With the ever-decreasing size of mobile terminals, the need for small and low profile antennas capable of operating at mobile frequencies is constantly growing. Internal antennas, such as microstrip antennas and planar inverted F antennas (PIFAs), are now frequently used in many mobile communication devices in place of more conventional external antennas, such as stub antennas and whip antennas. Internal antennas are typically placed inside the housing adjacent an upper end of the housing. Because users typically grasp the lower portion of the housing when using a mobile communication device, placement of the antenna near the upper end of the housing prevents the antenna from being obstructed by the user's hands. As the size of mobile communication devices decreases, however, the user's hand covers a relatively large portion of the housing, making it increasingly more difficult to place the internal antennas to avoid at least partial obstruction by the user's hand.
The present invention provides a method and apparatus to compensate for changes in antenna impedance caused by the placement of the user's hands on the housing in close proximity to the antenna. The invention is particularly useful in mobile communication devices having an internal antenna. Position sensors detect the position of the user's hand on the housing. The output signals from the sensors are used by the controller to adjust the source impedance of the transmitter and/or receiver based on the position of the user's hand to match the antenna impedance. In one exemplary embodiment, a configurable impedance matching circuit couples the transmitter and/or receiver to the antenna. The impedance matching circuit comprises one or more reactive elements, such as shunt capacitors and inductors, that are reconfigured responsive to control signals from the controller to vary the source impedance of the transmitter and/or receiver. In an alternate embodiment, the controller selectively switches between multiple antenna feed configurations based on the user's hand position to vary the impedance of the antenna.
Mobile communication device 10 comprises controller 12, memory 14, audio processing circuit 16, position sensors 18, user interface 20, transceiver 30, and antenna 50. Controller 12 controls the operation of mobile communication device 10 according to programs stored in memory 14. The controller 12 may comprise, for example, one or more microprocessors, hardware, firmware, or a combination thereof. Suitable microprocessors may include, for example, both general purpose and special purpose microprocessors and digital signal processors. Memory 14 represents the entire hierarchy of memory in a mobile communication device 10, and may include both random access memory (RAM) and read-only memory (ROM). Computer program instructions and data required for operation are stored in non-volatile memory, such as EPROM, EEPROM, and/or flash memory, which may be implemented as discrete devices, stacked devices, or integrated with controller 12.
One or more position sensors 18 are used to detect the position of the user's hands and/or fingers when holding the mobile communication device 10. As will be described in more detail below, controller 12 uses the detected hand position to adjust the source impedance of the transmitter 32 based on the position of the user's hands.
User interface 20 includes a keypad 22 and/or other input device, display 24, microphone 26, and speaker 28. Keypad 22 and display 24 enable the user to interact with the mobile communication device 10. Keypad 22 allows the user to dial numbers, enter commands, and navigate menus presented on display 24 to select desired options. Display 24 allows the user to see dialed numbers, status information, prompts, menus, and other information. Display 24 also allows the user to view and read messages and to view images and graphics. Microphone 26 converts the user's speech into electrical audio signals for transmission by the transceiver 30, and speaker 28 converts audio signals received by the transceiver 30 into audible signals that can be heard by the user. Audio processing circuit 16 provides basic analog output signals to speaker 28 and accepts analog audio input signals from microphone 26.
Transceiver 30 is coupled to antenna 50 for receiving and transmitting signals. Transceiver 30 is a fully functional cellular radio transceiver, which may operate according to any known standard, including the standards known generally as the Global System for Mobile Communications (GSM), TIA/EIA-136, cdmaOne, cdma2000, UMTS, and Wideband CDMA. Transceiver 30 includes a transmitter 32 and a receiver 34 coupled to the antenna 50 through an RF switching circuit 36. Electrical signals from transmitter 32 are applied to antenna 50, which converts the electrical signals into electromagnetic waves that radiate out from the antenna 50. Conversely, when antenna 50 is subjected to electromagnetic waves radiating through space, the electromagnetic waves are converted by the antenna 50 into an electrical signal that is applied to the receiver 34. In a preferred embodiment of the invention, transmitter 32 and/or the receiver 34 include an adaptive impedance matching circuit 38 to match the source impedance of the transmitter 32 to the antenna impedance, as will be described in greater detail below. Alternatively, the adaptive matching may be positioned between the RF switch 36 and the antenna 50.
Internal antenna 50 may be a planar antenna, such as a microstrip antenna, patch antenna, monopole antenna, or inverted F antenna.
The present invention compensates for changes in antenna impedance caused by the position of the user's hand on the back 44 of housing 40. According to the present invention, position sensors 18 disposed on a back 44 of housing 40 of mobile communication device 10 detect the position of the user's hand, which for purposes of this application includes the user's fingers. Controller 12 uses the output signals from the sensor 18 to adjust the source impedance of the transmitter 32 and/or the receiver 34 based on the position of the user's hand. More particularly, the impedance matching circuit 38 varies the source impedance of the transmitter 32. The impedance matching circuit 38 comprises one or more reactive elements, such as shunt or series capacitors and/or inductors that can be reconfigured responsive to control signals from the controller 12 to vary the source impedance of the transmitter 32. As is known to those skilled in the art, the impedance matching circuit may contain multiple elements in T, π, or other configurations. The impedance matching circuit 38 includes one or more RF switches which may include MEMS, pin diodes, Gallium Arcsine switches (GAS) or other switches for switching the various capacitors and inductors into and out of the transmission path responsive to a control signal from controller 12.
A variety of position sensors 18 may be used to detect the position of the user's hands, including capacitive sensors, light sensors, and resistive sensors. Preferred embodiments of the invention use film-type capacitive sensors that detect the variation in capacitance caused by the placement of the user's hands or fingers on the back 44 of housing 40. Film-type capacitive sensors can produce three-dimensional curved forms that conform to the housing geometry without losing its sensing function. One example of film-type capacitive sensors suitable for use with the present invention is marketed under the trade name GLIDEPOINT and is sold by ALPS Electric Company, Ltd. of Japan. Film-type capacitive sensors typically comprise two sets of orthogonal electrode arrays separated by a dielectric layer 106. The capacitively coupled electrode arrays form a grid with multiple sensing points that detect variations in capacitance caused by the proximity of the user's hand.
In one embodiment of the invention, settings for the impedance matching circuit 38 correlated with each possible codeword are stored in a look-up table in memory 14. The settings stored in the look-up table may, for example, comprise an m-bit codeword representing a particular configuration for the impedance matching circuit 38. For example, each bit in the m-bit codeword may correspond to a particular switch in the impedance matching circuit 38 and indicate the desired switch position.
In an alternate embodiment of the invention illustrated in
The present invention may, of course, be carried out in other specific ways than those herein set forth without departing from the scope and essential characteristics of the invention. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive, and all changes coming within the meaning and equivalency range of the appended claims are intended to be embraced therein.
This application is a divisional of U.S. patent application Ser. No. 10/837,829 filed May 3, 2004, which is incorporated herein by reference in its entirety.
Number | Date | Country | |
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Parent | 10837829 | May 2004 | US |
Child | 11766323 | Jun 2007 | US |