Abstract:
A power-supply filter that is built into an integrated circuit package is disclosed. An LC, RC, or RLC filter is built into the integrated circuit&#39;s chip carrier module and connected so as to filter the power supply entering the integrated circuit. By manufacturing the filter as part of the integrated circuit package, a chip manufacturer can eliminate the need for application-level developers to provide an external filtering network in the deployment of the integrated circuit in an application circuit.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention is directed generally toward integrated circuit technology. More specifically, the present invention is a power supply filter built into the chip carrier module of an integrated circuit.  
           [0003]    2. Background of the Invention  
           [0004]    Power supply noise is a fact of life in high-speed integrated circuit design. Particularly susceptible to such noise are high-frequency switching circuits, where load-induced switching noise may enter the power supply rails of the circuit, causing such problems as ground bounce.  
           [0005]    Phase-locked loops (PLLs), in particular, are quite sensitive to this noise. For this reason, sensitive subcircuits such as a PLL often have their own dedicated power supply terminals that are separate from the power supply terminals of the other components. But although a PLL can be manufactured in an integrated circuit with dedicated power supply rails, it is not easily deployed in practice, since external filtering networks must be carefully designed to allow power supply noise from interfering with the operation of the PLL. This filter network design process is difficult and time-consuming. Thus ideally, an application-level developer would prefer not to have to design power supply filter networks to use with PLLs or other integrated circuits. It would be preferable, then, for the filter circuitry to be somehow incorporated into the integrated circuit package itself, so that an application-level developer need not be concerned with the design of the filter; it would simply be prefabricated for immediate use.  
           [0006]    Ideally, this filter would be located on the integrated circuit itself to reduce the effects of parasitic inductance&#39;s and resistance&#39;s of connecting wires. This is not a practical solution, however, since at high frequencies, inductors are needed within the filter networks, and inductors are impractical to fabricate or simulate (e.g., with so-called “gyrator” circuits) in a silicon chip. Also, it should be noted that at low frequencies, although inductors are not necessary, relatively large capacitors are necessary, and these capacitors are not particularly practical to implement in an integrated circuit, either. Capacitors, in general, tend to take up a disproportionately large amount of space on an integrated circuit. Including a large number of capacitors on a integrated circuit may also cause leakage currents to be generated, which is also undesirable.  
           [0007]    Thus, what is needed is an integrated circuit, and in particular a PLL integrated circuit, that eliminates the need for external power supply filtering in an application circuit.  
         SUMMARY OF THE INVENTION  
         [0008]    The present invention provides a power-supply filter that is built into an integrated circuit package. An LC, RC, or RLC filter is built into the integrated circuit&#39;s chip carrier module and connected so as to filter the power supply entering the integrated circuit. By manufacturing the filter as part of the integrated circuit package, a chip manufacturer can eliminate the need for application-level developers to provide an external filtering network in the deployment of the integrated circuit in an application circuit.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]    The novel features believed characteristic of the invention are set forth in the appended claims. The invention itself, however, as well as a preferred mode of use, further objectives and advantages thereof, will best be understood by reference to the following detailed description of an illustrative embodiment when read in conjunction with the accompanying drawings, wherein:  
         [0010]    [0010]FIG. 1 is a diagram depicting the internals of an integrated circuit package in accordance with a preferred embodiment of the present invention;  
         [0011]    [0011]FIG. 2 is an electrical diagram depicting a preferred embodiment of the present invention;  
         [0012]    [0012]FIG. 3 depicts a T filter wherein one of the inductors is located on the circuit board, rather than on the chip module in accordance with a preferred embodiment of the present invention;  
         [0013]    [0013]FIG. 4 depicts a filter where both inductors are located on the chip module in accordance with a preferred embodiment of the present invention;  
         [0014]    [0014]FIG. 5 depicts a filter having a second off-module capacitor in parallel with the on-module capacitor in accordance with a preferred embodiment of the present invention;  
         [0015]    [0015]FIG. 6 depicts a T filter wherein one of the arms of the filter is an off-module resistor; and  
         [0016]    [0016]FIG. 7 depicts a variation on the filter in FIG. 5, wherein an additional inductor is connected between to the two capacitors.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0017]    [0017]FIG. 1 is a diagram depicting the internals of an integrated circuit package  100  in accordance with a preferred embodiment of the present invention. Integrated circuit package  100  would normally include a top portion that would hermetically seal the contents of integrated circuit package  100 , but the top portion has been removed in FIG. 1 so that the internal components of integrate circuit package  100  can be seen.  
         [0018]    Integrated circuit package  100  contains a monolithic integrated circuit  102 , which may be constructed of doped silicon (Si), gallium arsenide (GaAs), or any other suitable material. Integrated circuit  102  is mounted on a chip carrier substrate  104 , which is preferably constructed of some type of electrical insulator, such as plastic or ceramic. Integrated circuit package  100  contains a number of electrical contacts  106 , which allow integrated circuit package  100  to be used as a component in a larger circuit, manufactured, for instance, on a printed circuit board. Wires, such as wire  107 , connect integrated circuit  102  to contacts  106 . Other forms of connection between integrated circuit  102  and contacts  106  are possible, however, and the present invention does not require the use of any particular connection scheme. For instance, solder bumps placed below integrated circuit  102  may be used or a “bumpless” design such as that described in “Intel Technology Promises 20 GHz Chips,”  Computer , IEEE Computer Society, December 2001, pp.25-27 may be used.  
         [0019]    Contacts  106  are small balls of metal (such as solder balls) arranged in a grid. For this reason, integrated circuit package  100  is called a ball grid array (BGA). Many other different kinds of integrated circuit packages could be used in practice without departing from the scope and spirit of the present invention. Other integrated circuit package types include, but are by no means limited to, dual inline pin (DIP), single inline pin (SIP), pin grid array (PGA), plastic leadless chip carrier (PLCC), and the like. The choice of integrated circuit package type can have a significant effect on the frequency response of the complete integrated circuit package. For instance, each of contacts  106  has a particular level of inductance that must be taken into account in determining the frequency response of integrated circuit package  100  as a whole. Part of the motivation behind the present invention is to reduce the effects of these inductances on integrated circuit  102 &#39;s power supply rails.  
         [0020]    Also mounted on chip carrier substrate  104  are filter components  108 . Filter components  108  make up a filter circuit for filtering the power supply of sensitive subcircuits of integrated circuit  102 . Filter components  108  may include capacitors, inductors, resistors or any other circuit component suitable for inclusion within a filter. In a preferred embodiment, filter components  108  include a ceramic capacitor and one or more ferrite bead inductors. Filter components  108  are here depicted as surface components that are soldered to metal circuit traces  110  on substrate  104 , filter components  108  may comprise conventional leaded circuit components or any other form of circuit components suitable for assembly on or in substrate  104 .  
         [0021]    [0021]FIG. 2 is an electrical diagram depicting a preferred embodiment of the present invention. Power supply line AVdd  200  provides power to at least a portion of integrated circuit  202 , which is mounted on substrate  204 . Ferrite bead  206 , capacitor  208 , and ferrite bead  210 , surface mount components, are mounted to substrate  204  and connected in a standard low-pass T filter configuration, as depicted in FIG. 4. Ferrite bead  206 , capacitor  208 , and ferrite bead  210  filter the incoming power supply voltage AVdd  200  and supply power to AVdd connection  232  of integrated circuit  202 .  
         [0022]    As the components mounted on substrate  204  are all connected using wires or other conductors, parasitic effects of these conductors appear as parasitic components ( 212 - 227 ). In particular, parasitic resistance  224  and parasitic inductance  226  are a function of the contacts (e.g., contacts  106  in FIG. 1) used, whether they be pins, balls, vias, or other types of contacts, since circuit board ground  230  is connected to integrated circuit  202  through one or more metal contacts.  
         [0023]    Capacitor  208  and ferrite bead  210  not only reduce noise from AVdd  200 ; they also reduce ground bounce (i.e., variation in the integrated circuit&#39;s ground that is not reflected in the overall circuit board ground) that may occur at circuit ground  228 , which is the ground connection for integrated circuit  202 . Without capacitor  208  and ferrite bead  210 , ground bounce could occur at circuit ground  228  because of the effects of parasitic components  220 ,  222 ,  224 , and  226 . Since parasitic components  220 ,  222 ,  224 , and  226  appear as a high impedance high-frequency signals, a high frequency voltage could be dropped across parasitic components  220 ,  222 ,  224 , and  226 , which would result in ground bounce at circuit ground  228 .  
         [0024]    Including capacitor  208  and ferrite bead  210  creates a loop containing capacitor  208 , ferrite bead  210 , parasitic components  212  and  214 , integrated circuit  202  (which can be modeled as a capacitor  203 ), and parasitic components  216 ,  218 ,  225 , and  227 . In practice, the circuit components will be arranged so that parasitic components  216  and  218  appear as a lower impedance than parasitic components  220  and  222  (e.g., by keeping the conductor lengths in the loop short). High frequency noise at circuit ground  228  then has a low impedance path to follow through the loop, bypassing the path used by high transient currents resulting from I/O or core circuits in integrated circuit  102 , namely the path to ground formed by parasitic components  220 - 244  and  226 . The high-frequency noise is voltage-dropped across ferrite bead  210 , which reduces or eliminates the ground bounce at circuit ground  228 .  
         [0025]    In practice, when a T-configuration filter such as is shown in FIG. 2 is used, the value of the capacitor and the inductor closest to the integrated circuit (e.g., capacitor  208  and ferrite bead  210 ) are more critical to filter operation than is the other inductor (e.g., ferrite bead  206 ). Hence, it is more important for these more critical components to be placed on the substrate (also called a module). Thus, some variation with respect to the locations of the filter components is possible. FIGS.  3 - 6  depict a number of possible variations on the basic T filter described in FIG. 2.  
         [0026]    [0026]FIG. 3 depicts a T filter wherein inductor  300 , which represents the arm of the “T” that is connected to the external power source AVdd  301 , is located on the circuit board, rather than on the chip module (substrate). Capacitor  304  and inductor  302 , which make up the trunk and second arm of the “T,” are located on the chip module, with inductor  302  being connected to AVdd input  303  of the integrated circuit. FIG. 4 depicts the “T” filter described in FIG. 2, where inductor  400 , which is connected to AVdd  401 , is located on the module.  
         [0027]    [0027]FIG. 5 depicts another variation on the basic T-filter in which two capacitors  500  and  502  are used. In some circumstances it may be desirable to have one capacitor ( 500 ) located on the circuit board in parallel with the capacitor on the chip module ( 502 ). For instance, ceramic capacitors are easily manufactured as surface-mount components and have a high “quality factor” (also known as “Q” to those skilled in the art). Tantalum capacitors, on the other hand, have a low “Q,” but can be too bulky to be placed on the chip module. When a low “Q” is desired, then, a tantalum capacitor, such as capacitor  500 , can be wired in parallel with the ceramic capacitor ( 502 ) on the module.  
         [0028]    [0028]FIG. 6 depicts yet another variation on the basic T filter. A resistor  600  or other component (such as a linear regulator, for example) may be used in place of or in addition to the inductor (e.g.,  300  in FIG. 3) that would normally be connected to the power supply.  
         [0029]    [0029]FIG. 7 depicts an additional variation on the circuit in FIG. 5 in which an additional inductor  704 , which is on the circuit board, rather than the module, is connected between on-board capacitor  700  and on-module capacitor  702 .  
         [0030]    The description of the present invention has been presented for purposes of illustration and description, and is not intended to be exhaustive or limited to the invention in the form disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art. The embodiment was chosen and described in order to best explain the principles of the invention, the practical application, and to enable others of ordinary skill in the art to understand the invention for various embodiments with various modifications as are suited to the particular use contemplated.