Is there any advantage of the following op amp based voltage follower:-


over one made with discrete MOSFET components such as:-


other than component count?

  • \$\begingroup\$ Homework? What's the output impedance of the op-amp circuit? What's the output impedance of the FET circuit? What's the offset voltage of the opamp circuit? What's the offset voltage of the FET circuit? \$\endgroup\$
    – TimWescott
    Aug 31, 2019 at 17:08
  • \$\begingroup\$ @TimWescott No Tim. It's a generic question constructed to draw out an experienced answer :-) \$\endgroup\$
    – Paul Uszak
    Aug 31, 2019 at 20:13

1 Answer 1


Yes opamps are better. the opamp is two components: the opamp and the bypass capacitor. the mosfet follower is 5 components.

Additionally, opamps have lower offset voltages and better linearity, and better accuracy because of large amounts of negative feedback.

The only case where I would use a discrete follower would be with high voltages. Because it is more difficult to get high-voltage opamps that are cheap.

  • \$\begingroup\$ There is technically negative feedback in discrete version. \$\endgroup\$
    – DKNguyen
    Aug 31, 2019 at 16:58
  • \$\begingroup\$ Indeed it has. But very much less than the opamp. \$\endgroup\$
    – user55924
    Aug 31, 2019 at 17:01
  • \$\begingroup\$ Voltage: Is this why the discrete totem pole configuration is used as an oscilloscope input stage? \$\endgroup\$
    – Paul Uszak
    Aug 31, 2019 at 20:11
  • \$\begingroup\$ P.S The op amp circuit is shown as dual rail, and often you'd have a larger and smaller bypasser on each rail. That's 5 components too... \$\endgroup\$
    – Paul Uszak
    Aug 31, 2019 at 20:15
  • \$\begingroup\$ Bypass: there are no bypass caps drawn for the buffer, so that would be 7 components with one bypass cap per rail. \$\endgroup\$
    – user55924
    Sep 4, 2019 at 12:43

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