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I am trying to make a digital switch for a high frequency digital signal. As it's a voltage controlled switch, I am thinking of just using a MOSFET for it. What I am confused about is the bandwidth of the drain to source path. I mean, what effect it will have on the signal integrity. How can I determine it for a specific MOSFET?

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closed as unclear what you're asking by Olin Lathrop, Daniel Grillo, JYelton, Matt Young, Keelan Sep 9 '14 at 19:33

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    \$\begingroup\$ How fast is that signal? \$\endgroup\$ – venny Sep 9 '14 at 15:57
  • \$\begingroup\$ And what is the lowest frequency have to pass as well? \$\endgroup\$ – The Photon Sep 9 '14 at 16:16
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    \$\begingroup\$ We do engineering here, not handwaving. "High" is useless for specifying a frequency. \$\endgroup\$ – Olin Lathrop Sep 9 '14 at 16:21
  • \$\begingroup\$ @venny Very fast! So fast that you can't even see it blink! \$\endgroup\$ – hkBattousai Sep 9 '14 at 16:23
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    \$\begingroup\$ Can you specify, along with what's already been asked, the amplitude of the signal and the impedance of its source? \$\endgroup\$ – EM Fields Sep 9 '14 at 16:54
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A switch made from a single MOSFET or a pair driven with complementary signals (a transmission gate) will have capacitance between input and output, capacitance to the supply rails, and capacitance between the control line and input and output. The capacitance between the control line and the switch is often characterized as "charge injection".

It will also have leakage when off and will have resistance when on. The resistance when on will be modulated with the input voltage, which will generally cause distortion in the output.

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I am trying to make a digital switch for a high frequency digital signal.

If it's a digital signal why don't you use a logic gate to enable it, invert it, make if tri-state or whatever - why bother with the analogue domain offerings. If it's really fast (hundreds of MHz to small GHz) use ECL.

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