Keyboard Matrix Transition Circuit for Ghost-Free Key Detection
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Solution Overview
Problem
Conventional keyboard devices suffer from the 'ghosting' problem, where neighboring keys are erroneously detected as depressed due to the limited number of conductor lines in the keyboard matrix, leading to inaccurate key registration.
Innovation Solution
The keyboard device incorporates M driving circuits, N transition circuits, and a control module with M column and N row signal lines, using a scanning process to determine key depression by applying scan and un-scan voltages and utilizing transition circuits with BJTs to differentiate between depressed and undepressed keys, thereby preventing ghosting.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a conventional keyboard matrix with limited conductor lines is used, then the fabricating cost is reduced and assembling complexity is simplified, but the ghosting problem occurs where neighboring keys are erroneously detected as depressed
Solution Approach 1:
The scanning process is segmented into multiple scan cycles, with each cycle dedicating itself to scanning a specific column signal line. This temporal segmentation allows the system to isolate and accurately detect the state of each key unit individually, preventing the ghosting problem where multiple depressed keys cause erroneous detection. The control module sequentially activates one column at a time while maintaining the ability to detect all row states within that column's scan cycle.
Solution Approach 2:
Before detecting the state of key units in a particular column, the control module preliminarily sets the scan voltage level for the target column signal line and establishes the scanning sequence. This preliminary configuration ensures that when detection occurs, the electrical conditions are already optimized for accurate measurement, preventing ghosting by ensuring that only the intended column is actively being scanned at any given moment.
2Quantity of substance
If a conventional keyboard matrix with limited conductor lines is used, then the number of conductor lines is minimized, but the ghosting problem occurs leading to inaccurate key registration
Solution Approach 1:
The keyboard device employs periodic scanning action where the control module cycles through each column signal line in a predetermined sequence across multiple scan cycles. Each column is systematically activated and scanned at regular intervals, ensuring that all key units are periodically checked for their depressed state. This periodic scanning approach maintains reliable key registration with minimal conductor lines by efficiently reusing the same physical lines for different detection purposes at different time periods.
Solution Approach 2:
The scanning process operates continuously through repeated scan cycles, with each cycle completing the detection of all key units in a specific column before moving to the next column. This continuous operation ensures that the keyboard maintains accurate key registration capability at all times, preventing ghosting by ensuring that detection actions are perpetually ongoing rather than intermittent or static.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This solution accurately determines key depression states, eliminating ghosting errors and enhancing the keyboard's reliability and accuracy.
Implementation Method 1
The transition circuit TC(x) includes a base terminal Nb(x), a collector terminal Rc(x) and an emitter terminal Re(x) of a bipolar junction transistor (BJT). When the voltage level of the row signal line R(x) is higher than a threshold voltage, the BJT is turned on, so that an output voltage Rout(x) from the transition circuit TC(x) has a first voltage level. When the voltage level of the row signal line R(x) is lower than or equal to the threshold voltage, the BJT is turned off, so that the output voltage Rout(x) from the transition circuit TC(x) has a second voltage level.
Data Source
AI summary
A keyboard device includes M driving circuits DC(1)˜DC(M), N transition circuits TC(1)˜TC(N), a control module, M column signal lines C(1)˜C(M), N row signal lines R(1)˜R(N) and M*N key units KU(1,1)˜KU(M,N). The control module performs a scanning process to sequentially scan the M column signal lines C(1)˜C(M) in M scan cycles scan(1)˜scan(M). If the key unit KU(k,x) connected with the k-th column signal line C(k) and the x-th row signal line R(x) is depressed, a scan voltage is transmitted from the k-th column signal line C(k) to the x-th row signal line R(x) through a switch sw(k,x) of the key unit KU(k,x). The transition circuit TC(x) connected with the x-th row signal line R(x) is turned on according to the scan voltage. Consequently, an output voltage Rout(x) from the transition circuit TC(x) has a first voltage level.