1. ECE 3336 Introduction to Circuits & Electronics
Lecture Set #13
Amplifiers &
Operational Amplifiers
Part 2
Dr. Han Le
ECE Dept.

2. Outline Part 1 Introduction Amplifier basics
Gain: power, voltage, current
Other parameters of amplifiers
Operational amplifier (Op Amp) basics
Op amp technology
Op amp basic circuit concepts
Op amp with negative feedback

3. Outline Part 2 Op amp applications Limitation of op amp
Voltage follower
Transimpedance amplifier
Summing amplifier
Differential amplifier
Instrumentation amplifier
Periodic signal generator
Active filter and other signal processing
Limitation of op amp

4. Voltage Follower Advantages:
High input resistance (for low power signal)
Low output resistance (high power output signal
It is a gain in power via current, but maintain the same voltage.
This is known as impedance buffer for very low power voltage sensor signal, e. g. thermocouple.

5. Transimpedance Amplifier (TIA)
Advantages:
convert a non-ideal current source signal into voltage signal with effective zero input impedance
optional
Essential in optical signal detection with semiconductor photodiodes

6. Example Application

7. Summing Amplifier Advantages:
Weight-summing and amplifying several voltage signals
Ex: adding many sensor signals. Use in analog computing before the advance of digital electronics

8. Example: Music Synthesizing

9. Differential Amplifier
Advantages:
True measure of the difference between two signals and with amplification

10. Example: Automatic Control (proportional controller)
We have +-15 V and 5 V DC power input.
+15 V
Temperature sensor input
User preset (controllable) voltage input.
-15 V

11. Instrumentation Amplifier
See homework
Advantages: Differential amplifier with:
high input resistance
high common mode rejection ratio (CMRR)
for sensitive measurements

12. Square Wave Generator - + R vout C R1 R2 VS -VS Generate AC from DC
Bi-stability of charging- reversal charging of the capacitor
Period determined by RC time constant + -
vout C R1 R2 R
Let vout=VS
If C is “+”charged until
Then
C then is reverse charged until
Then
System is intrinsically bi-stable, switching between two extrema in response to capacitor charging-reverse charging to opposite polarities

13. Square Wave Generator - + R vout C R1 R2 VS -VS
Let vout switch from VS to – VS at t=0 v- v+
After time t=T/2 such that:
Then v+ >= v- again and vout switches back to VS
is the period

14. Square Wave Computer Simulation+ -
vout C R1 R2 R
Frequency change via
Maximum frequency is limited by op amp bandwidth

15. Example Low cost generic (analog) wave generators
Audio signal generators
General purpose oscillators

16. Level Shifter (DC Bias)
Advantages:
shift the signal by a DC bias level for ease of processing

17. Example
Move the trace up and down on the screen

18. Active Filter
For AC and harmonic signals, resistance is replaced with impedance. Hence:
Inverting configuration
Non-inverting configuration
Response function H(w) for filtering can be designed with appropriate ZF(w) and ZS(w)

19. Review: Frequency Transfer Function (Frequency Response Function)
For many linear RLC circuits, the frequency response function usually has the form:
With op-amp:
Advantages:
filter with gain and transimpedance
flexible filter design

20. Review: Example 1 Frequency Response or, Frequency Transfer Function R
input vin[t]
output vout[t]
i(t)
Frequency Response
or, Frequency Transfer Function R C
output vout[t]
i(t)
input vin[t]

21. Review: Example 2
RC band stop filter.
RC bandpass filters

22. Op-amp RC Low-Pass Filter
See Mathematica homework

23. Op-amp RC High-Pass Filter
See Mathematica homework

24. Op-amp RC Band-Pass Filter
See Mathematica homework

25. Op-amp Integrator Used in early days of analog computer
Useful but not as accurate as digital
Often for level detection and trigger-setting

26. Op-amp Differentiator
Used in early days of analog computer
Useful but not as accurate as digital
Often for edge-detection and trigger-level setting

27. Outline Part 2 Op amp applications Limitation of op amp
Voltage follower
Transimpedance amplifier
Summing amplifier
Differential amplifier
Instrumentation amplifier
Periodic signal generator
Active filter and other signal processing
Limitation of op amp

28. Output Voltage Saturation
The maximum voltage output is the supply voltage. Signal can be saturated
Care must be taken to be sure that signals are within acceptable input amplitude range.

29. Bandwidth
Op-amp, like any circuit, have finite bandwidth. It is like a built-in low-pass filter.
Select appropriate op-amps (which come in a wide range of bandwidth) for applications.

30. Slew Rate
Slew rate (also related to bandwidth and phase response) is caused by the fundamental gain-bandwidth product.
Finite slew rate results in the sloping of sharp edge (step function signal)- causing signal distortion

31. Conclusion
Op amp: the most versatile, ubiquitous device in many electronic circuits, especially linear circuits
If there is one IC you learn, that should be the op amp
The building block for many signal processing functions
Essential to both analog and digital circuits (for analog output)

32. Homework helps

33. A transimpedance amplifier, as we learn, converts a current source signal into a voltage signal. This HW is the opposite: convert a voltage source signal into a current source control. i1
Answer RL iL
vin - R1 +
Other designs: non-inverting or ground-based load will be accepted.

34. - + - + vin vin VCC i1 iL RL R1 R2 iL RL i1 R1 Non-inverting design
Answer + - RL
vin R1 i1 iL
Note: this can be used with a transistor (app: diode laser driver) R2 iL RL i1 - R1 +
vin
VCC