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What is an easy way to remove the negative portion of a signal without distorting the positive side of it?

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    \$\begingroup\$ Fast signal diode, with a low forward voltage. \$\endgroup\$ – Whiskeyjack Dec 12 '15 at 21:00
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    \$\begingroup\$ Have you access to a copy of 'The Art of Electronics'? It gives a nice explanation of an "Active Rectifier"; chapter 4, section 4.3.2 D in Ed 3. The circuit behaves like a diode without suffering from the forward voltage drop of a diode. It's pretty much an op-amp, diode and resistor. A quick search will probably find a good description. Oh, and what is the bandwidth and amplitude of the signal, and acceptable levels of distortion? \$\endgroup\$ – gbulmer Dec 12 '15 at 21:11
  • \$\begingroup\$ Maybe have a look at this lab worksheet for an explanation of an "Active Rectifier", niu.edu/~mfortner/labelec/lect/p575_01b.pdf. Please come back and ask for help if you need it. \$\endgroup\$ – gbulmer Dec 12 '15 at 21:29
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I would recommend a precision rectifier.

Precision rectifier

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The most basic op-amp circuit (it has to be the right op-amp of course) is this: -

enter image description here

It relies on a few special features of the LT1078 but is a pretty good half wave rectifier.

You can use most op-amps in this configuration: -

enter image description here

The cool thing about this circuit is that one op-amp can produce two outputs.

Note that both the op-amp circuits shown above are inverting configurations but that doesn't matter if you are dealing with waveforms that are amplitude symmetrical.

You can also make full wave rectifiers using two op-amps: -

enter image description here

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