channel is received. Therefore, the secondary higher harmonic can be reduced, and accordingly, a digital demodulating section 24 can operate stably without receiving unwanted signals from an electronic tuner 21, because the second higher harmonic becomes incapable of being returned.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electronic device in which a car navigation system and a television receiver are integrally provided.

[0002]

2. Description of the Related Art A conventional electronic device will be described below.

As shown in FIG. 4, a conventional electronic device includes an electronic tuner 1 to which a television signal is input, a demodulator 2 to which an output of the electronic tuner 1 is connected, and a demodulator 2 to which the output of the electronic tuner 1 is connected. The display unit 3 to which the output is connected and a digital signal having a predetermined specific frequency for car navigation are input, and the output is displayed on the display unit 3.
And a digital demodulation unit 4 connected to the digital demodulation unit.

The electronic tuner 1 has an input terminal 5,
A high-frequency amplifier 6 connected to the input terminal 5; a mixer 8 having an output connected to one input and a local oscillator 7 connected to the other input; An intermediate frequency amplifier 9 to which the output of the amplifier 8 is connected, and an output terminal 10 to which the output of the intermediate frequency amplifier 9 is connected. The local oscillator 7 is connected to a tank circuit 11 constituting the local oscillator 7. And a loop connection with the PLLIC12.

[0005]

However, in such a conventional configuration, assuming that the specific frequency of the car navigation is approximately 1575.42 MHz, the second harmonic of the local oscillator 7 is received when a broadcast of CH56 (in Japan) is received. The wave becomes approximately 1576 MHz, which substantially coincides with the input signal of approximately 1575 or 42 MHz of the digital demodulation unit 4 which is a specific frequency, and when the electronic tuner unit 1 and the digital demodulation unit 4 are arranged close to each other, the substantially same signal There is a problem that the interference wave is input and the digital demodulation unit 4 malfunctions.

The present invention solves such a problem, and provides an electronic device that does not interfere with a digital demodulation unit even when a specific channel of a television signal is received, and guarantees the operation of the digital demodulation unit. The purpose is to do so.

[0007]

In order to achieve the above object, a tank circuit constituting a local oscillator of an electronic device according to the present invention is provided with a direct resonance circuit of a capacitor and an inductance in parallel with the tank circuit. The resonance frequency of the resonance circuit is substantially equal to a specific frequency.

As a result, the digital demodulation section operates normally without any interference.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The invention according to claim 1 of the present invention provides an electronic tuner to which a television signal is inputted,
A demodulation unit to which the output of the electronic tuner unit is connected, a display unit to which the output of this demodulation unit is connected, and a digital signal of a predetermined specific frequency are input and the output is connected to the display unit. A digital demodulation unit, wherein the electronic tuner unit has an input terminal, a high-frequency amplifier connected to the input terminal, an output of the high-frequency amplifier connected to one input, and another input connected to the other input. A mixer to which the output of the local oscillator is connected, an intermediate frequency amplifier to which the output of the mixer is connected, and an output terminal to which the output of the intermediate frequency amplifier is connected, wherein the specific frequency is the television signal The frequency is set to be approximately twice the frequency of the specific channel, and the tank circuit constituting the local oscillator is provided with a capacitor and an inductor in parallel with the tank circuit. Of the series resonant circuit is provided, the resonant frequency of the series resonant circuit is substantially equal to the electronic device to the particular frequency, it is possible to reduce the level of the second harmonic component of the local oscillator. As a result, the leakage component from the electronic tuner section to the digital demodulation section is reduced, and is not affected by the electronic tuner section even when receiving a specific channel.
The digital demodulator operates normally.

The inductance of the series resonance circuit according to the second aspect of the present invention is the electronic device according to the first aspect, wherein the inductance is formed in a pattern, and the inductance can be arranged in an empty space of the substrate. I can do it. Furthermore,
Since it can be routed, the ground can be set at the optimum position.

The invention according to claim 3 is the electronic device according to claim 1, wherein the value of the inductance is adjustable.
When the specific frequency is changed, it is possible to easily react by adjusting the resonance frequency of the series resonance circuit.

According to a fourth aspect of the present invention, there is provided the electronic device according to the first aspect, wherein the resonance frequency is set to approximately 1576 MHz, the inductance value is set to approximately 18 nH, and the specific frequency of 1575.42 MHz is received. The fundamental frequency of the local oscillator is about 800 MHz, while the resonance frequency of the circuit is about 1576 MHz. By setting the inductance value to about 18 nH, the level of only the second harmonic component can be reduced without deteriorating the fundamental component. Further, since the Q is not extremely high, the attenuation can be secured even when the resonance frequency is shifted due to the variation of the components.

According to a fifth aspect of the present invention, the local oscillator is a balanced local oscillator, and a series resonance circuit is provided on one of the series resonance circuits forming the oscillator.
In the electronic device described above, since one series resonance circuit can be connected to both feedback circuits, the amount of attenuation by the series resonance circuit can be increased.

According to a sixth aspect of the present invention, the local oscillator is a balanced type local oscillator, and a series resonant circuit having a different resonant frequency is provided on both one and the other of the series resonant circuits forming the local oscillator. 2. The electronic device according to claim 1, wherein a series resonance circuit having a different resonance frequency can be connected to each of one side and the other side of the tank circuit to reduce another frequency component. In terms of circuit, two series resonance circuits may be connected to one side of the tank circuit, but it is better to connect to both tank circuits in consideration of circuit coupling. Also, mounting on both sides provides a larger mounting space.

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

FIG. 1 is a block diagram of an electronic device according to an embodiment of the present invention.

In FIG. 1, reference numeral 21 denotes an electronic tuner section housed in a substantially square metal case, and an input terminal 25 is provided on one side surface of a frame of the case. The signal input to the input terminal 25 is connected to one terminal of a mixer 28 through a high-frequency amplifier 26 for amplifying a television signal of approximately 90 MHz to 800 MHz.

The output of the local oscillator 27 is connected to the other terminal of the mixer 28. And the mixer 28
Is connected to an output terminal 30 via an intermediate frequency amplifier 29. The local oscillator 27 has a tank circuit 3.
1 and the PLLIC 35 is connected in a loop.

Here, a capacitor 32 is connected to the tank circuit 31.
And a series resonance circuit 34 having an inductance 33 are connected in parallel.

On the other hand, approximately 15575.42H is applied to the input terminal 40.
The specific frequency for car navigation of z is input.
After being processed by the digital demodulation unit 24, the display unit 2
3 is displayed.

The electronic tuner 21, demodulator 22, display 23 and digital demodulator 24 are incorporated in a car navigation set 41 (used as an example of an electronic device). In the layout of the set 41, they are arranged physically close to each other.

FIG. 2 shows a local oscillator 27 and a tank circuit 31.
FIG. 2, reference numeral 50 denotes a constant current source, which includes an oscillating transistor 51 and an oscillating transistor 5.
Two emitters are connected. 53,54,55,5
Reference numeral 6 denotes a feedback capacitor, each of which includes a transistor 5
1, 52 are connected to each terminal. The tank circuit 31 is formed by connecting the tuning variable capacitance diode 57 and the tuning coil 58 in parallel (not shown, but the diode 57 is connected via a resistor of about 27 kΩ to select a desired channel. And a capacitor is generally connected in series or in parallel to correct the tracking).

The tank circuit 31 and the oscillation transistor 51,
52 is connected by feedback capacitors 53, 54, 55 and 56. Further, a series resonance circuit 3 including a capacitor 32 and an inductance 33 is connected between one side of the tank circuit 31 and the ground.
4 are connected.

It is also possible to connect another series resonance circuit having a different resonance frequency to the other side of the tank circuit 31 to reduce another frequency component. Here, another frequency component includes not only the second harmonic, but also the third and higher harmonics. In terms of circuit, two series resonance circuits may be connected to one side of the tank circuit 31, but it is better to connect both to the tank circuit 31 in consideration of circuit coupling. Also, in consideration of the mounting space, it is easier to design when both sides are connected.

Here, the output of the local oscillator 27 is output from the collector terminal of the transistor 51. This output signal is fed back to the base terminal of the transistor 51 as an input terminal via the capacitor 56, the tank circuit 31, and the capacitor 53. At this time, the capacitors 56 and 53 respectively shift the phase of the output signal by 90 degrees (the output signal is phase-shifted by 180 degrees). Further, since the tank circuit 31 is connected to both ends of the transistors 51 and 52 constituting the differential amplifier,
The phase difference is 180 degrees. Therefore, the output signal is 3 by the capacitor 56, the transistor 51, and the tank circuit 31.
60 degrees phase shift. That is, the output signal and the input signal have the same phase, and positive feedback is applied, so that the oscillation operation is performed.

Similarly, the base terminal and the collector terminal of the transistor 52 have the same phase by the capacitors 54 and 55 and the tank circuit 31, so that a positive feedback is applied and an oscillating operation is performed.

Since the transistors 51 and 52 are non-linear elements, high-order harmonics such as second-order harmonics are simultaneously generated in addition to the fundamental signal in the oscillation operation. These signals are supplied to the capacitors 53, 54, 55, 56 and the tank circuit 31.
Is fed back from the output to the input via.

For this reason, a series resonance circuit 34 composed of a capacitor 32 and an inductance 33 is connected between one side of the tank circuit 31 and the ground, so that a second harmonic of the oscillation frequency at the time of receiving a specific channel (CH56) is obtained. By adjusting the strong and new frequencies of the series resonance circuit 34, the second harmonic component cannot be fed back, so that the second harmonic can be reduced.

Further, the fundamental wave and the second harmonic are approximately 788 MHz.
z apart, but the coil inductance is approximately 18 nH
, The Q of the series resonance circuit 34 is optimized, and only the second harmonic component can be reduced without deteriorating the fundamental component.

The circuit has a differential configuration. By connecting the series resonance circuit 34 to the tank circuit 31 which is a common part of the local oscillator 27 including the transistor 51 and the local oscillator 27 including the transistor 52, about 20 dB is obtained. A degree of attenuation is obtained. Of course, even if the series resonance circuit 34 is connected to any of the capacitors 53, 54, 55, 56, a certain effect can be obtained.

The specific frequency for car navigation is approximately 1
575.42 MHz. On the other hand, by setting the resonance frequency of the series resonance circuit 34 to approximately 1576 MHz,
The second harmonic component fed back from the output of the local oscillator 27 to the input is attenuated. As a result, the oscillation condition at the second harmonic frequency is deteriorated, and the oscillation component is reduced. For this reason,
The leakage component and the specific frequency from the electronic tuner 21 to the digital demodulation unit 24 are substantially the same, but are sufficiently small with respect to the car navigation input signal 40, so that the digital demodulation unit 24 is not adversely affected. Therefore, the digital demodulation unit 24 operates stably.

FIG. 3 is a mounting diagram of the series resonance circuit 34 provided on the substrate 60. In FIG. 3, reference numeral 32 denotes a capacitor constituting a series resonance circuit, and reference numeral 33 denotes an inductance. By patterning the inductance 33,
An empty space on the surface of the substrate 60 can be used. Also, the earth point can be freely set, and the earth point can be set at the connection point between the frame and the substrate. Thus, unnecessary signal components including the second harmonic component are dropped to the ground without leaking to other circuits.

[0033]

As described above, according to the present invention, a tank circuit constituting a local oscillator is provided with a series resonance circuit of a capacitor and an inductance in parallel with the tank circuit, and the resonance frequency of the series resonance circuit is specified. Since the frequency is almost doubled, the local oscillator 2
Since the second harmonic is reduced, the digital demodulation unit to which a specific frequency is input does not malfunction due to interference.
Stable operation can be performed.

[Brief description of the drawings]

FIG. 1 is a block diagram of an electronic device according to an embodiment of the present invention.

FIG. 2 is a circuit diagram of a local oscillator constituting an electronic tuner of the electronic device.

FIG. 3 is a perspective view of a series resonance circuit connected in parallel with a tank circuit of the local oscillator.

FIG. 4 is a block diagram of a conventional electronic device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 21 Electronic tuner part 22 Demodulation part 23 Display part 24 Digital demodulation part 25 Input terminal 26 High frequency amplifier 27 Local oscillator 28 Mixer 29 Intermediate frequency amplifier 30 Output terminal 31 Tank circuit 32 Capacitor 33 Inductance 34 Series resonance circuit 40 Input terminal 41 Car navigation set

Continued on the front page (72) Inventor ▲ Taka ▼ Bridge Kobo 1006 Kazuma Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. F term (reference) 5K020 AA02 BB05 DD01 EE01 EE04 EE05 GG16 HH07 MM12 MM13 NN03

Claims (6)

[Claims] 1. An electronic tuner to which a television signal is input, a demodulator to which an output of the electronic tuner is connected, a display to which an output of the demodulator is connected, and a predetermined specific frequency A digital demodulation unit whose output is connected to the display unit. The electronic tuner unit has an input terminal, a high-frequency amplifier connected to the input terminal, and a high-frequency amplifier. Is connected to one input and the other input is connected to a mixer connected to the output of the local oscillator, an intermediate frequency amplifier connected to the output of the mixer, and an output of the intermediate frequency amplifier. Connected to an output terminal, wherein the specific frequency is set to a frequency approximately twice as high as a specific channel of the television signal, and a tunable frequency constituting the local oscillator is provided. In the circuit, a series resonance circuit of a capacitor and an inductance is provided in parallel with this tank circuit.
An electronic device in which the resonance frequency of the series resonance circuit is substantially equal to the specific frequency. 2. The electronic device according to claim 1, wherein the inductance of the series resonance circuit is patterned. 3. The electronic device according to claim 1, wherein the value of the inductance is adjustable. 4. When the resonance frequency is set to about 1576 MHz and the inductance value is set to about 18 nH,
The electronic device according to claim 1, wherein the electronic device receives a specific frequency of 74.42 MHz. 5. The electronic device according to claim 1, wherein the local oscillator is a balanced local oscillator, and a series resonance circuit is provided in one of the tank circuits forming the local oscillator. 6. The electronic device according to claim 1, wherein the local oscillator is a balanced local oscillator, and series resonance circuits having different resonance frequencies are provided on both one and the other of the tank circuits forming the local oscillator. .