Amplifier modulation

• US 6,737,973 B2
• Filed: 10/15/2001
• Issued: 05/18/2004
• Est. Priority Date: 10/15/2001
• Status: Expired due to Term

• Current Assignee: 3M Innovative Properties Company (3M Company)
• Original Assignee: 3M Innovative Properties Company (3M Company)
• Inventors: Jesme, Ronald David
• Primary Examiner(s): Lee, Benjamin C.
• Assistant Examiner(s): Nguyen, Phung
• Application Number:
  US09/978,329
• Publication Number:
  US 20030071731A1
• Time in Patent Office: 946 Days
• Field of Search: 340/572.1, 340/572.7, 340/693.3, 340/10.3, 340/7-2-, 340/539.1, 455/127, 455/343, 455/108, 455/109, 330/10
• US Class Current: 340/572.1
• 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: H03F 3/2176 Class E amplifiers

Abstract

In general, the invention is directed to an efficient amplifier for use in radio-frequency identification (RFID) applications. In particular, the invention provides a highly efficient amplifier that requires little power, yet has significant modulation bandwidth to achieve high data communication rates. The amplifier makes use of many components of a class E amplifier including a first transistor, an inductor coupling the first transistor to a power supply, and a shunt capacitor connected in parallel to the first transistor. A second transistor is connected in parallel to the first transistor. A controller selectively controls the first and second transistors to achieve amplitude modulation at a high modulation bandwidth.

Claims

1. A radio-frequency (RF) reader comprising:

an amplifier outputting an amplitude modulated signal, wherein the amplifier comprises;

(i) a Class E amplifier having an inductor coupling a first transistor and a shunt capacitor to a power supply,

(ii) a second transistor controlling a current path in parallel to the first transistor of the Class E amplifier; and

(iii) a third transistor connected in parallel to a resistor limiting current to the inductor,

a controller to control the first and second transistors; and

an antenna to receive the amplitude modulated signal and output an RF communication.

2. The RF reader of claim 1, further comprising a receiver coupled to the antenna to receive an RF communication from an RFID tag.

3. The RF reader of claim 1, wherein the controller:

for a first period of time, simultaneously switching the first transistor at a frequency and deactivating the second transistor; and

for a second period of time, simultaneously deactivating the first transistor and activating the second transistor.

4. The RF reader of claim 3, wherein the frequency is at least 13.56 megahertz.

5. The RF reader of claim 1, wherein the controller activates and deactivates the first transistor at a frequency, and activates and deactivates the third transistor to produce the amplitude modulated signal.

6. The RF reader of claim 1, further comprising a communication interface for communicating with a computing device.

7. A system comprising:

a radio-frequency (RF) reader comprising an antenna and an amplifier, wherein the antenna receives an amplitude modulated signal from the amplifier and outputs an RF communication, and wherein the amplifier includes a first transistor coupled to a power supply, and a second transistor controlling a current path in parallel to the first transistor, and wherein the RF reader further comprises an inductor between the first transistor and the power supply, a resistor to limit current to the inductor, a third transistor connected in parallel to the resistor, and a controller to control the first, second and third transistors;

a processor to receive data from an RFID tag via the RF reader; and

a display coupled to the processor to display the data to a user.

8. The system of claim 7, wherein the RF reader, the processor and the display are integrated into a portable device.

9. The system of claim 7, wherein the RF reader, the processor and the display are integrated into a portable device.

10. The system of claim 7, wherein the RF reader further comprises a controller to control the first and second transistors.

11. The system of claim 10, wherein the controller:

switches the first transistor at a frequency and deactivates the second transistor simultaneously for a first period of time; and

deactivates the first transistor and activates the second transistor simultaneously for a second period of time.

12. The system of claim 11, wherein the controller switches the first transistor at least at 13.56 megahertz.

13. The system of claim 7, wherein the controller activates and deactivates the first transistor at a frequency, and activates and deactivates the third transistor to produce the amplitude modulated signal.

14. A radio-frequency (RF) reader comprising:

an amplifier outputting an amplitude modulated signal, wherein the amplifier comprises;

(i) a class E amplifier having an inductor coupled to a power supply, and a first transistor controlling a first current path from the inductor to a ground, (ii) a second transistor controlling a second current path from the inductor of the Class E amplifier to the ground, and (iii) a third transistor connected in parallel to a resistor limiting current to the inductor; and

a controller to control the first and second transistors.

15. The RF reader of claim 14, further comprising an antenna to receive the amplitude modulated signal and output an RF communication.

16. The RF reader of claim 15, further comprising a receiver coupled to the antenna to receive an RF communication from an RFID tag.

17. The RF reader of claim 16, wherein the frequency is at least 13.56 megahertz.

18. The RF reader of claim 14, wherein the controller:

for a first period of time, simultaneously switches the first transistor at a frequency and deactivating the second transistor; and

for a second period of time, simultaneously deactivates the first transistor and activating the second transistor.

19. The RF reader of claim 14, wherein the controller activates and deactivates the first transistor at a frequency, and activates and deactivates the third transistor.

20. A system comprising:

a radio-frequency (RF) reader comprising an amplifier to produce an amplitude modulated signal, wherein the amplifier includes a current source, a first transistor controlling a first current path from the current source to a ground, a second transistor controlling a second current path from the current source to the ground, and wherein the current source includes an inductor between the first transistor and a power supply, and the RF reader further comprises a resistor to limit current to the inductor and a third transistor connected in parallel to the resistor and controlled by the controller;

a processor to receive data from an RFID tag via the RF reader; and

a display coupled to the processor to display the data to a user.

21. The system of claim 20, further comprising an input device to receive input from the user.

22. The system of claim 20, wherein the RF reader, the processor and the display are integrated into a portable device.

23. The system of claim 20, wherein the RF reader further comprises a controller to control the first and second transistors.

24. The system of claim 23, wherein the controller:

switches the first transistor at a frequency and deactivates the second transistor simultaneously for a first period of time; and

deactivates the first transistor and activates the second transistor simultaneously for a second period of time.

25. The system of claim 24, wherein the controller switches the first transistor at least at approximately 13.56 megahertz.

26. The system of claim 20, wherein the controller activates and deactivates the first transistor at a frequency, and activates and deactivates the third transistor.

27. The system of claim 20, further comprising an antenna to receive the amplitude modulated signal and output an RF communication.