1. Opamps
Engineered for Tomorrow
Date
dd.mm.yy
Manju Khanna

2. Subject Name: Electronic Circuits Subject Code: 10CS32
Prepared By: Manju Khanna
Department: CSE
Date:30/8/2014
11/24/2018

3. Agenda
Filters
Classification
Active Filters
First Order Filter
Second Order Filter
Phase Shifters
Instrumentation Amplifier
Non-Linear Amplifier
Relaxation Oscillator
Current to Voltage Converter
Voltage to Current Converter

4. Filters
Filters
Active Filters
Passive Filters

5. Active Filters :
These filters use Active components such as opamps , transistors along with resistor and capacitor.
Order of an active filter depends on the number of RC sections used in the filter.
Passive Filters: These filters use Passive components such as resistor,capacitor,inductor.

6. Active Filters They are classified as first order and second order.
Order depends on RC sections in the filter.
Opamp Filters
Low Pass
High Pass
Band Pass
Band Reject

7. Frequency bands of Filters
Band Reject Filter

8. First Order Filters

9. Low Pass Filter
At low frequencies reactance offered by capacitor is larger than resistance value
At high frequencies reactance offered by capacitor is smaller forcing the output to zero.
Cut off frequency(fc)
fc = ½(pi) R C
Where R-resistance
C- Capacitance , pi – 22/7
To increase gain of opamp use R2 and R3 resistance as show below:
Av = 1 + R3/R2 where Av – gain

10. Figure shows low pass and High pass filters with gain

11. Inverting configuration of opamp
Low Pass and High Pass Filters

12. Low Pass Filter
fc = ½(pi) R2 C1
Av = - R2/R1 where R2 and C1 are the resistances and capacitances as shown in the figure.
High Pass Filter
fc = ½(pi) R1 C1
Av = - R2/R1 where R1 and C1 are the resistances and capacitances as shown in the figure.

13. Second Order Filters
Butterworth filters commonly used second order filters
Butterworth or Flat Filters
Offer a flat pass and stop band response

14. Low Pass 2nd Order Butterworth Filter
Z1=Z2=R
Z3=Z4=C
High Pass 2nd Order Butterworth Filter
Z1=Z2=C
Z3=Z4=R
fc = ½(pi) RC
Pass Band Gain(Av) = 1 + R2/R1

15. Second Order Band Pass Filters
Formed by cascading high pass and low pass filters in series
At Low frequencies : C1,C2 offers high reactance
At high frequencies :the output is shorted which converts the circuit to an inverting amplifier with zero gain.
Intermediate frequencies: the resonant frequency is given by
fR=2Q/2(pi) R2 C

16. Second Order Band Pass Filter
With respect to the above figure
For C1=C2=C
Q= [R1 R2/2R3] ½
Q- Quality Factor
C-Capacitance
R-Resistance
Av = Q/2(pi)R1fR C
fR –Resonant frequency

17. Second Order Band Reject Filter
Implemented by summing the output of low pass and high pass filters.
At Low frequencies: The output is through the path R1-R2-C3 acts as low pass filter.
At High frequencies: The output through path C1-C2-R3 acts as high pass.
At Intermediate frequencies: both the filters phase shift the signal and the result net is zero.
With reference to the figure:
R1=R2=R , R3=R/2
C1=C2=C, C3=2C
fR=1/2(pi)RC 0<= R4<=(R1+R2)

18. Second Order Band Reject Filter

19. .
Phase Shifters
Phase shifters shift the angle of an input signal by an angle Ө.
There are 2 type: Lagging phase shifter
Leading phase shifter
Lagging Phase Shifter: Output lags the input by an 0degrees to -180 degrees
Leading Phase Shifter: Output leads the input by an 0degree to 180degrees.

20. .

21. Instrumentation Amplifier
It is a differential amplifier that is optimized for DC performance.
It is designed to approach the ideal opamp.
It offers:
High differential gain
High CMRR
High Input Impedance
low Input offsets and low temperature drifts. .

22. It consists of 2 stages: Preamplifier stage and difference amplifier stage.
The opamp A1 and A2 in the preamplifier stage are in the non-inverting configuration.
Provide high gain, high input impedance.
Output of both is input to the difference amplifier.
The signal at R1 –R2 and R3,R4 are equal. .

23. .
Non-Linear Amplifier
The Gain of a non-linear amplifier is a function of the amplitude of the signal.
Gain is very large for weak Input.
Gain small for large Input signals.
A non-linear device is in the feedback path.
Weak Input: Diodes act as open circuit.
High gain due to minimum feedback.
Large Input: Diode offers resistance, short circuit.
low gain.

24. Relaxation Oscillator.
Relaxation Oscillator
Relaxation oscillator oscillator produces non –sinusoidal signals.
Time period is dependent on the charging time of the capacitor.
The capacitor is charged through resistance R.
Input of opamp at non-inverting input is
+ Vsat * R1/(R1+R2)
Forces the output to =+Vsat.
Input of opamp at non-inverting input is - Vsat * R1/(R1+R2)
Forces output to -Vsat

25. Relaxation oscillator.
Relaxation oscillator

26. Current to Voltage Converter.
Current to Voltage Converter
Current to voltage converter is a transimpedance amplifier.
Zero Input and Output impedance.

27. .
Voltage to Current Converter
It is transconductance amplifier used for voltage to current converter.