Patent Publication Number: US-11646857-B2

Title: Systems and methods for minimizing insertion loss in a multi-mode communications system

Description:
CROSS REFERENCE TO RELATED APPLICATION—CLAIM OF PRIORITY 
     The present application is a continuation of commonly owned co-pending U.S. patent application Ser. No. 16/201,938 filed on Nov. 27, 2018. application Ser. No. 16/201,938 is a continuation of commonly owned U.S. patent application Ser. No. 15/376,498 filed on Dec. 12, 2016, issued on Jan. 8, 2019 as U.S. Pat. No. 10,177,895. application Ser. No. 15/376,498 is a continuation of commonly owned U.S. patent application Ser. No. 14/742,567 filed on Jun. 17, 2015, issued on Jan. 31, 2017 as U.S. Pat. No. 9,559,830. application Ser. No. 14/742,567 is a continuation of commonly owned issued U.S. patent application Ser. No. 13/228,751 filed on Sep. 9, 2011, issued on Jun. 23, 2015 as U.S. Pat. No. 9,065,540; said application Ser. Nos. 16/201,938, 15/376,498, 14/742,567, 13/228,751 and U.S. Pat. Nos. 10,177,895, 9,559,830 and 9,065,540 are hereby incorporated by reference herein in their entirety. 
    
    
     1. Field 
     The present teachings relate to communications systems. In particular, the present teachings relate to using a multifunctional filter for minimizing insertion loss in a multi-mode communications system. 
     2. Description of Related Art 
     Multi-band, multi-mode cellular phones are quite popular because of the convenience and flexibility provided by such devices, especially when a user of such a cellular phone travels between areas that are serviced by service providers using different signal propagation modes. Two of these signal propagation modes are referred to in the art as a time division duplex (TDD) mode and a frequency division duplex (FDD) mode. 
     A cellular phone that is configured to selectably operate in either the TDD mode or the FDD mode, typically incorporates a first set of circuit elements that is optimized for TDD mode of operation and a second set of circuit elements that is optimized for FDD mode of operation. A switching mechanism is employed to cut out one set of circuit elements and insert the other set of signal elements in a signal propagation path when it is desired to change the cellular phone from one mode of operation to the other. 
       FIG.  1    shows a prior art communications system  100  that incorporates two sets of circuit elements as mentioned above. The first set of circuit elements is contained in TDD system  120  that is optimized for TDD mode of operation while the second set of circuit elements is contained in FDD system  105  that is optimized for FDD mode of operation. A mode selector switch  130  is used for changing communications system  100  from one mode of operation to the other. 
     Signal line  131  couples mode selector switch  130  to an antenna (not shown) and carries communications signals in either FDD or TDD modes to/from the antenna. Specifically, a FDD signal is carried on signal line  131  when mode selector switch  130  is configured to couple FDD system  105  to signal line  131 . FDD system  105  includes a band-pass filter  115  that may be a standalone element or may be a part of a duplexer  110  (shown as a dashed box). Duplexer  110  permits duplex mode of operation wherein a transmit side signal can be coupled from transmit amplifier  107  into mode selector switch  130  while a receive side signal can be coupled from mode selector switch  130  into receiver  106 . 
     A TDD signal is carried on signal line  131  when mode selector switch  130  is configured to couple TDD system  120  to signal line  131 . TDD system  120  includes a low-pass filter  125 , a transmit amplifier  116 , and a receiver  117 . In carrying out a comparison between signal losses in the TDD mode of operation and the FDD mode of operation, it will be relevant to point out that the insertion loss imposed by low-pass filter  125  is lower than that imposed by band pass filter  115 . 
     Typically, the insertion loss of low-pass filter  125  is of the order of 0.5 dB whereas the insertion loss of band pass filter  115  is of the order of 2.5 dB. As can be understood, insertion loss plays a significant role in signal transmission. Consequently, the prior art configuration depicted in  FIG.  1    provides for two separate circuits so as to minimize insertion loss when system  100  is operating in the TDD mode. 
     However, as can be understood, such a configuration can lead to various undesirable issues such as higher component count, higher production cost, bulkier packaging, and increased power consumption. 
     SUMMARY 
     According to a first aspect of the present disclosure, a method of minimizing insertion loss in at least one of two types of signals propagated through a communications system is provided. The method includes configuring a multifunctional filter to operate in a band-pass mode when a first type of signal is propagated through the multifunctional filter, and reconfiguring the multifunctional filter to operate in a low-pass mode when a second type of signal is propagated through the multifunctional filter, the low-pass mode providing a lower insertion loss upon the second type of signal than the band-pass mode. 
     According to a second aspect of the disclosure, a method of minimizing insertion loss in a duplexer is provided. The method includes configuring the duplexer to operate in a band-pass mode when a first type of signal is propagated through the duplexer, and reconfiguring the duplexer to operate in a low-pass mode when a second type of signal is propagated through the duplexer, the low-pass mode providing a lower insertion loss upon the second type of signal than the band-pass mode. 
     According to a third aspect of the disclosure, a communications system is provided. The system includes a multifunctional filter that is configurable to operate in a band-pass mode when a first type of signal is propagated through the multifunctional filter, and to operate in a low-pass mode when a second type of signal is propagated through the multifunctional filter, the low-pass mode providing a lower insertion loss to the second type of signal than the band-pass mode. 
     Further aspects of the disclosure are shown in the specification, drawings and claims of the present application. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Many aspects of the present disclosure can be better understood with reference to the following drawings. The components in the drawings are not necessarily drawn to scale. Instead, emphasis is placed upon clearly illustrating various principles. Moreover, in the drawings, like reference numerals designate corresponding parts throughout the several views. 
         FIG.  1    shows a prior art communications system that uses two separate sets of circuit elements for selectably operating the communications system in either a TDD mode or a FDD mode. 
         FIG.  2    shows a communications system incorporating a multifunctional filter that can be selectively configured for operating the communications system in either a TDD mode or a FDD mode. 
         FIG.  3    shows a few components that may be contained in the multifunctional filter shown in  FIG.  2   . 
     
    
    
     DETAILED DESCRIPTION 
     Throughout this description, embodiments and variations are described for the purpose of illustrating uses and implementations of the inventive concept. The illustrative description should be understood as presenting examples of the inventive concept, rather than as limiting the scope of the concept as disclosed herein. For example, it will be understood that terminology such as multi-functional, multi-mode, nodes, terminals, voltage drops, circuits, blocks, connections, lines, and coupling are used herein as a matter of convenience for description purposes and should not be interpreted literally in a narrow sense. Furthermore, the words “block” or “functional blocks” as used herein refer not only to a circuit containing discrete components or integrated circuits (ICs), but may also refer to various other elements such as a module, a sub-module, or a mechanical assembly. Similarly, the word “line” as used herein may refer to various connectivity elements such as a wire, a cable, a copper track on a printed circuit board, an optical fiber, or a wireless link. Also, it must be understood that the word “example” as used herein (in whatever context) is intended to be non-exclusionary and non-limiting in nature. It will be further understood that labels such as “band-pass” and “notch” filter are used herein solely for purposes of description. Consequently, other labels and other filtering functionalities are included in the scope of the concept disclosed herein. A person of ordinary skill in the art will understand the principles described herein and recognize that these principles can be applied to a wide variety of applications using a wide variety of physical elements. 
     In particular, described herein are some systems and methods pertaining to using a multifunctional filter for minimizing insertion loss in a multi-mode communications system. As can be understood by one of ordinary skill in the art, the described systems and methods can be incorporated into a wide variety of communications systems, and furthermore such communications systems may be used in a variety of devices and applications spanning a variety of operating conditions (frequencies, voltages, power etc). 
       FIG.  2    shows a communications system  200  having a multi-mode system  205  incorporating a multifunctional filter  210  that can be selectively configured for operating communications system  200  in either a TDD mode or a FDD mode. It will be understood that multifunctional filter  210  may be referred to alternatively as a dual-purpose filter, an integrated filter, or a combination filter. Persons of ordinary skill in the art can recognize the equivalency amongst such alternative labels. 
     It will also be understood that communications system  200  includes several other elements (in addition to multi-mode system  205 ), which are not shown in  FIG.  2   . These other elements have been omitted so as to avoid obscuring the primary focus of this disclosure. 
     Multi-mode system  205  further includes a wide band transmit amplifier  207  and a wide band receiver  117 , each of which is selected to have a bandwidth, as well as other characteristics that accommodate both FDD and TDD modes of signal propagation. In a first embodiment, multifunctional filter  210  is a standalone component that may be placed in either a transmit signal propagation path or a receive signal propagation path. In another embodiment, multifunctional filter  210  is a part of a duplexer  215  that is shown as a dashed box in  FIG.  2   . Duplexer  215  couples any signal that is received on line  211  from an antenna (not shown) and routes this received signal to wide band receiver  117 . Duplexer  215  further couples transmit-side signals from wide band transmit amplifier  207  into line  211  through which the transmit-side signals are coupled to the antenna. As can be understood, transmit-side signals are generally much stronger in signal amplitude than the received-side signals. Duplexer  215  prevents a large part, or all of, this stronger transmit-side signal from reaching wide band receiver  206  and causing damage to receiver  206 , which is designed to receive low amplitude signals and therefore, contains circuitry susceptible to overload damage. 
     As mentioned above, multifunctional filter  210  can be selectively configured in accordance with communications system  200  operating in either a TDD mode or a FDD mode. Specifically, multifunctional filter  210  is configurable as a band-pass filter when communications system  200  is placed in an FDD mode of operation. Conversely, multifunctional filter  210  is configurable as a low-pass filter when communications system  200  is placed in a TDD mode of operation. The low-pass filter configuration imposes a lower insertion loss upon a TDD signal than that imposed by the band-pass filter (if such a band-pass filter were permitted to be located in a signal propagation path of the TDD signal). 
     In various other embodiments, multifunctional filter  210  can be selectively configured in accordance with multi-mode system  205  operating in modes other than a TDD mode or a FDD mode. For example, in a first of other such operational modes, multifunctional filter  210  may be configurable to perform a first filtering function (such as, for example, low pass, high pass, band-pass, single notch, multiple notches, single band-stop, multi-band stop etc) and then re-configurable in a second operational mode to perform a second different filtering function. It can be understood that the first filtering function may be more suitable for the first operational mode but may not be optimal for the second operational mode (for example, as a result of having a higher insertion loss, or some other such undesirable characteristic). 
     Attention is now drawn to  FIG.  3   , which shows certain elements contained inside multifunctional filter  210 . The configuration shown is a generic ladder network solely for purpose of description, and it will be understood that various combinations and arrangements of series and shunt elements (capacitors, inductors, resistors etc in π and/or T-configurations) may be used in various alternative embodiments. Furthermore, it will be noticed that only two filter stages are shown in  FIG.  3   , with each stage having one shunt element and one series element. However, a single stage or more than two stages (‘n’ stages) may be employed in various other embodiments, furthermore with more than one element located in each shunt and/or series limb if so desired. 
     Switch  305 , which may be a normally-closed switch, is controllable via a control signal (not shown) that may be used to place switch  305  in an open position when it is desired to isolate shunt element  310  from signal propagation path  300 . Switch  315 , which may be a normally-open switch, is also provided a control signal (not shown) that may be used to place switch  315  in a closed position, thereby providing a low impedance shunt signal path that effectively eliminates series element  320  from signal propagation path  300 , when so desired. Switches  325  and  335  may be operated in a similar manner for configuring shunt element  330  and series element  340  respectively. 
     In one implementation, each of shunt elements  310  and  330  is a capacitor (C), while each of series elements  320  and  340  is an inductor (L). When all of these elements (having appropriately selected values) are included in signal propagation path  300 , multifunctional filter  210  operates as a band-pass filter. On the other hand, when some of these elements, for example, shunt element  310  and series element  340  are switched out of signal propagation path  300 , multifunctional filter  210  operates as an L-C low-pass filter. 
     Thus, by suitably operating one or more of switches  305 ,  315 ,  325  and  335 , multifunctional filter  210  can be configured as a single stage or a multi-stage filter having either a band-pass or a low-pass characteristic. The overall impedance characteristics of multifunctional filter  210  can be configured to any suitable value by not only operating one or more of switches  305 ,  315 ,  325  and  335  so as to insert or remove one or more filter stages, but also by inserting resistors in lieu of, or to complement, one or more of shunt element  310 , shunt element  330 , series element  320  and series elements  340 . 
     When configured as a band-pass filter, multifunctional filter  210  may be used to selectively attenuate certain frequencies, such as undesirable harmonics or transmit-side frequencies that may cause damage to receiver  206  ( FIG.  2   ). 
     Each of switches  305 ,  315 ,  325  and  335  may be implemented in several alternative ways. A non-exhaustive list of devices that may be used include relays, solid-state switches, discrete switching semiconductors (such as field effect transistors), micro-electro mechanical systems (MEMS), and controllable variable impedance devices. A few examples of controllable variable impedance devices include a varicap, a varactor, a varistor, a thyristor, and a barium strontium titanate (BST) capacitor. 
     Such devices may be configured to not only operate as switches (with a high impedance constituting an open switch condition and a low impedance constituting a closed switch condition), but may also, in some embodiments, be used as impedance modification devices. For example, when switch  315  is a variable inductor, the value of the inductance provided by switch  315  may be varied under suitable voltage control to provide a desired inductance value that operates in parallel with the inductance value provided by series element  320 . In another example, when switch  315  is a variable capacitor, the value of the capacitance provided by switch  315  may be varied under suitable voltage control so as to provide a desired capacitance value that operates in parallel with the inductance value provided by series element  320 . Such a combination may be used as part of a tuned circuit for selectively propagating certain frequencies while blocking certain other frequencies in the signal propagation path  300 . In yet another example, switch  315  is provided in the form of multiple elements, for example, a resistor in parallel (or in series) with an inductor or a capacitor. Such combinations may be used for example to obtain specific Q values in a tuned circuit formed in conjunction with series element  320 . 
     The other switches shown in  FIG.  3    may be also configured in similar ways. Furthermore, though not shown, it will be understood that additional switches may be located in various other limbs of multifunctional filter  210 . For example, an additional switch may be located on the limb connecting junction  306  to series element  320 . This additional switch may be operated in conjunction with switch  315 . Thus, when switch  315  is closed, the additional switch may be opened so as to isolate the input side of series element  320  and reduce signal loss in series element  320 , or to present a higher impedance value in parallel with closed switch  315 . 
     The person skilled in the art will appreciate that the systems, components, and methods described herein allow for using a multifunctional filter to minimize insertion loss in a multi-mode communications system. While the devices and methods have been described by means of specific embodiments and applications thereof, it is understood that numerous modifications and variations could be made thereto by those skilled in the art without departing from the spirit and scope of the disclosure. It is therefore to be understood that, within the scope of the claims, the disclosure may be practiced otherwise than as specifically described herein. 
     A number of embodiments of the present inventive concept have been described. Nevertheless, it will be understood that various modifications may be made without departing from the scope of the inventive teachings. 
     Accordingly, it is to be understood that the inventive concept is not to be limited by the specific illustrated embodiments, but only by the scope of the appended claims. The description may provide examples of similar features as are recited in the claims, but it should not be assumed that such similar features are identical to those in the claims unless such identity is essential to comprehend the scope of the claim. In some instances the intended distinction between claim features and description features is underscored by using slightly different terminology.