Abstract:
A device and method for generation of Intersymbol interference (ISI) effects on serial data by direct digital synthesis is described. The features of the present invention allow user to set parameters such as data rate, voltage amplitude, encoding scheme etc. as per requirements. An ISI parameter value is selected and applied to the serial data to produce ISI effects in the serial data. Alternatively according to another feature the patterns may be set as per industry standards.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates generally to signal generators and more specifically to a signal generator that produces intersymbol interference (ISI) effects on serial data by direct digital synthesis. 
       BACKGROUND OF THE INVENTION 
       [0002]    High speed serial data designers are required to design robust and reliable receivers to meet the required Bit Error Rate (BER) for specified conditions. Receiver testing of any high speed serial data standard will include compliance testing and jitter tolerance testing. The compliance test comprises the testing of the receiver&#39;s performance for specified conditions to achieve the desired result. The tolerance tests involve subjecting the receiver to progressively increasing jitter until breakdown. The jitter can be classified as deterministic jitter D j  and random jitter R j  The deterministic jitter D j  is comprised of periodic jitter P j , duty cycle distortion (DCD) and Intersymbol interference (ISI). ISI is inevitable in most physical systems due to limited bandwidth. Both DCD and ISI depend on the type of data stream and data rate. These are correlated with data and are classified as data dependent jitter (DDJ). Therefore to carry out compliance and jitter tolerance tests, it is important that the serial data is subjected to jitter in a controlled manner. 
         [0003]    Intersymbol interference is currently generated using a circuit board on which signal traces are formed having various lengths, such as a differential Intersymbol interference (ISI) Test Board, manufactured and sold by Synthesys Research Inc., Menlo Park, Calif. One of the challenges of using such circuit boards is that the characteristic of the trace varies with the pattern and data rate. Further, the traces come with a Fixed ISI for a given data rate, hence it is not possible to generate intermediate ISI values. Typical trace lengths of a Synthesis Research ISI Test Board are 2.42″, 5″, 6.75″, 9″, 12″, 17″, 24″, 31″, and 40″ which does not allow for intermediate trace lengths between the set lengths. Normally, users would like to know the exact break point of their design but do not have the fine control over the ISI generated out of the ISI Test Board. 
         [0004]    Another issue is that changing from one trace to another needs calibration. This is often time consuming because not only the ISI needs to be calibrated but all the other associated jitters, such as P j  and R j , need to be calibrated. Additionally, the actual ISI output from the test board may not exactly match the ISI in the test board data sheet because of other components, such as connectors, cables and the like, in the test system which would interfere with the ISI generated. This requires the calibration of test system for each new test set-up. 
       SUMMARY OF THE INVENTION 
       [0005]    Accordingly, the present invention is to a signal generating device, such as a signal generator, and a method of setting serial data pattern parameters and an intersymbol interference effects parameter to generate a serial data pattern having intersymbol interference effects. The signal generating device has a display and a central processing unit generating a user interface on the display for setting parameters for the serial data pattern and the parameter for intersymbol interference effects on the serial data pattern. The central processing unit generates a waveform record file using the serial data pattern parameters and the intersymbol interference effects parameter. A waveform generation circuit receives the waveform record file and generates a serial data pattern analog output signal having intersymbol interference effects defined by the intersymbol interference parameter. 
         [0006]    The display maybe internal to the signal generating device or an external display coupled to the signal generating device. An external controller, such as a personal computer, may be coupled to the signal generating device with the external controller generating the user interface on an external display for setting parameters for the serial data pattern and the parameter for intersymbol interference effects on the serial data pattern and generating the waveform record file using the serial data pattern parameters and the intersymbol interference effects parameter for use by the waveform generation circuit. 
         [0007]    The intersymbol interference effects parameter has a range from 0.0 to 1.0 Unit Intervals or 1 picosecond to 2 microseconds depending on the unit value for the intersymbol interference effects parameter. The central processing unit increments the intersymbol interference effects parameter in units of 0.001 Unit Interval where the intersymbol interference effects parameter is expressed in Unit Intervals and 1.0 picosecond where the intersymbol interference effects parameter is expressed in time. The intersymbol interference effects in the waveform record file are generated by a single pole digital infinite impulse response (IIR) low pass filter controlled by the intersymbol interference effects parameter. 
         [0008]    A method of generating intersymbol interference effects on a serial data pattern has the steps of generating a user interface on a display device for setting serial data pattern parameters and an intersymbol interference effects parameter, selecting parameters for a serial data pattern and selecting a parameter for intersymbol interference effects on the serial data pattern. A waveform record file is generated from the serial data pattern parameters and the intersymbol interference effects parameter and a serial data pattern analog signal is generated from the waveform record file having intersymbol interference effects defined by the intersymbol interference effects parameter. 
         [0009]    The generation of the intersymbol interference effects on a serial data pattern of the waveform record file has the step of generating a single pole digital IIR low pass filter controlled by the intersymbol interference effects parameter for generating the intersymbol interference effects in the waveform record file. The generation of the waveform record file includes the step of compiling the serial data parameters to generate serial data pattern digital data modified by the single pole digital IIR low pass filter defined by the intersymbol interference effects parameter. 
         [0010]    A method of calibrating intersymbol interference effects on a serial data pattern in a signal channel includes the steps of connecting a signal generating device to a waveform display and processing instrument, selecting parameters for the serial data pattern, and selecting a parameter for intersymbol interference effects on the serial data pattern to an initial value of zero. A waveform record file is generated from the serial data pattern parameters and the intersymbol interference effects parameter, and a serial data pattern analog signal is generated from the waveform record file having intersymbol interference effects defined by the intersymbol interference effects parameter. An intersymbol interference value is generated in the waveform display and processing instrument from the received serial data pattern analog signal from the signal generating device and coupled to the signal generating device. The intersymbol interference effects parameter is incremented by 0.1 to a maximum intersymbol interference value of 1.0 with the steps of generating the waveform record file, the serial data pattern analog signal, the intersymbol interference value, and the coupling of the intersymbol interference value to the signal generating device being repeated for each incremental value on the intersymbol interference effects parameter. A linear equation is generated from a curve fit of the intersymbol interference values, with the parameters of the linear equation being applied to an IIR filter controlled by the intersymbol interference effects parameter for generating the intersymbol interference effects in the waveform record file. 
         [0011]    The objects, advantages and other novel features of the present invention are apparent from the following detailed description when read in conjunction with the appended claims and attached drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]      FIG. 1  is a front view of a signal generator for producing ISI effects on a serial data pattern according to the present invention. 
           [0013]      FIG. 2  is a representative block diagram of a signal generator according to the present invention. 
           [0014]      FIG. 3  is an initial user interface for producing ISI effects on a serial data pattern according to the present invention. 
           [0015]      FIG. 4  is representation of a base pattern pop-up window in the user interface for producing ISI effects on a serial data pattern according to the present invention. 
           [0016]      FIG. 5  is a representation of a Transmitter pop-up window in the user interface for producing ISI effects on a serial data pattern according to the present invention. 
           [0017]      FIG. 6  is a representation of a channel/cable pop-window in the user interface for producing ISI effects on a serial data pattern according to the present invention. 
           [0018]      FIG. 7  is a representation of a compile setting in the user interface for producing ISI effects on a serial data pattern according to the present invention. 
           [0019]      FIG. 8  is a representation of a graph setup in the user interface for producing ISI effects on a serial data pattern according to the present invention. 
           [0020]      FIG. 9  is a flow chart representing the steps in producing ISI effects on serial data pattern according to the present invention. 
           [0021]      FIG. 10  are graphs showing frequency and phase responses of a digital IIR filter producing ISI effects for different values of an ISI parameter “k”. 
           [0022]      FIGS. 11A and 11B  represent a flow chart for calibrating the digital Infinite Impulse Response (IIR) filter producing ISI effects. 
           [0023]      FIG. 12  is a chart showing jitter component setting for Display Port high speed serial data pattern. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0024]    Referring to  FIG. 1 , there is shown a signal generator  10 , such as the AWG7102 manufactured and sold by Tektronix, Inc. Beaverton, Oreg. The signal generator  10  has a front panel  12  with controls  14 , such as buttons and knobs or the like, and a display device  16 , such as a liquid crystal display, cathode ray tube or the like. The signal generator  10  also has a CD or DVD/CD drive for storing waveform data, executable programs and the like. User defined signals are generated and output by the signal generator  10  using the front panel controls in conjunction with a user interface displayed on the display device  16 . 
         [0025]    Referring to  FIG. 2 , there is shown a representative block diagram of the AWG7102 signal generator  10  for producing Intersymbol interference effects on serial data. The signal generator  10  has a central processing unit (CPU)  20  that controls the operation of the instrument according to programs stored on electronic media, such as a Compact Disc (CD). A memory  22 , such as RAM memory, is used for a work area for the CPU  20  to read programs from storage device  24 , such as a hard disk drive. A user can set up the signal generator  10  to generate an output test signal via the buttons, knobs and the like  14  on the front panel  12  of the instrument. The display device  16  may display a user interface for setting various parameters for the output test signal and visualizing an output signal as a function of the parameter settings. An external display output circuit  26  provides a video output which may be connected to an external display  28  for providing a larger display area in addition to the built-in display  16  of the signal generator. A waveform generation circuit  30  generates the output test signal based on user defined parameters. In this example, the waveform generation  30  circuit has a trigger input and an event input and two channel outputs. An input/output port  32  is used for connecting an external keyboard  34 , a pointing device, such as a mouse  36 , and the like to the signal generator. The external keyboard  34  and/or mouse  36  may be included as part of the front panel controls of the signal generator for setting parameters. The blocks are coupled together via a signal and data bus  38 . The bus  38  of the signal generator may have a Local Area Network (LAN) interface  40  for connecting the signal generator to an external controller, such as a personal computer (PC)  42  or other testing instruments. The LAN interface  40  allows the user interface to operate on the PC  42  and pass output signal data to the signal generator  10  and also enables the PC  42  to control the signal generator  10  over a network. Alternatively, a General Purpose Interface Bus (GPIB) interface may be used for the LAN interface  40 . 
         [0026]    Referring to  FIG. 3 , there is shown an initial user interface  50  for setting parameters to produce various levels of Intersymbol interference (ISI) effects on serial data patterns. The initial user interface  50  and subsequent user interfaces operate under program control of the CPU  20  with the user interface programs stored on the storage device  24 . The user interfaces may be displayed on the display device  16  or on the external display  28 . Alternately, the user interface programs may be stored and accessed by the PC  42  with the PC  42  processing the parameters and generating an output file that is coupled to the signal generator  10 . The programs controlling the various interfaces on the signal generator  10  may be accessed via an icon on the display device  16  or by clicking on a start tab and clicking the appropriate program from a list of programs stored in the signal generator  10 . The initial interface  50  includes a number of pop-up windows that are activated by clicking on various tabs  52  in the initial user interface  50 . The initial user interface  50  has a BASE PATTERN tab  54  that activates a BASE PATTERN pop-up window  56 . The BASE PATTERN pop-up window  56  is automatically activated with the initial user interface  50 . 
         [0027]      FIG. 4  is a more detailed representation of the BASE PATTERN pop-up window  56  showing four defined regions of the BASE PATTERN pop-up window  56 : BASE PATTERN  58 , SIGNAL  60 , ENCODING  62  and RISE/FALL  64 . The BASE PATTERN region  58  has buttons  66 ,  68  and  70  that allows a user to select a serial data pattern on which the ISI effects are generated. Clicking on the STANDARD button  66  activates a STANDARD box  72  and a PATTERN box  74 . Click on the STANDARD box  72  displays a general serial data pattern and various serial data standards requiring compliance testing. Once a particular serial data standard is selected, clicking on the PATTERN box  74  displays various waveform patterns defined by the selected serial data standard, such as PRBS7. Clicking on the FROM FILE button  68  highlights a FILE box  76  in which a user can enter a previously stored data file. Clicking on the USER PATTERN button  70  highlights a Pattern Box  78  in which a user may enter a serial data pattern. The pattern may be entered as “0” and “1” binary data or hexadecimal data by clicking on appropriate BINARY or HEX buttons  80 ,  82 . 
         [0028]    The SIGNAL region  60  has a DATA RATE box  84 , an AMPLITUDE box  86 , and an IDLE STATE box  88 . Clicking on the DATA RATE box  84  allows a user to set the data rate of the serial data. The data rate may be adjusted from 10 Mega Bits per second to 20 Giga bits per second. When the STANDARD button  66  is activated, the data rate is automatically selected as a function of the selected serial data standard. Clicking on the AMPLITUDE box  86  allows the user to select the voltage level of the serial data pattern. The user may vary the voltage level from 250 mV to 1V. The IDLE STATE box  88  is active when SATA is selected in the STANDARD box  72  and Idle Pattern is selected in the PATTERN box  74 . The Idle State may be viewed as selectable periods of DC within the Idle State pattern. 
         [0029]    The ENCODING region  62  has an ENCODING SCHEME box  90  that allows the user to set the type of coding scheme for the serial data pattern. A user may select from NRZ or NONE NRZ. Clicking on the 8B10B box  92  activates an algorithm for the mapping of 8-bit symbols to 10-bit symbols to achieve DC-balance and bounded disparity. The RISE/FALL region  64  has RISE/FALL TIME buttons  96  and  98  for respectively selecting 10/90 or 20/80 percent rise and fall time. A RISE box  100  allows the user to select the rise time of the serial data pattern leading edges. A FALL box  102  allows the user to set the fall time of the serial data pattern trailing edges. The DCD box  104  allows the user to vary the amount of Duty Cycle Distortion in the serial data pattern. The rise, fall and DCD times may be defined in seconds or unit intervals using the respective SETTING boxes  106 . 
         [0030]    Clicking on the TRANSMITTER tab  110  activates a TRANSMITTER pop-up window  112  as shown in  FIG. 5 . The TRANSMITTER pop-up window  112  has boxes  114  that allow the user to set parameters for variable amounts of peak-to-peak Periodic Jitter and RMS Random Jitter, set Spread Spectrum Clock (SSC) parameters, Noise parameters in Volts (RMS) and Pre/De-emphasis parameters in dB or volts. The user has the option of placing the noise at the near end or the far end of the serial data pattern. 
         [0031]    Clicking on the CHANNEL/CABLE tab  120  activates a CHANNEL/CABLE pop-window  122  as shown in  FIG. 6 . The user activates an ISI box  124  and SETTING box  126  by clicking on an ISI button  128 . The user selects an amount of ISI to be applied to the serial data pattern by clicking on the ISI box  124  and entering an amount. The amount of ISI may be expressed in seconds or unit intervals. The selection range for the ISI is 0.0 to 1.0 Unit Interval that is incremented in units of 0.001 Unit Interval when ISI is expressed in Unit Intervals. The selection range for the ISI is 1 picosecond to 2 microseconds that is incremented in units of 1 picosecond when ISI is expressed in seconds. The user may also activate boxes that allow the user to select touchstone S-Parameters files and add ISI scaling to the files by clicking on an S-Parameter Filter button  130 . 
         [0032]    Referring back to  FIG. 3 , once the user has set the parameters for the serial data pattern and selected the amount of ISI to be applied to the serial data pattern, the user activates a COMPILE SETTINGS pop-up window  140 , shown in  FIG. 7 , by clicking on a COMPILE SETTINGS button  142  on the initial user interface  50  tool bar  144 . The COMPILE SETTINGS pop-up window  140  has a WAVEFORM NAME box  146  for providing a user defined name for a waveform file generated by the signal generator  10  using the user defined parameters and ISI value for the serial data pattern. The data rate for the serial data pattern entered using the BASE PATTERN pop-up window  56  is displayed next to “Data Rate”. The user can click on a SAMPLE RATE button  148  or a SAMPLES PER UI button  150  to activate respective SAMPLE RATE or SAMPLES PER UI boxes  152 ,  154 . The user may manually set the sampling rate or samples per UI by entering appropriate values based on the serial data pattern and the data rate. The sampling rate or samples per UI may be automatically set based on the data rate and the serial data pattern by clicking on AUTOMATIC box  156 . A BANDWIDTH EXPANSION FILTER region  158  may be activated by clicking on a BANDWIDTH EXPANSION FILTER button  160 . The BANDWIDTH EXPANSION FILTER region  158  allows a user to select or turn off various interleaving parameters. A COMPILE BUTTON PREFERENCES region  162  allows the user to select either COMPILE ONLY or COMPILE AND SENT TO parameters for the compiled waveform record defined by the serial data pattern parameters and the ISI parameter. Toward the bottom of the COMPILE SETTINGS pop-up window  140  are additional parameters that may be set by clicking on the appropriate boxes  164 . One of the parameters is SHOW GRAPH AFTER COMPILE which displays the serial pattern data in various forms in two graph regions  165  at the bottom of the initial user interface  50 . At the bottom of the COMPILE SETTINGS pop-up window  140  are COMPLE, OK, CANCEL and HEPL buttons  166 ,  168 ,  170  and  170  that allows the user to select various options related to the COMPILE SETTINGS pop-up window  140 . One option is to click on the COMPILE button  166  that initiates the compiling of the serial data pattern and ISI parameters to generate a waveform record file containing digital data for generating an analog serial data pattern from the signal generator  10 . Another option is to click on the OK button  168  that saves the parameters selected in the COMPILE SETTINGS pop-up window  140  and closes the window  140 . A further option is to click on the CANCEL button  170  that closes the COMPILE SETTINGS pop-up window  140  without saving the parameters selected in the window  140 . Clicking on the HELP button  172  activates a HELP pop-up window from which the user may seek help. 
         [0033]    Referring back to  FIG. 3  again, initial user interface  50  tool bar  144  has a GRAPH SETUP button  180  which may be clicked to activate a GRAPH SETUP pop-up window  182  as shown in  FIG. 8 . The GRAPH SETUP pop-up window  182  has an AVAILABLE GRAPHICS box  184  on the left side containing a number of graphic symbols  186  and wording describing each of the graphic symbols  186 . One the right side of window  182  is a SELECTED GRAPHICS box  188  containing graphic symbols  186  selected from the AVAILABLE GRAPHICS box  184 . Between the boxes  184  and  188  is ADD and REMOVE buttons  190  and  192 . These buttons  190 ,  192  add and remove the graphic symbols  186  from the SELECTED GRAPHICS box  188 . A user selects a graphic symbol  186  from the AVAILABLE GRAPHICS box  184  by clicking on the graphic symbol  186  to highlight the symbol. Clicking on the ADD button  190  copies the selected symbol from the AVAILABLE GRAPHICS box  184  to the SELECTED GRAPHICS box  188 . Clicking on a graphic symbol  186  in the SELECTED GRAPHICS box  188  to highlight it and clicking the REMOVE button deletes the selected graphic symbol  186  from the SELECTED GRAPHICS box  188 . The SELECTED GRAPHICS box  188  may contain up to two symbols matching the number of graph regions  165  at the bottom of the initial user interface  50 . At the bottom of the GRAPH SETUP pop-up window  182  are OK, CANCEL and HELP buttons  194 ,  196 ,  198 . The OK button  194  saves the selected graphs and closes the GRAPH SETUP pop-up window  182 . The Cancel button  196  closes the GRAPH SETUP pop-up window  182  without saving the selected graphs. The HELP button  198  activates a HELP pop-up window from which the user may seek help. 
         [0034]    The initial user interface  50  tool bar  144  has a COMPILE button  196 (as shown in  FIG. 3 ) that functions in the same manner as the COMPILE button  166  (as shown in  FIG. 7 ) in the COMPILE SETTINGS pop-up window  140  by initiating the compiling of the serial data pattern and ISI parameters to generate a waveform record file containing digital data for generating an analog serial data pattern from the signal generator  10 . 
         [0035]      FIG. 9  is a flow chart illustrating the steps in generating ISI effects on a serial data pattern with reference to previous figures. The process is entered by activating the program controls for generating the ISI effects on the serial data pattern at Step  200 . The BASE PATTERN and the COMPILE SETTINGS pop-up windows  56 ,  140  are activated for selecting parameters of a serial data pattern that include the data rate, amplitude, encoding scheme, raise and fall time, and sample rate of the serial data pattern at Step  202 . The Channel/CABLE pop-up window  122  is activated for selecting an amount of ISI that is to be applied to the serial data pattern at Step  204 . The COMPILE button  196  on the initial user interface  50  tool bar  144  is activated which initiating the compiling of the serial data pattern parameters and ISI parameter to generate a waveform record file containing digital data for generating an analog serial data pattern from the signal generator  10  at Step  206 . The waveform record file is stored in the memory  22  of the signal generator  10  and provided to the waveform generation circuit  30  that converts the waveform record file to an analog serial data pattern signal having ISI effects that is output by the signal generator  10  at Step  208 . The step order for producing ISI effects on a serial data pattern is by example only and the order of the steps may be changed without departing from the scope of the invention. For example, the order in which the parameters are selected may be changed as well as which COMPILE button (COMPILE button  196  or COMPILE button  166 ) is used to initiate the compiling of the serial data pattern parameters and the ISI parameter. 
         [0036]    In a specific example of generating ISI effects on a serial data pattern, the serial data pattern parameters are set as a general standard having a PRBS7 pattern having a data rate of 1 GB/s, a voltage amplitude of 1V, an encoding scheme that does not return to zero, rise and fall times of the leading and trailing edges of the serial data pattern of 200 psec at a 10 to 90 percent level and a sample rate of 10 Gs/s. The jitter, SSC, noise and Pre/De-emphasis parameters in the TRANSMITTER pop-up window  112  are set to zero. The ISI parameter is selected using the Channel/CABLE pop-up window  122 . The ISI effects are generated using a single pole digital IIR (Infinite Impulse Response) low pass filter that is based on the data rate, sampling frequency and the data pattern. The digital IIR filter is controlled by the single ISI parameter. The recursive equation of the IIR filter is: 
         [0000]        Y ( n )= A·x ( n )− B·y ( n −1), where 
         [0000]        A =1 /k  and  B =( k −1)/ k          x(n)=input serial data   Y(n)=output data with desired ISI   A=forward path multiplier   B=recursive path multiplier
 
The above recursive equation depicts a single pole IIR filter. The frequency and phase responses for the different values of k are shown in the graphs of  FIG. 10 . It is observed that as the single parameter k increases, the filter has a steeper fall off. The IIR filter is generated at the time the serial data parameters and the ISI parameter are compiled. The digital data representing the serial data pattern is generated and filtered by the IIR filter to modify the digital data to produce the ISI effects as a function of the selected ISI parameter.
         
         [0041]    The ISI generated through the above described IIR filter needs to be calibrated. Even with the ISI parameter set to zero, a certain amount of ISI is measurable on a measurement instrument, such as an oscilloscope, due to the data pattern, the low pass nature of the signal generator  10  and the oscilloscope, and the cabling between the signal generator  10  and the oscilloscope. Referring to  FIGS. 11A and 11B , there are shown a flow chart illustrating the steps in calibrating the ISI. The signal generator  10  is connected to the measurement instrument, such as a DPO72004 Digital Phosphor Oscilloscope using DPOJET Analysis Software, at step  220 . One connection is from an output of the signal generator  10  to an input to the oscilloscope. A second connection is made between the signal generator  10  and the oscilloscope via a LAN or a GPIB bus. Serial data pattern parameters are set at Step  222 . The ISI parameter is set to zero at step  224  and the data pattern parameters and the ISI parameter are compiled to generate a waveform record file containing digital data for generating an analog serial data pattern with ISI effects. The waveform record file is stored at step  226 . The waveform record file is processed by the waveform generation circuit  30  which converts the waveform record file to an analog serial data pattern with ISI effects and the signal generator  10  generates an analog serial data pattern with ISI effects output at step  228 . The signal output is coupled to the oscilloscope which measures the resulting ISI due to data and hardware characteristics and generates a value for the ISI at step  230 . The generated value for the ISI is coupled back to the signal generator  10  via over LAN or GPIB bus and stored at Step  232 . The ISI parameter is incremented by 0.1 UI at Step  234  and the compiling, the generating and measuring of the resulting analog signal with the dialed-in ISI, and the generation, sending and storing of the ISI value from the oscilloscope to the signal generator  10  is repeated at STEP  236 . The process continues with the ISI parameter being incremented by 0.1 UI until the ISI parameter is at 1 UI. A curve is fitted to the stored ISI values from the oscilloscope and a linear equation having slope and constant parameters is obtained at Step  238 . The parameters of the equation are applied to the IIR filter algorithm at Step  240 . The calibration of the ISI filter is valid for a given set of conditions. If the parameters of the data pattern or the signal path of the output signal are changed, then the resulting IIR filter will have to be calibrated again. The ISI calibration has been described in relation to Unit Intervals but may also be implements using seconds. 
         [0042]    With the IIR filter calibrated, the user can add additional impairments to the digital signal pattern to test various serial data patterns. For example, Draft  13  from the Video Electronics Standards Association for the Display Port high speed serial data standard compliance specification call for a specific amount of ISI as well as other signal impairment as shown in  FIG. 12 . The injected jitter is composed of three elements: Intersymbol interference (ISI), Random Jitter (R j ), and Sinusoidal Jitter (S J ). While the ISI and (R j ) elements are kept constant, S J  will differ based on its modulation frequency to achieve the required Total Jitter (T J ).  FIG. 12  lists the settings that have to be tested for a reduced bit rate for an assumed jitter model of: 12.3 R J (RMS)+D J =T J . The Random Jitter (R j ), and Sinusoidal Jitter (S J ) are set by the user using the Transmitter pop-up window  112  and the ISI is set using the CHANNEL/CABLE pop-up window  122 . 
         [0043]    Although the invention has been disclosed in terms of the preferred and alternative embodiments disclosed herein, those skilled in the art will appreciate that modifications and improvements may be made without departing from the scope of the invention.