ATT Test 6 (Latest 2024/ 2025 Update) Questions and Verified Answers| 100% Correct| Grade A
ATT Test 6 (Latest 2024/ 2025 Update)
Questions and Verified Answers| 100%
Correct| Grade A
Q: What is JFET cutoff?
Answer:
a large negative gate voltage that increases junction barrier so much that current flow stops (vgg
vdd)
Q: What is JFET saturation?
Answer:
A negative gate voltage so small that decreases the junction barrier to a point where it no longer
decreases, constant current flow
Q: What causes constant current flow in JFET?
Answer:
JFET saturation
Q: What causes current flow to stop in JFET?
Answer:
JFET cutoff
Q: What controls large source to drain currents?
Answer:
Small reverse bias voltages
Q: What class is the midpoint biased at in a FET?
Answer:
Class A
Q: What class is cutoff biased at in a FET?
Answer:
Class B
Q: What class is below cutoff biased at in a FET?
Answer:
Class C
Q: Transconductance (gm) = ?
Answer:
Output current divided by input voltage
Q: What is transconductance?
Answer:
Amount of control input voltage has over output control
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Which element in a FET controls current? Gate
What produces current flow in a FET? Positive bias attached to drain
What forms the barrier in a FET? Negative bias attached to gate
Is the gate to source forward or reverse biased in a FET? Reverse biased
What happens when negative gate voltage (Vgg) is increased in a FET? Source to drain current decreases
What is JFET cutoff? a large negative gate voltage that increases junction barrier so much that current flow stops (vgg > vdd)
What is JFET saturation? A negative gate voltage so small that decreases the junction barrier to a point where it no longer decreases, constant current flow
What causes constant current flow in JFET? JFET saturation
What causes current flow to stop in JFET? JFET cutoff
What controls large source to drain currents? Small reverse bias voltages
What class is the midpoint biased at in a FET? Class A
What class is cutoff biased at in a FET? Class B
What class is below cutoff biased at in a FET? Class C
Transconductance (gm) = ? Output current divided by input voltage
What is transconductance? Amount of control input voltage has over output control
How does transconductance relate to resistance? It is the opposite of resistance
FETs transfer _ from input to output conductance How is a FET biased? Positive voltage on drain, reverse bias source to gate What are 4 types of biasing for FETs? Gate, self, volt divider, source Which type of biasing is not stable and uses two voltage sources? Gate biasing Why are FETs used in amps instead of BJTs? HIGHER input resistance What is the most commonly used FET amp? Common source Which FET amp inverts the output signal? Common source What is the most common fault in FET amps? Semiconductor (FET) How do you check for normal operation in FET amps? Compare measured to calculated Av (gain) If gm is not known, what value is used? 2 milli mhos How much bias voltage is applied to gate in common source amp? 0V What gives common source amp temp stability? Self biasing Does Sierra like Bonnie or Clyde better? She loves them both equally 😉 During the positive input signal (common source amp), reverse bias (Vgs) decreases. What happens to source to drain current (Id)? Id INCREASES when Vgs decreases What causes reverse bias (Vgs) to decrease during positive input (common source amp)? Gate voltage (Vg) increases During the negative half cycle (common source amp) what happens to source to drain current (Id)? (Gate is P type) Gate to source becomes MORE reverse biased and Id decreases The gate of MOSFETs act like which type of component? Capacitors What makes input resistance high in MOSFETs? Gate isn’t connected to any other element What is threshold voltage? Point where volts applied to gate causes same number of positive/negative charges in channel region (typically 1 V) In an enhancement mode NMOS what happens when there is 0 voltage? Channel is P type material and there is NO CURRENT What type of switch does an enhancement mode MOSFET act like? Normally open switch What happens during inversion ? As gate voltage increases ABOVE THRESHOLD, polarity in the channel changes in channel to allow current to flow What determines channel size? Gate voltage What determines drain current (MOSFET)? Channel size What type of material is the channel made of in depletion mode MOSFET? SAME doping as source and drain (diffused channel) What type of material is the channel made of in enhancement mode MOSFET? Different material from source and gate (induced channel) What happens in depletion mode MOSFET when there is 0 or positive voltage on gate? Current is free to flow Increased voltage from gate (increases/decreases) current in depletion mode MOSFET? Decreases Increased voltage from gate (increases/decreases) current in enhancement mode MOSFET? Increases Depletion mode MOSFET acts like which type of switch? Normally closed What is pinch-off? (N-Channel) Negative voltage applied to gate causes channel to switch polarity, channel substrate becomes DIFFERENT from source/drain, NO CURRENT FLOW What type of biasing is applied to gate (N-Channel Enhancement MOSFET)? Positive with respect to source What type of biasing is applied to gate (P-Channel Enhancement MOSFET)? Negative with respect to source What are 4 advantages of MOSFETs? Low power consumption, high input impedance, high output gain, easy manufacture Which type of MOSFET amp has high voltage gain? Common source What separates metal gate from substrate? Oxide layer (SiO2) What type of MOSFETs are used in CMOS inverter? Complementary, PMOS and NMOS Which type of MOSFET amp is used as impedance transformers? common drain (source follower) What is the purpose of sine oscillators? Convert DC energy into sinusoidal AC energy Oscillators are modified amps that provide their own _ Input
What type of feedback is required to produce oscillations? Regenerative (positive) feedback
Applying noise to oscillator produces what? One frequency determined by feedback circuit
What part of an oscillator determines frequency? Feedback circuit
What is the initial input to oscillator circuit? Noise from amp
What are three types of oscillator circuits? RC, LC, Crystal
How much does each cap/resistor combo shift signal in RC oscillator? 60 degrees
How do you determine frequency on a crystal? It’s stamped on crystal
What type of oscillator has two inductors and a cap in feedback circuit? Hartley
What type of oscillator has two caps and an inductor in feedback circuit? Colpitts
What is the primary purpose of the amp circuit in oscillators? Add regenerative feedback to oscillator, compensate for flywheel effect
How is normal operation determined in oscillators? Compare measured resonant frequency to calculated resonant frequency
When can oscillator amps be biased class B/C? When output is taken from feedback circuit (as opposed to taken from transistor collector
Most faults cause what in sine wave oscillator circuits? No output
What steps are used to troubleshoot sine wave oscillator circuits? Check output, VCC, amp (transistor), feedback, output
What needs to be done to check the transistor in amp circuit? Turn power off
What effect do crystals exhibit? Piezoelectric
What is the piezoelectric effect? crystals vibrate when voltage is applied
What is the purpose of sawtooth generator? Turns AC square waves into sawtooth output
The sawtooth generator requires what to operate? Input signal (doesn’t use feedback)
What type of square wave is applied to base of transistor (sawtooth generator)? DC square wave (after clamping)
When does cap charge in sawtooth generator? When Q1 is reverse biased
When does cap discharge in sawtooth generator? When Q1 is forward biased