Extending beamforming capability of a coupled voltage controlled oscillator (VCO) array during local oscillator (LO) signal generation through frequency multiplication

A method includes separating phase of Local Oscillator (LO) signals generated by individual Voltage Controlled Oscillators (VCOs) of a coupled VCO array through varying voltage levels of voltage control inputs thereto. The method also includes frequency multiplying an output of each individual VCO of the coupled VCO array to increase a range of phase differences between the phase separated LO signals generated by the individual VCOs. Further, the method includes mixing the frequency multiplied outputs of the individual VCOs with signals from antenna elements of an antenna array to introduce differential phase shifts in signal paths coupled to the antenna elements during performing beamforming with the antenna array.

CLAIM OF PRIORITY

This application is a conversion application of U.S. provisional patent application No. 61/786,511 titled EXTENDING BEAM-FORMING CAPABILITY OF COUPLED VOLTAGE CONTROLLED OSCILLATOR (VCO) ARRAYS DURING LOCAL OSCILLATOR (LO) SIGNAL GENERATION THROUGH FREQUENCY MULTIPLICATION, filed on Mar. 15, 2013.

FIELD OF TECHNOLOGY

This disclosure generally relates to beamforming and, more specifically, to a method, a circuit and/or a system of extending beamforming capability of a coupled Voltage Controlled Oscillator (VCO) array during Local Oscillator (LO) signal generation through frequency multiplication.

BACKGROUND

A coupled Voltage Controlled Oscillator (VCO) array may be employed during Local Oscillator (LO) signal generation in a receiver (e.g., a wireless receiver) to generate differential phase shifts. The coupled VCO array may require an external reference signal injected therein to control an operating frequency thereof. Injection locking between the individual VCOs that are part of the coupled VCO array and between the VCOs and the external reference signal may limit the differential phase shift generation to a certain level, beyond which the injection locking breaks down. The phase difference between the VCOs may then become indeterminable.

SUMMARY

Disclosed are a method, a circuit and/or a system of extending beamforming capability of a coupled Voltage Controlled Oscillator (VCO) array during Local Oscillator (LO) signal generation through frequency multiplication.

In one aspect, a method includes separating phase of LO signals generated by individual VCOs of a coupled VCO array through varying voltage levels of voltage control inputs thereto. The method also includes frequency multiplying an output of each individual VCO of the coupled VCO array to increase a range of phase differences between the phase separated LO signals generated by the individual VCOs. Further, the method includes mixing the frequency multiplied outputs of the individual VCOs with signals from antenna elements of an antenna array to introduce differential phase shifts in signal paths coupled to the antenna elements during performing beamforming with the antenna array.

In another aspect, a beamforming system includes a coupled VCO array including a number of individual VCOs configured to have phase of LO signals generated therethrough separated by varying voltage levels of voltage control inputs thereto. The beamforming system also includes a number of frequency multiplier circuits, each of which is configured to frequency multiply an output of each individual VCO of the coupled VCO array to increase a range of phase differences between the phase separated LO signals generated by the individual VCOs. Further, the beamforming system includes an antenna array including a number of antenna elements, and a number of mixers, each of which is configured to mix the frequency multiplied output of the each individual VCO with a signal from an antenna element of the antenna array to introduce differential phase shifts in signal paths coupled to the antenna elements during performing beamforming with the antenna array.

In yet another aspect, a wireless communication system includes a beamforming system. The beamforming system includes a coupled VCO array including a number of individual VCOs configured to have phase of LO signals generated therethrough separated by varying voltage levels of voltage control inputs thereto. The beamforming system also includes a number of frequency multiplier circuits, each of which is configured to frequency multiply an output of each individual VCO of the coupled VCO array to increase a range of phase differences between the phase separated LO signals generated by the individual VCOs. Further, the beamforming system includes an antenna array including a number of antenna elements, and a number of mixers, each of which is configured to mix the frequency multiplied output of the each individual VCO with a signal from an antenna element of the antenna array to introduce differential phase shifts in signal paths coupled to the antenna elements during performing beamforming with the antenna array.

The wireless communication system also includes a receiver channel configured to receive a combined output of the number of mixers.

Other features will be apparent from the accompanying drawings and from the detailed description that follows.

Other features of the present embodiments will be apparent from the accompanying drawings and from the disclosure that follows.

DETAILED DESCRIPTION

Example embodiments, as described below, may be used to provide a method, a circuit and/or a system of extending beamforming capability of a coupled Voltage Controlled Oscillator (VCO) array during Local Oscillator (LO) signal generation through frequency multiplication. Although the present embodiments have been described with reference to specific example embodiments, it will be evident that various modifications and changes may be made to these embodiments without departing from the broader spirit and scope of the various embodiments.

FIG. 1shows a Radio Frequency (RF)-scanned beamforming system100, according to one or more embodiments. Beamforming may be a processing technique for electronically pointing fixed arrays of antenna apertures during wireless transmission and/or reception. For example, beamforming may be used to create a focused antenna beam by shifting a signal in time or in phase to provide gain of the signal in a desired direction and to attenuate the signal in other directions. Here, the arrays may be one-dimensional, two-dimensional, or three-dimensional, and the electronic pointing of an antenna array may be performed for transmission and/or reception of signals. Beamforming may be utilized to direct the energy of a signal transmitted from an antenna array and/or to concentrate the energy of a received signal into an antenna array. Electronically pointing an antenna array may be faster and more flexible than physically pointing a directional antenna.

By directing the energy from and/or concentrating the energy incoming to an antenna array, higher efficiency may be achieved when compared to implementations utilizing a standard antenna. This may result in a capability to transmit and/or receive signals correspondingly to and/or from more distant receiving and/or transmitting radios.

Beamforming may be commonly accomplished by introducing differential phase shifts in the signal paths connected to each of the antenna apertures (antenna elements). One conventional technique, shown inFIG. 1(e.g., an example beamforming system such as RF-scanned beamforming system100), may introduce the required phase shifts in the signal paths by using an RF-scanned array (e.g., including antenna array106), in which explicit phase shifters104are connected directly in series with the signal paths (e.g., signal paths from antenna array106). As shown inFIG. 2(another example beamforming system), another conventional technique may introduce the required phase shifts in the signal paths by using a Local Oscillator (LO)-scanned array, in which LO signals102with differential phases are generated and the differential phase LO signals102input to mixers111(see alsoFIG. 1) located in the signal paths (e.g., signal paths coupled to antenna array106).

Antenna array106may be utilized in beam-steering or directing and/or focusing of transmitted/received signals. By directing the energy from and/or concentrating the energy incoming thereto, a higher efficiency may be achieved compared to a standard antenna implementation. This may result in the capability to transmit and/or receive signals corresponding to and/or from more distant receiving or transmitting radios, as discussed above.

A voltage controlled oscillator (VCO)101(seeFIGS. 1-4) may be an electronic oscillator configured to vary oscillation frequency thereof based on a voltage input.FIGS. 1-4serve to describe the receiver (e.g., wireless receiver) context in which exemplary embodiments discussed herein may be practiced. The function of VCO101in LO signal generation (e.g., LO signal(s)102ofFIGS. 1-2) as applied to receivers is well known to one of ordinary skill in the art. In order to generate differential phase LO signals, a coupled VCO array may be utilized.FIG. 2shows an LO scanned beamforming system200including a coupled VCO array250. Here, coupled VCO array250may include two or more VCOs101mutually injection locked to each other. Injection locking may be the state in which the two or more VCOs101exchange oscillatory energy sufficient enough to lock to a same frequency. Injection locking may be accomplished based on coupling VCOs101together through a bidirectional coupling circuit (e.g., resistor103; other bidirectional circuits may also be used instead).

When a single VCO101is used, voltage control is utilized to vary the frequency thereof, as discussed above. In coupled VCO array250, once the two or more VCOs101are injection locked to each other, the voltage control inputs (e.g., control inputs306shown inFIG. 3) to the two or more VCOs101may still be utilized to vary the frequency of coupled VCO array250provided that the voltage control inputs have the same voltage levels and are varied in the same manner. If the voltage levels are different, the phase of the signals generated by the individual VCOs101may be separated. The aforementioned phase separation between the LO signals generated by the individual VCOs in coupled VCO array250may be utilized to perform beamforming when the phase-separated LO signals (e.g., LO signals102) are mixed (e.g., through mixers111) with transmit or receive signals to or from antenna array106. The outputs of mixers111may be combined at a combiner112(e.g., a combiner circuit).

FIG. 1also shows beamformer150; said beamformer150is shown as including a switch matrix113and combiner112; switch matrix113may be understood to be circuitry associated with routing signals (e.g., RF signals) between multiple inputs and outputs; combiner112, obviously, may combine the multiple outputs of switch matrix113. Here, the outputs of phase shifters104may serve as the multiple inputs to switch matrix113.

InFIG. 2, voltage control inputs of coupled VCO array250may be utilized exclusively for achieving phase separation between VCOs101. Therefore, the voltage control inputs may be no longer available to be used for controlling the operating frequency of coupled VCO array250. As the aforementioned operating frequency control is essential to a beamforming system, a separate reference signal may be injected into coupled VCO array250.FIG. 3shows coupled VCO array250with a reference input signal305thereto (e.g., shown as being coupled to VCOs101through unidirectional coupling circuit304). The frequency control of reference input signal305may be accomplished through a system independent of coupled VCO array250. The mechanism for injecting reference input signal305may also be based on injection locking. Thus, VCOs101ofFIG. 3may not only be mutually injection locked to each other, but also injection locked to reference input signal305. As discussed above, control inputs306may be utilized to vary the frequency of coupled VCO array250.

Coupled VCO array250may only generate differential phase shifts up to a certain level. Beyond this level, mutual injection locking may break down, and phase differences between VCOs101may be indeterminable. Thus, the range of possible LO phase differences generated through coupled VCO array250may be limited.

It will be appreciated that concepts disclosed herein may also be applied to two-dimensional or three-dimensional arrays of VCOs101, in addition to one-dimensional arrays thereof.FIG. 4shows frequency multiplication incorporation in an improved coupled VCO array400, according to one or more embodiments. In one or more embodiments, coupled VCO array400may be analogous to coupled VCO array250; elements of coupled VCO array400are numbered the same way inFIG. 4as elements of coupled VCO array250. In one or more embodiments, the range of possible LO phase differences of a differential phase LO system may be increased by frequency multiplying each output of a VCO101of coupled VCO array400.FIG. 4shows a frequency multiplier402placed in the individual signal path between a VCO101and a mixer (e.g., mixer111).

In one or more embodiments, the factor by which the frequency is multiplied may also be the factor by which the phase difference range is increased (relative to the period of the LO signal). For example, doubling the frequency of the phased LO signals may also double the phase difference therebetween. If M is the frequency multiplication factor (e.g., M=2 indicates frequency doubling), and P the phase difference between two LO signals (in degrees), then M×P is the resulting phase difference after frequency multiplication. Circuit configurations of frequency multiplier402are well known to one skilled in the art. The choice of frequency multiplier architecture may not influence the range of phase differences obtained through the teachings of the exemplary embodiments discussed herein.

In one or more embodiments, by increasing the range of phase differences, including frequency multipliers402in a beamforming LO generation system (e.g., LO scanned beamforming system200) may improve the beamforming performance of the system; the system may also be improved from a power, cost, and flexibility point of view. In one or more embodiments, wider beamforming angles may be used to aid performance and flexibility of design and/or implementation. Additionally, in one or more embodiments, when using frequency multipliers402, it may be possible to design coupled VCO array400at lower frequencies compared to coupled VCO array250, resulting in lower power, lower cost, and an easier, less-risky design. It should be noted that a length of coupled VCO array400(e.g., a number of VCOs101therein) may be extrapolated as shown inFIG. 4based on a requirement of the beamforming discussed above. Further, it should be noted that a combined output of mixers111inFIG. 2may be input to a channel of a wireless receiver incorporating the beamforming discussed above.

FIG. 5shows a process flow diagram detailing operations involved in extending beamforming capability of coupled VCO array400during LO signal generation through frequency multiplication, according to one or more embodiments. In one or more embodiments, operation502may involve separating phase of LO signals (e.g., LO signals102) generated by individual VCOS101of coupled VCO array400through varying voltage levels of voltage control inputs (e.g., control inputs306) thereto. In one or more embodiments, operation504may involve frequency multiplying an output of each individual VCO101of coupled VCO array400to increase a range of phase differences between the phase separated LO signals generated by the individual VCOs101. In one or more embodiments, operation506may then involve mixing the frequency multiplied outputs of the individual VCOs101with signals from antenna elements of antenna array106to introduce differential phase shifts in signal paths coupled to the antenna elements during performing beamforming with antenna array106.

Although the present embodiments have been described with reference to specific example embodiments, it will be evident that various modifications and changes may be made to these embodiments without departing from the broader spirit and scope of the various embodiments. Accordingly, the specification and drawings are to be regarded in an illustrative rather than a restrictive sense.