Abstract:
Reducing coupling and mismatch in multi-core VCOs, including: arranging a plurality of inductors in a plurality of VCO cores in a parallel differential inductor configuration with shared leads to form a single node, wherein the plurality of inductors includes at least a first inductor and a second inductor; connecting power/ground traces to the first inductor from a first side only; and connecting the power/ground traces to the second inductor from another side different from the first side only to avoid making a current loop.

Description:
BACKGROUND 
       [0001]    1. Field 
         [0002]    This invention relates to multi-core voltage-controlled oscillators (VCOs), and more specifically, to coupling and mismatch in the power/ground trace routing of the multi-core VCOs. 
         [0003]    2. Background 
         [0004]    Recent developments in wireless communication technology have allowed an entire radio frequency (RF) transceiver to be implemented on a single semiconductor chip. However, integrating the RF transceiver on a single chip presents a number of challenges. For example, a single-chip solution may require at least two voltage-controlled oscillators (VCOs) to be running on the chip at the same time. Such a configuration may produce undesired interaction between the cores of the VCOs due to various types of mutual coupling mechanisms, which may result in spurious receiver responses and unwanted frequencies in the transmit spectrum. The primary mutual coupling mechanism is the electromagnetic (EM) coupling between the inductors and/or capacitors of the resonators. 
       SUMMARY 
       [0005]    The present invention provides methods, systems, and apparatus for reducing coupling and mismatch caused by the power/ground trace routing in multi-core VCOs. 
         [0006]    In one embodiment, a method for reducing coupling and mismatch in multi-core voltage-controlled oscillators (VCOs) is disclosed. The method includes: arranging a plurality of inductors in a plurality of VCO cores in a parallel differential inductor configuration with shared leads to form a single node, wherein the plurality of inductors includes at least a first inductor and a second inductor; connecting power/ground traces to the first inductor from a first side only; and connecting the power/ground traces to the second inductor from another side different from the first side only to avoid making a current loop. 
         [0007]    In another embodiment, a system of multi-core VCOs is disclosed. The system includes: a plurality of VCO cores, each VCO core comprising at least one inductor and a bank of capacitors and devices, the at least one inductor in each VCO core forming a plurality of inductors, wherein the plurality of inductors, including at least a first inductor and a second inductor, is arranged in a parallel differential inductor configuration with shared leads to form a single node; a first connector configured to connect power/ground traces to the first inductor from a first side only; and a second connector configured to connect to the power/ground traces to the second inductor from another side different from the first side only to avoid making a current loop. 
         [0008]    In another embodiment, a multi-core VCO apparatus configured to reduce coupling and mismatch is disclosed. The apparatus includes: means for reducing coupling and mismatch among a plurality of inductors in a plurality of VCO cores by arranging the plurality of inductors, including at least a first inductor and a second inductor, in a parallel differential inductor configuration with shared leads to form a single node; means for connecting power/ground traces to the first inductor from a first side only; and means for connecting to the power/ground traces to the second inductor from another side different from the first side only to avoid making a current loop. 
         [0009]    Other features and advantages of the present invention should be apparent from the present description which illustrates, by way of example, aspects of the invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]    The details of the present invention, both as to its structure and operation, may be gleaned in part by study of the appended further drawings, in which like reference numerals refer to like parts, and in which: 
           [0011]      FIG. 1  is a multi-core VCO structure using a quasi-symmetric routing of the power/ground traces in accordance with one embodiment of the present invention; 
           [0012]      FIG. 2  is another embodiment of the multi-core VCO structure using a quasi-symmetric routing of the power/ground traces; and 
           [0013]      FIG. 3  is a functional flow diagram illustrating a method for reducing coupling and/or mismatch caused by the power/ground routing in multi-core VCOs in accordance with one embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0014]    As described above, integrating an RF transceiver on a single chip may require a plurality of voltage-controlled oscillators (VCOs) to be running on the chip at the same time. Such a configuration may produce undesired interaction between the cores of the VCOs due to various types of mutual coupling mechanisms. In multi-core VCOs, an asymmetric power/ground trace routing can cause an amplitude mismatch. However, a fully symmetric power/ground trace routing with connections from both sides of the VCO core also results in a closed loop of metal, which can pick up undesirable coupling noises and spurs. The mismatch in the electromagnetic (EM) coupling also leads to differences in the current flow on the positive node and the negative node of the differential inductor and results in an increased amplitude on one oscillation node but decreased amplitude on the other oscillation node. This can lead to performance degradation in phase noise. Further, the lower amplitude on one node can lead to failure of functions if the following buffer is not designed with enough tolerance of input amplitude. 
         [0015]    Certain embodiments as described herein provide for reducing coupling and mismatch caused by the power/ground routing in multi-core VCOs. As explained above, in multi-core VCOs, the asymmetric power/ground trace routing can cause amplitude mismatch, while the fully symmetric power/ground trace routing with connections from both sides of the VCO core results in undesirable coupling noises and spurs. To break the loop, the power/ground trace routing is connected only from one side, and the current flows only on one side of the VCO core. After reading this description it will become apparent how to implement the invention in various implementations and applications. Although various implementations of the present invention will be described herein, it is understood that these implementations are presented by way of example only, and not limitation. As such, this detailed description of various implementations should not be construed to limit the scope or breadth of the present invention. 
         [0016]    In one embodiment of the multi-core VCO structure  100  shown in  FIG. 1 , a quasi-symmetric routing of the power/ground traces is used. In one embodiment, the VCO structure  100  is a portion of a semiconductor chip, for example, an RF transceiver. In another embodiment, In the illustrated embodiment of  FIG. 1 , the VCO structure  100  includes two VCO cores  150 ,  152 , one  150  at the top and one  152  at the bottom (effectively forming a plurality of VCOs). The top core  150  includes a first inductor  160  and a first bank of capacitors and other active devices  166 . The bottom core  152  includes a second inductor  162  and a second bank of capacitors and other active devices  168 . The two cores  150 ,  152  are enclosed by a grounded metal guard ring  164 , which is useful for isolating the couplings of the inductors  160 ,  162  to other on-chip inductors as well as other components. 
         [0017]    In the illustrated embodiment of  FIG. 1 , the two inductors  160 ,  162  of the two cores  150 ,  152  share the leads and nodes and connect in a parallel configuration. For example, the two inductors  160 ,  162  share positive leads as a single node  140  and negative leads as a single node  142  in a differential inductor configuration. Each core  150 ,  152  is also powered by power (V DD )  110  and ground (G ND )  112  traces. For example, the top core  150  can be coupled to the power trace  110  through via connections  122  (right),  132  (left), while the bottom core  152  can be coupled to the power trace  110  through via connections  124  (right),  134  (left). Similarly, the top core  150  can be coupled to the ground trace  112  through via connections  120  (right),  130  (left), while the bottom core  152  can be coupled to the ground trace  112  through via connections  126  (right),  136  (left). 
         [0018]    However, as explained above, in multi-core VCOs, the fully symmetric power/ground trace routing with connections from both sides results in a closed loop of metal which causes undesirable coupling noises and spurs. Thus, the power/ground trace routing is connected only from one side for each VCO core. For example, in the illustrated embodiment of  FIG. 1 , the top core  150  is connected to the power trace  110  through a right-side via connection  122  only, while the bottom core  152  is connected to the power trace  110  through a left-side via connection  134  only. Therefore, to break the loop, the right-side via connection  124  to the power trace  110  for the bottom core  152  is disconnected, and the left-side via connection  132  to the power trace  110  for the top core is disconnected. Similarly, the top core  150  is connected to the ground trace  112  through a right-side via connection  120  only, while the bottom core  152  is connected to the ground trace  112  through a left-side via connection  136  only. Again, to break the loop, the right-side via connection  126  to the ground trace  112  for the bottom core  152  is disconnected, and the left-side via connection  130  to the ground trace  112  for the top core is disconnected. The disconnections are marked with an ‘X’ mark in  FIG. 1 . 
         [0019]    Accordingly, the power/ground traces of the top and bottom cores  150 ,  152  are separated with no direct metal connections, and no metal loops are formed. Thus,  FIG. 1  shows the current flow  144  from the power trace  110  to the bottom core  152  and the current flow  146  from the power trace  110  to the top core  150 .  FIG. 2  is another embodiment of a multi-core VCO structure  200  powered by the power trace  210  and the ground trace  212 .  FIG. 2  shows the current flow  222  from the top core  230  to the ground trace  212  and the current flow  220  from the bottom core  232  to the ground trace  212 . Therefore, the top core  150  has more current flow  146 ,  222  on the right side than the left side, while the bottom core  152  has more current flow  144 ,  220  on the left side than the right side. Accordingly, when analyzed separately, each core  150 ,  152  has mismatched current flowing out of the two nodes  140 ,  142 . 
         [0020]    In the illustrated embodiments of  FIG. 1  and  FIG. 2 , when the two cores are analyzed separately, the top core  150  has a larger current flow on the negative node  142  than the positive node  140 , while the bottom core  152  has a larger current flow on the positive node  140  than the negative node  142 . Thus, the difference in the current flow leads to an amplitude mismatch at the positive and negative oscillation nodes. However, when the two VCO cores  150 ,  152  are connected in parallel (as shown in  FIG. 1  and  FIG. 2 ) by sharing the positive node  140  and the negative node  142 , the amplitude mismatch is substantially reduced or even cancelled in some cases. This substantially reduces the performance degradation at no additional cost. 
         [0021]    In an alternative embodiment, the routing of the power/ground trace is made from top and bottom of the VCO cores rather than from left and right sides of the VCO cores. This alternative embodiment would address the asymmetric current problem. However, this embodiment would also make the routing of the traces challenging and may result in a mismatch for the top and bottom cores due to the power/ground IR drop and other couplings to capacitor bank routing traces. In a further embodiment, a symmetric routing on both right and left sides can be used, but with a break of the metal loop in the middle. 
         [0022]      FIG. 3  is a functional flow diagram illustrating a method  300  for reducing coupling and/or mismatch caused by the power/ground trace routing in multi-core VCOs in accordance with one embodiment of the present invention. In the illustrated embodiment of  FIG. 3 , the power/ground trace routing is connected from one side only. For example, the power/ground via connections for the first core of the multi-core VCOs are disconnected on one side, at step  310 . Then, the power/ground via connections for the second core of the multi-core VCOs are disconnected on the other side, at step  320 . Thus, in examples shown in  FIG. 1  and  FIG. 2 , the power/ground traces of the top and bottom cores  150 ,  152  are separated with no direct metal connections, and no metal loops are formed. However, when the two cores are analyzed separately, the top core  150  has a larger current flow on the negative node  142  than the positive node  140 , while the bottom core  152  has a larger current flow on the positive node  140  than the negative node  142 . Therefore, as described above, the differences in the current flow still lead to the amplitude mismatch at positive and negative oscillation nodes. Accordingly, the first and second cores of the multi-core VCOs are configured into a parallel differential inductor configuration, at step  330 , to substantially reduce or even cancel the amplitude mismatch. 
         [0023]    Although several embodiments of the invention are described above, many variations of the invention are possible. For example, although the illustrated embodiments make power/ground trace connections on the left and right sides, the power/ground trace connections can be made from the top and bottom, or from both top/bottom and left/right sides. Further, features of the various embodiments may be combined in combinations that differ from those described above. For example, although the connections for the power/ground traces are made with via connectors, other suitable connectors such as wire connections can be used in place of the via connectors. Moreover, for clear and brief description, many descriptions of the systems and methods have been simplified. Many descriptions use terminology and structures of specific standards. However, the disclosed systems and methods are more broadly applicable. 
         [0024]    Those of skill in the art will appreciate that the various illustrative blocks and modules described in connection with the embodiments disclosed herein can be implemented in various forms. Some blocks and modules have been described above generally in terms of their functionality. How such functionality is implemented depends upon the design constraints imposed on an overall system. Skilled persons can implement the described functionality in varying ways for each particular application, but such implementation decisions should not be interpreted as causing a departure from the scope of the invention. In addition, the grouping of functions within a module, block, or step is for ease of description. Specific functions or steps can be moved from one module or block without departing from the invention. 
         [0025]    The various illustrative logical blocks, units, steps, components, and modules described in connection with the embodiments disclosed herein can be implemented or performed with a processor, such as a general purpose processor, a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field programmable gate array (FPGA) or other programmable logic device, discrete gate or transistor logic, discrete hardware components, or any combination thereof designed to perform the functions described herein. A general-purpose processor can be a microprocessor, but in the alternative, the processor can be any processor, controller, microcontroller, or state machine. A processor can also be implemented as a combination of computing devices, for example, a combination of a DSP and a microprocessor, a plurality of microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration. Further, circuits implementing the embodiments and functional blocks and modules described herein can be realized using various transistor types, logic families, and design methodologies. 
         [0026]    The above description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles described herein can be applied to other embodiments without departing from the spirit or scope of the invention. Thus, it is to be understood that the description and drawings presented herein represent presently preferred embodiments of the invention and are therefore representative of the subject matter which is broadly contemplated by the present invention. It is further understood that the scope of the present invention fully encompasses other embodiments that may become obvious to those skilled in the art and that the scope of the present invention is accordingly limited by nothing other than the appended claims.