Automatic means to trigger RFID transmitters

• US 8,174,364 B2
• Filed: 04/12/2010
• Issued: 05/08/2012
• Est. Priority Date: 10/17/2008
• Status: Expired due to Fees

• Current Assignee: Michael Kenneth Pedigo
• Original Assignee: Michael Kenneth Pedigo
• Inventors: Pedigo, Michael Kenneth
• Primary Examiner(s): Bugg, George
• Assistant Examiner(s): Yacob, Sisay
• Application Number:
  US12/581,116
• Publication Number:
  US 20100194535A1
• Time in Patent Office: 757 Days
• Field of Search: 340/10.1, 340/10.4, 340/12.5, 340/12.51, 455/296, 455/503, 370/252, 345/45
• US Class Current: 340/10.1
• CPC Class Codes: G06K 19/0723 the record carrier comprising an arrangement for non-contact communication, e.g. wireless communication circuits on transponder cards, non-contact smart cards or RFIDs

Abstract

An RFID reader requires significant power supply current, upwards or beyond 0.5 amps. Much of this power is expended to activate the reader'"'"'s radio frequency transmitter. For example, the reader'"'"'s transmitter may constantly be active awaiting a RFID tag entering within its electromagnetic field. Sometimes an adequate power source, such as AC mains, is not available to provide continuous operation and instead a battery is powers the reader. This invention detects that a RFID tag is within reader range without using the reader'"'"'s RF transmitter at full power. As a RFID tag is brought within range of a reader'"'"'s antenna there is significant mutual inductance coupling between the tag antenna and the reader'"'"'s antenna and this invention provides a sensitive detector of this mutual inductance. The detection of mutual inductance automatically triggers the reader'"'"'s transmitter to a higher power which is necessary to fully activate the RFID tag.

Claims

1. A radio frequency identification (RFID) system that includes:

an antenna;

an antenna switch that is switchable into a first and second state;

a phase lock loop that includes a voltage controlled oscillator, a phase detector, and a loop filter;

a RFID decoder;

a microcontroller or microprocessor;

said voltage control oscillator in said phase lock loop connects to said antenna switch;

said RFID decoder connects to said antenna switch;

said antenna connects to said antenna switch;

a reactance of said antenna provides frequency tuning of said voltage controlled oscillator with said antenna switch in the said first state;

an output of said phase lock loop provides information of said frequency tuning of said voltage controlled oscillator,

said output of said phase lock loop connects to said microcontroller or said microprocessor;

an output on said microcontroller or said microprocessor changes logic level dependent upon said information provided on said output of said phase lock loop;

said output of said microcontroller or said microprocessor selects the state of said antenna switch between said first state and said second state; and

said antenna is connected to said RFID decoder with said antenna switch in the said second state.

3. The radio frequency identification (RFID) system of claim 1, wherein said antenna switch has a two pole two throw capability.

4. The radio frequency identification (RFID) system of claim 1, wherein a part of said reactance of said antenna is from a mutual inductance of a proximate RFID tag.

5. The radio frequency identification (RFID) system of claim 1, wherein said voltage controlled oscillator is a Colpitt'"'"'s oscillator.

2. A radio frequency identification (RFID) system that includes:

an antenna that has reactance affected by a mutual inductance from a proximity of a RFID tag;

a voltage controlled oscillator;

a microcontroller or microprocessor;

a means to connect said voltage controlled oscillator to said antenna so that a reactance of said antenna provides tuning to said voltage controlled oscillator;

a means to connect said voltage controlled oscillator to a phase lock loop for sensing said tuning of said voltage controlled oscillator whereas said tuning measures the proximity of said RFID tag;

wherein said phase lock loop for sensing said tuning of said voltage controlled oscillator is utilized to activate or deactivate a RFID decoder;

provides a phase detector output of said phase lock loop; and

a means to connect said phase detector output of said phase lock loop to said microcontroller or said microprocessor that provides a signal to said microcontroller or said microprocessor when to enable or disable said RFID decoder.

6. The radio frequency identification (RFID) system of claim 2, wherein said voltage controlled oscillator is a Colpitt'"'"'s oscillator.