APPARATUS AND METHOD FOR PHASE SYNCHRONIZATION IN RADIO FREQUENCY TRANSMITTERS

• US 20110279147A1
• Filed: 05/11/2010
• Published: 11/17/2011
• Est. Priority Date: 05/11/2010
• Status: Active Grant

• Current Assignee: Analog Devices, Inc.
• Original Assignee: Analog Devices, Inc.
• Inventors: Fan, Jianxun, Montalvo, Antonio
• Granted Patent: US 8,712,356 B2
• Time in Patent Office: Days
• US Class Current: 327/3
• CPC Class Codes: H04B 17/12 of transmit antennas, e.g. of the amplitude or phase
• CPC Class Codes: H04L 2027/0016 Stabilisation of local oscillators
• CPC Class Codes: H04L 2027/0022 using the carrier of the associated receiver of a transceiver
• CPC Class Codes: H04W 56/0035 detecting errors in frequency or phase

Abstract

Apparatus and methods are disclosed related to phase synchronization in transmitters. One such apparatus includes a wireless transmitter with two or more separate and unrelated local oscillators. The apparatus can provide RF signals to multiple antenna elements, which can be implemented in systems such as beamforming systems or multiple input multiple output (MIMO) systems. A phase difference between local oscillators is determined using outputs of receivers. The phase difference can be used to adjust a phase of signals associated with one or more of the local oscillators, such that the phase of each signal provided to the multiple antenna elements can be aligned.

Claims

1. An apparatus comprising:

a local oscillator configured to generate a local oscillator output signal;

a transmit path having a phase control input, the transmit path being configured to receive the local oscillator output signal as an input and to generate a first radio frequency (RF) output signal based at least partly on the local oscillator output signal, wherein a phase of the first RF output signal is controllable based at least partly on a control input provided to the phase control input; and

a receive path configured to receive the local oscillator output signal and a receive signal as inputs, wherein the receive signal is RF sampled from a second RF output signal, wherein the receive path is configured to generate a signal having a phase component that includes a relative phase difference between the first RF signal and the second RF signal as an output.

2. The apparatus of claim 1, wherein the local oscillator, the transmit path, and the receive path are embodied in a single integrated circuit.

3. The apparatus of claim 1, further comprising a first directional coupler coupled to the second RF output signal, wherein the first directional coupler is configured to generate the receive signal.

4. The apparatus of claim 1, wherein the transmit path comprises a processor configured to phase shift one or more signals digitally based at least partly on the control input provided to the phase control input, wherein the phase of the first RF output signal is based at least partly on the digitally shifted phase.

5. The apparatus of claim 1, further comprising:

a first directional coupler coupled to the first RF output signal, wherein the first directional coupler is configured to generate a second receive signal;

a second directional coupled to a second RF output signal, wherein the second directional coupler is configured to generate the receive signal for the receive path;

a second local oscillator separate from the local oscillator, wherein the second local oscillator is configured to generate a second local oscillator output signal;

a second transmit path configured to receive the second local oscillator output signal as an input and to generate the second RF output signal based at least partly on the second local oscillator output signal; and

a second receive path configured to receive the second local oscillator output signal and the second receive signal as inputs, wherein the second receive path is configured to generate a relative phase difference between the second local oscillator output signal and the second receive signal as an output.

6. The apparatus of claim 5, further comprising a processor coupled to outputs of the receive path and the second receive path, wherein the processor is configured to determine the relative phase differences using the outputs of the receive path and the second receive path, and to adjust at least the phase of the first RF output signal via the phase control input of the transmit path.

7. The apparatus of claim 5, further comprising a processor coupled to outputs of the receive path and the second receive path, wherein the processor is configured to determine the relative phase difference using the outputs of the receive path and the second receive path and to adjust the phase of the first RF output signal based at least partly on the relative phase difference, and wherein the transmit path comprises the processor.

8. The apparatus of claim 5, wherein the local oscillator, the transmit path, and the receive path are embodied in a first integrated circuit, and wherein the second local oscillator, the second transmit path, and the second receive path are embodied in a second integrated circuit separate from the first integrated circuit.

9. The apparatus of claim 5, wherein the local oscillator, the transmit path, the receive path, the second local oscillator, the second transmit path, and the second receive path are embodied in a single integrated circuit.

10. The apparatus of claim 1, further comprising:

a first directional coupler coupled to the first RF output signal, wherein the first directional coupler is configured to generate a second receive signal;

an N-th directional coupled to an N-th RF output signal, wherein the N-th directional coupler is configured to generate the receive signal for the receive path;

an N-th local oscillator separate from the local oscillator, wherein the N-th local oscillator is configured to generate an N-th local oscillator output signal;

an N-th transmit path configured to receive the N-th local oscillator output signal as an input and to generate the N-th RF output signal based at least partly on the N-th local oscillator output signal; and

an N-th receive path configured to receive the N-th local oscillator output signal and an N-th receive signal as inputs, wherein the N-th receive signal is not the second receive signal, wherein the receive path is configured to generate a relative phase difference between the N-th local oscillator output signal and the N-th receive signal as an output.

11. The apparatus of claim 1, further comprising:

a second receive path configured to receive the local oscillator output signal and a second receive signal as inputs, wherein the receive signal is RF sampled from the first RF output signal.

12. The apparatus of claim 11, wherein the local oscillator, the transmit path, the receive path, and the second receive path are embodied in a single integrated circuit.

13. The apparatus of claim 11, further comprising a first directional coupler coupled to the first RF output signal and a second directional coupler coupled to the second RF output signal, wherein the first directional coupler is configured to generate the second receive signal and the second directional coupler is configured to generate the receive signal.

14. The apparatus of claim 1, wherein the receive path is configured to downconvert the receive signal from RF to baseband based at least partly on the local oscillator output.

15. The apparatus of claim 1, wherein the receive path includes a quadrature path and an in-phase path.

16. The apparatus of claim 1, wherein the transmit path is configured to upconvert a baseband signal to RF based at least partly on the local oscillator output.

17. A method comprising:

generating a first RF signal in a transmission path based at least partly on a first local oscillator output signal;

providing an RF sample of the first RF signal to a receive path using a directional coupler;

generating a first baseband signal in the receive path based at least partly on the RF sample of the first RF signal and a second local oscillator output signal, wherein the second local oscillator output signal and the first local oscillator output signal are generated from separate local oscillators;

deriving, using a processor, a relative phase difference between the first local oscillator output and the second local oscillator output based at least partly on the first baseband signal.

18. The method of claim 17, further comprising using a phase shifter to adjust the phase of the first RF signal based at least partly on the relative phase difference.

19. The method of claim 18, wherein the phase shifter is implemented in the processor.

20. The method of claim 17, further comprising:

generating a second RF signal in a second transmission path based at least partly on the second local oscillator output signal;

providing an RF sample of the second RF signal to a second receive path using a second directional coupler; and

generating a second baseband signal in the second receive path based at least partly on the RF sample of the second RF signal;

wherein the deriving includes using the deriving uses the second baseband signal in determining the relative phase difference.

21. The method of claim 20, wherein the second baseband signal is based at least partly on the second local oscillator output.

22. The method of claim 17, wherein a non-transitory computer-readable storage media stores instructions for the deriving.

23. An apparatus comprising:

a local oscillator configured to generate a local oscillator output signal;

means for transmitting an RF signal having means for controlling a phase of the RF signal and means for upconverting a baseband signal to RF based at least partly on the local oscillator input; and

means for receiving a second RF signal having means for generating a signal with a phase component that includes a relative phase difference between the RF signal and the second RF signal.