Patent Document

TECHNICAL FIELD 
       [0001]    This invention relates generally to thermal management in electronic circuits, and more specifically to methods and apparatus for distributing heat in an oscillator system. 
       BACKGROUND OF THE INVENTION 
       [0002]    Historically, electronic communications systems have relied upon precise clock signals. Without precise clocks, communications systems may be inefficient or even inoperable. One example is the global positioning system (GPS), a space-based system which employs communications signals from satellites to provide location and time information to terrestrial receivers. A GPS receiver uses phase, frequency, and time information from radio frequency signals broadcast by satellites to determine the signals&#39; travel time. A very high precision and high performance clock is used to minimize its Time To First Fix (TTFF) and to maximize performance especially in weak-signal environments. If the clock deviates from a predetermined frequency, then errors in the GPS receiver&#39;s calculations will propagate and grow. Other communications systems, including mobile telephone handsets, wireless local area networks (WLANs), wireless broadband, and base stations, also need high precision clocks. 
         [0003]    Performance of electronic circuits may vary over temperature, including electronic components/devices in portable communications devices. Piezoelectric crystal oscillators, for example, may be used to generate precision clocks in communications systems, but the piezoelectric crystal&#39;s frequency may depend on the temperature. Electronic systems may not only absorb heat from their environment, but also produce heat themselves. Current flowing through active and passive electrical components results in power dissipation and increased temperatures. Greater integration and higher clock speeds result in greater heat generation. This temperature variability in electronic systems may adversely affect the clock signals generated by piezoelectric crystal oscillators and hence the operation of the whole system. Accordingly, there is a need to reliably generate precision clock signals over a range of temperatures. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0004]      FIG. 1  is a simplified block diagram of an electronic system. 
           [0005]      FIG. 2  is a simplified cross-sectional view of an electronic system according to some embodiments of the present invention. 
           [0006]      FIG. 3  is a simplified cross-sectional view of an electronic system according to some embodiments of the present invention. 
           [0007]      FIG. 4  is a simplified cross-sectional view of an electronic system according to some embodiments of the present invention. 
           [0008]      FIG. 5  is a simplified cross-sectional view of a substrate according to various embodiments of the present invention. 
           [0009]      FIG. 6  is a simplified functional block diagram of a wireless device. 
       
    
    
       [0010]    In the figures, elements having the same designation have the same or substantially similar function. The figures are illustrative only and relative sizes and distances depicted in the figures are for convenience of illustration and have no further meaning. 
       DETAILED DESCRIPTION OF THE INVENTION 
       [0011]    In the following description, certain details are set forth below to provide a sufficient understanding of the invention. However it will be clear to one skilled in the art that the invention may be practiced without these particular details. In other instances, well-known circuits, control signals, timing protocols, and software operations have not been shown in detail or omitted entirely in order to avoid unnecessarily obscuring the invention. 
         [0012]      FIG. 1  is a simplified block diagram of an electronic system  100  comprising a circuit  120 , resonator  130 , and heat source  140 . Circuit  120  and resonator  130  together may be referred to as an oscillator  110 . In operation, circuit  120  may apply a voltage to resonator  130 , causing resonator  130  to change its shape. When circuit  120  removes the voltage, resonator  130  may generate a voltage as it returns to its previous shape. Circuit  120  may repeat and maintain this process (i.e., resonator&#39;s  130  oscillations) by amplifying the voltage from resonator  130  and feeding it back to resonator  130 . Circuit  120  may convert the oscillation (pulses) from resonator  130  into signals (e.g., clock signals) suitable for analog and digital circuits. For example, oscillator  110  accuracy may be from 5 PPM to 0.1 PPM. In some embodiments, oscillator  110  has a 0.5 PPM accuracy. As another example, resonator  130  may be a piezoelectric crystal resonator. In various embodiments, resonator  130  is a quartz crystal resonator. In other embodiments, resonator  130  is a microelectromechanical systems (MEMS) resonator. 
         [0013]    Generally the frequency at which piezoelectric crystals oscillate will change with variations in temperature. For example, a crystal oscillator exactly on a predefined frequency (or range of frequencies) at 25° C. with a frequency variation of five parts per million (PPM) per degree Celsius change could experience a frequency offset of 25 PPM with only a 5° C. temperature rise. Since temperature effects on a crystal oscillator are, for the most part, consistent and reproducible, circuits may be designed to compensate for the temperature effects on oscillator frequency. 
         [0014]    Circuit  120  may include circuitry to compensate for temperature variations. For example, circuit  120  may include a temperature sensor and compensation circuitry which may operate with resonator  130  over a predefined range of temperatures. Oscillator  110 , for example, may have an operating temperature range of −40° C. to +85° C. In some embodiments, oscillator  110  has an operating range of −20° C. to +60° C. In operation, circuit  120  may use the compensation circuitry to compensate for temperature effects on the resonator  130 . 
         [0015]    Resonator  130  and circuit  120  (including temperature sensor and compensation network) together may form a temperature compensated crystal oscillator (TCXO). The compensation network may include capacitors, thermistors, compensating elements (e.g., in series), amplifiers, read only memories (ROMs), low dropout regulator (LDO), divider, and phase-lock-loop (PLL), as well as other circuit elements. 
         [0016]    As another example, circuit  120  may include a temperature sensor and an oven controller. Circuit  120  may use the output of the temperature sensor to control an oven. An oven may include a heating element. In operation, resonator  130  may be maintained at a constant temperature, for example, by heating the resonator to a temperature above an expected ambient temperature (e.g., 15° to 20° above the highest temperature to which resonator  130  will likely be exposed). An oven may optionally include a thermally insulated container or enclosure around resonator  130 . Resonator  130  and circuit  120  (including temperature sensor and oven controller) together may form an oven controlled crystal oscillator (OCXO). 
         [0017]    Other combinations and permutations are possible without deviating from the scope of the invention. Resonator  130  and circuit  120  together, for example, may form a voltage-controlled crystal oscillator (VCXO), digitally-controlled crystal oscillator (DCXO), voltage controlled/temperature compensated crystal oscillator (VCTCXO), as well as other oscillator systems. 
         [0018]    Heat source  140  may be one or more components in electronic system  100  which generate heat. Heat source  140 , for example, may be a baseband processor for a portable wireless device (e.g., for use in a global positioning system, cellular network, wireless local area network, wireless wide area network, etc.). Heat generated by heat source  140  may affect the temperature of electronic system  100  and in particular the temperature of circuit  120  and resonator  130 . Temperature compensation in TCXOs and OCXOs may operate properly when the temperature measured by circuit  120  is substantially the same as the temperature experienced by resonator  130 . That is, the amount of compensation provided by circuit  120  for the temperature effect on resonator  130  is based at least on part on the measured temperature. The assumption is that the measured temperature is approximately the same as the temperature of the resonator  130 . If the measured temperature, however, does not accurately reflect the temperature of the resonator  130 , the compensation provided by the compensation circuit of circuit  120  will not effectively compensate for the temperature impact on the resonator  130 . Hence, it is desirable for circuit  120  and resonator  130  to experience substantially the same temperature. 
         [0019]    A different temperature between the circuit  120  and the resonator  130  may result, for example, when due to spatial arrangement circuit  120  receives more heat from heat source  140  than resonator  130 , or resonator  130  receives more heat than circuit  120 . Such an arrangement, for example, may occur when circuit  120 , resonator  130 , and heat source  140  are arranged on the same plane of a substrate (e.g., printed circuit board) and the circuit  120  and the resonator  130  are located at significantly different distances from the heat source  140 . 
         [0020]    To facilitate circuit  120  and resonator  130  being heated to substantially the same amount by the heat from heat source  140 , embodiments of the present invention include at least one of the components (i.e., circuit  120 , resonator  130 , and heat source  140 ) embedded in a substrate onto which the other components may be attached. The other components may be arranged on the substrate in such a manner as to be heated substantially the same amount by the heat from heat source  140 . Embodiments of the present invention may also result in a low profile (i.e., height of components attached to the substrate). 
         [0021]      FIG. 2  illustrates an electronic system  200  according to some embodiments of the present invention. For clarity, the same reference numerals are used to designate elements analogous to those described above in connection with  FIG. 1 . For brevity, the description of  FIG. 1  is not repeated with respect to  FIG. 2 . Coupled to a surface  270  of substrate  220  are package  240  and optionally electrical device(s)  280 . Package  240  may include circuit  120  and resonator  130 . Circuit  120  and resonator  130  are coupled to each other and to package  240 . Heat source  140  may be embedded in substrate  220 , as will be discussed further below. As depicted in  FIG. 2 , circuit  120  and resonator  130  may be arranged horizontally alongside one another (i.e., side by side) on package substrate  260 . In some embodiments, circuit  120  and resonator  130  may be assembled into different packages. 
         [0022]    Electrical devices  280  may be active and/or passive electrical components, such as resistors, capacitors, discrete semiconductors, small ICs, memory (e.g., dynamic random access memory (DRAM), FLASH memory, etc.), controllers (e.g., touch-screen controller), applications processors, accelerometers, compasses, as well as other components. Circuit  120  may be an integrated circuit (IC) in die form or an IC die assembled in a package. In some embodiments of the present invention, circuit  120  may be an IC die assembled into a chip scale package (CSP) or land grid array (LGA). Resonator  130  may be a piezoelectric crystal or a MEMS resonator mounted in a package such as an LGA. 
         [0023]    Package  240  may include package substrate  260  and lid  250 , which may optionally be hermetically sealed. Package  240  may be a multi-chip module (MCM) corresponding to an LGA form factor. Package  240  may also be a laminated MCM with encapsulant applied over circuit  120  and resonator  130  (which are positioned side-by-side in package  240 ), or a system-in-a-package (SiP) with circuit  120  and resonator  130  stacked vertically. Package  240  may also include underfill, thermal gel/paste, and the like. Substrate  260  may be ceramic. Substrate  260  may also be a multi-layer laminated printed circuit board (PCB). Lid  250  may be metal. Lid  250  may also be ceramic or epoxy/plastic, and may include an optional heat spreader. 
         [0024]    In some embodiments where the resonator  130  is a MEMS device, resonator  130  may be stacked on the top of circuit  120  using die attach adhesive (not shown). Such a configuration may be referred to as “stacked die.” Interconnection and signal transfer between  130  and  120  may be through bond wires from the pads on  130  to the pads on  120  (not shown). Bond wires may also be used for interconnect and signal transfer from stacked die resonator  130  and circuit  120  to substrate  220 . In some embodiments, the stacked die resonator  130  and circuit  120  are assembled in package  240  and package  240  is mounted to substrate  220  as described above. Other combinations and permutations are possible within the scope of the invention. Other packaging technologies may be used. 
         [0025]    In practice, electronic system  200  may be a subassembly in a larger assembly (not shown). The surface  270  of substrate  220 , devices  280 , and package  240  may be covered by a metal lid or plastic/epoxy encapsulant  290 . The metal lid or plastic/epoxy encapsulant  290  may facilitate handling of the electronic system  200  by automated manufacturing machines (e.g., pick and place machine) during assembly of the larger assembly. In some embodiments, the combined height h of substrate  220  and metal lid or plastic/epoxy encapsulant  290  may be 1 mm or less. For example, substrate  220  may be 400 μm or less thick, and package  240  substantially covered by metal lid or plastic epoxy encapsulant  290  may be 400 μm or less tall, resulting in a combined height h of 1 mm or less. In some embodiments where resonator  130  is a MEMS resonator, package  240  may be omitted, and circuit  120  and resonator  130  may be coupled to surface  270  of substrate  220 , reducing height h further. 
         [0026]    In operation, heat generated by heat source  140  spreads through printed circuit board  220 . In some embodiments of the present invention, substrate  220  may include a heat conducting plane or layer  230  that may be disposed between heat source  140  and a surface  270  of substrate  220 . The heat conducting plane or layer  230  may contribute to heat distribution in substrate  220 . The heat conducting plane or layer  230  may be a layer of metal, such as copper, and may be substantially solid (with vias) or comprised of signal traces. Heat from heat source  140  may propagate through substrate  220  to package  240 , and within package  240  to circuit  120  and resonator  130 . Accordingly, circuit  120  and resonator  130  in package  240  may be positioned on a surface  270  of substrate  220  to be heated substantially the same amount by heat source  140  embedded within substrate  220 . 
         [0027]    For example, in some embodiments of the present invention, package  240  is approximately centered above heat source  140 . In the embodiment illustrated with reference to  FIG. 2 , the package  240 , which includes circuit  120  and resonator  130  therein, is positioned substantially over the heat source  140  so that the heat generated by the heat source  140  will heat both the circuit  120  and resonator  130  approximately the same. The circuit  120  and resonator  130  may be attached to the package  240  so that both components are approximately in the same horizontal plane. In some embodiments, the circuit  120  and resonator  130  are positioned within the package  240  so that the two are laterally disposed to one another and positioned relative to the heat source  140  within the package  240  to be heated substantially the same by the heat source  140 . For example, the space/distance between the circuit  120  and the heat source  140  is substantially the same as the space/distance between the resonator  130  and the heat source  140 . In some embodiments, the package  240  is located relative to the heat source  140  so that at least a portion of the package  240  is above the heat source  140 . In other embodiments, the package  240  does not overlap (as viewed from above) any portion of the heat source  140 , but positioned so that the circuit  120  and resonator  130  are heated substantially the same by the heat source  140 . 
         [0028]    As may be readily understood by one of ordinary skill in the art, different combinations and permutations are possible within the scope of the present invention. Assembly  210  is depicted in two dimensions such that package  240  may appear to be positioned along one dimension (i.e., left-right). However package  240  may be positioned in two dimensions over surface  270  of substrate  220 . Package  240 , for example, may be positioned on a surface  270  of substrate  220  off-center from heat source  140  embedded in substrate  220 . Heat conducting plane  230  may transfer heat approximately uniformly on the same horizontal plane to both circuit  120  and resonator  130 . It is desirable for the package  240  to be positioned so that circuit  120  and resonator  130  in package  240  are heated substantially the same amount by heat source  140 . 
         [0029]      FIG. 3  depicts an electronic system  300  according to other embodiments of the present invention. For clarity, the same reference numerals are used to designate elements analogous to those described above in connection with  FIGS. 1 and 2 . For brevity, the description of  FIGS. 1 and 2  are not repeated with respect to  FIG. 3 . Coupled to a surface  270  of substrate  220  are package  240  and optionally electrical devices  280 . Package  240  may include resonator  130 . Circuit  120  may be embedded in substrate  220 . 
         [0030]    Circuit  120 , for example, may be an IC in die form or an IC die assembled in a package. In some embodiments of the present invention, circuit  120  may be an IC die assembled into a CSP or LGA. Resonator  130  may be a piezoelectric crystal mounted in package  240 . Package  240  may be an LGA including package substrate  260  and lid  250 , which may optionally be hermetically sealed. Other combinations and permutations are possible within the scope of the invention. For example, other packaging technologies may be used in place of or in addition to those described above. In other embodiments, resonator  130  may be a MEMS die coupled to surface  270  of substrate  220  and package  240  may be omitted. 
         [0031]    Heat source  140 , optional heat conducting plane  230 , and metal lid or plastic/epoxy encapsulant  290  are analogous to that of  FIG. 2  except as described below. For brevity, the description of  FIG. 2  is not repeated with respect to  FIG. 3 . In operation, heat generated by heat source  140  spreads through printed circuit board  220 . In some embodiments of the present invention, heat is distributed through substrate  220  with optional heat conducting plane  230 . Heat from heat source  140  travels through substrate  220  to package  240 , within package  240  to resonator  130 , and to circuit  120  in substrate  220 . Accordingly, circuit  120  in substrate  220  and resonator  130  in package  240  may be positioned relative to each other to be heated substantially the same amount by heat source  140  within substrate  220 . 
         [0032]    In some embodiments of the present invention, package  240  is approximately centered above circuit  120 . Although shown in  FIG. 3  as having the resonator  130  located in the package  240  and the circuit  120  embedded in the substrate  220 , in other embodiments the circuit  120  may be located in the package  240  and the resonator  130  embedded in the substrate  220 . As illustrated for the embodiment of  FIG. 3 , at least one of the circuit  120  or oscillator  130  is embedded in the substrate  220 . Additionally, although the heat source  140  is illustrated in  FIG. 3  as being embedded in the substrate  220 , in some embodiments the heat source  140  may be coupled to the surface  270  of the substrate  220 . 
         [0033]    As can be readily understood by one of ordinary skill in the art, different combinations and permutations are possible within the scope of the present invention. For example, assembly  310  is depicted in two dimensions such that package  240  may appear to only be positioned along one dimension (i.e., left-right). However package  240  may be positioned in two dimensions over surface  270  of substrate  220 . Package  240 , for example, may be positioned on a surface  270  of substrate  220  off-center from circuit  120  embedded in substrate  220 . Heat conducting plane  230  may transfer heat approximately uniformly on the same horizontal plane to both circuit  120  and resonator  130 . It is desirable for the position of package  240  is that circuit  120  in substrate  220  and resonator  130  in package  240  be heated substantially the same amount by heat source  140 . 
         [0034]      FIG. 4  depicts an electronic system  400  according to some embodiments of the present invention. For clarity, the same reference numerals are used to designate elements analogous to those described above in connection with  FIGS. 1 ,  2 , and  3 . For brevity, the description of  FIGS. 1 ,  2 , and  3  are not repeated with respect to  FIG. 3 . Embedded in substrate  220  are circuit  120  and resonator  130 . As depicted in  FIG. 4 , heat source  140  may be embedded in substrate  220  and/or coupled to surface  270  of substrate  220 . 
         [0035]    In operation, heat generated by heat source  140  may propagate through substrate  220  to circuit  120  and resonator  130 . In some embodiments of the present invention, substrate  220  may include a heat conducting plane or layer  230  that may be disposed between heat source  140  and circuit  120  and resonator  130 . The heat conducting plane or layer  230  may contribute to heat distribution in substrate  220 . Accordingly, circuit  120  and resonator  130  may be positioned in substrate  220  to be heated substantially the same amount by heat source  140 . 
         [0036]    For example, in some embodiments of the present invention, circuit  120  and resonator  130  are approximately centered below heat source  140 . In the embodiment illustrated with reference to  FIG. 4 , circuit  120  and resonator  130  are positioned substantially below heat source  140  so that the heat generated by the heat source  140  will heat both the circuit  120  and resonator  130  approximately the same. Circuit  120  and resonator  130  may be embedded in substrate  220  so that both components are approximately in the same horizontal plane. In some embodiments, the circuit  120  and resonator  130  are positioned within the package  240  so that the two are laterally disposed to one another and positioned relative to the heat source  140  in substrate  220  to be heated substantially the same by the heat source  140 . For example, the space/distance between the circuit  120  and the heat source  140  is substantially the same as the space/distance between the resonator  130  and the heat source  140 . 
         [0037]    In embodiments of the present invention, circuit  120 , resonator  130 , and heat source  140  are embedded in substrate  220 . Circuit  120 , resonator  130 , and heat source  140  may occupy the same horizontal plane. As depicted in  FIG. 4 , circuit  120 , resonator  130 , and heat source  140  may appear to be arranged in one dimension (left-right). However, circuit  120 , resonator  130 , and heat source  140  may be arranged in substrate  220  in two dimensions so that circuit  120  and resonator  130  are heated substantially the same amount by heat source  140 . For example, the space/distance between the circuit  120  and the heat source  140  is substantially the same as the space/distance between the resonator  130  and the heat source  140 . Heat conducting plane  230  may transfer heat approximately uniformly on the same horizontal plane to both circuit  120  and resonator  130 . 
         [0038]    As may be readily understood by one of ordinary skill in the art, different combinations and permutations are possible within the scope of the present invention. Assembly  410  is depicted in two dimensions such that heat source  140  may appear to be positioned along one dimension (i.e., left-right). However heat source  140  may be positioned in two dimensions over surface  270  of substrate  220 . Heat source  140 , for example, may be positioned on a surface  270  of substrate  220  off-center from circuit  120  and resonator  130  in substrate  220 . Heat conducting plane  230  may transfer heat approximately unifomrly on the same horizontal plane to both circuit  120  and resonator  130 . It is desirable for circuit  120  and resonator  130  in substrate  220  to be positioned so that circuit  120  and resonator  130  are heated substantially the same amount by heat source  140 . 
         [0039]    As another example, circuit  120  and heat source  140  may be included in the same integrated circuit die (not depicted). In some embodiments, the combined circuit  120  and heat source  140  work in conjunction with resonator  130 . The combined circuit  120  and heat source  140  may be coupled to surface  270  of substrate  220  or embedded in substrate  220 . Resonator  130  may also be coupled to surface  270  of substrate  220  or embedded in substrate  220 . It is desirable for resonator  130  to be arranged so that circuit  120  (in the combined circuit  120  and heat source  140 ) and resonator  130  are heated substantially the same amount by heat source  140  (in the combined circuit  120  and heat source  140 ). 
         [0040]    In some embodiments of the invention, the arrangement of the resonator  130  and the circuit  120  may result in an encapsulated package that has a lower profile compared to conventional arrangements, for example, the resonator  130  and circuit  120  stacked within the package  240  that is attached to a surface of the substrate  220 . For example, the embodiment illustrated in  FIG. 2  may have a lower profile due to the side-by-side arrangement of the resonator  130  and circuit  120  in the package  240 . The embodiment illustrated in  FIG. 3  may also have a lower profile resulting from having the resonator  130  (or circuit  120 ) disposed in the package  240  and the circuit  120  (or resonator  130 ) embedded in the substrate  220 . Although not a requirement of the present invention, some embodiments may, however, provide the desirable benefit of a lower profile. 
         [0041]      FIG. 5  illustrates a cross-sectional view of a simplified printed circuit board (PCB) stackup including embedded component(s) and conventionally mounted component(s). Embedded component  525  may be attached to first layer  510 . First layer  510 , second layer  520 , third layer  530 , and fourth layer  540  may be stacked and may be pressed/bonded together to form a substrate. Vias or bumps  515  may be formed and filled for electrical coupling to the inputs/outputs (I/Os) of embedded component  520 . Metal foil on first layer  510  and fourth  540  layer may be patterned, etched, and plated. One or more conventionally mounted components  560  may be attached on the first layer  510  and/or fourth layer  540  using surface mount technology (SMT). 
         [0042]    First layer  510 , for example, may be a dielectric material with a layer of metal foil bonded on one side. Second layer  520  may be a dielectric material and may include a mechanically- and/or chemically-created opening for embedded component  525 . Third layer  530  and fourth layer  530  may be a dielectric material having a thin layer of metal foil bonded on one side. The dielectric materials of the first layer  510 , second layer  520 , third layer  530 , and fourth layer  540  may be cured (i.e., core) or uncured (i.e., prepreg) fiberglass-epoxy resin, such as FR-4, CEM, BT-Epoxy, polyimide, Teflon (polytetrafluoroethylene), and the like. The metal foil may be copper foil. 
         [0043]    Various combinations and permutations may be used without deviating from the scope of the present invention. The substrate may have a different number of (metal) layers (e.g., 2-24 layers). In some embodiments of the present invention, the substrate includes six layers. Although only one embedded component  525  and one conventionally mounted component  560  are depicted in  FIG. 5 , different numbers of embedded components  525  and conventionally mounted components  560  may be included. 
         [0044]      FIGS. 2-5  are simplified and offered by way of illustration only. As such,  FIGS. 2-5  do not show particular terminal configurations or electrical connections to packages, substrates, or layers. 
         [0045]      FIG. 6  illustrates a simplified functional block diagram of a portable wireless device  600 . Portable wireless device  600  comprises an antenna block  610 , radio frequency (RF) receiver/transmitter block  620 , TCXO block  630 , baseband and logic block  640 , and microcontroller block  650 . Antenna block  610  may be a transducer which transmits and receives electromagnetic waves and converts it into electric current. RF receiver/transmitter block  620  may receive the electric current from antenna block  610  and produce electrical signals based thereon, and/or drive electric current in antenna block  610 . Baseband and logic block  640  may convert the analog signal from the RF receiver/transmitter block  620  to a digital signal (and vice-versa) and may perform application-specific processing of the digital signal (e.g., location determination in a GPS receiver, data decoding/encoding in a wireless networking device, sound/voice decoding/encoding in a cell phone, etc.). TCXO block  630  may provide a high-precision clock. Microcontroller block  550  may provide a user interface, and/or run applications. 
         [0046]    Antenna block  610  may be designed for a specific frequency or range of frequencies. Antenna block  610  may be omnidirectional. RF receiver/transmitter, block  620  may include a low-noise amplifier (LNA), band-pass filter (BPF), and mixer. In some embodiments, RF receiver/transmitter block  620  includes only one of a receiver or transmitter (e.g., a GPS receiver may only include a receiver). Baseband and logic block  640  may include a digital signal processor (DSP), memory (e.g., SDRAM), memory management unit, input/output (I/O), and the like. TCXO block  630  may also, for example, be an OXCO and/or VCTCXO. In some embodiments, baseband and logic block  640  may be combined with a portion of the TCXO block on one integrated circuit die. In these embodiments, an oscillator (e.g., crystal or MEMS oscillator) may be used in conjunction with the one integrated circuit die. Microcontroller block  650  may include an interrupt controller, microcontroller, programmable I/O, etc. The microcontroller in microcontroller block  650  may be connected to the memory management unit in baseband and logic block  640 . 
         [0047]    From the foregoing, it will be appreciated that, although specific embodiments of the invention have been described herein for purposes of illustration, various modifications may be made without deviating from the spirit and scope of the invention. Such modifications are well within the skill of those ordinarily skilled in the art. Accordingly, the invention is not limited except as by the appended claims.

Technology Category: h