ELECTRIC CIRCUITSECSE-2010

Spring 2003 Class 10

ASSIGNMENTS DUE• Today (Tuesday/Wednesday):

• Will do Experiment #4 in Class (EP-4)• Activity 10-2 (There is no 10-1)

• Thursday:• Experiment #2 Report is Due• Will do Computer Project #1 in Class (CP-1)• Will spend second hour reviewing for Exam I

• Next Monday:• Exam I, 7-9, DCC 308• Homework #4 Due• Experiment #3 Report Due• Activities 12-1, 12-2 (In Class)

OPEN SHOP HOURS

• Wednesdays:• 9 – 11 am = Prof. Nagy• 12 – 2 pm = Prof. Millard• 2 - 4 pm = Prof. Jennings

• Thursdays:• 9 - 10 am = Prof. Millard

• JEC 4104:

REVIEW• Real Operational Amplifiers:

• Rin ~ 10 M; (Very Large)

• Rout ~ 100 ohms; (Very Small)

• Gain = A ~ 105; (Very Large)

• vout Can Never be Greater than VDC

• Building Blocks for Electronic Circuits

• Model Real Op Amp with Ideal Op Amp:• Rin = Infinite

• Rout = 0

• Gain = Infinite• Good Model for Almost All Op Amp Circuits

EXAMPLE OF REAL OP AMP

pv

nv

outv

DCV

DCV

Note Pin Layout

1,5 Used for Offsets

We will not UseNon-Inverting Input

Inverting Input

Pin 8 not connected

REAL OP AMP MODEL

pv

nv

inv

inR

outR

outv

inAv

in p nv v v out DCv can never be greater than V

Fig. 10.1 The 741 op-amp circuit. Q11, Q12, and R5 generate a reference bias current, IREF, Q10, Q9, and Q8 bias the input stage, which is

composed of Q1 to Q7. The second gain stage is composed f Q16 and Q17 with Q13 acting as active load. The class AB output stage is

formed by Q14 and Q20 with biasing devices Q18 and Q19 and an input buffer Q23. Transistors Q15, Q21, Q24, and Q22 serve to protect the

amplifier against output short circuit and are normally off.

TYPICAL 741 OP AMP CIRCUIT

From Sedra and Smith

IDEAL OP AMP

pv

nv

outv

pi 0

ni 0

out DCv can never be greater than V

DCUsually do not show V

REVIEW

• Ideal Op Amps:• ip = in = 0; Ideal Op Amp draws no current

• vout can never be greater than Vdc

• vout = + VDC if vp > vn

• vout = - VDC if vp < vn

• Comparator

• Can Model Most Real Op Amps with Ideal Op Amp:• Actual behavior will only vary slightly

REVIEW

• Op Amp with Negative Feedback:• Any circuit connection between vout and vn

• Creates Virtual Short at input to Op Amp

• ip = in = 0 AND vn = vp

• Output can be finite• Output determined by other circuit

elements• Find Output using Circuit Analysis• Look at Effects of Real Op Amps Later

(usually using PSpice)

IDEAL OP AMP WITH NEGATIVE FEEDBACK

pv

nv

outv

pi

ni

in p nv v v 0 with Negative Feedback p ni i 0 Always

inv

Negative Feedback

Virtual Short

REAL OP AMP WITH NEGATIVE FEEDBACK

pv

nv

inv

inR

outR

outv

inAvin p nv v v

p n

in

i i 0 Always

v 0 with Negative Feedback

Negative Feedback

ISOLATION AMPLIFIER

invoutv

out n p inv v v v

p n

p n

Virtual Short

i i 0

v v

pi

nv

pv

ni

NON-INVERTING VOLTAGE AMPLIFIER

inv

outv

Fout in

1

Rv 1 v

R

1R

FR

INVERTING VOLTAGE AMPLIFIER

inv

outv

1R

FR

Fout in

1

Rv v

R

SUMMING AMPLIFIER

2v

1v1R

2R

FR

outv

F F1 2

1 2

R Rv v

R R

Fi

1i2i

11

1

vi

R

22

2

vi

R

F 1 2i i i

0

out F Fv 0 i R

DIFFERENTIAL AMPLIFIERS

Can Use Op Amps to Eliminate Undesired Signals

Often have a Signal we want to Amplify, but

which contains some "Common-Mode" voltage

Example is 60 Hz adding to an Audio Signal

Want to Ampl

ify the Audio, but not the 60 Hz

Will Explore this with Activity 10-2

ACTIVITY 10-2

1v

2v

1RFR

outv

A

F 1 Fout 2 1

1 1

R R RShow that v v v

R R

ACTIVITY 10-2

1v

2v

1RFR

outv

A

1 2out 2 F F 2 F

1

(v v )v v i R v R

R

F 1i i

1i

1 21

1

v vi

R

2v

1 F Fout 2 1

1 1

R R Rv v v

R R

ACTIVITY 10-2

B

sv

cv

1R

2R

3R

FR

outv

outFind v

Common Mode

Signal

ACTIVITY 10-2

B

sv

cv

1R

2R

3R

FR

outv1v

2v

Common Mode

Signal

1 c sv v v

32 c

2 3

Rv ( )v

R R

ACTIVITY 10-2

• Part b): vout in Circuit B

3 cF 1 Fout s c

1 2 3 1

3 F 1 F Fc s

1 2 3 1 1

Use Equation from a):

R vR R R v (v v )

R R R R

R (R R ) R R v v

R (R R ) R R

1 c s

32 c

2 3

v v v

Rv v ; voltage divider

R R

ACTIVITY 10-2

B

sv

cv

1R

2R

3R

FR

outv

F 1 3 2Let R KR ; R KR

out sShow that v Kv

1v

2v

ACTIVITY 10-2

• Part c): RF = KR1; R3 = KR2

F

1

3 F 1 2 1 1

1 2 3 1 2 2

out c s s

RK

R

R (R R ) KR (KR R )

R (R R ) R (R KR )

K (K 1) K

1 Kv K K v K v K v

Common Mode is Rejected!

REAL OP AMPS

• On Thursday, we will explore what happens when we use Real Op Amps rather than Ideal Op Amps

• Will start Computer Project 1 where we will use the Circuit Model for an Op Amp and use finite Rin, non-zero Rout and finite Gain, A

• Will Spend Second Hour Reviewing for Exam I

EXPERIMENT #4

• Let’s Look at 741 Op Amp Circuit:• 741 is a Very Common Op Amp; Cheap, Good• Will Build a Non-Inverting Voltage Amplifier• Gain ~ 2 • Must Provide + 5 V, - 5 V to Amplifier• Use E3631A Power Supply• Use + 25 V, Common to get + 5 V• Use - 25 V, Common to get - 5 V• Adjust Separately• Remember this! We will use it often

EXPERIMENT #4, PARTS 1 & 2

outv

sv

10 k10 k

5 V

5 VFunction Generator

Oscilloscope

F

1

R1 2

R

EXPERIMENT #4• Will Use Oscilloscope:

• Tremendous Instrument• Does Great and Wonderful Things• Make Sure Probe Attenuation Factor = 1• Learn to Use the Functions

• Will Use Function Generator:• Rs for FG = 50 ohms

• Digital Voltage Readout on FG is Always Wrong when Output is plugged into Scope!

• Digital Voltage Readout on FG assumes it is plugged into something with Req = 50 ohms

• Always Measure Voltage Output of FG on Scope

741 LAYOUT

pv

nv

outv

DCV

DCV

Note Pin Layout

Used for Offsets

EXPERIMENT #4

1 2 3 4

5678

Note Indentation Op Amp Pin Layout

pvnv

outvDCV

DCV

For 741

EXPERIMENT #4

1 2 3 4

8 7 6 5

1 2 3 4

5678

Straddle Seam

in Protoboard

EXPERIMENT #4 Connect Output of FG to Both Scope and Circuit

Use BNC Tee to do this

Use Channel 1 on Scope for Input

Always want to look at Input

Connect Output of Circuit to Channel 2

Make sure that P

robe Attenuation Factor 1

Push Channel 1 and Channel 2 buttons to check

Also connect SYNC from FG to EXT TRIG on Scope

This will synchronize the scope to the FG Signal

EXPERIMENT #4, PARTS 1 & 2

Apply 1 kHz Triangle waveform to Circuit from FG

Push Button for Triangle Waveform

Push Frequency Button; Adjust to 1 kHz

Set Amplitude 1 Volt, Peak to Peak as

Measured on Scope (do not

out

s

measure on FG)

Observe Input and Output Waveforms

Increase Amplitude until you observe Distortion

v Measure the Voltage Gain, , with no Distortion

v

EXPERIMENT #4, PARTS 3-5

curR 100 k

svoutv

10 k 10 k

5 V

5 V

invini

EXPERIMENT #4, PARTS 3,4,5cur

cur

s,RMS

Add 100k Resistor to Circuit, R

Measure R accurately using MM

Set FG for Sinusoidal Waveform, f 1 kHz

Adjust Amplitude for No Distortion

Measure v using MM (Set to read AC Volts)

in, RMS s cur in,RMS in,RMS

in,RMSin

in,RMS

out

Measure v v R i ; Calculate i

v Calculate Input Resistance of Op Amp R

i

Determine R of Op Amp using method of Exp #3

EXPERIMENT 4, PART 5

sv

100 k iR

10 k

10 k

oR

PotR

in v

inAv

outi

out,RMSoutout

out out,RMS

vvR

i i

outv

Find Thevenin Equivalent Circuit

EXPERIMENT 4, PART 5

oc,RMSv

T outR R of Amplifier Ckt

PotRout,RMSv

out,RMSi

Thevenin Equivalent Circuit

EXPERIMENT 4, PART 5

sv

100 k

10 k

10 kiR

in v oR

inAv

PotRoc,RMSv

out,RMSi 0

out,RMS out,RMS oc,RMSWhen i 0, v v

EXPERIMENT 4, PART 5

out

s

out

out,RMS oc,RMS

Open Circuit Output (i 0)

May have to reduce v to make sure

v is undistorted

(Observe on Scope)

Measure v v with MM

(Could also measure with Scope)

EXPERIMENT 4, PART 5

Pot out,RMS oc,RMS

out,RMS Pot

out,RMSout,RMS

Pot

out,RMS oc,RMS out,RMS out

out

Connect 10 k Pot

Choose R such that v .9v

Measure v and R accurately with MM

vCalculate i

R

v v i R

Calculate R

EXPERIMENT 4, PART 5

oc,RMSv

T outR R of Amplifier Ckt

PotRout,RMSv

out,RMSi

out,RMS oc,RMS out,RMS outv v i R

out,RMSMeasure v with MM

PotChoose a Value for R

PotMeasure R with MM

out,RMSout,RMS

Pot

vCalculate i

R

outCalculate R