Abstract:
A method of utilizing passive circuit components in an integrated circuit comprising the steps of providing a plurality of integrated capacitive elements and a plurality of integrated inductive elements interconnected to form an electrical circuit wherein each inductive element has a width and creates a circumferential magnetic field. Each integrated inductive element is oriented such that the circumferential magnetic field is parallel to the plane of each adjacent integrated capacitive element and parallel to the width of the integrated inductive element so that the resistance of the electrical circuit is decreased and the quality factor is increased.

Description:
FIELD OF THE INVENTION  
         [0001]    This invention relates to multilayer integrated electronic circuits.  
           [0002]    More particularly, the present invention relates to electrical integrated circuits which utilize integrated capacitors and inductors.  
         BACKGROUND OF THE INVENTION  
         [0003]    Integrated circuits utilize a variety of circuit elements to process electrical signals. The circuit elements fall into two categories. One category includes active elements, such as transistors. The second category includes passive elements, such as resistors, capacitors, and inductors. Passive elements play an important role in signal processing circuitry, such as in electronic filters.  
           [0004]    However, the integration of passive elements into an integrated circuit creates numerous problems. One problem that arises is that electrical coupling between adjacent circuit elements within the same section can increase the crosstalk and noise within the electrical circuit. Crosstalk and noise may produce unwanted transmissions and results in performance degradation in communication systems utilizing these components. For example, FIG. 1 illustrates an isometric view of an integrated circuit  5  used in the prior art which utilizes an integrated inductive element  10  with a resistance and an integrated capacitive element  12  positioned adjacent to or within a dielectric substrate  7 , wherein integrated capacitive element  12  defines a surface. Integrated inductive element  10  has a width  15  that is parallel with the surface of integrated capacitive element  12 . Further, integrated inductive element  10  induces a circumferential magnetic field  17  that is perpendicular to both the surface of integrated capacitive element  12  and width  15 . Circumferential magnetic field  17  will therefore induce eddy currents which will impede the current flow and increase the resistance of integrated inductive element  10 . Circumferential magnetic field  17  will also make the current density across width  15  non-uniform, i.e. in this example, the current density along the inner edge of integrated inductive element  10  is approximately twice the current density along the outer edge. Consequently, the increased resistance of integrated inductive element  10  will degrade the quality factor and performance of the circuit.  
           [0005]    Crosstalk also occurs between circuit elements of different circuit sections. One method to decrease the electrical coupling between adjacent circuit sections is to insert an isolation wall. For example, FIG. 2 illustrates a prior art elliptical filter  20  which utilizes two adjacent elliptical filter sections  22  and  24  separated by an isolation wall  26 . The primary coupling occurs between the inductive components in adjacent circuit sections. The purpose of isolation wall  26  is to prevent the induced circumferential magnetic field from elliptical filter section  22  from penetrating into elliptical filter section  24 , and vice versa. However, the problem with using isolation wall  26  is that the size of the circuit is increased because the elliptical sections must be spaced further apart to accommodate the isolation wall. Thus, an isolation wall has a size that is prohibitive and dramatically increases the cost of the electronic circuit.  
           [0006]    It would be highly advantageous, therefore, to remedy the foregoing and other deficiencies inherent in the prior art.  
         SUMMARY OF THE INVENTION  
         [0007]    A method of utilizing passive circuit components in an integrated circuit involves orienting the integrated inductive elements at an angle with the integrated capacitive elements and with the width of the integrated inductive elements so as to minimize the magnitude of the eddy currents induced by the circumferential magnetic field created by the integrated inductive elements. The method also involves orienting adjacent integrated inductive elements so that the circumferential magnetic fields are anti-parallel in between integrated inductive elements and, consequently, cancel to minimize electromagnetic coupling. Minimizing electromagnetic coupling significantly reduces the crosstalk between adjacent inductive elements and improves the quality factor and frequency response of the integrated circuit. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]    The foregoing and further and more specific objects and advantages of the instant invention will become readily apparent to those skilled in the art from the following detailed description of a preferred embodiment thereof taken in conjunction with the following drawings:  
         [0009]    [0009]FIG. 1 is an isometric view of a prior art microstrip integrated inductor element interconnected with an integrated capacitor element;  
         [0010]    [0010]FIG. 2 is a plan view of a prior art elliptical filter which utilizes an isolation wall;  
         [0011]    [0011]FIG. 3 is an isometric view of an improved microstrip integrated inductor element interconnected with an integrated capacitor element;  
         [0012]    [0012]FIG. 4 is a plan view of an elliptical filter section illustrating the coupling between adjacent integrated inductor elements;  
         [0013]    [0013]FIG. 5 is a plan view of an improved elliptical filter section illustrating the reduced coupling between adjacent integrated inductor elements; and  
         [0014]    [0014]FIG. 6 is a plot illustrating the frequency response of an elliptical lowpass filter.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0015]    Turn now to FIG. 3, which illustrates an isometric view of an improved microstrip integrated circuit apparatus  30  in accordance with the present invention. The main purpose of this illustration is to demonstrate the basic idea behind minimizing the electromagnetic coupling between adjacent circuit elements. Hence, microstrip integrated circuit apparatus  30  will be used to illustrate the method of integrating passive circuit components within an integrated circuit so as to minimize the crosstalk and noise between circuit elements and improve the quality factor and performance.  
         [0016]    Microstrip integrated circuit apparatus  30  includes a dielectric substrate  33  onto which an integrated capacitive element  38  is positioned wherein integrated capacitive element  38  defines a surface. It will be understood that dielectric substrate  33  can include any suitable material, such as a low temperature cofired ceramic or a laminated ceramic, and can include multiple layers. By including multiple layers, the metal interconnects can be distributed both on and/or within the dielectric substrate. Metal interconnects positioned within the dielectric substrate minimizes the required area necessary to hold an electronic circuit since now the metal interconnects can be routed in three dimensions.  
         [0017]    An integrated inductive element  34  which has a width  31  is also positioned adjacent to or within dielectric substrate  33  and is interconnected with integrated capacitive element  38 . Further, integrated inductive element  34  has a resistance and an inductance and creates a circumferential magnetic field  36 . In this preferred embodiment, integrated inductive element  34  includes one metal coil and is formed within multiple layers of dielectric substrate  33  with each layer being interconnected by a via  37 . However, it will be understood that integrated inductive element  34  can include any number of metal coils and the use of one metal coil in this embodiment is for illustrative purposes only.  
         [0018]    In this preferred embodiment, integrated inductive element  34  has been rotated 90° with respect to the plane of integrated capacitive element  38 . Hence, circumferential magnetic field  36  is now parallel to the plane of integrated capacitive element  38  and width  31 . Consequently, the eddy currents induced by circumferential magnetic field  36  are significantly reduced and the current density along width  31  is more uniform. As a result, the resistance of integrated inductive element  34  is decreased and the quality factor of microstrip integrated circuit apparatus  30  is significantly improved.  
         [0019]    Thus, the method of utilizing passive circuit components in an integrated circuit involves orienting the integrated inductive element relative to the integrated capacitive element such that the induced circumferential magnetic field creates a minimal amount of eddy currents in the integrated capacitive element. The reduction of the eddy current results in equal current distribution on the conductor edges thereby minimizing the resistance of the integrated inductive element. Further, it will be understood that the improved method can be used in any integrated circuit that utilizes inductive and capacitive elements.  
         [0020]    Turn now to FIG. 4 which illustrates a plan view of another embodiment of an elliptical filter  40 . The main purpose of this illustration is to show the crosstalk that occurs between circuit elements of different circuit sections. In this embodiment, elliptical filter  40  utilizes two adjacent elliptical filter sections  44  and  46 . However, it will be understood that elliptical filter  40  can include more than two elliptical filter sections. Also in this embodiment, elliptical filter section  44  includes an integrated inductive element  48  and an integrated capacitive element  58  and elliptical filter section  46  includes an integrated inductive element  54  and an integrated capacitive element  55 . Integrated inductive elements  48  and  54  include a metal coil  50  and a metal coil  56 , respectively. Also, each metal coil of integrated inductive elements  48  and  54  has a width  52 . It will be understood that inductive elements  48  and  54  can include one or more metal coils, but are shown to include two metal coils in this embodiment for illustrative purposes only.  
         [0021]    Elliptical filter sections  44  and  46  each have a circumferential magnetic field  47  and  57 , respectively. Magnetic fields  47  and  57  are both oriented in a clockwise direction  41 . Hence, the circumferential magnetic fields are in phase in the area between elliptical filter sections  44  and  46  and, consequently, elliptical filter sections  44  and  46  are electromagnetically coupled.  
         [0022]    Turn now to FIG. 5 which illustrates an improved embodiment of an elliptical filter  60 . The main purpose of this illustration is to show that the electromagnetic coupling that occurs between circuit elements of different sections can be decreased by orienting the integrated inductive element in elliptical filter section  44  with the integrated inductive element in elliptical filter section  46 . The rotation direction of the circumferential magnetic fields can be controlled by changing the orientation of the inductor coils.  
         [0023]    For example, in FIG. 5 elliptical filter sections  44  and  46  each have circumferential magnetic fields  47  and  67 , respectively, only in this preferred embodiment, the circumferential magnetic field in elliptical section  66  is now oriented in a counter clockwise direction  42  while the circumferential magnetic field in elliptical section  44  is still oriented in clockwise direction  41 . The change in rotation direction is accomplished by making elliptical filter section  66  identical to elliptical filter section  44 , only rotated by 180°. Hence, the circumferential magnetic fields are anti-parallel in the area between elliptical filter sections  44  and  66  and, consequently, the circumferential magnetic fields essentially cancel. Thus, the electromagnetic coupling between elliptical filter sections  44  and  66  is significantly reduced.  
         [0024]    It will be understood that although elliptical filter section  44  and  66  are shown to be identical, the circumferential magnetic fields can be made to cancel in the area between the sections by making the inductance of integrated inductive element  48  substantially equal to integrated inductive element  62 . It is well known in the art that the inductance of an inductor is determined by the number of metal coils, the width of the metal coils, and the volume of the inductor element.  
         [0025]    In this preferred embodiment, elliptical filters are used to illustrate the improved method of utilizing passive circuit components in an integrated circuit. However, this method can also be used in other integrated circuits, such as high pass filters, band pass filter, low pass filters, voltage controlled oscillators, series resonant circuits, parallel resonant circuits, or any other integrated circuit that includes passive inductive elements or passive inductive and capacitive elements. b The reduction in electromagnetic coupling between elliptical filter  40  illustrated in FIG. 4 and improved elliptical filter  60  illustrated in FIG. 5 can be seen in a plot of the frequency response  70  illustrated in FIG. 6. The plot includes a frequency response  72  of elliptical filter  40  and a frequency response  74  of improved elliptical filter  60 . As can be seen in FIG. 6, the rejection ratio at high frequency is approximately 10 dB less for improved elliptical filter  60  indicating that the electromagnetic coupling has been significantly reduced.  
         [0026]    Thus, integrated inductive and capacitive passive elements can be integrated into an integrated circuit and oriented so as to minimize the crosstalk and noise in the system. Also, the resistance of the integrated inductive element can be reduced so that the quality factor of the integrated circuit is improved. The integration of passive components can be done without using an isolation wall, and, consequently, the size and cost of the integrated circuit can be substantially decreased.  
         [0027]    Various changes and modifications to the embodiments herein chosen for purposes of illustration will readily occur to those skilled in the art. To the extent that such modifications and variations do not depart from the spirit of the invention, they are intended to be included within the scope thereof which is assessed only by a fair interpretation of the following claims.