Patent Publication Number: US-10320379-B2

Title: Transistor-based radio frequency (RF) switch

Description:
RELATED APPLICATIONS 
     This application claims the benefit of provisional patent application Ser. No. 62/437,420, filed Dec. 21, 2016, the disclosure of which is hereby incorporated herein by reference in its entirety. 
    
    
     FIELD OF THE DISCLOSURE 
     Embodiments of the present disclosure relate to silicon-on-insulator technology and semiconductor-based radio frequency switches, both of which can be used in radio frequency communications circuits. 
     BACKGROUND 
     As technology progresses, wireless communications devices, such as smart phones, wireless capable computers, and the like, are becoming increasingly integrated, feature rich, and complex. Such wireless communications devices rely on semiconductor technologies, such as silicon-based technologies, which are evolving toward smaller circuit geometries, lower power consumption, higher operating speeds, and increased complexity. Complementary metal oxide semiconductor technology is an example of a silicon-based technology. Further, wireless communications devices may need to support multiple communications bands, multiple communications modes, multiple communications protocols, and the like. As such, wireless communications devices rely upon transistor-based radio frequency (RF) switches to select between different RF circuits depending on which communications bands, modes, and protocols are in use. Such complex RF systems may place strict linearity, insertion loss, and isolation demands on the transistor-based RF switches. 
     In general, transistor-based RF switches used to switch RF power within communications circuitry have a stringent linearity requirement. The already stringent linearity requirement is increasing due to downlink and uplink carrier aggregation. In some instances, the noise contributed by the circuit nonlinearities should be less than −115 dBm. Thus, there is a need for transistor-based RF switches having improved linearity performance to meet increased transistor-based RF switch linearity requirements. 
     SUMMARY 
     Disclosed is a transistor-based radio frequency switch having an N number of main field-effect transistors (FETs) stacked in series such that a first terminal of a first main FET of the N number of main FETs is coupled to a first end node and a second terminal of an Nth main FET of the N number of main FETs is coupled to a second end node, wherein N is a finite number greater than five. The transistor-based radio frequency switch further includes a gate bias network having a plurality of gate resistors, wherein individual ones of the plurality of gate resistors are coupled to gate terminals of the N number of FETs. A common gate resistor is coupled between a gate control input and a gate control node of the plurality of gate resistors, and a capacitor is coupled between the gate control node and a switch path node of the main FETs. 
     Those skilled in the art will appreciate the scope of the present disclosure and realize additional aspects thereof after reading the following detailed description of the preferred embodiments in association with the accompanying drawing figures. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING FIGURES 
       The accompanying drawing figures incorporated in and forming a part of this specification illustrate several aspects of the disclosure and, together with the description, serve to explain the principles of the disclosure. 
         FIG. 1  is a schematic diagram of a first embodiment of a transistor-based radio frequency (RF) switch that is structured in accordance with the present disclosure. 
         FIG. 2  is a schematic diagram of a second embodiment of the transistor-based RF switch that is structured in accordance with the present disclosure. 
         FIG. 3  is a schematic diagram of a third embodiment of the transistor-based RF switch that is structured in accordance with the present disclosure. 
         FIG. 4  is a schematic of a fourth embodiment of the transistor-based RF switch that is structured in accordance with the present disclosure. 
         FIG. 5  is a schematic of a fifth embodiment of the transistor-based RF switch that is structured in accordance with the present disclosure. 
         FIG. 6  is a schematic of a sixth embodiment of the transistor-based RF switch that is structured in accordance with the present disclosure. 
         FIG. 7  is a schematic of a seventh embodiment of the transistor-based RF switch that is structured in accordance with the present disclosure. 
         FIG. 8  is a schematic of an eighth embodiment of the transistor-based RF switch that is structured in accordance with the present disclosure. 
         FIG. 9  is a schematic of a ninth embodiment of the transistor-based RF switch of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     The embodiments set forth below represent the necessary information to enable those skilled in the art to practice the embodiments and illustrate the best mode of practicing the embodiments. Upon reading the following description in light of the accompanying drawing figures, those skilled in the art will understand the concepts of the disclosure and will recognize applications of these concepts not particularly addressed herein. It should be understood that these concepts and applications fall within the scope of the disclosure and the accompanying claims. 
     It will be understood that, although the terms first, second, etc. may be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another. For example, a first element could be termed a second element, and, similarly, a second element could be termed a first element, without departing from the scope of the present disclosure. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. 
     It will be understood that when an element such as a layer, region, or substrate is referred to as being “on” or extending “onto” another element, it can be directly on or extend directly onto the other element or intervening elements may also be present. In contrast, when an element is referred to as being “directly on” or extending “directly onto” another element, there are no intervening elements present. Likewise, it will be understood that when an element such as a layer, region, or substrate is referred to as being “over” or extending “over” another element, it can be directly over or extend directly over the other element or intervening elements may also be present. In contrast, when an element is referred to as being “directly over” or extending “directly over” another element, there are no intervening elements present. It will also be understood that when an element is referred to as being “connected” or “coupled” to another element, it can be directly connected or coupled to the other element or intervening elements may be present. In contrast, when an element is referred to as being “directly connected” or “directly coupled” to another element, there are no intervening elements present. 
     Relative terms such as “below” or “above” or “upper” or “lower” or “horizontal” or “vertical” may be used herein to describe a relationship of one element, layer, or region to another element, layer, or region as illustrated in the Figures. It will be understood that these terms and those discussed above are intended to encompass different orientations of the device in addition to the orientation depicted in the Figures. 
     The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the disclosure. As used herein, the singular forms “a,” “an,” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises,” “comprising,” “includes,” and/or “including” when used herein specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. 
     Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. It will be further understood that terms used herein should be interpreted as having a meaning that is consistent with their meaning in the context of this specification and the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein. 
       FIG. 1  is a schematic diagram of a first embodiment of a transistor-based radio frequency (RF) switch  10  that is structured in accordance with the present disclosure. The transistor-based RF switch  10  has an N number of main field-effect transistors (FETs)  12  that are stacked in series such that a first terminal  14  of a first main FET Q 1  is coupled to a first end node RF 1  and a second terminal  16  of an Nth main FET QN is coupled to a second end node RF 2 , wherein N is a finite number greater than five. In at least some embodiments, the N number of main FETs  12  are of the silicon-on-insulator type. The transistor-based RF switch  10  further includes a gate bias network  18  having a plurality of gate resistors RG. In general, individual ones of the plurality of gate resistors RG are coupled to gate terminals  20  of the N number of main FETs  12 . In particular, in the exemplary embodiment of  FIG. 1 , one of the plurality of gate resistors RG is coupled between gate terminals  20  of adjacent ones of the N number of main FETs  12 . The gate bias network  18  further includes a common gate resistor RGC 1  that is coupled between a gate control input  22  and a gate control node  24  of the plurality of gate resistors RG. In exemplary embodiments of the transistor-based RF switch  10 , the gate control node  24  is located between a first group of the plurality of gate resistors RG to the left and a second group of the plurality of gate resistors RG to the right, wherein the number of gate resistors RG in the first group is equal to the number of gate resistors RG in the second group. 
     A first gate capacitor CG 1  is coupled between the gate control node  24  and a switch path node  26  of the N number of main FETs  12 . In exemplary embodiments, the switch path node  26  is located between a first group Q 1  through QM of the N number of main FETs  12  and a second group QM+1 through QN of the N number of main FETs  12 , wherein the first group of the N number of main FETs  12  is equal in number to the second group of the N number of main FETs  12 . In the exemplary embodiment of  FIG. 1 , the first group is made up of four main FETS Q 1 , Q 2 , Q 3 , and QM, and the second group is made up of four main FETs QM+1, QM+2, QM+3, and QN, wherein M is set to 4 and N is set to 8. However, it is to be understood that N can be any counting number greater than 5. For example, if N is set to 32, then the first group and the second group each have 16 FETs apiece. 
     The transistor-based RF switch  10  further includes a plurality of source-to-drain resistors RSD that are coupled between source/drain terminals  28 . The transistor-based RF switch  10  still further includes a body bias network  30  having a plurality of body resistors RB, wherein one of the plurality of body resistors RB is coupled between body terminals  32  of adjacent ones of the N number of main FETs  12 . The body bias network  30  further includes a common body resistor RBC 1  that is coupled between a body control input  34  and a body control node  36  of the plurality of body resistors RG. A first body capacitor CB 1  is coupled between the body control node  36  and the switch path node  26  of the N number of main FETs  12 . In some embodiments a capacitance value of the gate capacitor CG 1  and the body capacitor CB 1  is between 0.1 picofarad and 10 picofarads. In some embodiments, the capacitance value of the gate capacitor CG 1  and the body capacitor CB 1  is between 0.1 picofarad and 1 picofarad. In yet other embodiments, the capacitance value of the gate capacitor CG 1  and the body capacitor CB 1  is between 1 picofarad and 10 picofarads. In some embodiments, both of the gate capacitor CG 1  and the body capacitor CB 1  capacitor are metal-insulator-metal type capacitors. Moreover, in some embodiments, a resistance value of the common gate resistor RGC 1  and the common body resistor RBC 1  is between 2 kΩ and 100 kΩ. In some embodiments, the resistance value of the common gate resistor RGC 1  and the common body resistor RBC 1  is between 2 kΩ and 10 kΩ. In other embodiments the resistance value of the common gate resistor RGC 1  and the common body resistor RBC 1  is between 10 kΩ and 100 kΩ. In at least some embodiments, the resistance of each of the plurality of gate resistors RG is equal to the resistance of the common gate resistor RGC 1  within ±10%. 
     In operation, bias voltages are applied to the gate control input  22  and the body control input  34 , causing the first gate capacitor CG 1  and the first body capacitor CB 1  to charge and thereby balance the gate bias voltage and body bias voltage applied to each of the N number of main FETs  12 . Harmonics generated by the transistor-based RF switch  10  are reduced as a result of the balanced gate bias voltage and balanced body bias voltage applied to each of the N number of main FETs  12 . In at least some embodiments, second harmonics are reduced by greater than 30 dB compared with the structure of the transistor-based RF switch  10  without the first gate capacitor CG 1  and the first body capacitor CB 1 . 
       FIG. 2  is a schematic diagram of an exemplary second embodiment of the transistor-based RF switch  10  that is structured in accordance with the present disclosure. In this exemplary second embodiment, the switch path node  26  is located such that the first terminal  14  of the first main FET Q 1  is coupled directly to the switch path node  26 . Moreover, in this exemplary second embodiment, the gate control node  24  is located between the common gate resistor RGC 1  and a first gate resistor RG 1  of the plurality of gate resistors RG and is coupled to one of the gate terminals  20  associated with the first main FET Q 1 . The first gate capacitor CG 1  is coupled between the gate control node  24  and the switch path node  26 . Further still, in this exemplary second embodiment, the body control node  36  is located between the common body resistor RBC 1  and a first body resistor RB 1  of the plurality of body resistors RB and is coupled to one of the body terminals  32  associated with the first main FET Q 1 . The first body capacitor CB 1  is coupled between the body control node  36  and the switch path node  26 . 
     A second gate capacitor CG 2  is coupled between the second terminal  16  of the Nth main FET QN and one of the gate terminals  20  associated with the Nth main FET QN through a last gate resistor RGN of the plurality of gate resistors RG nearest to the second end node RF 2 . A second body capacitor CB 2  is coupled between the second terminal  16  of the Nth main FET QN and one of the body terminals  32  associated with the Nth main FET QN through a last body resistor RBN of the plurality of body resistors RB nearest to the second end node RF 2 . 
       FIG. 3  is a schematic diagram of a third embodiment of a transistor-based RF switch  10  that is structured in accordance with the present disclosure. In this third exemplary embodiment, the first gate capacitor CG 1  is coupled to the gate control node  24  through a first middle gate resistor RGM 1 . Moreover, the second gate capacitor CG 2  is coupled between the gate control node  24  and a second switch path node  38  through a second middle gate resistor RGM 2 . Also, in this exemplary third embodiment, N is an odd number and the middle FET QM of the N number of main FETs  12  is coupled directly between the switch path node  26  and the second switch path node  38 . The resistance values of the first middle gate resistor RGM 1  and the second middle gate resistor RGM 2  are typically within ±10% of the same resistance value of the other ones of the plurality of gate resistors RG. However, a third middle gate resistor RGM 3  and a fourth middle gate resistor RGM 4  that are coupled directly to the gate terminal  20  of the middle FET QM typically have twice the resistance value ±10% of the other ones of the plurality of gate resistors RG. 
     Further still, in this third exemplary embodiment, the first body capacitor CB 1  is coupled to the body control node  36  through a first middle body resistor RBM 1 . Moreover, the second body capacitor CB 2  is coupled between the body control node  36  and the second switch path node  38  through a second middle body resistor RBM 2 . The resistance values of the first middle body resistor RBM 1  and the second middle body resistor RBM 2  are typically within ±10% the same resistance value of the other ones of the plurality of body resistors RB. However, a third middle body resistor RBM 3  and a fourth middle body resistor RBM 4  that are coupled directly to the body terminal  32  of the middle FET QM typically have twice the resistance value ±10% of the other ones of the plurality of body resistors RB. 
       FIG. 4  is a schematic of a fourth embodiment of the transistor-based RF switch  10  that is structured in accordance with the present disclosure. This exemplary fourth embodiment has a structure that is identical to the structure of the first embodiment of  FIG. 1  with an exception of an addition of a plurality of speed-up FETs  40 . Individual ones of the plurality of speedup FETs  40  are coupled across corresponding ones of the plurality of gate resistors RG such that the plurality of gate resistors RG are shorted when the plurality of speedup FETs  40  are in an ON state. 
       FIG. 5  is a schematic of a fifth embodiment of the transistor-based RF switch  10  that is structured in accordance with the present disclosure. This exemplary fourth embodiment has a structure that is identical to the structure of the second embodiment of  FIG. 2  with an exception of an addition of the plurality of speed-up FETs  40 . As with the fourth embodiment of  FIG. 4 , individual ones of the plurality of speedup FETs  40  are coupled across corresponding ones of the plurality of gate resistors RG such that the plurality of gate resistors RG are shorted when the plurality of speedup FETs  40  are in an ON state. 
       FIG. 6  is a schematic of a sixth embodiment of the transistor-based RF switch  10  that is structured in accordance with the present disclosure. Performance of the sixth embodiment is enhanced in some applications over the fifth embodiment of  FIG. 5  by fixing the resistance values of a nearest one of the plurality of gate resistors RG to the first end node RF 1  and a nearest one of the plurality of gate resistors RG to the second end node RF 2  to half the resistance value ±10% of individual ones of the remaining plurality of gate resistors RG. Performance of this sixth embodiment is further enhanced over the fifth embodiment in the same applications by fixing the resistance values of a nearest one of the plurality of body resistors RB to the first end node RF 1  and a nearest one of the plurality of body resistors RB to the second end node RF 2  to half the resistance value ±10% of individual ones of the remaining plurality of body resistors RB. For example, the fifth embodiment of  FIG. 5  can be realized as the sixth embodiment by fixing the resistance values of the first gate resistor RG 1  ( FIG. 5 ), the last gate resistor RGN ( FIG. 5 ), the first body resistor RB 1  ( FIG. 5 ), and the last body resistor RBN ( FIG. 5 ) to within ±10% of half the resistance of individual ones of the remaining gate resistors RG and body resistors RB, respectively. 
       FIG. 7  is a schematic of a seventh embodiment of the transistor-based RF switch  10  that is structured in accordance with the present disclosure. In this exemplary seventh embodiment, the gate bias network  18  is a parallel bias network, wherein individual ones of the plurality of gate resistors RG are coupled between the gate control node  24  and the gate terminals  20  of the N number of main FETs  12 . Also, the switch path node  26  is located between a first group of the N number of main FETs  12  and a second group of the N number of main FETS  12  such that the first group and the second group have an equal number of FETs. In the exemplary embodiment, the first group is made up of FETs Q 1 -Q 4  and the second group is made up of FETs Q 5 -Q 8 . In this exemplary embodiment, the first gate capacitor CG 1  is coupled between the gate control node  24  and the switch path node  26 . Further still, in this exemplary seventh embodiment, the body bias network  30  is a parallel bias network, wherein individual ones of the plurality of body resistors RB are coupled between the body control node  36  and the body terminals  32  of the N number of main FETs  12 . Also, the first body capacitor CB 1  is coupled between the body control node  36  and the switch path node  26 . 
       FIG. 8  is a schematic of an eighth embodiment of the transistor-based RF switch  10  that is structured in accordance with the present disclosure. In this exemplary eighth embodiment, a first group Q 1 -Q 4  of the N number of main FETs  12  has source terminals that are closer to the first end node RF 1  and drain terminals that are closer to the second end node RF 2 , and a second group Q 5 -Q 8  of the N number of main FETs  12  has drain terminals that are closer to the first end node RF 1  and source terminals that are closer to the second end node RF 2 , wherein the number of main FETs in the first group is equal to the number of FETs in the second group. It is to be understood that while the eighth embodiment of  FIG. 8  is depicted with N equal to 8 of the N number of main FETs  12 , Q 1 -Q 8 , a larger number of main FETs may be included without deviating from the scope of the present disclosure. 
       FIG. 9  is a schematic of a ninth embodiment of the transistor-based RF switch  10  of the present disclosure. In this exemplary embodiment, a first group Q 2 , Q 4 , Q 6 , and Q 8  of the N number of main FETs  12  has source terminals that are closer to the first end node RF 1  and drain terminals that are closer to the second end node RF 2 , and a second group Q 1 , Q 3 , Q 5 , and Q 7  of the N number of main FETs  12  has drain terminals that are closer to the first end node RF 1  and source terminals that are closer to the second end node RF 2 , wherein the number of main FETs in the first group is equal to the number of FETs in the second group. It is to be understood that while the ninth embodiment of  FIG. 9  is depicted with N equal to 8 of the N number of main FETs  12 , Q 1 -Q 8 , a larger number of main FETs may be included without deviating from the scope of the present disclosure. 
     Those skilled in the art will recognize improvements and modifications to the preferred embodiments of the present disclosure. All such improvements and modifications are considered within the scope of the concepts disclosed herein and the claims that follow.