Amplifier modulation

• US 20030071731A1
• Filed: 10/15/2001
• Published: 04/17/2003
• Est. Priority Date: 10/15/2001
• Status: Active Grant

• Current Assignee: 3M Innovative Properties Company (3M Company)
• Original Assignee: 3M Innovative Properties Company (3M Company)
• Inventors: Jesme, Ronald David
• Granted Patent: US 6,737,973 B2
• Time in Patent Office: Days
• 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. An apparatus comprising:

a class E amplifier having a first transistor;

a second transistor controlling a current path in parallel to the first transistor; and

a controller to control the first and second transistors.

2. The apparatus of claim 1, wherein the first and second transistors comprise metal oxide semiconductor field-effect transistors (MOSFET'"'"'s), and further wherein the second transistor has a source connected to ground and a drain connected to a drain of the first transistor by a resistor.

3. The apparatus of claim 1, wherein the apparatus produces an amplitude modulated signal in response to the controller by:

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 apparatus of claim 3, wherein the frequency is at least 13.56 megahertz.

5. The apparatus of claim 1, wherein the class E amplifier includes an inductor supplying current to the first transistor, and a shunt capacitor connected in parallel to the first transistor.

6. An amplifier comprising:

a first transistor;

an inductor coupling the first transistor to a supply voltage via a first resistor;

a shunt capacitor connected in parallel to the first transistor;

a second transistor connected to the inductor by a second resistor, wherein the second transistor controls a current path in parallel to the first transistor and the capacitor;

a third transistor connected in parallel to the first resistor; and

a controller coupled to the first, second and third transistors.

7. The amplifier of claim 6, wherein the controller selectively activates the first and second transistors.

8. The amplifier of claim 6, wherein the controller activates and deactivates the first transistor at a frequency, and activates and deactivates the second transistor.

9. The amplifier of claim 8, wherein the frequency is at least 13.56 megahertz.

10. The amplifier of claim 6, wherein the controller activates and deactivates the first transistor at a frequency, and activates and deactivates the third transistor.

11. The amplifier of claim 10, wherein the frequency is at least 13.56 megahertz.

12. An apparatus comprising:

a class E amplifier having a first transistor and an inductor coupling the first transistor to a supply voltage via a first resistor;

a second transistor connected in parallel to the first resistor; and

a controller coupled to the first and second transistors.

13. The apparatus of claim 12, wherein the controller activates and deactivates the first transistor at a frequency, and activates and deactivates the second transistor.

14. The apparatus of claim 13, wherein the frequency is at least 13.56 megahertz.

15. The apparatus of claim 12, wherein the amplifier further comprises:

a shunt capacitor connected in parallel to the first transistor; and

a third transistor controlling a current path in parallel to the first transistor and the capacitor.

16. The apparatus of claim 15, wherein the controller selectively activates the first and third transistors.

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

a controller to control the first and second transistors; and

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

18. The RF reader of claim 17, further comprising a receiver coupled to the antenna to receive an RF communication from an RFID tag.

19. The RF reader of claim 17, 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.

20. The RF reader of claim 19, wherein the frequency is at least 13.56 megahertz.

21. The RF reader of claim 17, further comprising a third transistor connected in parallel to a resistor limiting current to the inductor.

22. The RF reader of claim 21, wherein the controller activates and deactivates the first transistor at a frequency, and activates and deactivates the third transistor.

23. The RF reader of claim 17, further comprising a communication interface for communicating with a computing device.

24. 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 further 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,

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.

25. The system of claim 24, further comprising an input device to receive input from the user.

26. The system of claim 24, wherein the RF reader, the processor and the display are integrated into a portable device.

27. The system of claim 24, wherein the RF reader further comprises a controller to control the first and second transistors.

28. The system of claim 27, 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.

29. The system of claim 28, wherein the controller switches the first transistor at least at 13.56 megahertz.

30. The system of claim 24, wherein the RF reader further comprises a third transistor connected in parallel to the first resistor, and controlled by the controller.

31. The RF reader of claim 30, wherein the controller activates and deactivates the first transistor at a frequency, and activates and deactivates the third transistor.

32. A method of generating an amplitude modulated signal comprising:

generating an amplitude modulation signal with a class E amplifier; and

substantially maintaining an operational bias of the class E amplifier while generating the signal.

33. The method of claim 32, wherein maintaining the operational bias comprises maintaining a substantially constant current through the class E amplifier.

34. The method of claim 32, wherein generating the amplitude modulation signal comprises:

switching a first transistor of a class E amplifier at a frequency for a first period of time; and

when switching the first transistor, deactivating a second transistor connected in parallel to the first transistor.

35. The method of claim 34, wherein maintaining the operational bias comprises deactivating the first transistor and activating the second transistor for a second period of time.

36. The method of claim 34, wherein the frequency is at least 13.56 megahertz.