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Interface for shunt voltage regulator in a contactless smartcard

  • US 6,954,053 B2
  • Filed: 04/14/2003
  • Issued: 10/11/2005
  • Est. Priority Date: 07/10/2002
  • Status: Expired due to Fees
First Claim
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1. A voltage regulator circuit for a contactless smartcard that regulates an incoming inductively coupled and modulated signal comprising:

  • an inductor coil for converting an electromagnetic field into a current;

    rectifying means connected to said inductor coil for converting said current to a rectified output voltage carrying a demodulated data signal;

    a shunt device having at least one controllable conductive path for connecting the output of said rectifying means to ground, said shunt device diverting current from said output in accordance with control signals it receives at a controlling input, said controlling input being connected to a feedback path that is comprised of the following components;

    a voltage dividing means for taking said output voltage from said rectifying means as an input and outputting a proportionally lowered voltage;

    a low-pass filter means connected between the output of said voltage dividing means and said controlling input of said shunt device means for removing high frequency modulation components from the signal transmitted to said controlling input;

    means for transmitting modulation of the data signal at the output of said rectifying means to the controlling input of said shunt device, thereby imposing a modulation on the shunt current that is proportional to the modulation of the output voltage of said rectifying means, and thereby maintaining the proportionality of the voltage variation at the output of the rectifier caused by the modulation; and

    a non-linear processing means having a first, second and third input connected to said voltage dividing means, a reference voltage means and a controlling electrode of said shunt device, respectively, said non-linear processing means generating a voltage proportional to the difference in voltage between the output of said voltage dividing means and said reference voltage wherein the proportionality is modified to compensate for the non-linear nature of the transconductance of the shunt device by modifying the bias conditions of the circuit;

    the output voltage being further modified by a resistive means that compensates for the non-linear nature of the transconductance of the shunt device.

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