US4037225A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Keyboard encoding system with electronic hysteresis
Assignee: Xerox Corp
•
Filing: 1975-11-25
•
Granted: 1977-07-19
•
Expires: 1995-11-25
Abstract
Abstract A keyboard encoding system which utilizes electronic hysteresis to prevent undesired key stroke encoding. The output of a capacitive switch matrix is supplied to a sense amplifier which has its sensitivity increased if a particular switch of the switch matrix was closed the last scan cycle. The status of the switches of the switch matrix during the last scan cycle is provided by a shift register having a number of stages equal to the number of switches of the matrix. The sense amplifier includes a comparator which receives an input indicative of the state of a particular matrix switch during the present scan cycle and an input from the shift register indicative of the status of the particular matrix switch the previous scan cycle. If the input from the shift register is high, the sensitivity of the sense amplifier is increased.
Inventors
- 👤 Wilbur E. DuVall
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-28 17:49
CPC Classifications
H; H03; H03K; H03K17/00; H03K17/94; H03K17/965; H03K17/975; H03K17/98; H03M; H03M11/00; H03M11/02
Claims Analysis
Total Claims: 2
Claim 1
Independent Claim
285 words
A switching device encoding system comprising: a voltage source, an array of switching devices, each of which has a low impedance in a closed state and a high impedance in an open state, signal amplitude sensing means, first means coupled to said array, to said voltage source and to said signal amplitude sensing means for continuously, cyclically addressing in a predetermined sequence each switching device of said array such that each of said switching devices of said array couples said voltage source to said signal amplitude sensing means, whereby a signal of one amplitude is supplied to said signal amplitude sensing means when a closed switching device is coupled to said voltage source and said signal amplitude sensing means and a signal of a different amplitude is supplied to said signal amplitude sensing means when an open switching device is coupled to said voltage source and said signal amplitude sensing means, said signal amplitude sensing means providing an output signal of a high value when the input signal supplied thereto is above a certain amplitude, storage means coupled to said signal amplitude sensing means for storing the state of each of said switching devices during the previous scan cycle, feedback means coupled between said storage means and said signal amplitude sensing means for increasing the sensitivity of said signal amplitude sensing means if a switching device currently being sensed was in a closed state the previous scan cycle, and logic means coupled to the output of said storage means and to the output of said signal amplitude sensing means, said logic means providing an output signal only when the output of said storage means and the output of said signal amplitude sensing means are different.
Claim 2
Dependent Claim
285 words
A switching device encoding system comprising: a voltage source, an array of switching devices, each of which has a low impedance in a closed state and a high impedance in an open state, signal amplitude sensing means, first means coupled to said array, to said voltage source and to said signal amplitude sensing means for continuously, cyclically addressing in a predetermined sequence each switching device of said array such that each of said switching devices of said array couples said voltage source to said signal amplitude sensing means, whereby a signal of one amplitude is supplied to said signal amplitude sensing means when a closed switching device is coupled to said voltage source and said signal amplitude sensing means and a signal of a different amplitude is supplied to said signal amplitude sensing means when an open switching device is coupled to said voltage source and said signal amplitude sensing means, said signal amplitude sensing means providing an output signal of a high value when the input signal supplied thereto is above a certain amplitude, storage means coupled to said signal amplitude sensing means for storing the state of each of said switching devices during the previous scan cycle, feedback means coupled between said storage means and said signal amplitude sensing means for increasing the sensitivity of said signal amplitude sensing means if a switching device currently being sensed was in a closed state the previous scan cycle, and logic means coupled to the output of said storage means and to the output of said signal amplitude sensing means, said logic means providing an output signal only when the output of said storage means and the output of said signal amplitude sensing means are different.
References Cited (Backward Citations)
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1980-07-18 | 1981-01-17 | 1981-07-19 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1984-07-18 | 1985-01-17 | 1985-07-19 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1988-07-18 | 1989-01-17 | 1989-07-19 | $7700.00 | Window Closed / Lapsed |