ITEC 320 Exam 3 Flashcards
(139 cards)
1
Q
Field-effect transistor
A
A transistor controlled by voltage rather than by current. The flow of current is controlled by the effects of an electric field.
2
Q
Gate
A
An element in a FET. It is the control element of the devices. It corresponds to the base of a bipolar transistor.
3
Q
Drain
A
The terminal of a FET that is the drain for charge carriers from the FET channel.
4
Q
Source
A
In general, the origin of the electrical energy supplied to a device. In FET’s, it is one of the electrodes.
5
Q
The FET is a semiconductor device in which output current is controlled by
A
An electric field or gate
6
Q
The control element in a FET is the
A
Gate
7
Q
The point at which an increase in voltage from source to drain no longer produces an increase in current is called
A
Saturation current
8
Q
When the negative gate voltage (VGS) stops the current flow from source to drain, the FET has reached its
A
Cutoff voltage
9
Q
Does the FET have a high or low input impedance
A
High
10
Q
Common-source amplifier
A
An amplifier in which an FET is the active device. The source of the FET is common to the input and output circuits. Input is applied to the gate and the output is applied to the drain
11
Q
Does the common-source FET amplifier require complicated bias arrangements, why or why not
A
No, because we do not need reverse bias and its self-biased.
12
Q
Common-source FET amplifiers have a high input
A
Impedance
13
Q
How many degrees is the phase shift between input and output signals in a common-source amplifier
A
180 degrees
14
Q
What type of input signal does a common-source FET amplifier require to produce a large output signal
A
Powerful input signal (4/10v)
15
Q
Source-follower
A
An amplifier where the drain is common to the input and output circuits. Input is applied to the gate. Output occurs at the source. Voltage gain is less than 1
16
Q
Emitter-follower
A
A transistor stage in which the collector is common to the input and output circuits. Input is applied to the base. Output occurs at the emitter. Voltage gain is less than 1
17
Q
In a source-follower circuit, how many degrees is the output inverted from the input
A
Its not, they follow one another or zero
18
Q
Does a source-follower have a high or low output impedance
A
Low
19
Q
The voltage gain of a source-follower is less than
A
1
20
Q
The source-follower has a fairly poor what
A
Gain
21
Q
Does the source-follower circuit have a high or low input impedance
A
High
22
Q
The FET is a semiconductor device in which an electrical field within the device controls
A
Output current
23
Q
You can increase or decrease the electric field within a FET with the amount of voltage applied to the
A
Gate
24
Q
The electric field in a FET determines the amount of current flowing from the
A
Source to drain
25
An advantage of a FET is its
High input impedance
26
FET's use what as part of their circuitry
Self-bias
27
FET's need what to produce a large output at the load
A small amount of input power
28
A common-source amplifier accepts and amplifies a
Fairly wide range of frequencies
29
Voltage gain formula
Output voltage/input voltage
30
The output of a source-follower is take from a resistor in the
Source circuit
31
A source-follower is used in many
Impedance matching situations
32
MOSFET
Metal oxide semiconductor field-effect transistor. A FET with an insulated gate (IGFET.) The metal gate is insulated from the semiconductor by an oxide layer.
33
2 types of MOSFETs
Enhancement-types (turned off) or depletion-types (turned on)
34
Types MOSFETs can be divided into
N-types and P-types
35
IGFET
Insulated gate FET
36
Depletion mode
MOSFET operation in which changing the gate-to-source voltage from zero to some other value decreases the drain current. Turned on, but can be turned off when a control voltage is applied to the gate terminal
37
Enhancement mode
MOSFET operation in which changing the gate-to-source voltage from zero to some other value increases the drain current. Enhancement is turned off, but can be turned on when a control voltage is applied to the gate terminal
38
Majority carrier
The major carrier in semiconductor materials. Electrons in N-types. Holes in P-types.
39
Substrate
The surface, or under layer, on which electronic circuits are fabricated. It can be insulating materials, printed circuits, or photocells.
40
Dual-gate MOSFET
Also called a tetrode MOSFET. A MOSFET having two independent gates. Circuit action is controlled by either gate. Provides flexibility
41
Is there a PN junction between the gate and source in a MOSFET
No
42
A MOSFET has a (higher, lower) input resistance than a JFET
Higher
43
Is a depletion-mode MOSFET a normally off device
No
44
The enhancement-mode MOSFET has a (diffused, induced) conducting channel
Induced
45
In an enhancement-mode MOSFET with 0V bias, an AC signal operates the device on the
Positive AC alternations
46
VHF
The very high frequency range. It extends from 30 to 300 megahertz
47
UHF
The ultra high frequency range. It extends from 300 to 3000 megahertz
48
What are three basic circuit arrangements for a MOSFET
Common-source, common-gate, and common-drain
49
In what configuration is the source-follower circuit connected
Common-gate
50
The common-gate amplifier has a (higher, lower) voltage gain than the common-source amplifier
Lower
51
The common-gate circuit matches what to what impedance
Low source resistance impedance to a high source resistance impedance
52
The common what circuit inverts the signal 180 degrees
Source
53
Mixers
A circuit that accepts two or more input signals and combines them in some specific manner
54
Modulator
A circuit that varies the amplitude or frequency of sine-wave voltage according to variations of another voltage or current.
55
Automatic gain control (AGC)
A circuit or system that maintains the output signal level of an electronic device constant, compensating fro changes of input signal level.
56
Automatic volume control (AVC)
A circuit or system that maintains the output volume of a sound-producing system constant, compensating for changes of input signal level
57
Why are MOSFETs useful in communications circuits
High input resistance and low input capacitance
58
You can operate the gates in a dual-gate MOSFET
Independently
59
A gain control voltage appearing at one of the gates acts as an added
Additional bias voltage
60
For an N-channel MOSFET, a more (negative, positive) voltage is needed to reduce the gain of the device
Negative
61
The gate of a MOSFET is
Insulated from the channel by an oxide layer
62
An insulated gate of a MOSFET provides
An even higher input resistance than the JFET
63
A MOSFET can operate with either what appearing at its gate
Polarity
64
In an N-channel MOSFET, a (negative, positive gate voltage) increases drain current
Positive gate voltage
65
In an N-channel depletion-mode MOSFET, the drain-to-source voltage is always applied with
The drain more positive than the source
66
The depletion-mode MOSFET conducts a substantial amount of current
With a gate voltage of zero
67
The enhancement-mode MOSFET conducts almost no drain current
When the gate is zero
68
In the common-gate circuit, the gate is common to
Both the input and the output
69
The common-gate circuit is a
Voltage amplifier
70
The two gates of a dual-gate MOSFET can be operated
Independently
71
Photoelectric effect
The effect produced by some materials when they are subjected to light.
72
Light sensitive
When a device is sensitive to various amounts of light and converts the changes of light intensity into changes of some electrical characteristic
73
Photoconductive cell
A type of photocell which acts as a variable resistor
74
Photovoltaic cell
A type of photocell which builds up a charge depending on the amount of light hitting it
75
Photocells
Also called photoelectric cell (PEC). A light-sensitive cell that converts variations of light intensity into variations of some electrical characteristic
76
Photoresistive cells
A photoelectric cell where the electrical resistance varies inversely with the intensity of light which strikes it
77
Bulk photoconductor
A term used to describe large photoconductive cells because of their bulk construction
78
Wavelength
The distance between two corresponding points of two consecutive waves.
79
What is a photoelectric device
A device used to detect distance, absence, or presence of an object by using a light transmitter.
80
What is a photoconductive cell
A light variable resistor
81
Can a photoconductive cell be improperly biased
No
82
Does the resistance of a photoconductive cell increase or decrease with an increase in light
Decrease
83
In a photocell, is the increase in resistance exactly proportional to the decrease in light
No
84
Thyristor
A term used to describe a group of 4-layer semiconductor devices that can be pulsed into conduction, but can be turned off only by interrupting the applied voltage. SCRs and traics are thyristors
85
Silicon controlled rectifier (SCR)
A solid-state switching device that does not require any control current after it has been turned on. An SCR acts as an open circuit until a positive potential is applied to its gate terminal. The other two electrodes are the anode and cathode.
86
Forward breakover voltage
The value of forward bias voltage applied to the gate of a thyristor that causes it to become highly conductive
87
What is the control electrode in the SCR
Gate
88
The SCR does not turn on until the forward bias from the anode to cathode reaches a certain value. What is the value
Forward breakover voltage
89
In an AC circuit, what does an increase in an SCR's gate current cause
Forward breakover voltage may decrease
90
Does the gate of an SCR lose control once the SCR is turned on
No
91
During the negative half cycle of the waveform, the SCR is
Reverse biased
92
What must you increase to lower breakover voltage
Gate current
93
Will the amount of power received increase or decrease if the gate triggering pulses are delayed more
Decrease
94
Can you trigger a thyristor with a manually-operated circuit
Yes
95
Do you use SCRs to control electrical power
Yes
96
List three uses of SCRs
Relays, lamps, and dimmers
97
What is the main advantage of an SCR
Small current triggering a larger current or voltage
98
Two thyristors are the
Triac and diac
99
SCRs use
3 electrodes
100
The gate of an SCR
Is the control point
101
An SCR is off when it is
Reverse biased
102
An SCR does not turn on until the forward bias reaches
The forward breakover voltage
103
Once an SCR is turned on
THe gate loses control of the cathode-to-anode current
104
In a manually-operated SCR, the SCR and load are
In series with an AC supply voltage
105
In a manually-operated SCR, you can ignore the negative half of the cycle since it will
Reverse bias the thyristor during that half cycle
106
The main use of an SCR is to
Control electrical power and convert electrical power
107
SCRs are used in alarm circuits because they can be triggered with
Very small currents
108
A component that allows signal to remain electrically independent of the following circuit is called a
Isolater
109
Between what circuits is an isolator useful in coupling a signal
Control circuits and power circuits
110
A circuit that uses an isolator converts what energy to what energy
electrical energy to light energy
111
The signal output from a photoconductor used as an isolator is an amplified replica of the input. T or F
True
112
The signal output from a photoconductor used as an isolator is 180 degrees out of phase with the input. T or F
False
113
The resistance of a photoconductive cell decreases with
An increase in light intensity
114
The light-sensitive material in a photoconductive cell is formed in a thin layer on a
glass and ceramic substrate
115
Large photoconductive cells are able to withstand
Relatively high operating voltages (300 VDC)
116
In a schematic of a photoconductive cell, an arrow pointing toward the device indicates
The device is light sensitive
117
In an intrusion detector circuit, when an intruder interrupts the light beam
The resistance of the photocell suddenly increases
118
In an intrusion detector circuit
A photocell is placed in series with a relay coil and a power
119
In an intrusion detector circuit, focusing a narrow beam of light from a distant light source on the light-sensitive element of the photocell
Keeps the resistance of the series circuit low
120
An isolator is a device that
Couples a signal voltage between two isolated circuits
121
In a basic isolator circuit, a signal voltage causes the lamp to
Vary in intensity
122
In a basic isolator circuit, light from the lamp causes the resistance of the photoconductor to
Vary
123
Voltage regulator circuits are used to
Filter circuits and refine the filtering process
124
Voltage regulator circuits provide voltage regulation for
Power supplies
125
In a power source, each component adds up to
An internal resistance in series with the output current
126
A what is an effective shunt regulator
Zener diode
127
Voltage output changes can occur because of a variation in
Line voltage input
128
The smaller the percentage of regulation
The better the regulator
129
In a shunt voltage regulator, the regulator acts as an
Zener diode in parallel with the load
130
In a series voltage regulator, the regulator acts as an
Transistor in series with the load
131
One use of a series voltage regulator is as a
Ripple filter
132
An increase in current will cause the series voltage regulator to
Decrease in resistance
133
An amplifier is a circuit that increases the amplitude of a
Alternating waveform
134
To determine how much an amplifier can increase a signal, you determine
Gain
135
Amplifiers may amplify either
Current or voltage
136
When you need large gains, you can connect
Cascaded amplifiers
137
The total gain of two amplifiers connected in cascade is
The product of their individual gains
138
An enhancement mode MOSFET acts as a push button switch
Turned off
139
An depletion mode MOSFET acts as a push button switch
Turned on
