High Frequency Measurements
Douglas C. Smith
Address: P. O. Box 1457, Los Gatos,
A Specialized Component
The component shown above is a resistor that is specifically designed
for good high frequency and other performance characteristics. This resistor
is made by Barth Electronics and the features
that make it work well for high frequency measurements and equipment include:
Resistors of this type, when properly designed into circuits can yield
flat responses to tens of GHz. For an example, see the Technical Tidbit
from October, 1999: The Tapered Wall Cavity.
The resistor is not trimmed. It's value is held to within 1% by tight control
of the resistivity of the material from which it is made. Trimming, especially
laser trimming, of resistors often compromises their high frequency performance
due to either the capacitance across the trimming cut or the additional
inductance caused by the longer conductive path resulting from the cut.
The substrate upon which the resistive coating is placed is very smooth.
This leads to better control of the resistor's parameters.
The resistor has a low voltage coefficient of resistance (resistance is
not affected much by applied voltage). This makes this resistor well suited
for applications where high peak voltages are encountered, such as occurs
with ESD. Normal resistors can be non-linear at high peak voltages and
even change their values permanently after a short pulse (nanoseconds to
microseconds) of peak power that is 10X or more of the resistor's average
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Copyright © 2000 Douglas C. Smith