Abstract:
A time division multiplexing intra-chip communication system comprising at least one communication link. Such communication link comprises serialization and transmission circuitry, reception and deserialization circuitry, and at least one coaxial or wafer-level package transmission line interconnect therebetween. Such coaxial or wafer-level package transmission line interconnect may carry signals from such transmit circuitry to such receive circuitry. Such intra-chip communication links may achieve single-cycle operation or multi-cycle operation. Single single-cycle operation may be conducive to synchronous FSM design methodologies while multi-cycle operation may be conducive to data transfers to and from memory.

Description:
[0001]    This application claims the benefit of U.S. provisional patent application No. 61/464,186, entitled “Intra-chip Micro-coaxial TDM Communication Link and System,” filed Feb. 26, 2011 by applicant William Loh. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]    The present invention relates generally to intra-chip high-speed serial communication for integrated circuit semiconductor devices. Specifically, the communication system may provide one or more of high-speed, high-bandwidth, low-power, and transparent intra-chip communication by utilizing Time Division Multiplexing (TDM) of signals over one or more of coaxial or Wafer Level Package (WLP) waveguides. 
         [0003]    Serial links, so-called Serializer/Deserializers (SerDes), have already begun to replace parallel communication systems for inter-chip communications. Examples include Serial Advanced Technology Attachment (SATA) which replaces Parallel ATA (PATA), Peripheral Component Interconnect Express (PCI-e) which replaces parallel PCI (PCI-X), and Gigabit Ethernet (GbE) which replaces Fast Ethernet (100Base-T Ethernet). 
         [0004]    There are several advantages of SerDes over parallel communication systems. SerDes utilize low-loss LC transmission lines that can yield a 10× improvement in signal rise times versus the RC interconnects utilized by parallel communication systems. SerDes is more power efficient than parallel communication systems for transmission of multi-gigabit-per-second (multi-Gbps) data signals over distances greater than several millimeters on chip at deep submicron process technology nodes. Finally, SerDes provides embedded clock information in the transmitted data stream, overcoming many of the clock skew and clock jitter limitations of multi-Gbps parallel communication systems. 
         [0005]    Consequently, there has been much work to implement serial communication systems for intra-chip communication. These systems entail multiple SerDes communication links over standard on-chip metal-layer interconnect technology (for example Dally, “Interconnect-Centric Computing,” 2007). However, on-chip metal layer interconnect technologies suffer from high line losses that must be compensated for or managed by the communication system, resulting in one or more of unfavorable power consumption, circuit complexity, circuit gate count, and circuit area. Other on-chip communication systems have implemented standard data communication over Wafer Level Package (WLP) interconnect technology, but have not utilized SerDes methodologies (for example Carchon, “ Wafer-Level Packaging Technology for Extended Global Wiring and Inductors,” 2003). WLP has similar line-loss impairments as on-chip interconnects, but to a lesser extent, due to the utilization of thicker conductor and insulator layers deposited on the wafer. The present invention implements an intra-chip communication system that shares the benefits of inter-chip SerDes systems by mitigating the drawbacks of WLP or metal-layer communication systems. Such intra-chip communication system utilizes a TDM scheduling methodology to serialize and transceive intra-chip digital data over coaxial interconnects. Such intra-chip communication system does not preclude the use of WLP interconnects; in fact, an alternate embodiment is to use WLP interconnects in place of, or along with, coaxial interconnects. 
         [0006]    A coaxial interconnect is a transmission line comprising a central conductor surrounded by a conductive outer shield, with an insulator or gap disposed therebetween. Such total enclosure of the central conductor by the outer shield prevents electromagnetic fields from escaping the vicinity of the coaxial interconnect—similar to micro-strip, strip-line, or co-planar waveguide technologies—which results in lower crosstalk and more constant impedance. A commercially available coaxial interconnect technology is ‘microCoax,’ developed by Bridgewave Communications, Inc. of Santa Clara, Calif. (Pasternak, et. al. U.S. Pat. No. 7,520,054-B2). It has been designed and used for extremely high frequency inter-chip signal communication in the 30 to 300 GHz range, called Millimeter Wave (MMW) communication. An advantage of microCoax is that it is amenable to low-cost chip wire-bonding manufacturing techniques. microCoax, and other coaxial interconnect technologies, were neither explicitly designed for nor have been previously used for transceiving high-speed serial intra-chip signals, primarily due to the lack of a suitable, scalable, and practical intra-chip communication system, which the present invention addresses and solves. 
         [0007]    It is well known that multi-Gbps single-system-clock-cycle (single-cycle) cross-chip communication—distances greater than a few millimeters—has become impossible. This necessitates multi-cycle Finite State Machine (FSM) design methodologies for digital logic or implementation of high-speed intra-chip communication systems capable of transceiving signals across chip within a single system clock cycle. Because multi-cycle FSMs are much more complicated than single-cycle FSMs to implement, verify, and test, and due to well established Electronic Computer-Aided Design (ECAD) models for single-cycle FSM design, single-cycle FSMs are preferred for digital logic. 
         [0008]    Accordingly, what is desired, and has not heretofore been developed, is an intra-chip communication system that utilizes coaxial interconnects to achieve high-speed signal communication over distances greater than several millimeters. It is further desired that the intra-chip communication system be capable of transmitting and receiving such signals over such distances within a single system clock cycle, thereby being amenable to standard single-cycle FSM design methodologies. The intra-chip communication system utilizes TDM to aggregate multiple low-speed signals onto one or more high-speed coaxial interconnects using SerDes methodologies described in the following description of the invention. 
       BRIEF SUMMARY OF THE INVENTION 
       [0009]    It is an object of the present invention to provide a high-speed serial intra-chip communication link with low-loss transmission lines. 
         [0010]    It is an object of the present invention to provide an intra-chip serial communication link that may utilize at least one wire-bonded coaxial transmission line interconnect. 
         [0011]    It is a further object of the present invention to provide an intra-chip serial communication link that may utilize at least one WLP transmission line interconnect. 
         [0012]    It is an object of the present invention to provide an intra-chip serial communication link utilizing at least one coaxial transmission line interconnect that employs TDM. 
         [0013]    It is a further object of the present invention to provide a low-power intra-chip communication link. 
         [0014]    It is a further object of the present invention to provide an intra-chip serial communication link capable of achieving cross-chip signal transmission and reception within a single system clock cycle. 
         [0015]    It is a further object of the present invention to provide an intra-chip serial communication link capable of achieving signal transmission and reception within multiple system clock cycles. 
         [0016]    It is an object of the present invention to provide an intra-chip communication system comprising at least one intra-chip communication link. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]      FIG. 1   a  is a perspective view of an exemplary chip showing several coaxial interconnects. 
           [0018]      FIG. 1   b  is a cross-sectional view of a portion of a single coaxial interconnect adjoining a chip. 
           [0019]      FIG. 2   a  is an exemplary circuit diagram of an intra-chip TDM communication link of the present invention in which circuit elements may process local signals prior to serialization and after deserialization. 
           [0020]      FIG. 2   b  is an exemplary circuit diagram of an intra-chip TDM communication link of the present invention in which no circuit elements are present to process local signals prior to serialization and after deserialization. 
           [0021]      FIG. 3  is an exemplary waveform diagram of clock, parallel data, and serial data signals of the intra-chip TDM communication link of  FIG. 2   a  or  FIG. 2   b  in which single-cycle communication is achieved. 
           [0022]      FIG. 4   a  is an exemplary prior art FSM circuit diagram. 
           [0023]      FIG. 4   b  is an exemplary FSM circuit diagram with combinational logic partitioned. 
           [0024]      FIG. 5   a  is an exemplary circuit diagram of an intra-chip TDM communication link implementing single-cycle operation via combinational logic partitioning. 
           [0025]      FIG. 5   b  is an exemplary waveform diagram showing the TDM scheduling methodology of the single-cycle intra-chip TDM communication link of  FIG. 5   a.    
           [0026]      FIG. 6   a  is an exemplary circuit diagram of an intra-chip TDM communication link of the present invention in which circuit elements may process local signals prior to serialization and after deserialization. 
           [0027]      FIG. 6   b  is an exemplary circuit diagram of an intra-chip TDM communication link of the present invention in which no circuit elements are present to process local signals prior to serialization and after deserialization. 
           [0028]      FIG. 7  is an exemplary waveform diagram of clock, parallel data, and serial data signals of the intra-chip TDM communication link of  FIG. 6   a  in which multi-cycle communication is achieved. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0029]    Heretofore and henceforth the term ‘chip’ is used to describe an integrated circuit device, including but not limited to a Field Programmable Gate Array (FPGA), Application Specific Integrated Circuit (ASIC), a single- or multi-core microprocessor, a Standard Product (SP), or an Application Specific Standard Product (ASSP), od a System-on-Chip (SoC). 
         [0030]    Heretofore and henceforth the term ‘micro-coax’ is used to describe a transmission line comprising a central conductor surrounded by a conductive outer shield with an insulator or gap therebetween (a coaxial interconnect). 
         [0031]    Heretofore and henceforth the terms ‘circuit,’, ‘circuit element,’ ‘circuit block,’ ‘logic,’ ‘logic element,’ ‘logic block,’ and ‘logic cloud’ may be used interchangeably. 
         [0032]    Heretofore and henceforth the term ‘amount of combinational logic’ is used to describe any appropriate quantifiable parameter of a circuit including, but not limited to, number of logic gates, logic depth, or logic complexity; the terms ‘small,’ ‘smaller,’ ‘large,’ and ‘larger’ describe such relative amounts of combinational logic. 
         [0033]    Heretofore and henceforth the term ‘finite state machine’ and its abbreviation ‘FSM’ are used to describe any synchronous digital circuit. 
         [0034]    Heretofore and henceforth the terms ‘digital data,’ ‘data stream,’ ‘digital signal,’ ‘signal,’ ‘bits,’ and ‘bit stream’ may be used interchangeably. 
         [0035]    Heretofore and henceforth the terms ‘interconnect’ and ‘transmission line’ may be used interchangeably. 
         [0036]    Heretofore and henceforth the terms ‘multiplexer’ and ‘mux’ are used to describe any so-called serializer circuits known in the art that map m input signals to n≦m output signals; the terms ‘demultiplexer’ and ‘demux’ are used to describe any so-called deserializer circuits known in the art that map n input signals to m≧n output signals. 
         [0037]      FIG. 1   a  shows an exemplary chip  1  with several low-loss transmission line interconnects  10 , each end of which is wire-bonded thereto by means of a wire bond pad  20 . Wire bonds and wire bonding technology is well know in the art and is therefore not discussed herein.  FIG. 1   b  shows a cross-section view of a portion of a single low-loss transmission line interconnect  10 . The low-loss transmission line interconnect  10  consists of a central conductor  11  surrounded by an insulator  13 . The insulator  13  may be any suitable dielectric material, void, or air gap. Surrounding the insulator  13  is a conductive outer shield  12 . Micro-coaxial interconnect technology is commercially available and is therefore not discussed herein. 
         [0038]      FIG. 2   a  shows an exemplary circuit diagram of an intra-chip communication link utilizing a low-loss transmission line interconnect  10 . The local data signal lines  104  may carry signals from some local region of a chip  1  to the transmit logic block  31 . Also input to the transmit logic block  31  may be a transmit system clock line  100 . Output from the transmit logic block  31  are parallel data signal lines  102 .  FIG. 3  shows exemplary signals for an exemplary 8-to-1 TDM communication link: transmit system clock signal  100   s  may be carried on transmit system clock line  100  and transmit parallel data signals  102   s  may be carried on parallel data signal lines  102 . Although a positive edge-triggered synchronous design methodology is shown, any suitable methodology may be used, including but not limited to negative edge-triggered or level-sensitive. 
         [0039]    The transmit logic block  31  may alternatively comprise combinational and sequential logic which may implement one or more synchronous FSMs. Otherwise the transmit logic block  31  may be absent, as shown by the alternate embodiment in  FIG. 2   b , in which local data signal lines  104  are connected directly to parallel data signal lines  102 . Combinational and sequential logic of the transmit logic block  31 , if present, may be re-ordered in transmit sequence and synchronized via the transmit system clock signal  100   s.    
         [0040]    Input to the multiplexer  30  are the parallel data signal lines  102  and transmit serial clock line  101 . Output from the multiplexer  30  is the low-loss transmission line interconnect  10 . The multiplexer  30  performs a parallel-to-serial conversion of transmit parallel data signals  102   s  carried on the parallel data signal lines  102 , outputting the resulting high-speed serial data signal  10   s  to the low-loss transmission line interconnect  10 . Serialization is accomplished by strobing the transmit parallel data signals  102   s,  shown as d 1  through d 8  in  FIG. 3 , at periodic intervals of the transmit serial clock signal  101   s.  Although an ordered round-robin selection methodology is shown, any suitable methodology may be used. There are many circuits that are known in the art that may be used in part or in full to implement the multiplexer  30 , which are therefore not discussed herein. 
         [0041]    The high-speed serial data signal  10   s  may be, but is not limited to, single-ended, differential, current-mode, voltage-mode, non-return-to-zero (NRZ), return-to-zero (RZ), duobinary, Pulse Amplitude Modulated n (PAM-n), Manchester, differential Manchester, and so forth. Furthermore, although all exemplary circuit diagrams have been drawn with only one low-loss transmission line interconnect  10  between transmit and receive circuits of a single communication link, multiple low-loss transmission line interconnects  10  may be utilized for such single communication link. For example, two low-loss transmission line interconnects  10  may be used for differential signaling of high-speed serial data signal  10   s,  which is within the scope of the present invention. Similarly, a single low-loss transmission line interconnect  10  may be used for single-ended signaling of high-speed serial data signal. 
         [0042]    The transmit serial clock period  101   p  may be some suitable fraction of the transmit system clock period  100   p.  This is the fastest clock in the system. The serialization factor—the number of parallel signals that may be serialized by the multiplexer  30  per unit time interval—may be a function of the ratio of the transmit system clock period  100   p  to the transmit serial clock period  101   p.  Exemplary  FIG. 3  shows an 8-to-1 serialization factor. 
         [0043]    As shown in  FIG. 3 , there may be a data transport delay  120   a  of the high-speed serial data signal  10   s  from the time is was transmitted by the multiplexer  30  to the time it is received by the demultiplexer  40 . Input to the demultiplexer  40  are the low-loss transmission line interconnect  10  and receive serial clock line  201 . Output from the demultiplexer  40  are parallel data signal lines  202 . The demultiplexer  40  performs a serial-to-parallel conversion of the high-speed serial data signal  10   s,  outputting the resulting receive parallel data signals  202   s  to parallel data signal lines  202 . Deserialization is accomplished by strobing the high-speed serial data signal  10   s,  shown as d 1  through d 8  in  FIG. 3 , at periodic intervals of the receive serial clock signal  201   s.  There are many circuits that are known in the art that may be used in part or in full to implement the demultiplexer  40 , which are therefore not discussed herein. 
         [0044]    Input to the receive logic block  41  are the parallel data signal lines  202 . Also input to the receive logic block  41  may be a receive system clock line  200 . Output from the receive logic block  41  are local data signal lines  204 .  FIG. 3  shows exemplary signals: receive system clock signal  200   s  may be carried on receive system clock line  200  and receive parallel data signals  202   s  may be carried on parallel data signal lines  202 . The local data signal lines  204  may carry signals from the receive logic block  41  to some local region of the chip  1 . 
         [0045]    The receive logic block  41  may alternatively comprise combinational and sequential logic which may implement one or more synchronous FSMs. Otherwise the receive logic block  41  may be absent, as shown by the alternate embodiment in  FIG. 2   b , in which parallel data signal lines  202  are connected directly to local data signal lines  204 . Combinational and sequential logic of the receive logic block  41 , if present, may be synchronized and/or re-ordered in the transmit sequence via the receive system clock signal  200   s.    
         [0046]    The TDM communication system of the present invention may operate plesiochronously or mesochronously; there need not be any clock tree that distributes system clock signals or serial clock signals between transmit and receive circuits. The transmit system clock signal  100   s  corresponds to the system clock signal of the local clock domain of the transmit end of the TDM communication link; the receive system clock signal  200   s  corresponds to the system clock signal of the local clock domain of the receive end of the TDM communication link. The transmit serial clock signal  101   s  may be derived from the transmit system clock signal  100   s.  The receive serial clock signal  201   s  may be recovered from the high-speed serial data signal  10   s  using any suitable clock recovery methodology, including but not limited to bang-bang or Mueller-Müller, which are well known in the art and are therefore not discussed herein. Such clock recovery circuitry may be a functional portion of the demultiplexer  40 . Finally, the receive system clock signal  200   s  may be derived from the receive serial clock signal  201   s.  Clock signal derivation may be accomplished by any suitable means, including but not limited to Phase-Locked Loops (PLLs) and Delay-Locked Loops (DLLs), which are well known in the art and are therefore not discussed herein. 
         [0047]    The exemplary intra-chip TDM communication systems shown in  FIG. 2   a  and  FIG. 2   b , described by  FIG. 3 , and shown in  FIG. 5   a  and described by  FIG. 5   b , achieve single-cycle operation: transmit parallel data signals  102   s  are serialized and transmitted by the multiplexer  30  as high-speed serial data signal  10   s,  carried across low-loss transmission line interconnect  10 , and received and deserialized into receive parallel data signals  202   s  by the demultiplexer  40 , all within one transmit system clock period  100   p.  Consequently, such single-cycle operation may be entirely transparent to single-cycle FSM design methodologies, providing a great advantage for design, implementation, and test of FSMs versus multi-cycle FSM design methodologies. 
         [0048]      FIG. 4   a  shows an exemplary circuit diagram of a typical prior art single-cycle FSM; between transmit bistables  32  and receive bistables  42  may be combinational logic, depicted as combinational logic  50   a,  combinational logic  50   b,  and combinational logic  50   c.    FIG. 4   a ,  FIG. 4   b , and  FIG. 5   a  are drawn without fan-in or fan-out nets to or from the combinational logic clouds for simplicity only; in general, and within the scope of the present invention, there may exist fan-in or fan-out nets between transmit bistables  32  and receive bistables  42 . Such single-cycle FSM may be transformed into the circuit diagram shown in  FIG. 4   b . The combinational logic  50   a  is partitioned into transmit combinational logic  33   a  and receive combinational logic  43   a,  combinational logic  50   b  is partitioned into transmit combinational logic  33   b  and receive combinational logic  43   b,  and combinational logic  50   c  is partitioned into transmit combinational logic  33   c  and receive combinational logic  43   c.  The size of the logic clouds drawn in  FIG. 4   b  depicts the relative amount of combinational logic individually contained therein. The parallel interconnects  51  join such pairs of combinational logic clouds. 
         [0049]      FIG. 5   a  shows the exemplary circuit diagram of  FIG. 4   b  with the parallel interconnects  51  replaced by parallel data signal lines  103 , multiplexer  30 , low-loss transmission line interconnect  10 , parallel data signal lines  203 , and demultiplexer  40  in accordance with the present invention.  FIG. 5   b  shows a corresponding exemplary time-space diagram in which an ordered round-robin TDM selection methodology is used to serialize and transmit data across the low-loss transmission line interconnect  10 . The data associated with transmit combinational logic  33   a  is the first to be selected and transmitted; the data associated with transmit combinational logic  33   c  is the last to be selected and transmitted. Given m data units to be serialized and transmitted, the first data is selected at least m transmit serial clock periods  101   p  earlier than the last data (a data unit may be a bit, byte, or any convenient quantifiable unit). Thus, by partitioning combinational logic  50   a  into small transmit combinational logic  33   a,  which has correspondingly small transmit logic delay  110   a,  and large receive combinational logic  43   a,  which has correspondingly large receive logic delay  210   a,  the entire functionality of such original combinational logic  50   a  is preserved for such first data within one transmit system clock period  100   p.  Similarly, by partitioning combinational logic  50   c  into large transmit combinational logic  33   c,  which has correspondingly large transmit logic delay  110   c,  and small receive combinational logic  43   c,  which has correspondingly small receive logic delay  210   c,  the entire functionality of the original combinational logic  50   c  is preserved for such last data within one transmit system clock period  100   p.  All other combinational logic clouds, for example combinational logic  50   b,  are similarly partitioned according to such ordered round-robin selection schedule, for example into transmit combinational logic  33   b  and receive combinational logic  43   b,  to preserve the entire functionality of such original combinational logic cloud. Such TDM scheduling permits single-cycle and transparent FSM design methodologies. 
         [0050]    The logic delays shown in  FIG. 5   b  are maximum delays; the actual delay must be less than or equal to those shown. Furthermore, such logic delays may include delays associated with sequential circuit elements including but not limited to setup time and hold time. 
         [0051]    Single-cycle operation may not always be desired. For example, it may be advantageous to utilize multiple system clock cycles to transfer large amounts of data to or from memory. The exemplary intra-chip TDM communication system shown in  FIG. 6   a  and described by  FIG. 7  achieves multi-cycle operation: transmit parallel data signals  102   s  are serialized and transmitted by the multiplexer  30  as high-speed serial data signal  10   s,  carried by the low-loss transmission line interconnect  10 , and received and deserialized into receive parallel data signals  202   s  by the demultiplexer  40 , over the duration of multiple transmit system clock periods  100   p.    
         [0052]      FIG. 6   a  shows a transmit control signal line  105  that may be input to the transmit logic block  31 , which may carry a transmit control signal  105   s.  Alternatively, such transmit control signal  105   s  may be generated within the transmit logic block  31  via combinational and sequential logic that may be present therein. The transmit control signal  105   s  may control, re-sequence, or synchronize m transmit parallel data signals  102   s,  shown as d 1  through dm in  FIG. 7 , such transmit parallel data signals  102   s  originating or transformed from some local region of a chip  1 . Such m transmit parallel data signals  102   s  are serialized and transmitted by the multiplexer  30 , and received and deserialized by the demultiplexer  40 , as previously described. 
         [0053]    Input to the receive logic block  41  may be a receive control signal line  105 , which may carry a receive control signal  105   s.  Alternatively, such receive control signal  105   s  may be generated within the receive logic block  41  via combinational and sequential logic that may be present therein. The receive control signal  105   s  may control or synchronize m receive parallel data signals  202   s,  such receive parallel data signals  202   s  may be alternatively transformed and subsequently distributed to some local region of the chip  1 . The transmit logic block  31  and receive logic block  41  may alternatively comprise additional combinational and sequential logic which may implement one or more synchronous FSMs.  FIG. 6   b  shows an alternate embodiment of  FIG. 6   a  in which no transmit logic block  31  and no receive logic block  41  are present. 
         [0054]    One specific embodiment of the intra-chip communication system is the microCoax; many variations or modifications would be apparent that do not depart from the spirit and scope of the invention. For example, an alternate intra-chip communication link embodiment may utilize WLP interconnects in place of micro-coax interconnects throughout. Furthermore, a first alternate intra-chip communication system may utilize WLP communication links throughout; a second alternate intra-chip communication system may utilize both micro-coax and WLP communication links. Still further, carbon nanotubes and superconducting interconnects may be utilized in place of or in combination with micro-coax interconnects. Such deviations from the exemplary descriptions and illustrations provided are within the scope of the present invention, which is defined by the appended claims.