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PE4505 Flash Cards > #2 Exam 🥲 > Flashcards

#2 Exam 🥲 Flashcards

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1
Q

Op amps are very close to ideal voltage amplifiers, what does that mean in terms of characteristics?

A

-infinite voltage gain
-infinite bandwidth
-infinite input impedance
-zero output impedance

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2
Q

How many stages are in the construction on an op amp

A

3
-input (differential amplifier)
-2nd (voltage amplifiers)
-last (output amplifiers) class b

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3
Q

What kind of gain is an operational amplifier?

A

Very High voltage gain

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4
Q

How is the input signal taken from each terminal?

A

The voltage difference between terminals

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5
Q

If there is said to be no voltage difference between the 2 inputs what will be the output?

A

There will be zero output

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6
Q

Due to op amps having input infinitely high what is the the input current said to be?

A

So small it’s regarded as zero

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7
Q

What is the output resistance of an op amp

A

Ideally zero but so small to ignore

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8
Q

What is offset with respect to op amp

A

Offset is a small amount of dc voltage that passes with inputs at zero

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9
Q

How is offset cancelled or compensated for?

A

The use of external circuitry

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10
Q

What voltage do most op amps req

A

Plus or minus 5-20 volts

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11
Q

If the signal is applied to the +ve input and the other is grounded what is the output said to be?

A

Inphase

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12
Q

If the signal is applied to the -ve input and the other grounded the output is said to be?

A

Antiphase

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13
Q

What input would an op amp have if one input is grounded/fixed to a reference voltage?

A

Single ended input

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14
Q

What is the positive terminal of an op amp referred to as

A

The non-inverting terminal (inphase)

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15
Q

What is the negative terminal of an op amp referred to as?

A

Inverting terminal (antiphase)

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16
Q

How much input and output impedance does an op amp have

A

High input impedance, low output impedance

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17
Q

What feedback would you add to make an op amp more stable and predictable?

A

Negative feedback

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18
Q

What is slew rate measured in

A

Micro per second

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19
Q

If the slew rate is stated at 1 can the output change 10volts during each microsecond

A

No, slew rate 1 means it can’t change more than 1 volt per microsecond

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20
Q

What does V(oi) mean

A

Input offset voltage

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21
Q

What is offset voltage drift defined as

A

Change in output voltage resulting from temperature changes

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22
Q

What is feedback

A

When a portion of the output is reinserted at the input (can be intentional or unwanted coupling)

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23
Q

Describe positive feedback and its other name

A

Also called regenerative feedback, its inphase with the input so gets added to it. Meaning more input will be amplified from the previous this will cause oscillations.

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24
Q

Describe negative feedback and its other name

A

Also called degenerative feedback, this feedback is antiphase (180*) so will cancel some of the input out. This will reduce the overall gain of the op amp but improves stability and amplifiers performance.

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25
What is the name used when using a number of amplifier stages to produce a desired gain greater than 1 could provide
Cascade
26
What are the 3 types of distortion
-phase (signal delay through amplifier) -frequency (harmonics affecting wave) -amplitude
27
What windings would be found on the primary side of a step down transformer
Many turns of relatively small wire
28
What’s the primary purpose of a transformer core
Provide a circuit of low reluctance for magnetic flux
29
Why can’t you operate a transformer lower than the normal operating level (Hz decreased)
Because inductive reactance will decrease so current flow will increase, if large enough it will damage the transformer
30
Above or below a transformers normal operating level can you operate it safely?
Frequency above (increased) This is due to the inductive reactance being increased and causing a voltage drop over the load so it won’t damage the transformer
31
How are transformers rated
In volt amperes
32
What is in the equation to calculate the average
Average = peak x 0.637
33
What is the output ripple frequency of a full wave rectifier
Double the supply frequency
34
2 disadvantages of a full wave rectifier
-needs a centre tap transformer -diode PIV is double that of a half wave
35
2 disadvantages of a bridge rectifier
-needs 4 diodes -there’s 2 diodes in series resulting in greater FWD voltage drop
36
What does a filter do
Smooths out DC
37
A capacitor opposes change in……
Voltage
38
A inductor opposes change in…..
Current
39
In an inductor filter as the load current increases what happens to the filtering effect
It also increases
40
If the inductance value is becoming greater the filtering effect ……
Will become greater aswell
41
What’s are the 2 types of voltage regulators
Series and shunt
42
In a voltage regulator what are some reasons output voltage may vary
-Load current variations -input or line voltage variations -temperature variations (especially semiconductors)
43
Why is a resistor in series with the zener diode of a shunt voltage regulator
So enough current flows through it for the sender diode to operate within its zener breakdown region
44
What is the number corresponding to the positive supply in IC voltage regulators
Positive supply = 78xx
45
What is the number corresponding to the negative supply in IC voltage regulators
Negative supply = 79xx
46
An op amplifier has what gain
High voltage gain
47
What is the inverting input
The negative terminal
48
What class is the output amplifier (last stage of op amp)
Class b (180* of input cycle)
49
An ideal op amp is said to have a voltage gain of….
Infinity
50
What is a typical op amp voltage gain
About 200,000
51
What stage in the op amp provides the most amount of gain
The 2nd stage the high gain voltage amplifier
52
What input and output resistance should an op amp ideally have
Infinitely high input resistance with extremely low output resistance
53
What is TCV(os) or known as drift
Temperature coefficient of input offset voltage (A voltage that gets added to the input to force the output to zero)
54
What type of feedback can be used to create an oscillator
Positive or regenerative
55
What does V(os) stand for
Input offset voltage
56
What varies input offset voltage
Temperature
57
What is 78xx
Positive voltage regulator
58
79xx
Negative voltage regulator
59
What happens to the PIV for a halfwave rectifier containing capacitor filter
It will be double PIV=2V(max)
60
What happens to the PIV of a full wave or bridge rectifier with a capacitor filter
The PIV I’ll remain unchanged
61
What input line will the input offset voltage be applied to
In series with The inverting input terminal
62
What are the degrees of each class a,ab,b,c
A-current flows for all 360degrees AB-current flows less than 360 but more than 180 B-current flows for 180 C-current flows less than 180
63
What is a Darlington transitor
2 transitors connected to make a high gain NPN transistor
64
Drift can happen due to 3 things
-temp -power supply variations -ageing components
65
What is a RC filter used for
To eliminate a con power supply rail
66
What should phase splitters output be in respect to each other
Balanced
67
What is cross over distortion
Distortion at a point when both transitors are in the OFF state at the same time
68
How much cross over is there between classes, A,B,Ab
A-no crossover B-large crossover Ab-some crossover
69
What does a solid load phase splitter do
Has simultaneous outputs from the collector and the emitter
70
On a NPN in complementary symmetry what polarity needs to be applied for it to conduct
Positive on base
71
On a PNP in complementary symmetry what polarity needs to be applied for it to conduct
Negative to the base
72
How many stable states are there on an A stable multivibrator
No stable states
73
How many stable states are there on a mono stable multivibrator
1 stable state (with one set of timing components removed)
74
How many stable states are in a bistable multivibrator
2 stable states with no timing capacitors
75
In a positive pulse steering trigger is the anode of the cathode held at what polarity potential
The anode is held at a negative potential
76
In a negative pulse steering trigger is the anode of the cathode held at what polarity potential
The cathode is held at a positive voltage
77
An LC tank is what
The simplest oscillating circuit
78
What must the barkhausen feedback be
Must be exactly 1
79
If the barkhausen feedback is 1 but other components change what will happen
The oscillations will stop
80
The stability of an oscillator is due to what
The degree of which the output frequency or amplitude remain constant over predetermined period
81
Define a series fed LC oscillator
All the current flows through a portion of the tuned circuit
82
Define a shunt fed LC oscillator
None of the current flows through the tuned circuit
83
What does a higher Q mean for bandwidth
The higher the Q the narrower the bandwidth
84
Define f(s) in crystal oscillators
Frequency crystal has minimum impedance corresponding to series resonance
85
Define f(p) in crystal oscillators
Frequency crystal has maximum impedance corresponding to parallel resonance between the crystal and its holder
86
At operating frequency of a tank circuit is impedance at min or max
Maximum impedance and large feedback voltage developed
87
What frequencies is the bandwidth between
Lower cutoff and upper cutoff
88
How do you calculate decibel gain
The sum of decibel gains of the individual components
89
What does a higher Q point mean
The hump is more pronounced and bandwidth narrows
90
What do resonant circuits do
Designed to pass a range of frequencies and block others
91
Statement: Double power = +3db Half power = -3db
91
What is the -3db point on a response curve
The point where where the circuits gain falls off at high and low frequencies
92
Requirements of oscillator output wave form
-constant frequency -constant amplitude -waveform purity
93
Othe name for LC circuit
Tank circuit (inductor, capacitor)
94
Statement To over come the effect of the feedback factor being less that one is to have it more than one and reduced does to 1
95

PE4505 Flash Cards (6 decks)

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