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Different bandwidths for DIP vs SOIC (AD8001)
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PartialDischarge:
What is the rationale behind such big difference in the bandwidth of a PDIP vs SOIC packages in the AD8001?
This being a current op-amp I can only think of the capacitance in the negative feedback terminal to be higher in the DIP package, thus its bandwidth, but I'm not sure if there are other factors.
https://www.analog.com/media/en/technical-documentation/data-sheets/AD8001.pdf
dzseki:
Pins of the SOIC package are inherently much closer to eachother leading to more stray capacitance between the terminals, here the inverting IN and the output pins are the most concern.
Kleinstein:
In the smaller package the pins are closer to each other, but the lenght and area is also smaller. With a coax cable the capacitance per unit length only depends on the dielectric and the ratio of inner to outer diameter, not that absolute scale. So though much smaller distance a thin cable of same ratio would have the same capacitance per lenght. A similar scaling should apply to a scaled down leed-frame: similar capacitance per unit length and thus less capacitance for the smaller version.
Similar parasitic inductance can be smaller for the smaller case version.
It is already odd to find such a fast amplifier in the large DIP case.
Berni:
This is 500MHz we are talking about.
Picofarads matter a lot at these frequencies. Just 1 pF of capacitance can cause the same flow of current that a 300 Ohm resistor would pass.
So all the extra size of the DIP pins and the large flat areas inside the package leading to the die in the middle create both parasitic capacitance and inductance that is very noticeable at these speeds.
Im surprised they even made a DIP package available. For the really fast opamps even SOIC is too crappy of a package, so they instead use QFN or even BGA.
TheUnnamedNewbie:
Packaging is a nightmare at higher frequencies. You can't ignore bondwire inductance past a few hundreds of MHz and have to design with them in mind (esp in combination with your ESD-circuits having a good amount of capacitance).
Past a few dozen of GHz you get well into the range where packages just don't work. A lot of research is going on there (part of what I do is in this field too).
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