ECE 335 UTK Dr. McFarlane Final Exam Concept Review

(T/F) Amplifiers always have a positive gain

False

(T/F) Diodes and MOSFETs primarily carry diffusion currents while BJTs have both diffusion and drift currents.

False

(T/F) In a Zener based power supply, low load resistances cause the diode to go into forward bias.

False

(T/F) In a pn junction diode under reverse bias, large currents are possible and the diode is modeled as a constant voltage drop of 0.6 V.

False

(T/F) MOSFETs and BJTs have diffusion capacitances

False

(T/F) There are no diffusion or drift current in a zero biased diode

False

(T/F) To operate as amplifiers, MOSFETs and BJTs must be operated in the saturation region

False

(T/F) Under forward bias, a diode current is dominated by drift current.

False

(T/F) We can make npn or pnp BJTs in the lab by connecting the two diodes back to back.

False

(T/F) When a diode is reverse biased the voltage across it remains approximately the same.

False

In a PMOS the body/bulk/substrate terminal should be tied to the source or lower voltages.

False

In the enhancement-mode device, a channel is built into the device during its fabrication, and a voltage must be applied to the transistor's gate to quench conduction.

False

The threshold voltage of a MOSFET is independent of the source to body potential.

False

(T/F) There is a large drift current when a diode is in reverse bias.

False, there would be a strong drift current, but there are not enough charge carriers.

(T/F) While at zero bias, drift currents are greater than diffusion currents, resulting in a net current.

False, while at zero bias there is a balance of drift and diffusion currents resulting in no net current.

Reverse Bias Depletion Region (>/<) Forward Bias Depletion Region

Reverse Bias Depletion Region > Forward Bias Depletion Region

What are the conditions for a Zener Diode to operate as a regulator?

The Zener current must be positive and the diode must remain in reverse breakdown.

What conditions must be met for a diode to be in forward bias?

The positive terminal of the external voltage source must be connected to the anode and the negative to the cathode, as the current moves opposite of electron flow. Additionally, the external voltage source must exceed the barrier potential at the pn junction.

What conditions must be met for a diode to be in reverse bias?

The positive terminal of the external voltage source must be connected to the cathode and the negative to the anode, as the current moves opposite of electron flow. Additionally, the external voltage source must exceed the barrier potential at the pn junction.

(T/F) An unknown device with terminals labeled A and B is a diode if R_AB shows a high resistance and R_BA shows a low resistance.

True

(T/F) At zero bias, a diode has a built-in electric field known as a depletion region

True

(T/F) Base width modulation, modeled by adding (1+VCE/VA), is analogous to channel length modulation of a MOSFET, and is caused by decrease in base width due to increase in depletion region at the reverse-biased collector/base junction.

True

(T/F) For the simple Zener regulated power supply developed in this class, if the load resistance is too small, the Zener diode leaves reverse breakdown and the regulator stops working as intended

True

(T/F) If I have an unknown 3-terminal device, I can tell whether it is a BJT or MOSFET by simply measuring the impedance across all the terminals.

True

(T/F) If a step voltage is applied to a diode, the output shows a delayed signal due to parasitic capacitors.

True

(T/F) If an input sinusoidal signal is not "small" enough, then the output signal of an amplifier could suffer from distortion due to the effect of the higher-order terms of the Taylor series

True

(T/F) If too large a reverse voltage is applied to the diode, the internal electric field becomes so large that the diode enters the breakdown region, either through Zener breakdown or avalanche breakdown.

True

(T/F) In SPICE, AC analysis assumes that the network is linear and uses small-signal models for the transistors and diodes. Since the circuit is linear, any convenient value can be used for the signal source amplitudes, hence the common choice of 1-V and 1-A sources. In contrast, transient simulations utilize the full large-signal nonlinear models of the transistors.

True

(T/F) In reverse active the current is smaller as the collector is not as highly doped as the emitter.

True

(T/F) In the cutoff region of operation, both the base-emitter and base-collector junctions are forward biased.

True

(T/F) In the saturation region of operation, the current in the base is increased compared to forward active.

True

(T/F) MOSFETs and BJTs have depletion capacitances

True

(T/F) N type materials have more donors than acceptors

True

(T/F) The potential on the gate controls whether the transistor is in accumulation, depletion, or inversion.

True

(T/F) The small-signal model is a first-order approximation of the relationship between input and output AC signals, and represents a linearization around the Q point of the transistor

True

(T/F) There are four methods to solving diode problems, including graphical, iterative, ideal model, and constant voltage drop model.

True

(T/F) Under reverse bias, the applied electric field is in the same direction as the built-in electric field.

True

(T/F) Under reverse bias, there is a drift current, however it is small as the electric field is trying to move minority carriers which are small in numbers across the junction.

True

(T/F) Under zero bias, no current can exist at the diode terminals, and a space charge region forms in the vicinity of the pn junction. The region of space charge results in both a built-in potential and an internal electric field, and the electric field produces electron and hole drift currents that exactly cancel the corresponding components of diffusion current.

True

In a MOSFET, the source and drain terminals are determined by the voltages applied to the terminals.

True

In saturation the MOSFET channel is shorter than the drawn length. This effect is modeled using the parameter 'gamma'.

True

The I-V characteristic of the bipolar transistor are often presented graphically in the form of collector current vs the collector-emitter voltage and base-emitter voltage.

True

In the depletion region, Vs Vg Vd Vb charge under gate:

Vs = 0 0 < Vg < Vtn Vd > 0 Vb = 0 charge under gate: negative charge

In the accumulation region, Vs Vg Vd Vb charge under gate:

Vs = 0 Vg < 0 Vd > 0 Vb = 0 charge under gate: holes accumulate

In the cutoff region, Vs Vg Vd Vb charge under gate:

Vs = 0 Vg > Vtn Vd < Vg-Vtn Vb = 0 charge under gate: channel of electrons

In the saturation region, Vs Vg Vd Vb charge under gate:

Vs = 0 Vg > Vtn Vd > Vg-Vtn Vb = 0 charge under gate: pinch off

In forward bias, the positive terminal of a voltage source is applied to the [anode (p-region)/cathode (n-region)] of the diode.

anode/p-region

What is the definition of the small signal model?

linearization around the Q-Point

The n-region of a diode is the (anode/cathode) and the p-region is the (anode/cathode).

n-region ----> cathode p-region ----> anode