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The picture shows a series JFET switch. Is r_d itself the load or does the load have to be attached at the port v_out? If the second one is true then what is the purpose of r_d? Can't we replace r_d with the load we want?

  • \$\begingroup\$ There are three connection points plus earth in the left diagram and I'm unsure what the right diagram is meant to represent. \$\endgroup\$
    – Andy aka
    Jan 17, 2021 at 15:09
  • \$\begingroup\$ @Andyaka i'm sorry, let me edit the picture. \$\endgroup\$
    – Sayan
    Jan 17, 2021 at 15:11
  • \$\begingroup\$ @Andyaka it is edited now, these two figure shows equivalent circuits. \$\endgroup\$
    – Sayan
    Jan 17, 2021 at 15:15

1 Answer 1


my question is whether r_d itself is the load or the load has to be attached at the port v_out?

The only sensible option (without further context) is that \$R_D\$ is an attached load. It certainly cannot be part of the JFET because it makes no connection to ground. The Vout circle symbol is a little confusing but, I believe, it's just showing the point where you measure Vout.

\$R_{DS}\$ is typically the drain-source on-resistance of the JFET.


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