1. Transistor and Operational Amplifiers
Week of 29th September & 6th October 2008

2. Agenda for the day
The first test exam papers are graded. The highest is 57 marks.
There are many who have marks less than 50%. Please put more effort.
You can take a look at your papers. They will be kept in the lab. After seeing the papers please return them back.
The second exam is a week away

3. Content for the second in-semester exam
Node voltage and mesh current analysis
Problems on network theorems
Transistors
Basic operational amplifier circuits ( till Monday’s 8.30 am class)
The lab next week is on operational amplifier circuits.

4. Transistor circuit questions
Diode equivalent circuit
Electron flow in the amplifier circuit
Effect of the coupling Capacitors
Q point variation

5. Water model of transistor working!

6. The operation of triode

7. The operational amplifier

8. Analog computer to solve differential equations

9. Op amp Noninverting and inverting input Single-ended output
A perfect amplifier – a voltage-controlled voltage source
An ideal op amp has:
Infinite open-loop voltage gain
Infinite input resistance
Zero output impedance

10. Op amp symbol and equivalent circuit
Noninverting
input
+VCC
Output
Inverting
input
-VEE
Equivalent circuit
AVOL(v1-v2)
Rout
Rin v1 v2
vout

11. The 741C op amp is an industry standard.
Rout v1
vout
Rin
AVOL(v1-v2) v2
Rin = 2 MW
Rout = 75 W
AVOL = 100,000
Iin(bias) = 80 nA
Iin(off) = 20 nA
Vin(off) = 2 mV
funity = 1 MHz
CMRR = 90 dB

12. Bode plot of the 741C op amp funity AVOL 100 dB 80 dB 20 dB/decade
rolloff
60 dB
40 dB
20 dB
0 dB
10 Hz
100 Hz
1 kHz
10 kHz
100 kHz
1 MHz
funity

13. Inverting op amp The most basic op amp circuit
Uses negative feedback to stabilize the closed-loop voltage gain
Closed-loop voltage gain equals feedback resistance divided by input resistance

14. The inverting amplifierRf R1

15. Analyzing the inverting amplifierRf R1
iin
iin
vin
vout
vin = iinR1 and vout = iinRf
AO(CL) = = R1 Rf
vout
vin
zin(CL) = R1

16. Noninverting op amp A basic op amp circuit
Uses negative feedback to stabilize the closed-loop gain
Closed-loop voltage gain equals the feedback resistance divided by the input resistance plus 1

17. The noninverting amplifierRf R1

18. Analyzing the noninverting amplifier
vout
vin i1 Rf
vin = i1R1 and vout = i1(Rf+R1) i1 R1
AV(CL) = = R1
Rf+R1
vout
vin Rf
+ 1
zin(CL)  

19. Op amp application: summing amp
A summing amp has two or more inputs and one output
Each input is amplified by its channel gain
If all channel gains equal unity, the output equals the sum of the inputs

20. The summing amplifier R1 Rf v1 R2 v2 vout R2 Rf v2 R1 v1 + vout =
In a mixer, a summing amp can amplify and combine audio signals

21. Some questions for you ?
How many think that they have learnt something from this course ?
How many are enjoying this course ?
If I had to change two aspects of this course – what should they be ( to make it a better learning experience) ?

22. Voltage follower – unity gain amplifier

23. Negative feedback increases the closed-loop bandwidth.
AVOL
100 dB
funity
AV(CL)
80 dB
60 dB
40 dB
20 dB
0 dB
10 Hz
100 Hz
1 kHz
10 kHz
100 kHz
1 MHz

24. The second in-sem exam for EL-103
Node voltage and mesh current analysis
Problems on network theorems
Transistors ( see sections discussed in clas)
Basic operational amplifier circuits ( till Tuesday’s lecture and lab class this week)

25. feedback Provider ( short comings) Consumer ( responsibilities) Lab
Black box treatment of many components ( op-amp, transistor)
Multisim more accessible
Consumer ( responsibilities)

26. VDB transistor circuit