|An instrument used for measuring Q must measure a large
reactance and a very small resistance at the same time. If the Q is 100,
the resistance is 100 times smaller than the reactance, so a small change
in the resistance measurement causes a large error in the Q measurement.
Therefore, high Q factors are difficult to measure precisely. Our Q values
can only be as repeatable as the measurements used to create them. This is
why a minimum Q is often specified on the data sheets.
Our published Q values and curves are based on the most
accurate available method of measuring Q. This method uses an impedance
analyzer and an accurate phase calibration standard. Each datasheet
provides the measurement details. In order to provide fixture-deembedded
models at very high frequencies, a network analyzer is used with a
different fixture and a different set of calibration standards.
Calculations of Q based on the s-parameters from network analyzer
measurements produce greater error than the impedance analyzer method.
When creating our models, we use the impedance
analyzer measurement as a guideline to verify the Q values. Because our
models represent deembedded behavior, the Q will not always match the
published values. The simulated Q resulting from the model changes,
depending on the circuit board parameters entered into the simulation.