Abstract:
An RF diplexer is provided with an integrated diplexer that shares a primary inductor included in a channel within the RF diplexer.

Description:
TECHNICAL FIELD 
       [0001]    This application relates to an RF multiplexer, and more particularly to an RF multiplexer with integrated directional couplers. 
       BACKGROUND 
       [0002]    Front end components such as directional couplers and radio frequency (RF) multiplexers have numerous applications in devices such as cellular phones. For example, carrier aggregation provides increased bandwidth in modern 4G communication protocols in which a handset communicates over multiple component carriers. Each component carrier has a certain bandwidth centered about a corresponding center frequency. Although a 4G transmitter may thus communicate over different carrier components (and thus over different frequency bands), it is conventional that this communication occur through a common antenna (or antennas). For example, a transmitter may drive a low-pass channel corresponding to a lower frequency carrier component and also drive a mid-band channel corresponding to a higher frequency carrier component. The two channels couple through a diplexer (RF multiplexer) to drive the common antenna(s). In addition, the transmitter needs feedback information to control the power of the signals through the different frequency channels. 
         [0003]    It is thus conventional to include a directional coupler for each channel as shown in  FIG. 1  for a transmitter  100 . The low-band (LB) channel includes an LB power amplifier (PA) module that drives a LB directional coupler  105  that in turn drives an RF multiplexer  115 . RF multiplexer  115  may drive an antenna with the low-band signal from LB directional coupler  105 . A coupled port from LB directional coupler  105  provides a feedback signal (LB_cp) that is an attenuated version of the directional coupler output—e.g., LB_cp may be attenuated by −20 dB as compared to the LB directional coupler output signal driving RF multiplexer  115 . Transmitter  100  uses the low-band feedback signal LB_cp for power control of the LB band transmission. Similarly, a mid-band (MB) channel includes a MB PA module that drives an MB directional coupler  110  that in turn drives RF multiplexer  115  and ultimately the common antenna. MB directional coupler  110  provides a MB feedback signal (MB_cp) from its coupled port so that transmitter  100  may control the power of the MB signal. 
         [0004]    Given the serial arrangement of LB directional coupler  105  to RF multiplexer  115 , the insertion loss in the LB channel is thus a sum of the insertion loss from LB directional coupler  105  and also RF multiplexer  115 . Similarly, the insertion loss in the MB channel is a sum of the insertion loss from MB directional coupler  110  and RF multiplexer  115 . In addition, the three separate components (the pair of directional couplers and RF multiplexer) demand a significant amount of die space. 
         [0005]    Accordingly there is a need in the art for directional couplers and RF multiplexers providing increased density and lower insertion loss. 
       SUMMARY 
       [0006]    An RF diplexer is provided with a plurality of channels and a corresponding plurality of integrated directional couplers. The RF diplexer includes a plurality of primary inductors corresponding to the plurality of channels. The primary inductors are shared with the integrated directional couplers such that each integrated directional coupler includes a corresponding one of the primary inductors. Each integrated directional coupler also includes a secondary inductor arranged to form a transformer with the directional coupler&#39;s primary inductor. The resulting sharing of the primary inductor for each channel between the RF diplexer and the corresponding directional coupler is quite advantageous with regard to lowering insertion loss and manufacturing complexity and cost. 
         [0007]    These advantageous features may be better appreciated through the disclosure of the following example embodiments. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]      FIG. 1  illustrates a conventional transmitter including directional couplers and an RF multiplexer. 
           [0009]      FIG. 2  illustrates a transmitter including an RF diplexer integrated with a pair of directional couplers in accordance with an aspect of the disclosure. 
           [0010]      FIG. 3  is a circuit diagram of the integrated RF diplexer of  FIG. 2 . 
           [0011]      FIG. 4  illustrates a transformer in the integrated RF diplexer of  FIG. 3 . 
           [0012]      FIG. 5  is a flowchart for a method of operation for an RF diplexer integrated with a directional coupler in accordance with an aspect of the disclosure. 
       
    
    
       [0013]    Embodiments of the disclosure and their advantages are best understood by referring to the detailed description that follows. It should be appreciated that like reference numerals are used to identify like elements illustrated in one or more of the figures. 
       DETAILED DESCRIPTION 
       [0014]    To provide reduced insertion loss and dramatically improved density, an RF diplexer is provided in that includes an integrated directional coupler for each channel. Each integrated directional coupler includes a transformer having a primary inductor and a second inductor. The primary inductor also functions as part of the signal path for the corresponding channel in the RF diplexer. Each primary inductor may be formed as a plurality of coils in a corresponding plurality of metal layers covering a substrate such as a glass substrate in a passive-on-glass (PoG) embodiment. The use of a plurality of metal layers provides the primary inductor with a high quality (Q) factor, which is desirable to lower the insertion loss for the RF diplexer. The secondary inductor may be formed as a coil in another metal layer covering the substrate. Since this secondary inductor is used to form the channel&#39;s feedback signal, the Q factor for the secondary inductor need not be as high as the Q factor for the primary inductor. The secondary inductor may thus be formed in just a single metal layer in some embodiments to preserve density and lower manufacturing costs. A terminal for each secondary inductor forms a coupled port for the corresponding directional coupler to provide the directional coupler&#39;s feedback signal. Since the primary inductor and the secondary inductor in each channel are arranged to form a transformer, a channel transmission signal driven through the primary inductor magnetically couples into the secondary inductor to provide the channel&#39;s coupled port feedback signal. 
         [0015]    An example transmitter  200  including an RF diplexer  205  with integrated directional couplers is shown in  FIG. 2 , In RF diplexer  205 , a first channel is a low-band (LB) channel and a second channel is a mid-band (MB) channel. But it will be appreciated that the frequency of the channels may be changed in alternative embodiments. For the LB channel, integrated RF diplexer  205  include a low-band input port (LB_in) and a low-band coupled port (LB_cp) as discussed with regard to conventional LB directional coupler  105  of  FIG. 1 . Similarly, integrated RF diplexer  205  includes for the MB channel a mid-band input port (MB_in) and a mid-band coupled port (MB_cp) as discussed with regard to conventional MB directional coupler  110 . The low-band coupled port LB_cp provides the low-band (LB) feedback signal whereas the mid-band coupled port MB_cp provides the mid-band (MB) feedback signal. A LB power amplifier module  210  amplifies an input LB RF signal to drive the LB input port LB_in with the resulting amplified LB RF signal. LP power amplifier module  210  is configured to regulate its amplification responsive to the LB feedback signal so that the desired amount of power for the LB channel is delivered to an antenna  220 . Similarly, a MB power amplifier module  215  amplifies an input MB RF signal to drive the MB input port MB_in for RF diplexer  205  with the resulting amplified MB RF signal. MB power amplifier module  215  is configured to regulate its amplification responsive to the MB feedback signal so that the desired amount of power for the MB channel is delivered to antenna  220 . Both the amplified MB RF signal and the amplified LB RF signal couple through RF diplexer  205  to drive a common antenna (or antennas)  220 . 
         [0016]    An example circuit diagram for an RF diplexer  205  is shown in  FIG. 3 . For the LB channel, an inductor  305  is the primary inductor for an integrated LB directional coupler  375  whereas an inductor  356  is the secondary inductor. Inductors  305  and  356  are thus arranged to form a transformer as discussed further below. A first terminal of primary inductor  305  couples to the LB input port LB_in. The amplified LB RF input signal from LB PA module  210  ( FIG. 2 ) will thus conduct through primary inductor  305  and induce the LB feedback signal to conduct through secondary inductor  356 , which has a first terminal coupled to the LB coupled port LB_cp. A second terminal of primary inductor  305  couples through a capacitor  361  to a second terminal of secondary inductor  356 . The second terminal of secondary inductor  356  couples to an LB isolated port. In RF diplexer  205 , the characteristic impedance of the LB and MB channels is assumed to be 50Ω. The LB isolated port is thus terminated in a 50Ω matched-load resistor to match this port to the channel impedance. It will be appreciated that channel impedances greater than or less than 50Ω may be used in alternative embodiments. 
         [0017]    With regard to the LB channel in RF diplexer  205 , the amplified LB RF input signal passes through the LB input port LB_in to conduct through primary inductor  305 . The LB input port LB_in also couples to ground through a capacitor  300  and couples to a first terminal of a capacitor  310  coupled in parallel with primary inductor  305 . A second terminal of capacitor  310  couples to ground through a capacitor  315  and also couples to through an inductor  320  to drive antenna  220  ( FIG. 2 ) in common with primary inductor  305 . It will be appreciated that the inductance of the various inductors and the capacitance of the various capacitors in the LB channel in RF diplexer  205  and in integrated LB directional coupler  375  depend upon the center frequency of the LB channel. Moreover, other arrangements of such circuit elements may be implemented in alternative embodiments. Regardless of the specific implementation, RF diplexer  205  will include a primary inductor  305  that is shared by both the LB channel in RF diplexer  205  and integrated LB directional coupler  375 . 
         [0018]    The MB channel is analogous in that the MB input port MB_in couples to a first terminal of a primary inductor  335 . Primary inductor  335  is arranged to form a transformer with a secondary inductor  360  in an integrated MB directional coupler  380 . The MB input terminal MB_in couples to a first terminal of primary inductor  335 , which is arranged in parallel with a capacitor  330  analogously to the parallel arrangement of primary inductor  305  and capacitor  310  in the LB channel. A first terminal of secondary inductor  360  couples to the MB coupled port MB_cp to provide the MB feedback signal ( FIG. 2 ). A second terminal of secondary inductor  360  couples to a second terminal of primary inductor  335  through a capacitor  370  analogously to the coupling of the second terminals for primary inductor  305  and secondary inductor  356  through capacitor  361 . The second terminal of inductor  360  couples to an MB isolated port and is matched to the characteristic impedance through a matched-load 50Ω resistor. It will be appreciated that other characteristic impedance values may be used in alternative embodiments. In contrast to integrated LB directional coupler  375 , the MB coupled port MB_cp and the MB input port MB_in for integrated directional coupler  380  are coupled together through a capacitor  395 . 
         [0019]    The MB input port MB_in couples to ground through a capacitor  325  analogously to the coupling of the LB input port LB_in to ground through capacitor  300 . The second terminal of primary inductor  335  couples to ground through a parallel combination of an inductor  350  and a capacitor  340  that is in series with another capacitor  345 . In addition, the second terminal of primary inductor  335  couples to antenna  220  ( FIG. 2 ) through a capacitor  355 . It will be appreciated that the inductance of the various inductors and the capacitance of the various capacitors in the MB channel in RF diplexer  205  and in integrated MB directional coupler  380  depends upon the center frequency of the LB channel. Moreover, other arrangements of such circuit elements may be implemented in alternative embodiments. Regardless of the specific implementation, RF diplexer  205  will include a primary inductor  335  that is shared by both the MB channel in RF diplexer  205  and MB directional coupler  380 . 
         [0020]    The transformer formed by primary inductor  305  and secondary inductor  356  as well as the transformer formed by primary inductor  335  and secondary inductor  360  may be implemented as shown in  FIG. 4 . A primary inductor L1  400  includes a plurality of relatively thick coils formed in a plurality of metal layers on a substrate such as a semiconductor substrate or a glass substrate. In this fashion, primary inductor L1  400  will have a sufficiently high quality factor (Q), which is desirable for a channel in an RF diplexer. The formation of a secondary inductor L2  405  to provide the channel feedback signal does not require such as high quality factor because the channel feedback signal is much lower power as compared to the relatively high power RF signal driven through the corresponding channel in RF diplexer  205 . The secondary inductor L2  405  may thus be formed as a single relatively thin coil in a single metal layer although multiple metal layers and/or coils may be implemented in alternative embodiments. Primary inductor L1  400  and secondary inductor L2  405  are arranged on the substrate so that the central axis of their coils are aligned so that the channel signal driven through the primary inductor L1  400  will magnetically induce the channel feedback signal in the second inductor L2  405 . 
         [0021]    A method of operation of an RF diplexer including an integrated directional coupler for each channel will now be discussed with regard to the flowchart of  FIG. 5 . The method includes an act  500  of transmitting a first-band signal through a first-band channel of a diplexer to an antenna, wherein transmitting the first-band signal through the first-band channel includes transmitting the first-band signal through a first coil of a first transformer. An example of the first-band channel is either the LB channel or the MB channel of RF diplexer  205 . A corresponding first-band signal would thus be the amplified LB input RF signal (if the first-band channel is the LB channel) or the amplified MB input RF signal (if the first-band channel is the MB channel). An example of the first coil is primary inductor  305  or primary inductor  335 . Act  500  is thus supported by the transmission of the amplified LB input RF signal through primary inductor  305  or the transmission of the amplified MB input RF signal through primary inductor  335 . 
         [0022]    The method also includes an act  505  of generating a first-band feedback signal in a first directional coupler including a second coil of the first transformer responsive to the transmission of the first-band signal through the first coil of the first transformer. The generation of the LB feedback signal in secondary inductor  356  or the generation of the MB feedback signal in secondary inductor  360  is an example of act  505 . 
         [0023]    As those of some skill in this art will by now appreciate and depending on the particular application at hand, many modifications, substitutions and variations can be made in and to the materials, apparatus, configurations and methods of use of the devices of the present disclosure without departing from the scope thereof. In light of this, the scope of the present disclosure should not be limited to that of the particular embodiments illustrated and described herein, as they are merely by way of some examples thereof, but rather, should be fully commensurate with that of the claims appended hereafter and their functional equivalents.