RFID INTERROGATOR

• US 20090009292A1
• Filed: 05/12/2008
• Published: 01/08/2009
• Est. Priority Date: 05/18/2007
• Status: Active Grant

• Current Assignee: Cambridge Resonant Technologies Ltd. (Merck & Co., Inc.)
• Original Assignee: Cambridge Resonant Technologies Ltd. (Merck & Co., Inc.)
• Inventors: Hill, Nicholas Patrick Roland
• Granted Patent: US 8,085,133 B2
• Time in Patent Office: Days
• US Class Current: 340/10.100
• 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
• CPC Class Codes: H03K 17/162 without feedback from the output circuit to the control circuit
• CPC Class Codes: H04B 1/02 Transmitters

Abstract

Embodiments of the invention relate to the field of RFID interrogators, particularly RFID interrogators that combine low loss with high rates of communication from the interrogator to a tag. We describe a transmitter comprising a resonant circuit and a driver coupled to drive said resonant circuit, wherein said resonant circuit includes a resonance regeneration system such that during amplitude modulation of a resonant signal in said resonant circuit when an amplitude of said resonant signal is reduced energy from said reduction is stored and when said amplitude is increased said stored energy is used to regenerate said resonance signal.

Claims

1. A transmitter comprising a resonant circuit and a driver coupled to drive said resonant circuit, wherein said resonant circuit includes a resonance regeneration system such that during amplitude modulation of a resonant signal in said resonant circuit when an amplitude of said resonant signal is reduced energy from said reduction is stored and when said amplitude is increased said stored energy is used to regenerate said resonance signal.

2. A transmitter as claimed in claim 1 wherein said resonance regeneration system comprises a switch in series with said at least one capacitor, and an oscillator synchronised to said resonant signal to control said switch.

3. A transmitter as claimed in claim 1 further comprising a transient control system to dissipate energy not stored by said resonance regeneration system.

4. A transmitter as claimed in claim 3 wherein said transient control system comprises a switch coupled to an energy dissipating device, and an oscillator synchronised to said resonant signal to control said switch.

5. A transmitter as claimed in claim 4, wherein said resonance regeneration system comprises a switch in series with said at least one capacitor, and an oscillator synchronised to said resonant signal to control said switch, wherein said switch of said resonance regeneration system and said switch of said transient control system are controlled in synchronism such that when said resonance regeneration system is acting to store energy said transient control system is acting to dissipate energy and when said resonance regeneration system is acting to regenerate said resonant signal said transient control system is not substantially dissipating energy.

6. A transmitter as claimed in claim 5 wherein said switch of said resonance regeneration system and said switch of said transient control system each comprise an FET.

7. A transmitter as claimed in claim 1 wherein said driver comprises a push-pull driver.

8. A transmitter as claimed in claim 1 further comprising a negative feedback circuit to compensate for transient changes in amplitude of said resonant signal.

9. A transmitter as claimed in claim 8 wherein said feedback circuit comprises a PWM (pulse width modulating) circuit or a passive feedback circuit.

10. A transmitter as claimed in claim 1 wherein said resonant circuit comprises a non-linear resonant circuit.

11. A transmitter as claimed in claim 10 wherein said resonant circuit comprises an inductor coupled to a first capacitor to form a resonant circuit, the resonator further comprising a controllable element, a second capacitor controllably coupled across said first capacitor by said controllable element, and a control device to control said controllable element such that a total effective capacitance of said first and second capacitor varies over a duty cycle of an oscillatory signal in said resonator.

12. A transmitter as claimed in claim 10 wherein said controllable element comprises a transistor and wherein said control device comprises a bias circuit for said transistor.

13. An RFID tag interrogator incorporating a transmitter as claimed in claim 1.

14. A wireless power transmission system incorporating a transmitter as claimed in claim 1.

15. A resonant circuit comprising at least a capacitor, an FET switch coupled in series with said capacitor, and a signal generator synchronised to a resonant signal in said resonant circuit, wherein said signal generator is configured to control said FET switch, and wherein the circuit further comprises a controller to stop said signal generator to stop oscillation of said resonant signal in said resonant circuit.

16. A resonant circuit as claimed in claim 15 further comprising a second FET switch coupled to said resonant circuit, and a second-FET controller to control said second FET to apply damping to said oscillation of said resonant signal after said controller has stopped said oscillation.

17. An oscillator including a driver coupled to drive a resonant circuit as claimed in claim 15, and wherein said controller is further configured to stop drive by said driver of said resonant circuit when said signal generator is stopped.

18. A method of switching a resonant oscillation on and off in a resonant circuit using a switch coupled in series with said resonant circuit, the method comprising:

driving said resonant circuit with a stimulus;

determining a relative phase between said stimulus and an output current from said resonant circuit;

switching said oscillator off using said switch and stopping said stimulus; and

switching said oscillation on and restarting said stimulus using said determined relative phase to control a relative timing between said switching on and said stimulus restarting.

19. A method as claimed in claim 18 wherein said resonant circuit comprises a non-linear resonant circuit.

20. A method as claimed in claim 18 wherein said resonant circuit forms part of a transmitter and wherein said output current comprises a current to an antenna of said transmitter.

21. A system for switching a resonant oscillation on and off in a resonant circuit using a switch coupled in series with said resonant circuit, the system comprising:

means for driving said resonant circuit with a stimulus;

means for determining a relative phase between said stimulus and an output current from said resonant circuit;

means for switching said oscillator off using said switch and stopping said stimulus; and

means for switching said oscillation on and restarting said stimulus using said determined relative phase to control a relative timing between said switching on and said stimulus restarting.