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Flashcards in Op Amps Deck (106)
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1

What is an amplifier

An amplifier is a device used to increase the amplitude or power level of a small signal but without distorting it

2

Passive components ____ or ____ signal power

Active components ____ external power and ____

Passive components absorb or transfer signal power

Active components accept external power and amplify

3

Passive components __ ___ need power for them to work

Active components __ need power for them to work

Passive components do not need power for them to work

Active components do need power for them to work

4

For a voltage amplifier the Gain = ?

Gain = Vout / Vin 

5

Gain is a ____ so has no ____

Gain is a ratio so has no units

6

To calculate the voltage delivered to the load we need to know the amplifiers parameters...(3 things)

  1. Input resistance of amplifier rin
  2. Output resistance of amplifier rout
  3. Open circuit voltage gain Av

7

If we know the internal resistance of the source Rs , then the voltage across the input terminal of amplifier will be...(equation)

8

What is Rs?

The internal resistance of the source

9

Rs and rin form a...?

Voltage divider 

10

What does a voltage divider ciruit look like?

11

  • The larger the value of rin, the closer the value of Vin is to...?
  • This is the reason that in practice ___ ____ ____ is always required

  • The larger the value of rin, the closer the value of Vin is to Vs
  • This is the reason that in practice high input impedance is always required

12

What is the symbol for open circuit voltage gain and what is it larger than?

Av - always larger than 1, very, very large!

 

13

What is Open circuit voltage gain?

It is the voltage gain if the amplifier is not loaded i.e. if RL is replaced with an ∞ resistance

14

If a load is connected to the amplifier, the voltage across the load is...(equation)

15

A ____ output resistance is preferred in an amplifier

A small output resistance is preferred in an amplifier

16

What is IC and give an example

Intergrated circuit and an Op amp

17

Define inverting input

the phase angle of the output will be 180° different from that of the input applied at this terminal.

18

The ____ ____ is often omitted from circuit diagrams for simplicity, but it must be understood to be present at all times

The ground line is often omitted from circuit diagrams for simplicity, but it must be understood to be present at all times

19

A perfect amplifier should have...(5 things)

  • High gain
  • High input impedance so that any signal could be supplied to it without a loading problem
  • Low output impedance so that the power supplied by the amplifier is not limited
  • Zero gain for common-mode input signal
  • Infinite bandwidth

20

An ideal op-amp should have...(5 things)

• Infinite voltage gain, Av ≈∞

• Infinite input impedance, rin ≈∞

• Zero output impedance, rout ≈0

• Zero input offset voltage (i.e. exactly zero out if zero in)

• Infinite bandwidth

21

What is the current golden rule?

Because rin≈∞, virtually no current can flow into input

22

What is the voltage golden rule

Because Vout ≈Av(Vp-Vn) and Av ≈∞, Vp-Vn ≈0, i.e. virtually no voltage difference between inputs

23

Comparison between ideal and real op-amps

24

In a system, the ____ is compared with the desired ____

If there is a difference between the two, ____ is used to drive the output close to its intended value

In a system, the output is compared with the desired output

If there is a difference between the two, feedback is used to drive the output close to its intended value

25

V0 in a feedback amplifier = ?

Vo = Av x Vs

26

If the feedback amplifier circuit is modified such that a fraction β of the output is fed back into the input, then the new output becomes;

Vs = ?

V'o = ?

27

The new voltage gain Av ’ of the amplifier with feedback...(equation)

28

If ß Av>>1, then A'v = ?

29

What is ß?

The feedback fraction

30

Feedback voltage, Vn = ?