1. Cost Effective Time Domain Reflectometry
EECS 713 Final Project
Nick Theisen

2. Background What is Time Domain Reflectometry (TDR)? Where is it used?
Electrical and optical
TDR measures reflections along a conductor.
Used to measure cable impedance, locate discontinuities along cable, determine losses

3. Simple TDR from lab equipment
Basic lab experiment observed in college electronics lab
Requires basic lab equipment but may not be available at home or in the field
Required fast edges and high bandwidth oscilloscope
“Time Domain Reflectometry.” Wikipedia, The Free Encyclopedia, Wikipedia, The Free Encyclopedia, 22 Jan Web. 22 Jan 2011.

4. Block diagram Heart of analog design is LT1721 Ultrafast comparator.
2.5 ns rise/ 2.2 ns fall, low skew

5. Simulation schematic - LTspice
Based off Linear Tech/Analog devices example design -
RG-60/U cable – 50 ohm, velocity = 0.659c = 1.54 ns/ft, 13 ft test cable

6. Simulation Output - LTspice
Time domain simulation, transient analysis

7. Simulation Output - LTspice
Red trace is 40 ns, measuring the transmit/receive propagation time

8. PCB Design - EasyEDA 6 layer stackup using stack design from book.
Top/bottom layer microstrip 0.008” trace / 0.025” pitch

9. Deliverables Simulation Circuit Schematic PCB Layout
Power/thermal analysis
Timing analysis
Rough cost:
Prototype quantity 20 PCBs, 20 day turn $18/ea
2 high speed op-amps $20
ECL components $22
1 OSCILLATOR $10
Discretes $5

10. Questions?