Abstract:
A mixed-signal core disclosed herein is designed for efficient concurrent testing analog, mixed-signal, and digital components. One tester may test all components and, thereby, reduce test time without losing full test coverage. An analog module includes all the analog and mixed-signal components of the mixed-signal core, while a first digital module includes digital components required for functional/parametric verification of the mixed-signal components within the analog module. A first virtual boundary connects the analog and the first digital modules to gate the signal transfer during testing. A second digital module includes the remaining digital components of the mixed-signal core, whereby a second virtual boundary separates it from the first digital module. This type of partitioning enables the mixed-signal core to have three modes of operation, wherein the first mode of operation provides digital interface characterization testing of the first and second digital module and analog characterization/trimming testing of the analog module. In the second mode of operation, concurrent testing of the analog module and the first and second digital module is conducted; wherein analog characterization/trimming testing is performed on the analog module and digital interface characterization testing is performed on the first digital module, while SCAN/BIST testing is performed on the second digital module. In the third mode of operation, non-concurrent testing of the analog module, the first digital module, and the second digital module is enabled; wherein SCAN/BIST testing of the first digital module and the second digital module is enabled, while the analog module is powered down.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates to a method and structure for testing an embedded mixed signal core on a System-on-Chip (SoC) design, and, more particularly, to a method and apparatus for partitioning and testing the embedded mixed signal core on the SoC integrated circuit (IC).  
       BACKGROUND OF THE INVENTION  
       [0002]     In the advent of increased demand for consumer electronics and continued growth in semiconductor packing density, more system functionality is integrated onto an integrated circuit. Accordingly, there is an increased need for integration of analog and mixed-mode components (i.e. analog-digital, RF-analog-digital, and mechanical-analog-digital) on the same chip as digital components. Designing such mixed-signal systems-on-chip (SoC) is distinctively challenging since it entails managing system level abstractions while simultaneously dealing with physical effects at the transistor and parasitic levels. In addition, testing next-generation SoCs entails a substantial amount of complexity due to the cost and time-to-market requirements.  
         [0003]     An embedded core based SoC IC design conventionally includes various reusable functional blocks, such as microprocessors, interfaces, memory arrays, and digital signal processors (DSPs). These reusable functional blocks are generally referred to as cores. These cores generally include complex analog, mixed signal and digital sub-modules. For example, the SoC may include embedded cores such as an analog-to-digital (ADC) or a digital-to-analog (DAC) converter. In addition, they may include volatile and non-volatile memories.  
         [0004]     In general, testing of embedded analog/mixed-signal cores is considered a difficult problem in SoC IC testing. While various design-for-test (DFT) schemes are used to access the embedded analog blocks, the testing is performed by specialized hardware such as mixed-signal automatic test equipment (ATE) or an IC tester. ATEs are widely used by manufacturers of semiconductor components. An ATE executes a test pattern which defines inputs to the device under test (DUT) and the expected outputs. By executing the test pattern, the ATE determines whether the component is operating properly.  
         [0005]     Texas Instruments™ Inc.&#39;s Asymmetric Digital Subscriber Line (ADSL) client premise equipment (CPE) modem, Sangam™ (i.e.TNETD7300), has an ADSL line driver module, power management module and a variety of digital modules including memory, processor, and host interfaces. Testing such a device is a challenge regarding coverage as well as expense; where coverage implies the amount of silicon which must be tested before it is shipped to customers. For digital modules, coverage can be quantitatively derived from the scan test coverage. For analog modules, coverage is qualitative and is based on the amount of testing (functional/parametric) performed on each analog block. For SoC devices, the coverage for analog blocks may reduce in the absence of test modes to fully access these blocks. Test cost directly stems from the amount of time to perform all testing. Using an ATE each second of test time costs approximately three cents. Thus, for sequential testing of analog and digital modules incorporated within the SoCs using an ATE, the test time and expense may be double in a worst case scenario.  
         [0006]     The methodology for testing digital and analog blocks differs substantially. Digital blocks are tested for modeled defects largely using algorithmically generated test patterns, (e.g. automatic test pattern generator (ATPG) or memory built-in-self-test (MBIST)). On the other hand, analog blocks are tested for functionality and characterized for specific parameters. The digital test set typically comprises of scan patterns for different fault models that are applied under burn-in and virtual box builder (VBox) conditions where VBox is a condition which stresses the digital logic by changing the power supply rail voltage VDD to bring out latent defects of the digital blocks. For example, if the nominal operational voltage is 1.5V, VBox limits may be 1.1V and 2.1V. In such a case, a device may be stressed using a VDD of 2.1V volts and then tested at 1.1V to bring out a defect, which depends upon the process and the statistical data. Moreover, the digital test set includes memory tests typically in the form of memory BIST. These aforementioned digital test sets differ from I/O characterization and at-speed tests. During these tests, the device is configured into SCAN test mode where device functionality is lost. In contrast, during analog testing (i.e. signal-to-noise ratio (SNR) and total harmonic distortion (THD)), the tests are required to be performed only when the device is in a functional operating mode. This requirement imposes the restriction that each analog and digital block be separately and sequentially tested to avoid any conflict of the SCAN and functional testing.  
         [0007]     Accordingly, SoCs have been tested in the past by testing the analog and digital blocks of the chip separately and/or sequentially by enabling a power down feature for each individual block. In addition, the inputs and outputs of all blocks are multiplexed to external pins for access. The disadvantage of this approach is that a large amount of test time is required to test the entire SoC device since it is difficult to test various blocks having different test methodologies in parallel.  
         [0008]     The present invention is directed to overcoming, or at least reducing the effects of one or more of the problems set forth above.  
       SUMMARY OF THE INVENTION  
       [0009]     To address the above-discussed deficiencies of mixed-signal core design for testing, the present invention teaches a mixed-signal core designed for efficient testing capable of concurrent testing of the analog, mixed-signal, and digital components comprised within the mixed-signal core. A mixed-signal core in accordance with the present invention is enabled to use the same tester to test all components comprised within the core and, thereby, reduce test time without losing full test coverage.  
         [0010]     The mixed-signal core includes an analog module, a first and second digital module, and a first and second virtual boundary. The analog module includes a analog components and mixed-signal components. The first digital module includes a first subset of digital components required for functional/parametric verification of the mixed-signal components within the analog module. The first virtual boundary couples between the analog module and the first digital module. The first virtual boundary having at least one multiplexer to gate signals transmitted between the analog module and the digital module. The first virtual boundary partitions the analog module from the digital module. Each multiplexer couples to receive signals generated by the analog and mixed-signal components of the analog module and the digital components of the digital module. The second digital module includes a second subset of digital components. The second virtual boundary includes at least one multiplexer to gate signals transmitted between the first and the second digital module, wherein the second virtual boundary partitions the first digital module from the second digital module. Each multiplexer couples to receive signals generated by the first and second digital module.  
         [0011]     The mixed signal core design in accordance with the present invention includes at least three modes of operation for testing the mixed signal core. The first mode of operation provides digital interface characterization testing of the first and second digital module and analog characterization/trimming testing of the analog module. To initiate this first mode of operation, the first and second virtual boundary are inactive. In a second mode of operation, concurrent testing of the analog module and the first and second digital module is conducted. Analog characterization/trimming testing is performed on the analog module and digital interface characterization testing is performed on the first digital module, while SCAN/BIST testing is performed on the second digital module. To initiate the second mode of operation, the second virtual boundary is activated to gate signals transmitted between the first and second digital module.  
         [0012]     In a third mode of operation, non-concurrent testing of the analog module, the first digital module, and the second digital module is enabled. This third mode of operation supplies SCAN/BIST testing of the first and second subsets of digital components from the first digital module and the second digital module, while the analog module is powered down. The third of operation is initiated by the activation of both the first and second virtual boundaries to gate signals transmitted between the first digital module and the analog module and to gate signals transmitted between the first digital module and the second digital module, respectively.  
         [0013]     Advantages of this design include but are not limited to a structure for testing a mixed-signal core on an SoC IC at a reduced test time over conventional mixed signal cores. This method and structure required for partitioning the logic design of the mixed-signal core and providing test support in accordance with the present invention helps reduce the overall test time for the SoC, while providing thorough test coverage. The mixed-signal core having partitioned modules that can be tested in parallel on the same chip, thereby reducing the overall test time.  
         [0014]     The proposed technique not only assists in testing under normal conditions, but also during burn-in, wherein the analog module is dynamically burned using loop-back tests in the mixed-signal core for additional coverage and the digital modules is burned using scan and memory BIST patterns. This is in contrast to the traditional method where the analog module is powered down while the digital module is burned-in.  
         [0015]     This partitioning scheme also helps in isolating and debugging the noise coupling issues between the analog and digital blocks. The test program can also be independently developed for the different partitions, and integrated later; thereby reducing the test development time.  
         [0016]     These and other features and advantages of the present invention will be understood upon consideration of the following detailed description of the invention and the accompanying drawings.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0017]     For a more complete understanding of the present invention and the advantages thereof, reference is now made to the following description taken in conjunction with the accompanying drawing(s) in which like reference numbers indicate like features and wherein:  
         [0018]      FIG. 1  is a schematic diagram showing the conventional inner structure of a large scale integrated circuit (LSI) which is commonly called a system-on-chip (SoC) IC having a several embedded cores;  
         [0019]      FIG. 2  is a schematic diagram showing a known overall structure for testing an analog/mixed-signal core in the SoC IC;  
         [0020]      FIG. 3  shows the mixed signal core  300  designed on the SoC IC in accordance with the present invention;  
         [0021]      FIG. 4  displays the mixed signal core  400  designed on the SoC IC in accordance with the present invention during a functional testing mode of operation;  
         [0022]      FIG. 5  illustrates the mixed signal core  500  designed on the SoC IC in accordance with the present invention during a concurrent testing mode of operation;  
         [0023]      FIG. 6  shows the mixed signal core  600  designed on the SoC IC in accordance with the present invention during a non-concurrent testing mode of operation;  
         [0024]      FIG. 7  displays the schematic diagram of the first isolation unit in accordance with the present invention; and  
         [0025]      FIG. 8  illustrates the schematic diagram of the second isolation unit in accordance with the present invention.  
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0026]     The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set for the herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art.  
         [0027]     The present invention is best understood by comparison with the prior art. Hence, this detailed description begins with a discussion of known SoC IC similar to that shown in  FIG. 1  as disclosed in U.S. Pat. No. 6,408,412 entitled “Method and Structure For Testing Embedded Analog/Mixed-Signal Cores In System-On-A-Chip”.  FIG. 1  is a schematic diagram showing an example of the inner structure of such an SoC  100  that includes a memory core  102 , a phase lock loop (PLL)  104 , microprocessor core  106 , function specific digital cores  108  and  110 , an analog core  112 , and a mixed-signal core  114 , having an analog module  116  and digital module  118 .  
         [0028]      FIG. 2  is a schematic block diagram showing a structure for testing an analog/mixed-signal core in the SoC IC  100 . In  FIG. 2 , the ATE includes a host computer  200 , an I/O interface  202 , and a hard disk  204  which are provided outside of the SoC IC  100 . Typically, the hard disk  204  stores a test program to be used in testing the analog core  112  and mixed-signal core  114  in the SoC IC. The host computer  200  provides the executable code of assembly language test program to the microprocessor core  106  in the SoC chip  100  through the I/O interface  202 . The assembly language test program is converted into a binary form by the assembler of the microprocessor core  106 . This assembler may reside in the host computer  200  outside the SoC  100 . Thus, the microprocessor core  106  generates test patterns from the object code. These test patterns are applied to the analog/mixed-signal cores  112 ,  114 .  
         [0029]     The present invention is directed to a method and structure for testing such embedded cores, particularly, analog and/or mixed-signal cores, such as an ADC and DAC in an SoC IC.  FIG. 3  illustrates a mixed signal core  300  designed on an SoC IC that includes a top level pin multiplexing unit  302 , a mixed signal module  310  (including an analog module  312  and a first digital module  314 ), a second digital module  322 , a data multiplexer  320 , a first isolation unit  318 , a test clock generator  325  and a partition controller  330 . An important criteria required for creating partitions within mixed-signal core  300  provides that the analog and mixed signal components of the mixed signal core be grouped together to form the analog module  312 . In addition, a portion of the digital components, such as digital filters, that are required for the functional/parametric verification of any of the mixed-signal components, such as a sigma-delta ADC, must be grouped together to form the first digital module  314 . The rest of the digital logic components and memory units within the mixed-signal core  300  are grouped together to form the second digital module  322 .  
         [0030]     Specifically, as shown, the top level pin multiplexing unit  302  provides characterization pin signals and external serial data to the mixed-signal module  310 , data multiplexer  332  and the second digital module  322 . The first isolation unit  316  couples between analog module  312  and the first digital module  314 , while the second isolation unit  318  couples between the first digital module  314  and the second digital module  322 . In addition, the second isolation unit  318  couples to receive a parallel test enable signal (PT) generated by the partition controller  330 . Data multiplexer  320  couples between the first digital module  314  and the second digital module  322  to provide a multiplexed data interface signal to the first digital module  314 . The first digital module  314  provides a register control signal for the data multiplexer  320 . The data multiplexer  320  also couples to receive the parallel test enable signal from the partition controller  330 , the external serial data interface from the top level pin multiplexing unit  302 , and the internal parallel data interface from the second digital module  322 . Test clock generator  325  connects between the partition controller  330  and the first digital module  314  to provide a multiplexed clock. The partition controller  330  also couples to the first digital module  314  and the second digital module  322  to provide a SCAN signal (SCAN), a memory built-in self test (MBIST) signal (MBIST), a test clock control signal (Clk C ), a clock select signal (Select), a burn-in control signal (Burn) for analog and digital, and the parallel test enable signal (P T ), as discussed previously. The SCAN signal include a SCAN-in, SCAN-out, and SCAN-enable component. The MBIST signal includes a MBIST status and an MBIST control component. Within the mixed signal module  310 , an analog module  312  couples to first digital module  314 , wherein first digital module  314  provides a power down signal (P D ), a reset signal (Reset), a mixed-signal clock signal (Clk), an analog test signal (Test), and an analog trim signal (Trim) to analog module  312 . Specifically, first isolation unit  316  couples between the analog module  312  and the first digital module to provide isolation of the data transferred between the two modules during concurrent testing using a characterization testing method upon the analog module  312  and a SCAN/BIST testing method on the first digital module  314 . In operation, the parallel test enable signal generated by the partition controller  330  is used to control isolation unit  316 . Test clock generator  325  receives the test clock control signal (Clk C ) an initial clocking signal from the partition controller  330 . The test clock generator  325  includes a top level clock controller  324 , a digital clock controller  326 , and a clock multiplexer  328 . The clock multiplexer  328  couples to receive the clock select signal (Select) generated by the partition controller  330 .  
         [0031]     Partitioning and isolation of the digital and analog logic permits concurrent testing of both logic sections. Additional DFT (design-for-testability) features are built in to the SoC IC such as isolation units  316  and  318 , data multiplexer  320 , and test clock generation  325  and using dedicated test modes for the partitions created to provide intelligent decoding and control for handling the analog/digital interface.  
         [0032]     The individual partitioned modules,  312 ,  314 , and  322 , are separate entities that can be configured and tested independently and concurrently. This lends support to a dual (concurrent) operating mode such that normal scan and BIST tests can be applied to the digital partition unit  322 , while applying functional characterization tests to the analog and digital modules,  312  and  314 .  
         [0033]     Advantages of this design include but are not limited to a structure for testing a mixed-signal core on an SoC IC at a reduced test time over conventional mixed signal cores. This method and structure required for partitioning and test support in accordance with the present invention helps reduce the overall test time for the SoC, while providing thorough test coverage. A non-concurrent test mode is also supported. In this mode, the entire digital logic is put under test for obtaining additional coverage and ease of debug. Hence, each of the above partitions must have test mode information and relevant control signals.  
         [0034]     Support for these modes requires incorporation of clock multiplexing, isolation at partition interfaces, additional test modes and test pin multiplexing. In addition, separate scan chain stitching and grouping is required along with memory BIST control specifically for the first digital module  314 . In addition, a dual sequencer option on the ATE is required to provide independent timings for each module,  312  and  314 .  
         [0035]     In a first mode of operation, the mixed-signal core  400  of SoC IC as shown in  FIG. 4  includes all of the components as given in  FIG. 3 ; however, the components and connections that are activated during this first mode of operation are shaded. The first mode of operation is the normal mode of operation where functional testing is performed upon all modules  312 ,  314  and  322 . Accordingly, functional testing is applied to the analog module  312 , the first digital module  314 , the second digital module  322 , digital clock controller  326 , and the clock multiplexer  328 . These components are active as shown. The other components, the first isolation unit  318 , the second isolation unit  316 , the data multiplexer  332  and the top level clock controller  324 , are inactive. The data signals for operating the analog module  312  and the first digital module  314  inside the mixed signal core  310  come from the CPU within the digital core (not shown).  
         [0036]     In a second mode of operation, the mixed-signal core  500  of SoC IC as shown in  FIG. 5  includes all of the components as given in  FIG. 3 . Accordingly, the components and connections that are activated during this second mode of operation are shaded. Concurrent functional and SCAN/BIST testing is applied to the mixed-signal module  310  and the second digital module  322 . In this second mode of operation, the first and second digital modules,  314  and  322 , are under SCAN test and hence its registers are programmed by scanning in the data using a serial data interface input at the chip interface as shown through top level pin multiplexing unit  302  and data multiplexer  320 . The SCAN/BIST testing is selected using the SCAN enable component of the SCAN signal. Concurrently, functional tests are applied to the analog module  312  and the first digital module  314 , while the SCAN/BIST tests are applied to the second digital module  322 . The digital clock controller  326  provides the clocking for functional testing of the analog module  312  and first digital module  314 . Isolation unit  318  provides gating of signals between the first digital module  314  and the second digital module  322 . Characterization testing of the analog module  312  and the first digital module  314  is conducted by transferring of signals from the top level pin multiplexing unit  302  through the characterization pins as shown. Test clock and test control pins send test clock and test control signals to partition controller  330 . Partition controller  330  generates a separate SCAN-in and SCAN-out signal along with a SCAN enable through the SCAN input of the second digital module  322 . Partition controller  330  generates a separate MBIST signal and status control signal through the MBIST input to be supplied to the second digital module  322 . In addition, partition controller  330  supplies a clocking signal to the top level clock controller  324 . The clock multiplexer  328  provides a multiplexed clocking signal from the inputs of the top level clock controller  324  and the digital clock controller  326  to first digital module  314  which is transferred to analog module  312 .  
         [0037]     In the third mode of operation, the mixed-signal core  600  of SoC IC as shown in  FIG. 6  includes all of the components as given in  FIG. 3 . Accordingly, the components and connections that are activated during this third mode of operation are shaded. Non-concurrent functional and SCAN/BIST testing is applied to the mixed-signal module  310  and the second digital module  322 . Specifically, the analog module  312  is powered down while SCAN/BIST tests are applied to the first digital module  314  and the second digital module  322 . The digital clock controller  326  multiplexed with the top level clock controller  324  provides the clocking of the SCAN/BIST testing of the first digital module  314 . Isolation unit  316  provides gating of signals between the first digital module  314  and the analog module  312 ; while isolation unit  318  provides gating of signals between the first digital module  314  and the second digital module  322 . To initiate the powering down of the analog module  312 , first digital module  314  provides a power down signal to analog module  312 .           and test control pins send test clock and test control signals to          ler  330 . The partition controller  330  generates separate SCAN-in           signal along with a SCAN enable through the SCAN input to be          irst and second digital module,  314  and  322 . The partition controller          eparate MBIST signal and a status control signal through the MBIST          )plied to the first and second digital module,  314  and  322 . In          rtition controller  330  supplies a clocking signal to the top level clock          The clock multiplexer  328  provides a multiplexed clocking signal to          module  314 . Partition controller  330  provides the burn-in control          ong with the parallel testing control signal PT to first digital module            7 , the first isolation unit  316  between the analog module  312  and          module  314 . Isolation unit  316  provides the isolation required for          ixed-signal components, such as ADCs and DACs, power down          ick signals. During, the first mode of operation where functional          rmed, the parallel test signal PT is provided. Isolation unit  316 ,          aneously provides some additional control. Specifically, isolation is          he first digital module  314  is in the mode of operation where the          Ling is performed. Junk data from the ADC might enter DAC due to          testing. Similarly, the undetermined data may enter the DAC from          affect the BIST/SCAN testing. As such, the first isolation unit  316           r between these mixed-signal components to avoid the transfer of          ral purpose I/O (GPIO) pins provide a flexible parallel interface that          of custom connections and are used for this purpose. These GPIO          for functional characterization testing of analog module  312 .          illustrates the schematic of the second isolation unit  318  connected          at digital module  314  and the second digital module  322 . In this          on is required for the control signals, such as virtual bus (VBUS)          US signals (i.e. Read data, write data, clock ready, ready, byte          accordance with the Change Back Acknowledgment (CBA) standard          Thus, the external serial control interface couples to the second isolation unit  318  to provide these signals. A serial to parallel converter  318   a  couples to a format converter and post processing unit  318   b . A multiplexer  318   c  couples to receive the processed serial interface signals along with the internal parallel control interface signals. The parallel test control signal PT provides control from multiplexer  318   c . This isolation is required when BIST/SCAN testing is performed the second digital module  322  and functional testing is being performed upon the first digital module  314 . Since the output from second digital module  322  may contain junk data, isolation is necessary to shield the first digital module  314 .  
         [0038]     Advantages of this design include but are not limited to a structure and testing of a mixed-signal core on an SoC IC at a reduced test time over conventional mixed signal cores. This method and structure requires that the logic design of the mixed-signal core be partitioned. In addition, test support in accordance with the present invention helps reduce the overall test time for the SoC, while providing thorough test coverage. The mixed-signal core having partitioned modules that can be tested in parallel on the same chip, thereby reducing the overall test time.  
         [0039]     The proposed technique not only assists in testing under normal conditions, but also during burn-in, wherein the analog module  312  is dynamically burned using loop-back tests in the mixed-signal core  300  for additional coverage and the digital modules,  314  and  322 , are burned using SCAN and memory BIST patterns. This is in contrast to the traditional method where the analog module  312  is powered down while the first digital module  314  is burned-in.  
         [0040]     This partitioning scheme in accordance with the present invention aids in isolating and debugging the noise coupling issues between the analog and digital modules,  312  and  314 . A test program may be independently developed for the different partitions, and integrated later; thereby, reducing the test development time.  
         [0041]     Those of skill in the art will recognize that the physical location of the elements illustrated in  FIG. 3  can be moved or relocated while retaining the function described above.  
         [0042]     The reader&#39;s attention is directed to all papers and documents which are filed concurrently with this specification and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference.  
         [0043]     All the features disclosed in this specification (including any accompany claims, abstract and drawings) may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.  
         [0044]     The terms and expressions which have been employed in the foregoing specification are used therein as terms of description and not of limitation, and there is no intention in the use of such terms and expressions of excluding equivalents of the features shown and described or portions thereof, it being recognized that the scope of the invention is defined and limited only by the claims which follow.