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Post subject: IMS resistors with partial wraparound
postPosted: Wed Jun 29, 2005 4:12 pm
I am reading about IMS
resistors, that are said to be more suited for microwave performances
than standard SMT resistors.
Does anybody know if it is stricly
a question of wraparound?
For example I saw simulations with
manufacturer's model on ADS comparing kemet resistors and IMS. For 0805
package between 1 and 2 GHz there was a significant slope 1dB on the
attenuation. For the IMS resitors however this slope was minimal.
I am suprised that just this wraparound question would cause such
Anybody experienced the same? Any comments?
Tue Jul 05, 2005 1:08 pm
Wraparound certainly is a big part
of it. A lot depends on the value of the resistor and the intended use.
For large value resistors, the wraparound can add a signficant parallel
capacitance term. For low value resistors, the wraparound can add a
significant series inductive term. The method of attachment can also
be a significant factor.
For example, about 20 years ago I designed
a transimpedance amplifier that used a descrete resistor to set the
transimpedance gain (for a fiber optic receiver application). I use
a non-wraparound resistor (from IMS and others) because the sub-pF capacitance
from the wraparound termination would dramatically affect the bandwidth
(due to the multiplication from the amp).