Eye Diagram Bit Patterns


Other Eye Diagram topics

Bit Patterns

PLTS allows you to specify a synthesized bit pattern (sequence) of between 8 and 32 bits that is convolved with the calculated time domain data to generate the eye diagram.

This dialog appears once for each data set. After that, the same bit pattern is used until you change it.

How to open this dialog again to change the Bit Pattern

Click Tools, then Bit Pattern, then Apply

Choose a (Pre-defined) Digital Pattern  dialog box help

Choose from the following:

  • PRBS   Pseudo-Random Bit Sequence. An industry standard created from a specified pattern length. For example, when 2^7 is selected, 127 [(2^7) -1] unique data 'words' are assembled according to the industry standard.

  • K 28.5   Industry standard developed by IBM which includes comma (control) characters.

  • ABS   Arbitrary (Random) Bitstream. A random bit stream used to generate eye diagrams, the ABS pattern was designed to provide a large random pattern of bits that would quickly converge the eye diagram to show worst case tolerances.

  • Also listed are Bit Patterns that you have created.

Settings

Rise/Fall Time (pS)   The time that it takes a signal to transition from a low to a high (10% to 90%) condition (or the time that it takes a signal to transition from a high to a low (90% to 10%) condition).

Data Rate (Gb/S)   The speed in which data is transferred over a circuit or a communications line.

Pattern Length (bits)   The number of bits in the digital pattern used to create the eye diagram. This value is the limiting factor in creating unique digital patterns. The value of the Pattern Length may be changed for PRBS and ABS. Other defined bit patterns have the Pattern Length defined as part of the pattern and may not be changed except by changing the bit pattern definition.

Amplitude  Eye Diagram Y-axis scaling in millivolts. Negative voltages are allowed. For Differential Eye Diagrams, these scale values are doubled.

  • High  Upper plot scale.

  • Low  Lower plot scale.

About PRBS and ABS Bit Pattern Lengths

PRBS Pattern Length Selections

ABS Pattern Length Selections

Selection

Number of Bits

Selection

Number of Bits

2^5-1

(31 bits)

- -

 - -

2^7-1

(127 bits)

2^7

(128 - 2 = 126 bits)

2^9-1

(511 bits)

2^9

(512 - 2 = 510 bits)

2^10-1

(1023 bits)

2^10

(1024 - 2 = 1022 bits)

2^11-1

(2047 bits)

2^11

(2048 - 2 = 2046 bits)

2^13-1

(8191 bits)

2^13

(8192 - 2 = 8190 bits)

2^15-1

(32767 bits)

2^15

(32768 - 2 = 32766 bits)

If the Pattern Length = 2^7 bits, there are 128 unique patterns available if you count in binary from 0 to 127.

0000000
0000001
0000010
.
.
.

1111101
1111110
1111111

PRBS removes 00000000 as invalid.

ABS removes patterns 0000000 and 1111111 as invalid patterns so that you now have a total of 2Pattern Length - 2 = 27 - 2 = 126 unique patterns to choose from. Then ABS uses a random number generator to choose the first pattern to put into the virtual pattern generator and continues to pick new random patterns up to the number of patterns that you have defined within the interface (maximum is 126).

Using both of these values, a random number generator selects unique bit patterns until the appropriate number of patterns are identified. Each of these unique bit patterns are then used to create the eye diagram, one bit pattern at a time.

Import a Bit Pattern File

Beginning with PLTS release 5.0, you can import existing patterns that are saved in the following file types:

The maximum file size that can be imported is 64k Bytes..

These patterns can be generated using the FREE Keysight Pattern Editor and Sequencer 3.0 software.

How to Import a Bit Pattern

Click Tools, then Bit Pattern, then Import  

Import Digital Pattern dialog

Select File to Import  Click Browse, then navigate to the file to be imported.

File Description  Once selected, the pattern contents appear in the text box, along with Type, format, and number of bits.

Import Pattern

Pattern Name  Type a pattern name for this file. This name will appear in the 'Choose a Digital Pattern' dialog and also in the title of a displayed eye diagram plot, as in the following image:

Rise/Fall time (pico seconds) Enter the default time that it takes a signal to transition from a low to a high (10% to 90%) condition (or the time that it takes a signal to transition from a high to a low (90% to 10%) condition). This value can be changed each time the bit pattern is used.

Data Rate (Gb/S)  Enter the default speed in which the pattern is transmitted through your DUT. This value can be changed each time the bit pattern is used.

The following image shows examples of how these values are defined:

Design a Custom Bit Pattern

Although several bit patterns are available in PLTS, you can easily create custom bit patterns, from 8 to 32 bits.

How to Design a Custom Bit Pattern

Click Tools, then Bit Pattern, then Design

Digital Pattern Generator dialog

Click the numerical 'piano' keys to generate a bit pattern up to 32 bits in length.

Numeric Representation  Choose a numerical format in which to present the data.

Save Pattern  Enter a filename for the digital pattern. The pattern is saved to folder location specified by the File Storage User Preference.

Rise/Fall Time and Data Rate  Specify the pulse specifications. The following example shows the specs for a single pulse using 80ps Rise/Fall Time and 2.5 Gb/s Data Rate.

 

Pattern Length (bits)  The default value is 32. The allowable range is between 8 and 32 bits. You may change this if your pattern contains fewer bits. If this value is changed to a value less than 32, any remaining bits are ignored. For example if you enter 10 as the pattern length value, then bits 0 through 9 are used and bits 10 through 31 are ignored.

 

 


Last Modified:

21-Oct-2011

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