Abstract:
The invention provides a bond wire arrangement comprising a signal bond wire ( 1 ) for operably connecting a first electronic device ( 6 ) to a second electronic device ( 8 ), and a control bond wire ( 2 ) being arranged alongside the signal bond wire at a distance so as to have a magnetic coupling with the signal bond wire ( 1 ), and having a first end ( 11 ) coupled to ground, and a second end ( 12 ) coupled to ground via a resistive element ( 14 ). The proposed solution allows the control of the Q factor (losses) of wire bond inductors during assembly phase, which will save time and reduce overall design cycle as compared to known methods.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention generally relates to microelectronic interconnects and, more particularly wire bonds in connection to high-power power amplifiers and power amplifier integrated circuits. 
       BACKGROUND OF THE INVENTION 
       [0002]    Wire bond inductors are commonly used as a connection to package leads and as a part of matching networks for RF/MW (: Radio Frequency/Millimeter-Wave) high power amplifiers. A self-inductance of a wire bond (or array of wire bonds) is a function of height and shape of the wires, so by varying the height and/or shape during wire bonding, the self-inductance can be controlled. However, high quality factor Q of these wires is a function of used metal for example aluminium and in some cases extra losses are beneficial for overall performance of power amplifier. 
         [0003]    In multistage power amplifiers and also in integrated circuits, there is essential trade-off between stability and gain. An optimum is often found by introducing variation into sensitive components such as inductors, during design phase or by trimming/design modifications, which may be expensive and time consuming. So there is still a need for improving the performance of electronic circuits by way of optimizing the Q factor of wire bonds which is more flexible. 
       SUMMARY OF THE INVENTION 
       [0004]    The present invention provides a bond wire arrangement as described in the accompanying claims. The invention also provides a bypass network, a RF match network and power amplifier circuit comprising such a RF match network. It also provides an integrated circuit comprising such a bond wire arrangement. Specific embodiments of the invention are set forth in the dependent claims. 
         [0005]    These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]    Further details, aspects and embodiments of the invention will be described, by way of example only, with reference to the drawings. Elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. 
           [0007]      FIG. 1  is a perspective view of a signal bond wire and control bond wires with additional losses in the ground connection path according to an embodiment of the invention; 
           [0008]      FIG. 2  schematically shows an electronic scheme of the embodiment of  FIG. 1 , where the control bond wire is coupled to the ground with extra losses in the ground path created by a resistance; 
           [0009]      FIG. 3  shows a bond wire arrangement according to a further embodiment where the circuit comprises a capacitor arranged in series with the resistive element; 
           [0010]      FIG. 4  shows a graph of the quality factor vs. equivalent inductance Leq for an array of signal bonds, without the added control bond wire(s); 
           [0011]      FIG. 5  shows a graph of the quality factor vs. change of height of signal bond wires H 1  for an array of signal bond wire(s), with added control bond wire(s); 
           [0012]      FIG. 6  shows a graph of the equivalent inductance Leq vs. change of height of signal bond wires H 1  for an array of signal bond wire(s), with added control bond wire(s); 
           [0013]      FIG. 7  shows a graph of an equivalent resistance R eq  of the signal wire bond as a function of frequency for several heights H of the wires, where the grounded bond wire is in series with a 5 Ohm resistor; 
           [0014]      FIG. 8  shows another graph of the equivalent resistance R eq  as a function of frequency for several heights h for frequency selective added losses; 
           [0015]      FIG. 9  shows a power amplifier circuit comprising a bypass output network according to an embodiment; 
           [0016]      FIG. 10  shows a graph of simulation results of the an impedance seen by the switching device of the power amplifier circuit with and without coupled losses in the bypass network shown in  FIG. 9 ; 
           [0017]      FIG. 11  schematically shows an example of an RF integrated circuit comprising a bond wire arrangement according to an embodiment. 
       
    
    
       [0018]    Elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. In the Figures, elements which correspond to elements already described may have the same reference numerals. 
       DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0019]      FIG. 1  is a perspective view of a signal bond wire  1  and two control bond wires  2 ,  3  according to an embodiment of the invention. The signal bond wire  1  and the control bond wires  2 ,  3  could be part of an electronic circuit, such as for example an RF integrated circuit, as will be explained below in more detail. The signal bond wire  1  is arranged to operably connect a first signal line  4  of an electronic device  6  to a signal line  5  of another electronic device  7 . The ground bond wire  2  has a first end  11  and a second end  12 . The control bond wires  2  are arranged alongside the signal bond wire at a distance d so as to have a magnetic coupling with the signal bond wire  1 . It is noted that the second control bond wire  3  could be at different distance than the distance d between the signal bond wire and the first control bond wire  2 . 
         [0020]    The signal bond wire  1  and the control bond wires  2 ,  3  have heights Hs and Hc, respectively. However it is noted that the shapes and heights H 1 , H 2  may differ for the two types of bond wires. A bonding pad  8  for connecting the first control bond wire  2  to the device  7  is made of a metal, while a bonding pad  9  for connecting the first control bond wire  2  to the device  6  comprises a metal layer and a semiconductor layer  14  having a certain resistance. So the first end  11  of the control bond wire  2  is coupled to ground while the second end  12  of the control bond wire  2  is coupled to ground via a resistive element  14 . The same account for control bond wire  3 . 
         [0021]    Instead of comprising only one signal bond wire and two ground wires, the bond wire arrangement could comprise an array of signal bond wires and/or an array of ground wires. Each of the signal bond wires could be interlaced between two ground bond wires or in any other possible configuration where there is a magnetic coupling between a signal bond wire and a ground bond wire. 
         [0022]    Instead of the semiconductor layer  14 , any other suitable resistive element can be arranged in series with a control bond wire  2 , such as a resistor. Such resistive elements create losses in addition to the already present parasitic losses of control bond wire. 
         [0023]      FIG. 2  schematically shows an electronic scheme of the embodiment of  FIG. 1 , where control wire bond  2  is coupled to the ground with extra losses in the ground path created by the resistive element  14  having a value R 2 . As shown in  FIG. 2 , the signal bond wire has an inductance L 1  and the ground bond wire has an inductance of L 2 . 
         [0024]    The signal bond wire impedance Z 1 , when the terminal OUT is grounded, can be described as Z 1 =R 1 +jωL 1 . The equivalent quality factor Qeq is the ratio ωL 1 /R 1 . Resistive losses associated with R 1  are depending on the type of metal used and are usually small, whereas inductance L 1  at GHz frequency of operation creates several tens of times higher reactive impedance that resistive, therefore, Qeq is high, to reduce Qeq the control bond wire Z 2 =R 2 +jωL 2  is placed magnetically coupled to the signal bond wire with mutual inductance M=k√{square root over (L 1 L 2 ,)} where k is coupling factor having value 0.1-0.7. Due to presence of a magnetically coupled control bond wire, the signal bond wire  1  futures modified equivalent impedance 
         [0000]    
       
         
           
             
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                 R 
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                  
                 
                     
                 
                  
                 ω 
                  
                 
                     
                 
                  
                 
                   L 
                   1 
                 
               
               + 
               
                 
                   
                     ω 
                     2 
                   
                    
                   
                     M 
                     2 
                   
                 
                 
                   Z 
                   2 
                 
               
             
           
         
       
     
         [0000]    assuming ground termination of OUT. As a result the impedance of signal bond wire has additional term associated with control bond wire that is proportional to the frequency of operation and such term vanishes at DC frequency ω=0. By changing coupling k it is possible to control Qeq with resistive part R 2  of the control bond wire atop of control of Leq of the signal bond wire during wire bonding process. By changing shapes and heights of coupled bond wires it is possible to maintain original Z Σ =L 1  inductance that would have stand alone signal bond wire. Please note that such control of Qeq does not change the DC path of the signal bond wire, and therefore can be used to feed high current through the signal bond wire(s). 
         [0025]    In an embodiment the resistive element  14  has a resistance value between 0.2-5 Ω depending on power and frequency of operation. The distance d between the signal bond wire  1  and the ground bond wire(s)  2  may be less than 200 μm. 
         [0026]    By choosing an appropriate height and shape for the signal bond wire  1  and the control bond wire(s)  2 ,  3  during the bonding process, it is possible to adjust coupling factor k and thus the amount of losses in the signal wire bond  1  whereas the absolute inductance L 1  can be kept equal to the desired value. 
         [0027]      FIG. 3  shows a bond wire arrangement according to a further embodiment where the circuit comprises a capacitor  32  arranged in series with the resistive element  14 . By introducing a series capacitor into the ground path with losses, frequency selective losses in the signal wire bond are possible close to the frequency ω=1/√{square root over (L 2 C 2 )}. For example the value of C 2  can be selected in such a way to create resonance 200 MHz below the frequency of operation of the power amplifier for broad band input matching circuits. 
         [0028]      FIG. 4  shows a graph of the equivalent quality factor Qeq as a function of the equivalent inductance Leq of a signal bond wire without any magnetically coupled control bond wire. It is noted that changing the height Hs of the signal bond wire will result in a change of the equivalent inductance Leq. From  FIG. 4  it can be seen that changing the height Hs will not or nearly affect the equivalent quality factor Qeq, see line  104  which is (nearly) constant. 
         [0029]    However when applying the arrangement according to the embodiment of  FIG. 1 , the Qeq can easily be changed by changing the height Hs, Hc of the bond wires  1 , 2 , 3 , as will be shown in an example with reference to  FIG. 5 .  FIG. 5  shows a graph of the quality factor Qeq vs. a change of height H 1  of the signal bond wire  1  for an array of signal bond wire(s), with added control bond wire(s). In this simulation, the absolute height of each of the signal bond wires  1  is Hs=H 0 +H 1 , whereas the absolute height of each of the control bond wires  2 ,  3  is Hc=H 0 +H 2 . From  FIG. 5  it can be seen that Qeq is depending on both H 1  and H 2 . So by changing Hs and/or Hc, the Qeq can adequately be changed and determined during the bonding process. 
         [0030]      FIG. 6  shows a graph of the equivalent inductance Leq as a function of relative change of height of signal bond wire  1  for an array of signal bond wire(s), with the added control bond wire(s)  2 ,  3 . From  FIG. 6  is can be seen that by adjusting height of signal bond wire(s) and height of control bond wire(s) the equivalent inductance of signal bond wire can be controlled in wide range 0.4-1.2 nH. This enables additional design options for desired Leq and Qeq. 
         [0031]      FIG. 7  shows a graph of an equivalent resistance Req of the signal wire bond as a function of frequency for several heights (and thus several coupling factors) of the bond wires, where each control bond wires  2 , 3  is in series with a 5 Ohm resistor. From  FIG. 7  it shows that equivalent resistance of signal bond wire can be controlled (i.e. modified) from 0.7 to 2.2 Ohm enabling the modification of Qeq from 10 to 35 during wire bonding process. The lines in  FIG. 7  show Req for different coupling factors ranging from 0.1 to 0.5 with steps of 0.05. 
         [0032]      FIG. 8  shows another graph of the equivalent resistance Req as a function of frequency for several heights coupling factors. The graph of  FIG. 8  is made for the embodiment shown in  FIG. 3  with the resistive element  14  having a value of 5 Ω and the additional capacitor  32  having a value of 15 pF. By adding the capacitor  32 , the Req is made frequency dependent. Such frequency dependent losses can be advantageous in broad band power amplifier circuits when the input matching network comprises a shunt inductance to compensate an input capacitance of e.g. a RF LDMOSFET (lateral diffusion MOSFET). 
         [0033]    According to a further aspect, there is provided a bypass network for use in a RF match network of power amplifier circuit, the bypass network comprising a bond wire arrangement as described above. There is also provided a RF output match network for use in a power amplifier circuit, and a power amplifier circuit comprising such a RF match network.  FIG. 9  shows an example of such a power amplifier circuit  900  according to an embodiment of the invention. The power amplifier circuit  900  includes an amplifier device  918 , an output match network and a bypass network. The output match network comprises a shunt inductor  922  and a DC blocking capacitor  924 . The RF output match network is coupled to an output of the power device  918 . The RF output match network may be operable to provide a range of impedance matching over a signal bandwidth and a low frequency gain peak outside the signal bandwidth which corresponds to a low frequency resonance of the high quality factor RF path. The bypass network is coupled in parallel with the blocking capacitor of the RF output match network. The bypass network is operable to attenuate the low frequency gain peak while maintaining the high quality factor RF path. The bypass network comprises a bypass inductor  930  and a bypass capacitor  932  arranged in series with the bypass inductor  930 . A DC power is coupled to a connection of the bypass capacitor and will function as feed of the power amplifier or as extra lead of the power amplifier circuit. 
         [0034]    The power device  918  in this example is a RF LDMOSFET (lateral diffusion MOSFET) but it is noted that it can be any other switching device as appreciated by the skilled person. The amplifier device  918  comprises a gate terminal G coupled to a signal input  916  of the power amplifier circuit  900 . The amplifier device  918  also comprises a drain terminal D and a source terminal S. the source terminal S is coupled to ground and drain terminal D is coupled to the output lead. 
         [0035]    As can be seen from  FIG. 9 , the bypass inductor  930 , embodied by the signal bond wire  1 , is magnetically coupled with the control bond wire  2  which is coupled to ground via the resistive element  14 , also referred to as dumping resistor Rd. This will allow to reduce the effective inductance of the bypass inductor  930  (i.e. LBP) and to introduce losses at frequencies above DC while keeping the ability for the bypass inductor  930  to conduct a high DC feed current which is required for the operation of the power amplifier circuit. 
         [0036]      FIG. 10  shows a graph of simulation results of an impedance Z seen by the RF LDMOS  918  with and without coupled losses (i.e. lossy control bond wire). In  FIG. 10  a curve  950  represents the impedance as a function of frequency in case the output circuit shown in  FIG. 9  does not have the coupled ground wire  2  and resistive element  14 . In this case the impedance shows a very high peak at the frequency of about 0.4 GHz. Such impedance peak creates high risk of oscillation, can damage a power amplifier circuit and deteriorates linearity. 
         [0037]    A curve  951  in  FIG. 10  represents the impedance in case the ground wire  1  and resistive element  14  are present in circuit of  FIG. 9 . Curve  951  shows a peak, but this peak is a lot smaller than the peak of curve  950 . Arrow  952  indicates the improvement due to the coupling of the bond wires as described above. 
         [0038]    According to an aspect, there is provided an RF integrated circuit comprising a bond wire arrangement as described above with reference to  FIGS. 1-4 , wherein the bond wire arrangement is arranged in a driver and/or an final stage of the RF integrated circuit.  FIG. 11  schematically shows an example of such an RF integrated circuit. In the example a two-stage RFIC  700  is matched using one or more matching networks. The RF integrated circuit  700  comprises an input terminal  701  and a switching device  702  having a control terminal  703 , a first output terminal  704  and a second output terminal  705 . The control terminal  703  is coupled to the input terminal  701 . The second output terminal  705  of the switching device  702  is coupled to ground. A first inductance  724  is arranged with a first and second connector, wherein the first connector is coupled to the input terminal  701 . A first capacitance  725  is arranged with a first and second connector, with the first connector of the first capacitance  725  coupled to the second connector of the first inductance  724 . The second connector of the first capacitance  725  is coupled to ground. 
         [0039]    In the example of  FIG. 11 , the RF integrated circuit  700  also comprise an inductance  708  and a capacitance  709  coupled between the first output terminal  704  of the switching device  702  and ground. 
         [0040]    In the example of  FIG. 11 , the RF integrated circuit also comprises a final stage. The final stage comprises an input terminal  720  and a switching device  711  having a control terminal  713 , a first output terminal  712  and a second output terminal  715 . The control terminal  713  is coupled to the input terminal  720 . A first inductance  716  with a first and second connector, has its first connector coupled to the input terminal  720  via a capacitance  710 . A first capacitance  717  with a first and second connector has its first connector coupled to the second connector of the first inductance  716 , and its second connector coupled to ground. 
         [0041]    In the RF integrated circuit  700  the inductance  724  and the inductance  716  are responsible for the band of operation. By introducing a bond wire  706  and a resistive element  707 , see  FIG. 11 , desired losses are created in the inductance  724 . Similarly, by introducing a bond wire  718  and a resistive element  719  in the final stage of the integrated circuit  700 , desired losses are created in the inductance  716 . By introducing excessive losses at the input of the final stage and/or driver stage it is possible to get stable operation without losing gain. 
         [0042]    In the foregoing specification, the invention has been described with reference to specific examples of embodiments of the invention. It will, however, be evident that various modifications and changes may be made therein without departing from the broader spirit and scope of the invention as set forth in the appended claims. For example, the connections may be any type of connection suitable to transfer signals from or to the respective nodes, units or devices, for example via intermediate devices. Accordingly, unless implied or stated otherwise the connections may for example be direct connections or indirect connections. 
         [0043]    Because the circuits implementing the present invention is, for the most part, composed of electronic components known to those skilled in the art, circuit details will not be explained in any greater extent than that considered necessary as illustrated above, for the understanding and appreciation of the underlying concepts of the present invention and in order not to obfuscate or distract from the teachings of the present invention. Although the invention has been described with respect to specific conductivity types or polarity of potentials, skilled artisans appreciated that conductivity types and polarities of potentials may be reversed. 
         [0044]    It is to be understood that the architectures depicted herein are merely exemplary, and that in fact many other architectures can be implemented which achieve the same functionality. In an abstract, but still definite sense, any arrangement of components to achieve the same functionality is effectively “associated” such that the desired functionality is achieved. Hence, any two components herein combined to achieve a particular functionality can be seen as “associated with” each other such that the desired functionality is achieved, irrespective of architectures or intermedial components. Likewise, any two components so associated can also be viewed as being “operably coupled,” or “operably coupled,” to each other to achieve the desired functionality. 
         [0045]    In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim. The word ‘comprising’ does not exclude the presence of other elements or steps then those listed in a claim. Furthermore, the terms “a” or “an,” as used herein, are defined as one or more than one. Also, the use of introductory phrases such as “at least one” and “one or more” in the claims should not be construed to imply that the introduction of another claim element by the indefinite articles “a” or “an” limits any particular claim containing such introduced claim element to inventions containing only one such element, even when the same claim includes the introductory phrases “one or more” or “at least one” and indefinite articles such as “a” or “an.” The same holds true for the use of definite articles. Unless stated otherwise, terms such as “first” and “second” are used to arbitrarily distinguish between the elements such terms describe. Thus, these terms are not necessarily intended to indicate temporal or other prioritization of such elements. The mere fact that certain measures are recited in mutually different claims does not indicate that a combination of these measures cannot be used to advantage.