Patent Application
20130093605
The present invention relates to a signal generation circuit for a keyboard and particularly to a keyboard signal generation circuit with conductive lines doped with carbon powder to change impedance thereof.
Keyboard is one of important tools for communication between input signals and a computer. How to design circuits in the keyboard to mate the computer is a critical factor in keyboard quality. Most conventional circuits under the keys are laid according to a standard keyboard protocol. The keyboard protocol is arranged in series, and each key of the keyboard corresponds to a specific code except the composite keys such as Shift, Ctrl, and Alt. For instance, R.O.C. patent No. 1320939 entitled “Keyboard for eliminating ghost keys” provides a keyboard circuit as shown in its
However, testing the keyboard made according to a set matrix circuit shows that a conflicting phenomenon could still happen even if all elements and wiring of the keyboard are in normal conditions. For instance, when a key is depressed after depressing of another key, the system merely issues the signal of the last key being depressed rather than the signals of the two keys at the same time. This is because the key codes are mutually exclusive. The signal of the previous key is masked without being restored.
There is another phenomenon that when two keys at the corners of the matrix circuit of the keyboard are depressed at the same time, and another key is then depressed, the microprocessor cannot accurately judge the signal of the last depressed key, thus such a phenomenon is commonly called a ghost key. This could cause the problem of missing characters for users who press keys fast. Moreover, as game players often have to press a plurality of keys simultaneously to generate composite key signals to execute different game tactics, the phenomenon of ghost key generated by the keyboard hinders smooth playing of the game.
In order to solve the problem of ghost key that cannot display an effective signal without user's awareness, R.O.C. patent 486661 entitled “Input device with keys defined by multi-dimensional electrodes and coding method thereof” provides a technique to check whether a ghost key (or phantom key) has been depressed, and send back an error signal. Each key is defined by N-dimensional electrodes, where N is an integer greater than 2. It also provides a key scanning method by scanning each dimensional electrode and recording its positional data for comparison to identify the depressed key. Its technique requires alterations of electrodes and scanning process that result in more complex structure. An exclusive signal control IC has to be made for the keyboard, but its production cost is higher. Moreover, the control IC cannot be commonly shared with other keyboards.
In view of the number and functions of keys of the keyboard increase constantly, the difficulty and complexity for improving the phenomenon of ghost keys also grow. Moreover, changing the design of a signal control IC or scanning incurs higher cost, and the signal control IC cannot be commonly shared with other keyboards. All these increase the production cost.
Therefore, the primary object of the present invention is to provide a signal generation circuit for a keyboard which includes a plurality of keys and a signal generation circuit located beneath the keys. Each key is depressible onto the signal generation circuit to generate a matrix signal. The signal generation circuit includes a matrix circuit layer, an isolation layer located on the matrix circuit layer and a contact layer located on the isolation layer. The matrix circuit layer has a matrix circuit containing a plurality of signal terminals. The isolation layer is located on the matrix circuit layer and has a plurality of apertures corresponding to the signal terminals. The contact layer has at least one connecting circuit which includes a plurality of impedance terminals formed by mixing metal and carbon powder and a terminal line to form electric connection with the impedance terminals. The impedance terminals oppose to the signal terminals via the apertures and have varying impedances to allow the matrix circuit to generate different matrix signals upon contacting with the signal terminals.
By means of the signal terminals having varying impedances, when the signal terminals are contacted with the impedance terminals, different signals are generated. More specifically, the impedance terminals are respectively formed by mixing a silver compound and carbon powder. The carbon powder can significantly increase the impedance to intensify the electric signal being generated, therefore a greater difference is formed between varying key signals to avoid misinterpretation or generation of ghost keys. Moreover, forming and printing the impedance terminals on the circuit board by adding the carbon powder do not significantly increase the production cost. In addition, altering the composition of the impedance terminals does not need to change the design of the signal control IC, hence the technique of the invention is adaptable to various types of keyboards with the same signal control IC to save production cost.
The foregoing, as well as additional objects, features and advantages of the invention will be more readily apparent from the following detailed description, which proceeds with reference to the accompanying drawings.
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While the invention has been described by means of specific embodiments, numerous modifications and variations could be made thereto by those skilled in the art without departing from the scope and spirit of the invention set forth in the claims.
In summation of the above description, the present invention provides a significant improvement over the conventional techniques and complies with the patent application requirements, and is submitted for review and granting of the commensurate patent rights.
