Semiconductors: Atomic Structure

Chapter 1

• Every known element possess a unique type of atom.
• Atoms contain one nucleus and one or more electrons, or protons, electrons, and neutrons.
• An atom's nucleus is composed of protons and neutrons.
• Silicon's atomic number is 14.
• Germanium's atomic number is 32.
• Silicon's valence shell has the number designation of 3.
• Valence electrons reside in the most distant orbit from the nucleus.
• Positive ions form when a valence electron breaks away from the atom.
• Silicon is the most widely used semiconductive material in electronic devices.
• Free electrons exist in the conduction band.
• Ionization produces electron-hole pairs.
• Recombination occurs when an electron falls into a hole.
• Semiconductor crystal atoms are held together by covalent bonds.
• Each atom in a silicon crystal has four valence electrons.
• Current in semiconductors is produced by both electrons and holes.
• Intrinsic semiconductors have thermally produced free electrons with as many electrons as there are holes.
• The difference between insulators and semiconductors lies in a wider energy gap between the valence and conduction bands.
• Doping is the process of adding an impurity to an intrinsic semiconductor.
• A trivalent impurity is added to silicon to create a p-type semiconductor.
• The purpose of a pentavalent impurity is to increase the number of free electrons.
• Majority carriers in n-type semiconductors are conduction electrons.
• Holes in n-type semiconductors are minority carriers that are thermally produced.
• A PN junction is formed at the boundary of p-type and n-type materials.
• The depletion region is created by ionization and diffusion.
• A depletion region consists of positive and negative ions as well as no majority carriers.
• Bias refers to applying a DC voltage to control a device's operation.
• Forward-biasing a diode involves applying an external voltage that is positive at the anode and negative at the cathode.
• When a diode is forward-biased, the resultant current is produced by both holes and electrons.
• Although current is blocked during reverse bias, there is some current due to minority carriers.
• A silicon diode typically requires a forward-bias voltage greater than 0.7V.
• When forward-biased, a diode conducts current.
• A voltmeter placed across a forward-biased diode will read a voltage approximately equal to the diode's barrier potential.
• Assuming a silicon diode in series with a 1.0 kΩ resistor and a 5V battery setup, connecting the anode to the positive terminal means the cathode voltage with respect to the negative battery terminal is 4.3 V.
• With the positive lead of an ohmmeter connected to the anode of a diode and the negative lead connected to the cathode, the diode is forward-biased.

Chapter 2

• The average value of a half-wave rectified voltage with a peak of 200V is 63.7V.
• When a 60 Hz sinusoidal voltage is applied to the input of a half-wave rectifier, the output frequency is 60 Hz.
• With a peak input of 10V into a half-wave rectifier, the approximate peak of the output is 9.3V.
• In a circuit where the diode must withstand a reverse voltage, the diode must be able to withstand a reverse voltage of 10V.
• The average value of a full-wave rectified voltage with a peak value of 75V is 47.8V.
• With 60 Hz sinusoidal voltage to the input of a full-wave rectifier, the output frequency is 120 Hz.
• In a center-tapped full-wave rectifier with a total secondary voltage of 125 rms, the rms output voltage is 62.5V.
• For a center-tapped full-wave rectifier with a peak output of 100 V, the PIV for each diode is 200 V.
• When the RMS output voltage of a bridge full wave rectifier is 20V, the peak inverse voltage across the diodes is 28.3V.
• The ideal DC output voltage of a capacitor-input filter equals the peak value of the rectified voltage.
• A power supply filter that has an output with a ripple of 100 mV peak-to-peak and a DC value of 20 V has a ripple factor is 0.005.
• With a 60V peak full-wave rectified voltage applied to a capacitor-input filter where f=120Hz, RL=10kΩ, and C=10µF, ripple voltage is 5.0V.
• If the load of a capacitor-filtered full-wave rectifier is reduced, the ripple voltage increases.
• Line regulation is determined by changes in output voltage and input voltage.
• Load regulation is determined by changes in load current and output voltage.
• With a 10V peak-to-peak sinusoidal voltage applied across a silicon diode and series resistor, the maximum voltage across the diode is 0.7V.
• If the input voltage to a voltage tripler is 12V rms, the DC output voltage is approximately 50.9V.
• If one diode in a bridge full-wave rectifier opens, the output is a half-wave rectified voltage.
• One way to check a 60 Hz full-wave bridge rectifier is by observing that the output has a 60 Hz ripple which may indicate an open diode.
• A no-load condition means that the load has infinite resistance and the output terminals are open.
• A varactor diode exhibits a variable capacitance that depends on reverse voltage.
• An LED emits light when forward-biased.
• Compared to a visible red LED, an infrared LED produces light with a longer wavelength.
• The internal resistance of a photodiode decreases with light intensity when forward-biased.
• A diode that has a negative resistance characteristic is the tunnel diode.
• When an infrared LED is optically coupled to a photodiode and the LED is turned off, the ammeter reading in series with the reverse-biased photodiode will decrease.
• In order for a system to function properly, the circuits must properly connected, interfaced, and biased.

Chapter 3

• The cathode of a zener diode in a voltage regulator is normally more negative than the anode.
• A zener diode with a zener voltage of 3.6V operates in zener breakdown.
• With a certain 12V zener diode, a 10mA change in zener current produces a 0.1V change in zener voltage so the zener impedance for this current range is 10Ω.
• If the data sheet for a zener gives Vz=10V at Izt=500mA then, Zz for these conditions is 20Ω.

Chapter 4

• The emitter current is greater than the base current and collector current.
• The βDC of a transistor is its current gain.
• If Ic is 50 times larger than IB, then βDC is 50.
• The approximate voltage across the forward-biased base-emitter junction of a silicon BJT is 0.7V.
• The bias condition for a transistor to be used as a linear amplifier is called forward-forward.
• If the output of a transistor amplifier is 5 V rms and the input is 100 mV rms, the voltage gain is 50.
• Transistors act like a switch when operated in cutoff and saturation.
• In cutoff, VCE is maximum.
• In saturation, VCE is minimum.
• In order to saturate a BJT, IB ≥ IC(sat)/βDC.
• Once in saturation, a further increase in base current will not affect the collector current.
• With the base-emitter junction is open, the collector voltage is Vcc.
• The maximum value of collector current in a biased transistor is IC(sat).
• Ideally, a DC load line is a straight line drawn on the collector characteristic curves between VCE(cut off) and Ic(sat).

Chapter 5

• If a sinusoidal voltage is applied to the base of a biased npn transistor and the resulting sinusoidal collector voltage is clipped near zero volts, the transistor is being driven into saturation.
• The input resistance at the base of a biased transistor depends mainly on BDC and RE.
• With a voltage-divider biased transistor circuit, RIN (base) can generally be neglected in calculation when RIN(base )>10 R2.
• In voltage-divider biased npn transistor, if VB is 2.95 V, the dc emitter voltage is approximately 2.25 V.
• Voltage-divider bias can be essentially independent of BDC.
• The disadvantage of base bias is that it is too beta dependent.
• Emitter bias is essentially independent of BDC.
• In an emitter bias circuit, where RE = 2.7 kΩ and VEE = 15 V, the emitter current is 5.3 mA.
• Collector-feedback bias is based on the principle of negative feedback.
• In a voltage-divider biased npn transistor, if the upper voltage-divider resistor opens, the transistor goes into cutoff.
• In a voltage-divider biased npn transistor, if the lower voltage-divider resistor opens, the transistor may be driven into saturation.
• In a voltage-divider biased pnp transistor where there is no base current, but the base voltage is approximately correct, the most likely problem is that the base-emitter junction is open and a bias resistor is open.

Chapter 6

• A small-signal amplifier uses only a small portion of its load line.
• The parameter hfe corresponds to BDC.
• If the DC emitter current in a certain transistor amplifier is 3 mA, the approximate value of r'e is 8.33 Ω.
• In a certain common-emitter amplifier where the voltage gain is 100, removing the emitter bypass capacitor will cause the voltage gain to decrease.
• For a common-collector amplifier where RE = 100 Ω, r'e = 10 Ω, and βAC = 150, the ac input resistance at the base is 16.5 Ω.
• If a 10 mV signal is applied to the base of an emitter-follower circuit with information from Question 5, the output signal is approximately 10 mV.
• With a common-emitter amplifier where Rc = 1.0 kΩ, RE = 390 Ω, and βac = 75, assuming the RE is completely bypassed at the operating frequency, the voltage gain is 2.56.
• If, with the circuit of Question 7, the frequency is reduced to the point where XC(bypass) = RE, the voltage gain is less.
• With an emitter-follower circuit where the current gain is 50, the power gain is approximately 1.

Chapter 7

• The JFET is a unipolar device and voltage-controlled device.
• The channel of a JFET is between the drain and source.
• A JFET always operates with the gate-to-source pn junction reverse-biased.
• For VGS = 0 V, the drain current becomes constant when VDS exceeds Vp.
• The constant-current area of a FET lies between pinch-off and breakdown.
• IDSS is the maximum possible drain current.
• Drain current in the constant-current area increases when the gate-to-source bias voltage decreases.
• In a certain FET circuit, where VGS = 0 V, VDD = 15 V, IDSS = 15 mA, and RD = 470 Ω, decreasing RD to 330 Ω will keep IDSS at 15 mA.
• At cutoff, the JFET channel is completely closed by the depletion region.
• A certain JFET data sheet that provides that ​​VGS(off) = -4V reveals that the pinch-off voltage Vp, is +4V.
• An FET where ​​VGS(off) = -4V is an n-channel.
• For a certain JFET, where IGSS = 10 nA at VGS = 10 V, input resistance is 1000 MΩ.
• With a p-channel JFET where ​​VGS(off) = 8V, the value of VGS for an approximately midpoint bias is 4.
• MOSFETs differ from JFETs mainly because the JFET has a pn junction.
• With a D-MOSFET biased at VGS = 0 V, its data sheet that specifies IDSS = 20 mA and VGS(off) = -5 V, the value of the drain current is 20 mA.
• An n-channel D-MOSFET with positive VGS is operating in the enhancement mode.
• With a p-channel E-MOSFET that has a ​​VGS(th) = -2V, where VGS = 0 V, the drain current is 0 A.
• A TMOSFET is a special type of D-MOSFET.

Chapter 8

• In a common-source amplifier, the output voltage is 180° out of phase with the input and is taken at the drain.
• In a certain common-source (CS) amplifier where VDS = 3.2 V rms and VGS = 280 mV rms, the voltage gain is 11.4.
• In a certain CS amplifier, where RD = 1.0 kΩ, Rs = 560 Ω, VDD = 10 V and gm = 4500µS and where the source resistor is completely bypassed, the voltage gain is 4.5.
• Ideally, the equivalent circuit of a FET contains a current source between drain and source terminals.
• The value of the current source is dependent on the transconductance and the gate-to-source voltage.
• In a certain common-source amplifier where the voltage gain is 10, removing the source bypass capacitor will cause the voltage gain to decrease.
• A CS amplifier has a load resistance of 10 kΩ and RD = 820 Ω, If gm = 5 ms and Vin = 500 mV, the output signal voltage is 2.05 V.
• If the load resistance is removed in the transistor from the last question, the output voltage will decrease.
• With a certain common-drain with Rs = 1.0 kΩ, there is a transconductance of 6000 µS so the voltage gain is 0.86.
• The data sheet for the transistor used in a CD amplifier specifies IGSS = 5 nA at VGS = 10 V. If the resistor from ate to ground, RG, is 50 MΩ then the total input resistance is approximately. 50 MΩ.
• The common-gate (CG) amplifier differs from both the CS and CD configuration in that it has a much lower voltage gain.
• If you are looking for both good voltage gain and high input resistance, you must use a CS amplifier.
• For small-signal operation, an n-channel JFET must be biased at a ​​VGS(off) <VGS><OV.

Chapter 9

• With two FET amplifiers cascaded where the first stage has a voltage gain of 5 and the second stage has a voltage gain of 7, the overall voltage gain is 35.
• If there is an internal open between the drain and source in a CS amplifier, the drain voltage is equal to VDD.
• A Class A amplifier operates in the linear region at all times .
• If a certain Class A power amplifier delivers 5 W to a load with an input signal power of 100 mW, the power gain is 50.
• The peak current a class A power amplifier can deliver to a load depends on the quiescent current.
• For maximum output, a class A power amplifier must maintain a value of quiescent current that is at least as large as the peak load current.
• If a certain class A power amplifier has ​​VCEQ = 12 V and IcQ = 1 A, the maximum output is 6 W.
• The efficiency of a power amplifier is the ratio of the power delivered to the load to the power from the dc power supply.
• The maximum efficiency of a class A power amplifier is 25%.
• The transistor is a class B amplifier are biased into cutoff.
• Crossover distortion is a problem for class B amplifiers.
• A BJT class B push-pull amplifier with no transformer coupling uses complementary symmetry transistors.
• A current mirror in a push-pull amplifier should give an Ico that is zero.
• The maximum efficiency of a class B push-pull amplifier is 79%.
• The maximum efficiency of a class AB amplifier is higher than class B.
• The power dissipation of a class C amplifier is normally very low.
• The efficiency of a class C amplifier is greater than classes A, B, or AB.
• The transistor in a class C amplifier conducts for a very small percentage of the input cycle.

Chapter 10

• The low-frequency response of an amplifier is determined in part by the coupling capacitors.
• The high-frequency response of an amplifier is determined in part by the internal transistor capacitances.
• The bandwidth of an amplifier is determined by the critical frequencies.
• If the gain of a certain amplifier decreases by 6 dB when the frequency is reduced from 1 kHz to 10 Hz, the roll-off is - 6 dB/decade.
• The gain of a particular amplifier at a given frequency decreases by 6 dB when the frequency is doubled so the roll-off is -6 dB/octave.
• The miller input capacitance of an amplifier and is dependent on the voltage gain.
• An amplifier that has the following critical frequencies (1.2 kHz, 950 Hz, 8 kHz, and 8.5 kHz) has a bandwidth is 7550 Hz.
• Ideally, the midrange gain of an amplifier remains constant with frequency.
• The frequency at which an amplifier's gain is 1 is called the unity-gain frequency.
• With the voltage gain of an amplifier increased, the bandwidth decreases/
• With the fT of the transistor used in a certain amplifier is 75 MHz and the bandwidth is 10 MHz, the voltage gain must be 7.5.
• In the midrange of an amplifier's bandwidth, there is a peak output voltage is 6 V so peak output voltage has to be less than 6V at the lower critical frequency, 3.82 V.
• With the peak output voltage of a certain amplifier is 10 V at the upper critical frequency, the peak voltage in the midrange of the amplifier is 14.14 V.
• In the step response of a noninverting amplifier, a longer rise time means a narrower bandwidth and/or a lower fcl.
• The lower critical frequency of a direct-coupled amplifier with no bypass capacitor is 0 Hz.

Chapter 11

• A thyristor has four pn junctions.
• Common types of thyristors include UJTs and PUTs.
• A 4-layer diode turns on when the anode to cathode voltage exceeds the forward-breakover voltage.
• Once conducting, a 4-layer diode can be turned off by reducing the current below a certain value and/or disconnecting the anode voltage.
• An SCR differs from 4-layer diode because it has a gate terminal.
• An SCR can be turned off by forced commutation, a negative pulse on the gate, and/or anode current interruption.
• In the forward-blocking region, the SCR is in the off state.
• The specified value of holding current for an SCR means that the device will turn off when the anode current falls below this value.
• The diac is is a bilateral, two terminal device and like two parallel 4-layer diode in reverse directions.
• The triac is like a bi-directional SCR.
• The SCS differs from the the SCR because it has two gate terminals.
• The SCS can be turned on by an anode voltage that exceeds forward-breakover voltage and/or either b or c.
• The SCS can be turned off by a negative pulse on the cathode gate and a positive pulse on the anode gate and/or reducing the anode current to below the holding value.
• Bilateral conduction is not a characteristic of the UJT.
• The PUT is much like the UJT and triggered on and off by the gate-to-anode voltage but not a thyristor nor a four-layer device.
• In a phototransistor, base current is directly proportional to light with set by bias voltage.

Chapter 12

• An integrated circuit (IC) op-amp has two inputs and one output.
• The following does not are necessarily apply to an op-amp: low output impedance and low power increased
• A differential amplifier are is part of an op-amp, is increased.
• When an op-amp is operated in the single-ended mode, one input is grounded and a signal is applied to the other.
• In the differential mode, opposite polarity signals are applied to the inputs.
• In the common mode, an identical signal appears on both inputs.
• Common-mode gain is very low.
• If ​​Av(d) = 3500 and Acm = 0.35, the CMRR is 10,000.
• Given zero volts on both inputs, an op-amp ideally should have an output equal to zero , the positive supply voltage, the negative supply voltage, the CMRR
• Of the values listed, the most realistic value for open-loop gain of an op-amp is 80 db, 1. 2000, 100,000,
• A certain op-amp has a bias current of 50μA and 49.3μA so the input offset current is 700 nA, 99.3μA, 49.7μA.
• The output of a particular op-amp increases 8 V in 12 μs and slew rate is, 96 V/μs ,0.67 V/ .none of the above
• The purpose of offset nulling is limited.
• Given an op-amp with negative feedback, the output is fed back to the inverting input.
• The use of negative feedback reduces the voltage gain of an op-amp and/or makes linear operation possible.
• Negative feedback increases the input impedance and the bandwidth and/or decreases the output impedance.
• With an inverting amplifier that has an R₁ of 0.1 kΩ and an Rf of 100 kΩ., the closed loop gain is, 100,000, 1000, 100, .
• If the feedback resistor is open, the voltage gain decreases, remains, ,
• 553 If for example.
• increaseStayDecreases

Chapter 13

• For a zero-level detector, the output changes state when the input crosses zero.
• The zero-level detector is one application of a comparator
• Noise on the input of a comparator can cause the output to change back and forth erratically between two states.
• You can reduce the effect the noise by using hysteresis and/or positive feedback.
• A comparator with hysteresis has two trigger points.
• In a comparator with hysteresis, a portion of the output is feedback to the noninverting input.
• Using the output bounding in a comparator limits the output levels.
• A summing amplifier can have any number of inputs.
• If the voltage gain for each input of a summing amplifier with a 4.7 kΩ feedback resistor is unity, the input resistor must have a value of 4.7 kΩ.
• An average amplifier has five inputs so the ratio RfIR must be 0.2.
• In a scaling adder, the input resistors are each proportional to the weight of its input.

Chapter 14

• In an integrator, the feedback element is a capacitor.
• For a step input, the output of an integrator is a ramp.
• The rate of change of an integrator's output voltage set by all of these, the RC time constant, the amplitude of the step input, the current through the capacitor
• In a differentiator, the feedback element is resistor, zener diode, voltage divider
• The output of a differentiator is proportional to the rate at which the input is changing.
• What occurs when you apply a triangular waveform to the input of a differentiator is a square waveform.
• To make a basic instrumentation amplifier, it takes three op-amps and seven resistors.
• Typically, an instrumentation amplifier has an external resistor used for setting the voltage gain.
• Instrumentation amplifiers are used primarily in filter circuits, high-noise environments medical equipment test instruments
• Isolation amplifiers are used primarily in equipmentApplications where human safety is a concern

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