ECA1212 Introduction to Electrical & Electronics Engineering Chapter 7: Operational Amplifier by Muhazam Mustapha, November 2011

Learning Outcome Be able to explain and solve some problems involving operational amplifier By the end of this chapter students are expected to:

Chapter Content Reason for Op Amp Regular Op Amp Circuits

Why Operational Amplifier CO1Text Book page 410

Need for Semi-Finished Amplifier CO1Text Book page 412 The kind of amplifier that we can build from BJT as we learnt in Chapter 5 was constructed using raw components We need something more robust, flexible and easier to install

Need for Semi-Finished Amplifier CO1Text Book page 413 Operational Amplifier (Op-Amp) is a semi- finished amplifier fabricated on IC Its gain and operation is easily adjustable using some combination of resistors

Fundamentals CO1Text Book page 413 Input current i in is assumed to be zero because the input resistance is very high Virtual ground: inverting (v − ) and noninverting (v + ) inputs are assumed to be at the same voltage but no current going to ground (close loop mode) Inverting input Noninverting input Output V in v+v+ v−v− V out i in Symbol: Gain (A, open loop gain): v out = Av in –Value is high ranging 10 5 ~ 10 7

Op-Amp Circuits CO1Text Book page 414

Close Loop Mode Most of the time op-amp is used in close loop mode This is done by putting a resistor from the output to the input (mostly the inverted one) The resistor is the called feedback resistor This feedback resistor pulls down the voltage gain to a more manageable value –But we won’t discuss the detail CO1

Close Loop Mode In close loop mode the previous assumptions are always applied: CO1 i in = 0 v − = v + Text Book Eq. 8.19, 8.37, etc For all circuits that we are going to cover, we won’t go through into the derivation details, but references will be made to the respective pages in the text book

Inverting Amplifier Circuit: CO1Text Book page , Example 8.1 partly Voltage Gain:

Summing Amplifier Circuit: CO1Text Book page 418 Voltage Gain:

Noninverting Amplifier Circuit: CO1Text Book page 419 Voltage Gain:

Voltage Follower Circuit: CO1Text Book Example 8.2 Voltage Gain:

Differential Amplifier Circuit: CO1Text Book page Voltage Gain:

Integrator Circuit: CO1Text Book page 433, Example 8.7 Output Voltage: v out and v S are functions of time

Differentiator Circuit: CO1Text Book page 449 Output Voltage: v out and v S are functions of time