Negative Resistance Resonant Oscillator

The circuit

The generation of waveforms by negative resistance is typically found in ultra-high frequency applications. Gunn, Impatt and Tunnel diodes are used because these devices exhibit this unusual but useful voltage to current characteristic. A negative resistance region is characterized by an increase in voltage with proportional decrease in current. Among its many uses, negative resistance may be utilized for sine wave generation in resonant circuits. When negative resistance is added to inductors and capacitors, losses can be cancelled out causing rising oscillations if the circuit is unbalanced. Stabilization of the output amplitudes will take place when the bounds o the negative resistance are exceeded. In the following example, a tunnel diode is modeled by two complementary JFETs.

The input file (negative_resistance_resonant_oscillator.cir)

negative resistance resonant oscillator

* frequency of oscilation = 1 / (2 pi (l1 c1)^(1/2))

.control
tran 0.4ms 200ms uic
plot v(1) xlabel t[s] ylabel output[V] title 'TRAN analysis'
dc v0 0 10V 0.05V
plot -i(v0) xlabel voltage[V] ylabel current[A]
  + title 'UI characteristic of tunnel diode'
.endc

v0 2 0 dc 2.4V

r1 1 0 100meg

l1 2 1 1H

c1 1 0 1u ic=2.4V

j1 1 0 3 nkanal
j2 0 1 3 pkanal

.model nkanal njf
.model pkanal pjf

.end

The results