Abstract:
A digital beamforming apparatus for use in a radar system. The digital beamforming apparatus comprises i) a plurality of multichip modules, each of the multichip modules comprising a plurality of application specific integrated circuit (ASIC) devices; ii) at least a first serial bus configured to couple a first multichip module to an antenna element; and iii) at least a second serial bus configured to couple the first multichip module to a second multichip module, wherein a first ASIC device on the first multichip module is coupled to a second ASIC device on the first multichip module by means of a first parallel bus. The first and second ASIC devices perform beamforming operations. The first ASIC device outputs beamforming data to the second ASIC device on the first parallel bus.

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) AND CLAIM OF PRIORITY 
       [0001]    The present application is related to U.S. Provisional Patent No. 62/305,405, filed Mar. 8, 2016, entitled “POWER EFFICIENT DISTRIBUTED BEAM FORMING ARCHITECTURE USING INTERCONNECTED PROCESSING NODES”. Provisional Patent No. 62/305,405 is assigned to the assignee of the present application and is hereby incorporated by reference into the present application as if fully set forth herein. The present application hereby claims priority under 35 U.S.C. §119(e) to U.S. Provisional Patent No. 62/305,405. 
     
    
     TECHNICAL FIELD 
       [0002]    The present application relates generally to a digital aperture processing back-end architecture that interconnects smaller and less complex data processing nodes to reduce power consumption and allow continued operation when elements fail. 
       BACKGROUND 
       [0003]    Radio frequency (RF) sensors (e.g., radar) use an array of antenna elements whose outputs are combined with an analog summer (i.e., an analog beam former) to electronically scan one transmit beam or receive beam in the desired spatial direction. However, analog beam forming limits operation to a single beam at a time. The next generation of RF sensors (i.e., digital aperture devices) digitize every antenna element and combine the antenna outputs digitally using a single processing node or multiple processing nodes. Digital combination of data (i.e., digital beam forming) allows the formation of multiple simultaneous receive beams. These beams can be pointed simultaneously to several different locations in space. This significantly increases the capability of a sensor. 
         [0004]    However, digitizing every antenna element in an antenna array and forming multiple simultaneous beams produces large amounts of data. To handle this large data volume, digital beam-forming architectures use large, complex, and expensive application specific integrated circuits (ASICs) or field programmable gate arrays (FPGAs) that present large size, weight and power (SWAP) challenges. Significantly, this limits the use of element level digital apertures to large platforms, such as ships or ground based platforms, that can support a large SWAP installation. 
         [0005]    Thus, the problems of large power consumption and large size of the current digital beam-forming architectures have limited the applications for digital aperture systems. Applications that need low SWAP and low power consumption, including but not limited to, airborne systems, unmanned aerial vehicles (UAVs), 5G communications, and the like, continue to wait for a smaller, lower power system architecture to implement fully elemental digital beam forming. Current solutions reduce performance by reducing the bandwidth of operation and limit the use of digital arrays to platforms that can sustain large SWAP installations. This severely reduces the number of beams and reduces flexibility of where the beams can be pointed. 
         [0006]    Therefore, there is a need in the art for an improved beam-forming apparatus for use in radar systems. In particular, there is a need for a digital aperture system that does not require a large SWAP architecture. 
       SUMMARY 
       [0007]    To address the above-discussed deficiencies of the prior art, it is a primary object to provide, for use in a radar system, a digital beamforming apparatus comprising: i) a plurality of multichip modules, each of the multichip modules comprising a plurality of application specific integrated circuit (ASIC) devices; ii) at least a first serial bus configured to couple a first multichip module to an antenna element; and iii) at least a second serial bus configured to couple the first multichip module to a second multichip module, wherein a first ASIC device on the first multichip module is coupled to a second ASIC device on the first multichip module by means of a first parallel bus. 
         [0008]    In one embodiment, the first and second ASIC devices perform beamforming operations. 
         [0009]    In another embodiment, the first ASIC device outputs beamforming data to the second ASIC device on the first parallel bus. 
         [0010]    In still another embodiment, each of the plurality of multichip modules comprises a silicon interposer on which the plurality of ASIC devices is configured. 
         [0011]    In yet another embodiment, the first parallel bus is implemented in a silicon interposer associated with the first multichip module. 
         [0012]    In a further embodiment, the first parallel bus comprises a copper pillar in the silicon interposer associated with the first multichip module. 
         [0013]    In a still further embodiment, the digital beamforming apparatus further comprises at least a third serial bus configured to couple the second multichip module to a signal processor at the output of the digital beamforming apparatus. 
         [0014]    Before undertaking the DETAILED DESCRIPTION below, it may be advantageous to set forth definitions of certain words and phrases used throughout this patent document: the terms “include” and “comprise,” as well as derivatives thereof, mean inclusion without limitation; the term “or,” is inclusive, meaning and/or; the phrases “associated with” and “associated therewith,” as well as derivatives thereof, may mean to include, be included within, interconnect with, contain, be contained within, connect to or with, couple to or with, be communicable with, cooperate with, interleave, juxtapose, be proximate to, be bound to or with, have, have a property of, or the like. Definitions for certain words and phrases are provided throughout this patent document, those of ordinary skill in the art should understand that in many, if not most instances, such definitions apply to prior, as well as future uses of such defined words and phrases. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]    For a more complete understanding of the present disclosure and its advantages, reference is now made to the following description taken in conjunction with the accompanying drawings, in which like reference numerals represent like parts: 
           [0016]      FIG. 1  illustrates a conventional analog beam-forming apparatus according to one embodiment of the prior art. 
           [0017]      FIG. 2  illustrates a digital beam-forming apparatus according to one embodiment of the disclosure. 
           [0018]      FIG. 3  illustrates a top view of an exemplary digital architecture for efficient beam-forming according to one embodiment of the disclosure. 
           [0019]      FIG. 4  illustrates a side view of an exemplary digital architecture for efficient beam-forming according to one embodiment of the disclosure. 
       
    
    
     DETAILED DESCRIPTION 
       [0020]      FIGS. 1 through 4 , discussed below, and the various embodiments used to describe the principles of the present disclosure in this patent document are by way of illustration only and should not be construed in any way to limit the scope of the disclosure. Those skilled in the art will understand that the principles of the present disclosure may be implemented in any suitably arranged digital beam-forming architecture. 
         [0021]      FIG. 1  illustrates analog radar system  100  according to one embodiment of the prior art. Analog radar system  100  comprises a plurality of radio frequency (RF) front-end transceiver (T/R) circuit blocks  110 , including exemplary T/R circuit blocks  110   a  and  110   b,  analog beamformer  120 , receiver path circuitry  130 , exciter path circuitry  140 , analog-to-digital converter (ADC)  150   a , digital-to-analog converter (DAC)  150   b,  and signal and data processor  160 . Each of T/R circuit blocks  110  is coupled to an antenna element of an antenna array and comprises switching circuitry for transmission mode and receive mode. 
         [0022]    In the radar transmit path, signal and data processor  160  sends digital transmit data to DAC  150   b,  which converts the transmit data to analog format. Exciter  140  comprises frequency synthesizer circuitry and up-converter circuitry that produce a radio frequency (RF) output. Analog beamformer  120  splits the RF output of exciter  140  into multiple transmit path signals, and applies amplitude and/or phase changes in each of the transmit path signals going to the plurality of T/R circuit blocks  110  that drive an antenna element. The result is a single antenna beam formed by analog radar system  100 . 
         [0023]    In the radar receive path, multiple incoming RF signals from the plurality of T/R circuit blocks  110  are applied to analog beamformer  120 , which applies complex weights to the RF signals from each antenna in the array. The complex weights consist of both amplitude and phase components. Analog beamformer  120  comprises a summation network circuit that combines the weighted signals from all the antenna elements into a single analog output signal that is sent to receiver path circuitry  130  for further processing (i.e., filtering, down-conversion, etc.). The analog baseband (or IF) output from receiver path circuitry  130  is then converted to a digital signal by ADC  150   a.  The digitized output of ADC  150   a  is finally sent to signal and data processor  160 . 
         [0024]      FIG. 2  illustrates digital radar system  200  according to one embodiment of the disclosure. Digital radar system  200  comprises a plurality of radio frequency (RF) front-end transceiver (T/R) circuit blocks  210 , including exemplary T/R circuit blocks  210   a  and  210   b,  digital converter blocks  250 , including exemplary digital converter blocks  250   a  and  250   b,  digital beamformer  220 , and signal and data processor  260 . Digital converter blocks  210  comprise the necessary digital-to-analog converter (DAC) circuits and analog-to-digital converter (ADC) circuits to converter data between the analog and digital domains. 
         [0025]    In both the transmit and receive modes, the RF signals to and from every antenna element connected to T/R circuit blocks  210  is digitized, resulting in multiple simultaneous transmit and receive beams that are processed by digital beamformer  220  and signal and data processor  260 . Digitizing data in every antenna element in an array results in an enormous amount of data, high heat dissipation, high power consumption, large size and weight, and requires large ASICs or FPGAs to process the data. 
         [0026]    The present disclosure reduces the size, weight and power (SWAP) requirements of digital beamformer  220  by combining three improvements for efficient beamforming. These three improvements include: 1) the use of smaller processing nodes (i.e., ASICs) that service a small number of dual polarized antenna elements; 2) forming multichip modules (MCMs) by using copper pillars in parallel connections between adjacent ASICs; and 3) implementing a redundant data interconnect architecture for connecting multiple MCMs. 
         [0027]      FIG. 3  illustrates an exemplary digital architecture  300  for efficient beam-forming according to one embodiment of the disclosure.  FIG. 4  illustrates a cross-sectional view of exemplary digital architecture  300  for efficient beam-forming according to one embodiment of the disclosure. Exemplary digital architecture  300  may optimally be implemented in digital beamformer  220  shown in  FIG. 2 . 
         [0028]    Digital architecture  300  includes a plurality of multichip modules (MCMs)  310 , including exemplary MCMs  310   a  and  310   b.  The multichip modules are coupled to each other and to T/R circuit blocks  210 , digital converter blocks  250 , and signal and data processor  260  by means of serializer-deserializer (SERDES) interfaces  361 - 366 . In this manner, each MCM  310  receives incoming data in serial format and converts the received data to parallel format for internal processing within MCM  310 . At the output of each MCM  310 , the processed parallel data is converted back to serial format for transmission to, for example, another MCM  310  or signal and data processor  260 . 
         [0029]    The exemplary multichip module (MCM)  310   a  comprises a plurality of application specific integrated circuit (ASIC) devices  321 - 324  that are configured on silicon interposer  311   a  and coupled to each other by means of a plurality of copper pillar (CuP) parallel connection buses  331 - 334  within silicon interposer  311   a.  Similarly, multichip module (MCM)  310   b  comprises a plurality of application specific integrated circuit (ASIC) devices  341 - 344  that are configured on silicon interposer  311   b  and coupled to each other by means of a plurality of copper pillar (CuP) parallel connection buses  351 - 354  within silicon interposer  311   b.  Additional MCMs  310  (not shown) may be implemented in digital beamformer  220  depending on the size and performance requirements of the digital radar system  200 . It will be understood by those skilled in the art that ASIC devices may instead be field programmable gate array (FPGA) devices without departing from the scope of the present disclosure. 
         [0030]    The cross-sectional view in  FIG. 4  passes through SERDES interfaces  364 - 366 , ASIC devices  323 - 324  and  343 - 344 , CuP parallel connection buses  332  and  352 , and silicon interposers  311   a  and  311   b.  Each of ASIC devices  321 - 324  and ASIC devices  341 - 344  comprises a digital beamforming ASIC. Each ASIC device forms beams digitally using the data sampled from the local antenna element(s) that the ASIC device is servicing. The number of antenna elements serviced by each ASIC device is kept to a low number. Within each MCM  310 , each copper pillar (CuP) parallel connection bus is used to transfer digital beamformed data from one ASIC device to a nearby ASIC device in a parallel format through the corresponding silicon interposer  311 . 
         [0031]    ASIC devices  321 - 324  and  341 - 344  generates the digital beamformed data by applying steering weights to the I/Q samples of multiple receiver (RX) channels and adding the results to form beams in a particular direction. These steering weights may comprise complex phasors with amplitude and a phase progression. Alternatively, steering weights may be implemented through true time delays (TTDs) using methods such as digital fractional delay filters. The transfer of beamformed data in parallel format between ASIC devices greatly improves the performance of digital beamformer  220 . 
         [0032]    In sum, the present disclosure combines three concepts for efficient digital beamforming. First, the improved digital beamformer uses smaller processing nodes that convention digital beam formers. Second, the improved digital beamformer uses copper pillar CuP parallel connection buses for nearby ASICs for form the MCMs. Finally, the improved digital beamformer makes a redundant data interconnect architecture for connection amongst MCMs. 
         [0033]    The improved digital beamforming architecture provides reduced data processing throughput by forming beams within each ASIC device and reducing the amount of data that is passed around within the digital beamforming architecture. The improved digital beamforming architecture also provides reduced power consumption at the ASIC level since the ASIC devices are smaller and services fewer antenna elements. Power is further reduced at the system level by replacing power hungry SERDES serial connection interfaces between ASICs with more power efficient parallel CuP buses for connections of nearby ASICs. 
         [0034]    The improved digital beamforming architecture requires fewer hardware components since no additional hardware nodes are needed for beam forming. The ASIC devices that sample the digital data also do the beamforming in a distributed fashion. By using smaller processing nodes and having redundant connections, the improved digital beamforming architecture reduces the impact of ASIC failures in the system. 
         [0035]    Although the present disclosure has been described with an exemplary embodiment, various changes and modifications may be suggested to one skilled in the art. It is intended that the present disclosure encompass such changes and modifications as fall within the scope of the appended claims.