Liquid crystal television set having driving circuit on peripheral portion and method of fabrication of image display section

In a liquid crystal TV set, a liquid crystal panel includes an image display section constituted by a liquid crystal for displaying an image and a peripheral portion of the image display section having horizontal and vertical scanning circuits for driving the liquid cyrstal. A operating unit having a plurality of switches is arranged on the front of the peripheral portion. The switches of the operating unit includes at least a thin key switch are are arranged in matrix. This construction permits the liquid crystal panel to be arranged in the same plane as the operating unit, reducing both the size of a liquid crystal TV set and the number of assembly steps thereof at the same time.

BACKGROUND OF THE INVENTION 
The present invention relates to a liquid crystal television set, and more 
in particular, to a liquid crystal television set and a method of 
fabrication thereof having a feature in the arrangement of an operating 
unit thereof. 
Conventional liquid crystal television sets have an operating unit arranged 
on other than the liquid crystal panel as viewed from the front, as 
disclosed, for example, in JP-A(U)-61-94883. The front outline of such 
liquid crystal television sets thus requires a total area more than the 
sum of the areas of the liquid crystal panel and the operating unit. 
The aforementioned fact that an area more than the sum of the areas of the 
liquid panel and the operating unit is required for the front outline of a 
liquid crystal television set does not pose any problem so far as the 
television set is as small as two or three inches the in diagonal line of 
the liquid crystal panel. For liquid crystal panel sizes of four inches or 
more, however, such a fact poses a bottleneck against reducing the outline 
of a liquid crystal television set. 
SUMMARY OF THE INVENTION 
A first object of the present invention is to provide a compact liquid 
crystal TV set small in outer size even if the liquid crystal panel 
thereof is large in size. 
A second object of the present invention is to provide a method of 
fabricating a liquid crystal TV set convenient to assemble. 
The first object is achieved by arranging an operating unit on the front of 
the peripheral portion other than the image display section of a liquid 
crystal panel. 
The second object is achieved by holding an operating unit between a top 
case and a liquid crystal panel, mounting a center case thereon, securing 
the top case and the center case to each other, and securing a bottom case 
fixedly carrying a circuit board inside. 
According to one aspect of the present invention, there is provided a 
liquid crystal TV set, in which the arrangement of an operating unit 
within the size of the liquid crystal panel reduces the outer size of the 
TV set to a minimum necessary for housing the liquid crystal panel, and 
the construction of a thin operating unit permits it to be located in a 
clearance between a shield case of the liquid crystal panel and a TV case, 
thus assuring a small depth of the TV set. 
According to another aspect of the present invention, there is provided a 
method of fabricating a liquid crystal TV set, in which a plurality of 
cases, a liquid crystal panel, an operating unit, and other parts are 
assembled sequentially for an improved assembly efficiency.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
An embodiment of the present invention will be explained below with 
reference to FIGS. 1 to 6. 
An outer perspective view of a liquid crystal TV set according to the 
present invention is shown in FIG. 1. The housing of a liquid crystal TV 
set 1 is formed of three cases including a top case 2, a center case 3 and 
a bottom case 4. The top case 2 has a front plate 21 of a transparent 
material attached thereto. As shown by dashed lines in FIG. 3, a screen or 
image display section 51 of the liquid crystal panel 5 is seen through the 
front plate 21. 
The top case 2 has operating switches 81, 82, 83, 84, 85, 86, 87 in key 
form at the lower part. These operating switches 81, 82, 83, 84, 85, 86, 
87 are arranged above the lower peripheral portion of the liquid crystal 
panel described later. Each of the operating switches 81, 82, 83, 84, 85, 
86, 87 is operated so frequently as to affect the operability of the TV 
set. The operating switch 81 is for switching television and VTR (video 
tape recorder) monitor. A touch of the operating switch 81 starts the 
function of television and another touch that of a VTR monitor. These 
operations will be explained in detail later with reference to the block 
diagram of FIG. 6. The operating switches 82, 83 are for adjusting the 
brightness. When the left operating switch 82 is pressed, the brightness 
is decreased, and the brightness continues to be decreased if this switch 
is kept depressed. At the press of the operating switch 83, on the other 
hand, the brightness progressively increases. The operating switches 84, 
85 are for regulating the sound volume. If the left switch 84 is pressed, 
the sound volume decreases, and upon continued depression, the sound 
volume continues to decrease. The operating switch 85 is for increasing 
the sound volume upon depression thereof. The operating switches 86, 87 
are for tuning. Press the left operating switch 86, and the channel number 
selected by the tuner is decreased in number, and the continued depression 
thereof progressively decreases the channel number. The operating switch 
87 is for progressively increasing the channel number upon depression 
thereof. 
The liquid crystal TV set has on the right side of the body thereof control 
units lower in operating frequency than the operating switches 81, 82, 83, 
84, 85, 86, 87. These control units are mechanical switches either of knob 
or change-over type. A knob 11 is for regulating the color darkness, and 
by rotating this knob upward or downward, the color darkness is regulated. 
A knob 12, which is for regulating the hue, is adapted for turning upward 
or downward to adjust the hue. A knob 13 provides a power switch operable 
in three stages. By sliding this switch upward or downward, the on-off of 
power and the charging conditions are switchable. 
Although not shown in the drawing, a slide switch for switching VHF and UHF 
bands is disposed on the top of the body of the liquid crystal TV set. 
Input-output terminals of the TV set include an external antenna terminal 
on the top of the liquid crystal TV set body, and a video input terminal, 
an earphone terminal and an external power terminal on the left side of 
the TV set body. A contractable antenna of rod type is also mounted on the 
top of the liquid crystal TV set although not shown in the drawing. 
A front partial sectional view of the liquid crystal panel 5 is shown in 
FIG. 2. The liquid crystal panel 5 normally includes an image display 
section 51 made of transparent glass electrodes holding liquid crystal 
therebetween for displaying an image, and a peripheral section 52 having 
arranged thereon horizontal scanning units 701, 702, 703, 704 and vertical 
scanning units 711, 712, 713 for driving the image display section 51. The 
peripheral section 52 is covered with a metal shield plate 6 for 
preventing leakage of the scanning signal to an external unit. As a 
result, in appearance, the liquid crystal panel 5 has a part of the shield 
plate 6 cut away and the image display section 51 of the liquid crystal 
panel exposed from the central part. 
The horizontal scanning units 701, 702 are for controlling the pixels of 
odd-numbered lines and the horizontal scanning units 703, 704 for 
controlling those of even-numbered lines. The horizontal scanning units 
for the odd- and even-numbered lines are divided into two parts 
respectively. A liquid crystal panel five inches in diagonal line has 480 
horizontal scanning lines. 
The vertical scanning units 711, 712, 713 include three portions, and there 
are 240 vertical scanning lines for a liquid crystal panel five inches in 
diagonal line. 
The horizontal scanning units, instead of being divided into two parts, may 
be provided only under the image display section 51 of the liquid crystal 
panel without being divided. In such a case, the peripheral portion 52 is 
positioned in the form of L but not in the form of channel as shown in 
FIG. 2. Also, the vertical scanning units may be divided into two parts on 
the right and left sides. 
A front view of a liquid crystal TV set body is shown in FIG. 3. The liquid 
crystal panel 5 arranged inside of a top case 2 is shown by dashed line. 
Specifically, the image display section 51 is visible through a 
transparent front plate 21 and has an image displayed thereon. An 
operating unit 8 including operating switches 81, 82, 83, 84, 85, 86, 87 
of key type are arranged on the peripheral portion 52 of the liquid 
crystal panel 5. 
FIG. 4 shows a side sectional view of the liquid crystal TV set body. The 
liquid crystal panel 5 is mounted between the top case 2 and the center 
case 3. The operating unit 8 including the operating switches 81, 82, etc. 
is arranged between the top case 2 and the shield case 6 covering the 
peripheral portion 52 of the liquid crystal panel 5 along the peripheral 
portion 52 under the liquid crystal panel 5. Protrusions 81 of the 
operating switches 81, 82, etc. are projected from the top case 2 so that 
the protrusions 81 are adapted for pressing operation from the front side. 
Also, circuit boards 91, 92 and a back light 10 are mounted between the 
center case 3 and the bottom case 4. 
The back light 10 has a diffusion plate 14 at the front part thereof in 
contact with the image display section 51 of the liquid crystal panel 5 
thereby to render uniform the light from the back light 10 and from the 
reflector 15 behind the same. The back light 10 uses a single straight 
tube which may be replaced by a U-shaped tube or a couple of straight 
tubes as required with equal effect. 
The circuit boards include a main board 91 and a subordinate board 92, 
which are connected to each other by a post 24 having a lead wire built 
therein. The subordinate board 92 carries thereon a control section for 
controlling the liquid crystal panel 5 as described later. The vertical 
and horizontal scanning circuits of the liquid crystal panel 5 are 
connected to a connector 18, which in turn is connected to a connector 23 
on the subordinate board 92 by a flexible board 18. The operating unit 8 
including the operating switches 81, 82, etc are also connected to a 
connector 25 on the main board 91 by a flexible board 19. 
The top case 2 and the center case 8 are secured by a screw 20, with the 
result that the liquid crystal panel 5 is fixedly positioned between the 
top case 2 and the center case 3. The main board 91 is fixedly disposed on 
the bottom case 4 by screws 22, 26. The bottom case 4 is secured fixedly 
on the center case 3 by a screw 21. The back light 10, the diffusion plate 
14 and the reflector 15 fixed integrally to each other are secured fixedly 
on the center case 3. 
The bottom case 4 has mounted thereon stands 16, 17 foldable in two parts. 
These stands 16, 17 are bent as shown in their use with the angles thereof 
adjustable in three stages. The stages of angle for adjustment may 
alternatively be more than three. The stands 16, 17 are adapted to be 
extended and held in straight form in close contact with the bottom case 4 
when not in use. 
The operating unit 8 is arranged under the front part of the liquid crystal 
TV set. When the protrusion 82 of the operating unit 8 is pressed by 
finger as shown in FIG. 4, therefore, the stands 16, 17 are positioned 
along the direction in which the force is applied by the finger, thus 
assuring the stability and the operating ease of the liquid crystal TV 
set. 
The position of the operating unit 8 may alternatively be on the left side 
or above the image display section 51 in FIG. 2, provided, however, that 
it must be located on the peripheral portion 52. 
In the case of a stand of a type not held on the desk but hung on the wall 
or the like, the operating unit 8 arranged above or on the left side of 
the image display section 51 might be more easily operable depending on 
relative positions of the operator and the liquid crystal TV set. The 
arrangement may alternatively be determined from the standpoint of design 
appeal. 
FIG. 5 is an exploded sectional view showing steps of fabricating the 
liquid crystal TV set. First, the operating unit 8 is fitted in position 
at stepped portions 27 below the top case 2 to project a protrusion 82 of 
the operating unit 8 from the hole of the top case 2. 
Then, the recess (not shown) of the liquid crystal panel 5 is fitted in the 
upper protrusion 28 of the top case 2 to set the liquid crystal panel 5 in 
position. The center case 3 is mounted on this assembly. Relative 
positions of the assembly and the center case 3 are secured by stepped 
portions 29 on the outer periphery of the center case 3 and an output 
periphery 30 of the top case 2. After that, the top case 2 and the center 
case 3 are secured by screws 20. Out of the screws 20 including two upper 
screws and two lower screws, the lower ones are not shown in the drawing 
and one of the upper screws is hidden behind shown screw 20. The back 
light 10, the diffusion plate 14 and the reflector 15, after being fixed 
integrally, are secured on the center case 3 by being pressed on the 
center case 3. The bottom case 4, on the other hand, is assembled in the 
manner mentioned below. Specifically, the main board 91 is fixed on the 
bottom case 4 by screws 22, 26. The main board 91 has fixed thereon a 
connector 31. A lead wire built in the connector 31 and exposed from the 
ends of the latter is inserted in a post 24 to secure the connector 31. 
The lead wire exposed from the other end of the connector 31 is inserted 
into the hole of the subordinate board 92 and soldered therein. The IC and 
the like on the subordinate board 92 are connected with the lead wire by a 
printed wiring formed on the subordinate board 92. After this assembly 
work, the flexible wiring 18, 19 are connected to the connectors 23, 25. 
The assembly unit of the top case 2 and the center case 3 is fixedly 
secured to the bottom case 4 by a screw 21. 
As described above, the top case, the operating unit, the liquid crystal 
panel and the center case are mounted to fix the top case with the center 
case as a first step; a back light unit including the back light, the 
diffusion plate and the reflector is secured on the center case as a 
second step; a circuit board is secured in the bottom case as a third 
step; and the bottom case is fixed on the center case as a fourth step. 
The assembly process for fabrication involving only these four steps 
improves the assembly efficiency. 
The conventional methods of fabricating a liquid crystal TV set, in 
contrast, requires six steps of securing a liquid crystal panel on a top 
case (first step), fixing an operating unit on the top case (second step), 
fixing a back light unit on a center case (third step), securing a top 
case on the center case (fourth step), fixing a circuit board on a bottom 
case (fifth step), and finally fixing the bottom case on the center case 
(sixth step). 
The back light unit may alternatively be mounted on the bottom case 4. 
A block diagram of a liquid crystal TV set according to an embodiment of 
the present invention is shown in FIG. 6. The liquid crystal TV set 100 
receives a broadcasting wave at a tuner 41 through an antenna 40, and 
produces a video-audio signal of a channel (frequency) selected by a 
tuning circuit 48. This signal is separated into a video signal and an 
audio signal at an video-audio intermediate frequency amplifier circuit 
42. A signal from the video-audio intermediate frequency amplifier circuit 
42 and a signal from an external video unit are produced by being selected 
at an input change-over circuit 43. The audio signal is applied to a 
speaker 46 through an volume control circuit 44 and an audio output 
circuit 45. The audio signal is also led to an earphone terminal 47 as a 
signal audible by earphone. The video signal, on the other hand, is 
demodulated into a primary color signal by a video/chroma circuit 50, and 
subjected to .gamma.-compensation at a signal shaping circuit 52. Further, 
a polarity-reversed signal is taken out from a reverse amplifier circuit 
53, and applied to a horizontal scanning circuit through the vertical and 
horizontal scanning circuits of the liquid crystal panel 5. A screen 
display circuit 51 is for displaying characters on the screen and applies 
a control signal to the video/chroma circuit 50. The video signal applied 
to the sync separator circuit 54, on the other hand, is converted into 
horizontal and vertical sync signals and applied to a control IC 55. An 
output signal from the control IC 55 is applied through a flexible wiring 
18 to the scanning circuit of the liquid crystal panel 5 thereby to effect 
timing control of the vertical and horizontal operations. 
The reverse amplifier circuit 53 and the control IC 55 are provided on the 
subordinate board 92, and the remaining circuits on the main board 91. 
The power circuit 56 is supplied with a DC voltage from a DC power supply 
57 such as an AC adapter, a DC power supply of a battery 58, and a 
controlled output voltage is supplied to each circuit. Further, a 
microcomputer 49 is used for control operations by the operating unit 8 
including tuning, sound volume control, screen display and TV/video 
change-over. 
The operating unit 8 includes sound volume control switches 81, 82, 83, 84, 
85, 86, 87, the contacts of which correspond to A, B, C, D, E, F, etc in 
FIG. 6 respectively. The functions of these switches are discriminated by 
a key matrix signal from the microcomputer 49. Specifically, a scanning 
signal is sent from the microcomputer 49 sequentially through a diode, so 
that upon depression of a given contact of the switches, the scanning 
signal is read into the microcomputer 49, thus identifying the particular 
contact from the data on the line by way of which the scanning signal is 
read and the data on the timing at which it is read. As a result, the 
operating unit requires no circuit parts other than the key switches and 
is thus constructed in this form. 
Depending on the type of switch depressed, the microcomputer 49 sends a 
control signal to the tuning circuit 48, the input change-over circuit 43 
and the screen display circuit 51 thereby to effect control as desired by 
the operator. 
The key switch used in the embodiment under consideration is defined not as 
the one capable of self-holding a physical condition of binary or higher 
state, but as the one which has a contact thereof closed only during 
depression with its made discriminated by a read signal from the key 
matrix circuit. By using such a key switch, the operating unit is made 
thin, thereby making it possible to arrange a plurality of such switches 
in the space between the top case 2 and the liquid crystal panel 5. 
The key switch in the form of key top providing a protrusion used in this 
embodiment may be replaced with equal effect by a key switch in sheet form 
generally used with a card-type calculator or the like. Also, instead of 
the contacts, a device producing a binary state according to capacity 
change may be used. 
In the case where there is some margin of space between the top case 2 and 
the liquid crystal panel 5, the key switch may be superseded by a switch 
of such a type that the contact thereof is closed when given a touch to 
hold a state and opened when given another touch. The size of the liquid 
crystal TV set may be equally reduced even by use of the latter type of 
switch. 
The number of key switches is not limited to seven as in the present 
embodiment, but may be increased or decreased as desired. Further, the 
other types of switch such as zoom switch may be arranged on the front 
portion, the space permitting. Each switch should have a width slightly 
greater than the human finger to assure an operating ease and prevent a 
depression error even if adjacent switches are located closely to each 
other. The number of switches arranged in juxtaposition is determined by 
the lateral width of the liquid crystal TV set proper, the width of the 
switches and the distance between adjacent switches. If it is desired to 
arrange more switches on the front portion, they are preferably disposed 
in stages or divided into the upper and lower sides or the left and right 
sides of the image display section. 
According to the present invention, the front outline of a liquid crystal 
TV set is reduced substantially to the size of a liquid crystal panel, and 
therefore even a liquid crystal TV set having a large screen may be 
produced in compact form. 
Further, the fact that the operating unit may be arranged in the space 
between the top case and the shield case prevents the TV set from 
thickening. 
Furthermore, since the operating unit is located in the same plane as the 
screen, high visibility, pressing ease and stable operation are assured at 
the same time. 
If the operating unit is arranged on other than the liquid crystal panel as 
in the conventional liquid crystal TV sets, the area occupied by the 
operating unit would increase with the size of the liquid crystal panel 
due to the fact that the liquid crystal TV set is usually rectangular in 
shape requiring a side of the operating unit equal in size to one side of 
the liquid crystal panel. Specifically, as shown in FIG. 7, a 3-inch 
liquid crystal panel would require an operating unit of the size A; a 
5-inch liquid crystal panel, the size A+B; and a 7-inch liquid crystal 
panel, the size A+B+C. According to the present invention, in contrast, 
the area of the operating unit remains substantially the same regardless 
of the size of the liquid crystal panel because the operating unit is 
arranged along the peripheral portion of the liquid crystal panel.