Useful for B.Sc Electronics Students

1. Applications of Op-Amps
Dr. C.SARITHA
Lecturer in Electronics
S.S.B.N. DEGREE & PG.COLLEGE
ANANTAPUR

2. OVERVIEW
 Introduction
 Definitions
 Circuit Diagrams
 Derivations
 Applications
 Conclusion

3. Integrator
 The circuit in which the output wave form is
the integral of input wave form is known as
an integrator
 Such type of circuit is obtained by using
basic inverting amplifier configuration
where we use a capacitor in feed back

4. Circuit diagram
IR Ic
Vs

5. Explanation
 Input is applied to inverting terminal of the
op-amp.
 Non inverting terminal is grounded.
 If sin wave is applied terminal then the
output will be cosine wave.

6. For an ideal op-amp Ri=infinite
R0=0
For an ideal op-am
input current=output current
IR=IC
IR=Vi-Vs/Ri
The capacitor current Ic=c(d/dt(VS-V0)
Ic=-c(d/dtV0-VS)

7. Input current =Output current
(Vi-VS)/Ri=-C(d/dtV0-VS)
Vi/Ri-VS/Ri =-C(d/dtV0-VS)
V0=-AVS
VS=-V0/A
Substitute this Vs in the above equation
Vi/Ri+V0/ARi=-C(d/dt(V0+VS/A)
=-C(d/dtV0)-C(d/dtVS/A)

8. V0/A and V0/ARi
Are very less compare to V0 and hence this
terms are neglected.
Vi/Ri=-C(d/dtV0)
Integrating on both sides b/w 0 to t
t t
Vi/Ridt=- o Cd/dtV0
o

9. 1 t
Ri 0 Vidt= -CV0
V0= -1 t
RiC 0 Vidt
The output of the integrator is the integral of
input voltage with time constant that is V0 is
directly proportional to integral of Vidt and
inversely proportional to the time constant.

10.  The input is sine wave the output become
cosine wave
Input=
Output=

11. Similarly the input is square wave the
output become Triangle wave
Input=
Output=

12. Applications
 Analog computer
 A to D converters
 Many linear circuits
 Wave Shapping circuit

13. Differentiator
 The differentiator is the circuit whose output
wave form is the differential input wave
form.
 The differentiator may be constructed form
the basic inverting amplifier
 Here we replace the input resistor by a
capacitor.

14. Circuit Diagram

15. The capacitor current Ic=CI(d/dtVi-VS)
Current through the feed back resistor
IR=(VS-V0)/RF
Input current=Output Current
IC=IR
C(d/dt(Vi-VS)=(VS-V0)/RF
CiRF(d/dt(Vi-VS)=VS-V0
V0=-CiRF(d/dt(Vi-VS)+VS

16. Gain A=-V0/VS
VS=-V0/A
Substitute VS in the above equation
-CiRFd/dt(Vi-VS)+VS=V0
-CiRFd/dt(Vi-VS)-VO/A=V0
V0/A is very small and hence neglected
VO=-CiRFd/dt(Vi)

17. The input is cosine wave the output become
sine wave
Input=
Output=

18. Similarly the input is Triangle wave the
output become Square wave
Input=
Output=

19. Active Filters
 Filter is a circuit which gives the DC from
the given input AC.
 The filter which constructed by using an op-
amp is known as the active filter. (Because
the op-amp is an active component)

20. Types of filters
 High pass filter:
It allows the high frequency signals and
filter them (convert them into DC).
 Low pass filter:
It allows the low frequency signals and
filter them (convert them into DC).

21. Low pass filters
R
C

22. Working
 A first order filter consists of a single RC
network connected non inverting terminal of
the op-amp
 At low frequency the capacitor appears
open and the circuit acts like an inverting
amplifier with a voltage a gain of (1+R2/R1)

23. …Continues
 As the frequency increases the capacitive
reactance the capacitive reactance
decreases causing a decrease in the
voltage at the non inverting input and hence
at the output.

24. Frequency Response
 Here fcutoff the value of input signal frequency
at which the output decrease to 0.707 times
its low frequency value

25. High pass filters

26. Working
 A first order active high pass RC filter also
consist of a RC network connected to the
non inverting terminal of the op-amp in
case low pass.
 Here R and C are inter changed.

27. …Continues
 In this case at low frequencies the
reactance of the capacitor is infinite and it
blocks the input signal. Hence the output is
zero.
 As we increase the frequency, capacitive
reactance decreases, and out put increase

28. Frequency Response
 Here fcutoff the value of input signal frequency
at which the output increase to 0.707 times
its low frequency value