U.S. patent number 3,719,849 [Application Number 05/183,491] was granted by the patent office on 1973-03-06 for solid state displays.
This patent grant is currently assigned to Hewlett-Packard Company. Invention is credited to Robert L. Steward.
United States Patent |
3,719,849 |
Steward |
March 6, 1973 |
SOLID STATE DISPLAYS
Abstract
A decimal point element is located within the boundaries of the
charaCter element on a monolithic solid state character chip. When
a character string is displayed, only the decimal point is
energized on one character chip. This results in wide separation
between the decimal point and its nearby characters Hence
readability of the decimal point in improved in long character
strings.
Inventors: |
Steward; Robert L. (San Jose,
CA) |
Assignee: |
Hewlett-Packard Company (Palo
Alto, CA)
|
Family
ID: |
22673017 |
Appl.
No.: |
05/183,491 |
Filed: |
September 24, 1971 |
Current U.S.
Class: |
313/500; 257/92;
345/34 |
Current CPC
Class: |
H01L
27/15 (20130101); H01L 33/00 (20130101); G09F
9/33 (20130101) |
Current International
Class: |
G09F
9/33 (20060101); H01L 27/15 (20060101); H01L
33/00 (20060101); H01j 007/42 () |
Field of
Search: |
;313/109.5,18D
;340/324,336,343 ;235/64.3,60.15 ;315/169 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Kominski; John
Claims
I claim:
1. Visual display apparatus comprising:
a plurality of numeric display means disposed in lineal array to
display a plurality of adjacent digits;
the display means being substantially similar and each including
regions which emit light in response to applied excitation and
which are arranged in a seven-segment font; and
in each of said display means, an additional region which emits
light in response to applied excitation and which is located within
the periphery of the surrounding regions for displaying a decimal
point when excited in lieu of a digit in the digit place occupied
by the associated display means.
2. A display chip as in claim 1 wherein the decimal point is
located within the lower area of the font bounded by said regions.
Description
BACKGROUND AND SUMMARY OF THE INVENTION
The readability of a decimal point in a string of characters
depends on the relative position of the decimal point to its nearby
characters. In long character strings, for example, it may be
difficult to quickly determine the exact location of the decimal
point because it blends into the character string and becomes
"lost" in the maze of characters. To remedy this, a decimal point
is usually displayed well below the lowest portion of the
characters. This distance below the character is often one-fifth
the character height.
Positioning the decimal point below the characters sometimes
increases the manufacturing cost of a display. If a character is
formed from a single piece or chip of material, as in monolithic
displays, either the chip size must be increased to accommodate
both the character and the decimal point, or a special process must
be used to provide a separate smaller decimal point chip. Either
method increases the product cost.
The present invention locates the decimal point in the lower half
of the character font. When a character string is displayed, one
character position is dedicated to the decimal point. Thus,
readability of long character strings is improved because the
decimal point is well separated from its nearby characters.
The solid state displays using the monolithic process, this
invention locates both a character and a decimal point in some or
all of the display chips. When a character string is displayed,
either the decimal point or a selected character is energized in
each chip. Thus the same size chip is used to display a character
or a decimal point. This eliminates the extra process needed to
make a special decimal point chip. Since the decimal point is
located within the character boundaries in a chip, a larger chip is
not needed to accommodate the decimal point. As a result of this
invention, the product cost of solid state displays for medium to
long character strings can be decreased.
DESCRIPTION OF THE DRAWINGS
FIG. 1 shows a side view of a light-emitting diode made according
to the art.
FIGS. 2 and 3 show conventional methods of incorporating a decimal
point in monolithic displays.
FIG. 4 shows a perspective view of an improved monolithic character
chip made according to the preferred embodiment of this
invention.
FIG. 5 shows a character string using conventional decimal point
placement.
FIG. 6 shows the same character string as shown in FIG. 5, but with
the improved decimal point placement of this invention instead of
the conventional placement.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring to FIG. 1, a light-emitting diode, well-known in the art,
is made from a material that emits photons when minority and
majority carriers recombine. Such a material is gallium arsenide
phosphide. To make a light-emitting diode, an n-type alloy of
gallium arsenide phosphide 7 is grown epitaxially on a gallium
arsenide sustrate 3. A p region 5 is then created by diffusing a
charged material, such as p-type zinc, into the chip. This region
is capped with a metal contact 1. The contact provides the anode
terminal for the diode while the substrate contact 4 acts as the
cathode terminal.
When a forward bias is applied to the diode, the potential barrier
at the p-n junction is reduced so current can flow. Just as in the
operation of a standard diode, electrons are injected into the p
region and holes are injected into the n region. However, when
these minority carriers recombine with the majority carriers,
energy is given off as photons. Some of these photons are emitted
from the surface of the doped gallium arsenide phosphide. Thus the
diode emits light in response to forward bias voltage.
The light-emitting regions can be selectively arranged in a
monolithic chip by the positioning of the diffused p regions. In
this manner, chips can be constructed to provide numeric and
alphanumeric displays. To provide a numeric display chip, a
plurality of light-emitting regions are sometimes arranged in the
shape of a rectangular or rhomboidal figure eight. (See FIGS. 2-6.)
By forward biasing only selected regions, any digit from 0 to 9 can
be displayed. This type of display is commonly called a
seven-segment font because the figure eight is usually made by
seven linear regions. Sometimes small dot-like light-emitting
regions are aligned to form the seven segment font.
A problem with this type of font is decimal point location. To
maintain readability of a decimal point in a string of characters,
the decimal point is often located below the bottom of the
character string. In conventional monolithic displays, either the
chip size must be increased to accommodate both the character and
the decimal point, as shown in FIG. 2, or a separate smaller chip
must be made for the decimal point, FIG. 3. Either process
increases the cost of a display.
Referring now to FIG. 4, eight diffused regions 11 are positioned
to form a seven-segment display and a decimal point. The decimal
point is located within the lower half of the character font to
keep the chip the same size as a conventional seven-segment display
chip without a decimal point. Since the decimal point is contained
in the character chip, no additional process is needed to
manufacture a special decimal point chip.
This improved decimal point placement improves the readability of
long character strings. As shown in FIG. 5, the readability of a
decimal point in a character string using conventional decimal
point positioning depends primarily on the vertical separation
between the decimal point and the character string. In the improved
positioning, as shown in FIG. 6, the readability is increased by
greater horizontal spacing between the decimal point and its nearby
characters. One character position is dedicated to the decimal
point in a string of characters. This invention does require an
extra character position to display the decimal point, but the cost
of this extra position is less than the extra chip area or assembly
time required by conventional displays when used in displays of
more than seven characters.
* * * * *