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Post subject: IMS resistors with partial wraparound
Unread 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 a difference.
Anybody experienced the same? Any comments?
Unread postPosted: 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).