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Circuit Analysis > Ch. 6: Operational Amplifiers > Flashcards

Ch. 6: Operational Amplifiers Flashcards

1
Q

Major Op-Amp

Applications

A

Inverting Amplifier

Non-Inverting Amplifier

Voltage Follower (Unity Gain Amplifier)

Difference Amplifier

Summing Amplifier

Reliable Current Source

Reliable Voltage Source

Differentiator

Integrator

Comparator

Instrumentation Amplifier

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2
Q

Ideal Op-Amp Rules

(2)

A
  • No current ever flows into either input terminal
  • There is no voltage difference between the two input terminals

*Note that these are possible because Op-Amps are an active component, with their power external of the circuit.

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3
Q

Op-Amp

Circuit Diagram Symbol

A

Simple triangle,

two inputs, and one output.

The Inverting Input is labeled with a (-) sign,

the non-inverting input is labeled with a (+) sign

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4
Q

Op-Amps:

Closed-Loop

vs

Open-Loop

Operation

A

Closed Loop

There is an electrical connection between the output and inverting input, providing feedback.

(Preferred for Amplifiers)

Open Loop

No connection between output and input.

Useful for comparators.

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5
Q

Op Amps:

Saturation Regions

A

Saturation Regions are the negative and positive points at which an Op-Amp is providing maximum gain.

The Maximum Negative, and Maximum Positive values of the output.

They are determined by the specific op-amp component, and the supply voltages.

Between these regions, the op-amp operates linearly.

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6
Q

Negative Feedback

in

Op Amps

A

The process of subtracting a small portion of the output from the input.

This makes the output signal more stable.

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7
Q

Op-Amp

Slew Rate

A

The rate at which an Op-Amp can respond to changes in the input.

Most often expressed in units: V/µs

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8
Q

Important Op-Amp Concepts

A
  • Op-Amp circuit representation
  • Ideal Op-Amp Rules
  • Gain
  • Closed-Loop Operation
  • Open-Loop Operation
  • Saturation Regions
  • Negative Feedback
  • Slew Rate
  • Use with Zener Diode
  • Various Applications
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9
Q

Zener Diode:

Basic Description

A

A special type of diode designed to be used in a “reverse biased” configuration, with positive voltage applied at the cathode.

While voltage is above a certain threshold, called the Reverse Breakdown Voltage (vBR), the Zener Diode maintains the same voltage, but allows current to change.

Below vBR, the Zener Diode acts like a linear resistor.

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10
Q

Op-Amp:

Internal Model

and Equations

A

*Note: Image differs slightly in notation

*Note: This is a model, not the true internal structure of an op-amp

  • Values:
    • A (G) : Open Loop Gain
    • <span>R</span>o : Output resistance
    • <span>R</span>i : Input resistance
    • vd (vin) : Pin voltage difference
    • vout : voltage out
    • iin : current in at non-inverting input
    • iout : current out
  • Equations:
    • Vout = Avd
      • vd = vout / A
    • iin = vd/Ri
    • vout = Avd - Roiout
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11
Q

Inverting Amplifier:

Circuit and Equations

A

Current Flow from Source to vout

-vin + R1i + Rfi + vout = 0

vout = vin - (R1 + Rf)i

Current Flow from Source to Inputs

-vin + R1i + vd = 0 (vd = 0 by ideal op-amp rule)

i = vin / R1

Voltage out in terms of Voltage In

vout = - (Rf / R1) vin

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12
Q

Non-Inverting Amplifier:

Circuit

and Equations

A

Node 2 ( Inverting Input)

v2/R1 + (v2 - vout)/Rf = 0

Node 1 (Non-inverting Input)

v1 = vin

Output Voltage

vout = (1 + Rf/R1) vin

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13
Q

Voltage Follower

(Unity Gain Amplifier)

Circuit

and Equation

A

Very simply,

Output directly reflects input

vout = vin

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14
Q

Difference Amplifier:

Circuit

and Equation

A

Voltage out is just the difference in voltages

vout = v2 - v1

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15
Q

Summing Amplifier:

Circuit

and Equation

A

Acts like an inverting amplifier, with the sum of voltages as an input.

vout = - Rf [v1/R1 + v2/R2 + v3/R3]

When input resistances are the same:

vout = - (Rf/R) ( v1 + v2 + v3 )

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16
Q

Reliable Voltage Source:

Voltage Regulator

(No Op-Amp)

A

Used in low current applications

17
Q

Reliable Voltage Source:

High Current Circuit

with Op-Amp

A

Adjust R1 or Rref to change the output voltage

18
Q

Reliable Current Source

Circuit

A

The reference voltage is provided by a reliable voltage source.

Is = vref / Rref

regardless of RL

19
Q

Differentiator Circuit

and Equation

A

vout = - Rf C1 dvs/dt

20
Q

Integrator Circuit

and Equation

A

vout = - (1/R1Cf) * Integral[vsdt - vcf(0)]

21
Q

Comparator

Circuit

A

*Note that this just one possible configuration

  • vout has a constant value
  • vout is Positive when vref > vsignal
  • vout is Negative when vref < vsignal
22
Q

Instrumentation Amplifier

Circuit

and Equation

A

vout = (R4/R3)*[(1+ R2/R1) / (1+ R4/R3)] v+

  • (R2/R1)v-

Circuit Analysis (7 decks)

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