Patent ID: 6050488
Filing Date: 2000-04-18
Classification: G06K

Abstract:
A circuit for driving inductive sensors for reading and debiting prepaid cards comprising:m line conductors and n column conductors arranged in a matrix array;a plurality of inductive sensors, one connected between each intersecting line and column conductors;a capacitor connected in parallel to said inductive sensor, thereby forming a resonant circuit;a driving signal generator for applying a driving signal to each inductive sensor;a feedback network connected to each inductive sensor for determining the phase difference between the current and the voltage of the driving signal at each said inductive sensor;said feedback network comprising a closed feedback loop for applying a correction signal representative of said phase difference to said generator;said generator being capable of varying the frequency of said driving signal in response to the value of said correction signal;whereby the frequency of the driving signal generator output is varied in accordance with said phase difference.