JP2573661Y2 - Tuning circuit unit - Google Patents

Description

[Detailed description of the invention]

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a channel selection circuit unit, and more particularly to a channel selection circuit unit of a satellite broadcast receiving device housed in a shield case.

[0002]

2. Description of the Related Art A channel selection circuit unit (hereinafter abbreviated as a channel selection unit) of a satellite broadcast receiver having a structure shown in FIG. The tuning unit 1 has a structure in which a tuning circuit board 6 is covered by a shield case 5 including an upper cover 2, a side plate portion 3, and a lower cover 4 made of a steel plate. Signals are input and output to and from the tuning circuit board 6 via antenna input terminals 7 and 8 provided on the side plate portion 3.

FIG. 5 is a block diagram of a channel selection circuit provided on a channel selection circuit board 6 of a conventional channel selection unit 1. As shown in FIG. FIG.
At the antenna input terminal T ₁
Signal (high-frequency signal) is supplied, and the RF signal is
1, amplifier 22, AGC circuit (automatic gain control circuit) 23
Is input to a tracking filter 24 composed of two coils (not shown). The input signal is supplied to the mixer 27 via the amplifier 25 and the AGC circuit 26 after the image frequency is attenuated by the tracking filter 24.

The mixer 27 is supplied with an oscillation signal having a predetermined local oscillation frequency from an oscillator 28. The output signal of the AGC circuit 26 is mixed with the oscillation signal by the mixer 27 to output an intermediate frequency signal. The output oscillation signal of the oscillator 28 is frequency-divided by a frequency divider 29 to be PLL (Phase Locked Loop).
It is controlled by the local oscillation control voltage a from the circuit 30.

[0005] local oscillator control voltage a of the PLL circuit 30 level is changed according to the tuning control signal input to the terminal T _2. The local oscillation control voltage a is input to the oscillator 28 and also to the tracking filter 24 to vary the frequency characteristics of the tracking filter 24.

The output signal of the mixer 27 is supplied to the AGC circuit 3
1, amplifier 32, surface acoustic wave filter 33, amplifier 34
Is supplied to the AGC circuit 26 and the FM detection circuit 35 via the. The FM detection circuit 35 detects the input signal and outputs the signal to the terminal T _3.
A television signal is output.

The channel selection circuit of such a conventional satellite broadcast receiving apparatus is roughly composed of six blocks as shown in FIG. That is, an RF unit (high-frequency amplifier circuit) 36, a tuning filter unit (tuning circuit) 37, a frequency conversion unit (frequency conversion circuit) 38, a PLL unit (control circuit) 39, and an IF (In)
and a demodulation unit (detection circuit) 41.

[0008]

However, in the conventional channel selection unit, the respective components of the channel selection circuit electromagnetically interfere with each other, thereby deteriorating the S / N ratio of each signal and reducing the beat ratio. Etc. sometimes occurred. For this reason, there has been a problem that noise and moire are generated on the television screen.

To solve this problem, a tuning circuit board 6
As shown in FIG. 4, the RF unit 36 and the demodulation unit 41 are shielded by the shielding plate 9 and the tuned filter unit 37 and the IF
It is configured so as not to interfere with electromagnetic waves by dividing 0 as well. Further, the IF unit 40 and the demodulation unit 41 are separated and shielded by the shielding plate 10.

On the other hand, the PLL section 39 and the I
The F section 40 is shielded, and the tuning filter section 37 and the frequency conversion section 38 are separated so as not to interfere with each other electromagnetically. The frequency conversion section 38 and the PLL section 39 are separated and shielded by the shield plate 12. Further, the RF unit 36 is provided by the shielding plate 13.
And a tuning filter section 37 for shielding so as not to interfere electromagnetically.

The two coils of the tracking filter 24 constituting the tuning filter section 37 are shielded from each other by the shield plate 14.

In the conventional tuning unit, by providing the shielding plates 9, 13 as described above, each component of the tuning circuit is electromagnetically shielded to prevent noise and moire.

However, the shield case 5 having the structure shown in FIG.
After the side plate portion 3 and the shield plates 9, 10, 11 are punched out of a single steel plate and bent, the shield plates 12, 13, 1
4 is attached to the side plate portion 3. The side plate portion 3 of the conventional shield case 5 is formed by punching a single steel plate to form a shield plate 9.
It was impossible to bend together with No. 14 to form it by integral molding. For this reason, there has been a problem that the manufacturing process of the channel selection circuit unit of the conventional satellite broadcast receiver becomes complicated.

In view of the above, it is an object of the present invention to provide a channel selection circuit unit of a satellite broadcast receiving apparatus, which can prevent noise and moire by using a shield case that can be integrally formed from a single steel plate. .

[0015]

In order to solve the above problems, the present invention provides an antenna input terminal, a high frequency amplifier circuit connected to the antenna input terminal, and amplifying a high frequency signal from the antenna input terminal. A tuning circuit for selecting a high-frequency signal in a frequency band of a desired channel from high-frequency signals from the high-frequency amplifier circuit; an AGC circuit for controlling a gain of a high-frequency signal supplied from the tuning circuit by a first control signal; A frequency conversion circuit that mixes the signal from the circuit and the local oscillation frequency and converts the frequency to an intermediate frequency signal, a control circuit that variably controls the local oscillation frequency by a second control signal corresponding to a desired channel,
A power supply voltage supplied to each of the frequency conversion circuit and the control circuit, an intermediate frequency amplification circuit for amplifying an intermediate frequency signal from the frequency conversion circuit, and detection and output of the intermediate frequency signal from the intermediate frequency amplification circuit A tuning circuit unit comprising a tuning circuit board including
The tuning circuit board, a first circuit block including the high-frequency amplifier circuit and the tuning circuit, the frequency conversion circuit and the control circuit, the first and second control signal wiring, A second circuit block in which at least one of the power supply voltage lines is disposed between the frequency conversion circuit and the control circuit, a third circuit block including the intermediate frequency amplifier circuit, and the detection circuit. fourth a structure divided into a circuit block, instrumentation to said tuning circuit comprising
The first circuit block and the third and fourth
A first shielding plate for shielding a circuit block electromagnetically, before
The second circuit block and the first and third circuit blocks
A second shielding plate for shielding the click electromagnetically, the third round
Road block and the fourth circuit block are electromagnetically shielded
And a third shielding plate, wherein the first to third shielding plates
Has a configuration in which the end faces do not cross each other .

[0016]

According to the present invention having the above-described structure, the high-frequency amplifier circuit and the tuning circuit, which are close to the antenna input terminal side, perform coarse adjustment, and are not affected by high-frequency effects, are connected to the first circuit.
In the second circuit block, at least one of the first and second control signal wirings to which a DC signal is supplied and the power supply voltage wiring is provided. By disposing the two wires between the frequency wave number conversion circuit and the control circuit, the frequency conversion circuit and the control circuit can be separated by the wiring to which the DC signal is supplied, so that they do not interfere with each other, and furthermore, the output terminal by close intermediate frequency amplifying circuit and the detection circuit and another circuit block can reduce the frequency of influence from another circuit to the output signal, furthermore, the end of the first through third shielding plate
By keeping the surfaces from intersecting with each other,
Folds at the intersection without the force of the upper bending
The concentration of bending force is eliminated, and
And the end face intersect, so that the shielding plates can be reinforced,
Shielding plates must be distributed vertically.
Without bending, forming a shielding plate by bending one side
Also, the shielding plate is not the end faces, but the plate face and the end face
As it is connected, the shielding plates can be connected securely,
The effect of high frequency signals between circuits can be improved because the shielding effect can be improved.
The shielding structure can be simplified while minimizing the influence of a high-frequency signal between circuits that can simplify the shielding structure.

[0017]

BRIEF DESCRIPTION OF THE DRAWINGS FIG.

FIG. 1 is a perspective view of one embodiment of the present invention.
4, the same components as those of FIG. 4 are denoted by the same reference numerals, and the description thereof will be omitted. In FIG. 1, the tuning unit 1a has a configuration in which a tuning circuit board 6a is covered by a shield case 5a including a side plate 3a made of a steel plate. The side plates 3a are provided with shielding plates 9, 10, and 11 which are integrally formed.

FIG. 2 is a block diagram of a tuning circuit provided on the tuning circuit board 6a according to one embodiment of the present invention. 2, the block configuration is the same as the block configuration of the conventional tuning circuit shown in FIG. 4. In FIG. 2, the same reference numerals are given to the same components as those in FIG. 5, and the description thereof will be omitted. .

In FIG. 2, an RF signal (high-frequency signal) from an antenna input terminal T ₁ is filtered by a filter 21 and an amplifier 2.
2. AGC circuit, AGC circuit (automatic gain control circuit) 23
Is input to a tracking filter 42 composed of two coils (not shown). The tracking filter 42 attenuates the image frequency of the RF signal.

While the conventional tracking filter 24 has a complicated shape so that the bandwidth for attenuating the RF signal can be finely adjusted, the tracking filter 42 allows only coarse adjustment of the bandwidth, and is simple. U-shaped. For this reason, it is extremely difficult to receive electromagnetic interference from other circuit elements.

Further, a frequency converter 38 comprising a mixer 27 and an oscillator 28, a frequency divider 29 and a PLL circuit 3
The PLL section 39 constituted by 0 is separated by pattern wiring on the tuning circuit board 6a shown in FIG. Hereinafter, the tuning circuit board 6a will be described in detail.

FIG. 3 is a plan view of a main part of one embodiment of the present invention. FIG. 3 is a plan view of the frequency conversion unit 38 and the PLL unit 39 that are divided into one block by pattern wiring on the tuning circuit board 6a in FIG. 1, and a copper foil pattern printed and wired on the tuning circuit board 6a. Reference numeral 50 designates a wiring of a tuning circuit. Slot 51 formed in tuning circuit board 6a
Is inserted with a projection (not shown) of a shielding plate 11 integrally formed with the side plate portion 3a, soldered to the copper foil pattern 52, and the shielding plate 11 is mounted on the tuning circuit board 6a.

In the upper center of FIG. 3, transistors Q ₁ ,
Mixer 27 composed of an inductor L ₁ and the like, are spliced in the right side in the drawing of the shielding plate 11. In the mixer 27,
The configuration is such that an RF signal is supplied from an AGC circuit 26 provided at the upper left in the figure. A transistor Q ₂ , a resistor R ₂ , an inductor L ₂ ,
Oscillator 28 is spliced constituted by the capacitor C ₁ and the like.

A frequency divider 29 comprising a frequency divider ICIC ₁ , a capacitor C _{4 and the} like is arranged at the upper right end in the figure.
In the lower part of the figure, a PLL circuit 30 including a PLLIC IC ₂ , a crystal oscillator XT, capacitors C ₁ , C _{2, and the} like is provided along with a shielding plate 11.

The power supply voltage +5 V from the lower left in the figure is wired to the ninth pin 52 of the PLLICIC ₂ by a printed wiring indicated by 50c. Printed wiring 50c is branched and extended upward, and is connected to the second pin 53 of the divider ICIC _1. The printed wiring 50c further extends, is arranged on the periphery of the tuning circuit board 6a, and is configured to be connected to another circuit at the upper left in the figure. The printed wiring 50c is configured to separate the mixer 27 and the PLL circuit 30 as illustrated. The lower end of the frequency divider 29 and the mixer 27
And is configured to release.

The local oscillation control voltage a output to the twelfth pin 52 of the PLLIC ₂ passes through the through-hole 55 via a resistor on the back side wiring of the tuning circuit board 6a (not shown), and is then provided on the printed wiring 50a. Through hole 56
Connected to. The printed wiring 50a extends upward from the center of the figure, between the mixer 27 and the frequency divider 29, and
, A local oscillation control voltage a and a mixer 27, an oscillator 28 and a frequency divider 29.

On the other hand, the AGC control voltage b shown in FIG. 5 is supplied from the lower left in the figure by the printed wiring 50b.
The printed wiring 50b is attached to the printed wiring 50c and extends from the lower left part in the drawing to the center part in the drawing, further laid between the printed wiring 50a and the printed wiring 50c and extended upward in the drawing and then to the upper left in the drawing. And is supplied to the AGC circuit 26. The printed wiring 50a is configured to separate the mixer 27, the oscillator 28, the frequency divider 29, and the P circuit 30.

As described above, the printed wiring 50a, 50b,
By 50c, the frequency converter 38 composed of the mixer 27 and the oscillator 28 and the PLL unit 39 composed of the frequency divider 29 and the PLL unit 30 are separated from each other, and between the frequency converter 38 and the PLL unit 39, FIG. Shield plate 1 shown inside
2 becomes unnecessary, and can be made into one block.

The tuning circuit according to this embodiment is roughly divided into four blocks as shown in FIG. That is, RF
Unit 43, frequency conversion unit 44, IF (Inter Frequency)
Section (intermediate frequency amplification circuit) 40 and demodulation section (detection circuit) 4
Divided into one.

Returning to FIG. 1, the channel selection circuit board 6
Reference numeral a denotes a shielding plate 9 that separates the RF unit 43, the demodulation unit 41, and the IF unit 40 from each other to prevent electromagnetic interference. Further, the IF unit 40 and the demodulation unit 41 are separated and shielded by the shield plate 10. Further, the frequency conversion unit 44, the IF unit 40, and the RF unit 43 are separated by the shielding plate 11 so as to prevent electromagnetic interference.

According to the above configuration, the shielding plates 9, 10, 1
Since each 1 does not have a crossover portion, it can be integrally formed with the side plate portion 3a.

According to the present embodiment, the side plate portion 3a and the shielding plates 9, 10, and 11 are punched out of a single steel plate and bent to prevent electromagnetic interference of each part of the tuning circuit. Therefore, the S / N ratio of each signal is not degraded, and no beat or the like is generated. Therefore, there is an advantage that the manufacturing process of the tuning circuit unit does not become complicated and no noise or moire is generated on the television screen.

In the above embodiment, the frequency converter 38 and the controller 39 are separated by printed wiring of the AGC control voltage, the local oscillation control voltage, and the power supply voltage. As long as a DC voltage that does not interfere with a signal is wired, the same effect can of course be obtained even if it is separated by other printed wiring. Further, a ground wiring may be used.

Further, the arrangement of the mixer 27 and the oscillator 28, the frequency divider 29 and the PLL unit 30 is not limited to the above embodiment, and a DC voltage or ground is wired between the frequency conversion unit 38 and the control unit 39. It suffices if printed wiring is provided and these are separated.

[0036]

As described above, according to the present invention, a high-frequency amplifier circuit and a tuning circuit, which are close to the antenna input terminal side, are roughly adjusted, and are not affected by high-frequency effects, are used. The same circuit block is used as the first circuit block to simplify the shielding structure. In the second circuit block, the first and second control signal wirings to which a DC signal is supplied and the power supply voltage wiring By arranging at least one wiring between the frequency conversion circuit and the control circuit, the frequency conversion circuit and the control circuit can be separated by the wiring to which a DC signal is supplied, so that they do not interfere with each other.
By forming the intermediate frequency amplification circuit and the detection circuit close to the output terminal as separate circuit blocks, the influence of high frequency from other circuits on the output signal can be reduced .
To prevent the end faces of the shielding plate from crossing each other
More than two bending forces
When the force of bending does not concentrate at the junction
In particular, the plate surface and the end surface cross each other, reinforcing the shielding plates
And maintain the strength.
There is no need to provide, it can be formed by bending one side
Also, the shielding plate is not the end faces, but the plate face and the end face
As it is connected, the shielding plates can be connected securely,
The effect of high frequency signals between circuits can be improved because the shielding effect can be improved.
It is advantageous in that the shielding structure can be simplified while minimizing the size.

[Brief description of the drawings]

FIG. 1 is a perspective view of one embodiment of the present invention.

FIG. 2 is a block diagram of a tuning circuit to which an embodiment of the present invention is applied;

FIG. 3 is a plan view of a main part of one embodiment of the present invention.

FIG. 4 is a perspective view of a conventional tuning circuit unit.

FIG. 5 is a block diagram of a conventional tuning circuit.

[Explanation of symbols]

 1,1a Tuning circuit unit 6,6a Tuning circuit board 7 Antenna input terminal 9,10,11,12,13,14 Shielding plate 30 PLL circuit 36 RF unit (high frequency amplifier circuit) 37 Tuning filter unit (tuning circuit) Reference Signs List 38 frequency conversion unit (frequency conversion circuit) 39 PLL unit (control circuit) 40 IF unit (intermediate frequency amplification circuit) 43 RF unit 41 demodulation unit (detection circuit) 44 frequency conversion unit 50, 50a, b, c Printed wiring

Claims (1)

(57) [Scope of request for utility model registration] An antenna input terminal, a high-frequency amplifier circuit connected to the antenna input terminal for amplifying a high-frequency signal from the antenna input terminal, and a high-frequency signal from the high-frequency amplifier circuit in a frequency band of a desired channel. A tuning circuit for selecting a high-frequency signal;
An AGC circuit for controlling the gain of a high-frequency signal supplied from the tuning circuit in accordance with the control signal, a frequency conversion circuit for mixing the signal from the AGC circuit and a local oscillation frequency and converting the frequency to an intermediate frequency signal; A control circuit for variably controlling the local oscillation frequency by a second control signal corresponding to a channel; a power supply voltage supplied to each of the frequency conversion circuit and the control circuit; and an intermediate frequency signal from the frequency conversion circuit. And a tuning circuit board including a detection circuit that detects and outputs an intermediate frequency signal from the intermediate frequency amplification circuit, the tuning circuit board, A first circuit block including a high-frequency amplifier circuit and the tuning circuit; a frequency conversion circuit and the control circuit; A second circuit block in which at least one of the signal wiring and the power supply voltage wiring is disposed between the frequency conversion circuit and the control circuit; and a third circuit block including the intermediate frequency amplification circuit. And a fourth circuit block including the detection circuit, which is mounted on the channel selection circuit, and is connected to the first circuit block.
The third electromagnetically shields the third and fourth circuit blocks.
A first shielding plate, the second circuit block, and the first and third circuit blocks.
A second shielding plate that electromagnetically shields the third circuit block, and the third circuit block and the fourth circuit block.
And a third shielding plate for electromagnetically shielding, wherein the first to third shielding plates have end faces crossing each other.
Tuning circuit unit with no configuration .