Patent Publication Number: US-2012040628-A1

Title: Transceiver with Interferer Control

Description:
BACKGROUND 
     Modern mobile phone transceivers can support transmission and reception of data over a wide array of communication protocols, such as Global System for Mobile Communications (GSM), Bluetooth, FM radio, 3G, 4G, infrared, etc. In some instances, each of these communication protocols is carried out in the mobile phone transceiver by its own hardware subunit. For example, GSM communication can be carried out by a GSM hardware subunit, and FM radio reception can be carried out by another, separate FM Radio (FMR) hardware subunit. 
     Although these subunits may share some components, they often include distinct communication paths so they can transmit and/or receive data concurrently. On each path, a mixer often receives a local oscillator (LO) signal to convert the frequency of a signal-of-interest to another desired frequency. The inventors have appreciated that interference can arise when a harmonic of an LO signal over a second communication path (e.g., in an FMR subunit) downconverts a transmit signal of a first communication path (e.g., in a GSM subunit). This cross-talk interference can degrade the sensitivity of the second communication path. Similarly, LO harmonics generated by the first communication path can parasitically affect the second communication path. 
     Therefore, the inventors have devised improved transceivers that limit degradation between communication units within mobile phones and other communication devices. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram illustrating a transceiver in accordance with some embodiments. 
         FIGS. 2A-2B  collectively illustrate a more detailed example of transceiver functionality with sample frequency channels superimposed thereon. 
         FIG. 3  is a block diagram illustrating another transceiver in accordance with some embodiments. 
         FIG. 4  is a flow chart depicting a method in accordance with some embodiments. 
         FIGS. 5A-5D  collectively show an example method of changing an LO frequency in the context of a set of sample frequency diagrams. 
     
    
    
     DETAILED DESCRIPTION 
     The claimed subject matter is now described with reference to the drawings, wherein like reference numerals are used to refer to like elements throughout. In the following description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the claimed subject matter. It may be evident, however, that the claimed subject matter may be practiced without these specific details. 
     Some embodiments of the present disclosure relate to a transceiver that includes multiple communication subunits associated with multiple communication protocols, respectively. The transceiver includes a conflict detection and control unit that determines whether interference is present or anticipated to occur between two or more of the communication subunits. If interference is present or anticipated, a local oscillator (LO) tuning unit changes an LO frequency provided to at least one of the two or more communication units. For example, in some embodiments, the LO tuning unit changes the LO frequency from high-side injection to low-side injection, or vice versa, and/or changes an intermediate frequency (IF) associated with a given communication subunit. In these ways, the techniques disclosed herein limit signal degradation due to interference from communication subunits residing within the transceiver. 
     Referring now to  FIG. 1 , one can see a transceiver  100  in accordance with some embodiments. The illustrated transceiver  100  includes first and second communication subunits  102 ,  104 , respectively, which can be used to transmit and/or receive signals according to a first communication protocol (e.g., GSM) and a second communication protocol (e.g., FM radio), respectively. Although only two communication subunits are illustrated, it will be appreciated that the inventive concepts can be extended to any number of communication subunits, and/or to other communication protocols in addition to or instead of GSM and FM radio. 
     In any case, each subunit includes one or more communication paths on which signals are transmitted and/or received. For example, in FIG.  1 &#39;s embodiment, the first subunit  102  includes a first communication path  112  having a first antenna  106 , a first local oscillator  108 , and a first mixer  110 ; which are operably coupled as shown. When the first communication subunit  102  acts as a transmitter, a digital block  114  provides a first signal  116  to a first input of the first mixer  110 . The first mixer  110  then multiplies the first signal  116  with a first LO signal  118  to produce an up-converted RF signal  120 , which can be transmitted over the first antenna  106 . 
     The illustrated second subunit  104  includes a second communication path  130  having a second antenna  122 , a second LO  124 , a second mixer  126 , and a filter unit  128 ; which are operably coupled as shown. When the second subunit acts as a receiver, the second antenna  122  provides an RF signal  132 , which includes a wanted signal, to a first input of the second mixer  126 . The second mixer  126  mixes the wanted signal with a second LO signal  134  from the second LO  124 , and provides a down-converted wanted signal  136  (e.g., IF signal) therefrom. The down-converted wanted signal  136  is then passed through the filter block  128 , which rejects unwanted frequency components, to provide a filtered signal  142  which can be demodulated and otherwise processed in digital circuitry  114 . 
     Absent countermeasures, the first signal  116  or first LO signal  118  (and/or a harmonic frequency thereof) can lead to interference on the second communication path  130 . To limit or avoid such interference, a conflict detection and control unit  138  monitors the frequencies of the first and second LO signals  118 ,  134  and harmonics thereof in relation to the frequencies being transmitted or received on the communication paths  112 ,  130 . 
     If a conflict is detected, the conflict detection and control unit  138  notifies an LO tuning unit  140 , which selectively adjusts the frequency of the second LO signal  134  to mitigate the interference. In particular, the LO tuning unit  140  can induce a discrete change in the frequency of the second LO signal  134  such that the second LO signal is changed between a low-side injection mode and a high-side injection mode without changing an intermediate frequency (IF) associated with the corresponding communication path. In other embodiments, the detection and control unit  138  can change the frequency of the second LO signal  134  in a manner that changes the IF to limit or avoid interference. When the IF is adjusted, the conflict detection and control unit  138  also typically adjusts the passband of filter block  128  to allow the newly “tuned” IF to pass therethrough. 
     By continuously or intermittently monitoring the LO frequencies used by the various communication subunits (and harmonics associated therewith), and comparing these frequencies with the frequencies used for transmission and reception of RF signals, the disclosed techniques provide more efficient communication than previous solutions in some respects. 
     Referring now to  FIGS. 2A-2B  collectively, one can see a more detailed example of how a transceiver  200  (e.g., transceiver  100  of  FIG. 1 ) can change between high-side LO injection ( FIG. 2A ) and low-side LO injection ( FIG. 2B ) for a given communication path to limit interference between two communication subunits. 
       FIG. 2A  shows an example where the transceiver  200  transmits a GSM signal at  830 . 2  MHz via the first communication subunit  202  (GSM subunit) while concurrently receiving an FM signal at  92 . 0  MHz via the second communication subunit  204  (FM subunit). At this time, the FM subunit  204  is poised to use a high-side LO frequency of 92.275 MHz to down-convert the received 92.0 MHz FM signal to an IF of 0.275 MHz. However, the LO signal includes a fundamental frequency and harmonic frequencies, which are integer multiples of the fundamental frequency. In particular in  FIG. 2A , one of these harmonic frequencies, (e.g., the ninth harmonic of the second LO signal at  9 ×92.275 MHz=830.475 MHz), coincides with the sum of the GSM transmission channel frequency and the IF frequency (e.g., 830.2 MHz+0.275 MHz=830.475 MHz). Hence, when “high-side” injection is used, the ninth harmonic of the high-side LO signal at  830 . 475  MHz from the second LO  208  downconverts the 830.2 MHz frequency channel used for GSM transmission to 0.275 MHz. The downconverted signal appears at  0 . 275  MHz, i.e. within the passband of the second communication unit, leading to unwanted GSM signals passing through the filter  214  and causing FM Radio distortion. 
     The conflict detection and control unit  210  monitors the frequencies (and associated harmonics) of the LO signals and any transmitted or received signals. In the case of  FIG. 2A , the conflict detection and control unit  210  detects that the ninth harmonic of the 92.275 MHz LO frequency and 830.2 MHz signal of the GSM signal cause interference in the FMR subunit  204 , so it instructs the LO tuning unit  212  to tune the second LO signal to a low-side LO frequency of 91.725 MHz, as shown in  FIG. 2B . This switch from high-side injection ( FIG. 2A ) to low-side injection ( FIG. 2B ) mitigates the interference in the FMR subunit  204  without changing the IF (0.275 MHz) on the FM reception path. More particularly, in  FIG. 2B  the ninth harmonic of the second LO signal at  825 . 525  MHz converts the GSM transmission channel at  830 . 2  MHz down to 4.625 MHz (=830.2 MHz−825.525 MHz). The frequency of the downconverted signal is outside the passband of the filter in the FM subunit  204  Further, because the IF remains unchanged at  0 . 275  MHz in the FM subunit  204 , the filter block  214  can keep its previous filter characteristics. In other embodiments the switch could be from low-side injection to high-side injection and/or could alter the IF in the second communication path, depending on the implementation. 
     It will be appreciated that the frequencies in  FIGS. 2A-2B  are merely examples and that the concepts described herein are applicable to any frequencies and not limited to these examples in any way. Further, in some embodiments it will be appreciated that an IF of zero can be used. Thus, the frequencies used will vary widely depending on the communication protocols involved, as well as what particular channels within a given communication protocol are being used, as well as other factors. 
       FIG. 3  shows another embodiment of a mobile device  300  that supports multiple communication protocols. The mobile device includes a first communication subunit  302 A, a second communication subunit  302 B, as well as one or more additional communication subunits  302 C (not shown in detail). 
     Each subunit can include one or more communication paths that include an analog front end (e.g.  304 A,  304 B) and digital circuitry (e.g.,  306 A,  306 B), wherein an analog-to-digital converter (ADC) or digital-to-analog converter (DAC) is disposed therebetween, depending on whether the communication path is used for reception or transmission. Within the analog front ends, one or more local oscillators (LOs) (e.g.,  308 A,  308 B), which can comprise a phase-locked loop (e.g.,  310 A,  310 B) and a fractional divider (e.g.,  312 A,  312 B) in some instances, provide LO signals to the communication paths. Within the digital circuitry, a digital processor (e.g.,  314 A,  314 B), memory ( 316 A,  316 B), and JTAG interface ( 318 A,  318 B) are often found. 
     Although  FIG. 3  shows separate hardware blocks on each path, some of these hardware blocks may be shared between various communication subunits. For example, in some embodiments, two or more communication subunits can share an antenna. In such an instance, a duplexer or other switching element typically selectively couples the communication paths to the shared antenna. In these and other embodiments, the memory units and/or digital processor can also be shared between the communication subunits. Other variations are also possible, with all such variations falling within the scope of the present invention. 
       FIGS. 4-5  show some methods in accordance with some embodiments of the present disclosure. While these methods are illustrated and described below as a series of acts or events, the present disclosure is not limited by the illustrated ordering of such acts or events. For example, some acts may occur in different orders and/or concurrently with other acts or events apart from those illustrated and/or described herein. In addition, not all illustrated acts are required and the waveform shapes are merely illustrative and other waveforms may vary significantly from those illustrated. Further, one or more of the acts depicted herein may be carried out in one or more separate acts or phases. It will also be appreciated that the communication devices previously illustrated in  FIGS. 1-3  can include suitable hardware and/or software to implement these methods. 
       FIG. 4  relates to a method for mitigating interference between signals communicated over first and second communication paths in a mobile device. The method starts at  402 , when the method determines a fundamental frequency and harmonic frequencies of a first signal-of-interest to be provided on a first communication path in the mobile communication device. 
     At  404 , the method determines a fundamental frequency and harmonic frequencies of a second signal-of-interest to be provided on a second communication path in the mobile communication device. Typically the fundamental frequency of the second signal-of-interest differs from the fundamental frequency of the first signal-of-interest. For example, consistent with the example previously discussed in  FIG. 2A-2B , the fundamental frequency of the first signal-of-interest could be a GSM transmission frequency of 830.2 MHz, and the fundamental frequency of the second signal-of-interest could be a FM radio frequency of 92.0 MHz. 
     At  406 , the method sets a fundamental frequency of a first LO signal. This first LO signal is to be provided on the first communication path to convert (e.g., up-convert) the fundamental frequency of the first signal. The method also determines first LO harmonics associated the first LO signal in  406 . 
     At  408 , the method sets a fundamental frequency of a second LO signal. This second LO signal is to be provided on the second communication path to convert (e.g., down-convert) the fundamental frequency of the second signal. The method also determines second LO harmonics associated the second LO signal in  408 . 
     The method then proceeds to  410  and determines whether the fundamental or harmonic frequencies of the first signal or the fundamental or harmonic frequencies of the first LO signal cause interference in the second communication channel  420 . If so (‘YES’ at  410 ), the method changes the fundamental frequency of the second LO signal to mitigate the conflict in  412 . 
     If not (‘NO’ at  410 ), there is no detected conflict and the method proceeds to  414  where it uses the first and second LO signals to perform frequency conversion on the first and second signals of interest, respectively. 
       FIGS. 5A-5B  show frequency diagrams consistent with one embodiment of the present disclosure. These frequency diagrams collectively show one manner in which a transceiver (e.g., transceiver of  FIG. 1 ,  FIG. 2 , or  FIG. 3 ) can change between high-side LO injection ( FIG. 5A ) and low-side LO injection ( FIG. 5B ) to limit interference between two communication subunits. 
       FIG. 5A  deals with an example where the transceiver transmits a GSM signal at  830 . 2  MHz over a first communication path (not shown) while concurrently receiving a wanted signal at  92 . 0  MHz on a second frequency path. The wanted signal is mixed with a high-side LO frequency LO HS  having a fundamental frequency of 92.275 MHz, which is separated from the frequency of the wanted signal by an intermediate frequency IF of 0.275 MHz. 
     Furthermore, the ninth harmonic of the LO frequency is located at  830 . 475  MHz, which is separated from the frequency of the GSM by an intermediate frequency IF of 0.275 MHz, too. 
     As shown in  FIG. 5B , when the 92.0 MHz signal is mixed with the LO HS  signal. The downconverted signal S dnwanted , appears at  0 . 275  MHz. In addition, the 830.2 MHz GSM signal is mixed with the ninth harmonic of the LO Hs  signal and the downconverted signal S dnunwanted  occurs at  0 . 275  MHz, too. The unwanted signal S dnunwanted  interferes with the wanted signal S dwanted  and decreases the sensitivity of the second communication unit. 
     Consequently, to limit interference/cross-talk, the frequency of the LO HS  signal is shifted to LO Ls  (see arrow  504 ), as shown in  FIG. 5C . This switch from high-side injection to low-side injection, which occurs symmetrically about the wanted signal (i.e., +/− IF with regards to the frequency of the wanted signal), mitigates interference while leaving the IF unchanged. Consequently, as shown in  FIG. 5D , the end result of the shift is that the IF of the down-converted wanted signal remains the same (0.275 MHz) so it passes through the filter. The ninth harmonic of the low-side LO signal is located at  825 . 525  MHz and converts the GSM signal at  830 . 2  MHz down to 4.625 MHz, so it is attenuated by the filter. Notably, the cross-talk interference from the first to second communication unit is mitigated. 
     It will be appreciated that the frequencies in  FIGS. 5A-5D  are merely examples and that the concepts described herein are applicable to any frequencies and not limited to these examples in any way. For example, in some embodiments it will be appreciated that an IF of zero can be used. In other embodiments, the LO frequency can be shifted by than greater than 2*IF or by less than 2*IF, thereby causing a shift in the IF. These shifts can also be used to mitigate the interference, although they typically require a tunable filter with an adjustable frequency passband to allow the newly tuned mixing products of interest to pass therethrough. Thus, the frequencies used will vary widely depending on the communication protocols involved, as well as what particular channels within a given communication protocol are being used, as well as other factors. 
     Although the disclosure has been shown and described with respect to one or more implementations, equivalent alterations and modifications will occur to others skilled in the art based upon a reading and understanding of this specification and the annexed drawings. The disclosure includes all such modifications and alterations and is limited only by the scope of the following claims. In particular regard to the various functions performed by the above described components (e.g., elements and/or resources), the terms used to describe such components are intended to correspond, unless otherwise indicated, to any component which performs the specified function of the described component (e.g., that is functionally equivalent), even though not structurally equivalent to the disclosed structure which performs the function in the herein illustrated exemplary implementations of the disclosure. In addition, while a particular feature of the disclosure may have been disclosed with respect to only one of several implementations, such feature may be combined with one or more other features of the other implementations as may be desired and advantageous for any given or particular application. In addition, the articles “a” and “an” as used in this application and the appended claims are to be construed to mean “one or more”. 
     Furthermore, to the extent that the terms “includes”, “having”, “has”, “with”, or variants thereof are used in either the detailed description or the claims, such terms are intended to be inclusive in a manner similar to the term “comprising.”