JP2008064780A - Flat panel display and printed wiring board - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a printed wiring board having a wiring pattern which hardly causes reflection even when characteristic impedance is different between connected load and signal transmission line and hardly causes reflection when a signal of a frequency band where influence of skin effect becomes remarkable is transmitted. <P>SOLUTION: Signal transmission lines P3a, P3b as a distribution constant circuit are respectively connected to lands L3a, L3b through connection lines S3a, S3b. Loads having characteristic impedances different from that of the signal transmission lines P3a, P3b are connected to the lands L3a, L3b. The lands L3a, L3b have line widths which match with the characteristic impedances of the loads. The connection lines S3a, S3b are formed smoothly so as to have no angle while gradually increasing the line width and, by using such connection lines S3a, S3b, the characteristic impedances between the signal transmission lines P3a, P3b and the loads are smoothly reduced. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a flat panel display and a printed wiring board, and more particularly to a printed wiring board having a pattern that requires handling as a distributed constant circuit, and a flat panel display including the printed wiring board.

  In recent years, digital signals handled by electronic circuits have become higher in frequency, and how to reduce noise radiated from routes such as patterns and wiring when transmitting high-frequency signals is a problem from the viewpoint of electromagnetic compatibility (EMC). It has become.

  Especially in a digital circuit, when a pulse signal is applied to a line with mismatched characteristic impedance, some or all of the signal is reflected at the transmitting end and receiving end, causing distortion and ringing, causing noise generation. It was. A voltage due to reflection is generated in the transmission line, affects itself, changes the waveform, generates a false signal, and may cause the circuit to malfunction. Furthermore, since most circuits using CMOS logic circuits are open at the far end (the other side of the line) and the reflection coefficient at the far end is +1.0, there is a problem that reflection continues by repeating reflection coefficients with different signs. is there.

  It can be said that such reflection needs to be taken into account when the signal transmission line is a distributed constant circuit. That is, assuming that the wavelength of the signal frequency to be handled is λ and the length of the signal line is L, in the case of λ / 4 << L, or when the time for the signal to make a round trip on the line is larger than the rise time of the pulse, It is necessary to consider the line as a distributed constant circuit. It is known that such a distributed constant circuit does not cause a reflection phenomenon if terminated with its characteristic impedance (if matching is achieved).

The characteristic impedance Z ₀ is generally expressed as Z ₀ = (L / C) ^(1/2) (L: inductance per unit length, R: conductance per unit length ⁾ if the line loss is small. The TDR measuring device based on the TDR (time domain reflectometer) method is used. TDR instruments measure cable length, characteristic impedance (continuity), and cable problems by measuring the magnitude of the returned (reflected) signal, when it came back (delay), and its polarity. You can know the location of occurrence.

The followings are known as noise countermeasures in electronic circuits.
That is, it is known that the width of the wiring pattern is formed wider than the width of the branch pattern to reduce the impedance of the wiring pattern and to match the impedance so that reflection noise does not occur (for example, Patent Document 1) .) In addition, the line width of the connection part by the conductive pump is made wider than the line width of the signal transmission part, and a difference is provided so that the characteristic impedance is the same between the connection part and the signal transmission part. It is known to insert a taper-shaped auxiliary line that gradually increases between signal transmission portions (for example, Patent Document 2).
In addition, a circuit board that easily generates noise may be covered with a shield case (for example, Patent Document 3), or a filter circuit may be formed adjacent to a connector that generates unwanted radiation (for example, Patent Document 4). Are known.
Japanese Patent Laid-Open No. 9-214076 JP 2000-138507 A Utility model registration size 3075808 JP 2005-18849 A

  However, in the shield case, the influence on the circuit existing inside the shield case is unavoidable, and in the filter circuit, the number of parts increases, leading to an increase in cost. In addition, since clock signals used in electronic circuits tend to rise, the effect of the skin effect of the current transmitted in the circuit becomes large, and there is a concern that the shape of the pattern edge may have a large effect on circuit characteristics. . That is, when the line width of the signal transmission pattern as in Patent Document 2 is changed, the characteristic impedance of the connection portion and the signal transmission pattern is matched, but a gap of characteristic impedance is generated in the signal transmission pattern itself. In this case, reflection occurs and uneven current flow occurs. The influence of the gap of the characteristic impedance of the signal transmission pattern itself becomes more prominent due to the skin effect as the frequency becomes higher.

  The present invention has been made in view of the above problems, and even if the connected load and the signal transmission line have different characteristic impedances, reflection is unlikely to occur, and a signal in a frequency band in which the effect of the skin effect appears noticeably is transmitted. An object of the present invention is to provide a printed wiring board having a wiring pattern in which reflection is difficult to occur and a flat panel display including the printed wiring board.

  In order to solve the above-mentioned problem, the printed wiring board of the present invention is a printed wiring board in which a signal transmission line having a predetermined width for transmitting a signal to a land to which a predetermined load is connected is formed as a pattern. The transmission line is a distributed constant circuit, and the land has a characteristic impedance that matches the characteristic impedance of the load by adjusting the width of the land, and the signal transmission line and the land are smoothly changed while gradually changing the line width. The characteristic impedance between the signal transmission line and the load is smoothly changed by the connection line connecting the two.

  In the above configuration, the signal transmitted through the signal transmission line is transmitted to the land without reflection by the connection line whose line width changes smoothly and gradually. Moreover, since the characteristic impedance at the land side end of the connection line is matched with the load connected to the land, no reflection occurs when a signal is transmitted to the load. This pattern shape is suitable when applied to a distributed constant circuit, but it obstructs the flow of current transmitted concentrated on the outer edge of the line, especially when the transmitted signal is a signal in the frequency band where the skin effect is prominent. It is suitable without doing.

  Smooth so as not to have a corner means that discontinuity does not occur in the slope of the line segment formed by the edge in a portion continuous from the signal transmission line to the connection line. In addition, gradual means that discontinuity does not occur in the slope of the line segment formed by the edge of the connection line. Of course, since the edge of the signal transmission line is formed in a straight line, there is no discontinuity in the slope of the line formed by the edge. Therefore, the signal transmission line and the connection line are smoothly formed so as not to have a corner.

  Here, the distributed constant circuit in the present invention means a circuit that cannot be approximated as a lumped constant circuit. A lumped constant circuit is one in which the wavelength of a signal transmitted through a signal transmission line is sufficiently longer than the line length of the signal transmission line and can be ignored. That is, the circuit can ignore the impedance distributed on the signal transmission line. It is used in the case of a circuit in which the parameters are concentrated in a place in an electric circuit, and therefore the influence of the place spread need not be considered. Therefore, the distributed constant circuit in the present invention cannot be ignored because the wavelength of the signal transmitted through the signal transmission line is not sufficiently longer than the line length of the signal transmission line. This is a circuit in which the impedance distributed in the circuit cannot be ignored. Of course, there is no problem even if the present invention is applied to a lumped constant circuit.

  More specifically, when the characteristic impedance of the signal transmission line is larger than that of the load, the line width is gradually increased from the signal transmission line side toward the load side, and the signal transmission line from the load is increased. When the characteristic impedance is small, the line width is gradually reduced from the signal transmission line side toward the load side.

  The present invention is preferably applied to a differential pair. That is, the signal transmission line is a pair of signal transmission lines formed adjacent to each other and substantially parallel, and the pair of signal transmission lines is a differential pair for transmitting a differential signal, and the proximity sides are formed in parallel. In addition, it is possible to adopt a configuration in which the remote side gradually changes its width symmetrically with respect to the center line between the pair. In addition, it is more preferable that the magnetic flux generated from each signal transmission line is made closer to the differential pair so as to cancel each other. According to this configuration, the characteristic impedance between the signal transmission line and the load is changed smoothly, and the differential pairs are formed close to each other, so that the magnetic fluxes generated in both patterns have opposite phases. By canceling each other, noise radiated from the differential pair can be reduced.

  Further, the present invention may be applied to a land of a damping resistor. The damping resistor is a resistor connected in parallel to the LC resonance circuit. That is, the characteristic impedance is matched at the connection portion of the resistor, and the characteristic impedance smoothly changes from the signal transmission line to the land, so that the generation of noise due to reflection and ringing can be suppressed.

  Further, the present invention may be applied to a land connected to a filter circuit. The filter circuit is a filter circuit that handles high frequencies such as a band-pass filter and a directional coupler. In this case, the signal may be applied to a signal transmission line that transmits a signal output from the filter circuit to a load, or may be applied to a signal transmission line that transmits a signal and inputs the signal to a filter circuit as a load. That is, the signal output from the filter circuit and the signal input to the filter circuit are not easily reflected, and the occurrence of noise due to ringing can be suppressed.

  Further, as a more specific configuration for solving the above problems, an IC is mounted which outputs a display drive signal as a differential signal while performing digital video signal processing, and a connector to which an LVDS cable is connected. In a flat panel display that includes a printed wiring board formed as a pattern with a signal transmission line having a predetermined width for transmitting the differential signal to the land, and displaying an image on a predetermined screen based on an input video signal, The signal transmission line is a distributed constant circuit, and is a differential pair that is formed substantially in parallel with each other and transmits a differential signal output from a CMOS logic circuit. The differential pair includes a common mode filter. The adjacent side of the differential pair strikes the magnetic flux generated from each signal transmission line by the transmitted differential signal. Proximity sides are formed in parallel with each other at intervals, the remote side of the differential pair is gradually changed in width symmetrically with respect to the center line between the differential pairs, and the land is connected to the signal transmission line. Have different line widths, and when the characteristic impedance of the signal transmission line is larger than that of the LVDS cable, the line width is gradually increased gradually from the signal transmission line side to the LVDS cable side. When the characteristic impedance between the signal transmission line and the LVDS cable is smoothly changed and the characteristic impedance of the signal transmission line is smaller than that of the LVDS cable, the signal transmission line side is directed toward the LVDS cable side. Smoothly change the characteristic impedance between the signal transmission line and the LVDS cable by smoothly decreasing the line width. There as formed.

As described above, according to the present invention, it is possible to provide a printed circuit board having a pattern with less noise radiation while suppressing reflection and ringing.
According to the invention of claim 3, it is possible to provide a printed circuit board having a pattern with less noise radiation while suppressing reflection and ringing.
According to the invention of claim 4, it is possible to provide a printed circuit board having a pattern with less noise radiation while suppressing reflection and ringing.
Furthermore, according to the invention concerning Claim 5, in the printed circuit board which has a differential pair, reflection and ringing can be suppressed and noise radiation can be reduced.
According to the invention of claim 6, in a printed circuit board having a differential pair, noise radiation can be reduced by further suppressing reflection and ringing.
According to the seventh aspect of the invention, noise radiation can be reduced by suppressing reflection and ringing in a printed circuit board having a damping resistance.
Furthermore, according to the eighth aspect of the present invention, noise radiation can be reduced by suppressing reflection and ringing in a printed circuit board having a filter circuit.
Furthermore, it is needless to say that in a more specific configuration as in claim 1, the same effects as in the inventions of claims 2 to 6 described above are exhibited.

Hereinafter, embodiments of the present invention will be described in the following order.
(1) General configuration of the present invention:
(2) Wiring pattern of the present invention:
(3) CMOS logic differential pair:
(4) Land of damping resistance:
(5) Summary:

(1) General configuration of the present invention:
FIG. 1 is an external perspective view of a television device according to an embodiment of the present invention, and FIG. 2 is a perspective view in which the back cabinet of the television device is removed and the inside is exposed. In this embodiment, a television apparatus provided with a printed wiring board will be described as an example, but an input / output part to a computer such as a PC (Personal Computer), a filter system such as a band pass filter, a branch line coupler, and a directional coupler. The present invention can be applied to any form of electrical and electronic equipment that operates based on a clock signal of several hundred MHz or higher. In this embodiment, a liquid crystal television will be described as an example of a television device. However, it may be a cathode ray tube television, a plasma television, a flat panel display, or the like.

  In FIG. 1, a liquid crystal television 100 includes a front cabinet and a back cabinet made of resin, a liquid crystal panel 51 as a display for displaying video on a screen, and legs 53. The front cabinet holds the liquid crystal panel 51 so that the display surface of the liquid crystal panel 51 is exposed to the outside from the rectangular frame. The back cabinet is formed with a thick central portion on the back side, and various substrates disposed on the back surface of the liquid crystal panel 51 are accommodated in the thick portion. The front cabinet is combined with the back cabinet at the front and rear to form a cabinet 52. The leg portion 53 supports the cabinet so that the display surface of the liquid crystal panel 51 is oriented substantially vertically.

  In FIG. 2, the main substrate 50 and the digital substrate 10 are fixed to the back surface of the liquid crystal panel 51. The main board 50 is equipped with circuits for handling analog signals such as an outline, a tuner circuit, an input / output circuit, a power supply circuit, an inverter circuit, an analog signal processing circuit and the like, and the digital board 10 is roughly processed with digital video signal processing. A digital video signal processing circuit is mounted.

  The tuner circuit receives a television broadcast signal via an antenna (not shown) and extracts an intermediate frequency signal. The analog signal processing circuit performs predetermined analog video signal processing on the intermediate frequency signal, and then digitally transmits the signal through the cable 50a. A video signal is supplied to the substrate 10. The audio processing circuit extracts an audio signal from the intermediate frequency signal, and performs signal processing such as amplification on the audio signal. The power supply circuit receives a commercial power supply, generates various voltages, and supplies the generated voltages as power supply voltages to the respective units of the television apparatus. The inverter circuit is supplied with a power supply voltage from the power supply circuit, generates a high-frequency AC signal, and supplies it to the backlight of the liquid crystal module. The input / output circuit supplies various signals (video, audio, control) input from the outside via the jack to the analog signal processing board, and outputs various signals (video, audio, control) output from the analog signal processing board. Output to the outside through the jack.

  The digital substrate 10 includes an LSI that digitally processes video signals. The LSI digitizes the video signal supplied from the analog board, and digital video such as color management, noise reduction, edge enhancement, image quality adjustment, gamma correction, panel timing, gain adjustment, balance adjustment, etc. Apply signal processing. Further, the LSI generates a drive signal based on the digital video signal, supplies it to the connector CN via the wiring pattern P formed on the digital board, and supplies the drive signal to the liquid crystal panel 51 through the LVDS cable 10a. The liquid crystal panel 51 drives each liquid crystal cell based on the drive signal to display an image on the screen.

(2) Wiring pattern of the present invention:
FIG. 3 is a schematic plan view of a digital board 10 as a printed wiring board (printed board) according to the present embodiment.
In the figure, an LSI as an IC and a connector CN are mounted on the digital substrate 10, and a signal transmission line P and a connection line S are used as a pattern for transmitting a digital signal output from the terminal 12 of the LSI to the connector CN. Is formed. An LSI is an element that outputs a predetermined digital signal. A plurality of terminals 12 protrude from each side of a substantially rectangular shape, and these terminals 12 are brought into contact with end portions of a signal transmission line P formed on the digital substrate 10. Soldered and electrically connected. In FIG. 3, only four terminals are in contact with the signal transmission line P, but the other terminals are also connected to the signal transmission lines formed on the digital substrate 10. The other end of the signal transmission line P is connected to the connection line S. The other end of the connection line S smoothly continues to a land L formed under the connector CN, and a terminal of the connector CN is soldered to the land L. As a result, the LSI and the connector CN are electrically connected. A predetermined load such as a cable, a filter circuit (such as a bandpass filter or a directional coupler), or a circuit element is connected to the connector. Further, an element for outputting a signal is not limited to an LSI, and may be a cable, a filter circuit (a bandpass filter, a directional coupler, etc.), a circuit element, or the like.

  Each signal transmission line P is provided with a noise filter (EMI filter, EMC filter) F. The noise filter F blocks a frequency band of 500 MHz or higher, and prevents the occurrence of common mode noise and differential mode noise. Noise filters that prevent differential mode noise include ferrite beads, ferrite cores, three-terminal filters (such as three-terminal capacitors), feedthrough capacitors, and the like. The differential mode noise filter can remove in-system noise superimposed on the signal current. On the other hand, as a noise filter for preventing common mode noise, for example, a common mode filter such as TCM1005 (TDK (registered trademark)) is used, and one common mode filter is provided for one pair of differential pairs transmitting a differential signal. Provided. According to the common mode noise filter, it is possible to prevent the common mode noise current from passing due to the unbalance of the signal characteristics of the two signal lines by the differential transmission method, thereby preventing the common mode noise.

  Here, the signal transmitted through the signal transmission line P is a high-frequency signal that, when transmitted through the signal transmission line P, requires the signal transmission line P to be regarded as a distributed constant circuit. That is, when the pattern length (signal transmission line length) is short and the round trip time of the signal between the elements connected to the pattern is shorter than the rise time of the element, this pattern can be treated as a lumped constant circuit. However, if the length L of the pattern (signal transmission line) is long (λ / 4 << L) with respect to the wavelength λ of the frequency of the digital signal to be handled, it is necessary to consider the pattern as a distributed constant circuit. That is, the latter case corresponds to the signal transmission line P of the present invention. The high-frequency signal is often used for a digital signal, reflecting an increase in the amount of transmission information accompanying the recent high definition of video.

  Thus, when it is necessary to consider the signal transmission line P as a distributed constant circuit, the characteristic impedance of the load connected to the signal transmission line P and the connector CN is matched to suppress reflection and ringing. There is a need. On the other hand, it is possible to suppress reflection and ringing by smoothly changing the characteristic impedance according to the principle of stepped impedance. In the present invention, a pattern shape using both matching of characteristic impedance and smooth change is proposed. The characteristic impedance of each part can be known by a TDR measuring device. It is also known that if the other parameters are the same, the characteristic impedance in the pattern decreases when the pattern width is widened, and the characteristic impedance in the pattern increases when the pattern width is narrowed.

  FIG. 4 shows a pattern shape when the characteristic impedance of the load connected to the connector CN is lower than that of the signal transmission line P. In the figure, a signal transmission line P1 is connected to a land L1 by a connection line S1. The connection line S1 is formed so that the width is gradually and gradually increased gradually from the signal transmission line P1 side to the land L1 side. Further, the connection portion between the signal transmission line P1 and the connection line S1, and the connection portion between the connection line S1 and the land L1 are also connected so as to be smooth and have no corners.

Specifically, the signal transmission line P1 having a fixed line width x ₁ is smoothly connected to the left end portion of the first curved portion S1a of the same width. The first curved portion S1a has a curved edge, and the edge draws a gentle curve to increase the line width of the connection line S1, and smoothly connects to the tapered portion S1b when a predetermined inclination is obtained. The tapered portion S1b has a substantially straight edge, gradually increases the line width at a substantially constant increase rate, and smoothly connects to the second curved portion S1c. The second curved portion S1c has a curved edge, and the edge draws a gentle curve to reduce the increase rate of the line width of the connection line S1, the inclination is the same as that of the signal transmission line P1, and the line width is It becomes the same as the width y ₁ of the land L1 is connected to the lands L1.

That is, the pattern connected from the signal transmission line P1 to the land L1 via the connection line S1 has no corners and is connected smoothly and gradually with the line width being increased. Further, the signal transmission line P1 moiety Z ₁ the characteristic impedance _of the characteristic impedance of a load connected to the lands L1 and Z _2, the characteristic impedance in the land L1 is line width y ₁ is the Z _2. In this way, the characteristic impedance of the land L1 and the load are matched, and the line width is smoothly increased from the signal transmission line P1 to the land L1, and the characteristic impedance from the signal transmission line P1 to the land L1 is smoothly reduced. Therefore, the characteristic impedance between the signal transmission line P1 and the land L1 does not change abruptly in a staircase manner, and signal reflection hardly occurs. Therefore, it is possible to form a pattern that hardly generates radiation noise. Of course, the connection line S1 can adopt various shapes as long as it smoothly and gradually increases from the signal transmission line P1 to the land L1.

  FIG. 5 shows a pattern shape when the characteristic impedance of the load connected to the connector CN is higher than that of the signal transmission line P. In the figure, a signal transmission line P3 is connected to a land L2 by a connection line S2. The connection line S2 is formed so as to be smooth and gradually (gradually) narrow from the signal transmission line P2 side to the land L2 side. In addition, the connection part between the signal transmission line P3 and the connection line S2, and the connection part between the connection line S2 and the land L2 are smoothly connected so as not to form a corner.

Specifically, the signal transmission line P2 having a constant line width x ₂ is smoothly connected to the left end portion of the third bending portion S2a of same width. The third curved portion S2a has a curved edge, and the edge draws a gentle curve to reduce the line width of the connection line S2, and smoothly connects to the tapered portion S2b when a predetermined inclination is obtained. The tapered portion S2b has a substantially linear line width, gradually decreases the line width at a substantially constant reduction rate, and smoothly connects to the fourth curved portion S2c. The fourth curved portion S2c has a curved edge, and the edge draws a gentle curve to reduce the reduction rate of the line width of the connection line S2, the inclination is the same as that of the signal transmission line P2, and the line width is It becomes the same as y ₂ of land L2 is connected to the land L2.

That is, the pattern connected from the signal transmission line P2 to the land L2 via the connection line S2 has no corners and is connected smoothly and gradually with the line width increased. Further, the signal transmission line P2 portion of the characteristic impedance Z _3, when the characteristic impedance of a load connected to the land L2 and Z _4, the characteristic impedance in the land L2 is line width y ₂ is the Z _4. In this manner, the characteristic impedance of the land L2 and the load are matched, and the characteristic width from the signal transmission line P2 to the land L2 is smoothly increased by smoothly decreasing the line width from the signal transmission line P2 to the land L2. Therefore, the characteristic impedance between the signal transmission line P2 and the land L2 does not change abruptly in a stepped manner, and signal reflection hardly occurs. Therefore, it is possible to form a pattern that hardly generates radiation noise. Of course, the connection line S2 can adopt various shapes as long as it smoothly and gradually increases from the signal transmission line P2 to the land L2.

(3) CMOS logic differential pair:
Next, an example in which the above wiring pattern is applied to a differential pair will be described. FIGS. 6 and 7 are pattern shapes suitable for the case where the adjacent patterns in FIG. 3 are a pair of differential pairs that transmit differential signals having opposite polarities. 6 shows the pattern shape when the characteristic impedance of the load connected to the connector CN is lower than that of the signal transmission line P, and FIG. 7 shows the pattern shape when the characteristic impedance of the load connected to the connector CN is higher than that of the signal transmission line P. is there. As such a differential pair, an output line from a CMOS logic circuit, a signal supply line to a high-speed interface such as USB or IEEE1394, a signal supply line to a differential signal interface such as LVCS or TMDS, and the like can be considered.

  In FIG. 6, the signal transmission line P3a is connected to the land L3a by the connection line S3a, and the signal transmission line P3b is connected to the land L3b by the connection line S3b. The signal transmission line P3a and the signal transmission line P3b are formed so that the edges facing each other are parallel and close to each other. Proximity means that signal transmission lines P3a and P3b are close to each other so as not to contact each other, and in particular is a distance at which magnetic fluxes generated by signals transmitted in both patterns of the differential pair cancel each other. Is preferred. The connection line S3a and the connection line S3b are also formed in parallel and close to each other on the sides facing each other. The connection line S3a and the connection line S3b are connected to the land L3a and the land L3b, respectively, while increasing the line width by smoothly and gradually (gradually) changing the edges that do not face each other. Therefore, the signal transmission line P3a and the connection line S3a, the connection line S3a and the land L3a, the signal transmission line P3b and the connection line S3b, and the connection line S3a and the land L3b are smoothly connected without forming a corner.

That is, the pattern connected from the signal transmission line P3a to the land L3a via the connection line S3a and the pattern connected from the signal transmission line P3b to the land L3b via the connection line S3b are constant on the adjacent sides facing each other. The remote sides that are formed in parallel with each other and that do not face each other are connected to the connector connection portion with smooth and gradually widening of the line width without any angles symmetrical to the center line between the differential pairs. . The signal transmission lines P3a, _{Z 5} the characteristic impedance of P3b, when the characteristic impedance of a load connected to the land L3a and the land L3b and _{Z 6,} the land L3a and the characteristic impedance in the land L3b the line width becomes _{y 3} It is Z _6.

  In this way, the characteristic impedance of the land L3a, the land L3b and the load connected to the land is matched, and the line width is smoothly increased from the signal transmission lines P3a, P3b to the lands L3a, L3b, respectively. The characteristic impedance from the lines P3a and P3b to the lands L3a and L3b respectively decreases smoothly. Therefore, the characteristic impedance between the signal transmission lines P3a and P3b and the lands L3a and L3b does not change abruptly in a stepwise manner, and signal reflection is less likely to occur. Therefore, it is possible to form a pattern that hardly generates radiation noise. Furthermore, by forming the gaps of the differential pairs close to each other, the magnetic fluxes generated in both patterns become opposite to each other and cancel each other. Therefore, noise radiated from the differential pair is reduced.

  In FIG. 7, the signal transmission line P4a is connected to the land L4a by the connection line S4a, and the signal transmission line P4b is connected to the land L4b by the connection line S4b. The signal transmission line P4a and the signal transmission line P4b are formed so that the edges facing each other are parallel and close to each other. Also, the connection line S4a and the connection line S4b are formed in parallel and close to each other on the sides facing each other. The connection line S4a and the connection line S4b are connected to the lands L4a and L4b while reducing the line width by smoothly and gradually (gradually) changing the edges that do not face each other. Therefore, the signal transmission line P4a and the connection line S4a, the connection line S4a and the land L4a, the signal transmission line P4b and the connection line S4b, and the connection line S4a and the land L4b are smoothly connected without forming a corner.

That is, the pattern connected from the signal transmission line P4a to the land L4a via the connection line S4a and the pattern connected from the signal transmission line P4b to the land L4b via the connection line S4b are spaced apart from each other at a constant interval. The sides that do not face each other are smooth, without corners, and are gradually widened to be connected to the connector connecting portion. Further, the signal transmission line P4a, _{Z 7} the characteristic impedance of P4b, land L4a, when the characteristic impedance of a load connected to CN4b and _{Z 8,} land L4a the line width is _{y 4,} the characteristic impedance at L4b is _{Z 8} It is said.

  Thus, matching the characteristic impedance of the land L4a, the land L4b and the load connected to the land, and reducing the line width smoothly from the signal transmission lines P4a, P4b to the lands L4a, L4b, respectively, enables signal transmission. The characteristic impedance from the lines P4a and P4b to the lands L4a and L4b increases smoothly. Therefore, the characteristic impedance between the signal transmission lines P4a and P4b and the lands L4a and L4b does not change abruptly in a stepwise manner, and signal reflection hardly occurs. Therefore, it is possible to form a pattern that hardly generates radiation noise. Furthermore, by forming the gaps of the differential pairs close to each other, the magnetic fluxes generated in both patterns become opposite to each other and cancel each other. Therefore, noise radiated from the differential pair is reduced.

(4) Land of damping resistance:
Next, an example in which the above wiring pattern is applied to a land of a damping resistor will be described. The damping resistor is a resistor connected in parallel to the LC resonance circuit. Conventionally, for example, lands A1 and B1 as shown in FIG. 9 are formed and connected to the lands by soldering or the like. That is, rectangular lands A1 and B1 with widened line widths are formed at positions corresponding to the lines A and B extending in parallel, and resistors such as chip resistors are placed on the lands and soldered. Thus, the conventional damping resistor land has a shape having corners such as hexagons and squares.

  However, even if such a conventional land shape matches the characteristic impedance between the land and the load, if it is used in a circuit that is regarded as a distributed constant circuit, reflection will occur at the corners and ringing will occur. Cause noise. Therefore, in the present invention, a land having a shape as shown in FIG. In the figure, a damping resistor constitutes a load.

In the figure, lands C1 and D1 are formed at corresponding positions on signal transmission lines C and D extending in parallel. Land C1, D1, respectively the signal transmission line C, and to widen the smooth and gradual (progressive) wide from D to a predetermined width X _5, will further smoothly gradually reduced width signal transmission line C, D It is formed so as to be smoothly continuous to the opposite side. The predetermined width is a width in which a damping resistor can be connected to the land, and the characteristic impedance of the lands C1 and D1 matches the characteristic impedance of the damping resistor connected to the land. That is, each of the lands C1 and D1 is formed as a bulge having a gentle peak shape in both width directions on each of the signal transmission lines C and D, and having a maximum width of a predetermined width.

  Therefore, the characteristic impedances of the lands C1 and D1 and the damping resistor Rd are matched, and the characteristic impedance is also smoothly changed by smoothly connecting the signal transmission lines C and D and the lands C1 and D1, respectively. Accordingly, the digital substrate 10 having a land shape in which a signal to be transmitted is less likely to be reflected at a connection portion between the land and the signal transmission line, and noise and ringing are less likely to occur can be provided.

(5) Summary:
As described above, the signal transmission line P1, which is a distributed constant circuit, is connected to the land L1 by the connection line S1. A load having a characteristic impedance different from that of the signal transmission line P1 is connected to the land L1. The land L1 has a line width that matches the characteristic impedance of the load. The connection line S1 is formed smoothly so as not to have a corner while gradually increasing the line width, and the characteristic impedance between the signal transmission line P1 and the load is smoothly reduced by the connection line S1.

  Further, the signal transmission line P2 which is a distributed constant circuit is connected to the land L2 by the connection line S2. A load having a characteristic impedance different from that of the signal transmission line P2 is connected to the land L2. The land L2 has a line width that matches the characteristic impedance of the load. The connection line S2 is smoothly formed so as not to have an angle while gradually reducing the line width, and the characteristic impedance between the signal transmission line P2 and the load is smoothly increased by the connection line S2.

  The signal transmission lines P3a and P3b, which are distributed constant circuits, are connected to the lands L3a and L3b by connection lines S3a and S3b, respectively. A load having a characteristic impedance different from that of the signal transmission lines P3a and P3b is connected to the lands L3a and L3b. The lands L3a and L3b have a line width that matches the characteristic impedance of the load. The connection lines S3a and S3b are formed smoothly so as not to have an angle while gradually increasing the line width, and the characteristic impedance between the signal transmission lines P3a and P3b and the load is smoothly reduced by the connection lines S3a and S3b. .

  The signal transmission lines P4a and P4b, which are distributed constant circuits, are connected to the lands L3a and L3b, respectively, via connection lines S4a and S3b. A load having a characteristic impedance different from that of the signal transmission lines P3a and P3b is connected to the lands L3a and L3b. The lands L3a and L3b have a line width that matches the characteristic impedance of the load. The connection lines S3a and S3b are formed smoothly so as not to have a corner while gradually reducing the line width, and the characteristic impedance between the signal transmission lines P3a and P3b and the load is smoothly increased by the connection lines S3a and S3b. .

  In addition, the signal transmission lines C and D, which are distributed constant circuits, smoothly change the line widths so that the lands C1 and D1 swell. The lands C1 and D1 have a line width that matches the characteristic impedance of the damping resistor Rd. Due to the shape of the lands C1 and D1, the characteristic impedance between the connection lines C and D and the damping resistor Rd changes smoothly.

Needless to say, the present invention is not limited to the above embodiments. It goes without saying for those skilled in the art,
・ Applying mutually interchangeable members and configurations disclosed in the above embodiments by appropriately changing the combination thereof.− Although not disclosed in the above embodiments, it is a publicly known technique and the above embodiments. The members and configurations that can be mutually replaced with the members and configurations disclosed in the above are appropriately replaced, and the combination is changed and applied. It is an embodiment of the present invention that a person skilled in the art can appropriately replace the members and configurations that can be assumed as substitutes for the members and configurations disclosed in the above-described embodiments, and change the combinations and apply them. It is disclosed as.

It is an external appearance perspective view of the television apparatus concerning one Embodiment of this invention. It is the perspective view which removed the back cabinet of the television apparatus and exposed the inside. It is a schematic plan view of a digital board. It is a figure explaining the pattern shape in case the characteristic impedance of load is lower than a signal transmission line. It is a figure explaining the pattern shape in case the characteristic impedance of load is higher than a signal transmission line. It is a figure explaining the pattern shape in case the characteristic impedance of a load is lower than a signal transmission line in a differential pair. In a differential pair, it is a figure explaining the pattern shape in case the characteristic impedance of load is higher than a signal transmission line. It is a figure explaining the land shape of a damping resistor. It is a figure explaining the land shape of the conventional damping resistor.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Digital board (printed wiring board) 10a ... LVDS cable 12 ... Terminal 50 ... Main board 50a ... Cable 51 ... Liquid crystal panel 52 ... Cabinet 53 ... Leg part 100 ... Liquid crystal television F ... Noise filter (common mode noise filter)
P, P1, P2, P3a, P3b, P4a, P4b ... Signal transmission line S, S1, S2, S3a, S3b, S4a, S4b ... Connection line S1a ... First curved part S1b ... Tapered part S1c ... Second curved line Part S2a ... Third curved part S2b ... Tapered part S2c ... Fourth curved part CN ... Connector L1, L2, L3a, L3b, L4a, L4b ... Land Rd ... Damping resistor A, B, C, D ... Signal transmission line A1, B1, C1, D1 ... land _{x 1, x 2, x 3} , x 4, x 5, y 1, y 2, y 3, y 4 ... line width

Claims (8)

A signal having a predetermined width for transmitting a differential signal to a land of a connector to which an LVDS cable is connected, and an IC for performing digital video signal processing and outputting a display drive signal as a differential signal. A transmission line has a printed wiring board formed as a pattern,
In a flat panel display that displays video on a predetermined screen based on the input video signal,
The signal transmission line is a distributed constant circuit and is formed in a substantially parallel manner adjacent to each other, and is a differential pair for transmitting a differential signal output from a CMOS logic circuit,
The differential pair is provided with a common mode filter,
The proximity side of the differential pair is formed in parallel on the proximity side at an interval that cancels the magnetic flux generated from each signal transmission line by the transmitted differential signal,
The remote side of the differential pair is gradually changed in width symmetrically with respect to the center line between the differential pair,
The land has a line width different from the signal transmission line,
When the characteristic impedance of the signal transmission line is larger than that of the LVDS cable, the line width is gradually and gradually increased from the signal transmission line side to the LVDS cable side, and the signal transmission line and the LVDS cable Smoothly changing the characteristic impedance between
When the characteristic impedance of the signal transmission line is smaller than that of the LVDS cable, the line width is smoothly and gradually reduced from the signal transmission line side to the LVDS cable side, and the signal transmission line and the LVDS cable are Flat panel display characterized by smoothly changing the characteristic impedance between them. In a printed wiring board in which a signal transmission line having a predetermined width for transmitting a signal to a land to which a predetermined load is connected is formed as a pattern,
The signal transmission line is a distributed constant circuit,
The land has a characteristic impedance that matches the characteristic impedance of the load by adjusting the width of the land,
A printed wiring board characterized in that the characteristic impedance between the signal transmission line and the load is smoothly changed by a connection line that smoothly connects the signal transmission line and the land while gradually changing the line width.   3. The printed wiring according to claim 2, wherein when the characteristic impedance of the signal transmission line is larger than that of the load, the line width is gradually increased from the signal transmission line side toward the load side. Board.   The line width is gradually reduced from the signal transmission line side toward the load side when the characteristic impedance of the signal transmission line is smaller than the load. The printed wiring board as described. The signal transmission line is a pair of signal transmission lines formed adjacent to each other and substantially parallel,
The pair of signal transmission lines is a differential pair for transmitting a differential signal, the proximity side is formed in parallel, and the remote side is gradually changed in width symmetrically with respect to the center line between the pair. The printed wiring board according to any one of claims 2 to 4, wherein the printed wiring board is characterized by that. The distance on the near side is
6. The printed wiring board according to claim 5, wherein magnetic fluxes generated from the signal transmission lines by the differential signals transmitted in the pair of signal transmission lines are spaced apart from each other.   The printed wiring board according to claim 2, wherein the land is a land of a damping resistor.   5. The printed wiring board according to claim 2, wherein the land is a land connected to a filter circuit.

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