Op-Amps

Question 1

What are the fundamental characteristics of an Op-Amp

Answer 1

• Zi, Input impedance approx. 10*10^12 ohms

- Zo, output impedance

Question 2

why is not open loop behaviour not stable

Answer 2

gain varies with frequency and drifts over time

Question 3

what are the 3 basic assumptions that describe the ideal model

Answer 3

• infinite input impedance Zi: I- = I+ = 0
• infinite gain, K: diff. in V_ & V+ =0 thus V_ = V+
• zero output impedance, Zo: voltage doesnt depend on output current

Question 4

how is stable behaviour achieved

Answer 4

feedback between V_ & Vout

Question 5

find Vo/Vi for an inverting amplifier

Answer 5

K = Vo/Vi = -(feedback resistance/input resistance) = - Rf/i

Question 6

find Vo/Vi for a non-inverting amplifier

Answer 6

K = Vo/Vi = (feedback resistance/input resistance) +1

Question 7

find Vo/Vi for a voltage follower and explain its special case

Answer 7

• Vo/Vi = 1
• same as an inverting amplifier where Vo/Vi = (feedback resistance/input resistance) + 1
• Rf = 0 & Ri = infinity (open circuit) thus given by 1

Question 8

find Vo/Vi for a differential amplifier

Answer 8

K = Vo = (Rf/Ri) * (V1 - V2)

-there are 2 of each resistors, must be the identical

Question 9

find Vo/Vi for a summation amplifier

Answer 9

• Vo = -(RfV1/R1 + RfV2/R2)
• similar layout to differential amplifier
• R1 & R2 are separate input resistances
• use corresponding voltage with resistor