GB2324425A

GB2324425A - A TV tuner combined with a modulator for a VCR in which one crystal oscillator supplies both the tuner and the modulator

Info

Publication number: GB2324425A
Application number: GB9805392A
Authority: GB
Inventors: Hideharu Ootake
Original assignee: Alps Electric Co Ltd
Current assignee: Alps Alpine Co Ltd
Priority date: 1997-04-14
Filing date: 1998-03-16
Publication date: 1998-10-21
Anticipated expiration: 2018-03-16
Also published as: MY121700A; CN1196635A; KR100262777B1; GB2324425B; GB9805392D0; JP3599948B2; CN1110946C; JPH10290403A; KR19980081337A

Abstract

A TV tuner with a built-in RF modulator comprises: a housing; a wiring substrate arranged in the housing; a RF modulator unit (1) having a first phase lock loop circuit (3) provided on the wiring substrate and a crystal resonator (3c) connected to the first phase lock loop circuit; a TV tuner unit (2) having an input unit (12) and a second phase lock loop circuit (10) which are provided on the wiring substrate for connecting the crystal resonator to the second phase lock loop circuit, there being provided a grounding pattern (15) between the wiring pattern and the input unit to prevent interference.

Description

TV TUNER WITH A BUILT-IN RF MODULATOR The present invention relates to a TV (television) tuner with a built-in RF (high frequency wave) modulator, and more particularly to a TV tuner with a built-in RF modulator obtained by making a RF modulator and a TV tuner, which are used for a video apparatus such as a video tape recorder (VTR), integral with each other.

In recent years, in a video apparatus such as VTR, there has been used a TV tuner with a built-in RF modulator obtained by assembling a RF modulator and a TV tuner in a metallic housing to make them integral with each other.

Fig. 2 is a schematic view showing an example of such a conventional TV tuner with a built-in RF modulator, that is, structure in which a RF modulator and a TV tuner are integrally assembled in a metallic housing.

As shown in Fig. 2, the TV tuner with a built-in RF modulator is constructed such that one sheet of wiring substrate 11 is arranged in a housing 14, the whole of which is made of one metallic material, and a RF modulator unit 1 and a TV tuner unit 2 are mounted on the wiring substrate 11.

The RF modulator unit 1 comprises a first phase lock loop (PLL) circuit 3, a first RF amplifier 5, a distributor 6, a second RF amplifier 7, a mixer 8 and the like. The first phase lock loop (PLL) circuit 3 is provided with a first reference oscillation circuit 3a, a first voltage control oscillator (VCO) and the like.

A crystal resonator 3c for setting a reference frequency is connected to this first reference oscillation circuit 3a, and the first reference oscillation circuit 3a and the crystal resonator 3c constitute a first reference oscillator 3b. In this respect, this first reference oscillator 3b oscillates at a frequency of, for example, 4MHz.

On the other hand, the TV tuner unit 2 comprises at least an input unit 12, a third RF amplifier 13 and a second phase lock loop (PLL) circuit 10, and the second phase lock loop (PLL) circuit 10 has a second reference oscillation circuit 10a, a second voltage control oscillator (VCO) and the like. The crystal resonator 3c provided at the RF modulator unit 1 is connected to the second reference oscillation circuit 10a of the second phase lock loop (PLL) circuit 10 through a wiring pattern 17 disposed on the wiring substrate 11 so that the crystal resonator 3c and the second reference oscillation circuit 10a constitute a second reference oscillator 10b for oscillating at, for example, 4MHz.

Accordingly, the crystal resonator 3c is used in common by the first phase lock loop (PLL) circuit 3 in the RF modulator unit 1, and the second phase lock loop (PLL) circuit 10 in the TV tuner unit 2. The crystal resonator 3c for setting a reference frequency is not arranged in the TV tuner unit 2. Also, in the input unit 12, there is arranged on the wiring substrate 11 a coil (not shown) constituting an antenna tuning circuit for selecting a received signal, an intermediate frequency trap circuit for removing an external signal with the same frequency as an intermediate signal and the like.

On the wiring substrate 11, there is provided a first grounding pattern 15 close to the housing 14, for extending over both the RF modulator unit 1 and the TV tuner unit 2.

The wiring pattern 17 is interposed between the first grounding pattern 15, and the input unit 12 of the TV tuner unit 2 and a third RF amplifier 13. A second grounding pattern 16 is interposed between the RF modulator unit 1 and the TV tuner unit 2 so that the RF modulator unit 1 and the TV tuner unit 2 are electrically shielded respectively by the second grounding pattern 16.

In this respect, the first grounding pattern 15 and the second grounding pattern 16 are electrically connected to the housing 14, and are at a grounded potential.

Further, at a predetermined position in the second grounding pattern 16, there is formed an opening 16a separated from the second grounding pattern 16. Through this opening 16a, there is arranged the wiring pattern 17 for connecting the crystal resonator 3c disposed on the RF modulator unit 1 side to the second reference oscillation circuit 10a of the second phase lock loop (PLL) circuit 10 in the TV tuner unit 2.

The wiring pattern 17 for connecting the crystal resonator 3c to the second phase lock loop (PLL) circuit 10 is guided through between the first grounding pattern 15, and the input unit 12 and the third RF amplifier 13 in the TV tuner unit 2, and accordingly, is arranged in the vicinity of the input unit 12 and the third RF amplifier 13.

In this respect, the first grounding pattern 15, the second grounding pattern 16 and the wiring pattern 17 are formed by etching copper foil or the like on the wiring substrate 11.

In such structure as described above, a TV signal through an input terminal 4 provided on the RF modulator unit 1 side is inputted into a TV receiver (not shown) from an output terminal 9 through the first amplifier 5, the distributor 6, the second amplifier 7, the mixer 8 and the like. On the other hand, aTVsignal distributed by the distributor 6 is inputted into the TV tuner unit 2.

A video signal from a video signal input terminal 3d and a sound signal from a sound signal input terminal 3e modulate a carrier from the first phase lock loop (PLL) circuit 3 in a modulator (not shown) to transmit it to an output terminal 9 through the mixer 8 as a RF signal.

The first phase lock loop (PLL) circuit 3 in the RF modulator unit 1 is used to set the frequency of this carrier and for another purpose, and the second phase lock loop (PLL) circuit 10 in the TV tuner unit 2 is used for channel selection.

In a conventional TV tuner with a built-in RF modulator, however, the wiring pattern 17 is disposed for using the crystal resonator 3c in common by the first phase lock loop (PLL) circuit 3 in the RF modulator unit 1 and the second phase lock loop (PLL) 10 in the TV tuner unit 2. On this wiring pattern 17, there are flowing fundamental waves and their higher harmonics for respective oscillation signals of the first reference oscillator 3b of the first phase lock loop (PLL) circuit 3 in the RF modulator unit 1, and the second reference oscillator 10b of the second phase lock loop (PLL) circuit 10 in the TV tuner unit 2. Besides, this wiring pattern 17 is arranged in the vicinity of the input unit 12 and the third RF amplifier 13 in the TV tuner unit 2, and therefore, higher harmonics of reference-frequency signals of the first reference oscillator 3b and the second reference oscillator 10b, which are flowing on the wiring pattern 17, are prone to fly at the coil, or the like of the input unit 12. The higher harmonics thus flew cause distortion in each circuit of the TV tuner unit 2, and this distortion may pose a problem that beat interference appears on the display screen.

The present invention has been proposed to solve the above-described problem, and its object is to provide a TV tuner with a built-in RF modulator which does not cause any beat interference on the display screen.

A TV tuner with a built-in RF modulator according to the present invention comprises: a housing; a wiring substrate arranged in the housing; a RF modulator unit having a first phase lock loop circuit provided on the wiring substrate and a crystal resonator for setting a reference frequency, connected to the first phase lock loop circuit; a TV tuner unit having an input unit and a second phase lock loop circuit which are provided on the wiring substrate; and a wiring pattern formed on the wiring substrate for connecting the crystal resonator to the second phase lock loop circuit, and there is provided a grounding pattern between the wiring pattern and the input unit.

Also, in the TV tuner with a built-in RF modulator according to the present invention, the wiring pattern is provided between the grounding pattern and the housing.

Embodiments of the invention will now be desc~ibec', by way of example only, with reference to the accompanying drawings, in which: Fig. 1 is a schematic view showing the structure of an embodiment of a TV tuner with a built-in RF modulator according to the present invention; and Fig. 2 is a schematic view showing the structure of a conventional TV tuner with a built-in RF modulator.

Hereinafter, with reference to the accompanying drawings, the detailed description will be made of an embodiment according to the present invention.

Fig. 1 is a schematic view showing the structure of a TV tuner with a built-in RF modulator according to an embodiment of the present invention.

In this respect, in Fig. 1, the same numerals are attached to the same parts as those shown in the conventional example of Fig. 2.

As shown in Fig. 1, the first grounding pattern 15 of the TV tuner with a built-in RF modulator according to an embodiment of the present invention is provided with openings 15a and 15b on the RF modulator unit 1 side and on the TV tuner unit 2 side respectively, and the wiring pattern 17 is provided between the first grounding pattern 15 and the housing 14. In the abovedescribed two points, the TV tuner with a built-in RF modulator according to the present invention differs in structure from the conventional one shown in Fig. 2, and is the same as the conventional TV tuner with a built-in RF modulator in the other points.

In this case, in the TV tuner with a built-in RF modulator according to an embodiment of the present invention, the first grounding pattern 15 is provided on both the RF modulator unit 1 and the TV tuner unit 2, and is provided close to the housing 14.

One end of the wiring pattern 17 passes through the opening 15a, is guided through within the RF modulator unit 1, and is connected to the crystal resonator 3c in the RF modulator unit 1, while the other end of the wiring pattern 17 passes through the opening 15b, is guided through within the TV tuner unit 2, and is connected to the second reference oscillation circuit 10a in the second phase lock loop (PLL) circuit 10 in the TV tuner unit 2.

The first reference oscillator 3b in the first phase lock loop (PLL) circuit 3 is constituted by the crystal resonator 3c and the first reference oscillation circuit 3a which are arranged on the RF modulator unit 1 side, while the second reference oscillator 10b in the second phase lock loop (PLL) circuit 10 is constituted by the crystal resonator 3c and the second reference oscillation circuit 10a which are connected with each other through the wiring pattern 17.

Since the first grounding pattern 15 is arranged between the wiring pattern 17, and the input unit 12 and the third RF amplifier 13, which are in the TV tuner 2, the wiring pattern 17 is to be arranged in a position more remote from the input unit 12 and the third RF amplifier 13 by the first grounding pattern 15 than in the conventional case. In other words, the first grounding pattern 15 separates the wiring pattern 17 from the input unit 12 and the like. This arrangement of the wiring pattern 17 prevents the higher harmonics of reference-frequency signals of the first reference oscillator 3b and the second reference oscillator 10b, which are flowing on the wiring pattern 17, from moving to the input unit 12, the third RF amplifier and the like in which coils and the like are arranged.

Further, the wiring pattern 17 is arranged between the first grounding pattern 15 and the housing 14, that is, the wiring pattern 17 is interposed between members at the grounded potential, and therefore, even if the higher harmonic flowing on the wiring pattern 17 radiates, the higher harmonic is absorbed by the housing 14 made of metallic material. The amount of higher harmonic moving to the input unit 12, the third RF amplifier 13 and the like, in which coils ant the like are arranged, is further reduced by that much.

The TV tuner with a built-in RF modulator according to an embodiment of the present invention, having the above-described structure roughly operates as follows: First, a case where the RF modifier unit 1 is operated will be described. The frequency of an oscillation signal to be outputted from a first voltage control oscillator (VCO) (not shown) is stabilized by the first reference oscillator 3b using the crystal resonator 3c.

At this time, the oscillation signal (carrier) outputted from the first voltage control oscillator (VCO) is modulated by a video signal supplied to a video signal input terminal 3d and a sound signal supplied to a sound signal input terminal 3e for being inputted to a mixer 8. Also, a RF signal supplied from a distributor 6 through the second RF amplifier 7 is also inputted to the mixer 8, and is supplied to an antenna input terminal (not shown) for a TV receiver from an antenna output terminal 9 as either RF output signal.

Next, a case where the TV tuner unit 2 is operated will be described. The frequency of a local oscillation signal to be outputted from a second voltage control oscillator (VCO) (not shown) is stabilized by a second reference oscillator 10b comprising a crystal resonator 3c arranged on the RF modulator unit 1 side, and a second reference oscillation circuit 10a in the second phase lock loop (PLL) circuit 10.

At this time, through the local oscillation signal outputted from the second voltage control oscillator (VCO), a TV broadcast signal supplied through the input unit 12 and the third RF amplifier 13 is channel-selected, and an intermediate-frequency (IF) signal corresponding to the TV broadcast signal channelselected is obtained.

Thus, the intermediate-frequency signal corresponding to the TV broadcast signal channel-selected is supplied to an intermediate-frequency signal processing circuit (not shown) at the next stage from an intermediate-frequency signal output terminal 10c.

In this respect, in the embodiment according to the present invention, on using a crystal resonator 3c for setting a reference frequency in common between the first phase lock loop circuit 3 side and the second phase lock loop circuit 10 side, the description has been made of the embodiment in which the crystal resonator 3c is arranged on the RF demodulator unit 1 side, but it may be possible to arrange the crystal resonator 3c on the TV tuner unit 2 side.

As described above, according to the present invention, the wiring pattern for connecting the crystal resonator on the RF modulator unit side to the second reference oscillator circuit of the second phase lock loop circuit on the TV tuner unit side has been constructed so as to be arranged apart from the input unit of the TV tuner unit by the first grounding pattern. Therefore, a higher harmonic of an oscillation signal from the reference oscillator, which flows on the wiring pattern, becomes more difficult to move to the coil of the input unit than in a conventional TV tuner with a built-in RF modulator made integral within a metallic housing, and this leads to the effect that a problem such as beat interference is difficult to occur between it and an oscillation-frequency signal at the input unit or the like.

Further, according to the present invention, the wiring pattern is arranged between the first grounding pattern and the housing, whereby the wiring pattern is interposed between the first grounding pattern and the housing which are at grounded potential, and therefore, a higher harmonic radiated from the wiring pattern is absorbed by the housing, and the amount of the higher harmonic which move to the coil, and the like becomes further less, thus exhibiting a noticeable effect that a problem such as beat interference becomes further more difficult to occur.

Claims

1. A TV tuner with a built-in RF modulator comprising: a housing; a wiring substrate arranged in said housing; a RF modulator unit having a first phase lock loop circuit provided on said wiring substrate and a crystal resonator connected to said first phase lock loop circuit, for setting a reference frequency; a TV tuner unit-having an input unit and a second phase lock loop circuit which are provided on said wiring substrate; and a wiring pattern formed on said wiring substrate for connecting said crystal resonator to said second phase lock loop circuit, there being provided a grounding pattern between said wiring pattern and said input unit.

2. A TV tuner with a built-in RF modulator according to Claim 1, wherein said wiring pattern is interposed between said grounding pattern and said housing.

3. A TV tuner with a built-in RF modulator substantially as hereinbefore decribed with reference to, and as illustrated by, the accompanying drawings.