Computer graphics processing and selective visual display system – Display peripheral interface input device – Touch panel
Reexamination Certificate
1999-08-17
2001-05-29
Shankar, Vijay (Department: 2673)
Computer graphics processing and selective visual display system
Display peripheral interface input device
Touch panel
C178S018010, C178S018030, C178S018060
Reexamination Certificate
active
06239790
ABSTRACT:
TECHNICAL FIELD
The present invention relates generally to object position sensing transducers and systems and, more particularly, to semiconductive touchpads.
BACKGROUND ART
Numerous devices are available as object position detectors for use in computer systems and other applications. The most familiar of such devices is the computer mouse. While extremely popular as a position indicating device, a mouse has mechanical pans and requires a surface upon which to roll its position ball. The mouse translates movement of the position ball across the rolling surface as input to a computer. The growing popularity of laptop or notebook computers has created a significant problem for mouse type technologies which require a rolling surface. Laptop computers are inherently portable and designed for use in small confined areas such as, for example, airplanes, where there is insufficient room for a rolling surface. Adding to the problem is that a mouse usually needs to be moved over long distances for reasonable resolution. Finally, a mouse requires the user to lift a hand from the keyboard to make the cursor movement, thereby upsetting the prime purpose, which is usually typing on the computer.
As a result of the proliferation of laptop computers and the standardization of the Windows operating environment, a need for a reliable, portable, and integrated form of mouse control has arisen. To satisfy this need, mechanical ball or shaft rolling technologies, such as, for example, track balls have been designed for use with laptop computers. A track ball is similar to a mouse. A major difference, however is that, unlike a mouse, a track ball does not require a rolling surface. Track balls first appeared as clip-on attachments for laptop computers and then later were integrated within laptop computers.
A track ball is large in size and does not fit well in a volume-sensitive application such as a laptop computer. Furthermore, a track ball is quite cumbersome because it requires practiced dexterity by the user as he or she interacts with the device. Finally, a track ball is not durable and is easily subjected to contamination from environmental factors such as dirt, grease, and the like.
A. Cursor Control with Touchpads
Touchpads are pointing devices used for inputting coordinate data to computers and computer-controlled devices. A touchpad is typically a bounded plane capable of detecting localized pressure on its surface. A touchpad may be integrated within a computer or be a separate portable unit connected to a computer like a mouse. When a user touches the touchpad with a finger, stylus, or the like, the circuitry associated with the touchpad determines and reports to the attached computer the coordinates or the position of the location touched. Thus, touchpads may be used like a mouse as a position indicator for computer cursor control. Several types of touchpads are known in the art such as capacitive and resistive touchpads.
1. Capacitive Touchpads
Capacitive touchpads react to a capacitive coupling between an object placed near or on the surface of the touchpad and capacitors formed within the touchpad. For instance, U.S. Pat. No. 5,374,787 issued to Miller et al. and assigned to Synaptics, Inc., discloses a capacitive touchpad having two thin layers of electrically conductive lines or traces. A first set of traces runs in a first direction and is insulated by a dielectric insulator from a second set of traces running in a second direction generally perpendicular to the first direction. The two sets of traces are arranged in a crosswise grid pattern. The grid formed by the traces creates an array of capacitors that can store an electrical charge.
When a conductive object such as a finger or a metal stylus approaches or touches the touchpad, the capacitance of the capacitors are altered due to capacitive coupling between the object and the capacitors. The degree of alteration depends on the position of the object with respect to the traces. As a result, the location of the object in relation to the touchpad can be determined and monitored as the object moves across the touchpad.
Similarly, U.S. Pat. No. 3,921,166 issued to Volpe discloses a capartive matrix or grid in which an object such as a finger changes the transcapacitance between row and column electrodes.
Another variation of the capacitive touchpad is shown in U.S. Pat. No. 4,550,221 issued to Mabusth. The Mabusth patent discloses a capacitive touchpad having a substrate that supports first and second interleaved, closely spaced, non-overlapping conducting plates. The plates are aligned in rows and columns so that edges of each plate of an array are proximate to, but spaced apart from, the edges of plates of the other array. The first and second arrays are periodically connected in a multiplexed fashion to a capacitance measuring circuit which measures the change in capacitance in the arrays. In effect, the Mabusth patent discloses a grid of pixels which are capacitively coupled.
Capacitive touchpads suffer from many disadvantages. First, they are extremely sensitive to moisture contamination. As an object such as a finger moves over the touchpad, the moisture present in the skin disturbs the capacitor grid and measurements made from the disturbance determines the position of the finger. The operation of capacitive touchpads is, therefore, easily compromised in moist or damp environments or by perspiration of the user. In short, with moisture, capacitive touchpads become confused and lose their sensitivity.
Second, capacitive touchpads demand a constant power supply, offering no sleep mode option. Most capacitive touchpads draw a constant electrical current of 2.5 to 10 milliamps whether or not they are in use. With laptops, cordless keyboards, and even hand-held remote controls, battery life is a major concern. A touchpad that demands constant power is a major liability.
Third, capacitive touchpads are prone to inadvertent cursor positioning because they sense an object as it gets near their surface. This is problematic for the user because if the touchpad is installed near where the thumbs of the user naturally rest while typing, an inadvertent thumb simply moving over and above the touchpad can cause a false click and an unintended change in the cursor position. This can result in repeated, accidental repositioning of the cursor and high levels of user frustration. The user may also experience fatigue and extreme discomfort from intentionally holding his thumbs or fingers away from the touchpad to avoid false clicks.
Fourth, the electronic circuitry of capacitive touchpads is complex and expensive. Capacitive touchpads use a microprocessor for communicating with a computer. Between the touchpad and the microprocessor, electronic circuitry such as a semi-custom or fully-custom mixed signal gate array incorporating both analog and digital sections is provided. The cost of this circuitry is significant and, in most cases, higher than the cost of the microprocessor.
Fifth, capacitive touchpads indirectly measure the amount of applied pressure by measuring the surface area of the object applying the pressure. For instance, a capacitive touchpad measures the area of contact between a finger and the touchpad. Once that area is measured, relative pressure is determined by the change in the area over time. Illustratively, as a user pushes harder with his finger, more area is in contact and the touchpad estimates a greater pressure. Obviously, for applications such as signature capture, pressure-controlled scrolling and acceleration, 3D control, and the like, measuring the contact area to estimate the pressure is greatly inferior to measuring the actual pressure directly.
2. Resistive Touchpads
U.S. Pat. No. 5,521,336 issued to Buchanan et al. discloses a typical resistive touchpad. The disclosed resistive touchpad is a shunt mode device where electrons flow between interdigitating conductive traces when the traces are pressed together. A voltage potential between the interdigitating traces causes electrical current to flow through
Martinelli John K.
Martinelli Robert M.
Pickett Mark C.
Ritchey Wendell W.
Yaniger Stuart J.
Brooks & Kushman P.C.
Interlink Electronics
Shankar Vijay
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