Low cost power amplifier linearization in an RFID radio transmit chain

• US 20060273900A1
• Filed: 06/01/2005
• Published: 12/07/2006
• Est. Priority Date: 06/01/2005
• Status: Active Grant

• Current Assignee: Intel Corporation
• Original Assignee: Intel Corporation
• Inventors: Posamentier, Joshua
• Granted Patent: US 7,304,575 B2
• Time in Patent Office: Days
• US Class Current: 340/572.100
• CPC Class Codes: G06K 19/07749 the record carrier being capable of non-contact communication, e.g. constructional details of the antenna of a non-contact smart card
• CPC Class Codes: H03F 1/3241 using predistortion circuits H03F1/3211, H03F1/3217 take precedence
• CPC Class Codes: H03F 1/3247 using feedback acting on predistortion circuits H03F1/3264 takes precedence
• CPC Class Codes: H03F 1/3282 Acting on the phase and the amplitude of the input signal
• CPC Class Codes: H03F 2200/102 A non-specified detector of a signal envelope being used in an amplifying circuit
• CPC Class Codes: H03F 2200/132 Hybrid coupler placed in a feedback circuit of an amplifier
• CPC Class Codes: H03F 2200/261 Amplifier which being suitable for instrumentation applications
• CPC Class Codes: H03F 2200/327 Amplitude shift keying modulation being used in an amplifying circuit
• CPC Class Codes: H03F 3/24 of transmitter output stages
• CPC Class Codes: H04L 27/08 Amplitude regulation arrangements

Abstract

A power amplification system within an RFID reader uses feedback to linearize a transfer function of the system. ASK modulation is used in the system. An envelope of an output signal of a non-linear power amplifier is fed back to an input where it is combined in an integrator with an ASK modulation signal to generate a pre-emphasized modulation signal. The pre-emphasized modulation signal is then applied to the power amplifier to generate a linearized output signal.

Claims

1. An apparatus for use in an RFID reader, comprising:

a power amplifier having a non-linear transfer function, said power amplifier to generate an output signal;

a coupler to couple a portion of said output signal for use as a feedback signal;

an envelope detector to detect an envelope of said feedback signal; and

a high speed integrator to process said envelope of said feedback signal and an ASK modulation signal to generate a pre-emphasized modulation signal for delivery to said power amplifier, said pre-emphasized modulation signal to linearize the operation of said power amplifier.

2. The apparatus of claim 1, wherein:

said power amplifier is a class C amplifier.

3. The apparatus of claim 1, wherein:

said power amplifier is a class E amplifier.

4. The apparatus of claim 1, further comprising:

a linear preamplifier to amplify an input signal before it reaches said power amplifier.

5. The apparatus of claim 4, further comprising:

a variable gain amplifier to amplify said feedback signal before it reaches said envelope detector.

6. The apparatus of claim 5, further comprising:

a transmit power control unit to control a gain of said linear preamplifier.

7. The apparatus of claim 6, wherein:

said transmit power control unit is also to control a gain of said variable gain amplifier, wherein said transmit power control unit is to cause said gain of said variable gain amplifier to be inversely proportional to said gain of said linear preamplifier.

8. The apparatus of claim 1, further comprising:

a bandpass filter in a signal path between said power amplifier and said coupler.

9. The apparatus of claim 1, further comprising:

a filter in a signal path between said envelope detector and said high speed integrator.

10. The apparatus of claim 1, wherein:

said high speed integrator has a bandwidth specification of more than ten times the modulation symbol rate.

20. The RFID reader of claim 1, further comprising:

a linear preamplifier to amplify an input signal before it reaches said power amplifier.

21. The RFID reader of claim 20, further comprising:

a variable gain amplifier to amplify said feedback signal before it reaches said envelope detector.

22. The RFID reader of claim 21, further comprising:

a transmit power control unit to control a gain of said linear preamplifier.

23. The RFID reader of claim 22, wherein:

said transmit power control unit is also to control a gain of said variable gain amplifier, wherein said transmit power control unit is to cause said gain of said variable gain amplifier to be inversely proportional to said gain of said linear preamplifier.

11. A method for use in connection with an RFID reader, comprising:

amplifying an input signal in a power amplifier to generate an output signal;

coupling a portion of said output signal for use as a feedback signal;

detecting an envelope of said feedback signal;

combining said envelope with an amplitude shift keying (ASK) modulation signal to achieve a pre-emphasized modulation signal; and

applying said pre-emphasized modulation signal to said power amplifier.

12. The method of claim 11, wherein:

said power amplifier is a class-C power amplifier.

13. The method of claim 11, wherein:

said power amplifier is a class-E power amplifier.

14. The method of claim 11, wherein:

combining includes applying said envelope and said ASK modulation signal to corresponding inputs of a high speed integrator circuit.

15. The method of claim 11, further comprising:

pre-amplifying said input signal before amplifying said input signal in said power amplifier.

16. The method of claim 15, further comprising:

amplifying said feedback signal before it is input to said envelope detector, wherein amplifying said feedback signal includes amplifying said feedback signal by a gain that is inversely proportional to a gain used to pre-amplify said input signal.

17. The method of claim 11, further comprising:

bandpass filtering said output signal before coupling.

18. The method of claim 11, further comprising:

filtering said envelope before combining.

19. An RFID reader, comprising:

at least one dipole antenna;

a power amplifier having a non-linear transfer function, said power amplifier to generate an output signal, wherein an output of said power amplifier is in communication with said at least one dipole antenna;

a coupler to couple a portion of said output signal for use as a feedback signal;

an envelope detector to detect an envelope of said feedback signal; and

a high speed integrator to process said envelope of said feedback signal and an ASK modulation signal to generate a pre-emphasized modulation signal for delivery to said power amplifier, said pre-emphasized modulation signal to linearize the operation of said power amplifier.