Abstract:
GPS functionality is added to a wireless communication device in an efficient and cost effective manner. Disclosed is a wireless communications device that has a common mixer constructed to be used for a GPS signal and another signal, a common IF filter constructed to be used for a GPS signal and another signal, in addition to other cost effective embodiments.

Description:
RELATED APPLICATION 
     This application is a continuation of application Ser. No. 09/975,124 filed on Oct. 9, 2001 now U.S. Pat. No. 7,024,220 Application Ser. No. 09/975,124 is explicitly incorporated in full into this application. 
    
    
     FIELD 
     The field of the present invention is mobile communications devices. More particularly, the present invention relates to receivers for wireless communications devices. 
     BACKGROUND 
     Demands placed on wireless communications devices are continually increasing. While the number of functions required of wireless communications devices is increasing, consumers are simultaneously demanding lower cost devices with longer use times between battery charging and which are lighter and smaller than previous devices. 
     Particularly, there is a high demand for adding global positioning systems (GPS) services to the functions of wireless communications devices. More specifically, consumers want a wireless communications device that has both GPS and PCS services or GPS and cellular CDMA, among other services. Additionally, some government agencies, e.g., the FCC in the United States, are mandating that position location functionality be incorporated into wireless communications devices which is able to meet a specific accuracy. GPS is one solution which can meet this requirement and operates at a frequency of 1575.42 MHz, as is well known in the art. PCS is a wireless communication band at a frequency of about 1960 MHz, as is well known in the art. Cellular CDMA is a wireless communication system at a frequency of about 870 MHz, as is well known in the art. 
     In a typical wireless communications device receiver, an antenna assembly receives a radio frequency (rf) signal from the air. The antenna assembly may includes an antenna, an antenna matching circuit and any other component required to receive the rf signal. The signal is a series of electromagnetic fields travelling in waves in the air at a certain frequency, the radio frequency. The waves carry energy. The antenna captures some of this energy so that the energy can travel along a guided path. The guided path may be a wave guide or metal conductors, such as wires or strips of metal, known as microstrip lines, on a substrate, among other things. 
     The signal captured by the antenna may have waves of frequencies other than the desired rf. Filters are used to block any signal component at frequencies other than the desired rf. Thus, the rf signal is made to travel through one or more filters to select a desired frequency or range of frequencies. Also, the desired rf signal may be very weak. Amplifiers are used to magnify the strength of the rf signal. Thus, the rf signal is made to pass through one or more amplifiers. 
     The rf signal carries information. The information is contained in changing phase, amplitude or frequency of the rf signal. To get this information out of the signal, the signal is typically compared to an rf signal of constant phase, amplitude or frequency. The constant phase, amplitude or frequency rf signal is known as a local oscillator signal and comes from a precise rf signal generator in the communication device, known as a local oscillator. The local oscillator signal is combined with the rf signal by a device known as a mixer. The mixer produces sum and difference signals of the local oscillator signal and the rf signal. This process of producing sum and difference signals from two initial signals is known as mixing, producing mixed signals. 
     Commonly, the rf signal is mixed once down to an intermediate frequency (IF) signal and then again down to what is known as a baseband signal. Both the IF signal and the baseband signal are lower frequency signals. A baseband signal contains the coded information that the original rf signal was carrying. When the rf signal is mixed down to an IF signal, one of the mixed signals is typically chosen to carry the message contained in the rf signal. This chosen signal is known as the IF signal. The IF signal is typically selected by an IF filter designed to transmit the IF signal only. 
     After the IF filter, and possible further filtering and amplification, the signal encounters another mixer, where it is mixed with another local oscillator signal. This local oscillator signal has a frequency equal to the IF signal frequency. Again, sum and difference signals are produced. The signal of interest at this point is known as the baseband signal. The baseband signal is also known as the “zero frequency difference” signal, even though the frequency of the baseband signal is not zero. Its frequency is the frequency of the coded information that it carries. The baseband signal is then decoded to reveal whatever information was transmitted. It will be appreciated that the signal may be mixed directly from an rf signal down to baseband. In this case, there is no IF signal. 
     When GPS service is added to a wireless communication device, the GPS receiver portion typically has each of the above devices to process the GPS rf signal. In various designers&#39; attempts to combine PCS and GPS services in one device, separate mixers have been used for down converting PCS to an intermediate frequency (IF) and for down converting GPS to an IF. Additionally, separate IF filters have been used to filter the IF signal after down conversion to IF and before down conversion to baseband. The same is true of attempts to combine GPS and cellular CDMA. Separate mixers and IF filters have been used. Thus, the cost, size and power consumption of prior art GPS enabled devices is significantly more than that of those without GPS services. 
     SUMMARY 
     The cost, size and power consumption of prior art GPS enabled wireless communication devices is significantly more than that of those without GPS services. Accordingly, it would be desirable to have an rf communication device, particularly a PCS wireless communication device and a cellular CDMA wireless communication device with cost effective and size and power consumption efficient GPS functionality. 
     Generally, the invention allows GPS functionality to be added to a wireless communication device in an efficient and cost effective manner. Briefly, the present invention has a common mixer constructed to be used for a GPS signal and another signal, such as a PCS signal. In one embodiment, a common mixer and IF filter are used for both PCS and GPS signals. In another embodiment, a band select switch may be used to select either the PCS signal or the GPS signal. Alternatively, a duplexer or diplexer may couple the GPS signal and the PCS signal to the common mixer. In this way, a common mixer is enabled to be used for both GPS and PCS. 
     A dual band local oscillator may be configured to output a local oscillator signal facilitating selection of a GPS IF signal, a PCS IF signal or a cellular CDMA IF signal, using a common IF filter. In another embodiment, both the GPS low noise amplifier (LNA) and the PCS LNA may be switched on and off depending upon whether GPS or PCS reception is selected. In another embodiment, a common IF filter may be used for both GPS and cellular CDMA signals. 
     This reuse of a mixer and an IF filter desirably contain the cost, size and power consumption of a GPS/PCS enabled wireless handset. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a more complete understanding of the present invention, and the advantages thereof, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, tables and attachments, in which: 
         FIG. 1  is a block diagram of a receiver portion in accordance with the present invention. 
         FIG. 2  is a block diagram of a receiver portion showing a common IF filter for filtering a cellular CDMA IF signal and a GPS IF signal in accordance with the present invention. 
         FIG. 3  is a block diagram of a receiver portion showing use of a GPS/PCS diplexer in accordance with the present invention. 
         FIG. 4  is a block diagram of a receiver portion showing use of a GPS/PCS duplexer in accordance with the present invention. 
         FIG. 5   a  is a block diagram of a receiver portion showing an example circuit for powering up and down of the GPS and PCS LNA&#39;s in accordance with the present invention. 
         FIG. 5   b  is a graph showing a frequency response of an active mixer in accordance with the present invention. 
         FIG. 5   c  is a graph showing a frequency response of a passive mixer in accordance with the present invention. 
         FIG. 5   d  is a block diagram showing reuse of a passive mixer in accordance with the present invention. 
         FIG. 6  is a flow chart showing a method for mixing a GPS signal and a PCS signal in accordance with the present invention. 
         FIG. 7  is a flow chart showing an alternative method for mixing a GPS signal and a PCS signal in accordance with the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Referring now to  FIG. 1 , a receiver portion  10  is shown. Receiver portion  10  may be used, for example, as a receiver portion for a wireless communication device. In a preferred embodiment, the receiver portion  10  is arranged with other known components to constitute a CDMA wireless communication device with integral GPS compatibility. Advantageously, a single mixer  46  is used for both of the PCS and the GPS signals for down conversion to an IF. Using a single mixer to provide GPS and PCS functionality in a wireless communication device enables a lower cost, smaller size and lower power consumption wireless communication device having PCS and GPS functionality. 
       FIG. 1  is a schematic block diagram of the major assemblies of a multiband receiver portion  10 . A GPS antenna  14 , for receiving a GPS signal, is coupled to a first low noise amplifier (LNA)  18 , for amplifying the GPS signal. The first LNA  18  is coupled to a first band pass filter (BPF)  22  for filtering the GPS signal. The first BPF  22  is coupled to a first input  34  of a band select switch  38 . The band select switch  38  selects between the GPS and the PCS bands, responsive to a GPS control signal, generated by a GPS control signal generator  20 . 
     The PCS signal  50  may be received from a PCS duplexer (not shown), which is coupled to a second LNA  54 . The second LNA  54  is coupled to a second BPF  62  for filtering the PCS signal. The second BPF  62  is coupled to a second input  64  of the band select switch  38 . An output  42  of the band select switch  38  is coupled to a first input  44  of a first mixer  46 . This mixer is used for down converting both GPS and PCS signals to an IF signal, providing advantages over the prior art. An RF output  15  (also known as the local oscillator (LO) signal) of a dual band local oscillator  66  is coupled to a second input  17  of the first mixer  46 . The first mixer  46  mixes the LO signal with either the PCS signal or the GPS signal to produce the IF, responsive to the GPS control signal generated by the GPS control signal generator  20 . The GPS control signal selects which of the local oscillator signals is received by the first mixer  46 . 
     Preferably, a third BPF  21  filters the signal whether it is a GPS signal or a PCS signal. Due to the similar characteristics of CDMA and GPS signals it is possible for an IF signal indicative of a GPS signal and an IF signal indicative of a CDMA signal to pass through the same IF filter  21 . Preferably, the IF filter  29  (2 is optimized for CDMA. Thus, an output  19  of the first mixer  46  is coupled to the third BPF  21 . This output  19  comprises an IF signal indicative of either the GPS signal or the PCS signal, depending upon which of the GPS signal and the PCS signal is selected by the band select switch  38 , which is controlled by the GPS control signal generator  20 . Preferably, the same BPF  21  is used, for filtering the IF signal whether the IF signal is indicative of the GPS signal or of the PCS signal, providing advantages over the prior art. 
     The GPS control signal generator  20  is also preferably coupled to the LO  66 . The GPS control signal generator  20  thus selects which LO signal is mixed by the first mixer  46  with either the GPS signal or the PCS signal. If the GPS control signal is on, the LO signal used for down converting the GPS signal to an IF frequency is enabled. If the GPS control signal is not on, the LO signal used for down converting the PCS signal to an IF frequency is enabled. In this way, the same mixer  46  is enabled to be used in conjunction with a first LO signal to down convert a GPS signal to an IF signal and in conjunction with a second LO signal to down convert a PCS signal to an IF signal. 
     Referring now to  FIG. 2 , another embodiment will now be described, in which a single, first BPF  24  is enabled to filter either an IF signal from a GPS signal or an IF signal from a cellular band signal. Thus, an input  70  from a cellular duplexer (not shown) is coupled to a first LNA  75 . The first LNA  75  is coupled to a second BPF  79 . The second BPF  79  is coupled to a first input  83  of a first mixer  87 . A second input  43  of the first mixer  87  is coupled to a divide by two circuit  53 . The divide by two circuit  53  is coupled to an RF output  26  of a dual band local oscillator  28 . An output  89  of the first mixer  87  is coupled to the first filter  24 . In this way, the same filter, the first filter  24 , is enabled to be used to filter an IF signal that is indicative of either the GPS signal or the cellular signal. 
     The cellular signal may, optionally, be an FM signal, rather than a CDMA signal. In this case, the cellular signal will be processed by other baseband processing circuitry (not shown). For signal quality reasons, not fully described here, FM signals are processed also through a separate mixer  49  and IF filter  51  than the CDMA signals. These elements are shown for completeness. Thus, the second BPF  79  is also coupled to a first input  41  of a second mixer  49 . The divide by two circuit  53  is coupled to a second input  45  of the second mixer  49 . An output  47  of the second mixer  49  is coupled to a third BPF  51 . The GPS signal is coupled to the IF filter  24  analogously to how the GPS signal is coupled to the IF filter  21  in  FIG. 1 . This is not described again here with reference to  FIG. 2 . Note that a band select switch  30  is optional for the provision of a PCS receive path. A GPS filter  32  may be directly coupled to a mixer  35  for downconversion to an IF. Alternatively for tri-mode phone, the GPS signal may be coupled to the mixer  35  through a diplexer (not shown) or a duplexer (not shown) in lieu of the switch  30 . 
     Another embodiment is shown in  FIG. 3 . Components similar to those already described will not be described in detail. A diplexer  81  may be used in place of the band select switch  26 , shown in  FIG. 1 . The diplexer transmits both the PCS signal and the GPS signal to the first mixer  46 . In this case, both the PCS signal and the GPS signal are converted to an IF signal by the mixer  46 . But only one of the PCS signal and the GPS signal is converted to an IF signal that is in the passband of the third bandpass filter  21 . Which of the PCS signal and the GPS signal is converted to an IF signal in the passband of the third bandpass filter  21  depends upon which local oscillator signal is transmitted to the input of the first mixer  46 . Which local oscillator signal is transmitted to the first mixer  46  depends upon which local oscillator signal is selected by the GPS control signal generator  20 . 
     Another embodiment is shown in  FIG. 4 . Again, similar parts to those already described will not be described in detail. A duplexer  92  may replace the first bandpass filter  22 , the second bandpass filter  62  and the band select switch  38  shown in  FIG. 1  or first and second band pass filters and the diplexer  81  shown in  FIG. 3 . The duplexer  92  receives both the GPS signal and the PCS signal and filters them, transmitting only the GPS signal and the PCS signal to the first mixer  46 . Operation of the mixer  46  and filter  21  are as described previously with reference to  FIG. 3 . 
     Preferably, the GPS control signal generator  37  is used to switch the GPS and PCS LNAs&#39; on and off, as shown in  FIG. 5   a . When the GPS control signal is on, the GPS LNA  18  is powered on and the PCS LNA  54  is powered off. Conversely, when the GPS control signal is off, the GPS LNA  18  is powered off and the PCS LNA  54  is powered on. Then, regardless of whether a duplexer, a diplexer, or a switch is used for selecting the signals to be coupled to the mixer, only the selected signal reaches the mixer, and consequently, only the selected IF signal reaches the IF filter. 
     The powering on and off of the GPS LNA and the PCS LNA may be accomplished as shown in  FIG. 5   a . When the GPS control signal is on, a switch  11  is in a position to transmit current from a power supply  40  to the power line  13  of the GPS LNA  18 . In this position of the switch  11 , the power supply  40  is not coupled to the power line  16  of the PCS LNA  54 . Conversely, when the GPS control signal is off, the switch  11  is in a position to transmit current from the power supply  40  to the power line  16  of the PCS LNA  54  and not to the power line  13  of the GPS LNA  18 . It will be appreciated that other components and methods may be used to power on and off the LNA&#39;s. Indeed in some designs it may not be necessary to switch power on and off to the LNA&#39;s as the LO signal effectively selects which signal is converted to the IF frequency. 
     It will be appreciated that while the embodiments described with reference to  FIGS. 1-5  are separate embodiments, they may be combined in several ways. For example, a single mixer may be used to downconvert PCS and GPS signals to an IF signal, as shown in  FIG. 1 , while cellular CDMA may be downconverted using a separate mixer as shown in  FIG. 2 , but may use the same IF filter as used by the PCS and GPS signals. Thus,  FIGS. 1 and 2  can be combined to yield a receiver portion wherein a single mixer is used for GPS and PCS signals and a single IF filter is used for GPS, PCS and cellular CDMA signals. 
     Further its is possible to use a single mixer for all three bands (Cellular, GPS and PCS), providing the mixer is preceded by the requisite LNA and RF filter. Further still, a single mixer may be used for more or different bands, e.g. 3G CDMA at about 2.2 GHz, DCS at about 1.8 GHz or GSM about at 800 MHz. 
     It may be necessary to use a passive mixer to mix all the bands of interest. Present wireless communication devices use active mixers. As is well known in the art, an active mixer has a relatively narrowband response. Such a response is shown if  FIG. 5   b . The response may be broad enough to mix both PCS and GPS, but not broad enough to also mix cellular CDMA. An active mixer has a typical gain in the region of interest of between 10 and 12 dB. 
     A passive mixer has a more flat response, as shown in  FIG. 5   c . This allows for mixing of a broader range of frequencies. However, a passive mixer has a conversion loss, as shown in  FIG. 5   c . The conversion loss of a typical passive mixer is typically 6 to 8 dB, or a gain of −8 dB. Thus, there is a loss of between about 18 and 20 dB incurred by switching from an active to a passive mixer. A counterbalancing gain of about 18 to 20 dB is required to make up for the loss of a passive mixer as compared to an active mixer. An additional amplifiers can be used to provide the gain required. 
     A receiver portion using a passive mixer to down convert more than two signals to an intermediate frequency signal will now be described with reference to  FIG. 5   d . Advantageously, this receiver portion re-uses a single mixer for each of several frequencies. Example frequencies include about 2.2 GHz for 3G CDMA, about 1.9 GHz for PCS, about 1.8 GHz for DCS, about 1.575 GHz for GPS, about 900 MHz for cellular CDMA and about 800 MHz for GSM. All of these frequencies can be down converted to a lower frequency signal by one mixer. It will be understood by those skilled in the art that this list is not exhaustive, but is intended by way of example only. Other frequencies could also be down converted to a lower frequency signal by the same mixer. 
     Referring now to  FIG. 5   d , four input lines  122 ,  123 ,  124  and  125  are shown coupled to four LNA&#39;s  128 ,  129 ,  130  and  131 . Any of the signals of interest, such as, for example, 3G CDMA, PCS, GPS may be coupled individually to these input lines. The LNA&#39;s  128 ,  129 ,  130  and  131  are coupled to four BPF&#39;s  135 ,  136 ,  137  and  138 . Optionally, there may also be more input lines, LNA&#39;s and BPF&#39;s (not shown) for accommodating more than four signals. The BPF&#39;s  135 ,  136 ,  137  and  138  are coupled to a switch  141 . The switch is used to select between the input lines  122 ,  123 ,  124  and  125 . The output to the switch is coupled to a mixer  142 . Optionally, an LNA  143  is coupled between the switch  141  and the mixer  142 . In another option, an LNA  144  is coupled between the mixer  142  and an IF signal line  147 . In yet another option, both LNA  143  and LNA  144  are coupled on either side of mixer  142 . Either or both of LNA&#39;s  143  and  144  make up for the increased loss of the passive mixer  142  as compared to an active mixer. In this way, a single mixer  142  can be advantageously used to mix many bands down to an IF. The bands are not constrained to be near each other in frequency. 
     It will be appreciated by one skilled in the art that the increased loss of the passive mixer  142  as compared to an active mixer could be made up for in other ways. The LNA&#39;s  143  and  144  are shown by way of example only. It will also be understood by one skilled in the art that more than four signals may be downconverted to an IF in this way. More input lines, more LNA&#39;s and more BPF&#39;s (not shown) would be coupled to the switch  141 . The additional input lines, LNA&#39;s and BPF&#39;s are indicated by the dashed line  149 . 
     A method of converting a GPS signal to an intermediate frequency signal is shown in  FIG. 6 . First, in step  305 , a mixer is provided and configured to receive a PCS signal and a GPS signal. This mixer, for example, could be a mixer  46  such as shown in  FIG. 1 . It could, for example, be configured as shown in any of  FIGS. 1-4 , or in any other way that is well known in the art for providing two different signals to a mixer. 
     Second, in step  310 , the PCS signal is mixed, using the mixer, with a first local oscillator signal. The first local oscillator signal may come from a dual band local oscillator  66  as shown in  FIG. 1 . Alternatively, the first local oscillator signal may be coupled to the mixer in any configuration well known in the art. 
     Third, in step  315 , a GPS control signal, also known as a GPS control signal, is generated. This GPS control signal may be a result of a manual switch manipulated by a wireless communication device user or by any software or hardware method that is known in the art of electronic communication. The GPS control signal indicates whether the communication device is to be used at the moment in GPS mode or PCS mode. 
     Fourth, in step  320 , the PCS signal is decoupled from the mixer, responsive to the GPS control signal. A band select switch may be used to decouple the PCS signal from the mixer, such as is shown in  FIG. 1 . Alternatively, any known method of decoupling RF signals from mixers may be used. 
     Fifth, in step  325 , the mixer is used to mix the GPS signal with a second local oscillator signal, producing an intermediate frequency signal. 
     A method of converting a GPS signal to one IF signal and a PCS to another IF signal using the same mixer is shown in  FIG. 7 . An IF filter is used to select which IF signal to use for further processing. First, in step  405 , a mixer is provided and configured to receive a PCS signal and GPS signal. This mixer, for example, could be a mixer  46  such as shown in  FIG. 3 . It could, for example, be configured as shown in either of  FIGS. 3-4 , or in any other way that is well known in the art for providing two different signals to a mixer. 
     Second, in step  410 , a GPS signal and a PCS signal are coupled to the mixer. Third, in step  415 , a GPS control signal, also known as a GPS control signal, is generated. This GPS control signal may be a result of a manual switch manipulated by a wireless communication device user or by any software or hardware method that is known in the art of electronic communication. The GPS control signal indicates whether the communication device is to be used at the moment in GPS mode or PCS mode. 
     Fourth, in step  420 , either a first or a second local oscillator (LO) signal is coupled to the mixer, responsive to the GPS control signal. The first and second local oscillator signals may come from a dual band local oscillator  66  as shown in  FIG. 1 . Alternatively, the first local oscillator signal may be coupled to the mixer in any configuration well known in the art. 
     Fifth, in step  425 , the GPS signal and the PCS signal are mixed with the first or second local oscillator signal by the mixer, depending on which local oscillator signal is coupled to the mixer. Regardless of which local oscillator signal is coupled to the mixer, it will be mixed with both the GPS and the PCS signals. 
     Sixth, in step  430 , either the first or the second IF signal is selected by the IF filter for further processing. In this way, one IF filter is enabled to be used for both GPS and PCS IF signal filtering. 
     To make one filter usable for both GPS and PCS IF filtering, the local oscillator frequencies should be carefully chosen. A common IF is 183.6 MHz. To obtain this IF, a local oscillator frequency in the region of 2143.6 MHz is commonly used in conjunction with the PCS signal. This is injected on the high side of the PCS Rx signal, commonly in the region of 1960 MHz, giving an IF of 183.6 MHz. Thus, a local oscillator signal at 2143.6 MHz can be referred to as a PCS local oscillator signal. 
     To obtain an IF signal from a GPS signal, commonly at 1575.42 MHz, a low side injection of a local oscillator can be used, with a frequency of 1391.82 MHz. Thus, a local oscillator signal at 1391.82 MHz can be referred to as a GPS local oscillator signal. This way, whether the 1391.82 MHz local oscillator or the 2143.6 MHz local oscillator is coupled to the mixer, only one signal in the passband of the IF filter, at 183.6 MHz, will pass through the IF filter. It will be understood that alternative frequencies and injection schemes can be implemented and are within the scope of this invention. It is preferred that the GPS signal does not create harmonic or other undesired signals in the rage of the IF filter when mixed with the PCS local oscillator signal. It is also preferred that the PCS signal does not create harmonic or other undesired signals in the range of the IF filter when mixed with the GPS local oscillator signal. 
     It will be understood that the foregoing embodiments are intended by way of example only. It is to be understood that there are many ways of implementing the invention. The invention is only intended to be limited by the claims that follow.