Question 2 (30%)
  The left-hand side of Figure 2 shows the schematic model of an electronic circuit involving a tunnel diode. At time t ≥ 0, let u(t) denote the source voltage, i(t) denote the inductor current and u(t) denote the voltage across the capacitor (and thus the tunnel diode). For the sake of argument, suppose that the static non-linear current-voltage characteristic i_D(t) = f(u(t)) of the tunnel diode is as shown on the right in Figure 2, that the inductance L = 1 and that the capacitance C = 1. Applying Kirchoff's voltage and current laws yields the following differential equations: