Linear RF power amplifier with optically activated switches

• US 6,385,439 B1
• Filed: 10/31/1997
• Issued: 05/07/2002
• Est. Priority Date: 10/31/1997
• Status: Expired due to Term

• Current Assignee: Telefonaktiebolaget LM Ericsson
• Original Assignee: Telefonaktiebolaget LM Ericsson
• Inventors: Hellberg, Lars Richard Birger
• Primary Examiner(s): Chang, Vivan
• Assistant Examiner(s): APPIAH, CHARLES NANA
• Application Number:
  US08/962,329
• Time in Patent Office: 1,649 Days
• Field of Search: 332/144, 332/103, 332/105, 332/109, 455/91, 455/127, 455/103, 455/323, 455/118, 455/123, 455/313, 455/318, 359/180, 359/315, 359/181, 359/326, 327/103, 375/216, 375/295
• US Class Current: 455/123
• CPC Class Codes: H03D 7/165 at least two frequency changers being located in different paths, e.g. in two paths with carriers in quadrature combined with amplitude demodulation H03D1/2245, combined with angle demodulation H03D3/007; N-path filters H03H19/002
• CPC Class Codes: H03F 1/32 Modifications of amplifiers to reduce non-linear distortion by negative feedback H03F1/34
• CPC Class Codes: H03F 2200/421 Multiple switches coupled in the output circuit of an amplifier are controlled by a circuit
• CPC Class Codes: H03F 3/24 of transmitter output stages
• CPC Class Codes: H04L 27/362 Modulation using more than one carrier, e.g. with quadrature carriers, separately amplitude modulated H04L27/366 takes precedence

Abstract

A linear power amplifier amplifies a linear baseband signal having I and Q components. An up-converting mixer uses optically activated switches to mix the amplified baseband signal with a local oscillator signal at specified carrier frequency. The optically activated switches are activated according to a switching sequence that produces a constant impedance over each carrier frequency cycle. In this way, the optically activated switches prevents introduction of non-linearities during the up-conversion process.

Claims

1. A transmitter, comprising:

an amplifier stage that amplifies a baseband signal having linear In-phase (I) and Quadrature-phase (Q) components to produce an amplified baseband signal;

a local oscillator that generates a local oscillator signal corresponding to a specified carrier frequency; and

an up-converting mixer that mixes the amplified baseband signal with the local oscillator signal, wherein the mixer includes a plurality of optically activated switches that are switched according to a switching sequence.

2. The transmitter of claim 1 farther including a filter stage for isolating the amplifier stage from the up-converting mixer.

3. The transmitter of claim 1, wherein the switching sequence presents a constant impedance over each carrier frequency cycle.

4. The transmitter of claim 1, wherein each one of the plurality of the optically activated switches are switched at time periods that are non-overlapping.

5. The transmitter of claim 1, wherein the amplifier stage includes a first power amplifier that produces a pair of complementary I components and a second power amplifier that produces a pair of complementary Q components, wherein said complementary I and Q components are mixed with the local oscillator signal via the optically activated switches.

6. The transmitter of claim 1, wherein the plurality of the optically activated switches include first, second, third, and fourth optically activated switches, wherein the complementary I components include a first I component coupled to the first optically activated switch and a second I component coupled to the second optically activated switch, wherein the complementary Q components include a first Q component coupled to the third optically activated switch and a second Q component coupled to the fourth optically activated switch, and wherein over each carrier frequency cycle, the switching sequence sequentially closes, during corresponding time periods, the first optically activated switch, followed by the third optically activated switch, followed by the second optically activated switch, and then the fourth optically activated switch.

7. The transmitter of claim 4, wherein the optically activated switches are switched with approximately 25% duty cycles.

8. The transmitter of claim 3 further including an optical controller for controlling the switching sequence.

9. The transmitter of claim 8, wherein the optical controller includes at least one pulsed light source that generates pulsed light signals for controlling the optically activated switches.

10. The transmitter of claim 9, wherein the pulsed light source is a laser source.

11. The transmitter of claim 9, wherein the switching sequence is produced by generating interleaved pulsed light signals.

12. The transmitter of claim 11, wherein the interleaved pulse signals are produced in response to phase-shifted local oscillator signals.

13. The transmitter of claim 9, wherein the optical controller includes a single pulsed light source and multiple optical links having associated delay-lines, wherein the delay lines correspond to a period T of the carrier frequency cycles.

14. The transmitter of claim 13, wherein the delay lines correspond to multiples of 0.25 times T.

15. A method for linearly transmitting an RF signal, comprising:

amplifying a baseband signal having linear In-phase (I) and Quadrature (Q) components to produce an amplified baseband signal;

generating a local oscillator signal corresponding to a specified carrier frequency; and

mixing the amplified baseband signal with the local oscillator signal with a plurality of optically activated switches that are switched according to a switching sequence.

16. The method of claim 15, wherein the switching sequence presents a constant impedance over each carrier frequency cycle.

17. The method of claim 16, wherein each one of the plurality of the optically activated switches are switched at time periods that are non-overlapping.

18. The method of claim 15, wherein the step of amplifying produces a pair of complementary I components and a pair of complementary Q components, wherein said complementary I and Q components are mixed with the local oscillator signal via the optically activated switches.

19. The method of claim 18, wherein the plurality of the optically activated switches include first, second, third, and fourth optically activated switches, wherein the complementary I components include a first I component coupled to the first optically activated switch and a second I component coupled to the second optically activated switch, wherein the complementary Q components include a first Q component coupled to the third optically activated switch and a second Q component coupled to the fourth optically activated switch, and wherein over each carrier frequency cycle, the switching sequence sequentially closes, during corresponding time periods, the first optically activated switch, followed by the third optically activated switch, followed by the second optically activated switch, and then the fourth optically activated switch.

20. The method of claim 15, wherein the optically activated switches are switched with approximately 25% duty cycles.

21. The method of claim 15 further including the step of generating pulsed light signals for controlling the optically activated switches.

22. The method of claim 21, wherein the switching sequence is produced by generating interleaved pulsed light signals.

23. The method of claim 21, wherein the switching sequence is produced by multiple optical links having associated delay-lines, wherein the delay lines correspond to a period T of the carrier frequency cycles.

24. A transmitter, comprising:

an antenna for radiating a linear signal that is modulated over a carrier signal;

a radio transmitter coupled to the antenna, including;

an amplifier stage that amplifies a baseband signal having linear In-phase (I) and Quadrature-phase (Q) components to produce an amplified baseband signal;

a local oscillator that generates a local oscillator signal corresponding to a specified carrier frequency; and

an up-converting mixer that mixes the amplified baseband signal with the local oscillator signal, wherein the mixer includes a plurality of optically activated switches that are switched according to a switching sequence.

25. The transmitter of claim 24 further including a filter stage for isolating the amplifier stage from the up-converting mixer.

26. The transmitter of claim 24, wherein the switching sequence presents a constant impedance over each carrier frequency cycle.

27. The transmitter of claim 24, wherein each one of the plurality of the optically activated switches is switched at time periods that are non-overlapping.

28. The transmitter of claim 24, wherein the amplifier stage includes a first power amplifier that produces a pair of complementary I components and a second power amplifier that produces a pair of complementary Q components, wherein said complementary I and Q components are mixed with the local oscillator signal via the optically activated switches.

29. The transmitter of claim 24, wherein the plurality of the optically activated switches include first, second, third, and fourth optically activated switches, wherein the complementary I components include a first I component coupled to the first optically activated switch and a second I component coupled to the second optically activated switch, wherein the complementary Q components include a first Q component coupled to the third optically activated switch and a second Q component coupled to the fourth optically activated switch, and wherein over each carrier frequency cycle, the switching sequence sequentially closes, during corresponding time periods, the first optically activated switch, followed by the third optically activated switch, followed by the second optically activated switch, and then the fourth optically activated switch.

30. The transmitter of claim 29, wherein the optically activated switches are switched with approximately 25% duty cycles.

31. The transmitter of claim 27 further including an optical controller for controlling the switching sequence.

32. The transmitter of claim 31, wherein the optical controller includes at least one pulsed light source that generates pulsed light signals for controlling the optically activated switches.

33. The transmitter of claim 32, wherein the pulsed light source is a laser source.

34. The transmitter of claim 32, wherein the switching sequence is produced by generating interleaved pulsed light signals.

35. The transmitter of claim 34, wherein the interleaved pulse signals are produced in response to phase-shifted local oscillator signals.

36. The transmitter of claim 31, wherein the optical controller includes a single pulsed light source and multiple optical links having associated delay-lines, wherein the delay lines correspond to a period T of the carrier frequency cycles.

37. The transmitter of claim 36, wherein the delay lines correspond to multiples of 0.25 times T.