Virtual Labs

1. What is the primary equation used in the SPICE model for the forward I-V characteristic of a diode, neglecting non-ideal effects?

I_D = I_S \cdot (e^{\frac{V_D}{N \cdot V_T}} - 1)

Explanation

I_D = I_S \cdot e^{\frac{V_D}{V_T}}

Explanation

V_D = I_D \cdot R_S

Explanation

I_D = \frac{V_D}{R_S} \cdot (1 - e^{\frac{V_D}{N \cdot V_T}})

Explanation

2. In the SPICE diode model, what does the ideality factor 'N' primarily account for?

a: Only the diffusion current in the quasi-neutral regions. Explanation

Explanation

b: The effect of series resistance at high currents. Explanation

Explanation

c: The combination of diffusion (N=1) and space-charge region recombination (N=2) currents. Explanation

Explanation

d: The breakdown voltage in reverse bias. Explanation

Explanation

3. How is the saturation current 'IS' typically extracted from a forward I-V plot?

a: By measuring the current at a fixed voltage of 0.7V. Explanation

Explanation

b: By finding the slope of the linear

I_D

vs.

V_D

curve. Explanation

Explanation

c: By extrapolating the linear region of the

log(I_D)

vs.

V_D

plot back to the

V_D = 0

intercept. Explanation

Explanation

d: By measuring the current just before breakdown. Explanation

Explanation

4. At high forward currents, the measured I-V curve 'rolls off' and deviates from the ideal exponential behavior. What SPICE parameter is primarily responsible for this?

N

(Ideality Factor) Explanation

Explanation

IS

(Saturation Current) Explanation

Explanation

RS

(Series Resistance) Explanation

Explanation

BV

(Breakdown Voltage) Explanation

Explanation

5. The ideality factor 'N' is extracted from the slope of which plot, in the ideal region?

I_D

vs.

V_D

on a linear scale. Explanation

Explanation

log(I_D)

vs.

V_D

on a semi-log scale. Explanation

Explanation

log(I_D)

vs.

log(V_D)

on a log-log scale. Explanation

Explanation

dV_D / d(log(I_D))

vs.

I_D

. Explanation

Explanation

6. What does the SPICE parameter 'IKF' (High-injection knee current) model?

a: The onset of avalanche breakdown. Explanation

Explanation

b: The current level where series resistance

RS

begins to dominate. Explanation

Explanation

c: The decrease in emission coefficient (ideality factor trends towards 2) due to high-level injection. Explanation

Explanation

d: The current level where recombination in the space-charge region is dominant. Explanation

Explanation

7. If the series resistance 'RS' is NOT properly accounted for, how will it affect the extracted value of the ideality factor 'N' from the I-V curve?

a: The extracted 'N' will be lower than the true value. Explanation

Explanation

b: The extracted 'N' will appear to increase as current increases. Explanation

Explanation

c: The extracted 'N' will be unaffected, as 'RS' is a separate parameter. Explanation

Explanation

d: The extracted 'N' will become negative. Explanation

Explanation

8. On a

log(I_D)

vs.

V_D

plot, what physical effect typically dominates at the *lowest* forward currents, often showing N ≈ 2?

a: High-level injection. Explanation

Explanation

b: Ohmic series resistance. Explanation

Explanation

c: Ideal diffusion current. Explanation

Explanation

d: Recombination current in the space-charge region. Explanation

Explanation

9. The SPICE parameter 'XTI' models the temperature dependence of which other key parameter?

RS

(Series Resistance) Explanation

Explanation

N

(Ideality Factor) Explanation

Explanation

IS

(Saturation Current) Explanation

Explanation

CJO

(Zero-bias capacitance) Explanation

Explanation

10. A common method to extract 'RS' is to plot

V_D - N \cdot V_T \cdot ln(I_D / I_S)

vs.

I_D

, after 'N' and 'IS' are found. What should this plot ideally yield?

a: A constant value equal to

IS

. Explanation

Explanation

b: A straight line passing through the origin with a slope of

RS

. Explanation

Explanation

c: A straight line with a slope of

N

. Explanation

Explanation

d: A horizontal line at

V_T

. Explanation

Explanation

Extraction of diode SPICE parameters related to forward Current-Voltage (I-V)