Abstract:
An integrated circuit package houses and connects to a die to form an integrated circuit with internal matching. The package comprises a lead frame comprising at least one transmission line, a die paddle, and at least one input lead and at least one output lead. Bond wires connect select locations along the at least one transmission line to ground through impedance matching circuit components located within the integrated circuit to provide an impedance matching network associated with at least one of the output leads. A plastic mold compound substantially encases the lead frame, while exposing the die paddle and the input/output leads. Incorporating the transmission line into the lead-frame avoids having to place the matching network outside of the integrated circuit package. That is, etching the lead frame to provide the transmission line, and placing components (e.g., capacitors, inductors, etc.) of the impedance transform matching circuit within the integrated circuit and connecting the components between select locations on the transmission line and ground is relatively inexpensive.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    The present invention relates to the field of semiconductor devices, and in particular to an integrated circuit with internal impedance matching  
           [0002]    In cellular telephones, radio frequency (RF) power amplifiers (PA) are built using a semiconductor device (e.g., silicon or GaAs) that has a low output impedance (e.g., less two ohms). This impedance needs to be transformed to a higher impedance value (e.g., fifty ohms) to connect to filters, switches, diplexers and antennas in the rest of the radio. This impedance transformation network is typically referred to as the “output match.” 
           [0003]    In addition to transforming a two-ohm impedance to fifty ohms, the output match is typically tuned at the harmonic frequencies to increase efficiency and battery life (e.g., talk time) of the cellular telephone. These harmonic frequencies extend up to 6 GHz. At these frequencies, the distance between the capacitors and other passive components used to construct the output match is critical, for example a distance of 0.001″ is significant. For example, a vendor may specify distances of 0.062″ and 0.416″ in one one-thousandth of an inch of precision between the capacitors and other passive components of the output matching network.  
           [0004]    The harmonic frequencies present a second problem. The capacitors have parasitic values that become significant at the harmonic frequencies. Since the parasitic values differ from one manufacturer to another, changing vendors for the same value component will yield different results.  
           [0005]    In producing high volumes (e.g., 30,000,000 per year) these dependencies on a single vendor and tolerances of 0.001″ are costly to manage. Therefore, there is a need for an improved technique for providing an impedance matching network.  
         SUMMARY OF THE INVENTION  
         [0006]    Briefly, according to an aspect of the present invention, an integrated circuit includes a die that is electrically connected to and housed within a plastic package. The package includes a lead frame comprising a transmission line, at least one input signal lead, and at least one output signal lead that is connected to the transmission line. The die provides an output signal onto the transmission line. At least one select location along the transmission line is connected to a first electrical node through an impedance matching circuit within the integrated circuit.  
           [0007]    According to another aspect of the present invention, an integrated circuit package includes a lead frame comprising at least one transmission line, at least one input signal lead, and at least one output signal lead. At least one select location along the transmission line is connected to a first electrical node through an impedance matching circuit within the integrated circuit package, wherein the impedance matching circuit is associated with the output signal lead.  
           [0008]    The impedance matching circuit is located within the integrated circuit. For example, in one embodiment, the impedance matching circuit may be connected between the at least one select location along the transmission line and a die paddle of the lead frame. In another embodiment, the impedance matching circuit may be located within the die, and electrically connected (e.g., by bond wires) to the at least one select location along the transmission line.  
           [0009]    In one embodiment, at least one select location along the transmission line is wire bonded to a capacitor. The capacitance value of the capacitor and the dimensions of the transmission line are selected to provide the desired matching circuit (i.e., output impedance).  
           [0010]    Incorporating the transmission line into the lead frame avoids having to place the matching network outside of the integrated circuit. For example, etching the lead frame to provide the transmission line, and placing components (e.g., capacitors, inductors, etc.) of the impedance transform matching circuit on a die and connecting these components on the die between select locations on the transmission line and the first electrical node (e.g., ground) is relatively inexpensive. A second embodiment of placing the impedance matching circuit between the at least one select location along the transmission line and the die paddle is also relatively inexpensive.  
           [0011]    These and other objects, features and advantages of the present invention will become more apparent in light of the following detailed description of preferred embodiments thereof, as illustrated in the accompanying drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWING  
       [0012]    [0012]FIG. 1 illustrates a functional block diagram of a prior art matching circuit configuration for an RF output signal;  
         [0013]    [0013]FIG. 2 is a cut-a-way top view of a first integrated circuit that includes a first die, and a second die within a first plastic package;  
         [0014]    [0014]FIG. 3 is a functional block diagram illustration of the internal matching network associated with the first die illustrated in FIG. 2;  
         [0015]    [0015]FIG. 4 is a cut-a-way top view of a lead frame of a second integrated circuit that provides at least one output signal;  
         [0016]    [0016]FIG. 5 illustrates a section taken along line A-A in FIG. 4;  
         [0017]    [0017]FIG. 6 illustrates a bottom view of the second plastic package of FIG. 4;  
         [0018]    [0018]FIG. 7 illustrates a side view of the package of FIG. 6;  
         [0019]    [0019]FIG. 8 is a cut-a-way top view of a lead frame of a third integrated circuit that includes an internal matching circuit located within a die;  
         [0020]    [0020]FIG. 9 is a top view of the lead frame of FIG. 8 shown in cross hatch;  
         [0021]    [0021]FIG. 10 is a bottom view of the lead frame of FIG. 8 with exposed sections of the lead frame shown in cross hatch;  
         [0022]    [0022]FIG. 11 is a cut-a-way top view of a lead frame of a fourth integrated circuit that includes an internal matching network located between the die paddle and a first select location on the transmission line;  
         [0023]    [0023]FIG. 12 is a cut-a-way top view of a lead frame of a fifth integrated circuit that includes a first internal matching network component located between the die and a first select location on the transmission line, and a second internal matching network component located between the die paddle and a second select location on the transmission line; and  
         [0024]    [0024]FIG. 13 is a functional block diagram illustration of the internal matching network associated with the integrated circuit of FIG. 12. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0025]    [0025]FIG. 1 illustrates a functional block diagram of a prior art matching circuit configuration  100  that provides an output signal on a line  102 . In one embodiment, the output signal on the line  102  is from an RF power amplifier (PA) within an integrated circuit  104 . The integrated circuit  104  provides the output signal on the line  102  to an impedance transformation network  106  (also referred to herein as a “matching network”), which provides an impedance matched output signal on a line  108 . For example, the impedance matched output signal on the line  108  may for example have an output impedance of fifty ohms, whereas the impedance of the signal on the line  102  may for example be two ohms. The impedance matching network  106  includes a plurality of capacitors C 1    110  and C 2    112  that are precisely positioned to provide the required impedance transformation and harmonic filtering. For example, the capacitor C 1    110  is precisely positioned (e.g., to a 0.001″ tolerance) from edge  114  of the integrated circuit  104 , while the distance between capacitors C 1    110  and C 2    112  is also precisely controlled. As set forth above, these positioning constraints lead to a problematic and relatively costly matching network that is external to the integrated circuit  104 .  
         [0026]    [0026]FIG. 2 is a cut-a-way top view of a first integrated circuit  200  that includes a first die  202 , and a second die  204  within a plastic package. The first die  202  provides an output signal via bond wires  206 ,  208  to a first transmission line  210  located on a lead frame (e.g., etched copper). The second die  204  provides an output signal via bond wires  212 ,  214  to a second transmission line  216  located on the lead frame. The lead frame also includes a plurality of input/output (I/O) leads (e.g.,  218 - 222 ). Bond wires interconnect bonding pads on the dies and the I/O leads. According to an aspect of the present invention, the lead frame also includes at least one transmission line (e.g., 0.1 mm thick in non-exposed areas, and 0.2 mm thick in exposed areas) that cooperates with circuit components within the integrated circuit to provide an integrated circuit with internal matching. Specifically, in this embodiment matching circuit components such as capacitors and/or inductors (not shown) located on the first die  202  are connected to the first transmission line  210 . For example, a first capacitor located on the first die  202  is connected to a first selected location on the transmission line  210  by bond wires  230 ,  231 . Two bond wires are shown in this embodiment for current handling. However, a skilled person will recognize of course that more or less bond wires may be used to connect the matching circuit component on the die to the transmission line, depending upon the current handling required. In addition, a second capacitor (now shown) may be located on the die  202  and connected to a second location (e.g., location  240 ) on the transmission line  210  by bond wires (not shown) to provide a matching circuit that is functionally similar to the circuit  106  illustrated in FIG. 1. However, in the embodiment of FIG. 2, the matching network is located within the integrated circuit. That is, the integrated circuit of FIG. 2 includes internal matching.  
         [0027]    The second die  204  may also include an internal matching network that is established by connecting a matching circuit component(s) within the second die  204 , to the transmission line  216  for example via bond wires  242 ,  244 .  
         [0028]    [0028]FIG. 3 is a functional block diagram illustration of the internal matching network associated with the first die  202  illustrated in FIG. 2. For example an output amplifier  246  located on the die  202  provides an output signal that is conducted by the transmission line  210  to an I/O lead  248 . A first lead of a capacitor  252  located on the die  202  is connected to a first select location  254  on the transmission line  210  via the bond wires  230 ,  231 . A second lead of the capacitor  252  is connected to a first electrical potential, for example ground. Significantly, this provides an impedance matching circuit  258  that is located within the integrated circuit  200 .  
         [0029]    [0029]FIG. 4 is a cut-a-way top view of a second integrated circuit  300  that includes a die (not shown in FIG. 4), that is placed onto a die paddle  302  of a lead frame  306  (e.g., etched copper) that includes plurality of I/O leads (e.g.,  308 - 314 ). Interconnect bonding pads located on the die are connected for example via bond wires to the I/O leads. The lead frame  306  also includes a first transmission line  320  shown in cross hatch. In this embodiment, the package also includes a second transmission line  322  that is also not exposed on the exterior of the package. The first transmission line  320  is associated with a first output signal from the package, while the second transmission line is associated with a second output signal from the package. Matching circuit components such as capacitors and/or inductors (not shown) located on the die and associated with the first output signal, are connected between a first electrical potential (e.g., ground) and at least one select location on the first transmission line  320 .  
         [0030]    [0030]FIG. 5 illustrates a section taken along line A-A in FIG. 4. A die  402  is located on the paddle  302 , and at least one bond wire  404  connects lead  313  and a bond pad (not shown) on the die  402 . FIG. 6 illustrates a bottom view of the second integrated circuit. As shown, the lead frame includes the paddle  302  and the plurality of I/O leads, for example  308 - 314 . Referring to FIGS. 5 and 6, the package also includes a plurality of exposed wire bond support structures  510 - 517  that represent select locations along the transmission lines at which the matching circuit components may be connected. For example, in one embodiment, these support structures (e.g., etched copper) are connection points for bond wires between the matching components on the die, and the transmission lines within the lead frame of the package. For example, bonding wire  430  (FIG. 5) runs between a matching component (e.g., a capacitor) on the die  402  and the support structure  511  (i.e., a select location on the transmission line  320 ).  
         [0031]    [0031]FIG. 7 is a side view of the package of FIG. 5.  
         [0032]    [0032]FIG. 8 is a cut-a-way top view of a third integrated circuit  800  that includes a die  802 , and a lead frame  804  of a third plastic package. FIG. 9 is a top view of the lead frame  804  of FIG. 8 shown in cross hatch. The lead frame  804  includes a die paddle  806  and a plurality of I/O leads  808 - 823 . The lead frame also includes a transmission line  826  that connects an output  828  on the die  802  to selected I/O leads  808 - 812 . In this embodiment, the die output  828  is connected to the transmission line  826  by a plurality of bond wires  831 . The die  802  includes at least one component (e.g., a capacitor, inductor, etc) of an impedance matching/transformation network. The network matching component within the die is connected to a first select location  830  along the transmission line  826 . As a result, a circuit configuration as shown in FIG. 3 is provided. Depending upon the impedance matching and filtering requirements, the matching circuit component within the die  802  may be connected to the transmission line  826  at one of a plurality of select locations  832 - 836  along the transmission line, rather than at the selected location  830 . In the embodiment of FIG. 8, the integrated circuit  800  is 4 mm×4 mm (i.e., L  850  is equal to 4 cm). As shown in FIG. 8, the path length of the transmission line  826  will vary pending upon the select location (e.g.,  830 ) along the transmission line that the matching circuit component is connected to.  
         [0033]    [0033]FIG. 10 is a bottom view of the lead frame of FIG. 8 shown in cross hatch. In this view, support structures associated with the select locations  830 ,  836  along the transmission line  826  (FIG. 9) are exposed on the underside of the integrated circuit  800 .  
         [0034]    [0034]FIG. 11 is a cut-a-way top view of a fourth integrated circuit  1100  that includes a die  1102 , and a lead frame  1104  of a fourth plastic package. This embodiment is substantially the same as the embodiment illustrated in FIGS.  8 - 10 , with the principal exception that an internal matching network component  1106  (e.g., a capacitor) is located between die paddle  1108  and a first select location  1110  on the transmission line  826 . That is, the internal matching circuit component is not located on the die. However, the internal matching circuit is still resident within the integrated circuit to provide the internal matching.  
         [0035]    [0035]FIG. 12 is a cut-a-way top view of a fifth integrated circuit  1200  that includes a die  1202 , and a lead frame  1204  of a fifth plastic package. This embodiment is substantially the same as the embodiments illustrated in FIGS.  8 - 10 , and FIG. 11, with the principal exception that a first internal matching network component  1206  (e.g., a capacitor) is located between a die paddle  1208  and a first select location  1210  on the transmission line  826 , and second internal matching network component (not shown) is located within the die  1202  and connected to a second select location  1212  on the transmission line.  
         [0036]    [0036]FIG. 13 is a functional block diagram illustration of the internal matching network associated with the integrated circuit of FIG. 12. For example, an output amplifier  1302  located on the die  1202  provides an output signal that is conducted by the transmission line  826  to the I/O lead  808 . A first lead of a capacitor  1306  located on the die  1202  is connected to the second select location  1212  on the transmission line  826  via bond wires  1314 . A second lead of the capacitor  1306  on the die is connected to a first electrical potential, for example ground. A first lead of the capacitor  1206  is connected to the first selected location  1210  on the transmission line  826 , while a second lead of the capacitor  1206  is connected to the die paddle (i.e., ground).  
         [0037]    Advantageously, the integrated circuit and package of the present invention provide internal impedance matching, thus for example freeing a handset manufacturer (or board manufacturer) from having to provide room on the board for the impedance transformation matching circuitry.  
         [0038]    Although the present invention has been discussed in the context of a package for power amplifiers for wireless handsets, it is contemplated that the many other applications will find it desirable to replace applications that require impedance matching, conventionally performed on a circuit board or as lumped element components, with matching circuitry contained within the integrated circuit. Advantageously, this obviates many of the manufacturability problems associated with having to precisely position the components of the matching circuit. In addition, although the matching network components have been connected between the transmission line and ground, the first electrical potential does not necessarily have to be ground.  
         [0039]    Although the present invention has been shown and described with respect to several preferred embodiments thereof, various changes, omissions and additions to the form and detail thereof, may be made therein, without departing from the spirit and scope of the invention.