Coded data generation or conversion – Bodily actuated code generator – Including keyboard or keypad
Reexamination Certificate
2000-05-19
2003-06-10
Horabik, Michael (Department: 2635)
Coded data generation or conversion
Bodily actuated code generator
Including keyboard or keypad
C345S178000, C379S368000, C341S034000
Reexamination Certificate
active
06577250
ABSTRACT:
TECHNICAL FIELD
The present invention relates generally to keypad or keyboard data input devices (collectively referred to herein as “keyboards”) used with general purpose computers and in a wide variety of application specific electronic devices. The invention has particularly useful application in connection with keyboards, e.g., computer keyboards, employing printed membrane switch structures.
BACKGROUND OF THE INVENTION
To a large extent, the computer industry has settled on using a n(row)×m(column) matrix of sense lines/drive lines for carrying out keyboard key switch discrimination. Such a matrix provides a means for an integrated circuit (IC) micro-controller device to decode n×m keys (e.g. 8×17=136 keyboard keys), with n+m electrical interface pins (e.g. 8+17=25 pins). The micro-controller device sequentially drives a voltage on a plurality of drive lines of the matrix. Keyboard key depression will effect a closure of an associated switch creating an electrical connection between a particular drive line and one of a plurality of sense lines, with the result that the micro-controller device will detect this voltage on the sense line and determine therefrom a corresponding alphanumeric character or function.
Typically, a membrane switch structure is used to form the keyboard key switch matrix. Referring to
FIG. 1
, a conventional computer keyboard
1
may utilize a conventional membrane switch structure
3
, as shown in
FIG. 2
, which is installed underneath a set of keyboard keys
5
. Membrane switch structure
3
generally has three layers
7
,
9
and
11
. Outer layers
7
and
11
sandwich intermediate layer
9
. The three layers are generally made out of a thin insulative sheet of polyester (e.g., Mylar™) or other insulative material. Outer layers
7
and
11
each have, on their respective opposing inside surfaces
13
and
15
, switch circuit patterns (
17
and
19
, respectively) which may be printed (e.g., silk-screened).
Circuit patterns
17
and
19
are appropriately laid out to provide contact points and lines of conduction for each of keyboard keys
5
, within a conventional key switch matrix. The circuit patterns may be printed with suitable conductive inks, e.g., a polymer-based conductive ink having silver and/or carbon particles in suspension. Typically, each keyboard key
21
is coupled to a resilient or spring loaded plunger
23
positioned to make contact with a backside of upper outer layer
7
of membrane switch structure
3
. Depression of selected ones of keyboard keys
5
causes a corresponding plunger
23
to exert pressure on upper outer layer
7
. The resulting pressure causes a portion of electrical circuit
17
(e.g., a sense line) printed on the inner face of layer
7
to come resiliently into electrical contact with a portion of circuit
19
(e.g., a drive line) printed on the inner face of bottom outer membrane layer
11
. This contact occurs through contact apertures
23
(one shown) provided in intermediate layer
9
. The electrical contact allows passage of a drive signal on a particular sense line for input to an IC micro-controller device. By recognizing the sense line on which the signal is generated, and the timing of the appearance of the generated signal on the sense line, the IC can discriminate which of keyboard keys
5
has been depressed. The micro-controller device, in turn, provides a digital output signal readable by an associated computer.
FIG. 3
schematically illustrates a conventional arrangement of a computer keyboard switch circuit matrix
25
electrically connected with an IC die package
27
(typically mounted within the keyboard housing). In the conventional arrangement, a total of
17
drive lines
29
extend from IC die package
27
to corresponding drive lines
31
of switch circuit matrix
25
. Drive lines
31
are laid-out in intersecting relationship with a total of eight sense lines
33
. As previously described, and shown in
FIG. 2
, the drive lines are typically arranged on a first outer layer of a membrane switch structure, and the sense lines are typically arranged on a second outer layer of a membrane switch structure. This conventional arrangement requires IC die package
27
to accommodate a total of twenty-five (8+17=25) pin connections
35
spaced about the periphery of die package
27
, for the signal (drive and sense) lines alone. Additional pin connections (not shown) must also be provided, e.g., for V
cc
, Gnd, Osc, HostData and HostClk.
A silicon chip
37
centrally located within die package
27
contains IC logic (including the micro-controller device) for carrying out keyboard key discrimination and related functions. The logic circuitry integrated onto chip
37
is small relative to the available surface area of chip
37
and the high levels of integration attainable with available photolithographic IC fabrication techniques. A much smaller chip (and hence less silicon) could be utilized if it were not for the fact that a certain minimum size of chip
37
is required in order to accommodate pin connections
39
about the periphery of chip
37
. Also, the area of chip
37
is small relative to the overall size of die package
27
, due to the relatively large space requirements for making the pin connections
35
on the outer periphery of die package
27
, as well as pin connections
39
located around the periphery of chip
37
. But for the space required to accommodate the large number of required pin connections, the size of die package
27
could be reduced considerably, thus reducing the printed circuit board space required within the keyboard for accommodating die package
27
. In addition, a reduction in the number of pin connections would reduce the materials and manufacturing costs associated with making the required pin connections.
SUMMARY OF THE INVENTION
The invention provides, in a first aspect, a resistance based keyboard key discrimination system capable of reducing the number of required pin connections to an IC die package. The system includes a plurality of keyboard keys and a switch circuit which may take the form of a current divider circuit or a voltage divider circuit. A plurality of key switches are arranged in the switch circuit to be selectively closed by actuation of corresponding ones of the keyboard keys, and in parallel with each other along a resistive switch line. A voltage source is provided for applying a voltage to the switch line. An A/D converter (A/D) is arranged to sense a voltage in the switch circuit that varies, as a result of resistances in the switch line, in relation to which, if any, of the switches are closed. The A/D outputs a digital value indicative of an actuated keyboard key, for input to logic circuitry of an IC micro-controller.
The switch circuit may include a membrane switch structure with lines of conduction provided (e.g., by silk-screening) on a layer thereof Resistivities of the lines of conduction may be varied by varying one or more of the composition, thickness, width and length of the lines of conduction.
In a second aspect, the invention provides a method of performing keyboard key discrimination in a resistance based keyboard key discrimination system, including a plurality of keyboard keys and a switch circuit. The switch circuit includes a plurality of key switches arranged along a resistive switch line to be selectively closed by actuation of corresponding ones of the keyboard keys. In the method, a voltage is applied to the switch line. A voltage in the switch circuit varies, as a result of resistances in said switch line, in relation to which, if any, of said switches are closed. That voltage is sensed, and a value indicative of an actuated keyboard key is output.
The above and other features and advantages of the present invention will be readily apparent and fully understood from the following detailed description of preferred embodiments, taken in connection with the appended drawings.
REFERENCES:
patent: 3786497 (1974-01-01), Davis et al.
patent: 4015254 (1
Banner & Witcoff , Ltd.
Dang Hung Q
Horabik Michael
Microsoft Corporation
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