Transcript (ADS) Eye Diagrams

EELE 461/561 – Digital System Design
Eye Diagrams in ADS
EE 461 – Digital System Design
Spring 2010
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Eye Diagrams
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Objectives
1) Create a Pseudo Random Bit Sequence Generator Subcircuit
2) Learn how to use the Eye Diagram Front Panel in ADS
3) Enter interconnect discontinuities to observe eye degradation
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Helpful Hints
1) We want to have a smooth, adjustable risetime coming out of our PRBS generator. If you
copy your Gaussian step Subcircuit, you can simply replace the ideal voltage Step Source
with a Bit Sequence Source
EE 461 – Digital System Design
Spring 2010
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Eye Diagrams
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Part 1: PRBS Source Subcircuit
- Create a Subcircuit that outputs a PRBS data pattern.
- We want a smooth, adjustable output risetime so copy your Gaussian Step Subcircuit
as a starting point.
- Replace the Voltage Step Source component with the Bit Sequence source
- enter a bit sequence that energizes a system with a variety of data transitions. One way to
do this is to take the values from an n-bit binary counter and serialize them into a sequence
ex) 0000 0001 0010 0011 0100 …….. 1110 1111
- create a parameter that is passed into your Subcircuit that defines the data rate of the pattern.
EE 461 – Digital System Design
Spring 2010
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Eye Diagrams
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Part 1: Testing
- Test your PRBS source by creating the following system.
- Setup your source as follows:
Swing:
trise:
Rate:
0v to 2v
35ps
1G
- You'll need to run your simulation long enough to see all of the data patterns. You can use an
equation for your "Stop Time" (i.e., 64*UI or 64/PRBS_Rate)
EE 461 – Digital System Design
Spring 2010
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Eye Diagrams
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Part 1: Testing
- When you run your simulation, you'll see a data pattern like this:
EE 461 – Digital System Design
Spring 2010
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Eye Diagrams
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Part 2: Eye Diagrams using Front Panel in ADS
- In the Data Display Window (i.e., the plot window), launch the Front Panel Eye Viewer using:
Tools - Front Panel - Eye
- You'll be asked to select a signal. Choose your Lab 5 design and the signal name you gave for
the node at the end of the transmission line (i.e., Videal_Rx)
- Once the plot comes up, select:
Mode = Eye
- Click on the "Mask Button" to show
a potential data valid region. This
mask can be reshaped to represent
your receiver's input specifications.
EE 461 – Digital System Design
Spring 2010
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Eye Diagrams
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Part 3: Eye Degradation
- Now enter a circuit that has components in it that represent discontinuities caused by
real interconnect.
EE 461 – Digital System Design
Spring 2010
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Eye Diagrams
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Part 3: Eye Degradation
- Plot the eye diagram for your new circuit and observe the eye closure due to the interconnect.
Before
After
EE 461 – Digital System Design
Spring 2010
Page 8