Abstract:
A testing circuit includes a signal generator operative to provide a control signal in response to a reference clock signal. The control signal may include both alignment and timing information operative to synchronize the timing and output of the signal generator with a device under test. A clock recovery instrument is electrically coupled to the signal generator. The clock recovery instrument generates the reference clock signal in response to a clock signal from the device under test. The reference clock signal is synchronized with the clock signal from the device under test such that signal generator operation is synchronized with the device under test independent of the behavior of the device under test.

Description:
[0001]     The instant application claims the benefit of U.S. Provisional Application Ser. No. 60/746,958, filed on May 10, 2006. 
     
    
     FIELD OF THE INVENTION  
       [0002]     This invention generally relates to electronic test equipment and, more particularly, to test equipment utilizing a loop back in order to provide synchronization and alignment of signals and data while testing a device.  
       BACKGROUND OF THE INVENTION  
       [0003]     Several difficulties can appear when testing receivers and device input ports; including the difficulty in accessing how well the test signal was received. This is even more challenging when one is prohibited from or lacks easy access to information collected by the receiver at the input port of the device under test. A known way around this is to set the device under test in a loop back mode where all or some of the input port signal information is returned in either raw or processed format via one of the device under test&#39;s output ports. However such known ways work best when the test equipment and the device under test are operated in a synchronous manner. If the clocks of the test apparatus and the device under test are not synchronous then byte(s) of the signal or data may be deleted or inserted by the device under test (DUT) in order to prevent overflow or accumulation of data or signal information. Many devices further decode, encode or otherwise process the signals or data that are looped back. If signals or data are incorrectly aligned when decoding and/or encoding then the looped back signal or data will differ from the expected value.  
         [0004]     One such example is the electrical 10 bit to 8 bit (10 b/8 b) decoding and 8 bit to 10 bit (8 b/10 b) encoding used in high speed digital communications such as Fibre Channel, PCI-express and Serial ATA; if the first of the 10 data bits is not aligned then a different and perhaps invalid 8 bit word would be the outcome with possible errors as a result. Hence in the example there could be twenty different outcomes equivalent to the ten possible misalignments multiplied with the 2 different disparities that errors may cause.  
         [0005]     In creating alignment, often various tests are required. These tests are conventionally complicated by the need for a priori knowledge of the functionality of the DUT. For example, sometimes knowledge about specialized connections or control software is needed. Other times there is a need to repeat the setting of the DUT into various test modes for each desirable test pattern, data or signal.  
       SUMMARY OF THE INVENTION  
       [0006]     A testing circuit according to an exemplary embodiment of the present invention includes a signal generator operative to provide a control signal in response to a reference clock signal. The control signal may include both alignment and timing information operative to synchronize the timing and output of the signal generator with that of a device under test. A clock recovery instrument, for example, a phase locked loop, is electrically coupled to the signal generator. The clock recovery instrument generates the reference clock signal in response to a clock signal from the device under test. The reference clock signal is synchronized with the clock signal from the device under test such that signal generator operation is synchronized with the device under test independent of the behavior of the device under test.  
         [0007]     It is an object of this invention to provide a circuit and method for testing synchronous and asynchronous electronic devices.  
         [0008]     It is an additional object of this invention to provide such a circuit and method, which eliminates the need to have apriori detailed knowledge of the device under test (DUT).  
         [0009]     It is an additional object of this invention to provide a circuit and a method for testing asynchronous electronic devices where apriori detailed knowledge of the DUT is not required.  
         [0010]     In an exemplary embodiment of the circuit and method for testing synchronous and asynchronous electronic devices, the circuit employs clock recovery to synchronize the signal generator of the circuit with the clock of the DUT and a transmission of alignment data or signal to align the DUT with the data and signal of the circuit.  
         [0011]     Using this methodology, the method and circuit  8  in accordance with the invention the need for insertion of extra bit(s) of signal or data at the DUT is removed as a step in accordance with this invention. Additionally, by using the method and circuit  8  in accordance with the invention prevents overflow.  
         [0012]     In an exemplary embodiment the DUT is merely set into a loop-back test mode once and the circuit having a test signal generator sends the appropriate patterns that generate the desirable test data or signal on the output ports of the DUT.  
         [0013]     Noticeably then transmitter output on port(s) of the DUT will be synchronous with the test signal generator. In order to achieve such a synchronous result the DUT and the circuit need to be aligned. Once alignment is achieved the test results can be easily verified and compared with various standards or metrics.  
         [0014]     In another exemplary embodiment it may be faster or more convenient to have the test signal generator provide the test patterns and signals that are subsequently looped back from one of the device under test&#39;s receivers to one of the device under test&#39;s transmitters. A test signal generator in this embodiment is programmed to step through a sequence of test patterns or otherwise provide the test patterns faster than the device under test.  
         [0015]     It is an advantage of this invention to provide a circuit and method in accordance with this invention, which allows for testing of synchronous and asynchronous electronic devices where a minimum of detailed knowledge is required of the DUT. 
     
    
     BRIEF DESCRIPTION OF THE DRAWING  
       [0016]     For a further understanding of the objects and advantages of the present invention, reference should be had to the following detailed description, taken in conjunction with the accompanying drawing, in which like parts are given like reference numerals and wherein:  
         [0017]      FIG. 1  is a schematic representation of the circuit and method in accordance with this invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0018]     An exemplary embodiment of the present invention will now be described with reference to  FIG. 1 .  FIG. 1  is a schematic representation of the testing circuit  8  of the present invention used to test synchronous and asynchronous devices, for example, a device under test (DUT)  10 , according to the present invention. The testing circuit  8  includes a test signal generator  20  connected to a clock recovery instrument  40  by a clock synchronous with a reference clock  21 . The testing circuit  8  also includes a signal analyzer  110  having a clock input port  111  coupled to the clock recovery instrument  40  via signal line  112  and a signal input port  113  coupled to the clock recovery instrument  40  via instrument line  100 .  
         [0019]     The test signal generator  20  includes one or more output ports  121  coupled to the one or more input ports  200  of the DUT  10  via communication line  120 , and a clock input port  131  coupled to the reference clock  21 . In one embodiment the clock recovery instrument  40  is built into or enclosed within the test signal generator  20 .  
         [0020]     In an alternative embodiment, the circuit  8  includes an alternative signal generator  30 . As will be understood more fully hereinafter, the signal generator  30  comprises an arbitrary waveform generator and/or a protocol generator and is similarly connected to input ports  200  of the DUT  10 .  
         [0021]     The DUT  10  includes one or more input ports  200 , one or more output ports  300 , a FIFO buffer  202  and a decoding module  204 , for example, an integrated circuit, a software module being executed by a processor or other control mechanism (not shown) or other suitable device or combinations thereof configured to decode any data  203  provided by the FIFO buffer  202 . Typically, the DUT  10  includes a reference clock  208  and an encoding module  206 , for example, an integrated circuit, a software module being executed by a processor or other control mechanism (not shown) or other suitable device or combinations thereof configured to encode data  205  provided, for example, by the encoding module  204  or the clock signals from the reference clock  208 .The DUT  10  may be set in a loop back mode by either mechanical or electronic means. In order to electronically set the DUT  10  to the loop back mode, a corresponding signal  120  is transmitted to one or more of the input ports  200  of the DUT  10  by either the test signal generator  20  or the arbitrary waveform protocol generator  30 . The signal  120  may be in the form of a data stream, pattern or simple digital word.  
         [0022]     In the exemplary embodiment shown, the loop back circuit or mode  12  is initiated by the DUT  10  receiving a corresponding control signal  120  from test signal generator  20 . In another exemplary embodiment, the test waveform protocol generator  30  provides the control signal  120  that sets DUT  10  in the loop back mode. The test signal generator  30  comprises one of the following an out-of-band (OOB) signal generator or arbitrary waveform generator or a protocol generator.  
         [0023]     In the exemplary embodiment shown in  FIG. 1 , the clock recovery instrument  40  comprises a phase locked loop (PLL) circuit. The clock recovery instrument  40  recovers the clock timing signal  100  from at least one of the output ports  300  of the DUT  10 . The recovered clock signal  100  is subsequently used to clock the data or signals sent to one or more of the DUT input ports  120  via reference clock  21 .  
         [0024]     While the recovered clock signal  100  is commonly used to recover and analyze signals and/or data, the method in accordance with this invention uses the recovered clock signal, provided to the data signal analyzer  100  on line  112 , for sending signals and data  120  synchronized with the DUT  10 .  
         [0000]     Signal Alignment  
         [0025]     The circuit and method in accordance with the invention herein also aligns the signal as well as data. The test generator  20  or in the case of the alternative embodiment, the arbitrary waveform protocol generator  30 , transmits a control signal to the DUT  10  on line  120 . It will, of course, be appreciated that the control signal  120  may be in the form of data or a signal pattern.  
         [0026]     Typically the DUT  10  merely recognizes the beginning and the end of special byte or bytes or word(s) or symbol(s), for example, the ALIGN symbol used in Serial ATA. The circuit and method in accordance with the invention herein uses this functionality of the DUT  10  by either first transmitting a sequence of the special alignment byte or bytes or word(s) or symbol(s); or by embedding the special alignment byte or bytes or word(s) or symbol(s) within the sequence transmitted by the test signal generator  20  on line  120 . The DUT  10  thusly aligns its internal signal processing with the test signal generator  20  creating alignment between the circuit  8  and DUT  10 .  
         [0027]     In the exemplary embodiment, the alignment is done prior to decoding, encoding and other processing. Subsequent to alignment, a second test signal is generated of a second desired test data or signal sequence and provided to the DUT  10  on line  120 . In one implementation, the alignment signal and subsequent test signal (test data or signal sequences) are the same. More commonly there will be two different test signals. In other words, there will be an alignment signal where the DUT  10  recognizes the first and last bit(s) or byte(s) and subsequently a second test signal comprising a data or signal sequences. In some implementations the signals will be stored, generated or analyzed as a single stream where the one longer sequence contains both functions.  
         [0028]     In more common implementation of the alignment method above, the test signal generator  20  first sends the ALIGN words used in Serial ATA. The generator  20  uses an arbitrary clock frequency near the nominal clock frequency of the DUT  10 , while clock recovery instrument  40  recovers the clock  100  from the DUT  10 . The test signal generator  20  then continues to send the test pattern including alignment data or signals using the recovered clock  100  via reference clock  21 .  
         [0029]     The change to use the recovered clock is implemented in one of two ways. Firstly, the first arbitrary but near nominal clock frequency source is switched to the clock from the clock recovery instrument  40  after the clock recovery instrument  40  has completed the acquisition and recovery of the clock timing signal  100  from at least one of the output ports  300  of the DUT  10 . Or secondly, by starting the clock frequency instrument  40  at the near nominal clock frequency and continue to use said clock while waiting for the clock recovery instrument  40  to recover the clock timing signal  100  from at least one of the output ports  300  of the DUT  10 . It will be appreciated that during the alignment process, either of these implementations may be used. It will also be appreciated that the user may switch between implementations as desired.  
         [0030]     The combination of clock recovery combined with the transmission of alignment data or signals, such as the ALIGN words in Serial ATA, provides for fast synchronization of a device under test in loop back mode. Not only does the combination allow simultaneous settling of the clock frequency and data or signal alignment, but the combination also removes the difference between clock frequencies of test signal generator  20  and DUT  10 . This eliminates the need to deal with insertion or deletion of bit(s) of signal or data, for example insertion or deletion of extra ALIGN words in Serial ATA, otherwise used by the DUT  10  to fill or shorten the mis-match in clock frequency. Further, the signal or data returned at the one or more output ports  300  of the DUT  10  will be aligned with the internal processing, encoding/decoding of the DUT  10  and therefore will the expected value.  
         [0031]     Once loop back synchronization has been achieved, any combination of data or signal sequence(s) may follow, for example one of the following: high frequency, medium frequency, low frequency or lone-bit test pattern(s). Successful synchronization and alignment are achieved when there is an expected amount of bit(s) of data or signal appearing at the output ports  300  of the DUT  10 . For example, there will be no less and no extra ALIGN words in a Serial ATA application. This is sometimes easier to see when switching to another test pattern or signal, such as high frequency, medium frequency, low frequency or lone-bit test pattern(s), which do not include ALIGN words or by using a pattern, such as CJTPAT in Fibre Channel, which includes portions with and without ALIGN words.  
         [0032]     Using the circuit  8  and the method in accordance with this invention, loop back test mode synchronization is achieved in situations where the DUT  10  is unable to be set into a transmitter (output) test mode. In those cases the clock recovery instrument  40  and a data/signal analyzer  1   10  are used for the test, for measurement, verification or validation of a transmitter, the output ports  300  of DUT  10 .  
         [0033]     These tests are conventionally complicated by the need of a priori knowledge of the functionality of the DUT  10 . For example, sometimes knowledge about specialized connections or control software is needed. Other times there is a need to repeat the setting the DUT  10  into various test modes for each desirable test pattern, data or signal.  
         [0034]     This invention eliminates the above complications merely setting the DUT  10  in a loop-back test mode once and then allows the test signal generator  20  to send the appropriate patterns that generate the desirable test data or signal on the output ports  300  of the DUT  10 . Noticeably then transmitter output on port(s)  300  of the DUT  10  will be synchronous with the test signal generator  20  and the internal processes of the DUT will be aligned with the data or signal providing a expected output on ports  300  that can be easily verified and compared with various standards or metrics.  
         [0035]     It may be faster or more convenient to have the test signal generator  20  provide the test patterns and signals that are subsequently looped back from one of the device under test&#39;s receivers to one of the device under test&#39;s transmitters. A test signal generator  20  may for example be programmed to step through a sequence of test patterns or otherwise provide the test patterns faster than the DUT  10 .  
         [0036]     While the foregoing detailed description has described several embodiments of the circuit  8  and various methods of test synchronous and asynchronous electronic devices with clock signals in accordance with this invention, it is to be understood that the above description is illustrative only and not limiting of the disclosed invention. Particularly, there can be a variety of test input signal generators used initiating a variety of different signals or signal types. It will be appreciated there are but exemplary embodiments discussed above and that there are numerous embodiments that are not mentioned but within the scope and spirit of this invention. Thus, the invention is to be limited only by the claims as set forth below.