| 摘要 |
A secure digitizer control circuit and method which drives the digitizer with a random series of excitation signals. The control circuit includes a digitizer and a plurality of drivers for driving the digitizer. A controller varies the excitation signal and calculates stylus position. A stylus detects the potential at a point on the digitizer. Processing circuitry, including an analog front end and an analog-to-digital (A/D) converter, rectifies and filters the stylus signal and applies it to the A/D converter. An input/output link provides an interface between the control circuit and a host computer, such as a point-of-service terminal. A memory stores a lookup table of drive pattern sets and corresponding position equations. In a first embodiment, the controller repeatedly chooses a random sequence of patterns and applies the sequence until the controller senses liftoff of the sensing means from the digitizer. In a second embodiment, controller means repeatedly chooses and applies a sequence of patterns.
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