Patent Publication Number: US-2013237164-A1

Title: Radio frequency modules capable of self-calibration

Description:
BACKGROUND 
     1. Technical Field 
     The invention relates generally to radio frequency (RF) modules, and more particularly, to RF modules capable of self-calibration. 
     2. Related art 
     Wireless communications has gradually become a basic function of electronic devices, especially for portable ones. An electronic device capable of performing wireless communications generally includes a radio frequency (RF) module operative to handle RF signals. The RF module includes several electronic components. These components are frequently manufactured through mass production and as a result may not conform to their specifications precisely. For example, as compared with an ideal model, an RF module may be different on a transmission path as a whole, or on some sub-bands of the transmission path. As a result, the power level of the transmitted RF signal may deviate from the desired power level. Furthermore, as compared with the ideal model, the RF module may be different on a receiving path as a whole, or on only some sub-bands of the receiving path. As a result, the actual loss caused by the receiving path may deviate from the expected amount. 
     In response, several calibration mechanisms have been proposed. However, some of the mechanisms require too many additional components to be used, and hence significantly increase the overall hardware costs. Some of the mechanisms calibrate only a part of an RF signal path, which can be a transmission or receiving path, but does not compensate for the variance attributable to the rest part of the RF signal path. For example, if the RF module includes an antenna switch module (ASM) that allows a single antenna to be shared by several RF signal paths, the ASM will be a source of power/loss variations but the power/loss variations attributable to the ASM are seldom calibrated. 
     SUMMARY 
     Embodiments of radio frequency (RF) modules capable of self-calibration are proposed to resolve the aforementioned problems of the related art and to achieve some other objectives. 
     One of the proposed RF modules includes an RF signal processor, a plurality of RF signal paths, an antenna switch module (ASM), and a power detector. The RF signal paths are connected between the RF signal processor and the ASM. The ASM has an antenna port and selectively connects the RF signal processor to the antenna port through one of the RF signal paths. The power detector is operative to detect power of an RF transmission signal that exits the antenna port of the ASM and enters an antenna when the ASM connects an RF transmission path of the RF signal paths to the antenna port of the ASM. 
     Another one of the proposed RF modules includes an RF signal processor, a plurality of RF signal paths, an ASM, and a test tone generator. The RF signal paths are connected between the RF signal processor and the ASM. The ASM has an antenna port and selectively connects the RF signal processor to the antenna port through one of the RF signal paths. The test tone generator is operative to generate a test tone and feed the test tone into the antenna port of the ASM when the ASM connects the antenna port to an RF receiving path of the RF signal paths. 
     Still another one of the proposed RF modules includes an RF signal processor, a plurality of RF signal paths, and an ASM. The RF signal paths are connected between the RF signal processor and the ASM. The ASM has an antenna port and selectively connects the RF signal processor to the antenna port through one of the RF signal paths. A calibration component of the RF signal processor facilitates the calibration of at least one of the RF signal paths. 
     Other features of the present invention will be apparent from the accompanying drawings and from the detailed description which follows. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention is fully illustrated by the subsequent detailed description and the accompanying drawings, in which like references indicate similar elements. 
         FIGS. 1-10  show block diagrams of radio frequency (RF) modules according to ten exemplary embodiments of the invention. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  shows a block diagram of a radio frequency (RF) module according to a first embodiment of the invention. As used in this detailed description, the term “RE module” refers to an electronic module that can be incorporated into an electronic device to generate and transmit RF signals, or to receive and process RF signals, or to be responsible for both the transmission and reception of RF signals. In addition to the RF module, the electronic device can further include other components, such as a baseband circuitry that controls the operation of the electronic device as a whole. 
     In this embodiment, the RF module  100  includes an RF signal processor  110 , a plurality of RF signal paths  130 _ 1 ,  130 _ 2 , . . . , and  130 _M, an antenna switch module (ASM)  170 , a coupler  180 , and an antenna  190 , where M is a positive integer larger than one. The RF signal processor  110  has a power detector (PDET)  111  that is connected to the coupler  180 . The power detector  111  serves as a calibration component of the RF signal processor  110  and facilitates the calibration of at least one of the RF signal paths  130 _ 1 ˜ 130 _M. 
     As used in this detailed description, the term “RE signal processor” refers to an RF transmitter, an RF receiver, or an RF transceiver. In this embodiment, if the RF signal processor  110  is an RF transmitter, the RF signal paths  130 _ 1 ˜ 130 _M will be transmission paths. That is, the RF signal paths  130 _ 1 ˜ 130 _M receive RF signals from the RF signal processor  110  and output RF signals to the ASM  170  for transmission. If the RF signal processor  110  is an RF transceiver, the RF signal paths  130 _ 1 ˜ 130 _M can include at least one RF transmission path and at least one RF receiving path. The RF transmission path receives RF signals from the RF signal processor  110  and outputs RF signals to the ASM  170 ; the RF receiving path receives RF signals from the ASM  170  and outputs RF signals to the RF signal processor  110 . 
     Although not depicted in  FIG. 1 , the RF signal paths  130 _ 1 ˜ 130 _M have various internal components. For example, if an RF signal path  130 _N is an RF transmission path, where N is a positive integer equal to or smaller than M, the path  130 _N can include a power amplifier (PA). If the RF signal path  130 _N is an RF receiving path, the path  130 _N can include a surface acoustic wave (SAW) filter. In addition, more than one of the RF signal paths  130 _ 1 ˜ 130 _M, e.g. an RF transmission path and an RF receiving path of the paths  130 _ 1 ˜ 130 _M, can share a duplexer. The shared duplexer either connects the RF transmission path to the ASM  170  or connects the ASM  170  to the RF receiving path. 
     The ASM  170  allows the multiple RF signal paths  130 _ 1 ˜ 130 _M to share a single antenna  190 . Specifically, the ASM  170  only selects and connects one of the RF signal paths  130 _ 1 ˜ 130 _M to an antenna port  171  of the ASM  170  at a time. Because the antenna port  171  is connected to the antenna  190  through the coupler  180 , the selected one of the RF signal paths  130 _ 1 ˜ 130 _M will be able to send RF signals to the antenna  190  for transmission, or receive RF signals from the antenna  190  for processing. 
     The coupler  180  includes an input port  181 , a transmitted port  183 , and a coupled port  185 . If RF signals enter the coupler  180  through the input port  181 , a portion of the RF signals will leave the coupler  180  through the transmitted port  183 , while another portion of the RF signals will leave the coupler  180  through the coupled port  185 . If RF signals enter the coupler  180  through the coupled port  185 , at least a portion of the RF signals will leave the coupler  180  through the input port  181 . The coupler  180  can be realized by a directional coupler that has an input port, a transmitted port, a coupled port, and an isolated port. The isolated port can be terminated with a matched load. The input port, the coupled port, and the transmitted port of the directional coupler can serve as the input port  181 , the coupled port  185 , and the transmitted port  183  of the coupler  180 , respectively, or serve as the coupled port  185 , the input port  181 , and the transmitted port  183  of the coupler  180 , respectively. 
     The RF module  100  of this embodiment allows RF transmission path(s) of the RF signal paths  130 _ 1 ˜ 130 _M to be calibrated in real time. Taking the RF signal path  130 _K as an example and assuming that it&#39;s an RF transmission path, where K is a positive integer equal to or smaller than M, the frequency response of the RF signal path  130 _K may not always be exactly the same as that of an ideal model. For example, this may be true if the RF transmission path  130 _K, as manufactured, has variations from the ideal model. As another example, this may be true if the RF transmission path  130 _K is not in a perfect environment or under a perfect condition, e.g. the RF transmission path  130 _K has accumulated some heat and as a result can no longer function ideally. If the RF transmission path  130 _K cannot function ideally, the power of the transmitted RF signal, either as a whole or on some sub-bands, may vary from the ideal transmission power level. The difference in power level may affect the communication quality. To resolve the problem, this embodiment allows the RF transmission path  130 _K to be calibrated in real time, i.e. when the RF transmission path  130 _K is in use. 
     When the RF transmission path  130 _K is in use, the ASM  170  connects it to the antenna port  171 . Through the antenna port  171  of the ASM  170  and the input port  181  and the transmitted port  183  of the coupler  180 , RF transmission signals coming out from the RF transmission path  130 _K reach and are transmitted by the antenna  190 . In addition, the coupler  180  couples the RF transmission signals to generate coupled RF signals at the coupled port  185 . 
     After the coupled RF signals reach the power detector  111 , the power detector  111  detects the power level of the coupled RF signals. Theoretically, the power level of the coupled RF signals should be proportional to the power level of the RF transmission signals. Therefore, in effect, the power detector  111  inferentially detects the power of the RF transmission signals that leaves the ASM  170  and enters the antenna  190 . 
     If the detected power level is lower than a reference level, whether as a whole or only on some sub-bands, the RF transmission path  130 _K is not providing enough power amplification. In response, the RF module  100  can be calibrated to compensate for the insufficient amplification. If the detected power level is higher than the reference level, whether as a whole or only on some sub-bands, the RF transmission path  130 _K is providing more amplification than expected. In response, the RF module  100  can be calibrated to deal with the excessive amplification, e.g. in order to reduce power consumption. The comparison, determination, calibration, or a combination thereof, mentioned in this paragraph can be performed by the RF signal processor  110  itself, or by a baseband circuitry that is connected to the RF signal processor  110 . 
     Instead of using N power detectors, each being connected to the ASM  170  and one of N RF transmission paths of the M RF signal paths  130 _ 1 ˜ 130 _M, where N is a positive integer equal to or smaller than M, this embodiment uses only one power detector  111  and only one coupler  180 . Therefore, this embodiment does not involve much additional hardware costs. Furthermore, because the power detected by the power detector  111  reveals the power of the actually transmitted RF signal, which has been affected by not only the RF transmission path  130 _K but also the ASM  170 , errors in power level attributable to the ASM  170  will also be calibrated. On the contrary, if a power detector was connected to the transmission line between the RF transmission path  130 _K and the ASM  170 , the power detector would not be able to detect errors attributable to the ASM  170 , so the errors attributable to the ASM  170  would remain un-calibrated. 
     Moreover, because the RF transmission paths of the RF signal paths  130 _ 1 ˜ 130 _M can be calibrated in real time, it&#39;s possible that the manufacturer of the RF module  100  or the manufacturer of an electronic device that incorporates the RF module  100  can skip calibrating the RF transmission paths. After all, these paths will be calibrated when they are in actual use. Therefore, this embodiment has the potential of further reducing the manufacturer&#39;s overall costs. 
       FIG. 2  shows a block diagram of an RF module according to a second embodiment of the invention. Except for a few differences, this embodiment is very similar to the embodiment shown in  FIG. 1 . For the sake of simplicity, only the differences between these two embodiments will be discussed hereinafter. 
     Please refer to  FIG. 2 . An RF module  200  of this embodiment includes an RF signal processor  210 . Instead of having the power detector  111 , the RF signal processor  210  has a test tone generator (TTG)  213 . The test tone generator  213  serves as a calibration component of the RF signal processor  210  and facilitates the calibration of at least one of the RF signal paths  130 _ 1 ˜ 130 _M. If the RF signal processor  210  is an RF receiver, the RF signal paths  130 _ 1 ˜ 130 _M will be RF receiving paths. If the RF signal processor  210  is an RF transceiver, the RF signal paths  130 _ 1 ˜ 130 _M can include at least one RF transmission path and at least one RF receiving path. 
     The RF module  200  of this embodiment allows RF receiving path(s) of the RF signal paths  130 _ 1 ˜ 130 _M to be calibrated automatically, especially after an electronic device incorporating the RF module  200  has already been sold to an end user. Taking the RF signal path  130 _L as an example and assuming that it&#39;s an RF receiving path, where L is a positive integer equal to or smaller than M, the frequency response of the RF receiving path  130 _L may not be exactly the same as that of an ideal model. For example, this may be true if the RF receiving path  130 _L, as manufactured, is different from its ideal model. As another example, this may be true if the RF receiving path  130 _L is not in a perfect environment or is not under a perfect condition, e.g. it has accumulated some heat and as a result can no longer function ideally. If the RF receiving path  130 _L cannot function ideally, it may cause more loss than expected. To resolve this problem, this embodiment allows the RF receiving path  130 _L to be calibrated soon before it is going to be used. 
     To calibrate the RF receiving path  130 _L, the ASM  170  needs to connect the antenna port  171  to the RF receiving path  130 _L. The test tone generator  213  generates and feeds a test tone into the coupled port  185  of the coupler  180 . To enable precise calibration, the power level of the test tone should be as close to a predetermined level as possible. The coupler  180  couples the test tone to generate a coupled test tone at the input port  181 . Theoretically, the power level of the coupled test tone should be proportional to the power level of the test tone that enters the coupled port  185 . Therefore, in effect, the test tone generator  213  is feeding the test tone, after some attenuation, into the antenna port  171  of the ASM  170 . 
     After passing through the ASM  170  and the RF receiving path  130 _L, the coupled test tone reaches the RF signal processor  210 . The RF signal processor  210  then detects the power level of the received signal. If the detected power level is lower than a reference level, whether as a whole or only on some sub-bands, the RF receiving path  130 _L and the ASM  170  are causing more loss than expected. In response, the RF module  200  can be calibrated to compensate for the excessive loss. If the detected power level is higher than the reference level, whether as a whole or only on some sub-bands, the RF receiving path  130 _L and the ASM  170  are causing less loss than expected. If there is such a need, the RF module  200  can be calibrated to deal with the less-than-expected loss. The comparison, determination, calibration, or a combination thereof, mentioned in this paragraph can be performed by the RF signal processor  210  itself, or by a baseband circuitry that is connected to the RF signal processor  210 . 
     The aforementioned calibration can be performed for all the RF receiving paths of the RF signal paths  130 _ 1 ˜ 130 _M soon after the end user of an electronic device incorporating the RF module  200  has turned on the electronic device and before the RF receiving paths are used to pass RF signals containing useful information. 
     The RF module  200  of this embodiment has several advantages. For example, it uses only one test tone generator  213  and only one coupler  180  to allow all the RF receiving paths of the RF signal paths  130 _ 1 ˜ 130 _M to be calibrated. Therefore, this embodiment does not involve much additional hardware costs. Furthermore, this embodiment allows the RF receiving paths of the RF signal paths  130 _ 1 ˜ 130 _M to be calibrated when an electronic device incorporating the RF module  200  is already in an end user&#39;s hand. Therefore, it&#39;s possible that the manufacturer of the RF module  200  or the manufacturer of the electronic device incorporating the RF module  200  can skip calibrating the RF receiving paths. As a result, this embodiment has the potential of further reducing the manufacturer&#39;s overall costs. Moreover, because the ASM  170  is a potential source of loss variations, it&#39;s valuable that the RF module  200  can nullify the loss variations attributable to the ASM  170 . 
       FIG. 3  shows a block diagram of an RF module according to a third embodiment of the invention. This embodiment combines the concepts and spirit of the first and second embodiments and has only a few differences from the first and second embodiments. For the sake of simplicity, only these differences will be discussed hereinafter. 
     Please refer to  FIG. 3 . An RF module  300  of this embodiment includes an RF signal processor  310 . Instead of having either the power detector  111  or the test tone generator  213 , the RF signal processor  310  has both. The RF signal processor  310  is an RF transceiver; the RF signal paths  130 _ 1 ˜ 130 _M include at least one RF transmission path and at least one RF receiving path. If the power detector  111  and the test tone generator  213  cannot be connected together, the RF signal processor  310  can further include a switch that selects and connects only one of the power detector  111  and the test tone generator  213  to the coupled port  185  at a time, and isolates the power detector  111  and the test tone generator  213  from each other. 
     Similar to the RF module  100 , the RF module  300  also allows RF transmission path(s) of the RF signal paths  130 _ 1 ˜ 130 _M to be calibrated in real time. Similar to the RF module  200 , the RF module  300  also allows RF receiving path(s) of the RF signal paths  130 _ 1 ˜ 130 _M to be calibrated, especially after an electronic device incorporating the RF module  300  is already in an end user&#39;s hand. As a result, the RF module  300  combines the functions and advantages of both the RF modules  100  and  200 . 
       FIG. 4  shows a block diagram of an RF module according to a fourth embodiment of the invention. An RF module  400  of this embodiment includes an RF signal processor  410 . The RF signal processor  410  can be either an RF transmitter or an RF transceiver. Instead of being an internal component of the RF signal processor  410 , the power detector  111  is either a stand-alone component or an internal component of a module  475  that further incorporates the ASM  170  and the coupler  180 . When the ASM  170  connects the RF transmission path  130 _K to the antenna port  171 , the power detector  111  can report its power detection results to a baseband circuitry that is connected to the RF signal processor  410 . The baseband circuitry can then calibrate the RF transmission path  130 _K and the ASM  170  according to the power detection results. Except for these differences, this embodiment is very similar to the embodiment shown in  FIG. 1 , and these two embodiments share several common advantages. 
     Because the power detector  111  is either a stand-alone component or an internal component of the module  475 , the manufacturer of either the power detector  111  or the module  475 , rather than the manufacturer of the RF signal processor  410 , will bear the manufacturing costs of the power detector  111  and have to ensure that the power detector  111  has acceptable precision. 
       FIG. 5  shows a block diagram of an RF module according to a fifth embodiment of the invention. Instead of being connected to the ASM  170  through a coupler  180 , the power detector  111  in this embodiment is connected to a path between the ASM  170  and the antenna  190 . When the RF transmission path  130 _K is in use, the ASM  170  connects it to the antenna port  171 . The power detector  111  senses voltages on the path between the ASM  170  and the antenna  190  so as detect power of the RF transmission signals that have passed through the RF transmission path  130 _K and the ASM  170 . The power detector  111  can report its power detection results to a baseband circuitry that is connected to the RF signal processor  410 , so that the baseband circuitry can calibrate the RF transmission path  130 _K and the ASM  170  according to the power detection results. Except for these differences, this embodiment is very similar to the embodiment shown in  FIG. 4 , and these two embodiments share several common advantages. 
     Because the power detector  111  is either a stand-alone component or an internal component of a module  575  that further incorporates the ASM  170 , the manufacturer of either the power detector  111  or the module  575 , rather than the manufacturer of the RF signal processor  410 , will bear the manufacturing costs of the power detector  111  and have to ensure that the power detector  111  has acceptable precision. 
       FIG. 6  shows a block diagram of an RF module according to a sixth embodiment of the invention. An RF module  600  of this embodiment includes an RF signal processor  610  that can be an RF transceiver. Instead of being internal components of the RF signal processor  610 , the power detector  111  and the test tone generator  213  are either stand-alone components or internal components of a module  675  that further incorporates the ASM  170  and the coupler  180 . When the ASM  170  connects the RF transmission path  130 _K of the RF signal paths  130 _ 1 ˜ 130 _M to the antenna port  171 , the power detector  111  can report its power detection results to a baseband circuitry that is connected to the RF signal processor  610 , so that the baseband circuitry can calibrate the RF transmission path  130 _K according to the power detection results. Except for these differences, this embodiment is very similar to the embodiment shown in  FIG. 3 , and these two embodiments share several common advantages. 
     Because the power detector  111  and the test tone generator  213  are either stand-alone components or internal components of the module  675 , the manufacturer(s) of either the power detector  111  and the test tone generator  213  or the module  675 , rather than the manufacturer of the RF signal processor  610 , will bear the manufacturing costs of the power detector  111  and the test tone generator  213  and have to ensure that these two components have acceptable precision. 
       FIG. 7  shows a block diagram of an RF module according to a seventh embodiment of the invention. Instead of being connected to the coupled port  185  of the coupler  180 , the power detector  111  is connected to either the path between the ASM  170  and the coupler  180 , or the path between the coupler  180  and the antenna  190 . When the RF transmission path  130 _K is in use, the ASM  170  connects it to the antenna  190  through the coupler  180 . The power detector  111  senses voltages on either the path between the ASM  170  and the coupler  180  or the path between the coupler  180  and the antenna  190  so as detect power of the RF transmission signals that have passed through the RF transmission path  130 _K and the ASM  170 . 
     Except for the aforementioned differences, this embodiment is very similar to the embodiment shown in  FIG. 6 , and these two embodiments share several common advantages. The manufacturer(s) of either the power detector  111  and the test tone generator  213  or a module  775  that incorporates these two components, the ASM  170 , and the coupler  180 , rather than the manufacturer of the RF signal processor  610 , will bear the manufacturing costs of the power detector  111  and the test tone generator  213  and have to ensure that these two components have acceptable precision. 
       FIG. 8  shows a block diagram of an RF module according to an eighth embodiment of the invention. An RF module  800  of this embodiment includes an RF signal processor  810  that can be an RF transceiver or an RF receiver. Unlike the RF module  700  shown in  FIG. 7 , the RF module  800  of this embodiment includes a module  875  that does not have a power detector  111 . Therefore, unlike the RF module  700 , the RF module  800  may not allow the RF transmission path  130 _K to be calibrated when the path  130 _K is in use. 
     The embodiment shown in  FIG. 8  shares some common advantages with the embodiment shown in  FIG. 2 . The manufacturer of the test tone generator  213  or the module  875  that incorporates the test tone generator  213 , the ASM  170 , and the coupler  180 , rather than the manufacturer of the RF signal processor  810 , will bear the manufacturing costs of the test tone generator  213  and have to ensure that this component has acceptable precision. 
       FIG. 9  shows a block diagram of an RF module according to a ninth embodiment of the invention. In this embodiment, a switch  979  rather than a coupler  180  is used. When the RF module  900  is in use, the switch  979  connects the antenna port  171  of the ASM  170  to the antenna  190 . When the RF transmission path  130 _K is in use, the ASM  170  and the switch  979  connect it to the antenna  190 ; the power detector  111  senses voltages on either the path between the ASM  170  and the switch  979  or the path between the switch  979  and the antenna  190  so as detect power of the RF transmission signals that have passed through the RF transmission path  130 _K and the ASM  170 . When the RF module  900  is not in use and the RF receiving path  130 _L needs to be calibrated, the switch  979  connects the test tone generator  213  to the antenna port  171  of the ASM  170  so as to allow the test tone generator  213  to feed a test tone into the RF receiving path  130 _L. 
     Except for the aforementioned differences, this embodiment is very similar to the embodiment shown in  FIG. 7 , and these two embodiments share several common advantages. The manufacturer(s) of either the power detector  111  and the test tone generator  213  or a module  975  that incorporates these two components, the ASM  170 , and the switch  979 , rather than the manufacturer of the RF signal processor  610 , will bear the manufacturing costs of the power detector  111  and the test tone generator  213  and have to ensure that these two components have acceptable precision. 
       FIG. 10  shows a block diagram of an RF module according to a tenth embodiment of the invention. An RF module  1000  of this embodiment includes an RF signal processor  810  that can be an RF transceiver or an RF receiver. Unlike the RF module  900  shown in  FIG. 9 , the RF module  1000  of this embodiment includes a module  1075  that does not have a power detector  111 . Therefore, unlike the RF module  900 , the RF module  1000  may not allow the RF transmission path  130 _K to be calibrated when the path  130 _K is in use. 
     The embodiment shown in  FIG. 10  shares several common advantages with the embodiment shown in  FIG. 2 . The manufacturer of the test tone generator  213  or the module  1075  that incorporates the test tone generator  213 , the ASM  170 , and the switch  979 , rather than the manufacturer of the RF signal processor  810 , will bear the manufacturing costs of the test tone generator  213  and have to ensure that this component has acceptable precision. 
     In the foregoing detailed description, the invention has been described with reference to specific exemplary embodiments thereof. It will be evident that various modifications may be made thereto without departing from the spirit and scope of the invention as set forth in the following claims. The detailed description and drawings are, accordingly, to be regarded in an illustrative sense rather than a restrictive sense.