Assessing Impedance, Dielectric Constants, Velocity Factors, and Lengths of Printed Circuit Boards, Cables, and Interconnects
Affordable TDR System Simplifies PCB and Cable Testing
A new low-cost Time Domain Reflectometry (TDR) and Time Domain Transmission (TDT) measurement system, the PerfectPulse® J2151A from Picotest, offers a simple and cost-effective solution for testing Printed Circuit Board (PCB) test coupons, cables, and other transmission line components.
Measuring Impedance, Length, Dielectric Constant, and Velocity Factor
The PerfectPulse® J2151A measures the impedance of PCB test coupons by sending a pulse into the PCB trace and measuring the reflected signal caused by impedance mismatches. By comparing the reflected waveform to a reference and analyzing the reflection coefficient, the characteristic impedance of the PCB trace can be extracted.
For cable length measurement, the TDR pulse travels down the cable until it reaches an impedance discontinuity, causing a reflection. The time delay between the sent pulse and reflection corresponds to twice the signal travel time, from which cable length is calculated, knowing the velocity factor.
The velocity of the pulse propagation in the PCB substrate is related to the dielectric constant of the material. By measuring the time delay and knowing the physical length of the trace, the propagation velocity is derived, which is then used to calculate the dielectric constant. The velocity factor is the ratio of the signal's propagation velocity in the PCB material or cable to the speed of light in vacuum, and it is directly measured from the time delay of the reflected or transmitted pulse over a known length.
Efficient Workflow for Accurate Measurements
The measurement workflow involves sending fast-rise pulses into the item under test, capturing reflected and transmitted signals versus time, and analyzing timing and amplitude of those signals to derive impedance (through reflection magnitude), physical length (from delay), dielectric constant (from velocity), and velocity factor.
High-Quality Components for Optimal Results
To ensure accurate results, it is essential to use high-quality cables and probes and, if RF adapters are required, use calibration-quality adapters.
Conclusion
The PerfectPulse® J2151A offers a cost-effective approach for effective signal integrity testing for PCB traces and cables, including essential parameters such as impedance and dielectric characteristics. This compact, pocket-sized pulse generator simplifies the testing process, making it accessible for engineers and technicians who require accurate and reliable results without the need for expensive frequency-domain equipment.
[1] More detailed product-specific descriptions may be found on Picotest's official website.
- This compact, pocket-sized pulse generator, the PerfectPulse® J2151A from Picotest, functions as an impedance calculator by sending fast-rise pulses into the item under test and analyzing the resulting reflection coefficient to extract the characteristic impedance of the PCB trace, making it a valuable tool in the science of technology and data-and-cloud-computing.
- To optimize results with this affordable TDR system, it's crucial to use controlled impedance, ensuring high-quality cables, probes, and calibration-quality RF adapters, as the precision of the measurements directly impacts the scientific accuracy of the data obtained, thus enhancing the efficiency of the testing process in various fields, including science, technology, and engineering.
