ITEC 320 Exam 3 Flashcards
Field-effect transistor
A transistor controlled by voltage rather than by current. The flow of current is controlled by the effects of an electric field.
Gate
An element in a FET. It is the control element of the devices. It corresponds to the base of a bipolar transistor.
Drain
The terminal of a FET that is the drain for charge carriers from the FET channel.
Source
In general, the origin of the electrical energy supplied to a device. In FET’s, it is one of the electrodes.
The FET is a semiconductor device in which output current is controlled by
An electric field or gate
The control element in a FET is the
Gate
The point at which an increase in voltage from source to drain no longer produces an increase in current is called
Saturation current
When the negative gate voltage (VGS) stops the current flow from source to drain, the FET has reached its
Cutoff voltage
Does the FET have a high or low input impedance
High
Common-source amplifier
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
Does the common-source FET amplifier require complicated bias arrangements, why or why not
No, because we do not need reverse bias and its self-biased.
Common-source FET amplifiers have a high input
Impedance
How many degrees is the phase shift between input and output signals in a common-source amplifier
180 degrees
What type of input signal does a common-source FET amplifier require to produce a large output signal
Powerful input signal (4/10v)
Source-follower
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
Emitter-follower
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
In a source-follower circuit, how many degrees is the output inverted from the input
Its not, they follow one another or zero
Does a source-follower have a high or low output impedance
Low
The voltage gain of a source-follower is less than
1
The source-follower has a fairly poor what
Gain
Does the source-follower circuit have a high or low input impedance
High
The FET is a semiconductor device in which an electrical field within the device controls
Output current
You can increase or decrease the electric field within a FET with the amount of voltage applied to the
Gate
The electric field in a FET determines the amount of current flowing from the
Source to drain
An advantage of a FET is its
High input impedance
FET’s use what as part of their circuitry
Self-bias
FET’s need what to produce a large output at the load
A small amount of input power
A common-source amplifier accepts and amplifies a
Fairly wide range of frequencies
Voltage gain formula
Output voltage/input voltage
The output of a source-follower is take from a resistor in the
Source circuit
A source-follower is used in many
Impedance matching situations
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.
2 types of MOSFETs
Enhancement-types (turned off) or depletion-types (turned on)
Types MOSFETs can be divided into
N-types and P-types
IGFET
Insulated gate FET
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
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
Majority carrier
The major carrier in semiconductor materials. Electrons in N-types. Holes in P-types.
Substrate
The surface, or under layer, on which electronic circuits are fabricated. It can be insulating materials, printed circuits, or photocells.
Dual-gate MOSFET
Also called a tetrode MOSFET. A MOSFET having two independent gates. Circuit action is controlled by either gate. Provides flexibility
Is there a PN junction between the gate and source in a MOSFET
No
A MOSFET has a (higher, lower) input resistance than a JFET
Higher
Is a depletion-mode MOSFET a normally off device
No
The enhancement-mode MOSFET has a (diffused, induced) conducting channel
Induced
In an enhancement-mode MOSFET with 0V bias, an AC signal operates the device on the
Positive AC alternations
VHF
The very high frequency range. It extends from 30 to 300 megahertz
UHF
The ultra high frequency range. It extends from 300 to 3000 megahertz
What are three basic circuit arrangements for a MOSFET
Common-source, common-gate, and common-drain
In what configuration is the source-follower circuit connected
Common-gate
The common-gate amplifier has a (higher, lower) voltage gain than the common-source amplifier
Lower
The common-gate circuit matches what to what impedance
Low source resistance impedance to a high source resistance impedance
The common what circuit inverts the signal 180 degrees
Source
Mixers
A circuit that accepts two or more input signals and combines them in some specific manner
Modulator
A circuit that varies the amplitude or frequency of sine-wave voltage according to variations of another voltage or current.
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.
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
Why are MOSFETs useful in communications circuits
High input resistance and low input capacitance
You can operate the gates in a dual-gate MOSFET
Independently
A gain control voltage appearing at one of the gates acts as an added
Additional bias voltage
For an N-channel MOSFET, a more (negative, positive) voltage is needed to reduce the gain of the device
Negative
The gate of a MOSFET is
Insulated from the channel by an oxide layer
An insulated gate of a MOSFET provides
An even higher input resistance than the JFET
A MOSFET can operate with either what appearing at its gate
Polarity
In an N-channel MOSFET, a (negative, positive gate voltage) increases drain current
Positive gate voltage
In an N-channel depletion-mode MOSFET, the drain-to-source voltage is always applied with
The drain more positive than the source
The depletion-mode MOSFET conducts a substantial amount of current
With a gate voltage of zero
The enhancement-mode MOSFET conducts almost no drain current
When the gate is zero
In the common-gate circuit, the gate is common to
Both the input and the output
The common-gate circuit is a
Voltage amplifier
The two gates of a dual-gate MOSFET can be operated
Independently
Photoelectric effect
The effect produced by some materials when they are subjected to light.
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
Photoconductive cell
A type of photocell which acts as a variable resistor
Photovoltaic cell
A type of photocell which builds up a charge depending on the amount of light hitting it
Photocells
Also called photoelectric cell (PEC). A light-sensitive cell that converts variations of light intensity into variations of some electrical characteristic
Photoresistive cells
A photoelectric cell where the electrical resistance varies inversely with the intensity of light which strikes it
Bulk photoconductor
A term used to describe large photoconductive cells because of their bulk construction
Wavelength
The distance between two corresponding points of two consecutive waves.
What is a photoelectric device
A device used to detect distance, absence, or presence of an object by using a light transmitter.
What is a photoconductive cell
A light variable resistor
Can a photoconductive cell be improperly biased
No
Does the resistance of a photoconductive cell increase or decrease with an increase in light
Decrease
In a photocell, is the increase in resistance exactly proportional to the decrease in light
No
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
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.
Forward breakover voltage
The value of forward bias voltage applied to the gate of a thyristor that causes it to become highly conductive
What is the control electrode in the SCR
Gate
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
In an AC circuit, what does an increase in an SCR’s gate current cause
Forward breakover voltage may decrease
Does the gate of an SCR lose control once the SCR is turned on
No
During the negative half cycle of the waveform, the SCR is
Reverse biased
What must you increase to lower breakover voltage
Gate current
Will the amount of power received increase or decrease if the gate triggering pulses are delayed more
Decrease
Can you trigger a thyristor with a manually-operated circuit
Yes
Do you use SCRs to control electrical power
Yes
List three uses of SCRs
Relays, lamps, and dimmers
What is the main advantage of an SCR
Small current triggering a larger current or voltage
Two thyristors are the
Triac and diac
SCRs use
3 electrodes
The gate of an SCR
Is the control point
An SCR is off when it is
Reverse biased
An SCR does not turn on until the forward bias reaches
The forward breakover voltage
Once an SCR is turned on
THe gate loses control of the cathode-to-anode current
In a manually-operated SCR, the SCR and load are
In series with an AC supply voltage
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
The main use of an SCR is to
Control electrical power and convert electrical power
SCRs are used in alarm circuits because they can be triggered with
Very small currents
A component that allows signal to remain electrically independent of the following circuit is called a
Isolater
Between what circuits is an isolator useful in coupling a signal
Control circuits and power circuits
A circuit that uses an isolator converts what energy to what energy
electrical energy to light energy
The signal output from a photoconductor used as an isolator is an amplified replica of the input. T or F
True
The signal output from a photoconductor used as an isolator is 180 degrees out of phase with the input. T or F
False
The resistance of a photoconductive cell decreases with
An increase in light intensity
The light-sensitive material in a photoconductive cell is formed in a thin layer on a
glass and ceramic substrate
Large photoconductive cells are able to withstand
Relatively high operating voltages (300 VDC)
In a schematic of a photoconductive cell, an arrow pointing toward the device indicates
The device is light sensitive
In an intrusion detector circuit, when an intruder interrupts the light beam
The resistance of the photocell suddenly increases
In an intrusion detector circuit
A photocell is placed in series with a relay coil and a power
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
An isolator is a device that
Couples a signal voltage between two isolated circuits
In a basic isolator circuit, a signal voltage causes the lamp to
Vary in intensity
In a basic isolator circuit, light from the lamp causes the resistance of the photoconductor to
Vary
Voltage regulator circuits are used to
Filter circuits and refine the filtering process
Voltage regulator circuits provide voltage regulation for
Power supplies
In a power source, each component adds up to
An internal resistance in series with the output current
A what is an effective shunt regulator
Zener diode
Voltage output changes can occur because of a variation in
Line voltage input
The smaller the percentage of regulation
The better the regulator
In a shunt voltage regulator, the regulator acts as an
Zener diode in parallel with the load
In a series voltage regulator, the regulator acts as an
Transistor in series with the load
One use of a series voltage regulator is as a
Ripple filter
An increase in current will cause the series voltage regulator to
Decrease in resistance
An amplifier is a circuit that increases the amplitude of a
Alternating waveform
To determine how much an amplifier can increase a signal, you determine
Gain
Amplifiers may amplify either
Current or voltage
When you need large gains, you can connect
Cascaded amplifiers
The total gain of two amplifiers connected in cascade is
The product of their individual gains
An enhancement mode MOSFET acts as a push button switch
Turned off
An depletion mode MOSFET acts as a push button switch
Turned on
