Abstract:
Wireless communication device tuning an antenna matching circuit to favor a receive band efficiency over a transmit band efficiency in an acquisition state. Systems and methods are provided that increase the antenna efficiency in the receive band when the wireless communication device is searching for a synchronization message in order to acquire a communication channel. The antenna efficiency may be changed incrementally or may be optimized completely for the receive frequency. The increase in antenna efficiency in the receive band is accomplished by tuning the antenna matching circuit. One way to tune the antenna matching circuit is to apply a voltage to a ferro-electric capacitor in the matching circuit, thereby changing the capacitance of the ferro-electric capacitor, thereby changing the impedance of the matching circuit.

Description:
RELATED APPLICATIONS  
       [0001]     This application relates to the following two U.S. patent applications filed on the same day, having the same inventors, and assigned to the assignee of the present invention, and which are hereby incorporated herein by reference: “MOBILE STATION ACCESS AND IDLE STATE ANTENNA TUNING SYSTEMS AND METHODS” and “MOBILE STATION TRAFFIC STATE ANTENNA TUNING SYSTEMS AND METHODS”.  
       BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The invention relates generally to wireless electronic communications and more particularly to antenna tuning systems and methods.  
         [0004]     2. Background  
         [0005]     In a communication system with different transmit and receive frequencies, mobile station antenna efficiency is a balance between optimization for the transmit frequency and optimization for the receive frequency. Under typical operating conditions, the typical antenna efficiency balance allows for the best use of the transmit and receive resources. However, commonly, conditions occur in which the typical antenna efficiency balance is not preferred. In such conditions, it can be said that the forward and reverse links are not balanced.  
         [0006]     The forward link is the communication link for data (voice data or other data) travelling from a base station transmitter to a mobile station receiver. The reverse link is the communication link for data (voice data or other data) from the mobile station transmitter to the base station receiver.  
         [0007]     When a mobile station is in an acquisition state, the mobile station does not transmit any signal. Acquisition state means that the mobile station is attempting to acquire a channel, that is, the mobile station is attempting to find a pilot channel or a synchronization (SYNC) channel of a base station. This is commonly referred to as scanning for a channel.  
         [0008]     A mobile station in acquisition state typically uses a preferred roaming list (PRL) to control the scanning. The PRL is a prioritized list of channels that the mobile station scans when looking for a pilot channel of a base station. A PRL is stored in the memory of the wireless communication device. The PRL contains records of all of the wireless communication systems or networks that the wireless communication device can communicate with. Several examples of using PRL&#39;s are described in U.S. Pat. No. 5,995,829, issued Nov. 30, 1999; U.S. Pat. No. 6,415,148 B1, issued Jul. 2, 2002; U.S. Pat. No. 6,466,802 B1 issued Oct. 15, 2002; U.S. Pat. Appl. No. 2003/0134637 A1 published Jul. 17, 2003; U.S. Pat. Appl. No. 2004/0110503, published Jun. 10, 2004; and U.S. Pat. Appl. No. 2004/0121781 A1, published Jun. 24, 2004, which are each hereby incorporated in whole herein by reference.  
       SUMMARY OF THE INVENTION  
       [0009]     When scanning for a channel (that is, in the acquisition state), a mobile station is only receiving, and is not transmitting any signal. It is advantageous to tune an antenna matching circuit for optimum antenna efficiency in the receive frequency band. The antenna efficiency may be shifted a small amount or a large amount toward the receive frequency band. The antenna efficiency may even be optimized completely for the receive frequency band.  
         [0010]     The antenna efficiency balance is tuned by tuning the antenna matching circuit. One way to tune the antenna matching circuit is to apply a voltage to a ferro-electric capacitor in the matching circuit, thereby changing the capacitance of the ferro-electric capacitor, thereby changing the impedance of the antenna system (antenna and matching circuit).  
         [0011]     Other aspects, advantages, and novel features of the invention will become apparent from the following Detailed Description of Preferred Embodiments, when considered in conjunction with the accompanying drawings.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]     Preferred embodiments of the present inventions taught herein are illustrated by way of example, and not by way of limitation, in the figures of the accompanying drawings, in which:  
         [0013]      FIG. 1  is a block diagram illustrating a wireless communication device tuning an antenna match in an acquisition state.  
         [0014]      FIG. 2  is a plot illustrating a tunable antenna efficiency.  
         [0015]      FIG. 3  is a flow chart illustrating a method for tuning an antenna efficiency in an acquisition state. 
     
    
     DETAILED DESCRIPTION  
       [0016]      FIG. 1  is a block diagram illustrating a wireless communication device tuning an antenna match in an acquisition state. Wireless communication device  100  may be a cellular telephone for communicating with a base station, such as, for example, a code division multiple access (CDMA) mobile station. However, wireless communication device  100  may be any wireless communication device that enters an acquisition state and communicates in at least two frequency bands, for example, a frequency division duplex (FDD) system where Tx and Rx signals don&#39;t share the same frequency band, for example in a CDMA system.  
         [0017]     Wireless communication device  100  includes antenna  102  for radiating electromagnetic signals into the air and for receiving electromagnetic signals from the air. Only one antenna  102  is shown, though multiple antennas are possible. Antenna  102  is connected to tunable matching circuit  104 . Tunable matching circuit  104  may be a ferro-electric tunable matching circuit as described in any of co-pending U.S. patent application Ser. Nos. 10/899,218; 10/899,278; 10/899,285; each filed Jul. 26, 2004; and Ser. No. 10/806,763, filed Mar. 22, 2004, which are each hereby incorporated by reference. Alternatively, tunable antenna matching circuit may be tunable by means of a varactor diode, micro-electrical mechanical switches or other switches switching various reactive components in and out of matching circuit  104  or switching complete matching circuits in and out of the signal path, or by any other convenient means of tuning matching circuit  104 .  
         [0018]     Matching circuit  104  is connected to duplexer  106 . Duplexer  106  duplexes transmit and receive signals. Alternatively, duplexer  106  could be a switch for duplexing transmit and receive signals. Duplexer  106  is connected to transmit path  107 , represented by power amplifier (PA)  108 . Duplexer  106  is also connected to receive path  109 , represented by low noise amplifier (LNA)  110 . Transmit path  107  and receive path  109  are connected to processor  115 . Processor  115  may be a Qualcomm™ mobile station modem (MSM), such as a commercially available Qualcomm™ 6000 series MSM, for CDMA communications.  
         [0019]     Processor  115  includes controller  120 . Processor  115  demodulates the received signal on receive path  109 . User interface devices, such as speaker  154 , microphone  157 , display  160  and keypad  163  are also connected to processor  115 . In one embodiment, the mobile station  100  communicates in an IS-2000 cellular communication system. See TIA/EIA/IS-2000, New York, N.Y., USA.  
         [0020]     Controller  120  may include one or more of optimum receive (Rx) table  135 , and transmit/receive (Tx/Rx) table  140 . Controller  120  uses Tables  135  and  140  to control antenna matching circuit  104 . An example optimum Rx table  135  is shown below as Table 1. An example Tx/Rx table  140  is shown below as Table 2.  
         [0021]     The values in Table 1 may be optimally determined by experiment, and other rows may be added to Table 1 as a result of experimental determinations. In Table 1, only two receive channels are shown for illustration. In practice many more channels may be be stored. Further, the channel designations shown in Table 1 may not be actual receive channels. Instead, the channel designations may refer to groups of channels. For example, the lowest 200 channels may be designated as channel (or group)  1  in Table 1. The second group of 200 channels may be designated as channel (or group)  2  in Table 1. Thus, the lowest 200 channels may have the same matching circuit setting, for any given temperature.  
         [0022]     Processor  115  is connected to matching circuit  104  by control line  142 . Control line  142  supplies a control voltage to matching circuit  104 , such as, for example, 0.12 Volts in the above example. A separate voltage source (not shown) may be provided for supplying the control voltage to matching circuit  104 . Or, as shown, the control voltage is supplied by processor  115  directly, responsive to the output of Table 1 or 2, as determined by controller  120 . Some commercially available processors, such as the above-referenced Qualcomm™ 6000 series MSM, available control voltages on general purpose input/output (GPIO) lines. The maximum voltage available on these lines is about 2.6 volts. Thus, it may be advantageous to limit the matching circuit control voltages to a maximum of 2.6 volts, to avoid using additional voltage sources. Multiple control lines may be used to control multiple matching circuits or multiple matching circuit components, such as multiple FE capactors, depending on the matching circuit topology.  
         [0023]     Controller  120  is shown internal to processor  115 . In practice, controller may be external or partially external to processor  115 . A separate controller may be provided. For example, a controller may be a separate integrated circuit or may include one or more discrete components. In that case, processor  115  might provide channel or group designations to controller externally.  
         [0024]     Processor  115  is connected to memory  144 . Tables 1-2 are shown internal to controller  120 , which is shown internal to processor  115 . Tables 1-2 may be stored in memory  144 . Tables 1-2 are shown internal to controller  120  for illustration, since controller uses Tables 1-2 to look up matching circuit settings.  
                                     TABLE 1                               Matching Circuit       Channel or Group   Temperature (° C.)   Setting (Volts)                                1   &lt;0   2.52       1    0 to 35   2.26       1   35 to 60   2.12       1   &gt;60   2.0       2   &lt;0   2.60       2    0 to 35   2.44       2   35 to 60   2.30       2   &gt;60   2.18                  
 
         [0025]     Another table, such as Table 2, stores matching circuit settings for moving stepwise toward better transmit matching or stepwise toward better receive matching. Either stepwise movement or optimum Rx settings can be used. An example Table 2 is shown below. As is the case for Table 1, experiment will give optimum values for Table 2.  
                                         TABLE 2                                   Bin Number   Matching Circuit Setting (Volts)                                        1   0.0           2   0.13           3   0.26           4   0.38           5   0.50           6   0.62           7   0.73           8   0.83                      
 
         [0026]     Table 2 does not include temperature as a parameter. Temperature may be included, increasing the complexity and accuracy of Table 2. Further, only eight bins are shown in Table 2. In practice, many more bins are recommended.  
         [0027]     As described above, controller  120  determines a matching circuit setting for matching circuit  104 .  FIG. 2  is a plot illustrating a tunable antenna efficiency which can be tuned responsive to the determined matching circuit setting. Antenna efficiency  147  is plotted against frequency  150 . An example antenna efficiency  153  is shown as curve  153 . Antenna efficiency  153  can be tuned by tuning matching circuit  104 . As matching circuit  104  is tuned, curve  153  can be moved to higher or lower frequencies, as shown by arrows  156  and  159 . As described in the above referenced copending U.S. patent application Ser. Nos. 10/899,278 and 10/899,218, curve  153  may be tuned to provide maximum efficiency for the currently used receive channel. Further, curve  153  is tuned responsive to commands from controller  120 , based on Tables 1-2.  
         [0028]     For example, if controller (or processor) calls for an optimum Rx setting, controller retrieves the optimum Rx setting from Table 1, and tunes curve  153 , so that peak  162  is positioned at the frequency corresponding to the current Rx channel or group of channels and the current temperature. Advantageously, the antenna efficiency is improved in the current Rx channel when improved Rx efficiency is necessary, that is, when the wireless communication device is in an acquisition state. In such a case, the Tx antenna efficiency may be degraded, but this occurs at a time when Tx antenna efficiency is not needed. Thus, the forward link is optimized when needed and system resources are more optimally utilized.  
         [0029]     As described above with respect to Table 2, if a stepwise shift in matching circuit setting is called for, then a matching circuit setting will be selected from Table 2. Controller  120  keeps track of which bin the matching circuit setting is currently in. Then, when a stepwise shift in matching circuit setting is called for, controller  120  looks up the new matching circuit setting in Table 2, based on the current bin. For example, if the current matching circuit setting is 0.13 Volts, that is, bin number  2 , and controller or processor calls for a stepwise shift in matching circuit setting to improve the Rx efficiency, then controller  120  will look up the next bin, bin  3 , and find the matching circuit setting corresponding to bin  3 , which, in this case, is 0.26 Volts. Controller  120  will tune matching circuit  104  by applying 0.26 Volts to matching circuit  104 , thereby moving curve  153  one bin toward the Rx frequency band.  
         [0030]      FIG. 3  is a flow chart illustrating a method for tuning an antenna efficiency (such as curve  153  in  FIG. 2 ) in an acquisition state. The method of  FIG. 3  is one method for implementing acquisition state antenna tuning as described herein. It will be understood that variations are possible.  
         [0031]     The method starts in step  165 . In step  170 , the mobile station enters an acquisition (ACQ) state. In step  175 , the mobile station selects a communication channel to be searched, typically from a system determination algorithm involving a preferred roaming list. In step  180 , the matching circuit is adjusted to favor the receive band of the selected communication channel. The adjusting of step  180  may include adjusting the matching circuit based on Table 1 or Table 2, above. If an optimum Rx setting is chosen in step  180 , such as based on Table 1, then the method may end after  180  (end not shown). Alternatively, the method may continue whether step  180  is based on Table 1 or 2.  
         [0032]     In step  185 , the mobile station starts scanning for a SYNC channel message or a pilot channel. Systems and methods for scanning for a SYNC channel message are described in U.S. Pat. No. 5,103,459, issued Apr. 07, 1992; U.S. Pat. No. 6,714,526 B2, issued Mar. 30, 2004; and U.S. Pat. No. 6,754,251, issued Jun. 22, 2004, which are hereby incorporated by reference. In step  190 , a system determination (SYSDET) return counter is started. SYSDET return counter is used to indicate when the mobile station should return to a SYSDET software module to identify the next communication channel to be searched for, commonly based on a PRL. SYSDET return counter may be timer T 21   m , as identified in the above-referenced TIA/EIA/IS-2000. SYSDET return counter may be one second, but in any case, SYSDET return counter period is determined by the requirements of the wireless communication system.  
         [0033]     In step  195 , a match adjust counter is started. Match adjust counter is set to indicate when the antenna matching circuit should be adjusted if the SYNC channel message has not been found. Ideally, match adjust counter period is significantly shorter than SYSDET return counter and significantly longer than the cycle period of SYNC channel message. SYNC channel message cycle period may be 0.0267 second. See TIA/EIA/IS-2000. Match adjust counter may be one sixth of SYSDET return counter, that is, about 0.167 second, if SYSDET return counter is one second.  
         [0034]     In decision step  200 , the mobile station checks whether the SYNC channel message has been found. If SYNC channel message has been found, then the mobile station goes into idle state, as shown in step  220 .  
         [0035]     If SYNC channel message has not been found, then the method continues to step  205 , in which the mobile station checks whether SYSDET return counter has expired. If SYSDET return counter has expired, then the method returns to step  175 . If SYSDET return counter has not expired, then the method continues to decision step  210 , in which the mobile station determines whether match adjust counter has expired.  
         [0036]     If match adjust counter has not expired, then the method returns to decision step  200 . If match adjust counter has expired, then the method continues to step  215 , in which antenna matching circuit is adjusted to favor the Rx band more. After step  215 , the method returns to step  195 . By repeated cycles from step  195  to step  200  to step  205  to step  210  to step  215  and back to step  195 , mobile station can scan all matching circuit bins (such as in Table 2) for the best matching circuit setting for optimum receive performance.  
         [0037]     The shifting of antenna efficiency of steps  180  and  215  can be accomplished by any convenient means, such as, for example, by employing a table like Tables 1 or 2. Alternatively, Table 2 may be avoided if, for example, the matching circuit settings are all equally spaced. Then, the shift step  215  may be accomplished without Table 2, merely by changing the matching circuit setting by a predetermined amount in the Rx direction. For example, responsive to step  180  or  215 , 0.1 Volt may be added to the current matching circuit setting.  
         [0038]     The method shown with respect to  FIG. 3  can be modified many ways. For example, the steps can be taken in different orders, or some steps can be left out. While embodiments and implementations of the invention have been shown and described, it should be apparent that many more embodiments and implementations are within the scope of the invention. Accordingly, the invention is not to be restricted, except in light of the claims and their equivalents. 
        What is claimed is: