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Keysight Technologies
Generating Looped Test Patterns
or PRBS Signals with a Preamble



                                  Application Note
                    Some digital integrated circuits (IC) use special modes to test all the internal states of opera-
Problem statement   tion. To get into such a mode the IC requires a defined command be sent to the device under
                    test (DUT). As shown in Figure 1, in some instances a portion of the test pattern is used once
                    to advance the special IC mode to an area of operation that requires repetitive use of a test
                    pattern in order to thoroughly test the device.



                                 Play once                                  Play multiple times

                                 Preamble                                       Test pattern


                    Figure 1: Flow chart of the test signal generation


                    It is very important that the test pattern and the preamble are correctly timed and generating
                    such a sequence may not be a trivial task. If the test pattern is not received at the necessary
                    time, the device can time out and return into a pre-defined state, delaying testing, because the
                    preamble must be rerun to bring the DUT back into the desired test mode.




                    Both the Keysight Technologies, Inc. 81150A and 81160A pulse function arbitrary generators
Solution proposal   have the capability to generate such test signals. They offer two ways to create these signals.
                    One way is through the use of the built-in pattern sequencer; the other is using the channel
                    add capability. To illustrate these functions, this application note provides examples using the
                    81160A model shown in Figure 2, though they also apply to the 81150A. Additionally, this paper
                    highlights the advantages and disadvantages of each of the options.




                    Figure 2: The Keysight Technologies 81160A pulse function arbitrary generator.




                                             2
                    Using the pattern sequencer is a very simple and straight forward way to generate test signals.
Pattern sequencer   In the Pattern Editor menu of the 81160A (shown in Figure 3) the user defines the preamble and
solution approach   the required test data pattern, then uses a pointer to define the beginning of the loop sequence.
                    The number of loops is defined in the Burst menu and typically the user defines when the test
                    signal should start playing. Once the output is activated, the test signal can be captured and
                    visualized with the help of an oscilloscope.




                    Figure 3: Pattern Editor menu of the 81150A and 81160A.




                                           3
                    A pattern sequencer is easy to use. Setup requires only one cable connection between the
Pattern sequencer   generator and the DUT. Creating a short, user-defined pattern is done directly on the front panel
solution approach   of the generator instead of programming the pattern using a computer and then downloading it
                    to the instrument.
(continued)
                    While a one-channel generator unit is sufficient for testing one channel of the device, a two-
                    channel unit can be used to generate signal distortions and add them internally to the signal
                    waveform to refine the test of the DUT.

                    For longer and more comprehensive test patterns, such as a PRBS, a free Pattern Editor
                    and Sequencer software tool is available for downloading at: Download Pattern Editor and
                    Sequencer. A screenshot of the software tool's user interface is shown in Figure 4.




                    Figure 4: Screen shot of the Pattern Editor and Sequencer user interface




                                            4
                    A second method for generating an initial test mode signal is through the use of the channel
Channel add         add capability of the 81150A and 81160A instruments. As shown in Figure 5, the principle is
solution approach   very simple:

                      

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