Page 1EE 461 – Digital System Design Spring 2010 EELE 461/561 – Digital System Design Eye Diagrams in ADS

Page 2EE 461 – Digital System Design Spring 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 Design Spring 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) …… create a parameter that is passed into your Subcircuit that defines the data rate of the pattern.

Page 4EE 461 – Digital System Design Spring 2010 Eye Diagrams Part 1: Testing - Test your PRBS source by creating the following system. - Setup your source as follows:Swing: 0v to 2v t rise :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 Design Spring 2010 Eye Diagrams Part 1: Testing - When you run your simulation, you'll see a data pattern like this:

Page 6EE 461 – Digital System Design Spring 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 Design Spring 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 Design Spring 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