three questions need your help

[lhlbluesky]

1, for ac noise simulation of opamp (single-ended and fully differential), which frequency bandwidth should be used? i usually use frequency from 0Hz to GBW Hz to calculate the integration noise and then average it, and the noise unit is V^2/Hz or V/sqrt(Hz), is that OK? or any other advice?
besides, how to simulate the transcient noise for opamp? for example: sc circuit.

2, in pcb board, for a wire of 2cm long, what is its equivalent capacitance and resistance? someone tells me, the resistance can be very small, less than 0.1 ohm, because the wire can be thick enough, that is, the cross area can be large enough, then the resistance can be very small. however, for a thick wire in pcb board, the capacitance may be large, so, i want to know, what is the capacitance of a 2cm long wire, if its resistance is less than 1 ohm? can it be 1pF~3pF? or larger? or smaller? please give me some advice.

3, what is the pad capacitance in 0.18 um process in general? someone says, it is about 4pF, but for our chip, we tested the pin capacitance,and it is in the range of 9pF ~ 12pF, it is so big, is it usual? the chip package type is PGA.
besides, what is the relationship between pad capacitance and package type?
which package type has a smaller pad capacitance? and what is the pad capacitance for LCC package type in 0.18 um process? can it be smaller than the PGA package type? please help me, and explain to me more about this.

thanks all for reply, thanks all.

 

[dick_freebird]

2 - your capacitance depends more on the dielectric thickness
interlayer, and spacing to closest in-layer neighbors. And there
is the question, "capacitance to what?" (ground is one thing,
for a niose-sensitive function capacitance to a clock or another
asynchronous signal could be a real headache). If you know the
from:to and the wire lengths you can use line capacitance
formulae.

3 - your measurement evidently includes package trace and
wirebond (no mention of flip chip) capacitances. Package
vendor should have bare package capacitance info, bond
capacitances will depend onbond wire length / space, again
a line-capacitance calc should be close if you have the
geometry. You also have some capacitance to the lid on
a metallic-lid ceramic package, which is sort of complex
as the wire-lid spacing is an arc, not uniform.

 

[lhlbluesky]

thanks, and any other advice or ideas? i really need your help, thanks.