Impedance matching of an electromagnetic transponder reader

• US 20050285718A1
• Filed: 06/23/2005
• Published: 12/29/2005
• Est. Priority Date: 06/23/2004
• Status: Active Grant

• Current Assignee: STMicroelectronics SA (STMicroelectronics NV)
• Original Assignee: STMicroelectronics SA (STMicroelectronics NV)
• Inventors: Enguent, Jean-Pierre
• Granted Patent: US 7,603,082 B2
• Time in Patent Office: Days
• US Class Current: 340/10.1
• CPC Class Codes: G01S 13/758 using a signal generator powered by the interrogation signal
• CPC Class Codes: G06K 7/0008 General problems related to the reading of electronic memory record carriers, independent of its reading method, e.g. power transfer

Abstract

A terminal for generating an electromagnetic field, including an oscillating circuit capable of receiving a high-frequency A.C. excitation voltage via an amplifier and a directional coupler, the oscillating circuit having at least one element of variable capacitance, and circuitry for modifying the value of this capacitance according to the amplitude of a signal extracted from the coupler.

Claims

1. A terminal for generating an electromagnetic field, comprising an oscillating circuit capable of receiving a high-frequency A.C. excitation voltage via an amplifier and a directional coupler, wherein the oscillating circuit comprises at least one element of variable capacitance, and said terminal comprises, for modifying the value of said capacitance according to the amplitude of a signal extracted from the coupler, a comparator comparing the voltage extracted from the coupled line of the coupler with a reference voltage selected to maintain the impedance of the oscillating circuit at a predetermined value.

2. The terminal of claim 1, wherein the oscillating circuit is formed of a capacitor, in series with an inductance and a resistor, the variable-capacitance element comprising a MOS transistor, controlled by said means and connected in parallel with the series association of the inductance and of the resistor, the stray capacitance of the MOS transistor being used to modify the capacitance of the oscillating circuit.

3. The terminal of claim 1, wherein said coupler comprises discrete elements.

4. The terminal of claim 1, wherein the electromagnetic field remotely supplies at least one transponder.