EE 461 Digital System Design

1
EE 461 Digital System Design

• Lecture 34
• Agenda
• Lab 11 (TDR)
• Announcements (Monday, 4/21)
• All PCB's will be in this week.

2
Time Domain Reflectrometry

• TDR- A TDR is an oscilloscope that has a built
  in step generator. - The instrument sends out a
  fast step and simultaneously observes the
  reflected energy.- The system built to be
  50ohms.- This means if you terminated the
  system, the TDR would observe the initial step
  then no ensuing reflections- If there were
  impedance discontinuities (i.e., from
  interconnect), then the TDR would observe the
  reflections.- By looking at the magnitude,
  duration, spatial location of the reflections,
  the source of the impedance discontinuity can
  be isolated and analyzed.

3
Time Domain Transmission

• TDT- We can also connect the Far-End of our
  system back into another channel of the TDR
  oscilloscope- Observing the transmitted signal
  is called Time Domain Transmission (TDT)- This
  observation point gives the amount of energy that
  was successfully transmitted through the
  interconnect structure.- The inputs to the
  TDR/TDT oscilloscope are all 50ohms, so
  connecting the Far-End of the system to a TDT
  input is a convenient method to terminate the
  system.

4
TDR/TDT

• Literature- The following Application Notes
  give some additional theory on TDR/TDT some
  practical methods to use the information.-
  These are located on the Course Website under
  "Information"
• Time Domain Reflectrometry Theory, Agilent
  Technologies Measuring Parasitic Capacitance
  Inductance Using TDR, Agilent Technologies
  Signal Integrity Analysis using TDR, Agilent
  Technologies Time Domain Methods for Measuring
  Crosstalk for PCB Quality Verification, Tektronix