Op Amps

Question 1

Name 5 passive op amps

Answer 1

Inverting
Non-inverting
Differential 
Unity gain
Summing

Question 2

Name 3 active op amps

Answer 2

Integrator
Differentiator
Negative impedance converter

Question 3

What is the gain of an inverting amplifier?

Answer 3

A = -Rf/R1

Question 4

What is the gain of a non-inverting amplifier?

Answer 4

A = 1 + Rf/R1

Question 5

What is the output voltage of a differential amplifier?

Answer 5

Vout = -R2/R1(V2-V1)

Question 6

What is the gain of a unity gain amplifier?

Answer 6

1

Question 7

What is the output voltage of a summing amplifier?

Answer 7

Vout = -Rf(V1/R1 + V2/R2 + V3/R3)

Question 8

What is the gain of a differentiating amplifier?

Answer 8

A = -sCR

Question 9

What is a negative impedance converter?

Answer 9

An op amp circuit acting as a negative load which injects energy into circuits in contrast to an ordinary load that consumes energy from them. Zin = -Z

Question 10

What is the gain of an integrator circuit?

Answer 10

A = -1/sCR

Question 11

What is a Miller integrator?

Answer 11

Problem: cap blocks DC - open circuit - infinite OL gain
Solution: place a really large resistor in parallel with cap, therefore if AC resistance is so large that the current will flow through the cap anyway; if DC the cap is open circuit and the current can flow through the resistor

Question 12

What is the gain of Miller integrator circuit?

Answer 12

A = -(Rf/R)/(1+SCRf)

Question 13

What are three applications of op amps?

Answer 13

1. Sensors and control - addition, subtraction, feedback
2. Communication - amplification, active filtering
3. Digital Systems - buffers, ADCs, DACs

Question 14

What are the six features of the ideal op amp model?

Answer 14

1. No current into inputs
2. Equal voltage at inputs
3. Zero output impedance
4. Infinite open loop gain
5. Infinite bandwidth
6. No temperature dependence

Question 15

What are 7 non-ideal characteristics of the op amp?

Answer 15

1. Inputs draw small currents (0.5 pico amps)
2. Input offset voltage (500 micro volts)
3. Output impedance is not zero (380 ohms)
4. Open loop gain is finite
5. Finite bandwidth
6. Temp dependence (Vos = 4 micro volt/degree)
7. Limited slew rate (1 volt/ microsecond change)

Question 16

What is Kirchhoff’s current law?

Answer 16

Sum of currents at a node is zero.

Question 17

What is the time constant of a circuit?

Answer 17

The amount of time it takes for voltage or current values to change approximately 63% from their starting values to their final values in a transient situation.
tau = total resistance * total capacitance