Patent ID: 9412213
Filing Date: 2016-08-09
CPC Classification: A01K,E05F,G01V,G06K,G07C

Claim Text:
1. An RFID tag reader, the reader comprising: an electromagnetic (EM) field generator having a resonant circuit for generating an electromagnetic (EM) field for modulation by said tag, said modulation comprising modulating load of said EM field by said tag, the resonant circuit arranged such that current in the resonant circuit is responsive to said load modulation; a detector system responsive to fluctuations in strength of said EM field at said reader; a demodulator responsive to said detector system to demodulate said EM field modulation by said tag; a stimulus circuit for exciting resonance of the resonant circuit, the stimulus circuit comprising a switch circuit having a coupling to the EM field generator; and a rectified power supply output for powering the EM field generator, the power supply output coupled to a capacitor and to the switch circuit, wherein the switch circuit is coupled to, when the stimulus circuit is controlled to excite the resonance, pass charge from the EM generator to charge the capacitor until voltage on the capacitor reaches voltage on the EM field generator and then pass charge from the power supply to the EM field generator, wherein an increase in said load reduces a duration of said charging said capacitor and increases a duration of said passing charge to the EM field generator to compensate for variations in amplitude of resonance of the resonant circuit with variation of power delivered to the resonant circuit by the power supply.