Page 1EE 461 – Digital System DesignSpring 2010

EELE 461/561 – Digital System Design

Eye Diagrams in ADS

Page 2EE 461 – Digital System DesignSpring 2010

Eye Diagrams

• 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

• 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

Page 3EE 461 – Digital System DesignSpring 2010

Eye Diagrams

• 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.

Page 4EE 461 – Digital System DesignSpring 2010

Eye Diagrams

• Part 1: Testing

- Test your PRBS source by creating the following system.

- Setup your source as follows: Swing: 0v to 2v trise: 35ps Rate: 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)

Page 5EE 461 – Digital System DesignSpring 2010

Eye Diagrams

• Part 1: Testing

- When you run your simulation, you'll see a data pattern like this:

Page 6EE 461 – Digital System DesignSpring 2010

Eye Diagrams

• 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.

Page 7EE 461 – Digital System DesignSpring 2010

Eye Diagrams

• Part 3: Eye Degradation

- Now enter a circuit that has components in it that represent discontinuities caused by real interconnect.

Page 8EE 461 – Digital System DesignSpring 2010

Eye Diagrams

• Part 3: Eye Degradation

- Plot the eye diagram for your new circuit and observe the eye closure due to the interconnect.

Before After