OPERATIONAL AMPLIFIERS Why do we study them at this point??? 1. OpAmps are very useful electronic components 2. We have already the tools to analyze practical circuits using OpAmps 3. The linear models for OpAmps include dependent sources TYPICAL DEVICE USING OP-AMPS

OP-AMP ASSEMBLED ON PRINTED CIRCUIT BOARD APEX PA03 PIN OUT FOR LM324 DIMENSIONAL DIAGRAM LM 324 LM324 DIP LMC6294 MAX4240

CIRCUIT SYMBOL FOR AN OP-AMP SHOWING POWER SUPPLIES LINEAR MODEL OUTPUT RESISTANCE INPUT RESISTANCE GAIN TYPICAL VALUES

CIRCUIT WITH OPERATIONAL AMPLIFIER DRIVING CIRCUIT LOAD OP-AMP

TRANSFER PLOTS FOR SOME COMERCIAL OP-AMPS SATURATION REGION LINEAR REGION IDENTIFY SATURATION REGIONS OP-AMP IN SATURATION

CIRCUIT AND MODEL FOR UNITY GAIN BUFFER WHY UNIT GAIN BUFFER? BUFFER GAIN PERFORMANCE OF REAL OP-AMPS

THE IDEAL OP-AMP

THE UNITY GAIN BUFFER – IDEAL OP-AMP ASSUMPTION USING LINEAR (NON-IDEAL) OP-AMP MODEL WE OBTAINED PERFORMANCE OF REAL OP-AMPS IDEAL OP-AMP ASSUMPTION YIELDS EXCELLENT APPROXIMATION!

WHY USE THE VOLTAGE FOLLOWER OR UNITY GAIN BUFFER? THE VOLTAGE FOLLOWER ACTS AS BUFFER AMPLIFIER THE SOURCE SUPPLIES POWER THE SOURCE SUPPLIES NO POWER THE VOLTAGE FOLLOWER ISOLATES ONE CIRCUIT FROM ANOTHER ESPECIALLY USEFUL IF THE SOURCE HAS VERY LITTLE POWER CONNECTION WITHOUT BUFFER CONNECTION WITH BUFFER

LEARNING EXAMPLE

LEARNING EXAMPLE: DIFFERENTIAL AMPLIFIER THE OP-AMP IS DEFINED BY ITS 3 NODES. HENCE IT NEEDS 3 EQUATIONS THINK NODES! KCL AT V_ AND V+ YIELD TWO EQUATIONS (INFINITE INPUT RESISTANCE IMPLIES THAT i-, i+ ARE KNOWN) OUTPUT CURRENT IS NOT KNOWN DON’T USE KCL AT OUTPUT NODE. GET THIRD EQUATION FROM INFINITE GAIN ASSUMPTION (v+ = v-)

LEARNING EXAMPLE: DIFFERENTIAL AMPLIFIER INVERTING TERMINAL NON INVERTING TERMINAL IDEAL OP-AMP CONDITIONS

LEARNING EXAMPLE: USE IDEAL OP-AMP 6 NODE EQUATIONS + 2 IDEAL OP-AMP FINISH WITH INPUT NODE EQUATIONS… USE INFINTE GAIN ASSUMPTION USE REMAINING NODE EQUATIONS ONLY UNKWONS ARE OUTPUT NODE VOLTAGES

LEARNING EXTENSION

“inverse voltage divider” INFINITE INPUT RESISTANCE NONINVERTING AMPLIFIER - IDEAL OP-AMP LEARNING EXTENSION SET VOLTAGE INFINITE GAIN ASSUMPTION

LEARNING EXAMPLE UNDER IDEAL CONDITIONS BOTH CIRCUITS SATISFY DETERMINE IF BOTH IMPLEMENTATIONS PRODUCE THE FULL RANGE FOR THE OUTPUT EXCEEDS SUPPLY VALUE. THIS OP-AMP SATURATES! POOR IMPLEMENTATION