JP2822482B2 - Drive circuit device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a receiver such as a television receiver and a video tape recorder, and a driving circuit such as a digital signal processing circuit and an analog signal processing circuit which constitute an electric circuit of a display. Related to the mounted device.

2. Description of the Related Art Conventionally, a receiver such as a television receiver is an analog circuit from an antenna input to a circuit for driving a cathode ray tube, and the tuner is surrounded by a shield case having a local oscillation circuit and taking measures against interference. .

By the way, in recent years, digital technology has advanced, and microcomputers have already been adopted for channel selection, and digitalization of television signal processing has been attempted. There are technologies that are indispensable for high-definition television receivers and new functions to achieve high image quality. Further, as a new display, there is a display using a liquid crystal or a plasma, a display using a multi-cathode in which an electron beam is generated, and a flat display device.

Here, as a problem when digitizing a television signal, a clock signal (basic clock), which is a basic digital signal, uses about 14 MHz or about 28 MHz, but the clock signal is a square wave, and the digital signal processing uses the basic clock. , Many harmonics of the clock are generated. This will jump into the television or radio as interference noise. In addition, the signal receiving circuit also causes interference noise.

Conventionally, as a method for preventing the above interference, the digital circuit 3 is wrapped in shield cases 20, 21 and 22 as shown in FIG. Attenuate around 100MHz, which is easy to use, and further enhance the shielding effect by using a feedthrough capacitor,
The harmonics of the clock are not output to the outside.

However, such a shield case requires a very large volume, and the overall thickness is also large, so that it cannot be used for compact equipment such as a flat-screen TV.

Also, attaching the feedthrough capacitor 23 to the center of the shield case 20 and further connecting the digital circuit 3 in the middle requires manual work, which requires a lot of man-hours. Also, it is not easy to connect the feedthrough capacitor 23 to an external circuit (analog circuit).

Problems to be Solved by the Invention As described above, conventionally, as a method of reducing clock noise from a digital circuit, a shield case, a feedthrough capacitor, and a filter have been used. However, it requires a very large volume, the overall thickness is also thick,
There is a problem that it cannot be used for compact equipment such as a flat-screen TV. In addition, the use of a feedthrough capacitor increases the number of external connection terminals, but has a problem that the connection between the external terminals and the internal circuit is performed manually, which increases the place and man-hours.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and has an object to reduce the interference of a digital circuit and to make it thinner, to facilitate workability, and to facilitate connection with other circuits.

Means for Solving the Problems To solve the above problems, a drive circuit device of the present invention
The surface of the multilayer printed circuit board on which the drive circuit is mounted is the component mounting surface, the back surface is the ground pattern surface of the circuit, and the digital signal processing circuit of the drive circuit is disposed at the center of the multilayer printed circuit board. The internal analog signal processing circuit is disposed around the multilayer printed circuit board so as to surround the digital signal processing circuit. Also,
The ground pattern on the back surface of the multilayer printed circuit board is electrically divided by the digital signal processing circuit and the analog signal processing circuit, and the ground pattern of the analog signal processing circuit on the surface of the multilayer printed circuit board surrounds the entire periphery of the digital signal processing circuit. And the ground pattern of the front side analog signal processing circuit and the ground pattern of the back side analog signal processing circuit of the multilayer printed circuit board are connected so as to surround the digital signal processing circuit using connection means such as through holes or jumper wires. It is characterized by doing.

Further, according to the present invention, one end of each of a first filter and a second filter is connected to a terminal such as an input terminal, an output terminal, or a power supply terminal of the digital signal processing circuit,
Filter and the other end are connected to the ground pattern of the analog signal processing circuit on the surface of the multilayer printed circuit board.
The other end of the filter is connected to an input terminal or an output terminal of an analog signal processing circuit mounted around the multilayer printed circuit board.

Further, according to the present invention, a metal plate or a conductor film similar thereto is provided on the surface of the multilayer printed circuit board so as to enclose the digital signal processing circuit, and is connected to an analog ground pattern. It is characterized by providing a conductor film similar to that.

Effect of the Invention The present invention greatly reduces disturbance to a tuner circuit and other image receiving devices by preventing noise from a digital signal processing circuit from being output from a circuit board to the outside without impairing the thickness of the image display device. Can do things.

Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings.

FIGS. 1a, 1b and 2 are a plan view and a side sectional view of a drive circuit device according to an embodiment of the present invention, and an exploded perspective view of an image display device with the device mounted.

Reference numeral 15 in FIG. 2 is a thin image display element, and one of drive terminals for projecting an image by driving the electrode of the image display element 15 is a beam flow control electrode terminal 16 in FIG. Connected to the beam flow control electrode terminal 16 is a beam flow control terminal 11 provided on the multilayer printed circuit board 9 for the drive circuit.
It is.

The multilayer printed circuit board 9 for a drive circuit of the present embodiment is a four-layer board, which will be described in detail below. On the upper (first layer) of the multilayer printed circuit board, there is a digital circuit 3 for sampling the video signal, storing it in a memory, and performing digital processing.
And an analog circuit 7 for amplifying a digital signal by pulse width modulation or A / D conversion by an analog circuit. The digital circuit 3 is arranged at the center of the upper surface of the multilayer printed circuit board 9, the periphery thereof is surrounded by the analog circuit 7, and the periphery is surrounded by the analog ground 2. The second layer in FIG. 2 is a wiring section 17 for connecting each circuit element (digital IC or the like) of the digital circuit 3 to each other. The second layer is a power foil for supplying power to the digital circuit 3. The fourth layer has a digital circuit ground 4, an analog circuit ground 2, and a slit 18 for electrically separating the digital circuit ground 4 and the analog circuit ground 2 on the back side. 2 and a large number of through holes 12 connecting them. A large number of through holes 12 are provided so as to surround the digital circuit 3. The through holes are also provided in the second and third layers, and the components, patterns and ground of the first to fourth layers are electrically connected through the through holes. Although not shown, each layer is, of course, insulated by an insulating layer.

To configure a television receiver, a tuner circuit is located in parallel with or near the multilayer printed circuit board 9 for a drive circuit.

In such a configuration, when the power is turned on and each circuit is operated, the digital circuit 3 operates and digitally processes the video signal with a clock near 14 MHz. At this time, there are two types of sources of clock disturbance. The first is the digital circuit wiring section 17 of the second layer in FIG. In other words, the wiring has an inductance component, and the clock 14 MHz is coupled with the circuit mismatch, so that the harmonic components 28 MHz, 42 MHz, 56
MHz, 70 MHz, 84 MHz, 98 MHz..., And conventionally jumped into the tuner. In this configuration, the digital circuit wiring section 17 of the second layer serving as the antenna is replaced with the other first, third, and third layers. It is surrounded by the pattern of the fourth-layer printed circuit board and absorbs the harmonic components of the clock.

And, in order to enhance the effect of absorbing the harmonic components,
Further, the ground pattern is formed on the upper surface of the multilayer printed circuit board 9 for the drive circuit except for the component mounting surface of the digital circuit 3. Here, the effect will be greater if the distance between the analog grounds is set to several mm. With this configuration, it is possible to prevent the harmonics of the clock from leaking from the gap between the layers of the printed circuit board, and to reduce the jump (interference) of the harmonics of the clock into the tuner circuit by 15 to 20 dB. It becomes possible.

Next, the second source of clock disturbance is the emission of disturbance noise from the first other circuit connection lead 14, which is a case where the disturbance noise is guided from another circuit to a tuner circuit through a power supply or the like. Therefore, depending on the present configuration, the input / output terminal from the digital circuit 3 in FIG. 1 may be a filter 10 (made of a coil and a container) or a filter 13 made of a resistor and a capacitor, as shown in FIG. The other end of the capacitor 13 is connected to the analog ground 2 and the second
It is arranged at the position of the connection portion 12 connected to the analog ground 2 on the back surface of the multilayer printed circuit board 9 in the figure. As a result, the clock noise generated in the digital circuit 3
At 0,13, only the signal from which the clock noise has been removed is input / output to the other circuit connection lead 14 which has been completely absorbed by the analog ground 2 surrounding the digital circuit 3 and passed through the filters 10,13. 20 interference to receiver
It became possible to reduce by more than dB.

Further, the upper shield case 1 is configured to sandwich the LC filter 10 and the RC filter 13, and has two effects of a feedthrough capacitor and a filter. Further, the shield plate 6 can be easily formed by sandwiching the insulator 5 (resist or spacer or the like), using an iron plate or a conductive film, and a complete shield case can be formed on a multilayer printed circuit board.

Advantageous Effects of the Invention As described above, according to the present invention, it is possible to reduce the thickness and the size while having the same or more effects as the shield case,
The elimination of the feedthrough capacitor enables a significant reduction in man-hours. Also, one digital circuit and one analog circuit
Can be created on a single substrate. As a result, it is possible to reduce the thickness of the receiver. In this embodiment, the ground patterns of the respective layers are connected by through holes, but may be connected by other connection means, for example, by using a jumper connection. Also, the filter may be connected to necessary terminals.

[Brief description of the drawings]

1a and 1b are a plan view and a sectional view of a drive circuit device according to an embodiment of the present invention, FIG. 2 is an exploded perspective view of the device, and FIG. 3 is an exploded perspective view of a conventional example. 2 ... Analog circuit ground, 3 ... Digital circuit, 4
…… Digital circuit ground, 7 …… Analog circuit, 9…
… Multilayer printed circuit board for drive circuit, 10,13 …… Filter, 1
2 Connection part (through hole), 17 Digital circuit wiring part, 18 Slit, 19 Digital power supply (5 V)
Foil.

Claims (2)

(57) [Claims] 1. A drive circuit device comprising a multi-layer printed circuit board comprising a plurality of digital signal processing circuits and an analog signal processing circuit having a front surface as a component mounting surface and a back surface as a ground pattern surface of the circuit. The analog signal processing circuit is arranged at the center of the multilayer printed circuit board, and the analog signal processing circuit is arranged around the multilayer printed circuit board so as to surround the digital signal processing circuit. Electrically divided by the analog signal processing circuit,
The ground pattern on the surface of the analog signal processing circuit is arranged so as to surround the entire periphery of the digital signal processing circuit,
A drive circuit device, wherein a ground pattern on a front surface of the analog signal processing circuit and a ground pattern on a rear surface of the analog signal processing circuit are connected so as to surround the digital signal processing circuit. 2. One end of each of a first filter and a second filter is connected to an input terminal, an output terminal, a power supply terminal, or the like of a digital signal processing circuit, and ground terminals of the first filter and the second filter. Is connected to a ground pattern of an analog signal processing circuit on the surface of the multilayer printed circuit board, and the other ends of the first and second filters are output terminals or inputs of an analog signal processing circuit mounted around the multilayer printed circuit board. 2. A connection to a terminal.
The drive circuit device according to any one of the preceding claims.