JP2543343Y2 - Tuning circuit board - 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 board, and more particularly to a channel selection circuit board of a satellite broadcast receiving device housed in a shield case.

[0002]

2. Description of the Related Art FIG. 3 is a perspective view of a tuning circuit unit (hereinafter abbreviated as a tuning unit) of a satellite broadcast receiving apparatus to which a conventional tuning circuit board is applied. The tuning unit 1 has a configuration in which a tuning circuit board 6 is covered by a shield case 5 including an upper cover 2, a side plate 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. 4 is a block diagram of a channel selection circuit provided on a conventional channel selection circuit board. In FIG. 4, RF signal from the antenna to the antenna input terminal T ₁ (radio frequency signal)
Is supplied, and the RF signal is supplied to the filter 21, the amplifier 22,
The signal is input to a tracking filter 24 composed of two coils (not shown) via a GC (automatic gain control) circuit 23. Input RF signal is tracked by filter 24
After the image frequency is attenuated by the
The signal is supplied to the mixer 27 via the GC circuit 26.

[0004] A mixer 27 is supplied with a local oscillation frequency of a desired channel from an oscillator 28. On the other hand, an output signal of the AGC circuit 26 is supplied and mixed to output an intermediate frequency signal of a predetermined intermediate frequency. The output local oscillation frequency of the oscillator 28 is divided by a frequency divider 29 and
The signal is input to an L (Phase Locked Loop) unit 30, where it is phase-synchronized and controlled by a control voltage a according to a desired channel data input to the PLL unit 30 from the outside.

The local oscillation control voltage a of the PLL unit 30 (second
Control signal) level is changed according to the tuning control signal input to the terminal T _2. The local oscillation control voltage a is
8 and 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 FM detection circuit 35 via the. FM detection circuit 35 outputs a television signal from a terminal T ₃ by detecting the input signal. The output of the amplifier 34 is used as an AGC control voltage b (first control signal) and supplied to the AGC circuit 26 and the FM detection circuit 35.

The channel selection circuit of such a conventional satellite broadcast receiving apparatus is roughly divided into six blocks as shown in FIG. That is, the RF unit 36, the tuning filter unit 37,
A frequency conversion unit (frequency conversion circuit) 38, a PLL unit (control circuit) 39, an IF (Intermediate Frequency) unit 40,
And a demodulation unit 41.

FIG. 5 is a specific circuit diagram of a frequency conversion section and a PLL section of a channel selection circuit provided on a conventional channel selection circuit board. In FIG. 5, the frequency converter is a transistor Q ₁
It consists configured mixer 27 and the transistor Q ₂ and the like by constituted oscillator 28 by like.

The mixer 27 mixes the RF signal from the AGC circuit 26 with the oscillation signal supplied from the oscillator 28 by electromagnetic coupling of the inductors L ₁ and L ₂ formed by a printed wiring pattern on the tuning circuit board. And the intermediate frequency signal is A
Output to the GC circuit 31.

The frequency divider 29 inputs the oscillation signal supplied from the oscillator 28 to the eighth pin of the frequency divider ICIC ₁ and
The frequency is divided into 128 and output to the PLL section 30 from the fourth pin.

The PLL unit is PLLICIC ₂ , one of IC ₂
It is composed of a crystal oscillator XT and the like connected to the No. 14 pin and the No. 14 pin. A clock signal is input to the sixth pin of the IC ₂ , and a tuning control signal is input to each of the fifth and seventh pins via the resistor R. The signal from the frequency divider 29 is input to the 8th pin, and the local oscillation control voltage a (second control signal) is output to the 12th pin. Local oscillation control voltage a resistor R _1, R _2, inductor L _2, is supplied to the transistor Q ₂ through a capacitor C _1.

Mixer 27, oscillator 28, frequency divider 29, P
Each of the LL units 30 is supplied with a power supply voltage of +5 V indicated by c from the power supply terminal V _CC1 . The power supply voltage +12 V is supplied to the oscillator 28 from the power supply terminal V _CC2 .

[0013]

However, in the conventional channel selection circuit board, the above-mentioned respective circuit portions electromagnetically interfere with each other, thereby deteriorating the S / N ratio of each signal, and further reducing the beat and the like. May occur. For this reason,
There is a problem that noise and moire are generated on the television screen.

In order to solve this problem, a tuning circuit board 6
As shown in FIG. 3, 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 unit 4 are shielded.
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 in this manner, 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.
Has a portion where the shielding plate crosses the cross. For this reason, after the side plate part 3 and the shielding plates 9, 10, and 11 are punched out of one steel plate and bent, the shielding plates 12, 1
The shield case 5 is configured by attaching the side plates 3 and 14 to the side plate portion 3.

Therefore, it is impossible to form the side plate portion 3 of the conventional shield case 5 by punching out a single steel plate and bending it together with the shield plates 9,. There is a problem that the manufacturing process of the tuning circuit unit of the receiving device becomes complicated.

In view of the above, the present invention provides a tuning circuit board which can be applied to a tuning circuit unit of a satellite broadcast receiving apparatus which can prevent noise and moire by using a shield case which can be integrally formed from a single steel plate. The purpose is to provide.

[0021]

According to the present invention, in order to solve the above-mentioned problems, an AGC circuit for controlling the gain of a high-frequency signal by a first control signal is mixed with a signal from the AGC circuit and a local oscillation frequency. A frequency conversion circuit for performing frequency conversion to an intermediate frequency signal, a control circuit for variably controlling a local oscillation frequency by a second control signal, and a power supply voltage supplied to each of the frequency conversion circuit and the control circuit. Second
The control signal wiring and the power supply voltage wiring are each printed wiring, and at least one of the first and second control signal wirings and the power supply voltage wiring is a frequency conversion circuit and a control circuit. And was arranged between.

[0022]

According to the present invention having the above-described structure, the wiring for the first and second control signals and the power supply voltage is provided between the frequency conversion circuit and the control circuit. Therefore, the frequency conversion circuit and the control circuit are separated, and the signals of each other do not interfere with each other. Further, since the first and second control signals and the power supply voltage are DC signals, they do not interfere with the signals of the frequency conversion circuit or the control circuit.

[0023]

FIG. 1 is a plan view of a main part of an embodiment of the present invention, and FIG. 2 is a perspective view of a tuning circuit unit to which a tuning circuit board of an embodiment of the present invention is applied. Hereinafter, an embodiment of the present invention will be described with reference to FIGS.

In FIG. 2, the tuning unit 1a has a structure in which a tuning circuit board 6a is covered by a shield case 5a including a side plate 3a made of a steel plate. Side plate 3a
Are provided integrally with shielding plates 9, 10, 11.

FIG. 1 is a plan view of the frequency converter 44 divided into one block on the tuning circuit board 6a in FIG. 2, and the tuning is performed by the copper foil pattern 50 printed and wired on the tuning circuit board 6a. Circuit wiring is done. A not-shown projection of the shielding plate 11 integrally formed with the side plate portion 3a is inserted into the elongated hole 51 formed in the tuning circuit board 6a, and is soldered to the copper foil pattern 52.
Is provided with a shielding plate 11.

In the upper center of FIG. 1, 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 unit 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.

A power supply voltage of +5 V from the lower left in the figure is wired to the ninth pin 52 of the PLLIC IC ₂ by a printed wiring indicated by 50c. Printed wiring 50c (the power supply voltage line) 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 unit 30 as illustrated. In addition, the lower end of the frequency divider 29 and the mixer 27 are separated.

The local oscillation control voltage a (second control signal) output to the twelfth pin 52 of the PLLIC IC ₂ is passed through a through-hole 55 through a resistor R _{1 (} not shown) through the back wiring of the tuning circuit board 6 a (not shown). After that, the printed wiring 5
0a (second control signal wiring). The printed wiring 50a is located at the center in the figure,
It extends upward from between the mixer 27 and the frequency divider 29, supplies the local oscillation control voltage a to the oscillator 28, and
7. The oscillator 28 and the frequency divider 29 are configured to be separated.

On the other hand, the AGC control voltage b shown in FIG.
(First control signal) is printed wiring 50b from the lower left in the figure.
(The first control signal wiring). 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 includes the mixer 27, the oscillator 28
And the frequency divider 29 and the PLL unit 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, and a shielding plate is provided between the frequency converter 38 and the PLL unit 39. 12 becomes unnecessary and can be made into one block.

The tracking filter 24 has a simple U-shape, which allows only coarse adjustment of the bandwidth. For this reason, it is extremely difficult to receive electromagnetic interference from other circuit elements. Therefore, the RF unit 3
6 and the tuning filter unit 37 can be formed as one block without providing the shielding plates 13 and 14.

In FIG. 2, the tuning circuit board 6a is divided by a shielding plate 9 into an RF unit 43, a demodulation unit 41, and an IF unit 40, each of which constitutes one block, so as to shield them from 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, which are one block, are separated by the shielding plate 11 so as not to interfere electromagnetically.

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, 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 the printed wiring of the AGC control voltage, the local oscillation control voltage, and the power supply voltage +5 V. 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 mixer 27
The arrangements of the oscillator 28, the frequency divider 29 and the PLL unit 30 are not limited to those in the above-described embodiment. It does not matter if it is released.

[0037]

According to the present invention, as described above, the frequency conversion circuit and the control circuit of the tuning circuit board are formed as one block, and the shielding plate is provided so as to be integrally formed from one steel plate.
It has the feature of preventing noise and moire on the television screen.

[Brief description of the drawings]

FIG. 1 is a plan view of a main part of one embodiment of the present invention.

FIG. 2 is a perspective view of a tuning circuit unit to which the tuning circuit board according to the embodiment of the present invention is applied;

FIG. 3 is a perspective view of a tuning circuit unit to which a conventional tuning circuit board is applied.

FIG. 4 is a block diagram of a channel selection circuit provided on a conventional channel selection circuit board.

FIG. 5 is a circuit diagram of a part of a channel selection circuit provided on a conventional channel selection circuit board.

[Explanation of symbols]

 6, 6a Tuning circuit board 9, 10, 11, 12, 13, 14 Shielding plate 26 AGC circuit 30 PLL section 38 Frequency conversion section (frequency conversion circuit) 39 PLL section (control circuit) 44 Frequency conversion section 50 Printed wiring 50a Printed wiring (second control signal wiring) 50b Printed wiring (first control signal wiring) 50c Printed wiring (power supply voltage wiring) a Local oscillation control voltage (second control signal) b AGC control voltage (second 1 control signal) c Power supply voltage

Claims (1)

(57) [Scope of request for utility model registration] An AGC circuit for controlling a gain of a high-frequency signal by a first control signal; a frequency conversion circuit for mixing a signal from the AGC circuit and a local oscillation frequency to convert the frequency into an intermediate frequency signal; A control circuit for variably controlling the local oscillation frequency by the control signal, and a power supply voltage supplied to each of the frequency conversion circuit and the control circuit,
In the tuning circuit board formed by printing and wiring the first and second control signal wirings and the power supply voltage wiring, at least one of the first and second control signal wirings and the power supply voltage wirings A tuning circuit board, one of which is disposed between the frequency conversion circuit and the control circuit.