How does the ADG2128 have such small input capacitances. Each of the 8 inpits can connect to one of 12 outputs. The input cap off is only 3pF thus each switch is 3pF/12.
The off capacitance of each ADG2128 switch input is 11pF. When the switch is off it is not connected to any other outputs.
the data sheet says Coff 6pF typ Con 9.5pF typ nothing here about 11pF. So this Coff 6pF typ Con 9.5pF implies that an additional 3.5pF is on the other end of the switch. And that other end would be connected as a common to 8 inputs in total as it is a crosspoint switch. Can you give me a diagram of the correct construction of these switches?
I see where you got your 11pF that is when you use a single supply of 12V but why would I do that when if I use +/-5v I get 6pF Coff?
Yes you are correct. The Coff is 6pF for +/-5V. I wasn't aware where the 3pF was coming from.
I'm sorry but we do not give out diagrams showing the internal topology of a device.
Hi, I have the same question as tombrighton, and I don't see the answer here. Taking the 12V datasheet figures as Coff = 11pF, Con = 18.5pF:
A: If these apply to the available package pins, we have (for example)
All switches off: Cy0 = 11pF, Cx0 = 11pF
Switch y0 to x0 ON, all others OFF: Cy0 = Cx0 = 18.5 pF, so switch "channel capacitance" = 18.5 - (2 x11) = - 2.5 pF, which seems unlikely - especially as each OFF switch contributes only ~ 1 pF to the Cy0 or Cx0 line.
B: Alternately, if the figures apply to each (internal) switch, and there is negligible pin capacitance:
All switches off: Cy0 = 12 x 11 pF = 131 pF, Cx0 = 8 x 11 pF = 88 pF
Switch y0 to x0 ON: Cy0 = Cx0 = (11 x 11) + (7 x 11) + 18.5 = 216 pF (and the channel capacitance is again negative).
The smaller ADG2188 8x8 crosspoint gives exactly the same datasheet figures, Coff = 11pF, Con = 18.5pF. The datasheets don't give any parameter measurement information to clarify this. What is the correct interpretation?
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