Once virtually destroyed the ohmic resistance of a movement

https://www.researchgate.net/post/How_do_we_improve_the_real_ammeter_How_do_we_create_an_almost_ideal_ammeter_What_does_the_op-amp_really_do_in_the_circuit_of_an_op-amp_ammeter2

and a resistor

https://www.researchgate.net/post/Is_there_any_connection_between_the_humble_resistor_and_the_transimpedance_amplifier_What_does_the_op-amp_really_do_in_this_electronic_circuit,

why not try to virtually destroy the nonlinear diode resistance? Thus we will obtain a virtual “ideal diode” with zero forward voltage drop Vf.

The arrangement is the same – we add a variable voltage source in series with the diode so that its voltage adds to the voltage of the exciting voltage source and make it equal to the forward voltage drop Vf across the diode. As a result, the voltage drop as though disappears and the new “diode” looks as a “piece of wire” to the input source. What a magic – we increase the current through the “diode” but the voltage across it stays zero!

Finally, to obtain a true “diode”, we just replace the “helping” voltage source with a properly supplied op-amp and make it “observe” the difference between the voltage drop across the diode and its output voltage... and change the latter so that to keep the virtual ground. Practically, this means to connect the diode between the op-amp output and its inverting input and to inject the input current into the node at the inverting input (I will place a picture immediately below the question). As a result, its output voltage will always be equal to the voltage drop and the voltage across the whole network (seen by the input source) will be almost zero. Thus we have used a real diode to create a “virtual diode” with zero threshold voltage.

If you like this idea, visit the page below to see how my students applied it at the laboratory in 2008 (one of them is now an assistant professor in the same Computer Systems department)

http://en.wikibooks.org/wiki/Talk:Circuit_Idea/How_to_Make_Perfect_Components

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