Abstract:
An impedance matching circuit for a radio receives antenna signals and has its matching elements, such as capacitors, progressively switched into the circuit, with the matching element configuration resulting in the highest RSSI being subsequently used until a succeeding test or antenna impedance change. The effect of the matching circuit is accounted for in the transmitter calibration routine so that the matching circuit works for both half duplex and full duplex.

Description:
FIELD OF THE INVENTION 
     The present invention relates generally to circuits for adaptively matching impedance in a radio. 
     BACKGROUND OF THE INVENTION 
     Radios are commonly used in wireless notebooks, wireless consumer electronics devices such as mobile telephones, etc. to provide wireless connectivity to a network. As understood herein, the impedance of the radio&#39;s antenna can be affected by the placement of a user&#39;s hand on the device and by other nearby objects, which can degrade radio performance. 
     As further understood herein, not only would it be advantageous to address the problem noted above but to do so in a way that works not only in a half-duplex mode, in which transmitter performance is not necessarily affected by a change in antenna receiver-side impedance, but in a full-duplex mode as well, in which the transmitter performance typically is affected as antenna impedance changes. 
     SUMMARY OF THE INVENTION 
     A system has a transceiver communicating with an antenna and a matching network in a communication path between the antenna and transceiver. The matching network includes at least a first set of matching elements switchable from a first configuration, in which at least a first matching element in the set is not in the communication path, and a second configuration, in which the first matching element is in the communication path. A processor controls the matching network to establish the first and second configurations and to determine first and second respective measures of performance. The processor establishes the configuration having the best measure of performance. 
     The matching elements can be capacitors, inductors, or resistors. In some embodiments the measure of performance is received signal strength indication (RSSI) and more specifically may be an average RSSI. 
     Some examples envision that the system can operate in at least first and second frequency bands. In this case the matching network can include least a second set of matching elements, with the first set of matching elements being selected by the processor when the system operates in the first frequency band and the second set of matching elements being selected by the processor when the system operates in the second frequency band. 
     The transmitter can be calibrated as more fully described below to account for the first and second configurations to facilitate full duplex mode operation while the matching network is in use. A set of matching elements can establishes a π configuration or a “T” configuration or an “L” configuration, and present principles may be used, without limitation, with PCS, TDMA, GSM, Edge, UTMS, CDMA 1x-RTT, 1X-EVDO, 802.11a, 802.11b, 802.11g, 802.11n, Wimax, LTE. 
     In another aspect, a system includes a transceiver communicating with an antenna. The transceiver includes a receiver and a transmitter. A matching circuit is in a communication path between the antenna and transceiver. The matching circuit includes a first set of matching elements switchable from a first configuration, in which at least a first matching element in the set is not in the communication path, and a second configuration, in which the first matching element is in the communication path. A processor controls the matching circuit to establish the first and second configurations and to determine first and second respective measures of performance. The processor establishes the configuration having the best measure of performance. The transmitter can be configured to account for the matching circuit such that the matching circuit is useful in full duplex modes. 
     In still another aspect, a method includes determining whether an index of receiver performance of a receiver fails a threshold. Only of the index fails the threshold, the method then includes establishing plural configurations for an impedance matching circuit communicating with a radio antenna and determining an index of receiver performance for each configuration. The method includes establishing one of the configurations in circuit based on the act of determining an index of receiver performance. 
     The act of establishing plural configurations may be executed only when the receiver is not actively receiving a data call. Also, a calibration of a transmitter associated with the receiver may be established to account for an effect of the impedance matching circuit. Furthermore, the method may include, in non-limiting examples, determining a modulation currently being used in connection with the receiver, with the threshold depending on the modulation currently being used. 
     The details of the present invention, both as to its structure and operation, can best be understood in reference to the accompanying drawings, in which like reference numerals refer to like parts, and in which: 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram of an example radio with the present matching circuit; 
         FIG. 2  is a block diagram of an example matching circuit in accordance with present principles; 
         FIG. 3  is a flow chart of example logic that is embodied by a matching circuit; 
         FIG. 4  is a schematic diagram of a threshold lookup table; and 
         FIGS. 5-7  show alternative matching circuits. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring initially to  FIG. 1 , a radio  10  that may be incorporated in a portable electronic device  11  such as a portable computer or wireless telephone includes an antenna  12  sending signals to and receiving signals from a matching circuit  14 , an example of which is described further below in reference to  FIG. 2 . The matching circuit  14  may be connected to one or more filter-type components such as duplexers. In the example shown the matching circuit  14  communicates with a cellular duplexer  16 , a personal communication service (PCS) duplexer  18 , and a long-term evolution (LTE) duplexer or transmit/receiver (T/R) switch  20 . 
     In turn, each of the components  16 - 20  communicates with a receiver/downconverter  22  of a radiofrequency (RF) transceiver  24 . The receiver/downconverter converts signals in the RF domain to intermediate frequency (IF), which is sent to a receiver I&amp;Q demodulator  25  of a host processor  26  for demodulation of the IF to baseband, which is processed by the host processor. 
     The apparatus disclosed thus far also has a transmitter side, and more particularly a transmitter I&amp;Q modulator  28  is provided in the processor  26  for modulating baseband signals to IF, which are upconverted to the RF domain by an upconverter  30  in the transceiver  24 . When three transmission schemes are contemplated as shown in the non-limiting example of  FIG. 2 , the upconverter  30  sends RF signals to a cellular filter  32  which communicates with a cellular power amplifier  34 , which in turn may be connected to a cellular directional coupler  36 . The cellular directional coupler  36  communicates with the cellular duplexer  16  as shown. 
     Also, the upconverter  30  sends RF signals to a PCS filter  38  which communicates with a PCS power amplifier  40 , which in turn may communicate with a PCS directional coupler  42 . The PCS directional coupler  42  communicates with the PCS duplexer  18  as shown. In the example of  FIG. 2 , the upconverter  30  sends RF signals to a LTE filter  44  which communicates with a LTE power amplifier  46 , which in turn may communicate with a LTE directional coupler  48 . The LTE directional coupler  48  communicates with the LTE duplexer or T/R switch  20  as shown. If desired, all three couplers  36 ,  42 ,  48  may communicate with each other, and at least one coupler  48  may communicate with a power detector  50  in the transceiver  24  for purposes to be shortly disclosed. 
     Completing the description of  FIG. 1 , the host processor  26  may execute a switch control register or I/O  52  for configuring the matching circuit  14  in accordance with principles below. Also, the processor  26  may access a memory such as disk-based memory or solid state memory such as a flash memory  54  that can store, among other things, a lookup table described further below. 
     Now referring to  FIG. 2 , details of an example matching circuit  14  may be seen. The matching circuit  14  may have only a single set of matching elements but in the example shown, the matching circuit  14  has three sets  56 ,  58 ,  60  of matching elements  62 , one set communicating with a respective duplexer  16 - 20  as shown. A switch  64  controlled by the processor  26  establishes which set  56 - 60  of matching elements communicates with the antenna  12 . It will readily be appreciated that the processor  26  configures the switch  64  as appropriate for the particular mode the radio  10  is being operated in. In this way, one otherwise large and comparatively bulky set of matching elements is avoided, because the respective sets  56 - 60  of matching elements can be advantageously smaller sized since they must be adapted to only the frequency band they happen to correspond to, e.g., cellular, PCS, or LTE. 
     In the example of  FIG. 2 , the matching elements in a single set are capacitors and are connected in parallel to each other as shown to establish a π-shaped configuration. Alternatively, a “T” shaped configuration or an “L” shaped configuration for the matching elements may be used as described further below in reference to  FIGS. 5-7 . Instead of capacitors, inductors or resistors less preferably may be used as matching elements. Each set  56 - 60  of matching elements may be grounded as shown through respective opposed inductors “I”. If desired the inductors “I” may also be switched into and out of the circuit as part of configuring the matching circuit  14 . 
     Example logic of the processor  26  in configuring the matching circuit  14  is shown in  FIG. 3 . Commencing at power up and network connection state  66 , in some embodiments the logic can move to decision diamond  68  to determine whether an active call or other data communication is in progress through the radio  10 . Also, a counter “n” can be initialized to zero. 
     If a call is in progress the logic may move to block  70  to prevent the below-described tuning process until the call is over and to establish a default configuration for the network of matching elements in the matching circuit  14 . In other embodiments the tuning process may proceed regardless of whether a call is active. 
     In the example shown, when no call is active (or immediately upon power up when the active call test at decision diamond  68  is omitted) the logic moves to block  72  to check a measure of performance. In one embodiment the processor  26  determines received signal strength indicator (RSSI) in the transceiver. In other implementations other measures of performance may be used, e.g., signal to noise ratio, bit error rate, etc. 
     Also at block  72  the processor  26  determines the current modulation protocol in use. In the example of  FIGS. 1 and 2  the current protocol would be cellular or PCS or LTE. 
     Proceeding to decision diamond  74  the processor  26  determines whether, for the modulation protocol in use, the measure of performance (e.g., RSSI) violates a sensitivity threshold. This may be done by accessing the memory  54  to enter a lookup table of values of RSSI thresholds for the current modulation protocol in use. An example table is discussed further below in reference to  FIG. 4 . If desired, the looked up threshold may be compared against current instantaneous RSSI but in the example shown in  FIG. 3  the processor  26  calculates an average RSSI over multiple cycles, e.g., two or more and compares the average actual RSSI against the threshold at decision diamond  74 . 
     If the actual RSSI does not violate the threshold, in some implementations, to limit excessive processing the logic may flow to decision diamond  76  to determine whether the number of recent RSSI tests at decision diamond  74  equals a threshold number, e.g., 2. If not, “n” is incremented by unity at block  78  and the logic loops back to block  72 . On the other hand, if “n” meets the threshold the logic moves to block  70 . 
     In the event that the RSSI value fails to meet the threshold at decision diamond  74 , in some embodiments the logic may include another test at decision diamond  80  to determine if the low noise amplifier (LNA) gain of the receiver is set to its highest state, setting it to the highest state at block  82  if not. In any case, the tuning of the selected set  56 - 60  of matching elements  62  in the matching circuit  14  begins at block  84 , in which a first matching element  62  is switched into the circuit and RSSI recorded at block  86 , then the second element, and so on, recording RSSI values as the matching elements are progressively switched into the circuit one at a time. If desired, in less preferred embodiments the progressive switching may include switching in two or more elements  62  at a time. When all matching elements  62  have been switched in accordingly, the configuration with the highest RSSI is selected at block  88 . Thus, for example, if the first three elements  62  result in the highest RSSI then that is the configuration selected for the matching circuit  14  at block  88 . The process ends at state  89 . 
     An example non-limiting lookup table  90  that may be stored in the medium  54  and used at block  74  as described above is shown in  FIG. 4 . 
     Present principles envision use in a number of communication protocols including, without limitation, PCS, TDMA, GSM, Edge, UTMS, CDMA 1x-RTT, 1X-EVDO, 802.11a, 802.11b, 802.11g, 802.11n, Wimax, LTE. Also, present principles envision use in both half-duplex modes and full duplex modes, and in this latter regard the degradation of transmitter performance is avoided by incorporating the effects of the matching circuit  14  in the transmitter calibration routines. 
     Specifically, during transmitter calibration the above-described receiver matching elements are switched in and out of the circuit in various combinations, singly and in groups. This results in changes of the transmitter impedance, which in turn can affect transmitter output power, gain, spurious emissions, and so on. Accordingly, for each matching element combination the transmitter is tuned during calibration to optimize transmitter performance. The transmitter chain may be tuned by establishing particular gain, input power, etc. for each impedance presented by each matching element combination. The transmitter settings for each impedance may be stored in a calibration table which can be accessed during operation so that as matching elements in the receiver are switched in and out of the circuit as described above, the transmitter settings corresponding to the related impedances are changed to optimize transmitter performance. 
       FIG. 5  shows a “T”-style matching circuit  100  in which two sets  102 ,  104  of matching elements are connected to a common cross line  106 , one end of which is connected to the switch and the other end of which is connected to the duplexer or T/R switch. In  FIGS. 6 and 7 , “L”-style circuits are shown in which a matching circuit  108  is connected to cross-line  110  which in turn is connected to the switch and the duplexer or T/R switch as shown. The difference between  FIGS. 6 and 7  is that in  FIG. 6 , the cross-line  110  is grounded through an inductor  112  on the duplexer/T/R switch side whereas in  FIG. 7  it is grounded through the inductor  112  on the switch side. 
     While the particular MATCHING CIRCUIT FOR ADAPTIVE IMPEDANCE MATCHING IN RADIO is herein shown and described in detail, it is to be understood that the subject matter which is encompassed by the present invention is limited only by the claims. 
     For example, all or parts of the matching circuit  14  may be moved into the integrated circuit of the transceiver. Further, all or parts of the logic of  FIG. 3  may be implemented as part of a software routine.