On Mon, 19 May 2014, Uncle Peter wrote:

I see. I was reading this and thought "hmmmm....":
http://en.wikipedia.org/wiki/Negative_resistance


What is called ``Negative resistance'' is not quite the same. It is
different than just letting Z1. Negative resistance normally refers to a
device where increasing current decreases the voltage, but the sign of the
voltage and current remain the same. i.e. 1mA through the device produces
1V across the device, but 1.1mA produces .9V. Basically, they are equating
R=dV/dI in a non-linear case while I was refering to letting R go complex
but staying linear.

A battery or a generator has current opposite the voltage but an increase
in the magnitude of current also produces a decrease in magnitude
of the voltage. i.e. -100mA @ 3V goes to -150mA @ 2.8V

A resistance which is negative in the strict sense of Ohm's law should
give a current in the opposite direction as the applied voltage that is
proportional to the voltage. The article does show how to make such a
device with an op amp which provide the power. Since capacitors can be
made that are closer to idea than inductors, this idea is used to make a
capacitor look like a close to ideal inductor.

Ron