Mapping High Speed Power Grid Transfer Impedance to Emissions Limits
Mapping high-speed power rail transfer impedance limits directly to radiated emissions limits prevents costly EMC chamber re-tests and batch rejections.
De-Embedding
Signal Extraction
A mathematical calibration process removes the unwanted electrical effects of test fixtures, cables and transitions from the measured response of a device under test. When characterizing high-frequency circuit board traces, de-embedding isolates the performance of the trace itself by subtracting the scattering parameters of the coaxial connectors and launching vias used to connect the test equipment. This calculation yields the true behavior of the transmission line or component, which allows engineers to compare measured losses directly with simulation models.
It provides the foundation for accurate high-speed material characterization.
Calibration Method
Executing this mathematical subtraction requires precise measurement of specialized calibration standards fabricated on the same panel as the device under test. These standards, such as a short line, open circuit, or through connection, represent the exact physical transition of the test fixture without the trace of interest. By measuring the scattering parameters of these fixture standards, the vector network analyzer can calculate the mathematical transfer matrix of the launch transition and then invert that matrix to strip its influence from the total measured response.
This procedure must be carried out carefully because any variation in board fabrication tolerances between the calibration standards and the test fixtures will introduce errors into the de-embedded results.
Integrity Verification
Verifying the accuracy of the extracted data involves checking the passivity and causality of the resulting scattering parameters. If the mathematical process yields non-physical gain or unrealistically abrupt phase transitions, the calibration standards were likely fabricated with geometric discrepancies or the measurement cables were disturbed. This verification stage ensures that the extracted material properties, like dielectric constant and loss tangent, are reliable for design use.
Extracting Out-Of-Plane Dielectric Tensor in Heterogeneous Packaging Core
Extracting out-of-plane permittivity requires guarded parallel-plate or re-entrant cavity tests to isolate vertical flux fields from in-plane glass weave effects.