Patent Publication Number: US-6667723-B2

Title: System and method for a GPS enabled antenna

Description:
This is a continuation-in-part of co-pending U.S. patent application Ser. No. 09/898,269 filed on Jul. 3, 2001 and entitled “System and Method for Providing a GPS Enabled Antenna”. Priority is claimed to the above-identified co-pending U.S. Patent Application which is hereby incorporated by reference in its entirety. 
    
    
     FIELD OF THE INVENTION 
     The present invention generally relates to a system and a method for providing a global positioning system (GPS) enabled antenna. 
     BACKGROUND OF THE INVENTION 
     A conventional hand-held global positioning system (GPS) device provides positional information about the location of the GPS device by receiving and processing GPS band signals from a GPS system including satellites and base stations. Although such positional information can be quite useful, it is not convenient to carry a conventional GPS device along with a multitude of mobile wireless communications devices such as laptops, mobile phones, PDAs, or other mobile devices on which users now depend. It is therefore desirable that a GPS positioning function be included with another device, such as a wireless mobile handset. 
     Unfortunately, the integration of GPS technology with other mobile wireless communications devices such as, for example, cellular or personal communications services (PCS) phones has proven difficult. In particular, three alternatives have been identified for adding GPS capability to a wireless device or handset, but have proven unsatisfactory in use. 
     A first choice is to add GPS capability in a wireless handset by adding a separate antenna for GPS reception. Since the wireless network antenna is not modified, network communications quality is not adversely affected. However, as mobile handsets for wireless networks have become much smaller, less space is available on the handset housing to accommodate a separate, custom-designed GPS antenna. Furthermore, a GPS antenna disposed within the handset housing typically suffers from a number of reception problems. For example, poor reception can be caused by electromagnetic shielding within the handset housing and by the handset housing itself. Adjusting the electromagnetic shielding to accommodate the GPS antenna may cause substantial redesign and testing of the handset. Even the hand of the user of the wireless handset may interfere with the reception by the internal GPS antenna as the user grips the handset housing. Also, adding a separate antenna and its associated circuitry to the wireless handset adds expense and design complexity. 
     A second choice is to add GPS capability to a wireless handset by enabling the existing network antenna on the wireless handset to adequately receive a GPS band signal. For example, a typical dual-band antenna may be constructed to receive a PCS signal at approximately 1900 MHz and a cellular signal at approximately 800 MHz. It may therefore be possible that the existing dual-band antenna may be able to receive a GPS signal at approximately 1575 MHz. However, the GPS signal is at a non-resonant frequency for the dual-band antenna, so the received GPS signal would be less than optimal resulting in degraded signal transfer. In this regard, known dual-band antenna systems are not able to receive a GPS signal with sufficient strength and quality to implement a robust GPS location functionality on a wireless handset. 
     A third choice is to add GPS capability to a wireless handset by using a tri-band antenna. A tri-band antenna is constructed to receive the cellular, PCS and GPS frequencies, for example. Although such an antenna enables the GPS signal to be received, due to the limitations of antenna design such an antenna normally compromises either the cellular or PCS performance, or both. Using a tri-band antenna also substantially adds extra cost to the antenna. 
     Accordingly, there exists a need to add GPS position location capability in a wireless handset in a robust, economical manner. Furthermore, it would be desirable that the GPS position location capability be provided in a convenient, aesthetically pleasing manner. 
     SUMMARY OF THE INVENTION 
     The present invention alleviates to a great extent the disadvantages of conventional systems and methods for providing a global positioning system (GPS) enabled antenna in a wireless communications device. 
     In an exemplary embodiment, a system and a method for providing a global positioning system (GPS) enabled antenna system are provided. The GPS enabled antenna may be used, for example, on a wireless communications device such as a wireless handset. The wireless communications device may include a switching module that can selectively switch communications signals between the antenna and one of a plurality of communications band circuitries. A respective impedance matching circuit may be provided between the switching module and particular communications band circuitry to match or to tune the antenna to the particular communications band circuitry. 
     Advantageously, the present invention enables an existing antenna in a wireless communications device to be adapted to robustly receive GPS band signals. Using the existing communications antenna to provide a GPS signal is a cost effective and efficient way to provide GPS position location functionality in a wireless communications device. Furthermore, phone aesthetics are unaffected as no separate GPS antenna is required. Adapting an existing antenna frees up space within the wireless communications device that otherwise might have been reserved for a separate and internal GPS antenna. In addition, since the existing antenna extends from the wireless communications device, the present invention benefits from improved reception of GPS band signals. 
     These and other features and advantages of the present invention will be appreciated from review of the following detailed description of the present invention, along with the accompanying figures in which like reference numerals refer to like parts throughout. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows a representation illustrating an exemplary embodiment of a wireless communications system according to the present invention; 
     FIG. 2A shows selected components of an exemplary embodiment of the wireless communications device according to the present invention; 
     FIG. 2B shows selected components of another exemplary embodiment of the wireless communications device according to the present invention; 
     FIG. 3A is a plot of a frequency response according to an exemplary embodiment of the present invention; 
     FIG. 3B shows a plot of a frequency response according to another exemplary embodiment of the present invention; 
     FIG. 4 shows some components of another exemplary embodiment of the wireless communications device according to the present invention; 
     FIG. 5 is a plot of a frequency response according to another exemplary embodiment of the present invention; 
     FIG. 6 shows an example of a conventional matching network; 
     FIG. 7 shows an example of a conventional switching circuit; 
     FIG. 8 shows some components of another exemplary embodiment of the wireless communications device according to the present invention; 
     FIG. 9 shows some components of yet another exemplary embodiment of the wireless communications device according to the present invention; 
     FIG. 10 shows some components of yet another exemplary embodiment of the wireless communications device according to the present invention; and 
     FIG. 11 shows some components of yet another exemplary embodiment of the wireless communications device according to the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1 illustrates an exemplary embodiment of a wireless communications system including a wireless communications device  100  according to the present invention. The wireless communications device  100  may include, for example, a handheld wireless communications device, a mobile phone, a car phone, a cellular or a personal communications services (PCS) phone, a cordless phone, a laptop computer or other computing device with a wireless modem, a pager, or a personal digital assistant (PDA). The wireless device  100  may be digital or analog or some combination thereof. Indeed, the present invention contemplates other forms of wireless communications devices known to one of ordinary skill in the art. 
     The wireless communications device  100  includes an antenna  110 . The antenna  110  is structured to transmit and receive wireless communications signals. In FIG. 1, the antenna  110  is in two-way communications with a base station  120 . The base station  120  may be, for example, one of a plurality of base stations  120  in a wireless communications network. The antenna  110  is in at least one-way communication with one or more satellites, such as satellite  130 . The satellite  130  may be, for example, one of a plurality of satellites such as in, for example, a constellation of global positioning system (GPS) satellites and their ground stations. 
     In a particular example, the wireless communication device  100  is a wireless handset having the antenna  110  adapted, for example, to receive and transmit wireless communications signals on at least two different communications bands. The two bands may include, for example, the cellular band, a band at approximately 800 MHz, and the PCS band, a band at approximately 1900 MHz. In this exemplary embodiment, the antenna  110  is an existing dual-band antenna constructed to receive and transmit wireless signals on both the PCS and cellular bands. It will be appreciated that more or fewer communication bands may be accommodated by appropriate selection of known antennas and associated circuitry. For example, the wireless device may be constructed to use only the PCS band, or may be constructed to receive and transmit on three or more communication bands. The present invention also contemplates using other wireless communications bands known to one of ordinary skill in the art. 
     The antenna  110  on wireless communication device  100  is configured to robustly receive position location signals, such as a GPS signal from satellite  130 . Advantageously, the antenna  110  may be a known, conventional antenna, such as a standard dual-band antenna. In such a manner, GPS position location functionality may be economically and conveniently added to the wireless communications device. 
     FIG. 2A shows a circuit for robustly receiving a GPS signal using a conventional communications antenna  110 . The wireless communications device  100  may include, for example, the antenna  110 , a diplexer  140 , a first band (e.g., cellular band) duplexer  150 , a second band (e.g., PCS band) duplexer  160 , a GPS switching module  170  and a GPS module  175 . As an alternative to the diplexer  140 , a two-way switch (as illustrated in FIG. 9) may be used. As shown in FIG. 2A, the switching module  170  may include, for example, a switch  165 . The GPS module  175  may include, for example, an impedance matching module  180  coupled to a GPS low noise amplifier (LNA)  190 . It will be appreciated that the circuit illustrated in FIG. 2A is for explanation purposes and that additional well-known circuitry must be added to construct a working communications device. 
     As illustrated in FIG. 2A, the antenna  110  is coupled to the diplexer  140 . The diplexer  140  is coupled to the first band duplexer  150 . The diplexer  140  is also coupled to the switching module  170 . The switching module  170  is coupled to the second band duplexer  160 . The switching module  170  is also coupled to the GPS module  175 . In an exemplary embodiment, the switching module  170  is coupled to the impedance matching module  180  which, in turn, is coupled to the GPS LNA  190 . 
     Although not shown, the present invention also contemplates that additional components may be included in the wireless communications device  100 . For example, a GPS signal processor may be coupled to the GPS LNA  190 . In another example, transmitters and/or receivers may be coupled to the duplexers  150 ,  160 . Such additional components are known to one of ordinary skill in the art and are not described here in further detail. 
     A diplexer is typically used to direct communications signals responsive to the particular communications bands being used. For example, the diplexer  140  separates a signal received on the antenna  110  into a PCS path or cellular path. FIG. 3A shows an exemplary composite frequency response  200  for the diplexer  140 . The frequency response  200  includes a low pass filter characteristic  210  of a low pass filter and a high pass filter characteristic  220  of a high pass filter of the diplexer  140 . The low pass filter characteristic  210  is illustrated with a cutoff frequency of approximately 1000 MHz and is designed to pass the cellular band. The high pass filter characteristic  220  is illustrated with a cutoff frequency of approximately 1600 MHz and is designed to pass the PCS band. It will be appreciated that the cutoff frequencies may be adjusted to accommodate particular applications, and that other cutoff frequencies may be selected for other communication bands. The high pass filter characteristic  220  is designed to pass, with some acceptable level of attenuation, a signal in the GPS band. 
     In operation, a wireless communications signal from at least one wireless communications band is received by the antenna  110 . The diplexer  140  splits the wireless communications signal into at least a first signal and a second signal. The first signal is filtered by the low pass filter of the diplexer  140  and then coupled to the first band duplexer  150 . The second signal is filtered by the high pass filter of the diplexer  140  and then coupled to the switching module  170 . 
     In an exemplary embodiment, if the wireless communications signal includes, for example, cellular band communications signals, then the low pass filter passes the cellular band communications signals to the first band duplexer  150 . The first band duplexer  150  may then couple the incoming cellular band communications signal to, for example, a cellular receiver (not shown). In addition, the low pass filter blocks higher frequency bands from passing to the first band duplexer  150 . 
     If the wireless communications signal includes, for example, PCS band communications signals, then the high pass filter of the diplexer  140  passes the PCS band communications signals to the second band duplexer  160  via the switching module  170 . If the wireless communications signal includes, for example, GPS band signals, then the high pass filter passes, with some small amount of attenuation, the GPS band signals to the GPS module  175  via the switching module  170 . In an exemplary embodiment, the attenuation is caused, in part, because the antenna  110  is an existing dual-band antenna that was not originally optimized for the GPS band. 
     In the GPS module  175 , the impedance matching module  180  provides an impedance match that is tuned for the GPS band. The GPS signal is then amplified in the GPS LNA  190  before being processed by conventional GPS circuitry (not shown). The high pass filter also blocks lower frequency bands. 
     The wireless communications device normally operates with the switching module  170  coupling the diplexer  140  to the duplexer  160 . However, at selected times or intervals it may be desirable to obtain position location information. For example, position information may be useful when a user dials an emergency number. The wireless device may also be operating an application, such as a mapping application, where position location is periodically needed. In another example, a user may instruct the wireless device to obtain position location information. It will be appreciated that many applications exist for a wireless communications device in which position location information is useful. 
     When position location may be needed, the switching module  170  is switched by control circuitry (not shown) to couple the antenna  110  to the GPS module  175 . When configured in this manner, a GPS band signal at approximately 1575 MHz will be received by the antenna and transmitted to the GPS module  175 . Since the antenna  110  is, for example, a dual-band antenna tuned to receive at approximately 800 MHz and at approximately 1900 MHz, the GPS signal at approximately 1575 MHz is unmatched. Accordingly, matching module  180  includes matching circuitry to more closely match the impedance between the GPS module  175  and the antenna  110 . In such a manner, a high quality GPS signal may be robustly received by the GPS LNA  190 . 
     In another exemplary embodiment, the composite frequency response  200  present in the diplexer  140  can be adapted to pass, with less attenuation, the GPS band. Thus, the high pass filter characteristic  220  can be modified by shifting the cutoff frequency from, for example, approximately 1600 MHz to, for example, approximately 1400 MHz, as illustrated by adapted characteristic  230  in FIG.  3 A. The adapted characteristic  230  may also have other differing parameters such as, for example, a different attenuation slope  235 . As a result, the GPS band is attenuated even less by the adapted high pass filter characteristic  230  than by the high pass filter characteristic  220 . For example, as a result of lowering the cutoff frequency from approximately 1600 MHz (as in a normal cellular/PCS diplexer) to approximately 1400 MHz, the GPS band at approximately 1575 MHz is less attenuated by the diplexer  140  from approximately −1.3 dB to approximately −0.3 dB. 
     FIG. 2B illustrates another example of a circuit for robustly receiving a GPS signal using a conventional communications antenna  110 . The circuit is similar to the circuit illustrated in FIG. 2A, except that the diplexer  140  separates a signal received on the antenna  110  into a PCS path or a cellular/GPS path. Accordingly, the switching module  170  is on the cellular/GPS path. Another example of the frequency response  220  of the diplexer  140  is illustrated in FIG.  3 B. In this example, the low pass filter characteristic  210  of the low pass filter of the diplexer  140  extends to higher frequencies to include the GPS band at approximately 1575 MHz. Accordingly, the low pass filter of the diplexer  140  passes the GPS band signals or passes the GPS band signals with a small amount of attenuation to the cellular/GPS path. 
     FIG. 4 shows selected components of another exemplary embodiment of the wireless communications device  100  according to the present invention. The wireless communications device  100  may include, for example, the antenna  110 , the first band duplexer  150 , the second band duplexer  160 , the GPS module  175  and a triplexer  240 . The triplexer  240  couples the antenna  110  to the first band duplexer  150 , the second band duplexer  160  and the GPS module  175 . 
     In another example, the wireless communications device  100  may provide an impedance matching module  300 ,  310  for each circuit branch corresponding to a respective communications band. For example, FIG. 11 illustrates an impedance matching module  300  that is disposed in the first communications band circuit branch and that is coupled to the triplexer  240  and to the first band duplexer  150 . Furthermore, an impedance matching module  310  is disposed in the second communications band circuit branch and is coupled to the triplexer  240  and to the second band duplexer  160 . The impedance matching modules  300 ,  310  provide circuitry that tunes or matches the antenna  110  to the particular communications band circuitry. Thus, for example, the impedance matching module  300  effectively tunes the antenna  110  for the first communications band; and the impedance matching module  310  effectively tunes the antenna  110  for the second communications band. In another example, the impedance matching modules  300 ,  310  provide a complex conjugate match between the antenna  110  and the particular communications band circuitry. In yet another example, the impedance matching modules  300 ,  310  are adapted to provide maximum energy transfer from the antenna  110  to the particular communications band circuitry or vice versa. The impedance matching modules  300 ,  310  may employ similar technologies available for use with the impedance matching module  180 , except that the circuitry contained in the impedance matching modules  300 ,  310  are optimized for their respective communications band circuitry. 
     An exemplary frequency response  200  for the triplexer  240  is illustrated in FIG. 5 including a low pass filter characteristic  210  of a low pass filter, a high pass filter characteristic  220  of a high pass filter and a band pass filter characteristic  250  of a band pass filter of the triplexer  240 . The low pass filter characteristic  210  is illustrated with a cutoff frequency of, for example, approximately 1000 MHz and is designed to pass, for example, the cellular band. The high pass filter characteristic  220  is illustrated with a cutoff frequency of, for example, approximately 1600 MHz and is designed to pass, for example, the PCS band. The band pass filter characteristic  250  is centered, for example, at approximately 1575 MHz and is designed to pass, for example, the GPS band. The characteristics  210 ,  220 ,  250  may or may not overlap. The present invention also contemplates using other filter characteristics designed for these and other wireless communications bands. 
     In operation, a wireless communications signal from at least one wireless communications band is received by the antenna  110 . The triplexer  240  splits the wireless communications signal into at least a first signal, a second signal and a third signal. The first signal is filtered by the low pass filter of the triplexer  240  and then coupled to the first band duplexer  150 . The second signal is filtered by the high pass filter of the triplexer  240  and then coupled to the second band duplexer  160 . The third signal is filtered by the band pass filter of the triplexer  240  and then coupled to the GPS module  175 . This coupling mechanism may also include the impedance transformation for optimum performance. 
     In an exemplary embodiment, if the wireless communications signal includes, for example, cellular band communications signals, then the low pass filter of the triplexer  240  passes the cellular band communications signals to the first band duplexer  150 . In addition, the low pass filter blocks higher frequency bands from passing to the first band duplexer  150 . 
     If the wireless communications signal includes, for example, PCS band communications signals, then the high pass filter passes the PCS band communications signals to the second band duplexer  160 . In addition, the high pass filter blocks lower frequency bands from passing to the second band duplexer  160 . 
     If the wireless communications signal includes, for example, GPS band signals, then the band pass filter passes the GPS band signals to the GPS module  175 . In an exemplary embodiment, in the GPS module  175 , the impedance matching module  180  provides an impedance match that is tuned for the GPS band. The GPS signal is then amplified in the GPS LNA  190  before being processed by conventional GPS circuitry. In addition, the band pass filter blocks higher and lower frequency bands from passing to the GPS module  175 . 
     FIG. 8 illustrates another exemplary embodiment in which a switching module  260  is used instead of the triplexer  240  according to the present invention. The antenna  110  is coupled to the first band duplexer  150 , to the second band duplexer  160  and to the GPS module  175  via the switching module  260 . The switching module  260  may include, for example, a three-way switch  270 . The switching module  260  may be controlled via a main controller (not shown) of the wireless communications device  100  such as, for example, a processor (e.g., a mobile station modem (MSM)). The switching module  260  switches the signal received via the antenna  110 . Thus, for example, a cellular band signal may be switched to the first band duplexer  150 ; a PCS band signal may be switched to the second band duplexer  160 ; or a GPS signal may be switched to the GPS module  175 . The cellular communications circuitry and the PCS communications circuitry may include, for example, band-optimized signal matching circuitry for use with the respective band. 
     In another example, the wireless communications device  100  may provide an impedance matching module  300 ,  310  for each circuit branch corresponding to a respective communications band. For example, FIG. 10 illustrates an impedance matching module  300  that is disposed in the first communications band circuit branch and that is coupled to the first band duplexer  150  and to the three-way switch  270  of the switching module  260 . Furthermore, an impedance matching module  310  is illustrated as being disposed in the second communications band circuit branch and being coupled to the second band duplexer  160  and to the three-way switch  270  of the switching module  260 . As described above, the impedance matching modules  300 ,  310  may provide circuitry that tunes or matches the antenna  110  to the particular communications band circuitry. 
     FIG. 9 illustrates yet another exemplary embodiment of the wireless communications device  100  according to the present invention. In this exemplary embodiment, the wireless communications device  100  is configured to receive a GPS signal or a communications band signal (e.g., a cellular band signal or a PCS band signal). The antenna  110  is coupled to the GPS module  175  and to the communications band duplexer  290  via the switching module  260 . Optionally, an impedance matching module (not shown) may be provided between the communications band duplexer  290  and the switching module  260 . The switching module  260  may include, for example, a two-way switch  280 . The switching module  260  may be controlled via a main controller (not shown) of the wireless communications device  100  such as, for example, a processor (e.g., a mobile station modem (MSM)). The switching module  260  switches the signal received via the antenna  110 . Thus, if the wireless communications device  100  is, for example, a cellular phone, then the cellular band signal may be switched to the communications band duplexer  290  or a GPS signal may be switched to the GPS module  175 . The communications band circuitry may include, for example, band-optimized signal matching circuitry for use with the communications band. 
     It will be appreciated that matching module  180  or other matching circuitry may be implemented using a wide variety of circuits. FIG. 6 shows one such variant implementing a matching circuit. In FIG. 6, an input to the matching module  180  is coupled to a first inductor L 1 . The first inductor L 1  is coupled to the output of the matching module  180  via a second inductor L 2 . The first inductor L 1  is also coupled to a voltage potential V 1  (e.g., electrical or chassis ground) via a capacitor C 1 . Such matching circuits are well known in the art. The matching module  180  may include other varieties of matching circuits and their dual equivalents. Such matching circuits may also include, for example, passive elements and/or active elements as is known to one of ordinary skill in the art. 
     It will also be appreciated that switch module  170  may be implemented in several circuit arrangements. FIG. 7 shows one such arrangement of the switching module  170  according to the present invention. An input to the switching module  170  is coupled to a first capacitor C 2 . The first capacitor C 2  is coupled to a voltage potential V 2  (e.g., battery supply voltage) via a first inductor L 3 . The first capacitor C 2  is also coupled to two output branches. In a first branch of the circuit, the first capacitor C 2  is coupled to a first diode D 1 . The first diode D 1  is coupled to the first output via a second capacitor C 3 . The first diode D 1  is also coupled to a first control signal via a second inductor L 4 . In a second branch of the circuit, the first capacitor C 2  is coupled to a second diode D 2 . The second diode D 2  is coupled to the second output via a third capacitor C 4 . The second diode D 2  is also coupled to a second control signal via a third inductor L 5 . Briefly, the first control signal and the second control signal provide desired potential differences across the diodes D 1 , D 2  which turn each diode D 1 , D 2  either on or off (i.e., an approximately short circuit or an approximately open circuit). The switching module  170  may implement other variation and examples of switching circuitry known to one of ordinary skill in the art. 
     Thus, it is seen that a system and method for providing a GPS enabled antenna are provided. One skilled in the art will appreciate that the present invention can be practiced by other than the preferred embodiments which are presented in this description for purposes of illustration and not of limitation, and the present invention is limited only by the claims that follow. It is noted that equivalents for the particular embodiments discussed in this description may practice the present invention as well.