Patent Application
20160036482
The present invention relates generally to wireless communication devices, and more specifically to optimizing antenna tuning for a wireless communication device.
Wireless communication devices, and in particular handheld wireless communication devices, have at least one antenna used for communications. The antenna may be used to radiate a transmit signal many times during a communication session. The transmit signal radiated from the antenna is affected by many variables, such as the position of the fingers and hand of a user holding the wireless communication device, the position of the wireless communication device with reference to other parts of the user's body, such as the head, the operational frequency of a transmitter coupled to the antenna, and the modulation used for the wireless signal being transmitted by the antenna. The antenna may be coupled to a power amplifier output of the wireless communication device by an antenna matching network, which may be adjusted by selections of values at inputs to the antenna matching network that are determined in an attempt to optimize the signal that is radiated from the antenna. One technique for optimization is to choose a setting for the antenna matching network that optimizes the power radiated by the antenna.
The accompanying figures, where like reference numerals refer to identical or functionally similar elements throughout the separate views, together with the detailed description below, are incorporated in and form part of the specification, and serve to further illustrate embodiments of concepts that include the claimed invention, and explain various principles and advantages of those embodiments. The description is meant to be taken in conjunction with the accompanying drawings in which:
Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of the embodiments.
In the description below, like reference numerals are used to describe the same, similar or corresponding parts in the several views of the drawings.
Embodiments described herein generally relate to determining a setting for an antenna matching network that optimizes a wireless communication signal radiated by an antenna that is coupled to the matching network, using a unique technique that uses both power maximization and return loss to achieve an optimized signal.
Referring to
The radio controller 120 may comprise a processing system or be a portion of the processing system of the human interface and support electronics function 110. The radio function 115 may be a wide area radio function, a Bluetooth radio function, or a local area network function, a satellite radio function, or any other radio function that is susceptible to antenna impedance changes due to the use and environment of the wireless communication device. The radio function 115 may provide transmitting and receiving functions (e.g., a cellular system transmitter-receiver), or a transmitting only function (e.g., a sign-post transmitter). The wireless communication device 100 may be a cellular telephone, an electronic tablet, an electronic pad, a local area network device, a vehicular communication device, or other radio device that is used in a way that causes changes to the antenna impedance of the antenna. The transceiver 125, the duplex filter 130, the antenna matching network 135, the power detector 140, and the antenna 145 may be conventional devices. The radio controller 120 may be a conventional device having unique program instructions, and is coupled to the transceiver 125 by signals 122 which control the parameters of the transceiver such as operational frequency, maximum power output, and modulation.
The RF PA of the transceiver 125 is designed to generate an RF signal at a selected power when coupled to a designed output impedance of the RF transmitter, e.g., 50 ohms resistive. The RF signal is coupled through the duplex filter 130, the antenna matching network 135, and the power detector 140 to the antenna 145. The duplex filter 130 provides isolation between the RF energy of signals intercepted by the antenna 145 that are within a receiving bandwidth and the RF energy generated by the transceiver 125 that is within a transmitting bandwidth. The duplex filter 130 may be a device that can be switched to accommodate different transmit and receive operating frequencies used in different radio networks or within a radio network at differing times. The setting of the duplex filter 130 to accommodate different transmit and receive operating frequencies is coupled from the radio controller 120 by signal 131. The antenna matching network 135 is a circuit that provides a selected impedance transform, also termed a setting, which is selected by control signals 137 from the radio controller 120. The antenna matching network 135 may comprise stages of passive impedance devices, each stage able to be set to one of a plurality of gains and/or phases that are primarily within a narrow frequency band. The narrow frequency bands of the stages are combined to provide an impedance transform over a wider frequency band. The selection may involve the use of transistor switches. Other types of circuits for providing a set of impedance transforms in an antenna matching network 135 may alternatively be used.
The controls signals 137 may convey a tuning selection input, which represents a particular set of environmental conditions that are converted by a tuning table (not shown in
A method used in certain embodiments to select a setting for the antenna matching network 135 is to determine a setting output that maximizes radiated antenna power for a given input power (i.e., maximizing power efficiency) at the beginning of a communication session, and maintain the setting while the operational frequency, modulation, and other environmental conditions are not changed. The radiated antenna power can be maximized by maximizing the power delivered to the antenna 145, which is the forward matching network power from the antenna matching network 135 to the antenna 145 minus the reflected antenna power from the antenna 145 to the antenna matching network 135. The maximum power delivered to the antenna 145 can be achieved by maximizing the scalar gain, /G/=/S21/, of the antenna matching network 135, the delivered power in dB units being 20*Log10/S21/, where S21 is the s-parameter defining the forward voltage gain with the output port impedance set to the antenna impedance. Thus the power detector 140 can be employed to measure the power delivered to the antenna 145 by measuring the scalar gain of the antenna matching network. Power detector 140 can also be used to measure the return loss of the antenna matching network 135 by measuring the scalar reflection coefficient, /S11/, of the antenna matching network 135, the return loss in dB units being equal to −20*Log10/S11/, where S11 is the s-parameter defining the voltage reflection coefficient at the input port of antenna matching network 135. In an embodiment power detector 140 measures the parameters or signal levels that are used by the radio controller 120 to determine the scalar gain and the and reflection coefficient of the matching network 135. In another embodiment power detector 140 includes programmable functionality for determining the scalar gain and reflection coefficient. The operational frequency is the spectrum resource that is allocated at the beginning of a communication session to convey payload information (voice, video, data files, etc.). For example, in some cellular systems, it is termed a band. However, recent investigations of combinations of wireless communication devices and environmental conditions have shown that setting the antenna matching network 135 to achieve maximum power efficiency can generate signal distortion that prevents the wireless communication device 100 from meeting certain newer performance specifications that have been established for certain radio systems. The investigations have shown that when the power efficiency is maximized subject to a constraint on return loss, the performance specifications can be met, whereas when power efficiency is maximized without constraining the return loss the performance specification are not always met. For example when return loss exceeds a threshold, error vector magnitude (EVM) and adjacent channel leakage ratio (ACLR) specifications can fail to be met. The constraint on return loss depends substantially upon the operational frequency, the modulation, the transmit portion of the duplex filter, and the antenna design. Since the antenna design does not change, the constraint may be determined using the operational frequency, the modulation, and the duplex filter. As noted above, the duplex filter may be determined solely by the operational frequency and modulation, reducing the constraint to be determined using the operational frequency and modulation.
Referring to
The methods described below rely on the use of a tuning selection input within a wireless communication device 100 to determine a setting for the antenna matching network 135. A tuning selection input may be used to obtain an initial setting of an antenna matching network that can then be optimized efficiently to provide a maximum transmitted power for the wireless control device, subject to the constraint of a maximum return loss. This results in improved performance. The tuning selection input may include information of any the following types: operational frequency identification, modulation type identification, call type (voice v. data), a speakerphone activation state, a speaker activation state, a wireless local area network activation state, a user identity, grip information, body proximity information, sensor input information, a transmit power level, a transmit receive level, and a receive signal to noise ratio. Modulation type may comprise a modulation method (18QAM, QPSK, SC-FDMA, etc.) and symbol or chip rate, and other related parameters. For example, a quantity of resource blocks that are in a frame may serve to convey the modulation information. In certain embodiments, selected ones of these information types, which are available within the wireless communication device, may be used during a design phase of a particular model of a wireless communication device to create a tuning table that establishes a best estimated setting for an antenna matching network that is to be used in the particular model of wireless communication devices for various combinations of the selected information types. Each combination of the selected information type is a tuning selection input. In the design phase, the effect of the environment on the antenna impedance is estimated for a nominal set of components used in the model of the wireless communication device, for a plurality of tuning selection inputs. This is converted to a tuning table that is stored in the wireless communication device. There are several embodiments that combine the use of a table with the technique of maximizing the forward power under the constraint of a maximum return loss.
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It should be apparent to those of ordinary skill in the art that for the methods described herein other steps may be added or existing steps may be removed, modified or rearranged without departing from the scope of the methods. Also, the methods are described with respect to the apparatuses described herein by way of example and not limitation, and the methods may be used in other systems.
In this document, relational terms such as first and second, top and bottom, and the like may be used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. The terms “comprises,” “comprising,” or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. An element preceded by “comprises . . . a” does not, without more constraints, preclude the existence of additional identical elements in the process, method, article, or apparatus that comprises the element. The term “coupled” as used herein is defined as connected, although not necessarily directly and not necessarily mechanically.
Reference throughout this document are made to “one embodiment”, “certain embodiments”, “an embodiment” or similar terms The appearances of such phrases or in various places throughout this specification are not necessarily all referring to the same embodiment. Furthermore, the particular features, structures, or characteristics attributed to any of the embodiments referred to herein may be combined in any suitable manner in one or more embodiments without limitation.
The term “or” as used herein is to be interpreted as an inclusive or meaning any one or any combination. Therefore, “A, B or C” means “any of the following: A; B; C; A and B; A and C; B and C; A, B and C”. An exception to this definition will occur only when a combination of elements, functions, steps or acts are in some way inherently mutually exclusive.
Reference may be made in this document to actions that are related to signals (that is, electrical values such as serial or parallel voltage or current values that are described with or without using the word “signal”). These actions are variously described as “coupling”, “receiving”, “transmitting”, “using”, “transferring” “generating”, “returning”, “conveying” and the like, in various verb forms. These actions are often described in a form in which the signal performs the action or the action acts upon the signal between two entities or functions. For example, “Signal X is coupled from function A to function B”, or “entity A transfers signal X to function B”. Often times one or the other or both of the entities or functions are not explicitly stated. For example, “Signal X is returned from entity A”. In these cases one or both of the entities or functions are often clearly implied by the context. It will be appreciated that the actions may include the storage and retrieval of the signal in a memory that is an entity in addition to the two entities or functions, or a memory that is part of one or the other of the entities or functions, and that the use of the memory may add a delay in the action described. (Such delays would have a duration that is appropriate for the embodiment being described.) Accordingly, the actions described for signals that occur between two entities or functions may imply storage in memory as part of the action. This is particularly true when the entities or functions are embodied within the same device. (In some instances one of the entities or functions that is related to the action may be explicitly stated to be, or may be implied to be, a memory.) As a consequence, the actions described above may be interpreted in many instances as meaning “storing” or “retrieving” the signal in/from a memory, or as including “storing” or “retrieving” the signal in/from a memory as a first part of the action. Just one example of this includes “transmitting a signal”, which may be interpreted in some embodiments to mean “storing a signal and transmitting the stored signal”, wherein the signal is to be later transmitted to an entity or function that may not be explicitly named.
The processes illustrated in this document, for example (but not limited to) the method steps described in
In the foregoing specification, specific embodiments have been described. However, one of ordinary skill in the art appreciates that various modifications and changes can be made without departing from the scope of the present invention as set forth in the claims below. Accordingly, the specification and figures are to be regarded in an illustrative rather than a restrictive sense, and all such modifications are intended to be included within the scope of present invention. The benefits, advantages, solutions to problems, and any element(s) that may cause any benefit, advantage, or solution to occur or become more pronounced are not to be construed as a critical, required, or essential features or elements of any or all the claims. The invention is defined solely by the appended claims including any amendments made during the pendency of this application and all equivalents of those claims as issued.
