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Description  |
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BACKGROUND OF THE INVENTION
This invention relates to liquid crystal display (LCD) devices and means
for receiving data from a human operator, such as keyboards, and more
particularly to a liquid crystal display device which may be used for
receiving information from a human operator as well as displaying
information.
LCD's are very well known in the art and are frequently used as display
devices for displaying information outputted from a calculator, a watch,
appliances, or other electronic apparatus. The LCD devices have undergone
considerable improvement in the last several years and are presently used
in many applications; LCD's are particularly well suited for use with
portable, battery-powered electronic apparatuses, such as calculators and
watches, because LCD's require very little power to display information in
these battery-powered apparatuses. It should be appreciated, however, that
the instant invention may be used, if desired, in any application using
LCD's to display information.
The electronic appliances and apparatuses which utilize LCD's often
frequently include a keyboard, that is, an array of key switches or push
buttons, or other types of electrical switches and contacts to input
information to the appliance or apparatus. In the embodiment of a
calculator, for example, the keyboard may include ten numeral keys, a
decimal point key, and five or more function keys (plus, minus, multiply,
divide and equals). Further, those familiar with the calculator art will
realize that as the complexity of the calculator increases, the number of
functions which the calculator may accomplish likewise increases. Of
course, given the small size of these hand-held calculators and the size
of the human finger, there is a practical limit on the number of keys
which may be provided on a calculator or other such electronic device to
access the functions which it may perform. Of course, other small
appliances may benefit from having additional keys. Additionally, having
the capability to program the functions which the keys perform can greatly
increase the flexibility of the calculator or other appliances.
It was therefore, one object of this invention that a combination display
device and keyboard device be provided for an electronic calculator or
other electronic apparatus. It was another object of this invention that a
liquid crystal display device be adapted for receiving inputs from a human
operator in addition to displaying information to the human operator. It
was yet another object that the number of keys presented to the operator
be selectable. It was still yet another object that the legends associated
with the keys be selectable.
The foregoing objects are achieved as is now described. A LCD device having
a rear substrate, a transparent front plate, a plurality of segments
formed on the substrate and on the plate, and a liquid crystal material
disposed between the substrate and plate is provided with a plate which
will deflect toward the substrate in response to the application of
pressure by a human operator. The segments of the LCD device are actuated
by conventional means to output information to the operator. This
information will include selected segments which are actuated to define
one or more regions on the device where the operator may depress the front
plate to input information to the apparatus to which the LCD is coupled.
The segments in these one or more regions are sensed for a change in
capacitance between the segments mounted upon the substrate and the
segments mounted upon the front plate within these regions. The change in
capacitance occurs when the operator depresses the cover thereby
increasing the capacitance imposed by the liquid crystal material between
opposing segments. By appropriating energizing and sensing the segments of
the LCD device, the number of regions (that is, the number of keys) is
selectable as are the legends displayed in conjunction with these regions.
BRIEF DESCRIPTION OF THE FIGURES
The novel features believed characteristic of the invention are set forth
in the appended claims. The invention itself, however, as well as further
objects and advantages thereof, will be best understood by reference to
the following detailed description of an illustrative embodiment, when
read in conjunction with the drawings, wherein:
FIGS. 1 and 2 are plan views of a calculator embodying the present
invention;
FIG. 3a is a top plan view of a portion of a liquid crystal display (LCD)
device;
FIG. 3b is a side sectional view of an LCD display during its normal mode
of operation;
FIG. 3c is a side sectional view of an LCD display which is being depressed
by a human operator;
FIG. 4 is a block diagram of the LCD drive and impedance sensing circuits
and the LCD display device;
FIG. 5 is a block diagram of an impedance comparison circuit; and
FIG. 6 is a simplified schematic diagram of a LCD device utilizing a
silicon substrate.
DETAILED DESCRIPTION
Referring now to FIG. 1, there is shown an electronic calculator or
computer which utilizes the present invention. The electronic calculator
or computer is housed in a housing 1 which includes a liquid crystal
display device 2. In this embodiment, display device 2 has a surface area
nearly as large as the top portion of housing 1. Those skilled in the art
will recognize that LCD device 2 shown in FIG. 1 is generally larger than
that which is commonly available. However, while larger and larger area
LCD devices are becoming commercially available, those skilled in the art
will also recognize that the present invention may be utilized with any
size of LCD display device. The present invention is particularly useful,
however, for use with LCD devices having an area larger than, for
instance, the area of a keyboard having ten to fifty or more push buttons
when the present invention is used with a calculator or a computer, for
instance. In the embodiment of a calculator or computer, the LCD device is
preferably at least as large as a keyboard having ten or more keys since,
as will be seen, the LCD device serves as a keyboard in addition to
serving as a display.
It must be appreciated, moreover, that the present invention is here
illustrated in conjunction with a calculator/computer for purposes of
illustration only. The LCD display systems employing the present invention
may be used in many other applications, including telephones, televisions
and other communication equipment, kitchen appliances, such as microwave
oven, and a wealth of other applications.
In FIG. 1, LCD display 2 is shown with information being displayed thereat
at reference A and additional information being displayed at reference B.
Additionally, at reference numeral B, selected areas of LCD display 2 are
sensitized to the touch by a human operator for inputting information. In
this particular embodiment, the calculator or computer is shown somewhere
in the middle of an income tax program wherein the operator's taxable
income has just been computed and is being displayed in the reference A
portion of the display. In addition, the reference A portion displays a
legend calling for the inputting of the number of dependents being claimed
by the taxpayer. In the reference B portion of LCD display 2, there is
being displayed a representation of a ten digit keyboard with an "enter"
key. At this point the operator is being instructed to input the number of
dependents (including self), and the operator will respond by depressing
LCD display 2 at the appropriate numerals and at the "enter" legend. As
will be seen, depressing display 2 causes a change in the capacitance
between opposing segments of the display 2. This permits the sensing of
the change in capacitance between selected segments of the display (1) to
indicate whether or not the operator is inputting information at the LCD
display 2 and (2) if the operator is inputting information, to identify
the inputted information.
It is to be appreciated, of course, that the calculator or computer may be
provided with any one of a number of different programs or may include
hard-wired, predetermined functions. Also, as will be seen, the particular
areas which are sensitized to the touch of a human operator may be
selected, as desired, thereby permitting any desired figuration of a
keyboard or data inputting device, the configuration merely being limited
by size and design of the LCD display 2. Additionally, the legends used in
conjunction with the keys may be altered, that is modified while the
calculator or computer is being used.
Assuming, for the time, that the computer or calculator does include the
aformentioned income tax program and assuming the operator depresses the
numeral "4" and then the "enter" legend when the LCD was showing the
display of FIG. 1, the calculator or computer is preferably designed or
programmed to respond by showing a display such as that shown in FIG. 2,
for instance.
Referring now to FIG. 2, there is again shown the calculator or computer of
FIG. 1, but at the next display sequence in the income tax program. Now
the number of dependents is being shown. If the human operator made an
error in entering the number of dependents, he or she is given the
opportunity to depress a selected portion of the display (at reference C)
causing the calculator or computer to give the operator another
opportunity to input the number of correct dependents, by reverting to the
display shown in FIG. 1, for instance. Assuming the correct number of
dependents has been inputted, the operator is next asked in this
embodiment whether or not the operator or his or her spouse is either
blind or over 65, which, of course, under present income tax laws, affects
the amount of tax owed.
As can be easily seen by comparing FIG. 1 and FIG. 2, the keyboard areas,
that is, the areas of the LCD which respond to depressions thereof by the
operator of the device may be selectively altered. Thus, any given area of
the display may preferably be used to output data or information at one
time and to receive data at some other time. The foregoing income tax
program demonstration shows the tremendous flexibility which results from
use of the instant invention thereby permitting different portions of LCD
device 2 to serve as a data inputting device at different times in a
program. Of course, the disclosed LCD device may be used with other
programs and in other types of equipment, as well as that described here.
Referring now to FIGS. 3a-3b, there are shown a top plan view and a side
sectional view of a conventional LCD device. In the side sectional view of
FIG. 3b, the LCD display includes a rear substrate 10 and a front
substrate 11 with a liquid crystal material 12 being sandwiched
therebetween. The liquid crystal material 12 is sealed in the space
between substrates 10 and 11 by conventional sealing means, not shown here
for simplicity's sake. Protuberances 13 on front substrate 11 may be used,
if desired, to help assure a proper spacing between the front and rear
substrates is maintained. In FIG. 3a, two different arrangements of
character forming electrodes are shown at references A and B. At reference
A, there is shown the well known sixteen segment "British Flag"
arrangement of segments while at reference B there is shown a 5.times.7
dot matrix of segments. Of course, for each of strobing the LCD, usually
only one such arrangement (or some other arrangement) repeats itself over
the area of the LCD. However, different arrangements could of course be
used in the same LCD at the same time, if desired. Other arrangements of
the character forming electrodes are either known or will be readily
apparent to those skilled in the art.
The character forming segments are typically disposed on either one or both
of the substrates 10 and 11 on the side thereof which contacts liquid
display material 12. The segments may be formed either on both substrates
10 and 11 or alternatively one of the substrates 10 or 11 in which case a
common electrode is then disposed on the other substrate. A display
arrangement showing segmented electrodes on both substrates is shown in
U.S. patent application Ser. No. 799,807 filed May 23, 1977 and an
arrangement showing segmented electrodes on one substrate and a common
electrode on the other substrate is shown in U.S. Pat. No. 4,005,403. The
character forming segments are preferably formed by depositing a
transparent conductor, such as tin oxide, on the surface of the substrates
10 and 11.
In the embodiment shown in FIGS. 3a-3b, substrate 11 is the substrate
through which the operator views the segments which are being actuated.
Thus, substrate 11 is preferably formed of glass or other transparent
material. Substrate 10 may or may not be formed of a light transmissive
material but generally is provided with a reflective surface at either the
front or rear side thereof which reflects light back through substrate 11.
Not shown in FIGS. 3b and 3c, for sake of clarity, are polarizers which
may be used when the liquid crystal material 12 is of the twisted nematic
type. The spacing between substrates 10 and 11 is generally closely
maintained in the LCD art to assure proper actuation of the display. The
separation between the substrates depends upon the particular liquid
crystal material utilized and the voltage levels used to strobe the
segment electrodes; however, separations on the order of 5 to 10 microns
are known and actuation voltages as low as three to four volts are known.
Various direct and multiplexed drive schemes are known for actuating the
display. Exemplary drive schemes are described in U.S. patent application
Ser. No. 799,807, filed May 23, 1977. As is well known to those in the
art, coupling appropriate voltage potentials to appropriate opposing
segments (on substrates 10 and 11) sets up electrical fields between these
segments which induce a change in the liquid crystal material, which
change is manifested by a change in display contrast levels at these
segments.
In FIG. 3c, there is shown a portion of a human finger at reference C
depressing a portion of substrate 11 toward substrate 10. As
aforementioned, character forming segments are formed on one or both of
the inside surfaces of substrates 10 and 11 facing liquid crystal material
12. As can be seen from FIG. 3c, in the area which the operator's finger
applies pressure to substrate 11, the spacing between substrates 10 and 11
decreases, because substrate 11 has sufficient flexibility to deflect
under the slight pressure applied by a human to a typical key-board. I
have found that using glass having a thickness on the order of 10 mils
provides excellent flexibility and thus excellent results. However, it
should be apparent to those skilled in the art that other flexible
materials, such as many plastics, also exhibit sufficient flexibility to
permit substrate 11 to deflect toward substrate 10 upon the application of
a small amount of pressure by a human operator. The amount of deflection
is exaggerated in FIG. 3c for ease of illustration. As long as the
deflection reduces the spacing between the front and rear substrate by 10
to 20 percent, the impedance measuring circuit can easily detect the
depression. Thus, assuming a normal spacing of 10 microns, the thin
flexible substrate need only locally deflect 1 to 2 microns.
Preferably, rear substrate 10 is sufficiently rigid so that it does not
deflect in parallel with front substrate 11 when the human operator
depresses the front substrate. This may be accomplished by (1) appropriate
choice of materials (2) using a thicker rear substrate or (3) supporting
rear substrate 10 (for instance, a portion of calculator case 1 could be
used, if desired, to support rear substrate 10).
Those skilled in the art will appreciate that an LCD device performs better
if the spacing between substrates 10 and 11 remains essentially constant
during normal operations. This may be accomplished, for example, by the
addition of protuberances 13 from one of the substrates (here shown from
substrate 11). It has been found that such protuberances (which have an
essentially uniform height) help to assure that the normal spacing between
substrates 10 and 11 remains essentially constant and thus the spacing
between the electrodes formed on substrate 11 and the electrodes formed on
substrate 10 likewise remains essentially constant during normal
operation. However, in the area in which the operator's finger causes
deflection of substrate 11 toward substrate 10, the spacing between the
segments formed on substrate 11 and the segments formed on substrate 10 is
decreased. Thus, the spacing between adjacent protuberances 13 (if used)
is preferably selected to permit localized deflection of substrate 10
under the application of pressure by a human's finger. In the embodiment
shown in FIGS. 3a and 3c, the protuberances 13 have been located between
adjacent character positions. The decrease in spacing between opposing
segment electrodes may be measured in external LCD drive circuits by
sensing the impedance of the liquid crystal material. I have found that
the mechanical motion of depressing substrate 11 will compress the liquid
crystal material and, in general, cause a reorientation of the liquid
crystal material at the point of contact. The reduced spacing causes the
aforementioned impedance change, which may be detected by the computer,
calculator or other appliance or circuit used to drive the LCD device. LCD
drive and impedence sensing circuits 14 are shown interconnected with LCD
device to via bus 15 in FIG. 4.
I have previously mentioned that the impedance between opposing segments
changes with depression of substrate 11 by the operator's finger, which
change in impedance may be measured by impedance sensing circuits coupled
to LCD device 2. Referring now to FIG. 5, there is shown, in block diagram
form, an impedance comparison circuit 18 which is coupled to opposing
segments 16 and 17 formed on substrates 10 and 11, respectively. As can be
seen, segments 16 and 17 are more closely spaced at reference A than they
are at either reference B or reference C. The narrow spacing occurs (at
reference A) in response to the depression of substrate 11 by the human
operator whereas the wider spacing at references B and C is the normal
spacing in the areas of an LCD display which are not being depressed by a
human operator. The opposing segments at references A and B represent two
of the opposing segments on the front and rear substrates of the LCD
device of FIG. 3a. Of course, the LCD device has 35 segments per character
position (assuming 5.times.7 dot matrices are used--for instance) and a
plurality of character positions. Therefore, the impedance comparison
circuit 18 is preferably selectively coupled to a plurality of similar
opposing segment pairs such as those depicted at references A and B. Only
two such opposing segment pairs are shown at references A and B, merely
for sake of clarity. The opposing segment pair at reference C is
preferably a standard cell in the area of the display which preferably is
not or cannot be depressed, thereby permitting the impedence comparison
circuit to selectively compare first cell A with cell C and then cell B
with cell C and so forth for the various cells of the LCD display. Of
course, the comparison could also be made against a capacitance of
predetermined value. A specific impedance comparison circuit is not shown
here; however, such should be well within the skill of a person skilled in
the art of driving LCD devices. Of course, it is the matter of design
choice whether those practicing the present invention decide to test the
impedance of one, some or all of the opposing segment pairs making up a
character position to be tested for the inputting of data. This occurs
because the character electrodes position formed by a set of segments,
such as those shown at references A or B in FIG. 3a, are conventionally on
the order of the size of the tip of a human finger; thus, it is not
necessary to test, in most embodiments, all of the cells formed by
opposing segments in the area of the display to be tested, with the
aforementioned reference cell. Furthermore, certain cells or opposing
segment pairs in the area to be tested with the reference cell may be
actuated for the display of information. This occurs, for example, in the
keyboard area of FIG. 1 where the numerals are being displayed by
appropriate actuation of selected segments. The dielectric constant of the
liquid crystal material changes by a factor of two or so with actuation,
therefore, it is preferable that the cells which are selected for
comparison with the reference cell be unactuated cells (assuming, of
course that the reference cell is likewise unactuated, however, if the
reference cell were being actuated, then the comparison would preferably
be made with actuated cells). This may be easily accomplished as will now
be explained.
Assuming that the display utilizes a plurality 5.times.7 dot matrices, and
assuming that the dots aligned in columns on one substrate are connected
in common and assuming that the dots arranged in rows on the other
substrate are similarly connected in common, selected cells of the display
may be actuated by appropriately strobing the rows of cells on one
substrate and, at the same time, strobing selected columns of cells on the
other substrate. This results in a 1/7th duty cycle for each actuated
cell. Of course, the selective strobing of the columns of cells is
preferably controlled by a thirty-five bit code stored for each possible
character in a character ROM, such as ROM 20 in FIG. 6. The thirty-five
bit code for each displayable character will typically include a series of
ones and zeroes indicating whether or not the thirty-five cells in any
given 5.times.7 dot matrix LCD character position are to be actuated.
Thus, the selection of unactuated (or actuated) cells for comparison with
the reference cell may be easily accomplished by examining the thirty-five
bit code for each character position to be sensed.
It will also be appreciated by those skilled in the art, that using a
5.times.7 dot matrix strobed as aforementioned, yields a character
position requiring twelve conductors (five column conductors and seven row
conductors). Each additional character position, of course, requires five
additional conductors for the five columns of cells in each character
position, assuming the column conductors are connected in common for
similarly situated columns of dots in each character position. Thus, if
the entire LCD device has, for purposes of illustration, two hundred
character positions, then more than one thousand conductors would
typically be used in bus 15 to interconnect the LCD drive and sensing
circuits with LCD display 2. One way of reducing this large number of
interconnections is by incorporating a data memory, drivers and the
impedance test circuit 18 onto the same substrate 10 on which LCD device 2
is formed. This may be accomplished, for example, if LCD device 2 utilizes
a silicon substrate 10, such as that which is described in U.S. Pat. No.
3,765,747, by J. M. Pankrantz and K. E. Bean which issued Oct. 16, 1973.
U.S. Pat. No. 3,765,747 is hereby incorporated herein by reference. Then,
the aforementioned memory, drivers and impedance test circuit may be
integrated into the same silicon substrate if desired.
Referring now to FIG. 6, there is a shown a simplified schematic diagram of
such an LCD device and strobing circuitry. Here, the data is applied to a
35.times.64 bit ROM 20 which stores up to sixty-four different 35 bit
character codes (of course, the number of different characters is a design
choice, just as the number of bits used to represent each character is a
design choice). The 35 bits for each character code is shown here being
supplied in parallel (although either a serial arrangement or integrating
ROM 20 on the aforementioned silicon substrate may be used to further
reduce interconnect) for loading into the data memory or latches at a
location defined by a character position address on bus 21 and under
control of a load control line 22. The display is actuated by a signal on
line 23 enabling the data memory to drive the drivers which in turn strobe
the cells in displaying that which is stored in the memory. Thereafter,
addresses may be applied on lines 21 in combination with a keyboard strobe
on line 24 to test for depression of the display at the character position
specified by the address on bus 21. The results of the test would be
indicated by a key-down signal, for example, on line 25 in this
embodiment. As can be clearly seen, the number of conductors needed to
interconnect the microprocessor device or other data processing device
with LCD display 2 has been significantly reduced.
Having described my invention in connection with several embodiments
thereof, other embodiments will be readily apparent to those skilled in
the art. It is intended that my invention is not to be limited to the
embodiments described except as specifically set forth in the appended
claims.
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