Patent Publication Number: US-9837714-B2

Title: Extending beamforming capability of a coupled voltage controlled oscillator (VCO) array during local oscillator (LO) signal generation through a circular configuration thereof

Description:
CLAIM OF PRIORITY 
     This application is a conversion application of the U.S. provisional application No. 61/799,181 titled EXTENDING BEAM-FORMING CAPABILITY OF COUPLED VOLTAGE CONTROLLED OSCILLATOR (VCO) ARRAYS DURING LOCAL OSCILLATOR (LO) SIGNAL GENERATION THROUGH A CIRCULAR CONFIGURATION THEREOF, 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 a circular configuration thereof. 
     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 a circular configuration thereof. 
     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 coupling the individual VCOs of the coupled VCO array to one another in a closed, circular configuration to increase phase difference between the phase separated LO signals generated by the individual VCOs compared to a linear configuration of the coupled VCO array. Further, the method includes mixing outputs of the individual VCOs of the circular coupled VCO array 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 individual VCOs of the coupled VCO array are coupled to one another in a closed, circular configuration to increase phase difference between the phase separated LO signals generated by the individual VCOs compared to a linear configuration of the coupled VCO array. The beamforming system also includes an antenna array including a number of antenna elements, and a number of mixers, each of which is configured to mix an output of each individual VCO of the circular coupled VCO array 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 individual VCOs of the coupled VCO array are coupled to one another in a closed, circular configuration to increase phase difference between the phase separated LO signals generated by the individual VCOs compared to a linear configuration of the coupled VCO array. The beamforming system also includes an antenna array including a number of antenna elements, and a number of mixers, each of which is configured to mix an output of each individual VCO of the circular coupled VCO array 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 of the beamforming system. 
     Other features will be apparent from the accompanying drawings and from the detailed description that follows. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
       Example embodiments are illustrated by way of example and not limitation in the figures of the accompanying drawings, in which like references indicate similar elements and in which: 
         FIG. 1  is a schematic view of a Radio Frequency (RF)-scanned beamforming system. 
         FIG. 2  is a schematic view of a Local Oscillator (LO) scanned beamforming system. 
         FIG. 3  is a schematic view of a coupled Voltage Controlled Oscillator (VCO) array of the LO scanned beamforming system of  FIG. 2 . 
         FIG. 4  is a schematic view of a closed, circular architecture of the coupled VCO array of the LO scanned beamforming system of  FIG. 2 , according to one or more embodiments. 
         FIG. 5  is a process flow diagram detailing operations involved in extending beamforming capability of the coupled VCO array of  FIG. 4  during LO signal generation through a circular configuration thereof, according to one or more embodiments. 
     
    
    
     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 a circular configuration thereof. 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. 1  shows a Radio Frequency (RF)-scanned beamforming system  100 , 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 in  FIG. 1  (e.g., an example beamforming system such as RF-scanned beamforming system  100 ), may introduce the required phase shifts in the signal paths by using an RF-scanned array (e.g., including antenna array  106 ), in which explicit phase shifters  104  are connected directly in series with the signal paths (e.g., signal paths from antenna array  106 ). As shown in  FIG. 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 signals  102  with differential phases are generated and the differential phase LO signals  102  input to mixers  111  (see also  FIG. 1 ) located in the signal paths (e.g., signal paths coupled to antenna array  106 ). 
     Antenna array  106  may 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  (see  FIGS. 1-4 ) may be an electronic oscillator configured to vary oscillation frequency thereof based on a voltage input.  FIGS. 1-4  serve to describe the receiver (e.g., wireless receiver) context in which exemplary embodiments discussed herein may be practiced. The function of VCO  101  in LO signal generation (e.g., LO signal(s)  102  of  FIGS. 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. 2  shows an LO scanned beamforming system  200  including a coupled VCO array  250 . Here, coupled VCO array  250  may include two or more VCOs  101  mutually injection locked to each other. Injection locking may be the state in which the two or more VCOs  101  exchange oscillatory energy sufficient enough to lock to a same frequency. Injection locking may be accomplished based on coupling VCOs  101  together through a bidirectional coupling circuit (e.g., resistor  103 ; other bidirectional circuits may also be used instead). 
     When a single VCO  101  is used, voltage control is utilized to vary the frequency thereof, as discussed above. In coupled VCO array  250 , once the two or more VCOs  101  are injection locked to each other, the voltage control inputs (e.g., control inputs  306  shown in  FIG. 3 ) to the two or more VCOs  101  may still be utilized to vary the frequency of coupled VCO array  250  provided 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 VCOs  101  may be separated. The aforementioned phase separation between the LO signals generated by the individual VCOs in coupled VCO array  250  may be utilized to perform beamforming when the phase-separated LO signals (e.g., LO signals  102 ) are mixed (e.g., through mixers  111 ) with transmit or receive signals to or from antenna array  106 . The outputs of mixers  111  may be combined at a combiner  112  (e.g., a combiner circuit). 
       FIG. 1  also shows beamformer  150 ; said beamformer  150  is shown as including a switch matrix  113  and combiner  112 ; switch matrix  113  may be understood to be circuitry associated with routing signals (e.g., RF signals) between multiple inputs and outputs; combiner  112 , obviously, may combine the multiple outputs of switch matrix  113 . Here, the outputs of phase shifters  104  may serve as the multiple inputs to switch matrix  113 . 
     In  FIG. 2 , voltage control inputs of coupled VCO array  250  may be utilized exclusively for achieving phase separation between VCOs  101 . Therefore, the voltage control inputs may be no longer available to be used for controlling the operating frequency of coupled VCO array  250 . As the aforementioned operating frequency control is essential to a beamforming system, a separate reference signal may be injected into coupled VCO array  250 .  FIG. 3  shows coupled VCO array  250  with a reference input signal  305  thereto (e.g., shown as being coupled to VCOs  101  through unidirectional coupling circuit  304 ). The frequency control of reference input signal  305  may be accomplished through a system independent of coupled VCO array  250 . The mechanism for injecting reference input signal  305  may also be based on injection locking. Thus, VCOs  101  of  FIG. 3  may not only be mutually injection locked to each other, but also injection locked to reference input signal  305 . As discussed above, control inputs  306  may be utilized to vary the frequency of coupled VCO array  250 . 
     Coupled VCO array  250  may only generate differential phase shifts up to a certain level. Beyond this level, mutual injection locking may break down, and phase differences between VCOs  101  may be indeterminable. Thus, the range of possible LO phase differences generated through coupled VCO array  250  may be limited. 
     It will be appreciated that concepts disclosed herein may also be applied to two-dimensional or three-dimensional arrays of VCOs  101 , in addition to one-dimensional arrays thereof.  FIG. 4  shows a coupled VCO array  400  having a closed, circular architecture, according to one or more embodiments. In one or more embodiments, coupled VCO array  400  may be formed by wrapping around and coupling VCOs  101  of the linear coupled VCO array  250 , along with bidirectional coupling circuits  103 . In one or more embodiments, coupled VCO array  400  may still function through mutual injection locking, and may still require an independent reference frequency source (e.g., independent reference source  404 ) to control operating frequency thereof. In one or more embodiments, coupling VCOs  101  in a circle as coupled VCO array  400  may not limit a number thereof; the number of VCOs  101  may be increased by addition of one or more bidirectional circuits  103 . 
     In one or more embodiments, the circular configuration of coupled VCO array  400  may allow for increased phase difference between the LO signals (e.g., LO signals  102 ) generated compared to the linear coupled VCO array  250 . In or more embodiments, as individual VCOs  101  in coupled VCO array  400  are generally in equal proximity to one other, any subset thereof may be chosen to generate a requisite phase difference between the LO signals. In contrast, linear arrays may limit the number of VCOs that can be chosen because the outermost VCOs  101  therein have fewer VCOs  101  adjacent thereto; the potential phase differences that can be generated based on VCOs  101  located at the ends of coupled VCO array  250  may also be limited. 
     Additionally, in one or more embodiments, as each VCO  101  of coupled VCO array  400  is connected to multiple VCOs  101 , all VCOs  101  thereof may mutually exchange energy. In contrast, the end VCOs  101  of the linear coupled VCO array  250  may have fewer adjacent VCOs  101  thereto, which results in reduced mutual exchange of energy. Also, in one or more embodiments, coupled VCO array  400  may provide for an improved ability to mutually injection lock VCOs  101  thereof, thereby improving the possible LO phase difference range. Through the increase in the range of usable phase differences, in one or more embodiments, coupled VCO array  400  may improve the beamforming performance of a system (e.g., LO scanned beamforming system  200 ), and may also improve the system from a power, cost, and flexibility point of view. 
     In one or more embodiments, coupled VCO array  400  may be broken at any point, or points, to form independent linear coupled VCO sub-arrays, thereby providing flexibility in system architecture. In one or more embodiments, the mechanism of breaking coupled VCO array  400  into multiple arrays may be achieved by transforming selected bidirectional coupling circuits  103  into isolation circuits. In one or more alternate embodiments, the mechanism of breaking coupled VCO arrays  400  into multiple arrays may be achieved through the inclusion of switches in bidirectional coupling circuits  103  that can be opened, thereby providing isolation. 
     Flexibility in system architecture may be advantageous for a variety of purposes. For example, half of coupled VCO array  400  may be used to track one transmitter, and the other half may be used to independently track another transmitter. Additionally, independent linear coupled VCO sub-arrays of coupled VCO array  400  may provide for omni-directional reception/transmission, with all of the antennas in the system receiving/transmitting independently. 
     It is obvious that VCOs  101  in coupled VCO array  400  may generate the LO signals (e.g., LO signals  102 ). The LO signals may be mixed at mixers  111  with signals from antenna elements of antenna array  106  to introduce differential phase shifts in signal paths coupled to the antenna elements during beamforming with antenna array  106 . Further, it should be noted that a combined output of mixers  111  in  FIG. 2  may be input to a channel of a wireless receiver incorporating the beamforming discussed above. 
       FIG. 5  shows a process flow diagram detailing operations involved in extending beamforming capability of coupled VCO array  400  during LO signal generation through a circular configuration thereof, according to one or more embodiments. In one or more embodiments, operation  502  may involve separating phase of LO signals generated by individual VCOs  101  of coupled VCO array  400  through varying voltage levels of voltage control inputs (e.g., control inputs  306 ) thereto. In one or more embodiments, operation  504  may involve coupling the individual VCOs  101  of coupled VCO array  400  to one another in a closed, circular configuration to increase phase difference between the phase separated LO signals generated by the individual VCOs  101  compared to a linear configuration of the coupled VCO array (e.g., coupled VCO array  250 ). In one or more embodiments, operation  506  may then involve mixing outputs of the individual VCOs  101  of the circular coupled VCO array  400  with signals from antenna elements of antenna array  106  to introduce differential phase shifts in signal paths coupled to the antenna elements during performing beamforming with antenna array  106 . 
     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.