J2154a perfect pulse differential tdr

A time domain reflectometer (TDR) is generally a large, expensive benchtop instrument that measures impedance, PCB coupons, dielectric constants, PCB signal traces, interconnects, connectors, and cables using reflected waves. The TDR measures the time a pulse takes to issue from and to the source and using that data can compute a number of characteristics of the transmission medium. PCB designers can use TDRs to ensure signal integrity in their system architecture and qualify vendor dielectric constant variation of impedance. Test engineers use it to make sure their test setups are free from defective interconnects. 

Picotest has solved a number of usage drawbacks (e.g., cost, portability, compatibility) with its J2154A PerfectPulse Differential TDR and P2105A/P2103A series of transmission line probes. The PerfectPulse TDR is a low-cost, pocket-sized, high-speed pulse generator that works with the internal resistive power divider and almost any real-time oscilloscope to measure the same parameters as the benchtop TDR.  

To complete the TDR setup, Picotest has available two hand-held browser-style probes: the low noise P2105A 1-port probe and the P2103A differential probe. 

Challenges Solved by the J2154A Differential TDR 

Past implementations of TDRs have been bulky, expensive, and hard to use. The large size made probing difficult, leading system designers to weigh the benefits of including a TDR against the cost and difficulty of implementing it. 

The J2154A is USB-powered and extremely portable. At 10.5GHz it can discern key PCB features and discontinuities when paired with a high-speed oscilloscope. It is capable of both single-ended and differential measurements. 

The J2154A is easier to use than traditional TDRs in that it does not require special software. Engineers can set up the J2154A either manually with basic math capabilities found in most scopes or by loading readily available oscilloscope setup files provided by Picotest, creating a seamless scope integration.  

By packaging the TDR and probes into a pocket-sized envelope, the reduced footprint offers easier testing for dense PCBs and physically tight locations.  

Added Benefits of the J2154A 

With solving the primary challenges users face when measuring impedance, there are additional benefits the J2154A provides: 

  • Versatility: The J2154A presents two complementary (differential) pulses to be used as a differential TDR. However, when using two or more oscilloscope “receiver” channels, the J2154A can also be used for single-ended and precise differential TDR in a single package for added versatility. One component is dual-usage versatility. 
  • Any application requires a fast, precise 10.5GHz edge. There are timing and reference signal tests used to compare the signal with a known value. The J2154A enables users to generate a 30ps edge for signal comparison. 
  • Compatibility: Compatible with the Picotest P2105A and P2103A TDR Browser Probes, as well as other manufacturers’ 50 Ohm probes for ease of use. Integration with these probes is expanded in detail in our TDR measurement application guide. Picotest’s probes offer the ability to change head pin spacing, are available in both single and differential styles, and (for the P2105A) can include multiple heads. These probes inject and read TDR signals through smooth compatibility. 

TDR Capabilities Spans Many Uses 

The small size, economic construction, and versatility of the J2154A enables it to be used for an array of applications. Below is a summary of use cases: 

  • Measure and confirm cable and PCB trace length, characteristic impedance, and dielectric constant 
  • Locate and detect impedance mismatches and variations from vendor specification 
  • Measure parasitic values of inductance and capacitance such as bond wires, vias, and ESL 
  • Verify the integrity of cable crimps and connector launches 
  • Measure PCB trace path rise/fall time and overshoot/undershoot 
  • Support cable and trace loss modeling 
  • Troubleshoot clock jitter and crosstalk 
  • Measure microwave filters 
  • Test the frequency bandwidth, rise/fall time, and flatness of lab instruments and probes 

Conclusion and Tips to Realize the Benefits of TDR 

Picotest has introduced a pocket-sized, 10.5GHz TDR that works with most scopes, making it easy to add the benefits of a Time Domain Reflectometry to your test bench. Along with the P2105A single-ended and P2103A differential probes, this ‘TDR Bundle’ replaces what was once an expensive bulky standalone instrument. 

References/App Notes 

TDR Measurement using the J2154A PerfectPulse® Differential TDR and the MSO68B Oscilloscope 

Measuring PCB, Cable and Interconnect Impedance, Dielectric Constants, Velocity Factor, and Lengths 

The 2-port Shunt Through Measurement and Groundloop Problem (picotest.com)

Measuring pH and fF With a TDR Using a Cursor Measurement 

Measuring pH and fF With a TDR Using a Cursor Measurement | Picotest Test & Measurement Publications

The Goldilocks TDR – Exploring TDR Capabilities 

The Goldilocks TDR | 2020-08-30 | Signal Integrity Journal

Measuring the Bulk Dielectric Constant (Dk) on a Microstrip with a TDR