Abstract:
A high isolation wideband switch is disclosed. In one aspect, the switch includes an integrated circuit package having an integrated circuit die with a first plurality of leads that is positioned on a package substrate that has a second plurality of leads. The first leads of the integrated circuit die are connected to the second the leads of the package substrate via bond wires and a first electrical coupling occurs between the first leads and the integrated circuit die in response to an RF signal applied to the integrated circuit package. The bond wires have a second electrical coupling in response to the RF signal and the bond wires are arranged such that the second electrical coupling is matched to the first electrical coupling within a selected frequency band so as to reduce the overall electrical coupling of the integrated circuit package for RF signals within the selected frequency band.

Description:
CROSS-REFERENCE TO RELATED PATENT APPLICATION 
       [0001]    This application claims the benefit of U.S. Provisional Application No. 62/058,507, filed Oct. 1, 2014, which is herein incorporated by reference in its entirety. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The described technology generally relates to a high isolation wideband switch. 
         [0004]    2. Description of the Related Art 
         [0005]    Wideband control products, such as quad flat no lead (QFN) packages for switches or attenuators, include wire bonds to electrically connect a small integrated circuit (IC) die containing the switch or attenuator to a package substrate. In applications including such wideband control products, costs can be reduced by minimizing the IC die and package size. However, the isolation and loss parameters of the product are related to the size and spacing of the IC die, bond wires, and package. Two of the main contributing factors to isolation of the switch are on-die coupling and package crosstalk. 
       SUMMARY OF THE INVENTION 
       [0006]    In one implementation, an embodiment of the invention comprises an integrated circuit package having an integrated circuit die with a first plurality of leads that is positioned on a package substrate that has a second plurality of leads. In this implementation, the first plurality of leads of the integrated circuit die are connected to the second plurality of the leads of the package substrate via bond wires and a first electrical coupling occurs between the first plurality of leads through the integrated circuit die in response to an RF signal applied to the integrated circuit package. The bond wires that interconnect the first plurality of leads and the second plurality of leads have a second electrical coupling in response to the RF signal and the bondwires are arranged such that the second electrical coupling is matched to the first electrical coupling within a selected frequency band so as to reduce the overall electrical coupling of the integrated circuit package for RF signals within the selected frequency band. 
         [0007]    In one implementation, the integrated circuit die includes a first surface and a second surface that are located distal to each other and one of the bond wires comprises an RF input bond wire and another one of the bond wires comprises an RF output bond wire and the RF input bond wire is attached to a lead located on the integrated circuit die on the first surface and the RF output bond wires is attached to a lead located on the second surface. In one further implementation, the RF input and RF output bond wires are attached to the integrated circuit die so as to be located as far from each other. 
         [0008]    In one implementation, the bond wires define a vertical portion that extends upwards from the first plurality of leads on the integrated circuit die and a horizontal portion that extends outward from the first plurality of leads on the integrated circuit die. In this implementation, the bond wires are positioned into a predetermined orientation so that the component of the electrical coupling between the horizontal bond wires reduces the overall electrical coupling of the integrated circuit within the selected frequency band. 
         [0009]    In one implementation, the first electrical coupling of the integrated circuit package includes a capacitive coupling occurring between the RF input and output leads of the first plurality of leads on the integrated circuit die and an inductive coupling occurring between the horizontal portion of the RF input bond wire and the RF output bond wire. In this implementation, the horizontal components of the RF input bond wire and the RF output bond wire are angularly adjusted with respect to each other such that the inductive coupling is out of phase with the capacitive coupling between the RF input and output bond wires and the integrated circuit die. In one implementation, the relative angular orientation of the horizontal portions of the RF input and RF output bond wires are adjusted so as to define an isolation notch on an isolation graph as a result of the bond wire inductive coupling being out of phase with the die capacitive coupling on the integrated circuit die at about the selected frequency band. 
         [0010]    In one implementation, the RF output bond wire is positioned proximate to a ground bond wire adjacent the RF output bond wire so as to reduce the inductive coupling between the RF input and output bond wires. The RF output bond wire is then oriented with respect to the RF input bond wire to reduce the overall electrical coupling of the integrated circuit package. 
         [0011]    In another implementation, an embodiment of the invention comprises a radio frequency (RF) switch package having an integrated circuit (IC) die including an RF switch placed on a package substrate. The IC die is electrically connected to the package substrate via an RF input bond wire and an RF output bond wire. When an RF signal is applied to the RF switch package, a first electrical coupling is formed between the RF input and output bond wires and a second electrical coupling is formed in the IC die. In this implementation, the first electrical coupling between the RF input and output bond wires is selected to cancel out at least a portion the second electrical coupling of the IC die within a predetermined frequency range. 
         [0012]    In one implementation, an integrated circuit (IC) package comprising an IC die comprising a plurality of first input leads and a plurality of first output leads, the first input leads respectively corresponding to the first output leads; a package substrate comprising a plurality of second input leads and a plurality of second output leads, the IC die being positioned on the package substrate; a plurality of bond wires respectively connecting: i) the first input leads to the second input leads and ii) the first output leads to the second output leads, wherein each corresponding pair of first input and output leads is configured to transmit a radio frequency (RF) signal therebetween, and wherein the bond wires are arranged so as to define an isolation notch on an isolation graph for a selected frequency band of each RF signal as a result of the electrical coupling due to the transmission of the RF signals. 
         [0013]    For purposes of summarizing the invention and the advantages achieved over the prior art, certain objects and advantages of the invention have been described herein. Of course, it is to be understood that not necessarily all such objects or advantages may be achieved in accordance with any particular embodiment of the invention. Thus, for example, those skilled in the art will recognize that the invention may be embodied or carried out in a manner that achieves or optimizes one advantage or group of advantages as taught or suggested herein without necessarily achieving other objects or advantages as may be taught or suggested herein. 
         [0014]    All of these embodiments are intended to be within the scope of the invention herein disclosed. These and other embodiments will become readily apparent to those skilled in the art from the following detailed description having reference to the attached figures, the invention not being limited to any particular embodiment(s) disclosed. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]    These aspects and others will be apparent from the following detailed description and the accompanying drawing, which is meant to illustrate and not to limit the invention, wherein: 
           [0016]      FIG. 1  is a diagram illustrating the bond wire connections between an IC die and a QFN package substrate according to an embodiment. 
           [0017]      FIG. 2  is a side view illustrating an exemplary wire bond shape according to an embodiment. 
           [0018]      FIG. 3  is a diagram illustrating example sources of coupling in an IC package according to an embodiment. 
           [0019]      FIG. 4  is a diagram illustrating one method of altering the coupling between bond wires according to an embodiment. 
           [0020]      FIG. 5  is a diagram illustrating various RF output bond wire configurations according to an embodiment. 
           [0021]      FIG. 6  is a graph illustrating the isolation of the RF output bond wire configurations illustrated in  FIG. 5 . 
           [0022]      FIG. 7  is a diagram illustrating the bond wire connections between an IC die and a QFN package substrate according to an embodiment. 
       
    
    
     DETAILED DESCRIPTION 
       [0023]    Various embodiments disclosed herein relate to the electrical connections between IC dies and package substrates having improved isolation. An IC die can be mounted on a package substrate to electrically communicate with a larger electronic device or system via the package. In the following embodiments, a radio frequency (RF) switch is described in detail as an exemplary embodiment of the IC die. However, the IC dies disclosed herein can include any suitable type of IC die, such as an attenuator, which is commonly used in applications such as transceivers, sources, analyzers, etc. The IC die may be packaged in a package body using various packaging techniques. The packaged integrated device can be mounted to a system board for integration into a larger electronic device or system. 
         [0024]    In some implementations, the IC die is connected to a package substrate via a plurality of wire bonds. The wire bonds form an electrical connection between the leads of the IC die and the leads of the package substrate. Various design considerations in the manufacture of the IC die and package substrate affect the isolation and loss (or gain) of the package. For example, the insertion loss and isolation of the package can be altered due to the on-die coupling or package crosstalk. This will be described in greater detail below with reference to the figures. 
         [0025]      FIG. 1  is a diagram illustrating the bond wire connections between an IC die and a QFN package substrate according to an embodiment. In the  FIG. 1  embodiment, the IC die  20  includes a plurality of leads  30  including an RF input lead  33  and an RF output lead  31 . The QFN package substrate also includes a plurality of leads  40  which are electrically connected to the leads  30  of the IC die  20  via a plurality of bond wires  51  and  53 . In the embodiment illustrated in  FIG. 1 , the RF input and output leads  33  and  31  of the IC die  20  are respectively connected to the QFN package substrate  10  via an RF input bond wire  53  and an RF output bond wire  51 . 
         [0026]    In the embodiment of  FIG. 1  and the following description, the IC die  20  is described as being embodied by an RF switch which is connected to a QFN package  10 . However, the embodiments of the described technology are not limited thereto and the IC die  20  may be any suitable type of IC die  20  connected to any type of suitable package substrate. In the following description, the term RF switch may be used to refer to the IC die  20  itself or to the overall package including the IC die  20 , the bond wires  51  and  53 , and the QFN package  10 . 
         [0027]      FIG. 2  shows an exemplary wire bond shape according to an embodiment.  FIG. 2  is a side view of the RF input and output bond wires  53  and  51 , the RF input and output leads  33  and  31 , and QFN package input and output leads  43  and  41 .  FIG. 2  illustrates an exemplary geometry of the RF input and output bond wires  53  and  51 , however, the illustrated bond wire shape may be applied to any of the bond wires  51  and  53 . In order to form the electrical connections between the leads  30  and  40  of the IC die  20  and the QFN package substrate  10 , the bond wires  53  and  51  first extend from the IC die leads  33  and  31  in a substantially vertical direction and then extend substantially horizontally to the QFN package leads  43  and  41 . The shape of the bond wires  53  and  51  shown in  FIG. 2  is merely one embodiment and the shape of the bond wires  51  and  53  is not limited to the illustrated shape. 
         [0028]      FIG. 3  is a diagram illustrating example sources of signal coupling in an IC package according to an embodiment. When an RF signal is transmitted through the RF input and output bond wires  53  and  51 , the physical structure of the bond wires  53  and  51  and IC die  20  introduces coupling in the signal which can have a negative impact on the isolation of the RF switch package.  FIG. 3  conceptually illustrates three different sources of coupling that can occur in-between the RF input and output bond wires  53  and  51 . The coupling of the IC die  20  itself can be modeled as capacitive coupling between the leads  33  and  31  of the IC die  20 . The IC die  20  coupling may be referred to as on-die coupling and the coupling results from the finite off-state capacitance of the RF switch. 
         [0029]    Additionally, signal coupling is introduced between the RF input and output bond wires  53  and  51  and can be conceptually divided into coupling generated due to the vertical portions of the bond wires  53  and  51  and coupling generated due to the horizontal portions of the bond wires  53  and  51 . The coupling between the RF input and output bond wires  53  and  51  can be modeled as inductive coupling. The inductive coupling between the vertical portions of the RF input and output bond wires  53  and  51  enhances the capacitive on-die coupling of the IC die  20 . Accordingly, in at least one embodiment, the geometry of the horizontal portions of the RF input and output bond wires  53  and  51  is manipulated to offset the combined capacitive coupling of the IC die  20  and the vertical portions of the RF input and output bond wires  53  and  51 . 
         [0030]    In the standard RF switch, each of these three sources of signal coupling is individually minimized so as to minimize the overall coupling of the RF switch. One method of reducing the coupling between the RF input and output bond wires  53  and  51  is to maximize the spacing between the bond wires  53  and  51 . However, this technique is limited by the sizes of the package  10 , paddle (not shown), and IC die  20 . For example, as the overall size of the RF switch decreases, the maximum distance at which the RF input and output bond wires  53  and  51  can be spaced may not sufficiently limit the coupling between the bond wires  55  and  51  to obtain a desired isolation bandwidth. Additionally, IC die coupling can be reduced by changing the size of the IC die  20  or decreasing the effective off state capacitance of the switch circuit, however, this can have a negative impact on other performance parameters of the RF switch such as insertion loss and power handling, thus resulting in limited isolation between the RF input and output ports of the package. Effects on the isolation of the RF switch may also be addressed by changing the packaging technology used (e.g., by using flip-chip packages), however, these changes increase both the cost and complexity of the switch. 
         [0031]    Another method used to minimize signal coupling is shown in  FIG. 4 .  FIG. 4  is a diagram illustrating one method of altering the coupling between bond wires according to an embodiment. In this embodiment, the coupling between the bond wires  51  and  53  can be reduced by placing a ground bond  55  in close proximity to one of the bond wires  51  or  53  with a termination. In one example, the termination is a 50 Ohms termination. In the example shown in  FIG. 4 , the ground bond  55  is placed near the RF output bond wire  51 . Here, the current input into the RF input bond wire  53  induces a current in the ground bond  55 , which in turn induces a reverse current in the RF output bond wire  51 , thus canceling the coupling between the RF input and output bond wires  53  and  51 . 
         [0032]    Referring back to  FIG. 3 , in certain embodiments, the configuration or geometry of the bond wires  51  and  53  is selected such that the inductive coupling generated in the bond wires  51  and  53  cancels the capacitive coupling generated in the IC die  20 . Thus, instead of minimizing each of the coupling sources, the coupling from the bond wires  51  and  53  is manipulated by altering the geometry of the bond wires  51  and  53  such that it is substantially out of phase with the coupling introduced due to the IC die  20 . In particular, over the frequency band of interest for the RF switch, the coupling introduced by the bond wires  51  and  53  is selected to be substantially out of phase with and to have a magnitude that is similar to the coupling introduced by the IC die  20 . Depending on the design requirements of the RF switch, the phase and magnitude of the bond wire coupling can be selected to introduce a notch in the isolation graph of the switch in a desired frequency band. By introducing the notch into the isolation graph, the isolation bandwidth can be increased over traditional isolation methods. 
         [0033]    The phase and magnitude of the coupling between the bond wires  51  and  53  is a function of the bond wire geometry. Thus, these parameters of the signal coupling between the bond wires  51  and  53  can be selected by adjusting, for example, the angle, length, and/or orientation of the bond wires  51  and  53 . However, the described technology is not limited to adjusting the above described geometric characteristics. Any design factors that affect the coupling of the bond wires  51  and  53  can be used to adjust the phase and magnitude of coupling in the bond wires  5 . For example, as illustrated in  FIG. 4 , a ground bond  55  can be placed near one of the bond wires  51  and  53 . In this implementation, the magnitude of the coupling between the bond wires  51  and  53  can be reduced due to the current induced in the ground bond  55 . Additionally, any design factors which affect the coupling introduced by the IC die  20  can be adjusted to cancel the overall signal coupling with the bond wires  51  and  53 . Accordingly, any such design factors which affect the phase and amplitude of the coupling of the RF bond wires  51  and  53  and/or the IC die  20  are considered to be within the scope of the described technology. 
         [0034]      FIG. 5  is a diagram illustrating various RF output bond wire configurations according to an embodiment.  FIG. 5  illustrates a top view of the IC die  20 , RF input and output leads  33  and  31 , and RF input and output bond wires  53  and  51 . The angle between the RF input and output bond wires  53  and  51  is adjusted to form a number of states (state  1  to state  5 ) by changing the angle of the RF output bond wire  51 . In state  1 , the RF output bond wire  51  forms a 180° angle with respect to the RF input bond wire  51 . In state  5 , the RF input and output bond wires  53  and  51  form a 90° angle. Similarly, in states  2 ,  3 , and  4 , the RF input and output bond wires  53  and  51  respectively form angles of about 157.5°, 135°, and 112.5°. 
         [0035]      FIG. 6  is a graph illustrating the isolation of the RF bond wire configurations of  FIG. 5 . The graph illustrated in  FIG. 6  show the isolation in dB for a plurality of RF switches in which the angle of the RF output bond wire  5  is adjusted between states  1  and  5 , as shown in  FIG. 5 . 
         [0036]    As shown in the plots of the states  1  to  5 , the notch in the isolation graph changes based on the angle the RF output bond wire  51  makes with the RF input bond wire  53 . As the RF output bond wire  53  approaches an orthogonal orientation with respect to the RF input bond wire  51 , the coupling between the RF bond wires  53  and  51  increases in the low frequency region (i.e., in the 1-2 GHz region). As shown in the plot of state  3 , a notch is formed in the isolation over frequency performance at the point where the bond wire coupling is out of phase with the IC die coupling and the magnitudes of the bond wire and IC die coupling are similar. The notches in each of states  4  and  5  are formed at increasing frequencies. Thus, as shown in the isolation graph of  FIG. 6 , while the frequency isolation degrades in the lower frequency region, a wider band of frequency isolation can be obtained by outphasing the isolations from the two mechanisms thus introducing an isolation notch in the isolation over frequency performance. 
         [0037]    At each of the notches in the isolation graph of  FIG. 6 , the overall electrical coupling of the IC package is reduced compared to the adjacent frequencies. Thus, the term reduced as used in this disclosure may refer to the reduction of electrical coupling of the IC package for a selected frequency band with respect to frequencies that are adjacent to the selected frequency band. According to at least one embodiment, a reduction in electrical coupling, e.g., an isolation notch, is produced due to cancelling between different sources of electrical coupling. When the different coupling sources are out of phase with each other, the overall coupling of the IC package will be reduced for a certain frequency range. 
         [0038]    According to at least one embodiment, the geometry of the bond wires  53  and  51  is selected to increase the isolation bandwidth of an RF switch. This appears as an isolation notch within the bandwidth. In multi-pole RF switch packages, the effects may appear as a plurality of isolation notches within the desired bandwidth. 
         [0039]      FIG. 7  is a diagram illustrating the bond wire connections between an IC die and a QFN package substrate according to an embodiment. Specifically, the embodiment of  FIG. 7  includes a QFN package  11  having an IC die  21 . The IC die  21  includes a plurality of leads  30  including a plurality of RF input leads  32 ,  34 , and  38  and a plurality of RF output leads  31 ,  32 , and  36 . The QFN package also includes a plurality of leads  40  which are electrically connected to the leads  30  of the IC die  21 . Specifically, RF input leads  33 ,  24 , and  38  are respectively connected to the QFN package leads  43 ,  44 , and  48  via bond wires  53 ,  54 , and  58  and the RF output leads  31 ,  32 , and  36  are respectively connected to the QFN package leads  41 ,  42 , and  46  via bond wires  51 ,  52 , and  56 . 
         [0040]    In the illustrated embodiment, the IC die  21  connects a plurality RF input and output leads  31  to  38  which may experience electrical signal coupling. In particular, each of the bond wires  51  to  58  may include electrical signal coupling with the other bond wires  51  to  58  due to the RF signals applied thereto. Further, as described above in connection with  FIG. 3 , the bond wires  51  to  58  may experience inductive and capacitive coupling due to the geometry of the bond wires  51  to  58 , for example, due to the vertical and horizontal portions of the bond wires  51  and  58 , and may further experience capacitive coupling generated in the IC die  21 . 
         [0041]    In some embodiments, the geometry and positioning of each of the bond wires  51  to  58  is selected such that the inductive and capacitive coupling generated in the bond wires  51  to  58  cancels at least a portion of the capacitive coupling generated in the IC die  21 . Since each of the bond wires  51  to  58  may be inductively or capacitively coupled to each of the other bond wires  51  to  58 , the selected geometry may be based on the location and geometry of the other bond wires  51  to  58 . Additionally, the notches in the isolation graphs for each pair of bond wires  51  to  58  can be selected by altering the geometry and positioning of the bond wires  51  to  58  based on the intended operating frequency band for the pair of bond wires  51  to  58 . 
         [0042]    Devices employing the above described schemes can be implemented into various electronic devices. Examples of the electronic devices can include, but are not limited to, consumer electronic products, parts of the consumer electronic products, electronic test equipment, etc. Examples of electronic products can include, but are not limited to, medical devices, a mobile phone, a telephone, a tablet computing device, a television, a computer monitor, a computer, a hand-held computer, a personal digital assistant (PDA), a microwave, a refrigerator, an automobile, a stereo system, a cassette recorder or player, a DVD player, a CD player, a VCR, an MP3 player, a radio, a camcorder, a camera, a digital camera, a washer, a dryer, a washer/dryer, a copier, a facsimile machine, a scanner, a multi-functional peripheral device, a wrist watch, a clock, etc. Further, the electronic device can include unfinished products. 
         [0043]    Although this invention has been disclosed in the context of certain preferred embodiments and examples, it will be understood by those skilled in the art that the present invention extends beyond the specifically disclosed embodiments to other alternative embodiments and/or uses of the invention and obvious modifications and equivalents thereof. In addition, while several variations of the invention have been shown and described in detail, other modifications, which are within the scope of this invention, will be readily apparent to those of skill in the art based upon this disclosure. It is also contemplated that various combinations or sub-combinations of the specific features and aspects of the embodiments may be made and still fall within the scope of the invention. It should be understood that various features and aspects of the disclosed embodiments can be combined with, or substituted for, one another in order to form varying modes of the disclosed invention. Thus, it is intended that the scope of the present invention herein disclosed should not be limited by the particular disclosed embodiments described above, but should be determined only by a fair reading of the claims that follow.