Download ECE1250F14_HW2_1p3soln

1250
HOMEWORK #2-1 prob 3 solution
F14
EX:
Ohm's Law: v = iR where v = voltage drop across resistor R that carries current i
On the plot below, sketch a curve passing through the origin that you think would
represent a component that has negative resistance for some range of voltages.
(Tunnel diodes behave this way.) If the curve is strictly positive, what characteristic
of the curve's shape would lead us to describe it as having negative resistance.
SOL'N:
While a passive device (i.e., one without a power source) that is a pure
negative resistance is akin to a perpetual motion machine, one can make a
powered circuit (with op-amps, for example) that behaves like a negative
resistance. A pure negative resistance would appear as a line passing
through the origin and residing in the second and fourth quadrants:
If we restrict the devices current to be strictly positive for positive voltage,
we get something like a voltage source in series with a negative resistance
if we have a negative slope for some region of the curve.
It might seem like the above plot is unachievable in practice, since an
increase in voltage leads to a decrease in current at some point.
Nevertheless, it turns out that tunnel diodes have this behavior, and they
can be employed as negative resistances in some circuits.