The voltage-current characterization of a p-n diode is given by (see Figure 2.22)

i(t) = I_s(e^qv(t)/kTˆ’1)

where i(t) and v(t) are the current and the voltage in the diode (in the direction indicated in the diode) I_s is the reversed saturation current, and kT/q is a constant.

(a) Consider the voltage v(t) as the input and the current i(t) as the output of the diode. Is the p-n diode a linear system? Explain.

(b) An ideal diode is such that when the voltage is negative, v(t) < 0, the current is zero, i.e., open circuit; and when the current is positive, i(t) > 0, the voltage is zero or short circuit. Under what conditions does the p-n diode voltage-current characterization approximate the characterization of the ideal diode? Use MATLAB to plot the current-voltage plot for a diode with I_s = 0.0001 and kT/1 = 0.026 and compare it to the ideal diode current-voltage plot. Determine if the ideal diode is linear.

(c) Consider the circuit using an ideal diode in Figure 2.23, where the source is a sinusoid signal v(t) = sin(2Ï€ t) u(t) and the output is the voltage in the resistor R = 1 ­or v_r(t). Plot v_r(t). Is this system linear? Where would you use this circuit?

Figure 2.22:

Figure 2.23:

Transcribed Image Text:

i(t) v(t) i(t) ↑ v(t) ww- ideal diode v(t) i(t)