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Electronics A/S WJEC > Chapter 4: Operational Amplifier > Flashcards

Chapter 4: Operational Amplifier Flashcards

1
Q

How is the voltage gain of an amplifier defined as?

A

G=Vout/Vin

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2
Q

What is bandwidth?

A

This is the range of frequencies over which the gain is greater than 70% of the maximum gain

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3
Q

What is gain-bandwidth product?

A

GBP=gain x bandwidth
GBP is a constant of the op amp. If the gain doubles, the bandwidth halves and vice versa

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4
Q

What is saturation?

A

If the output voltage is too large, the output of the op−amp saturates. The saturation voltage is limited by the power supply. Solutions are to have a larger power supply and reduce the gain of the amplifier or the input voltage.

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5
Q

What is slew rate?

A

This is the rate at which Vout changes when input changes.

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6
Q

What is the equation to calculate slew rate?

A

Slew rate=ΔVout/Δt

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7
Q

What is open-loop gain?

A

there is no feedback – no signal path between the output of the op-amp and its inputs.

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8
Q

What is the ideal open loop gain?

A

Infinite,implying that a significant
output voltage would result from an input voltage of virtually zero

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8
Q

What is virtual earth?

A

when one input is connected directly to 0 V, the other sits at 0 V provided that the output is not saturated.

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9
Q

What is input impedance?

A

‘Resistance’ reduces the flow of electricity in a circuit. ‘Impedance’ can be considered as the equivalent for AC circuits. It determines the current drawn from an input device

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10
Q

What is the ideal value for input impedance?

A

infinite

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11
Q

What is output impedance?

A

the amplifier provides an output to the remainder of the circuit. We do not want to
lose any of the signal in the amplifier itself

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12
Q

What is the ideal value for output impedance?

A

Zero

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13
Q

What is common-mode rejection ratio?

A

MEasures the ability to reject input signals common to both input leads

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14
Q

What is the ideal vale for CMRR?

A

infinite

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15
Q

What is feedback?

A

‘Feedback’ means adding a fraction of the output signal to the input signal.

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16
Q

What is positive feedback?

A

When the fraction of output signal is returned in phase with the input signal, it is called ‘positive feedback’.

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17
Q

What is negative feedback?

A

When it is out of phase with the input
signal, it is called negative feedback.

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18
Q

How is the feedback supplied in an amplifier circuit?

A

With a feedback resistor connected between the input and output.

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19
Q

Draw an inverting amplifier

A

-Non-inverting input grounded
-Rin on the inverting input
-Feedback resistor between inverting input and the output

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20
Q

How is gain calculated on an inverting op amp?

A

G=-Rf/Rin

21
Q

Is the gain always positive or negative on an inverting op amp?

A

negative

22
Q

For an inverting op amp, the gradient of the graph is equal to what?

A

The gain

23
Q

On an inverting op amp, if the output reaches its maximum value, it is said to have reached what kind of saturation?

A

Positive

24
Q

On an inverting op amp, if the output reaches its minimum value, it is said to have reached what kind of saturation?

A

Negative saturation

25
Q

For an inverting op amp, if the input voltage is switched to AC, how does this change the way the graph looks

A

The output has the same frequency but inverted

26
Q

How is gain calculated for a non-inverting amplifier?

A

G=1+Rf/Rin

27
Q

Is gain always positive or negative for a non-inverting op amp?

A

Positive

28
Q

Draw a non-inverting op amp circuit

A

-Vin through the non-inverting input.
-Feedback resistor connected between vout and the inverting input
-R1 grounded and connected to the inverting input

29
Q

On a non-inverting op amp, when does positive saturation occur?

A

When the output reaches the maximum possible value

30
Q

On a non-inverting op amp, when does negative saturation occur?

A

When the output reaches the minimum possible value

31
Q

Name the two types of op amp distortion

A

Clipping and slew rate

32
Q

What is clipping distortion?

A

This occurs when the peak Vout is larger than the saturation voltage

33
Q

State 3 solutions for clipping?

A

Higher the power supply
Lower the gain
Lower the input voltage

34
Q

What is slew rate distortion?

A

This is where the output cannot change fast enough to replicate input at high frequencies

35
Q

How can slew rate be avoided?

A

Purchasing an op amp with a greater slew rate
The slew rate needs to be=2πfVp

36
Q

What is the gain of a voltage follower?

A
  1. This means Vout=Vin
37
Q

Draw a voltage follower circuit

A

-Vin through the non-inverting input
-Inverting input connected directly to the output providing feedback
No resistors

38
Q

Draw a summing amplifier circuit

A

-3 different inputs, which all have their own resistor.
-The resistors are all connected to the inverting input
-Rf is also connected to the inverting input’
-non-inverting is grounded

39
Q

How do you calculate gain of a summing amplifier?

A

Vout=-Rf(V1/R1 + V2/R2 +…

40
Q

The voltage follower is a form of what op amp?

A

Non-inverting

41
Q

What is the ideal feedback resistance of a voltage follower?

A

0Ω

42
Q

What is a comparator?

A

A comparator is a sub-system that compares two voltages. Its output indicates which is larger.

43
Q

Does a comparator have feedback?

A

No

44
Q

How is the comparator powered?

A

By a single-rail power supply, with the negative power terminal

45
Q

What is used to amplify the difference in input voltages?

A

Full open loop gain

46
Q

True or false: The output of the of a comparator will always be saturated

A

True
Vout:G0-(V1-V2)

47
Q

For a comparator.If the non-inverting input is greater than the inverting input, what saturation will the output be?

A

Positive saturation

48
Q

For a comparator.If the inverting input is greater than the non-inverting input, what saturation will the output be?

A

Negative saturation

49
Q

On a comparator which input is the reference voltage?

A

The inverting input

50
Q

On a typical comparator circuit, what is usually connected via the non-inverting input?

A

A sensor circuit. An LDR or thermistor can be used to change the output voltage response

51
Q

What is reference voltage in a comparator?

A

Reference voltage is a fixed voltage

Electronics A/S WJEC (7 decks)

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